Optimizing management of a new invasive species, swede midge, on small-scale organic farms: Part II

Final report for ONE16-262

Project Type: Partnership
Funds awarded in 2016: $14,999.00
Projected End Date: 11/30/2019
Grant Recipient: Cornell
Region: Northeast
State: New York
Project Leader:
Christine Hoepting
Cornell Cooperative Extension - Cornell Vegetable Program
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Project Information

Summary:

Swede midge (SM) is an invasive insect pest that is threatening the viability of organic production of brassica crops in the Northeastern US. This is the second year of a three-year project for which the objectives were to understand SM population dynamics on small-scale at-risk organic brassica farms as they relate to management practices, as well as to develop appropriate and feasible management strategies for this potentially devastating pest. We worked on four working farms in Cattaraugus, Allegany, Seneca and Schuyler counties, and on the Cornell Organic Research Farm in Tompkins Co. A total of 34 SM traps were deployed to monitor SM population at seven spring emergence sites, 16 brassica plantings and two transplant production sites. Nine on-farm research trials and demonstrations were established to study various aspects of SM management strategies.

Small-cage studies confirmed that an overwintering SM population continued to emerge from the soil until late-July/early-August, although peak emergence occurs from late-May until late-June. Current year spring SM emergence was as strong following previous year both SM-infested summer and fall plantings. This information is important to consider when making crop rotation decisions. Instead of having to take a field or farm out of brassica production for three years, we clearly demonstrated that a crop rotation of about 2.5 months (mid-May to end of July) away from brassicas was enough time (wide enough) for crop rotation away from brassicas to be effective. The caveats to this rule include: 1) The field must be secluded; for example, surrounded by wooded areas and about 500 ft from the SM-infested area. 2) Transplants must be free of SM. And, 3) There must be no brassica-type weeds or cover crops to sustain the SM population in the field in the absence of a cultivated brassica crop.

Highest levels of SM damage occurred in broccoli, followed by Romanesco, kohlrabi (especially green), and cauliflower, which were followed by Red Russian kale, purple/Dinosaur kale and cabbage (especially red), while turnips and green (Winterbor) kale were much less preferred, and Asian brassicas (Bok Choy, Napa cabbage) appeared to be quite tolerant. In a trap crop study, Red Russian kale resulted in significantly higher SM infestation than broccoli. Compared to monoculture broccoli, broccoli grown beside Red Russian kale had significantly less SM damage, which increased marketable yield by 25% to 36%. Applying essential garlic oil 1% + Nufilm-P 0.25% v/v to brassica plants did not result in reduced SM damage compared to the untreated control in two out of three trials. In a non-replicated demonstration in Red Russian kale, the garlic oil treatment had less than half the SM infestation as the untreated (garlic oil: 40%; untreated: 90%).

Insect exclusion netting resulted in 100% control of SM, and significantly reduced damage from flea beetle and caterpillar pests compared to open air. IEN also hastened plant maturity compared to open air when used in combination with bare ground and black plastic. In another trial, compared to hay mulch + white IEN, white and silver mulch + white IEN did not result in lower temperatures or differences in maturity as we had expected. Instead, they had numerically 3.3 and 1.6-times higher incidence of heat stress. Compared to hay + white IEN, hay + green IEN had lower weekly average temperature by ~1 to 2 ⁰F, which significantly delayed maturity. When the cost of IEN was factored in, there was no difference in net return between 0% SM crop loss with IEN and 50% SM crop loss without IEN on plastic mulch. These results clearly demonstrate that in order for IEN to be economical, both the potential loss due to SM and the price earned for broccoli need to be high. Green IEN cost only slightly more than white IEN, and because it was more durable, its economic feasibility could increase with each re-use.

Our preliminary results indicated that plastic mulch may serve as a barrier to SM pupation when SM larvae drop from infested plants grown on plastic mulch, and that plastic mulch and tarp may serve as a barrier to SM emergence when these ground barriers were placed over SM-infested soil. Additionally, SM was trapped in a cage underneath a tarp, indicating that SM could emerge successfully beneath a ground barrier, but remain trapped at the soil surface until they perish. Further research is underway to develop use of ground barriers as an effective and affordable management strategy to reduce SM populations and damage, especially on farms with a single land base.

Over 300 growers attended 10 presentations on managing SM on small-scale at-risk brassica farms at summer field days, twilight meetings, winter conferences and schools. Our SM diagnostic video has been viewed almost 700 times. Continued development of educational materials and outreach efforts will ensure that all small-scale organic brassica growers in New York adopt feasible management strategies that mitigate economic losses from SM, which will result in thousands of dollars in increased profits and preservation of lucrative markets, and ultimately, sustainability of organic brassica industry in the Northeast US.

Project Objectives:
  1. Advance understanding of swede midge (SM) population dynamics on small-scale organic brassica farms as related to management practices.

 

  1. The definitive end date of emergence of the overwintering generation.
  2. The intensity and duration of SM emergence in the spring at a site where an SM-infested crop was grown the previous summer (compared to the fall).
  3. Annual SM population dynamics per individual farm.
  4. Differences in SM damage among crop types. 

 

2. Optimize management strategies including newly developed disruption tactics, insect exclusion netting (IEN) and garlic oil repellent, crop selection and rotation strategies.

    1. Evaluation of IEN compared to open air over bare ground and black plastic mulch for SM control and crop quality in summer broccoli.
    2. Effect of white plastic and reflective silver plastic mulches, and green vs. white IEN on crop quality in fall broccoli (planted in heat of July).
    3. Evaluation of garlic oil used with spreader-sticker adjuvant as a repellant of SM.  
    4. Evaluation of using a SM-preferred crop as a trap crop to protect the less preferred crop (broccoli) from SM compared to broccoli grown in monoculture.
    5. Evaluate effect of plastic mulch compared to bare ground on SM pupation and subsequent emergence.
    6. Effect of post-harvest practices, shallow-tillage and plastic mulch on SM emergence.
    7. Effect of tillage practices and tarp on spring SM emergence.

3. Increase awareness of SM and knowledge of its management among at-risk small-scale organic brassica growers.

 

 

Introduction:

Swede midge (SM) is an invasive insect pest that is threatening the viability of organic production of brassica crops in the Northeastern US. SM attacks all brassica crops, including broccoli, cauliflower, cabbage, kale, kohlrabi, etc., as well as canola and mustard-type weeds. SM is a fly (Fig. 1) that lays eggs in the growing meristems of these crops, and secretions of the feeding midges/larvae cause scarring and distortion of plant tissues, including lack of head formation, resulting in unmarketable crops (Fig. 2). Larvae pupate in the soil and emerge as adults with 4-5 overlapping generations per year. Once SM becomes established, it can cause complete loss of marketable crops.

            Starting in 2009, reports of brassica crop losses from SM in small-scale organic production increased. SM is now known to occur throughout New York and in Vermont, New Hampshire, Massachusetts, Connecticut, New Jersey, Pennsylvania and most recently in Michigan, Wisconsin, Minnesota, Maine and Virginia in the United States, and in Canada from New Brunswick to British Columbia. SM can become economically devastating after a lag time of 6-7 years following the first occurrence within a region. Recent models predict that SM could potentially colonize all of the Northeastern US, the Great Lakes states, south to Colorado and west to Washington State. Ultimately, we estimate that 25,679 acres of brassica crops worth $116 million may be invaded by SM in the US. Within the Northeast US, brassicas are grown on 62% of organic vegetable farms and are critical sources of income for these farms; 663 acres of just organic broccoli, cabbage and cauliflower, grown on 364 farms and worth $2.5 million are at risk. New York accounts for 79% of this production that is at risk. SM is quite small (< 2 mm) and its damage difficult to identify, so it is commonly misdiagnosed.   There is an urgent need to develop effective pest management tools and to conduct outreach/education to familiarize at-risk small-scale organic growers with SM diagnosis and best management practices to protect them from devastating SM outbreaks.

In 2015, we started a project that was funded partially by NESARE Partnership grant (ONE15-237) to optimize SM management on at-risk small-scale organic brassica farms. Our first year of monitoring SM populations on five farms provided important information for improving SM management. For example, we observed higher rates of SM damage in crops that were planted in fields during emergence of the overwintering SM population compared to fields where the crops were planted after spring emergence was complete. These results indicated that crop rotation can be an effective SM management strategy, but timing the planting of the next brassica crop is critical. Although our data indicates that spring emergence finishes within the first half of July, it was not definitive, because open-air traps could have captured individuals from either overwintering or subsequent generations; thus, determining the definitive end date of spring emergence is a priority. When a SM-infested crop is harvested in the summer, it is likely that instead of staying in the soil as pupae, SM adults emerge and leave the site for another brassica crop. Whether is it is safe to plant a brassica crop in the spring at a site where an infested Brassica crop occurred the previous summer warrants further investigation. If it is safe, this could expand crop rotation options on small farms. Although crop rotation is an effective SM management strategy, many factors drive rotation decisions and actual implementation can be difficult. Some farms are simply too small for crop rotation/separation to be effective and other effective management strategies are needed.

In our 2015 trials, insect exclusion netting (IEN) was highly effective in protecting the crop from SM damage. No broccoli was damaged when netting was used, whereas without IEN 94-100% of the broccoli was damaged and 50-85% was unmarketable. Exclusion netting was effective when used over newly broken ground in relatively close proximity (~ 75 ft) to a known SM emergence site. When IEN was applied on top of an emergence site, it resulted in 100% SM damage and 89 to 95% unmarketable broccoli when it was used by itself or with straw mulch. However, when IEN was applied over plastic mulch, SM damage and unmarketable heads were reduced to 57% and 33%, respectively. These results suggest that plastic mulch provided a barrier to SM emergence from the soil. We suspect control would have been better in our trial if the plastic mulch spanned the entire width of the netting. Most importantly, weeds were better kept in check underneath IEN when it was combined with a mulch. Differences in plant development and quality occurred between netting and open air as well as among mulch types under the netting. Some combinations trialed resulted in increased yield, while others decreased yield. For example, compared to open air, broccoli under IEN was advanced in the spring planting, but suffered heat stress in the fall planting. Similarly, under IEN, fall broccoli suffered more heat stress with black plastic than with straw mulch or bare ground. Also, netting provided beneficial exclusion of flea beetles and detrimental inclusion of cabbage worms (from infested transplants) and slugs. Optimizing IEN and mulch use regarding the effects on plant development, heat stress, and the entire pest complex warrants further attention.

                Garlic oil repellant showed promise in recent laboratory studies by Yolanda Chen (UVM), but failed in our on-farm trials in 2015. It rained a lot that growing season and we suspect that the garlic oil got washed off by the rain. Before rejecting garlic oil repellent as a potential management strategy for SM, we will trial it with a spreader-sticker adjuvant. In studies conducted by Abby Seaman, all OMRI insecticides failed unless they were used with Nufilm-P adjuvant.

                Differences in SM damage among different types of brassica crops exposed to the same SM population occurred. At one site, average SM damage rating at harvest of red cabbage, green cabbage and pointed cabbage in the same planting were 2.8, 1.8 and 1.5 out of 4.0. At another site, winterbor and purple kale had 20% and 30% of plants had SM damage, respectively, while 75% of Red Russian kale plants had damage. Better understanding of crop tolerance and SM preference would increase the usefulness of crop rotation and separation management strategies.Fig. 1 Fig. 2

Cooperators

Click linked name(s) to expand
  • Andy Fellenz
  • Lou Johns
  • Ryan Maher
  • Liz Martin
  • Mark Printz
  • Denny Reynolds

Research

Materials and methods:

We planned to build on the success of our first year study by partnering again with four small-scale organic farms that suffer from swede midge (SM) infestations, located in Cattaraugus, Allegany, Schuyler and Seneca counties. Each farm was a case study where we monitored the SM population, and trialed/optimized management strategies that were appropriate for each farm. In addition, in 2016, we worked with the Cornell Organic Research farm in Tompkins Co. (Table 1).Table 1 2015 farm summary, 2016 plans

Objective 1 i-iv. Advance understanding of swede midge (SM) population dynamics on small-scale organic brassica farms as related to management practices.

Blue Heron Farm, in Lodi, NY (Seneca Co.) grows 12 acres of mixed vegetables in three main fields (No. 1, 4 & 6) that are separated by wooded areas. They also have six high tunnels where brassicas crops and transplants are produced. In 2016, the farm was sold and we worked with both previous and new farm owners during this transition period during which management practices were mostly status quo. The new owners were from Pennsylvania were not familiar with SM. Canticle Farm, in Allegany, NY, grows over 40 different kinds of vegetables year round on about 8 acres and in three high tunnels, of which about 1 acre (12.5%) is cropped to brassicas from mid-April until mid-December.

For monitoring SM populations, pheromone traps were deployed. These consisted of a Jackson trap with sticky card insert and pheromone lure (Distributions Solida Inc., Quebec, Canada), which was secured to a metal stake about 1 ft above ground within the crop canopy (Fig. 3)Fig. 3. A total of 24 traps were set up at Blue Heron (Table 2, Figs. 4, 5 and 6) Table 2 Fig. 4, 5 and 6 and Canticle (Table 3, Fig. 7) Table 3 Fig. 7. These trap sites included seven spring emergence sites where SM-infested brassicas grew the previous fall (2) or summer (3) in 2015, four spring, five summer and four fall brassica plantings, one high tunnel where brassicas were produced, and one transplant hardening off site.  Monitoring occurred from early-May until early-November and traps remained at each site for an average of 12.5 weeks.  The number of SM adults per trap was reported to growers via email on a weekly basis.  At crop maturity, SM damage of the different brassica crops associated with each trap was rated separately on a 5-point (0-4) scale (Fig. 8) Fig. 8. Trap catch and damage information was used to help the grower cooperators make real-time management decisions based on current knowledge. 

Additionally, to accurately determine completion of spring emergence we placed the SM traps under hand-made 2 ft x 2 ft x 1.5 ft inclusion cages that were made of insect exclusion netting (Fig. 9) Fig. 9 to capture only the SM that emerged from the soil while excluding those that originated elsewhere. At Blue Heron, emergence cages were set up at two sites following summer SM-infested brassicas and at one site following fall SM-infested brassicas. Two and three cages were also set up at Muddy Fingers and Quest, respectively, following fall planted SM-infested brassicas (Table 4). Table 4

Objective 2. i. Evaluation of IEN compared to open air with bare ground and black plastic mulch.

Summer Broccoli Mulch/IEN trial. At Canticle, we trialed insect exclusion netting (IEN) with bare ground and plastic mulch for protection against SM in summer broccoli. Treatments included, 1) bare ground in open air; 2) bare ground + IEN; 3) biodegradable black plastic mulch in open air; and 4) biodegradable black plastic mulch + IEN. Our IEN was white ProtekNet, 25 gram, 14-ft width (Dubois Agrinovation). On Jul 5, black plastic mulch was laid and the Canticle crew transplanted the broccoli. On Jul 7, we set up the trial and applied the IEN. There was one 3-ft wide bed of black plastic beside a similar bare ground bed. Broccoli was planted with 2 rows per bed and 1-ft plant spacing. IEN was placed over top of metal hoops that were 4-ft high and 4-ft wide and spaced 6-ft apart; netting was secured to the hoops with clamps and to the ground with sod (Fig. 10) Fig. 10. Each IEN treatment was divided into two 30-ft replicates. The open air treatments were not replicated. A SM pheromone trap and a temperature sensor (Onset Hobo pendant temperature data logger) were placed inside each replicate of each treatment on Jul 7. Traps were serviced as in the monitoring project. Sleeves were installed in the netting so traps could be serviced without risking entrance of SM into the netting.

The grower did not end up harvesting this trial, because the heads were undersized from heat and nutrient stresses. On Sep 2, in 3 sub-samples of 10 plants in a row in each replicate, incidence of heat stress and maturity stage was recorded, and both SM and flea beetle damage rated. SM damage was rated on a 4-point scale, as previously described for the monitoring project, and flea beetle damage was rated on a 6-point scale where 0 = no damage; 1 = minor damage; 2 = minor to moderate damage; 3 = moderate damage; 4 = moderate to severe damage; and 5 = severe damage. Plant height was measured in a sample of 10 plants in a row per replicate. Since the crop was not harvested, we estimated what the marketable yield would be based on SM damage. We estimated that healthy heads and those with minor SM damage would weigh 0.6 lb, while SM-infested heads with moderate damage would weigh 0.4 lb and those with major and severe damage would be unmarketable. We used our grower cooperator’s quoted price of $3/lb for marketable broccoli.

 Objective 2. ii. Effect of white plastic and reflective silver mulch, and green IEN on broccoli quality.

Fall Broccoli Mulch/IEN trial. At Muddy Fingers, we tested mulch and IEN combinations that might create cooler microclimates and reduce plant stress in fall broccoli, which is planted in the heat of July. Treatments included: 1) Hay mulch + white IEN; 2) Hay mulch + green IEN; 3) White plastic mulch + white IEN; and 4) Silver reflective plastic mulch + white IEN. The white IEN was our standard as was used in the trial at Canticle and the green IEN (Filet Anti-Insect AF4040, 70 gram, 16 ft width, HarvestTech) was more durable than the white IEN and had claims of creating a cooler microclimate. The grower cooperator set up the mulch and IEN treatments and planted the broccoli. Mulch treatments were set up in 3-ft wide beds on Jul 12, and broccoli was planted with 2 rows per bed and 1-ft plant spacing on Jul 13. IEN was placed over top of metal hoops as previously described after the broccoli was planted on Jul 13. Each of the four treatments consisted of a 4-ft wide by 150 ft long bed, which was divided into two replications of about 75-ft long. A SM pheromone trap and Hobo temperature sensor were placed inside each replicate of each treatment on Jul 13. Traps were serviced as per the monitoring project. Access sleeves were installed so traps could be serviced without risking entrance of SM into the netting. The grower did not secure the IEN to the ground and by Aug 25, weeds had grown up along the edges of the mulch, which had begun to lift the IEN (Fig. 11) Fig. 11. On Aug 25, the treatments were hand-weeded and IEN secured to the ground with rocks. Since the grower cooperator was harvesting the broccoli from this trial to sell, on Sep 22, plant maturity was recorded for each of 10 plants in a row in three sub-samples per replicate. Plant maturity categories included: 1) unmarketable due to heat stress, and marketable categories 2) first cut – cut wound was already callused over; 3) second cut – cut wound was fresh); 4) head 4-6-inch diameter; 5) head 2-3-inch diameter; and 6) head up to 1-inch in diameter. On Oct 28, plant height was measured for a total of 30 plants per replicate in the same manner as for crop maturity.

Objective 2. iii. Evaluation of garlic oil with spreader-sticker as repellent of SM.

Canticle Farm hosted three trials evaluating food-grade essential garlic oil repellent 1% (Bulk Apothecary) used in combination with adjuvant, Nufilm-P 0.25% v/v (Miller) compared to an untreated check. Trials were set up in Red Russian kale in spring and fall plantings and in kohlrabi in a summer planting with 4-5 replicates (only 1 rep in spring trial) and 10 plants/treatment-replicate. Treatments were applied to individual plants to run-off using a spray bottle, starting within 1 week of transplanting and continued weekly until harvest for a total of nine, four and six applications per trial. At harvest, SM damage per plant was rated on the 5-point scale described previously.  

 Objective 2. iv. Crop preference/trap crop study.

To understand the dynamics of SM in preferred and less preferred crops, we set up a replicated small-plot trial on Quest Farm at a site where severely SM-infested broccoli occurred during the fall of 2015. Treatments included broccoli c.v. ‘Belstar’, Red Russian kale and Bok Choy c.v. ‘Prize Choy’ (Asian brassica), which were planted in monoculture and in two-crop combinations for a total of six treatments, which were replicated four times; Reps 1 and 2 were planted on May 6 and reps 3 and 4 were planted on Jun 3. Organic transplants were produced by Quest Produce. The trial was planted on a 3 ft wide bed with plastic mulch and drip irrigation, which was prepared by the grower cooperator. Individual plots were one bed wide by 12 ft long with about 20 plants of broccoli or Bok Choy with 1 foot plant spacing and 1.5 foot row spacing, and 40 plants of Red Russian kale with 6 inch plant and 1.5 ft row spacing.  In the combination treatments, different crop types were grown side-by-side with each row being a different crop.  At maturity, SM damage was rated and SM incidence quantified on Jul 26, 80 and 53 days after planting reps 1 and 2, and reps 3 and 4, respectively.

Objective 2.v. Effect of plastic mulch on SM pupation and emergence. 

After the crop preference study at Quest Produce was complete, we took advantage of the severely SM-infested Red Russian kale to evaluate the effect of black plastic mulch compared to bare ground on SM pupation and emergence.  Growers question whether plastic mulch may serve as a barrier to SM larvae pupating in the soil, and if so, whether this could be used as a strategy to reduce SM populations.  Each Red Russian kale plot was divided in half and the plastic mulch removed from one-half of the plot.  Emergence cages were set up over the infested kale on both the bare ground and black plastic mulch sides of each plot in each of the four replicates (Fig. 12) Fig. 12.  SM trap catches within each cage were monitored from Aug 12 to Oct 19.

Objective 2. vi. Effect of post-harvest practices on SM emergence: Large-cage study.

At Canticle, we took advantage of an SM-infested Red Russian kale crop that the grower was going to disk up to set up a trial to evaluate post-harvest practices on SM emergence.  We set the trial up just after SM larvae dropped to the soil to pupate, as indicated by the fact that we could not find any larvae in plants exhibiting SM damage or in new growing tips.  Treatments included, 1) Plants left intact (=Untreated); 2) Shallow tillage to 4 inch depth (grower practice); and 3) biodegradable black plastic mulch, which was placed over the top of living kale plants (Fig. 13) Fig. 13.  Treatments were replicated two times. The large cages consisted of a section of 4 ft wide by 6 ft long bed which had IEN placed over 4 ft x 4 ft electrical conduit hoops in each plot. A SM pheromone trap was placed inside each cage. SM trap catches were collected for 16 weeks from Jul-7 until Oct-28.

 Objective 2. vii. Effect of minimum tillage and tarping on SM emergence: Small-Cage Study.

At the Cornell HTC Vegetable Research Farm in an intensive systems study, cabbage suffered SM-infestation in 2015. The project was studying six tillage systems overlaid with three mulch types. In our 2016 study, we compared the effect of 1) No tillage, 2) Fall minimum tillage and 3) No tillage + tarping on SM spring emergence (Table 5) Table 5. On May 9, SM emergence cages (2 ft x 2 ft x 1.5 ft) with pheromone traps were placed in each treatment in each of three reps. For the no tillage + tarping treatment, the SM emergence cage was placed underneath the tarp. A pheromone trap was also placed in the open air in the no tillage treatments. SM trap catches were monitored weekly until Jul 27.

Analysis.

Data collected from replicated trials was analyzed using General Analysis of Variance and means were separated using Fisher’s Protected LSD test with 5% significance. Monitoring data was summarized and related to the unique circumstances of each farm/trial.

Objective 3. Educational outreach.

See Educational Activities section.

Research results and discussion:

Objective 1 i-iv. Advance understanding of swede midge (SM) population dynamics on small-scale organic brassica farms as related to management practices.

Objective 1. i. Definitive end date of emergence of the overwintering generation.

At Quest Produce and Blue Heron, we set up three small SM emergence cages per field following a 2015 fall planting of SM-infested brassicas (Table 2 & 4). At Muddy Fingers, we set up a single small cage in each of two fields where SM-infested brassicas were grown the previous fall (Table 4). Unfortunately, at Canticle, all of our small cages had to be removed, and we were unable to obtain any usable data. In the paired open-air traps, first SM were captured on May 20 at Quest (1 of 3 traps), May 24 at Blue Heron (all three fields) and on May 25 at Muddy Fingers (both fields) (Figs 14, 15 & 16) Fig. 14 Fig. 15 Fig. 16. This was about a week later than we observed in 2015. At Blue Heron and Muddy Fingers, we observed a bimodal spring emergence peak in late-May and mid- to late-June (Fig. 15 & 16). At Quest, SM emergence occurred in a single peak from late-June to mid-July (Fig. 14). Trap catches inside small cages were low compared to the open-air traps due to the small area (4 ft2) to draw from. Although first trap catches were later in the small cages than in the open air, fluctuations in trap catches were similar. Inside the cages, first SM were captured on May 31 at Blue Heron (Fig. 15), Jun 6 at Muddy Fingers (Fig. 16) and Jun 10 at Quest (Fig. 14). The last SM small cage captures were on Jul 2 at Quest (Fig. 14), Jul 21 at Muddy Fingers (Fig. 16) and Aug 5 at Blue Heron (Fig. 15). Although we know that the majority of SM emergence occurs during May and June, these results confirm that a small proportion of SM will continue to emerge from an overwintering site throughout July and into early August.

 Objective 1. ii. Intensity and duration of SM emergence in the spring at a site where an infested crop was grown the previous summer.

At Blue Heron, we set up three small cages each in two locations in Field No. 4 that followed a summer planting of SM-infested crop (Table 2). Unfortunately, our traps at Canticle had to be removed and we did not get usable data. In open-air, the first SM trap catch in the field following a 2015 SM-infested summer crop occurred at the same time as the first catch following a SM-infested fall planting (Fig. 15). Interestingly, at both locations, only a single peak of emergence occurred in late-June following a SM-infested summer planting, which was about two weeks after the first peak emergence following a SM-infested fall plantings. Although first trap catches were slightly later in the small cages than in open-air, fluctuations in trap catches were similar. Inside cages, the last SM were captured on Jul 21 and Aug 5, which was the same as the spring emergence sites following SM-infested fall crops (Fig. 15). We hypothesized that spring emergence following a SM-infested summer planting would be much lower than following a SM-infested fall planting, because we thought that in the summer SM would emerge and leave the site in search of another suitable host, whereas in a fall planting, most SM would drop to the soil to pupate and overwinter at the same site. These results indicate that SM emergence in the spring may be equally as strong following both SM-infested summer and fall plantings, which must be considered when making crop rotation decisions. Since our data was only collected from two fields, it would be worthwhile to continue to study this phenomenon on different farms under different pest pressures and different post-harvest practices.    

 Objective 1. iii. Annual SM population dynamics per farm.

Blue Heron. SM pressure generally increased at Blue Heron from 2015 to 2016, primarily due to lack of crop rotation, use of SM-infested transplants and lack of post-harvest crop destruct. In field No. 1 in 2015, SM populations were moderate-high with peak SM trap catch of 16/trap/day on Sep 15 and 25% infestation in red cabbage (data not shown). In 2016 in field No. 1, spring SM emergence was moderate (Table 6) Table 6with a bimodal peak (1st: 5.2 SM/trap/day on May 31; 2nd: 5 SM/trap/day on Jun 22) followed by two consecutive weeks of no trap catches until Jul 12 when the trap was taken down (Fig. 17 top) Fig. 17. SM populations built slowly and a summer planting of broccoli was harvested with only minor SM damage (data not shown). Unfortunately, the crop was not destructed post-harvest and the SM population eventually built up in late September and remained high (Table 6) until late-October (peak: 38 SM/trap/day on Sep 22) (Fig. 17 top). After main harvest and leaving plants intact, the SM population increased almost 10-fold in just three weeks from 4 SM/trap/day on Aug 26 to 38.3 SM/trap/day on Sep 22. This is an example of how SM population can build after harvest in absence of post-harvest crop destruct. It is expected that there will be a large spring emergence of overwintering SM at this site in spring 2017.

In field No. 4, in 2015, brassicas were planted from early May until late July with brassicas remaining in the ground when the last traps were taken down on Nov 11. Peak trap catches in fall included 72.2, 43.7 and 39 SM/trap/day on Aug 26 in fall Romanesco/cauliflower (73% infested, 40% unmarketable), on Aug 26 in fall cauliflower (80% infested, 37% unmarketable) and on Oct 14 in fall broccoli (97% infested, 23% unmarketable), respectively (data not shown). In 2016, spring SM emergence was moderate-high (Table 6) following 2015 fall SM-infested site with a bimodal peak (1st: 17.7 SM/trap/day on May 31; 2nd: 9 SM/trap/day on Jun 28). Spring SM emergence from 2015 summer planting sites were high (35.1 SM/trap/day on Jun 22) and moderate-high (12 SM/trap/day on Jun 21) and had only a single peak (Fig. 17 bottom). Despite our recommendations, the growers implemented their usual practices and planted green cabbage in early June, which was followed by a summer planting of red cabbage in mid-June. SM trap catches were high (Table 6) in green cabbage (peaks: 31 SM/trap/day on Jun 22 and Jul 27) and very high in red cabbage (peaks: 67.9 SM/trap/day on Aug 17) (Fig. 17 bottom). The red cabbage had 48% infested plants and 3% unmarketable heads (Table 7) Table 7. Fall plantings of cauliflower/Romanesco/red & green cabbage and broccoli had 55% infestation/33% unmarketable heads and 95% infestation/55% unmarketable heads in Romanesco and broccoli, respectively (Table 7). Essentially, SM population consistently doubled between the peaks of spring emergence, to peak of spring cabbage planting, to peak of summer cabbage planting and to the peak of fall broccoli planting for a total 8-fold increase across the growing season (Fig. 17 bottom). This is an example of how SM population builds in the absence of far and wide crop rotation and timely post-harvest crop destruct. SM pressures in the fall were similar between 2015 and 2016 in this field. We expected that this field would have very high emergence of SM in spring 2017.

In 2015, field No. 6 had a moderate level of SM (Table 6) in fall planting of Romanesco (10 SM/trap/day on Oct 14) (data not shown). It was expected that this field would have the lowest SM emergence in the spring of the three fields at Blue Heron. In fact, it had higher SM spring emergence in 2016 than field No. 1, but was similar to field 4 and also had a bimodal peak (1st: 31 SM/trap/day on May 31; 2nd: 2 SM/trap/day on Jun 21) (Fig. 18 top) Fig. 18. This field was planted to fall cabbage after the majority of SM spring emergence was complete and the fall cabbage suffered no losses from SM (data not shown). Unfortunately, the fall transplants were infested with SM and the SM population increased to moderate-high levels (peak: 17.4 SM/trap/day on Oct 6) (Fig. 18 top). This is an example of how good crop rotation may be defeated when SM is introduced on infested transplants. Spring SM emergence was expected to be lowest in field No. 6 compared to field Nos. 1 and 4 in 2017.

In 2015, the odd SM was captured in the high tunnels at Blue Heron (<1 SM/trap/day), while much higher levels (peak: 7 SM/trap/day on Jul 8) were captured in the open air transplant hardening off area outside of the high tunnels (data not shown). In 2016, SM were captured in the hardening off area with similar peak as the previous year (9 SM/trap/day on Jun 22) and generally less than 2 SM/trap per day from May 24 to Oct 13 (Fig. 18 bottom). We only monitored tunnel No. 2, which had open sides and kale and Asian brassicas planted in the ground. Here, SM pressure was moderate-high (Table 6) throughout June and July (peaks: 16.6 SM/trap/day on Jun 22; 13.8 SM/trap/day on Jul 7; 10.3 SM/trap/day on Jul 23) despite brassicas being removed and replaced with peppers in early July (Fig. 18 bottom). SM damage was observed in brassica plantings in the high tunnels and transplant hardening off area (data not shown). Apparently, at one time the grower had transplanted kale plants from the field into the high tunnel. The field-grown kale must have been infested with SM, as this could explain the SM population in the high tunnel. The constant SM catches in the open-air trap in the hardening off area also indicated a constant presence of SM in this area of the farm, despite it being about 500 ft away from the brassica production fields (Fig. 4 top). SM could also enter into the open sided high tunnels from the outside. Finding SM-infested transplants in the hardening off area implies that the newly planted transplants in field No. 6 exhibiting SM damage were most likely infested during transplant production instead of in the field.

 Canticle. Generally, it appeared that the SM population at Canticle increased slightly from 2015 to 2016, primarily due to a small land base and constant production of brassica production that make crop rotation ineffective. In 2015, in the Back field, a fall planting of broccoli suffered 92% infestation and 69% unmarketable heads in fall broccoli where SM pressure was high (peaks 20.2 SM/trap/day on Aug 28 and Sep 10). Similarly, Red Russian kale had 75% SM infestation in a summer planting in the Middle field under high pressure (40.4 SM/trap/day on Aug 28 and 30 SM/trap/day on Sep 10). In the Front field, Red and white Russian kale had 82% and 75% SM infestation, respectively under moderate-high SM pressure (peak: 13.4 SM/trap/day on Sep 17) (data not shown).

In 2016, interestingly, SM emergence was lower than expected in the Middle field following 2015 summer mixed brassicas (peak: 4.1 SM/trap/day on Jul 7) (Fig. 19) Fig. 19. Trap catches were generally slow to increase, until in the Front field SM pressure climbed to high levels (Table 6) in a spring planting of kohlrabi (peaks: 21.1 SM/trap/day on Jul 2 and 35.8 SM/trap/day on Jul 15), which had 60% SM-infested and 23% unmarketable bulbs (Table 7). The high SM population (peaks: 30 SM/trap/day on Aug 17 and 73 SM/trap/day on Sep 16) moved to the Front Corner field where it caused 97%, 63% and 46% SM-infestation in broccoli, kohlrabi and cauliflower, respectively and 53% of the broccoli was unmarketable (Fig. 19, Table 8) Table 8. In the Back field, the fall brassica plantings suffered from 40%, 18% and 13% unmarketable crop loss in broccoli, cauliflower and turnip, respectively (Table 8) despite low trap catches (3.6 SM/trap/day on Sep 2) (Fig 19). In the Middle field, under moderate pressure (peak: 5.8 SM/trap/day on Oct 12), a fall planting of mixed leafy brassicas had 15 to 60% SM-infestation (Table 8). In the absence of a break from brassica production on this small farm, SM population at least doubled from early July until mid-September (Fig. 19) and highest trap catches in September were almost doubled from the previous year. It is expected that highest levels of SM emergence in spring of 2017 will occur in the front corner field, followed by the back field, while the middle field and the field behind the barn will have lowest. Planting susceptible brassicas like broccoli, kohlrabi and Red Russian kale should be avoided in the front corner field in spring 2017.

Objective 1. iv. Differences in SM damage among crop types.

Of the five plant types in three plantings at Blue Heron and 15 crop types in four plantings at Canticle that we evaluated, the highest proportion of unmarketable produce at harvest was broccoli. In a fall planting under very high SM pressure at Blue Heron (Field No. 4) broccoli had 55% unmarketable heads, which was numerically 35% more than cauliflower (Table 7). At Canticle, in a summer planting under high SM pressure (Front Corner), broccoli had 53% unmarketable heads, which was significantly more than kohlrabi (11%), cauliflower (0%), red cabbage (3.3%) and green cabbage (0%). Also, in a fall planting under moderate SM pressure (Back Field), broccoli had 40% unmarketable heads, which was significantly more than cauliflower (17.5%) and turnips (12.5%) (Table 8). At Blue Heron, in a fall planting under very high SM pressure, Romanesco had significantly more unmarketable heads (33%) than cauliflower (0%), while both had high levels of SM infestation (Romanesco – 77.5%; cauliflower – 57.5%). In these plantings, red cabbage and green cabbage had 0-3% (n=3) and 0% (n=2) unmarketable heads (Table 7). Although we never observed significant differences between red and green cabbage, numerically red cabbage tended to have higher SM infestation and damage ratings (Table 7 & 8). At Canticle, green kohlrabi had significantly higher SM infestation and damage ratings than red kohlrabi, although they had the same proportion of unmarketable heads (24%) (Table 8). At Canticle, kale and collards did not result in unmarketable produce under moderate SM pressure. In this planting, collards (60%) and Red Russian kale (45%) had significantly higher SM infestation than purple kale (15%), green kale (17.5%) and Bok Choy (2.5%), while Napa cabbage and Lacinato kale were free of SM (Table 8).

In general, highest levels of SM damage occurred in broccoli, followed by Romanesco, and then by kohlrabi (especially green), and cauliflower. Our studies indicate that these crops are not only preferred by SM, but also cannot withstand as much SM damage, as any scarring in the head renders the produce unmarketable. Alternatively, although we tend to observe high SM infestation in Red Russian kale, because the leaves are marketed and the plants have many leaves, this crop can withstand much more SM damage before a single plant is deemed unmarketable. After broccoli, Romanesco, Kohlrabi and cauliflower, purple/Dinosaur kale and cabbage appear to be most preferred by SM. Although in 2015 we observed high levels of SM infestation and unmarketable heads in cabbage, we have observed that this crop is quite tolerant to SM when SM occurs after head formation. Turnips and green (Winterbor) kale are even less preferred and impacted by SM, while Asian brassicas (Bok Choy, Napa cabbage) are rarely attacked at all. These results are similar to our 2015 findings. Whether SM populations build to a greater degree in their more preferred brassica plant types warrants further investigation. Understanding SM plant damage is a valuable tool for growers to make crop management decisions, especially with respect to crop rotation and selection.

 Objective 2. Optimize management strategies including newly developed disruption tactics, insect exclusion netting (IEN) and garlic oil repellent, crop selection and rotation strategies.

 Objective 2. i. Evaluation of IEN compared to open air with bare ground and black plastic mulch.

Summer Broccoli Mulch/IEN trial (Canticle). In this trial, Insect Exclusion Netting (IEN) resulted in zero SM damage or 100% control compared to the broccoli that was grown in open-air, which had 97% and 100% SM-infested plants with 50% and 70% unmarketable heads on black plastic mulch and bare ground, respectively, with minor to moderate severity of SM damage (Table 9) Table 9. The open-air traps caught a total of 330 and 358 SM per 8-week trial with maximum trap catches of 97 and 102 SM per week (Table 10) Table 10. This level of SM pressure and damage is considered to be moderate-high (Table 6). In the bare ground + IEN replications, a total of 22 and 28 SM were captured inside the netting, which likely made their way into the netting when the access sleeves fell off (Table 10). Fortunately, these low levels of SM did not result in SM damage in the broccoli inside the netting. In addition to protecting the broccoli from SM, IEN also significantly reduced flea beetle damage from severe in the broccoli grown in the open air to none in the broccoli grown under the netting (Table 9, Fig. 20) Fig. 20. IEN increased marketable broccoli yield by an estimated 68 lb to 92 lb and crop value by $204 to $276 per 100-ft of bed in just SM protection alone, which is 2.3 to 4.3 times higher than broccoli grown in open-air (Table 9).

Although there were no significant differences in incidence of heat stress among treatments, heat stress ranged from 0 to 46.7% (Table 11) Table 11 Canticle mulch IEN trial maturity. The highest level of heat stress occurred in the black plastic open-air treatment, which was 14-times higher than black plastic + IEN, which suggests that IEN can greatly reduce heat stress of broccoli grown on black plastic mulch in the heat of summer. In the bare ground treatments, heat stress was numerically higher (23.3%) with IEN than without (0%). Plant maturity as indicated by plant maturity rating, was most advanced in bare ground + IEN, which was not significantly different than black plastic + IEN, which were both significantly more advanced than black plastic open-air, while bare ground + IEN was significantly the least advanced in maturity than all other treatments (Table 11, Fig. 20). With both bare ground and black plastic, but especially with black plastic, broccoli grown under IEN matured significantly faster than broccoli in open-air. Eighty percent of the plants were not ready on Sep 2 in bare ground open-air treatment, which was significantly higher than all other treatments (6.7%, 10%, 20%). Plants were also significantly 3.7 and 6.5-in taller under IEN in both bare ground (OA: 19.7-in; IEN: 23.4-in) and black plastic (OA: 20.6-in; IEN: 26.8-in), respectively (Table 11, Fig. 21). Fig. 21

The greatest differences among treatments occurred in maximum weekly temperatures, which differed by as much as 5 to 16 ⁰F, while minimum and average weekly temperatures differed by 0 to 3 ⁰F, and 1 to 6 ⁰F, respectively (Fig. 22 and 23) Fig. 22 & 23. Most notably, for the first four weeks of the trial (Jul 7 to Jul 28), black plastic + IEN had the hottest maximum temperature, while black plastic open-air was the coolest. Bare ground treatments were between the plastic extremes with open-air being hotter than bare ground + IEN (Fig. 22 top). From Aug 4 to Aug 11, bare ground open air was the hottest treatment in the trial, while bare ground + IEN was the coolest. During the last two weeks of the trial (Aug 18 to Sep 1), both bare ground treatments had cooler maximum temperatures than black plastic. Black plastic + IEN consistently had higher maximum temperatures than black plastic open-air, while bare ground open air consistently had higher maximum temperatures than bare ground + IEN (Fig. 22 top). These bare ground temperature results are similar to our observations in 2015, where bare ground open-air was hotter than bare ground + IEN from Jul 22 to Aug 26. Likely, with bare ground, the cooler temperatures inside the netting significantly advanced crop maturity compared to open-air, because broccoli does not grow well when temperatures exceed 80 ⁰F. When used with black plastic, it appeared that the netting trapped heat inside, but surprisingly the increased maximum temperatures did not delay crop maturity (Table 11). Perhaps, the added protection from flea beetles and worm pests provided by the netting reduced plant stress from pest attack, which may explain why plant height and maturity was improved when broccoli was grown with IEN (Table 11).  

 Economic analysis. In our 2015 study (NESARE Partnership ONE15-237), we estimated that IEN cost $236 per 100-ft bed on bare ground ($175.61 for IEN + $60 for setting up netting and hand weeding), and $205 per 100-ft bed with mulch (no hand weeding expense). These costs do not include initial investment in hoops, stakes and clamps, which are reusable. With no SM damage, the broccoli crop was valued at $360 per 100-ft bed (2 rows/3 ft), which would result in $124 and $155 net profit with IEN + bare ground and IEN + plastic mulch, respectively (Table 9). Interestingly, when the cost of IEN was factored in, there was no difference in net return between 0% SM crop loss with IEN and 50% SM crop loss without IEN on plastic mulch. When crop loss was 70% without IEN on bare ground, net profit was $40 (1.5-times) higher with IEN on bare ground. When we use average price of organic broccoli according to USDA ($2.32/lb) instead of $3/lb that Canticle gets, 100% SM control with IEN would result in $278 per 100-ft bed in our study, minus $205 in cost of IEN (with mulch) for a net profit of only $73 per 100-ft bed. This is less than half of the profit of absorbing 50% crop loss without netting. These results clearly demonstrate that in order for IEN to be economical, that both the potential loss due to SM and price earned for broccoli, need to be high (e.g. > 50% crop loss, at least $3/lb). However, use of IEN can also provide value via 100% control of flea beetle, a healthy beautiful crop to sell (instead of losing customers when crop is short or nonexistent due to SM damage), advanced maturity and reduced heat stress (at least with black plastic) . Also, economic feasibility of IEN will increase as it is used multiple times. For example, IEN used for broccoli may be re-used over low hoops in kohlrabi.    

 Objective 2. ii. Effect of white plastic and reflective silver mulch, and green IEN on broccoli quality.

Fall Broccoli Mulch/IEN trial (Muddy Fingers). This trial was designed to investigate whether different insect exclusion netting (IEN) and mulch combinations would alleviate heat stress when broccoli was planted during the heat of July. No SM damage occurred in any of the IEN treatments resulting in 100% control (data not shown) despite a few SM being captured inside the netting (Table 12) Table 12 and 13. This was likely a result of the unsecured sides being lifted when the weeds at the edges of the beds grew large (Fig. 11). There were no significant differences among treatments for incidence of heat stress, although numerically white plastic + white IEN had the highest (46.4%), followed by silver mulch + white IEN (22.3%), while the hay mulch treatments had the least with no difference between white (13.7%) and green IEN (13.3%) (Table 13). Significant differences occurred among treatments in maturity for the first cut and the 2-3-inch head categories (Table 13). Hay + green IEN had significantly the most delayed maturity compared to all the other treatments with only 6.6% heads in the first cut category and numerically the highest proportion of heads in the 2-3 inch head (27.6%) and ≤ 1 inch head (18.1%) categories. White and silver plastic mulches with white IEN had relatively similar maturity, which was slightly behind hay mulch + white IEN. Hay + white IEN had significantly the tallest plants (28.3 inch), which were significantly ~ 3 inch taller than all other treatments. White plastic mulch + white IEN had the shortest plants (24.2 inch), which were not significantly different than silver plastic mulch + white IEN (Table 13.)

It was our hypothesis that all treatments would have resulted in cooler temperatures and reduced heat stress compared to hay + white IEN. The greatest differences among treatments occurred in maximum weekly temperatures, which differed by as much as 6 to 10 ⁰F, while minimum and average weekly temperatures differed by 1 to 8 ⁰F, and 1 to 4 ⁰F, respectively (Fig. 24 and 25) Fig. 24 & 25. Silver plastic mulch + white IEN had the highest maximum temperature throughout the trial and the highest minimum and average temperature until Sep 2, after which white plastic + white IEN had the highest minimum and average temperatures (Fig. 24 and 25). Perhaps, these higher temperatures are the reason why white plastic mulch + white IEN and silver plastic mulch + white IEN had higher incidences of heat stress than the straw treatments. In 8 out of the 10 weeks, hay + green IEN had a lower weekly average temperature than hay + white IEN by ~1 to 2 ⁰F, while their average weekly minimum temperatures were similar and, the average weekly maximum temperatures toggled back and forth as to which was higher. Our results support the manufacturer’s claims that green netting keeps temperatures cooler. Perhaps, silver plastic mulch resulted in the highest temperatures because heat was reflected back and trapped in the netting. It is unknown why minimum temperatures in white plastic + white IEN increased compared to all other treatments after minimum temperatures dropped below 57 ⁰F (Fig. 24). The only treatment that significantly affected crop maturity was green IEN, which significantly delayed crop maturity. White and silver mulch + white IEN did not result in lower temperatures or reduced heat stress compared to hay mulch + white IEN in this study. However, determining the effect of these treatments on yield is warranted. The cooler temperatures of green IEN may result in a significant reduction in heat stress and consequent yield increase in a summer planting trial when broccoli is harvested in August, a timing that is usually prohibitive due to heat stress. Since black plastic is the most commonly used mulch type, trialing it in combination with green IEN would also be worthwhile. We observed that the green IEN was definitely more durable than white IEN, and could likely be re-used several more times than white IEN could be. Since green IEN ($187/100-ft) is similar in price to white IEN ($175/100-ft), it may actually be more economically feasible than white IEN if it can be re-used more often.    

Objective 2. iii. Evaluation of garlic oil with spreader-sticker as repellent of SM (Table 14) Table 14.

In 2015, we did not observe any efficacy with garlic oil as a repellant of SM. In 2016, we tested it with the addition of spreader sticker Nu-film P in hopes that the adjuvant would reduce plant runoff and improve the longevity of the essential oil on the plants. In the two replicated trials, there were no significant differences between untreated plots and those treated with 1% essential garlic oil + Nufilm-P 0.25% v/v for % SM incidence, % unmarketable plants, and average SM damage rating. The untreated controls averaged 90%, 46% and 45% SM incidence in the spring (Red Russian kale), summer (kohlrabi) and fall (Red Russian kale) planted trials where SM pressure was moderate, high and moderate, respectively (Table 6). SM incidence was reduced by almost half from 90% in the untreated to only 40% with garlic oil + Nu-film-P in the spring Red Russian kale trial, which was not replicated. SM was numerically lower in the garlic oil treatments than the untreated for average SM damage per plot and for average SM damage per infested plants in the summer and fall trials, and for % unmarketable plants in the summer trial. Despite promising results in laboratory trials with garlic essential oil as a repellant of SM, it unfortunately did not work in any of our field trials, even with the addition of a spreader-sticker. However, this strategy may be worth trialing again, because there were some weeks when the technicians were either sloppy making their garlic oil applications, or forgot to treat the garlic oil trials altogether. And, a fresh batch of garlic oil mixture was only prepared when the premixed supply ran out, instead of before each application.

 Objective 2. iv. Crop preference/trap crop study (Table 15) Table 15.

We set up a trial in open air to determine whether a more preferred by SM brassica crop than broccoli could be used as trap crop to protect the broccoli. We compared more and less SM-preferred crops in combination to each in monoculture. Significant differences occurred among treatments for % SM incidence, % unmarketable and mean SM damage rating per plant. Incidence of SM infestation was significantly higher in Red Russian kale than in any other plant type with 94% in monoculture, 95% when grown beside broccoli and 86% when grown beside Bok Choy. Bok Choy had zero SM infestation in monoculture and when grown beside broccoli and Red Russian kale. With shorter days to maturity than broccoli, it was possible that by the time the SM population began to build at this site that Bok Choy had already began head formation, after which time brassicas are generally no longer preferred by SM, because the meristematic tissue where they lay their eggs is protected deep within the developing head. However, Bok Choy in rep 3 & 4, which was planted on Jun 3, one month later than reps 1 & 2, was exposed to moderately-high SM pressure (Fig. 26, Table 6) Fig. 26 and still did not sustain any SM damage.

Broccoli monoculture had 60% SM infestation, which was significantly reduced to about half to 34% when grown beside Red Russian kale. When it was grown beside Bok Choy it was numerically reduced to 41%. Red Russian kale grown beside broccoli had the highest % unmarketable plants (66%), which was not significantly different than Red Russian kale grown beside Bok Choy (58%) and Red Russian kale monoculture (58%). Broccoli monoculture had 43% unmarketable heads, which was numerically reduced to 30% when grown beside Red Russian kale, and to 23% when grown beside Bok Choy. These results demonstrated that Red Russian kale was more preferred by SM than broccoli, while Bok Choy appeared to be completely tolerant to SM. Consequently, broccoli grown beside the more preferred Red Russian kale sustained less SM infestation and had more marketable heads than broccoli grown in monoculture. Interestingly, when broccoli was grown beside Red Russian kale, even though the % SM infestation and % unmarketable heads were less than monoculture broccoli, the severity of damage in the SM-infested heads was significantly higher than broccoli monoculture and broccoli beside Bok Choy. Although the concept of using a more preferred brassica as a trap crop to protect broccoli from SM holds promise, more research is needed, specifically the concept should be tested under different SM pressure and in different planting configurations. Also, management of the trap crop needs to be considered and tested to ensure that the SM population does not build and spill into marketable brassica crops, which would defeat its purpose.

Economic analysis: According to our yield estimates, growing broccoli beside Red Russian kale and Bok Choy increased marketable yield by 25% and 36%, respectively compared to monoculture broccoli, which resulted in an additional $51 and $72 per 100 feet of bed. This could be as much as $3,703 to $5,227 per acre (assuming 3-foot wide beds with 3 feet between beds). However, these figures do not take into consideration the planting configuration used in this study where half of each bed was used to grow the trap crop instead of broccoli. In this case, if half of each broccoli bed was cropped to Red Russian kale, marketable yield of broccoli would also drop in half to 41.5 lb and $125 per 100 ft bed, which would be even lower than growing monoculture broccoli with 43% unmarketable heads. Ideally, a planting configuration that utilizes proportionately less trap crop than cultivated crop will be found to be effective, because this will enhance the economic feasibility of this potential SM management strategy.

Objective 2.v. Effect of plastic mulch on SM pupation and emergence: Small Cage Study

In this study, we wanted to determine whether SM pupation and emergence was reduced when SM-infested plants were grown on black plastic mulch compared to bare ground. Our hypothesis was that plastic mulch would reduce SM trap catches, presumably because some of the SM larvae that dropped from the plant to the ground to pupate would land on the plastic, which would hinder their ability to get into the soil to pupate. Consequently, fewer SM adults would emerge if fewer SM pupated successfully. It is unknown whether or how far SM larvae can crawl over top of plastic mulch to find a plant hole in the plastic through which to enter the soil.

Although lower in number, peaks in SM trap catches inside the small cages generally resembled those of the open air traps (Fig. 27 top) Fig. 27. SM trap catches were similar between bare ground and plastic mulch in the first and third generations with bare ground having very slightly higher catches than plastic (Fig. 27 bottom). The greatest difference between treatments in trap catches occurred during the second-generation peak, where SM population in bare ground was 74-260% higher than plastic (Fig. 27 bottom). In total, SM trap catches were significantly 37% higher where Red Russian kale was grown on bare ground compared to black plastic (Fig. 28) Fig. 28. Presumably, there were no differences between treatments during the first generation because the plastic had just been removed and the SM that were captured were generated before the bare ground treatment was established. The dramatic difference between SM trap catches in the second generation suggests that in bare ground many more SM larvae dropped to the soil where they successfully pupated and subsequently emerged compared to plastic mulch. Thus, these results suggest that plastic mulch may serve as a barrier to SM pupation.

 Objective 2. vi. Effect of post-harvest practices on SM emergence: Large-Cage Study.

In this study, we investigated the effect of post-harvest practices on SM emergence. We assumed that the majority of SM from the infested Red Russian kale plants had already dropped to the soil to pupate when post-harvest treatments were applied, because we found hardly any SM feeding in the plants. Although lower in number, peaks in SM trap catches inside the large cages generally resembled SM population trends of the open-air traps (Fig. 29 top) Fig. 29. Shallow tillage to 4 inch following harvest of SM-infested kale resulted in a significant 72% reduction in total subsequent SM captures over a 4-month period compared to intact plants (= untreated) (Fig. 29 bottom). It is unknown whether the reduced trap catches in the tillage treatment occurred, because tillage destroyed SM larvae feeding in the plants, which then never pupated or emerged, or because tillage displaced SM pupae in soil from top 1 inch to deeper depths that reduced subsequent SM emergence. What happens to SM pupa when it is displaced to greater than 1 inch in soil profile is unknown. They could perish, wait until they resurface (via tillage) to emerge, or attempt to emerge from greater depths with varying success. It is believed that deep tillage is an effective management strategy to reduce SM pressure. It is important to note that in our trial there was some re-growth of the kale plants in the shallow tillage treatment, which we pulled out as soon as we discovered them. However, these plants could have served as a host for SM during this time. Perhaps the tillage treatment could have reduced SM populations even further had there not been any plant regrowth.  

Applying biodegradable black plastic mulch over top of intact SM-infested kale plants resulted in an 88% reduction in subsequent total SM captures compared to intact plants with no cover, which was not significantly different from shallow tillage. When the trial was taken down, we observed tears in some of the plastic through which SM could have emerged. Nonetheless, these results indicate that the plastic mulch served as a barrier to SM emergence. It is unknown whether the SM emerged under the plastic and then perished in the absence of an exit, or if they were alive and waiting to emerge when the barrier was removed. Further work to determine whether plastic mulch or another ground barrier could be used as a management strategy to prevent SM emergence and reduce the SM population is warranted. However, to be effective, the ground barrier would have to be thicker and more resistant to tearing than the biodegradable black plastic mulch that we used in this study.

Objective 2. vii. Effect of minimum tillage and tarping on SM emergence: Small-Cage Study.

SM trap catches in small cages were about a third of that in the open-air traps with peak emergence occurring in late June (Fig. 30) . There were no significant differences among treatments in average 11-week total SM trap catches in the small cages (Fig. 31) Fig. 30 and 31. Numerically, fall tillage and no tillage with tarp (= no tillage after tarp removed) captured 3-times as many SM as no tillage. We hypothesized that the no tillage system would result in higher SM emergence, because the cabbage re-growth in the fall could have been a favorable host for SM, unlike the tarp and fall tillage treatments in which cabbage residue was destroyed (Table 5). Presumably, there would have been no disturbance of SM pupa deeper into the soil profile in the no tillage treatment, leaving them all within the top 1 inch for easier emergence compared to shallow tillage, similar to our results from the post-harvest study at Canticle. Although our results suggest that no tillage did not increase SM population, this warrants further research, because the sample areas (3 reps of 4 ft2 area) were rather small. First SM emergence occurred at the same time (May 25) in all the small cages as it did in the open air (Fig. 30 bottom), which suggests that the tillage practices and tarp did not have any effect on timing of SM emergence. Theoretically, the different treatments could have resulted in different soil temperature (such as warmer underneath tarp) and moisture levels that could have affected timing of SM emergence.

The fact that SM emerged in the cages underneath the tarp is encouraging. If SM are capable of emerging underneath a tarp, then perhaps use of tarp or another type of ground barrier such as landscape fabric or plastic mulch might be a pragmatic means of crashing a SM population at a spring emergence site. In this study, the tarp was laid over a 1.5 ft tall cage instead of being pressed against the ground. Whether SM emerge and consequently perish underneath a ground barrier laid directly on the ground surface warrants further investigation. Alternatively, they might be alive and waiting to emerge once the ground barrier is removed.  

Although overall trap catches might be too low to draw any conclusions, we did observe that the fall tillage treatment appeared to have two emergence peaks (Jun 15 & Jul 13) compared to the two no tillage treatments and open air, which had a single emergence peak on Jun 22 (Fig. 30). Perhaps the bimodal SM emergence peak in fall tillage was a result of the tillage displacing a portion of the SM pupa deeper into the soil causing them to emerge later. In general, the effect of minimum/no tillage on SM population should be investigated further.

Research conclusions:

Objective 1 i-iv. Advance understanding of swede midge (SM) population dynamics on small-scale organic brassica farms as related to management practices.

 Objective 1. i. Definitive end date of emergence of the overwintering generation.

Although we know that following a swede midge(SM)-infested fall brassica crop, the majority of spring emergence of the overwintering SM population occurs during May and June, it was uncertain when it finally ended, because open-air traps may capture SM from subsequent generations after the end of June. However, the results from our small-cage SM emergence study where trap captures were limited to the ground within the cages, confirmed that a small proportion of SM did continue to emerge from an overwintering site throughout July and into early August. This is especially important information to consider when making crop rotation and planting decisions.

Objective 1 ii. Intensity and duration of SM emergence in the spring at a site where an SM-infested crop was grown the previous summer.

We hypothesized that spring emergence following a SM-infested summer brassica planting would be much lower than following a SM-infested fall planting. We thought that in the summer, SM would emerge and leave the site in search of another suitable host, whereas in a fall planting, most SM would drop to the soil to pupate and overwinter at the same site. However, the results from both our open-air and small-cage traps indicated that SM emergence in the spring may be as strong following both SM-infested summer and fall plantings. The first and last trap catches of SM spring emergence were the same following summer and fall SM-infested plantings. Interestingly, only a single peak of SM spring emergence occurred following SM-infested summer planting, which was about two weeks after the first peak emergence following SM-infested fall plantings (summer: late-June vs. fall: mid-June). Spring SM emergence following a SM-infested fall planting had bimodal peaks. This is very important information to consider when making crop rotation and planting decisions.

 Objective 1. iii. Annual SM population dynamics per farm.

Blue Heron. SM pressure generally increased at Blue Heron from 2015 to 2016, primarily due to lack of crop rotation, use of SM-infested transplants and lack of post-harvest crop destruct. In Field No. 4, continuous season-long planting of brassicas and lack of post-harvest crop destruct resulted in an 8-fold increase in trap catches across the growing season. Lack of post-harvest crop destruct in field No. 1 resulted in overwintering SM populations that were more than double what they were in this field the previous fall. Alternatively, in Field No. 6, fall cabbage suffered no losses from SM when it was planted after the majority of SM spring emergence was complete in early July. Unfortunately, the red cabbage transplants must have been infested with SM, because in the transplant hardening off area we observed SM damage and infestation on red cabbage transplants and captured SM in the traps. Although the SM population was too low to cause economic damage prior to head formation of the red cabbage, eventually, in the absence of post-harvest crop destruct, the SM population exploded to moderate-high levels during September and October as SM larvae fed on the numerous secondary side-shoots post-harvest.

Canticle. Primarily due to a small land base (8 acres) and continuous season-long production of brassicas, the SM population at Canticle doubled from moderate to very high from early-July to mid-September, which was double the SM pressure on the farm in fall of 2015. Crop rotation from back to front field or from corner to corner was not effective in this situation.

Objective 1. iv. Differences in SM damage among crop types.

Of the five plant types in three plantings at Blue Heron and 15 crop types in four plantings at Canticle that we rated for SM damage, broccoli had the highest proportion of unmarketable produce at harvest. In general, highest levels of SM damage occurred in broccoli, followed by Romanesco, and then by kohlrabi (especially green), and cauliflower. In addition to being more preferred by SM, these plant types also cannot withstand as much SM damage, because any scarring in the head renders the produce unmarketable. Alternatively, in plant types where leaves are marketed such as kale, multiple leaves may compensate for those infested with SM, making the plant at least partially marketable and not a total loss. After the susceptible head brassicas, Red Russian kale, purple/Dinosaur kale and cabbage were the next most susceptible/preferred by SM. Turnips and green (Winterbor) kale were much less preferred and impacted by SM, while Asian brassicas (Bok Choy, Napa cabbage) appeared to be quite tolerant. Understanding the relative impact that SM has on the different types of brassicas is a valuable tool for growers to make crop management decisions, especially with respect to crop rotation and selection.

Objective 2. Optimize management strategies including newly developed disruption tactics, insect exclusion netting and garlic oil repellent, crop selection and rotation strategies.

Objective 2. i. Evaluation of IEN compared to open air with bare ground and black plastic mulch.

IEN resulted in 100% control of SM while broccoli grown in open-air had 97% and 100% SM-infested plants with 50% and 70% unmarketable heads on black plastic mulch and bare ground, respectively. IEN also significantly reduced flea beetle damage from severe to none in broccoli grown in the open air to none in the broccoli grown under the netting. Contrary to our hypothesis, black plastic + IEN had higher maximum temperatures than black plastic open-air, while bare ground + IEN had cooler temperatures than bare ground open-air, as expected. Compared to broccoli grown in open air, IEN significantly hastened maturity and increased yield by 2.3 to 4.3 times. Interestingly, when the cost of IEN was factored in, there was no difference in net return between 0% SM crop loss with IEN and 50% SM crop loss without IEN with plastic mulch. This demonstrates the challenge of making this highly effective management strategy affordable.

 Objective 2. ii. Effect of white plastic and reflective silver mulch, and green IEN on broccoli quality.

IEN resulted in 100% control of SM in broccoli where adjacent open-air trap recorded moderate SM pressure. Compared to hay mulch + white IEN, white and silver plastic mulch + white IEN did not result in lower temperatures or differences in maturity as we had expected. Instead, they had numerically 3.3 and 1.6-times higher incidence of heat stress, respectively, and shorter plants by 8-10 inches. Compared to hay + white IEN, hay + green IEN had lower weekly average temperature by ~1 to 2 ⁰F, which significantly delayed maturity. Green IEN cost only slightly more than white IEN, and because it was more durable, its economic feasibility could increase with each re-use.

Objective 2. iii. Evaluation of garlic oil with spreader-sticker as repellent of SM.

Essential garlic oil 1% + Nu-Film-P 0.25% v/v did not reduce SM incidence or damage severity in a summer planting of kohlrabi under moderate-high SM pressure with four weekly applications or in a fall planting of Red Russian kale under moderate pressure with six weekly applications. In a non-replicated demonstration, nine weekly applications of garlic oil + Nu-Film-P resulted in less than half as many SM-infested plants (40%) as the untreated (90%) under moderate SM pressure in a spring planting of Red Russian kale.

Objective 2. iv. Crop preference/trap crop study.

Under moderate-high SM pressure, Red Russian kale resulted in significantly higher SM infestation than broccoli, while Bok Choy appeared to be completely tolerant to SM. Compared to monoculture broccoli, broccoli grown beside Red Russian kale or Bok Choy had significantly less SM damage, which increased marketable yield by 25 to 36%. Unfortunately, if half of each broccoli bed had to be cropped to Red Russian kale, marketable yield of broccoli would also drop in half, which would only begin to break even when more than half of the heads of broccoli grown in monoculture were unmarketable due to SM damage.

Objective 2.v. Effect of plastic mulch on SM pupation and emergence.

In our small-cage study, total 10-week SM trap catches were significantly 25% lower where SM-infested Red Russian kale plants were grown on black plastic compared to bare ground. Presumably, after dropping from the plants, more SM larvae made it into the soil where they successfully pupated and subsequently emerged in bare ground compared to plastic mulch. Thus, plastic mulch may serve as a barrier to SM pupation and reduce SM population/pressure.

 Objective 2. vi. Effect of post-harvest practices on SM emergence. In our large-cage study, shallow tillage to 4 inch following harvest of SM-infested Red Russian kale resulted in a significant 72% reduction in total subsequent SM captures over the 4-month period compared to intact plants (= untreated). Similarly, SM trap catches were significantly reduced by 88% where biodegradable black plastic was placed over the top of SM-infested Red Russian kale plants. We suspect that trap catches would have been zero had the plastic not ripped. Nonetheless, our results indicate that the plastic mulch served as a barrier to SM emergence.

Objective 2. vii. Effect of reduced tillage practices and tarping on SM emergence. Although overall trap catches in our small-cage study might be too low to draw any conclusions, we did observe that: i) There were no significant differences in 11-week total SM trap catches among no tillage (cabbage re-growth in fall), no tillage + fall tarp (cabbage residue destroyed) and shallow 4 inch fall tillage (Cabbage residue destroyed). 2) First trap catches were the same among tillage treatments, suggesting that any differences among them with respect to temperature, soil moisture or placement of SM pupae in soil had no effect on SM emergence. 3) Only the fall shallow tillage treatment resulted in a bimodal SM emergence peak, which may be related to tillage practices displacing SM pupae deeper into the soil profile. And, 4) SM emerged underneath the tarp; although not flat on the soil surface when in a 1.5 ft tall cage; this was intriguing from the perspective of using tarp as a ground barrier to prevent SM emergence.

Participation Summary
4 Farmers participating in research

Education & Outreach Activities and Participation Summary

37 Consultations
2 Curricula, factsheets or educational tools
9 On-farm demonstrations
4 Published press articles, newsletters
12 Webinars / talks / presentations
2 Workshop field days
3 poster displays

Participation Summary

318 Farmers
203 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

Presentations:

 

Twilight Meetings:

  • Cornell Small Farms Program: Reduced Tillage in Organic Vegetables Field Day. Swede midge management in organic brassicas. Hoepting, C.A. Freeville, NY: August 17, 2016 (47 participants).

 

  • 3rd Annual vegetable pest management field day. Swede midge on organic and low-spray Cole crops.  Hoepting, C.A. 2018.  Portland, NY: August 23, 2018 (12 participants).

 

Statewide Grower Conference/Expo:

  • 2016 NOFA-NY Winter Conference. Swede midge: What Brassica growers should know. C.A. Hoepting and C.A. Hall. Saratoga Springs, NY; January 23, 2016 (52 participants).

 

  • NOFA Vermont’s 35th Annual Winter Conference.  The swede midge situation and management updates.  Y. Chen and E. Hodgdon.  Burlington, VT: February 20, 2017 (32 participants).

 

  • 2017 Empire State Producers Expo (Cole crop session).  New developments in spread and development of swede midge.  C.A. Hoepting.  Syracuse, NY: January 19, 2017 (43 participants).

 

  • Great Lakes Expo (Leafy greens and Brassicas session). Swede midge: What brassica growers should know. C.A. Hoepting.  Grand Rapids, MI: December 6, 2017 (50 participants).

 

  • Great Lakes Expo (Organic market vegetable production). Swede midge: What organic brassica growers should know. C.A. Hoepting.  Grand Rapids, MI: December 7, 2017 (20 participants).

 

  • Mid-Atlantic Fruit and Vegetable Convention (Cole crops session). Insect control in Cole crops featuring worms and swede midge. C.A. Hoepting. Hershey, PA: January 30, 2019 (85 participants).

 

Winter Educational Grower Meetings and Schools:

  • 2016 Chautauqua Produce Auction Meeting. Swede midge: What Brassica growers should know. C.A. Hoepting. Clymer, NY: March 10, 2016 (25 participants).

 

  • 2016 Chautauqua Vegetable School. Swede midge: What Brassica growers should know. C.A. Hoepting. Jamestown, NY: March 17, 2016 (18 participants).

 

Professional Conferences/Meetings:

  • Northeast Plant Pest and Soils Conference (NEPPSC). Prevention of Brassica crop losses from new invasive species swede midge (Contarinia nasturtii) on at-risk small-scale organic farms. C.A. Hoepting and C.A. Hall. Philadelphia. PA: January 6, 2016 (25 participants).

 

  • Great Lakes Vegetable Working Group Annual Meeting. Prevention of brassica crop losses from new invasive species, swede midge on at-risk small-scale organic farms.  C.A. Hall.  London, Ontario, Canada: March 2 & 3, 2016 (45 participants). 

 

  • Northeastern IPM Center, Online Conference. Prevention of brassica crop losses from new invasive species swede midge for at-risk small-scale organic farms. C.A. Hoepting. November 9, 2016 (43 participants).

  

General Interest Groups:

  • Cornell Toward Sustainability Foundation Research Report Meeting. Prevention of Brassica crop losses from new invasive species swede midge on at-risk small-scale organic farms: Part II. C.A. Hoepting, Ithaca, NY: October 20, 2016 (12 participants).

 

  • Cornell Toward Sustainability Foundation Reporting Meeting Hoepting, C.A. Prevention of brassica crop losses from new invasive species, swede midge in at-risk small-scale organic farms: Part III. C.A. Hoepting.  Ithaca, NY, USA: October 6, 2017 (12 particpants).

 

Newsletter articles:

 

  • Veg Edge – Newsletter for CCE Cornell Vegetable Program. Do you have swede midge? New pest of Brassicas often overlooked. Hoepting, C.A. 2016.  Veg Edge, 12(22): 3-5.

 

  • Veg Edge – Newsletter for CCE Cornell Vegetable Program. How to Identify and Control Swede Midge in Cole Crops. Hoepting, C.A. 2017. Veg Edge, 13(19): 4-6.

 

  • Veg Edge – Newsletter for CCE Cornell Vegetable Program. New organic management strategies for swede midge. Hoepting, C.A. 2018. Veg Edge, 14(17): 3-5.

 

 

 Public Display:

 

  • 2017 Empire State Producers Expo.  Do you have swede midge? New pest of brassicas often mis-diagnosed. C.A. Hoepting. Syracuse, NY: January 19, 2017 (~1500 participants).

 

  • Cornell University Organic Program Work Team Symposium. New developments for managing invasive insect, swede midge in small-scale organic brassica production.  C. A. Hoepting. Ithaca, NY: April 27, 2018 (70 participants). AVAILABLE ONLINE: https://organic.cals.cornell.edu/sites/organic.cals.cornell.edu/files/shared/documents/Hoepting%20poster%20pdf.pdf

 

Factsheet:

 

Video:

 

Planned Outreach Projects:

  • Publish on-farm SM population dynamics and crop damage as related to management practices from 2015-2017 studies in a peer-reviewed manuscript.

 

  • Prepare Extension bulletin/2 min video for: 1) New crop rotation recommendations; 3) Relative crop type susceptibility/preference; 4) Use of pheromone traps to monitor SM on-farm; and 4) Use of insect exclusion netting for SM management.

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Swede Midge Monitoring Efforts Help Growers To Understand and Manage SM on Their Farms.

In 2017, we continued to monitor swede midge (SM) on Blue Heron and Canticle farms through a Cornell Toward Sustainability (TSF) grant, so we can share the learning outcomes of these farms.

 

Blue Heron. SM pressure generally increased at Blue Heron from 2015 to 2016, primarily due to lack of crop rotation, use of SM-infested transplants and lack of post-harvest crop destruct. We expected that in spring 2017, SM emergence would be the highest and very high in Field No. 4, while Field No. 1 would be lower than Field No. 4 but still high, and Field No. 6 would be the lowest. In 2017, we did observe that Field No. 4 had the highest SM emergence of the three fields, which was very high with peak trap catches as high as 100 SM/trap/day, while Field No. 1 and Field No. 6 had similarly high SM emergence at 28 SM/trap/day. Spring SM emergence pressure was similar in size to overwintering SM pressure in fall 2016 in Field No. 4 and No. 1, but had had increased in Field No. 6.

                Blue Heron had transitioned fully to new ownership in 2017. In the spring, the grower planted Field No. 4 to mixed cabbage as per usual, because it was the only field with dry enough ground to plant. We also planted two beds of broccoli and Red Russian kale in this field for a trial. Interestingly, it looked like the more preferred crops in our trial acted as a trap crop for SM in this field, because we had 100% 100% SM infestation and none of the broccoli was marketable, while the grower harvested more than 90% of the spring planted cabbage. After these crops were removed/disked, SM dropped to moderate levels (< 10 SM/trap/day). Winterbor kale was planted in late-July and did not suffer from SM. In field No. 1, in 2017, the grower waited until after spring emergence had subsided and trap catches were below 1 SM/trap/day for several weeks before planting fall brassicas. SM trap catches remained low at less than 1 SM/trap/day for the entire production of these crops. At crop maturity on 10-Nov, no SM damage was detected in any of the brassicas grown including green, red and savoy cabbage, Winterbore kale and Brussels sprouts. In field No. 6, in 2017, the grower planted mixed brassicas in mid-May on the opposite side of the field from where the infested cabbage was grown in fall 2016. SM pressure in the spring brassica planting was very low until mid-June, SM damage was minor and all of the crops were marketable. Unfortunately, failure to crop destruct after main harvest resulted in SM trap catches increasing 12-fold from less than one to 48 SM/trap/day on 19-Aug. A summer planting of mixed brassicas was planted in mid-July and a fall planting of broccoli and kale was planted in mid-August in this field. With constant supply of susceptible brassica plantings, SM trap catches tripled to very high levels in this field and the broccoli and cauliflower had 65% and 20% unmarketable heads, respectively. In 2017, Blue Heron reduced losses from SM considerably from previous years by implementing effective crop rotation of about 3.5 months (mid-May 1 to Aug 25) and 450 to 525 ft between secluded fields. In the future, timely post-harvest crop destruct coupled with crop rotation will eliminate economical losses from SM on this farm.

 

Canticle. By fall 2016, SM pressure on this farm had doubled from the previous fall primarily due to their small land base (8 acres) and continuous season-long production of brassicas. It was expected that the highest levels of SM emergence in spring of 2017 would occur in the front corner field, followed by the back field, while the middle field and the field behind the barn would have the lowest level of spring SM emergence. As predicted, highest SM emergence in spring 2017 occurred in the front corner field with the same very high pressure (peak: 60 SM/trap/day) as the overwintering SM population was in fall 2016 (peak: 73 SM/trap/day). Spring SM emergence in the middle field was not as high as in the front corner field (peak: 25 SM/trap/day), but was much higher than the SM overwintering population in fall 2016. We did not have any spring SM emergence traps in the back field.

Despite crop rotation efforts made throughout the growing season, SM continued to find the broccoli, cauliflower, kohlrabi and Red Russian kale plantings and cause economic damage in these crops wherever and whenever they where planted, while leaving most of the other brassica crops alone. Interestingly, SM trap catches remained strong from spring emergence through August in the front corner field, despite it being planted to green beans in 2017. Since this field was heavily infested with a brassica weed, as was the whole farm, we wonder whether this weed is contributing to the SM population on this farm. Ultimately, progress was made in 2017 at Canticle, because instead of doubling SM pressure from the previous year, the farm finished the growing season with similar SM pressure as at the end of the 2016 season.

 

The outcome of understanding SM population dynamics on individual farms is the grower’s ability to use trap catch and damage information to make real-time management decisions and to make plans for future management strategies. Trap catch data from the same farms over multiple years has allowed us to test our predictions, monitor annual variability in SM populations and evaluate efficacy of implemented management strategies over time.

Project Outcomes

5 Farmers changed or adopted a practice
6 Grants applied for that built upon this project
4 Grants received that built upon this project
$70,000.00 Dollar amount of grants received that built upon this project
3 New working collaborations
Project outcomes:

Outcomes

 

New Recommendations for Far and Wide Crop Rotations. For managing swede midge (SM), entomologists conservatively recommended far and wide crop rotation out of brassicas for 1 km (= 3168 ft) and three years. This is based on the knowledge that a portion of the overwintering pupae can survive in the soil for more than two years, and the fact that SM adults are considered weak fliers. On small organic farms like Canticle and Blue Heron, these parameters for far and wide crop rotation are impossible. Fortunately, this project provided new insight into SM dynamics as they relate to management practices via detailed whole-farm SM population monitoring with pheromone traps and SM crop damage assessments. We clearly demonstrated that a crop rotation of about 2.5 months (mid-May 1 to end of July) away from brassicas was enough time (wide enough) for crop rotation away from brassicas to be effective. Essentially, a field that was infested with SM during the previous summer or fall should not be planted to brassicas until after the majority of the overwintering SM generation have emerged, which our studies have shown to be in mid-July to early-August. Fall plantings of brassicas during the month of August in such fields should produce marketable crops. The caveats to this rule include: 1) The field must be secluded, such as is the case at Blue Heron, where the three production fields were surrounded by wooded areas where 450 to 525 ft from SM-infested fields was far enough. Alternatively, at Canticle, with no significant barriers to separate fields on the 8 acre farm, 840 ft was not far enough away for SM to find and infest a brassica crop. 2) Transplants must be free of SM. And, 3) There must be no brassica-type weeds or cover crops to sustain the SM population in the field in the absence of a cultivated brassica crop.

 

Insect Exclusion Netting Highly Effective for Managing SM, but May Be Cost-Prohibitive. In our 2015 and 2016 trials, insect exclusion netting (IEN) was highly effective in protecting brassica crops from SM damage, especially on farms that were too small for crop rotation to be effective. Four on-farm trials showed that broccoli could be grown under IEN with no losses from SM, compared to 50-85% unmarketable plants grown in open-air. As long as the ground where the brassica crop was grown under IEN had not recently been cropped to brassicas, IEN was effective. Use of various mulches in combination with IEN proved important for effective weed management. Differences in plant development and quality occurred between IEN and open air and among mulch types under IEN that resulted in both increased and decreased yield. For example, compared to open air, broccoli under IEN was advanced in spring and summer, but suffered heat stress in fall. Similarly, under IEN, summer broccoli suffered more heat stress with black plastic than with straw mulch or bare ground. Green IEN created a cooler microclimate under the netting than white IEN, which delayed broccoli maturity significantly. IEN also excluded other pests such as flea beetles and caterpillar pests, but could also detrimentally include caterpillar pests if the transplants were infested, and slugs (presumably from increased moisture and uncontrolled weeds under netting). Muddy Fingers Farm has readily adopted use of IEN to control SM in their broccoli, while Canticle and Blue Heron are still deliberating on the economic feasibility of this expensive and labor-intensive strategy. In our 2016 trials, when cost of IEN was factored in, there was no difference in net return between 0% SM crop loss with IEN and 50% SM crop loss without IEN with plastic mulch. This demonstrates the challenge behind making this highly effective management strategy affordable. Green IEN costs only slightly more than white IEN and is much more durable, so its economic feasibility would increase with each re-use.

 

Making IEN Economically Feasible by Re-Using It Over Low Hoops.

The challenge with managing SM at Canticle Farm is that brassicas are grown from April until November in an open 8 acre field. Our SM population and crop damage monitoring showed that SM clearly prefer and seek out broccoli, cauliflower and kohlrabi on this farm. In 2017, Canticle trialed re-used IEN over low hoops, since kohlrabi was usually impacted by SM, grows fairly low to the ground and was grown in a relatively small patch. At harvest, after being exposed to moderately high SM pressure, 100% of the unprotected kohlrabi was infested with SM with 67% of the heads unmarketable, compared to zero SM infestation or damage in the kohlrabi that was grown under IEN. Kohlrabi plants grown under netting were also significantly 7.8 inch taller and 1 inch wider than those grown in open-air. Because 100% of the crop was marketable instead of only 33%, the value of the crop increased by $425 from $214 to $638 for the 50 foot long planting. Even with brand new netting, the grower would still have net twice as much by protecting the kohlrabi with IEN compared to leaving it exposed to SM. Cost-benefit would only increase with every re-use of the netting. Clearly, use of IEN over low hoops to protect kohlrabi from SM under moderately high pressure was economically feasible and very successful on this farm.

 

 

Other Grant Funding:

 

Detection, biology and control of the exotic Swede midge (Contarinia nasturtii) for California Cole crops. Alejandro Del Pozo-Valdivia et al. 2020. California Department of Food and Agriculture (CDFA)

Office of Pesticide Analysis and Consultation (OPCA). Note: Hoepting to travel to Central California in fall 2020 to give a couple of workshops to brassica growers about swede midge.

 

Testing ground barriers for swede midge IPM on at-risk small-scale brassica farms. Chen, Y. and C.A. Hoepting. Northeast IPM Partnership. April 1, 2018 to March 31, 2020. $50,000.

 

Prevention of Brassica crop losses from new invasive species, swede midge, on at-risk, small-scale, organic farms: Part III. Hoepting, C.A. Cornell Toward Sustainability Foundation. January 1, 2017 to December 31, 2017. $10,000.

 

Prevention of Brassica crop losses from new invasive species, swede midge, on at-risk, small-scale, organic farms: Part II. Hoepting, C.A. Cornell Toward Sustainability Foundation. January 1, 2016 to December 31, 2016. $10,000.

 

Other Grant Funding – Pending:

Managing the invasive swede midge using ground barriers. Hodgdon, E.A. and C.A. Hoepting. New York Specialty Crop Block Grant (SCBG). October 1, 2020 to September 30, 2022. $98,004.

 

 

 

 

Assessment of Project Approach and Areas of Further Study:

Areas of future study:

 

Effective management of SM on any farm is unique, as each farm is unique. With such a serious and potentially devastating SM infestation at Blue Heron, we continued to work with this farm in 2017 during the first full year under management by the new owners from Pennsylvania. The new owners had only a crash course on SM in 2016 as they transitioned into the farm, so we wanted to help them to develop a sustainable SM management plan. Other effective and affordable management strategies are critically needed for small single land base farms such as Canticle where crop rotation is ineffective.

 

Although our small-cage study results indicated that SM emergence in the spring was as strong following both previous year SM-infested summer and fall plantings, it would be worthwhile to continue to study this phenomenon on different farms under different pest pressures and different post-harvest practices, as our data was only collected from two fields.

 

The situation at Blue Heron shed light on the importance of not producing SM-infested brassica transplants on-farm. Further attention to the production of brassica transplants that are free of SM-infestation is warranted. This may include use of IEN over high tunnel/greenhouse vents, open sides, etc. to prevent SM from entering in, use of ground barrier to prevent SM from pupating and becoming established inside transplant production facilities, as well as excluding SM from hardening off sites.

 

The utility of green IEN should be further explored, especially since it appeared to be much more durable than white IEN, which would improve the economic feasibility of using IEN every time it can be re-used. In our first trial with green IEN + hay mulch, this combination resulted in cooler temperatures under the netting and significantly delayed crop maturity. The cooler temperatures under green IEN may result in a significant reduction in heat stress and consequent yield increase in a summer trial when broccoli is harvested in August, a production timing that can be prohibitive due to heat stress. Since black plastic is the most commonly used mulch type, trialing it in combination with green IEN would also be worthwhile. Any IEN + mulch trials designed to reduce heat stress in summer broccoli should be taken to yield.

 

Before giving up on the strategy of using garlic oil as a repellant, especially since our non-replicated demonstration showed that the garlic oil treatment reduced SM-infestation by more than 50%, it should be noted that there were some issues with our trials that could have affected the efficacy of garlic oil. There were some weeks when the technicians were either sloppy in making the garlic oil applications, or forgot to treat the garlic oil trials altogether. And, a fresh batch of 1% garlic oil + Nufim-P 0.25% v/v was only prepared when the premixed supply ran out, instead of before each application. Even if garlic oil is not effective as a stand-alone strategy, it may be an important tool that could be used in a push-pull strategy with a trap crop, reflective mulch or mating pheromone disruption, for example.

 

Although our preliminary results of using the more SM-preferred Red Russian kale brassica as a trap crop to protect broccoli from SM are very encouraging, more research is needed to develop this strategy before we recommend its use. Specifically, this strategy should be tested under different SM pressure and in different planting configurations, especially to determine its economic feasibility. Proper management of the trap crop needs to be determined to ensure that SM does not build and spill out of the trap crop into marketable brassica crops, which would defeat its purpose. For example, studies should explore if, when and how the trap crop should be destructed. Ideally, a planting configuration that utilizes proportionately less trap crop to cultivated crop would be found to be effective, because this would improve the economic feasibility of this strategy. It would also be interesting to know whether SM populations build to a greater degree in their more preferred brassica plant types, as this could be important in making crop rotation and planting decisions.

 

Our results indicated that black plastic mulch significantly reduced SM emergence, and that SM emerged underneath tarp, which led us to the idea of using a ground barrier on SM-infested ground to prevent SM emergence in order to crash an SM population. Theoretically, ground barrier could be placed over a SM-infested bed to prevent SM emergence, which would allow for a broccoli crop or other susceptible brassica crop to be planted nearby without suffering economic damage from SM. More information is required in order to move forward with this potential strategy, including; 1) Whether the SM emerged under the plastic and then perished in the absence of an exit, or, if they were still alive and waiting to emerge when the barrier was removed (which we never did in the post-harvest study at Canticle. 2) If effective in preventing SM emergence, how long or until when does the barrier have to be left on? 3) Instead of having to take ground out of crop production, could a crop be grown through the barrier, or would the emerging SM escape through the plant holes? To be effective, the ground barrier would have to be thicker and more resistant to tearing than the biodegradable black plastic mulch that we used in our study.

 

The effect of minimum/no tillage on SM population should be investigated further in general and on a larger scale, because our small-cage study was too small to draw concrete conclusions.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.