Integrating Perimeter Trap Crops and Row Covers into Cucurbit-crop Farming Systems

Integrating Perimeter Trap Crops and Row Covers into Cucurbit-crop Farming Systems

Summary

This project is modifying innovative strategies for managing bacterial wilt and cucumber beetles to make them more practical for conventional and organic muskmelon growers. Field experiments in Iowa and Ohio focused on perimeter trap cropping (PTC) in conventional systems and delayed row-cover removal (DRCR) in organic systems. In replicated PTC trials at university research farms in 2014, muskmelon (cv. Athena) was the main crop; the experiment compared performance with and without a 2-row perimeter of Buttercup squash (cv. Space Station). Results were similar in both states: although incidence of bacterial wilt in muskmelon was significantly (Iowa) or numerically (Ohio) lower when surrounded by Buttercup squash than when surrounded by ryegrass, neither marketable yield nor the number of required insecticide sprays differed between the treatments. Therefore, this result did not show a clear advantage of PTC for growers. In Iowa, plots of ‘Athena’ muskmelon protected by row covers had significantly higher marketable yield and lower incidence of bacterial wilt than non-covered plots, but delaying row cover removal by 10 days did not increase yield. Removing row covers at anthesis saved 4 Surround sprays, and delaying row cover removal saved 5 sprays, compared to non-covered plots. In Iowa cooperator trials, row covers resulted in higher yields except at one farm where an aphid infestation reduced yield under the covers. In Ohio cooperator trials, yields were unusually low due to heavy weed pressure and high cucumber beetle populations. Project activities were shared with growers in field days and winter meetings in each state.

Objectives/Performance Targets

 Objective 1: In a conventional muskmelon production system, evaluate perimeter trap cropping (PTC) for bacterial wilt suppression and yield at a spatial scale that is representative of North Central Region vegetable farms, and without neonicotinoid insecticides.
On university research farms in both Iowa and Ohio, four replications of two subplots (PTC vs. No PTC) were separated by at least 500 ft to avoid interplot interference. PTC subplots (200 x 42 ft) were surrounded by two rows Buttercup squash (cv. Space Station), whereas non-PTC plots had annual rye planted as a border. Paired PTC and non-PTC subplots were separated by at least 500 ft to minimize interplot interference by pest insects. Populations of cucumber beetles were monitored weekly in both border rows and main-crop rows along four transects within each plot. Synthetic pyrethroid insecticides (Asana XL or Pounce) were sprayed on the squash border rows or main crop muskmelons when threshold numbers of cucumber beetles were reached. Threshold numbers for cucumber beetles varied according to melon plant size as follows: pre-flowering = 0.5/plant; during fruit pollination = 1.0/plant; and at vine touch = 3.0/plant. Bacterial wilt incidence (% wilted plants) was recorded one week before harvest. Harvested fruit were assessed for marketability, then counted and weighed. In Iowa, incidence of bacterial wilt was significantly (P<0.0001) less in PTC than non-PTC plot. However, both PTC and non-PTC plots received approximately the same number of insecticide sprays, so the Butternut squash barrier apparently did not reduce numbers of cucumber beetles in the muskmelon main crop, and did not reduce the use of insecticides. Muskmelon yields were not statistically different in PTC vs. non-PTC plots. A contributing factor may have been the fact that Buttercup squash plants grew poorly during an exceptional rainy (15 inches) June, so may not have created a very effective barrier against cucumber beetle entry into the main crop. In Ohio, results were generally similar, although incidence of bacterial wilt was only numerically rather than statistically less in PTC compared to non-PTC plots, and the PTC plots received one fewer insecticide spray than the PTC plots. As in Iowa, yields did not differ significantly between the treatments. In both states, synthetic pyrethroid insecticide sprays were substituted for neonicotinoid insecticides in the treatments.
Objective 2: In an organic muskmelon production system using delayed row cover removal, evaluate alternative strategies for managing bacterial wilt and cucumber beetles during the period between row cover removal and harvest.
In Iowa, 5-wk-old organic transplants of ‘Athena’ muskmelon were planted 2 ft apart in black plastic mulch with drip irrigation on 7-ft centers. Subplots consisted of 30-ft-long rows of 15 plants. Spunbond polypropylene row covers (Agribon® AG-30) were installed on wire hoops immediately after transplanting. Weed management was achieved with 6 inches of corn stalk mulch between rows. A 3×2 factorial experiment (3 row cover treatments x 2 insecticide treatments) was conducted in a randomized complete block design with 4 replicate subplots per treatment. Row cover treatments included: 1) No row covers (NRC) 2) Row covers applied at transplanting and removed at anthesis (when female flowers start to open) (RC) and 3) Row covers applied at transplanting with the ends opened at anthesis and removed 10 days later (DRC). The two insecticide regimes were: a) Surround (kaolin clay) applied to plants and reapplied after removal by rainfall, and b) Surround was applied as the previous treatment, but Pyganic EC (pyrethrin) and Trilogy (neem oil) were also applied when cucumber beetle thresholds exceeded the following thresholds: 0.5 beetle/plant before anthesis, 3 beetles/plant from anthesis to vine touch (vines in adjacent rows start to grow together), and 10 beetles/ plant from vine touch to harvest. Insecticides were not applied while plants were under row covers. Striped and spotted cucumber beetle adults were counted weekly from transplant through the beginning of harvest using a) yellow sticky cards and b) visual monitoring of 3 randomly chosen plants per subplot. Disease incidence was monitored weekly, and the number and weight of marketable and cull melons harvested from each subplot were recorded. Using row covers resulted in twice the marketable and total yield compared to the non-covered control. Row cover treatments required an average of 4.5 fewer insecticide sprays than the non-covered control. Row cover treatments significantly (P<0.05) suppressed incidence of bacterial wilt compared to the non-covered control. Delaying row cover removal saved one Surround spray compared to the RC treatment, but did not significantly reduce bacterial wilt or enhance yield compared to the RC treatment. Analysis of results of a 2014 field experiment in Ohio that had an almost identical design to that in Iowa is still in progress; however, extremely rainy weather during June disrupted the planting schedule and resulting in very heavy weed pressure than reduced yields throughout the trial.
A laboratory bioassay at Ohio State was conducted to determine the impact of various organic insecticides on muskmelon feeding by cucumber beetles and beetle mortality. The point of this experiment was to find the most effective products or combination of products for using after row covers are removed. Cucumber beetles were placed in screen cages with muskmelon plants that had been previous sprayed with the insecticides, and beetle behavior was tracked over the next 48 hours. Three formulations – Evergreen, a newer formulation of pyrethrum insecticide; Entrust (spinosad); and Entrust plus Cide Trak (a pheromone-based insect attractant) – stood out as providing significantly (P<0.0001) better suppression of cucumber beetle feeding and higher beetle mortality than the other formulations tested (Pyganic, Pyganic plus Cide Trak, Cide Trak, Trilogy, Surround, Trilogy plus Cide Trak, Mycotrol, and a water control.
Objective 3. Estimate costs and profits of the modified alternative IPM strategies in Objectives 1 and 2.
Economic analysis awaits completion of Year 2 field trials.
Objective 4. Share project results with cucurbit growers throughout the region by means of on-farm demonstration trials, virtual and on-site field days, extension bulletins, webinars, and regional meeting presentations.
In Iowa, cooperators in on-farm trials were Jan Libbey (One Step at a Time Farm, Kanawha), Susan Jutz (ZJ Farm, Solon), Ben Saunders (Wabi Sabi Farm, Grimes), and Tony Thompson (New Family Farm, Elkhart). With these cooperators, we tested the row cover strategy with removal at anthesis (RC) and/or the delayed-removal row cover (DRC) strategy, using ‘Athena’ muskmelon and ‘Marketmore’ cucumber in 30-ft-long rows in non-replicated trials. Project scouts monitored striped and spotted cucumber beetle numbers weekly and also monitored incidence of bacterial wilt. Cooperators harvested and recorded data on marketable yield. Cucumber beetle and bacterial wilt pressure was generally light. At New Family Farm and ZJ Farm, row cover strategies resulted in considerably higher yield than the non-row cover control treatment. At Wabi Sabi Farm, however, in the absence of significant cucumber beetle and bacterial wilt pressure, an outbreak of aphids under the row covers suppressed yield in the RC treatment, resulting in higher yield for the control treatment. At One Step at a Time Farm, miscommunication with the grower resulted in harvest data being combined for the treatments, so evaluation of the impact of row cover treatments on yield was not possible. On-farm trials in Ohio in 2014 focused on perimeter trap cropping at two conventional farms (Burkholder Vine Crops, Shiloh, and Noah Hostetler Farm, West Salem) and row covers at two organic farms (That Guys Family Farm, Clarksville, and OSU Student Farm, Columbus). All trials were scouted weekly by OSU scouts. For all trials, the crop was sprayed with insecticide by OSU scouts when cucumber beetle thresholds were exceeded, and harvest yields were recorded by the growers. Yield in the row cover trials at the organic farms was very low, most likely due to high beetle pressure as well as high weed pressure. Yield data for the PTC trials have not yet been analyzed.
Field days featuring the SARE project experiments were held at the ISU Horticulture Research Station near Gilbert, IA, on August 11, 2014, and a presentation was made to the Iowa Fruit and Vegetable Growers Association annual meeting, Ankeny, IA, on January 30, 2015.
Additional outreach products will be forthcoming in Year 2.

Accomplishments/Milestones

 Results of our Year 1 field experiments have emphasized potential limitations of the perimeter trap cropping (PTC) strategy for conventional production of muskmelon in the Midwest. Although we suppressed the incidence of bacterial wilt (significantly in Iowa), we did not realize the significant savings in insecticide sprays on the main crop (muskmelon) that was the chief motivation for attempting PTC. A possible contributor to this result was that the perimeter of Buttercup squash was challenging to establish in IA and OH in 2014 due to record rainfall in June 2014; as result, they may not have produced a sufficient barrier for and attractant to cucumber beetles to prevent excessive movement into the main crop, as we have observed in other years using the same main and perimeter crops. It is generally recommended, form research in new England, that the perimeter trap rows be well established before the main crop is transplanted, but the perimeter rows remained small in stature during the critical early weeks of the growing season when emerging, overwintered adult cucumber beetles are highly mobile.
The Iowa field experiment assessing delayed row cover removal for organic muskmelon production yielded mixed results. Row covers provided a clear advantage over the non-covered control treatment in suppressing bacterial wilt, raising marketable yield, and substantially reducing insecticide sprays. However, delaying row cover removal by 10 days after anthesis (the start of the bloom period for female flowers) saved an additional insecticide spray but did not reduce bacterial wilt incidence or enhance marketable yield compared to row cover removal at anthesis. A significant accomplishment of this experiment was show that, once row covers were removed, sole reliance on sprays of Surround (kaolin clay) was as effective in deterring cucumber beetles as adding Trilogy (neem oil) and Pyganic (pyrethrum) to Surround. Additional insight on organic insecticide strategies once row covers are removed came from the OSU lab bioassay results that showed a clear superiority of Evergreen, Entrust, and Entrust plus Cide Trak over Surround, Trilogy, Pyganic, and various combinations of these products. Although these results must be confirmed in field trials, we plan to use the best-performing products from the lab bioassays during the post-row-cover-removal period in 2015 field experiments.

Impacts and Contributions/Outcomes

 Year 1 results have impacted our plans for Year 2 trials. For example, we will redouble our efforts to have vigorously growing perimeter rows of Buttercup squash in place before muskmelon seedlings go into the field, in order to make sure than the ability of the perimeter row to interdict cucumber beetles is maximized. In addition, we will use one or more of the best-performing organic insecticides from the lab bioassays to protect muskmelon seedling once row covers are removed. In cooperator trials, our scouts will assist with harvest activity in order top make certain that we can distinguish treatment effects on marketable yield.

Collaborators: