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

The goal of this project was to modify innovative strategies for managing bacterial wilt and cucumber beetles, in order to provide practical alternatives to exclusive reliance on insecticides for conventional and organic muskmelon growers in the North Central Region. Field experiments in Iowa and Ohio focused on perimeter trap cropping (PTC) in conventional systems and delayed row-cover removal (DRC) in organic systems. In replicated PTC trials at university research farms in 2015, muskmelon (cv. Athena) was the main crop; the experiment compared performance with and without a 2-row perimeter of Buttercup squash (cv. Space Station). In 2015, as in 2014, results were similar in both states: neither strategy proved to be effective. In Iowa, marketable weight of muskmelon was actually significantly lower in the PTC plots than in the no-PTC controls, and the number of insecticide sprays applied to the PTC vs. no-PTC melon plots was nearly identical. In Ohio, there was no impact of PTC treatment on yield, incidence of bacterial wilt on muskmelon did not differ significantly with the no-PTC control, and number of insecticide sprays applied to muskmelon was about equal between the two treatments. Collectively, these two years of results in two states indicate that a PTC strategy for protecting muskmelon in the North Central Region is not advisable. In Iowa field experiments, muskmelon protected by row covers did not differ significantly from non-covered controls in either marketable yield or bacterial wilt incidence. In four Iowa on-farm demonstration trials in 2015, the impact of row covers on yield was variable, and no impact or row covers on incidence of bacterial wilt could be discerned. These results indicate that the use of row covers described in this project would not be recommended for muskmelon production in the North Central Region.

Objectives/Performance Targets

Objective 1: In a muskmelon production system under conventional pesticide management, 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 paired subplots (PTC vs. No PTC) were separated by at least 500 ft to avoid interplot interference. PTC subplots (200 x 42 ft) of muskmelon (cv. Athena) were surrounded by two rows of buttercup squash (cv. Space Station), whereas non-PTC plots had annual rye planted as a border. Pairs PTC and non-PTC subplots were separated from other pairs of subplots 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 in 2015 (Year 2), incidence of bacterial wilt was not significantly different in PTC than non-PTC plots, and both treatments 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, did not reduce the use of insecticides, and did not reduce bacterial wilt incidence. Muskmelon yields were not statistically different in PTC vs. non-PTC plots. Cutworm feeding early in the season resulted in weakened squash perimeters in the two of the four PTC fields, which may have compromised the barrier effect of the squash rows in impeding cucumber beetle movement into the muskmelon plantings. In Ohio, results were generally similar in the absence of treatment effects as well as number of insecticide sprays, although incidence of bacterial wilt (23-35%) at harvest was considerably higher than in Iowa.

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, 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. A 6-inch-deep layer of corn stalk mulch controlled weeds 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, applied to uncovered plants only, were: a) Surround (kaolin clay) reapplied after removal by rainfall, and b) Surround, applied as in the previous treatment, but with Pyganic EC (pyrethrin) and Trilogy (neem oil) when cucumber beetle thresholds exceeded 0.5 beetle/plant from transplant to four-leaf stage, and 1 beetle/plant from the four-leaf stage until harvest. Striped and spotted cucumber beetle adults were counted weekly from transplant through the beginning of harvest, using yellow sticky cards and visual monitoring of three randomly chosen plants per subplot. Champ WG was applied twice on all subplots to control anthracnose. Disease incidence was monitored weekly, and the number and weight of marketable and cull melons harvested from each subplot was recorded. Unlike 2015, there was no significant difference in marketable yield, insect cull number or weight, bacterial wilt incidence, or total yield between the row-covered treatments and non-covered control. Row-covered treatments received an average of 3.5 insecticide sprays, whereas non-covered treatments received an average of 6.5 sprays. Results of the Ohio Objective 2 field trial are still being compiled.

Objective 3. Estimate costs and profits of the modified alternative IPM strategies in Objectives 1 and 2.

Economic analysis is ongoing.

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 in Year 2, cooperators in on-farm trials were again 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 Wabi Sabi Farm, cucumber beetle and bacterial wilt pressure were minimal, yield was equivalent for row-covered and non-row covered treatments, and harvest was about one week earlier for the non-covered treatment. At One Step at a Time Farm, marketable yield was about 17% higher in row-covered than non-covered plots, with no difference in harvest dates between the treatments; bactyerial wilt incidence was less than 1%. At New Family Farm, bacterial wilt incidence was high (73% average) in row-covered and non-covered treatments, and yields were low and equivalent in all treatments. At ZJ Farm, bacterial wilt incidence was also high in all treatments (about 25%), and yield of marketable fruit was low but similar in all treatments. No data on 2015 Ohio cooperative trials have been made available to the Project Director at this time.

Field days featuring the SARE project experiments were held at the ISU Horticulture Research Station near Gilbert, IA, on August 10, 2015, and a presentation was made to the Iowa Fruit and Vegetable Growers Association annual meeting, Ankeny, IA, on January 29, 2016.

Additional outreach products are in development.

Accomplishments/Milestones

Results of our Year 2 field experiments have placed even stronger emphasis on limitations of both strategies under test in the project. The data indicate that the perimeter trap cropping (PTC) strategy does not appear to be promising for conventional production of muskmelon in the Midwest. The 2015 field results showed that the trap crop had minimal to no impact on suppression of bacterial wilt, we did not save insecticide sprays on the main crop, and marketable yield was not increased with the use of PTC. Contributing factors to this outcome were several. First, it is challenging to manage two different crops (squash and muskmelon) in the same field; damage to the squash perimeter rows by cutworms or other injuries sometimes created gaps in protection that may have compromised the intended barrier effect against cucumber beetles. Second, it is possible that muskmelon is simply too attractive to cucumber beetles to function as the main crop in a PTC scheme, which relies on a difference in beetle attractiveness between the perimeter crop (highly attractive) and the main crop (less attractive). In New England, the PTC strategy has succeeded with butternut squash as the main crop, but butternut squash is considerably less attractive to cucumber beetles than muskmelon. Bacterial wilt is not a significant threat to butternut squash in the Upper Midwest (unlike in New England), so using PTC with a butternut squash main crop in our Region would not be a helpful management strategy.  In sum, the PTC strategy as an alternative tactic against bacterial wilt does not look feasible for North Central Region muskmelon growers at this time.

The Iowa field experiment assessing delayed row cover removal for organic muskmelon production again yielded mixed results. Unlike 2014, there was no advantage over the non-covered control in suppressing bacterial wilt or raising marketable yield, even though insecticide sprays were roughly halved by using the row covers. There were no discernible differences between removing row covers at the start of bloom or delaying their removal for 10 more days, except that one insecticide spray was saved with the delayed removal treatment. Given the considerable expense and labor associated with using row covers, it appears from our results that use of low tunnels covered by spunbonded polypropylene (e.g., Agribon, Reemay) should not be recommended for organic muskmelon production, or suppression of bacterial wilt, in the Upper Midwest.

Impacts and Contributions/Outcomes

Variability in bacterial wilt disease pressure among sites and years, as well as a lack of consistently positive outcomes in our field trials and on-farm demonstrations, have left us skeptical about the viability of the strategies we tested for muskmelon production in our Region. Perimeter trap cropping, using muskmelon as the main crop, does not seem to have enough impact on arresting cucumber beetle movement into the muskmelon fields to justify the extra expense and management difficulty of growing two very different cucurbit crops – muskmelon and squash – in the same field. Would other cucurbit crops benefit from a PTC strategy in the Midwest? We are doubtful. The major successes with PTC in reducing the need for insecticide sprays in managing cucurbit bacterial wilt have come in New England, with using butternut squash as a main crop. However, the subspecies of the bacterial wilt pathogen (Erwinia tracheiphila) that is highly pathogenic on squash (Cucurbita species) is limited in distribution to the Northeast, whereas the predominant subspecies of the bacterium in North Central Region is pathogenic mainly on Cucumis crops (muskmelon and cucumber); as a result, there is minimal reason to protect butternut squash against bacterial wily in our Region, and thus no reason to try PTC with a butternut (or other squash) main crop. Summing up, the future of using PTC for sustainable management of cucurbit bacterial wilt in the North Central Region does not appear promising.

The potential for row tunnels in organic muskmelon production may not be as discouraging as the highly variable results of our project imply. We hypothesize that a re-design of the strategy is needed in order to effectively suppress bacterial wilt while delivering consistently high marketable yield. Elements of such a re-design could include 1) a different type of row cover material, 2) more space for plant growth under the covers, and 3) deploying the covers for the entire season rather than only until bloom or shortly thereafter. All three of these elements are present in a redesigned system that is now being field tested by project PD Gleason and colleagues at Iowa State University and University of Kentucky, funded by USDA’s Organic Transitions program. These elements are 1) a nylon mesh row cover material that is more breathable than spunbonded polypropylene, 2) growing muskmelon and squash in much larger tunnel structures (triple rows, 3.5 ft high) to accommodate both crop growth and pollinator access to flowers, and 3) use of purchased hives of bumblebees to provide pollination in tunnels that remain in place for most or all of the growing season. We anticipate that the result will be more consistent packout of both muskmelon and winter squash, along with season-long suppression of bacterial wilt with minimal or no insecticide use.

Collaborators: