Final Report for FNE10-686
Project Information
In previous SARE-funded studies, we developed organic perimeter trap cropping (PTC) methods for control of cucumber beetle (CB) in winter squash settling on Entrust for CB control the PTC plants and Surround as a CB deterrent in the main crop plants. We then added internal trap crop (ITC) rows to PTC plots to see if they act as additional sinks for CB and further reduce their numbers in main crops (vs. acting as a source to increase CB).
In 2009, we found an apparent sink effect, where ITCs further reduced total CB numbers beyond PTCs alone. Here we proposed to continue studying this sink effect and also compare PyGanic with Entrust as another possible trap crop organic insecticide treatment. Our hope was to find an alternative pesticide in order to help slow the evolution of insect resistance and to offer a cheaper alternative than Entrust. CB were scouted, counted and controls were applied as needed according to threshold levels. CB numbers in all plants were mapped to show CB distributions.
While below-threshold levels of CB were maintained in all non-trap plants regardless of treatment, we did see differences in beetle reactions to Entrust as opposed to PyGanic.
Our results were presented during a workshop at the 2010 NOFA summer conference and will be published in a spring issue of UMass Vegetable News Notes. Our multi-year results are also being submitted to the Journal of Entomological Science for possible publication.
Introduction:
Cucumber Beetle (CB) is a major insect pest in winter squash. CB feeds on squash plants, particularly in the cotyledon stage, causing extensive damage. CB also serves as a vector for the bacterium Erwinia tracheiphila, which causes bacterial wilt. CB over-winter in the brushy edges of field and then move into the fields in early summer often causing significant yield loss in winter squash. Organic control can be difficult, even with trap crops, often involving the use additional sprays or other methods, such as row covers over the young plants that can be expensive and labor intensive.
Trap cropping is a technique that relies on the fact that many insects, including CB, often prefer one variety of a particular crop over another. Often a more attractive variety is grown as a perimeter trap crop (PTC) border around the main cash crop effectively acting as a pest sink. As insects move into fields from the edges, the pest will congregate in the more palatable border rows where they can be controlled, usually with pesticides. Growers using PTCs may achieve effective control of CB by spraying only the border rows and thus reduce the amount of pesticide used and the labor required for spraying. The use of PTCs has now become a somewhat common practice in production fields. If control in the border rows is good, the border crop can be marketed in addition to the main crop. Interior trap crops (ITC) can offer more chances for control if insects get past the PTCs.
Since 2003, Ruth Hazzard and others at the University of Massachusetts have been conducting field trials for PTC techniques in winter squash and other crops. They have found success growing Blue Hubbard and other C. maxima squash varieties, such as Buttercup, as a trap crop around fields of Butternut squash. The majority of their work was done using conventional pesticide sprays for CB control in the borders. Growers are able to reduce the cost of control by spraying only the border rows and not the entire field.
In previous SARE funded on-farm research projects at Hampshire College in 2006, 2008 and 2009, we developed organic winter squash PTC methods for the control of cucumber beetles. We then also tested the effect of added ITC rows as a potential method for improving organic control of CB by acting as a sink for CB that may get past the PTCs. In 2009, we found that the ITCs did indeed seem to act as a sink, where ITCs improved control beyond PTCs alone. Beetles first entering the field built up higher numbers per plant in the ITCs than in the PTCs. Numbers of beetles in the main winter squash stayed the same or decreased, even though the total number of beetles in the field increased.
In these previous experiments, we settled on Entrust (spinosad) for control of CB in the PTC and ITC crops, and Surround (kaolin clay) for the main winter squash crop. Surround acts as a CB deterrent, keeping more of the CB away from the main crops and in the trap crops. We now proposed to compare PyGanic to Entrust as the control in the trap crops. Entrust performed better than vacuuming in our previous work, but we did not previously compare PyGanic, which is also suggested as an organic pesticide by New England extension agencies for CB in squash. Entrust is rather expensive and it could be useful to have more than one organic pesticide as an option to slow and/or compensate for the evolution of CB resistance to Entrust. Entrust is also known to be hard on some natural enemies and some predators, such as spiders that may otherwise contribute to CB control. Another advantage of diversifying the types of pesticide products used is the possibility for smaller side effects on some beneficial or non-target organisms.
Our objective was to compare the efficacy of Entrust vs. PyGanic as a control for cucumber beetle in organic trap cropping systems in winter squash.
Cooperators
Research
On 5/27/10 Buttercup and Butternut squash seeds were started in the greenhouse in plastic flats.
On 6/15/10 transplants were set out into the field in 8 plots each plot containing 6 rows of plants with each row 9 plants long. Rows were spaced at 80 inches with 36 inch in-row spacing. Burgess Buttercup plants were planted as a trap crop around the perimeter of each plot one plant deep. Buttercup plants were also planted as 3 interior trap crop plants in the center of each plot. All other plants in each plot were Waltham Butternut. Plots were randomized as to trap crop spray treatment, 4 receiving Entrust and 4 receiving Pyganic. (See figure 1) All, non-trap Butternut squash transplants were treated with Surround at a rate of 25 lbs/ac only at transplanting and not subsequently.
We examined every plant in the experiment and counted any live cucumber beetles on each plant, starting the day after transplanting (June 16) and then on 10 subsequent dates: June, 18, 21, 22, 23, 24, 25, 28, 29, and 30 and July 2. Trap plants were sprayed with either Entrust or PyGanic on June 21, 24 and 30 when trap crops generally exceeded economic thresholds for Cucumber Beetle (1 per plant). All trap crop plants were sprayed on those days after insect sampling. Entrust was applied to trap plants with a backpack sprayer at the rate of 2.5 oz/ acre. PyGanic was similarly applied at a rate of 9 oz/ac.
Data for insect numbers per plant were analyzed using split plot and repeated measures analysis of variance (anova), where pesticide was the main plot effect, with crop type (PTC, ITC, or main butternut) as a split plot factor within the main plots, and date as a repeated measure within the other factors; insect numbers per plant were transformed as y = sqrt(x + .5).
Plots treated with either one of the organic trap crop pesticides, Entrust or PyGanic, showed acceptably low numbers of beetles in the main squash crop, though there were interesting differences between the two pesticides in how they affected beetles numbers, especially in the trap crops. PyGanic seemed to have a stronger knock down effect in the trap crops where live beetle numbers dropped more quickly at first with PyGanic and then returned faster, compared to in the traps with Entrust (Figure 2a,b), which seemed to act more slowly but have a longer residual effect after a spray. For example, after the first spray on June 21, beetle numbers in the perimeter trap crops (Figure 2a) dropped 91% by the next day with PyGanic (from 0.58 per plant to 0.05, almost zero) vs. dropping 26% with Entrust (0.73 to 0.54 beetles per plant). However, the beetles rebounded back upward in PyGanic the day after that (June 23) in the perimeter traps, but beetle numbers continued to drop that next day in perimeter traps with Entrust (Figure 2a).
Over time, by the end of the season, beetle numbers became greater in the PyGanic plots. Entrust clearly killed more beetles outright on traps (Figure 2c,d) Some of the changes over time are also evident in the main squash plants within plots, even though these were not sprayed, so clearly control in the trap crops affected beetle numbers in the main plots as well, either by preventing beetles from entering or killing those that went back to the traps from the main plot.
Regardless of the differences between pesticides in the trap crops, overall seasonal mean numbers in the main butternut squash for both pesticide treatments were well below economic thresholds (one beetle per plant) (Figure 2c), even though much higher numbers appeared in the nearby traps. Once again, as in previous years, the internal trap crops showed more beetles per plant than did the perimeter trap crops especially toward the end of the season.
We feel that over the course of several years of experimentation we have established a workable trap cropping system for organic winter squash.
Education & Outreach Activities and Participation Summary
Participation Summary:
Our results were presented during a workshop at the 2010 NOFA summer conference and will be published in a spring issue of UMass Vegetable News Notes. Our multi-year results are also being submitted to the Journal of Entomological Science for possible publication.
Project Outcomes
Potential Contributions
Our work has provided growers with another organic insecticide option for control of cucumber beetles in a winter squash trap cropping system.
Although Entrust seems to kill more cucumber beetles and have a longer residual affect, PyGanic seemed to knock back the beetles long enough to keep levels below economic thresholds in the main crop.
Growers can choose to use the less expensive PyGanic or alternate the use with Entrust with PyGanic to combat the development of insect resistance.