Evaluation of organic strategies to control a new invasive pest, swede midge, Contarinia nasturtii (Diptera: Cecidomyiidae)

Evaluation of organic strategies to control a new invasive pest, swede midge, Contarinia nasturtii (Diptera: Cecidomyiidae)

Summary

Several on-farm studies were conducted at the Intervale Community Farm and the Farmstand at the Cobble. Due to Hurricane Irene, we had a unique opportunity to examine how field flooding affected midge populations. We found that midge populations were generally unaffected by the flooding. We monitored male midge populations in four farms, and found that the Intervale of Burlington appears still to be the epicenter for the midge invasion. Early season row covers were not effective because midge populations were still low at that time. None of the OMRI-listed pesticides were particularly effective, but Azadirachtin was the most promising among them.

Objectives/Performance Targets

1) Evaluate the use of row covers for early season crop protection (season 1 and 2)
We evaluated the use of row covers for early season crop protection

2) Conduct an organic insecticide trial for swede midge control
We collected data on this trial late in the season on fall broccoli.

3) Evaluate the field efficacy and application dosage of entomopathogenic nematodes for swede midge control
We conducted this study on a smaller scale. Because of Hurricane Irene in 2011, we were not able to examine the effects of predator midges in a larger replicated field trial. We were concerned that midge populations were locally killed off, so it was uncertain whether there would be sufficient populations in the soil. We are currently counting in the lab how predatory nematodes affect the abundance of midge emergence from the soil.

Accomplishments/Milestones

We conducted all of the major studies that we set out to do. The project progressed as expected. Due to the flooding by Hurricane Irene, we were concerned that low midge populations this year would prevent us from fully testing the effects of the different treatments. Therefore, this affected our ability to test for the effects of predator nematodes on swede midge populations. We conducted a test at the Farmstand at the Cobble (Wendy Ordway) because we knew that it was an infested area, but the plot was too small to really replicate the treatments. We did engage in the audiences as proposed.
The only deviation from our timeline is that we conducted a twilight meeting in September rather than in August. All other events progressed as proposed.

Impacts and Contributions/Outcomes

• We did not find any damaged plants in the row cover study. Therefore, it was difficult to determine whether the lack of difference between our treatments was due to an absence of an active midge population early in the spring.

  We found that midge populations appeared to be higher in the Intervale than the outlying farms. Although this difference was not significant using a Repeated Measures ANOVA, we still believe that the differences appear to be biologically significant.

  Swede midge caused significant damage within the experimental plots. A total of 40.2% of the assayed plants were significantly damaged and unmarketable commercially. We found that midge damage did not statistically differ among the treatments (Fig. 2). In other words, the pesticide sprays did not reduce the frequency of midge damage below the control. Among the pesticides tested, the only pesticide that appeared to show some protection against the midge was Azadirachtin.

  We conducted a Grower twilight meeting at the Intervale Community Farm in September. Due to heavy rains, the attendance was lower than expected. However, there were still 12 attendees. We have been invited by Dr. Vern Grubinger to report on our results at the Vermont Vegetable and Berry Growers Association in January of 2013.

Collaborators: