Integrating Biological Control into Cole Crop Production in the Pacific Northwest

Integrating Biological Control into Cole Crop Production in the Pacific Northwest

Summary

We are examining predatory beetle conservation to improve biocontrol of root maggots, important pests of cole crops in the Pacific Northwest. In the winter, field margins and in-field refuges support higher abundances of predators than bare soil. In spring and summer, beetle abundance in conventional fields adjacent to well-vegetated margins was similar to that in fields adjacent to poorly vegetated margins. Higher densities of predators were observed in organic fields with in-field refuges than in fields without refuges. Field experiments revealed factors that potentially limit root maggot control by beetles. Outreach emphasized identification and ecology of beneficial beetles.

Objectives/Performance Targets

Evaluate field margins and in-field refuges for predator conservation.
Document the seasonal abundance of different types of beneficial arthropods relative to the seasonal peaks in adult Delia spp. populations.
Evaluate the impact of the various natural enemies as biocontrol agents of root maggots.
Disseminate information to organic and conventional cole crop growers

Accomplishments/Milestones

To date we have conducted pitfall trap and soil surveys of field-margins and in-field refuges over two growing seasons. These surveys have been conducted in both organic and conventional fields. We have completed a series of six large-scale field experiments designed to evaluate the efficacy of predator beetles for root maggot control. These experiments have involved isolating the factors that could potentially limit the efficacy of predators in the field. These limiting factors include predation of smaller predators by larger beetles and predator distraction, from feeding on fly eggs, by aphid alternative prey. We have conducted a field experiment examining predation of sentinel fly eggs in fields with varying abundances of predators. Information dissemination involved presentation of beetle collections and demonstrating natural enemy collecting techniques at farms walks. We also made several formal presentations of our data to grower meetings during the fall of 2004-2005. A revised web site has been started to provide growers with pictures of predators commonly occurring in fields.

The remaining activities for this project in 2005 include sorting and analyzing field survey data, completing field cage experiments, collecting root maggot phenology data, and continuing in grower outreach. In particular we will complete and post our web site and provide information to growers about its availability in grower newsletters. Also natural enemy collecting kits and checklist of common natural enemies will be distributed to growers during farm walks and field days. A field day highlighting in-field refuges will be conducted during the 2005 field season.

Impacts and Contributions/Outcomes

Our research demonstrates to growers the diversity and abundance of beneficial insects in their fields. It highlights how the availability of refuge habitat in fields can enhance natural enemy abundance. We also document the factors that ultimately limit how much predatory beetles can contribute to root maggot control by emphasizing the ecological context in which these insects live. Thus we are providing accurate information to growers not only on the identification and biology of predators, but also on their impact for pest control. Growers are often not provided with data on the level of control they can reliably expect from beneficial insects.

Collaborators: