Aphids and caterpillars can be some of the most troublesome pests on mixed-vegetable farms, in particular for organic farmers who have few chemical-control options. So, we were surprised when a group of longtime organic farmers told us that these two pests were hardly ever a problem on their farms. This is in contrast to beginning organic farmers, who struggle mightily to control aphids and caterpillars. Our “experienced” farmers were some of the earliest adopters of organic agriculture, and actively work to build biodiversity on their farms by, for example, planting hedgerows of native plants, avoiding chemical applications whenever possible, and using green and animal manures.
With the support of a large grant from USDA’s Organic Transitions program ($750K over 3 years), we are searching for the ecological basis of natural pest control on “old” and “new” mixed-vegetable farms across ID, WA, OR and CA. Our working hypothesis is that biodiversity among communities of pest-killing natural enemies (predators, parasitoids, and entomo-pathogens) builds through time. As natural enemy communities become increasingly species-rich, pests might have a harder time reaching outbreak densities. We will track predation on the farms of our cooperating growers by, in part, using molecular gut-content analysis to detect prey DNA within the stomachs of their predators. We also are examining whether increasingly nutrient-rich soils on organic farms encourage “healthier” plants that are better able to defend themselves against pests.
In addition to a large group of cooperating farmers, key collaborators include Snyder-lab postdoc Daisy Fu and PhD student Jake Asplund, James Harwood in the Entomology Department at the University of Kentucky, John Reganold in WSU’s Crop and Soil Sciences Department, and Alex Stone and her eOrganic team at Oregon State University.