What can older organic farms teach us about natural pest control?

Long-established organic farms hold important clues about how organic practices work to control pests. Bill Snyder, professor of entomology at Washington State University, aims to find out why older organic farms have fewer pests than newer organic farms, and he hopes the answers will help farmers transitioning to organic reap the benefits sooner.

“Organic farmers that got started 20 years ago were some of the first. They definitely know what they’re doing,” Snyder said. The key, he explained, is to identify which organic practices contribute to improved pest control and how. Snyder is the lead investigator for the BAN-Pests Biodiversity and Natural Pest Suppression project recently funded by a USDA grant for $750,000.

The idea for the project was born from a previous study by project partners at Oregon State University documenting the observations of mixed vegetable growers in California, Idaho, Oregon and Washington. Those who had been farming organically for more than 15 years reported seeing fewer aphids and caterpillars on their farms than those with less established organic farms.

This difference tells Snyder that something about the ecology of organic farms changes over time. The question is what, exactly? He suspects the answers are related to greater predator insect diversity, improved soil quality and stronger plant immunity.

To tease out these factors, the three-year study will compare factors on both older and newer organic farms throughout the four previously studied western states. Snyder’s team will measure the level of biodiversity of natural pest enemies, quantify the number of pests that natural enemies kill (by studying the pest DNA in predators’ stomachs), and assess the ability of plants to fight off predators.

Snyder explained that because organic farming has now been around long enough, research can compare differences among organic farms rather than between organic and conventional farming. “When the general farming approach is the same among the farms being studied, it is easier to evaluate the effects of different practices on pest levels,” he said.

“Hopefully, we’ll reach a point where we can create recommendations to give to new and transitioning farmers, so it doesn’t take them 20 years to get to this point,” Snyder said. He thinks the results will also be useful to a broader group of farmers, including conventional growers.

Additional researchers at WSU include Daisy Fu, Department of Entomology, and John Reganold, Department of Crop and Soil Sciences. The project partners are Alex Stone, Oregon State University; James Harwood, University of Kentucky; and Helen Atthowe, Woodleaf Farm, Calif.