Abstract: Summary of Introduction and Session 1

This conference was set up as an exchange between farmers and scientists about alternatives to insecticides. Kim Stoner identified vegetable farmers who had information to share from lists of SARE farmer research projects, participation in previous "Farmer-to-Farmer" conferences in Massachusetts, and contacts in organic farming organizations. These farmers were invited to the conference, asked what information they could share and what insect problems they wanted more information about. She invited scientists who could either supplement the farmers’ information or who had expertise on an insect problem the farmers wanted to solve.

Session 1: The Effects of Plant Health and Soil Health on Susceptibility to Pests

A History of the Idea that Healthy Plants are Resistant to Pests

The purpose of this talk was to present a theory which holds that plants are inherently resistant to pests and thus pest problems indicate that the growing conditions are inadequate. Eliot Coleman, a farmer and writer from Maine, explained that this idea goes back to the botanist Theophrastus in 300 B.C. and continued up through the "Predisposition" school of plant pathology in the early 1900’s. This school of thought emphasized that healthy plants have a natural immunity to attack by fungi and bacteria and sought to understand how to cultivate plants that would have this immunity. The ideas of Sir Albert Howard, the father of organic farming, grew out of his studies with the Predispositionist H. Marshall Ward.

One possible mechanism of greater susceptibility to insects of stressed plants is greater availability of nitrogen in the form of free amino acids, suggested by the entomologist T.C.R. White.

On his own farm, Eliot Coleman said he seeks to optimize every facet of the physiological well-being of the crop plant, including drainage, moisture, balance of nutrients in fertilizers, and organic matter in the soil. He referred to this philosophy as a plant-positive (as opposed to pest-negative) approach.

The Relationship between Soil-Management History and Corn Susceptibility to Pests

Larry Phelan, an entomologist from Ohio, compared infestations of corn insect pests in organic and conventionally managed corn fields, and also did controlled greenhouse comparisons of oviposition of European corn borer moths on plants grown in soil from organic and conventionally managed fields. He found lower levels of European corn borer infestation in the organic fields and lower oviposition on corn grown in soil from organic farms in the greenhouse tests. He is currently conducting research on the connection between soil management and pest susceptibility, but he believes that the maintenance of plant mineral balance is important in reducing corn susceptibility, and that pest susceptibility in organically managed soils is lower because of the greater capacity of these soils to buffer mineral availability.

Discussion-Session 1

Eliot Coleman described his experience testing the effects different soil amendments on plant growth and pests. He divided a field into strips and put different amendments in each strip (leaves, manure, seaweed, etc.) He planted each of his crops across these strips. He observed different insect pests (e.g. cabbage maggot, squash bug) and different diseases in different strips.

Larry Phelan explained how he is studying plant biochemistry, including the amounts and forms of nitrogen in relation to insect resistance. Eliot Coleman mentioned cytokinin (present in seaweed) as a possible factor in insect resistance.

Both of them discussed the importance of reducing costs by making nutrient cycles into closed loops as much as possible, reducing or eliminating inputs from outside the farm. Larry Phelan responded to questions about soil quality and soil microbiology by saying that we do not yet know enough to give farmers simple tests to measure the quality of their soils.

Plant health may not be the solution to every problem -- Larry Phelan suggested that insects of fruits may be more difficult to control because fruits are meant to be eaten -- but both presenters agreed that we need to see how far we can go in reducing plant stress and increasing plant health as a way to manage pests.