Late Blight Suppression in Tomatoes Using Competing Fungi on Leaf Surfaces
Late blight (Phytophthora infestans) is a major problem for tomato production in the Southeast. It is by far the biggest problem with the production of organic tomatoes in Western North Carolina. This area is known for its tomatoes because the warm days and the cool nights allow fruit set to proceed through the summer when other areas are too hot to reliably set fruit. With the cool nights come foggy mornings and ideal conditions for fungus growth. Late blight can defoliate a tomato plant within a week. Conventional growers minimize this problem with a weekly or more frequent spray program. An organic spray (copper sulfate) serves as a protectant and is fairly effective on late blight but it is water soluble and must be applied after each rain. Recoating all leaf surfaces after each rain is impractical, not to mention the problem of copper buildup in the soil. Without some late blight treatment, organic tomato production is possible only about one year in five in an area known for its conventional tomatoes.
An alternative to conventional fungicides (or copper sulfate for organic producers) would improve the sustainability of agriculture in the Southeast. The approach of this project is to explore the colonization of leaf surfaces with benign microbial populations that will compete with late blight when it arrives in late summer. Several compost extracts will be tested for their ability to counter the effect of late blight on tomato leaf surfaces by providing benign microbial populations that will outcompete the late-blight microrganisms. If this alternative approach proves successful, spray programs could be cut back or switched to a more environmentally benign material. In addition to reducing off-farm inputs, this approach may allow organic growers to avoid the build-up of copper in agricultural soils.