Fungicidal Effects of Compost Tea on Organic Strawberry Production
Strawberry growers in the Southeast have long been challenged by fungal diseases. The main fungal threats to strawberry plant health seem to be botrytis and anthracnose. These diseases can often dramatically reduce yields or even cause crop failure if left unchecked. Although there are cultural and sanitation procedures (plant spacing, dead tissue removal, etc.) that seem to provide some benefit, most growers rely heavily on chemical fungicides to try to keep these diseases under control. The dramatic increase in strawberry plasticulture throughout the Southeast has seemingly compounded the problem by introducing strawberry cultivars with little or no resistance to southeastern diseases. So, with increasing consumer concerns about the long-term health effects of fungicides and pesticides, the passage of the Food Quality Protection Act, and reports showing strawberries as the “most contaminated” fruit or vegetable (see Environmental Working Group website http://www.ewg.org/), it seems timely to search for safer and more sustainable ways to deal with fungal infections in strawberries.
There is a growing body of research suggesting that compost tea can be effective in controlling fungal diseases (see ATTRA website for article on compost tea http://www.attra.org/). In these studies, late blight, gray mold, fusarium wilt, downy and powdery mildew and apple scab have all been controlled to some degree by compost teas. The mechanisms of this control are not completely understood yet, but in lay terms it seems to be an issue of encouraging enough “good guys” (beneficial microbes) on the plant surfaces to out-compete the “bad guys” (plant pathogens). It is important to see whether compost tea can prove effective on strawberries in the Southeast, particularly on botrytis and anthracnose.
Each year I rotate my crop through one of three fields. In my project, I will lay out a research plot in the field designated for the 2001-2002 growing season. After consulting with Professor Steve Bost on the design of the experiment, we decided on three replications of four different treatments. These treatments will be: 1) Control (no spraying or leaf sanitation), 2) No spraying with leaf sanitation, 3) Spraying without leaf sanitation, and 4) Spraying with leaf sanitation. (Although it is often practiced for botrytis control, there is conflicting research evidence for the need of leaf sanitation. Furthermore, leaf sanitation may or may not enhance the performance of compost tea against botrytis.) The whole design will be repeated both on plastic and on straw. The compost tea will be made in a commercial compost tea maker which I have arranged to rent from the manufacturer.