Potting Mix May Replace Fungicide

United States Department Of Agriculture (USDA) researchers have discovered a way to make potting mixes more successful than fungicide in reducing Botrytis gray mold, the most common disease affecting greenhouse floral crops such as begonia, carnation, chrysanthemum, cyclamen, geranium, impatiens, petunia and marigold. In a test with begonias, plant pathologists Leona Horst, James Locke and Charles Krause found that a mix of peat, compost and the beneficial fungus Trichoderma hamatum strain 382 reduced Botrytis gray mold better than the standard fungicide chlorothalonil did.

Beneficial Trichoderma seems to enter the plants through the roots and spread through the entire plant internally. One advantage of systemic biocontrol is that it doesn’t leave residue on the plant, harming plant market value. Begonias in this mix had fewer gray mold symptoms. The improvement in plant quality and market value makes the Trichoderma compost mix promising for greenhouse operations. Also, Botrytis has developed resistance to several fungicides.

Trichoderma works by preventing Botrytis from infecting fresh wounds and producing compounds that keep Botrytis spores from germinating. Surprisingly, the compost mix had a similar effect even without Trichoderma. To learn more, visit the USDA’s Agricultural Research Service Web site at www.ars.usda.gov.