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Harmless Fungus Protects Cotton Plants

By Linda Cooke
September 24, 1997

Coating cotton seeds with a harmless fungus and a touch of commercial fungicide allows more cotton plants to survive, Agricultural Research Service scientists report.

The researchers pitted the fungus Trichoderma virens and the fungicide metalaxyl against Rhizoctonia solani and Pythium ultimum, two fungi that kill cotton seedlings. Using harmless fungi such as T. virens as biological control weapons against damaging fungi promises to reduce the reliance on chemical fungicides for cotton, the scientists say.

In field tests, Charles R. Howell and colleagues at ARS’ Southern Crops Research Laboratory, College Station, Texas, coated cotton seeds with the G6 strain of T. virens and metalaxyl. The result: 85 percent of the seedlings survived, compared with 25 percent for untreated seeds. Three years of field tests in California and the southern Cotton Belt confirmed that the combination of harmless fungus and metalaxyl allows more plants per acre to survive and reach maturity than the untreated controls.

In addition to fending off R.. solani and P. ultimum, the combination of fungus plus fungicide protects cotton seedlings against other diseases. Alone, metalaxyl is only effective against one seedling disease caused by P. ultimum.

This year, seedling diseases caused $1.9 million in losses to cotton growers. In 1995, cotton producers in six major cotton-producing states applied 719,000 pounds of fungicides to control seedling diseases.

Scientific contact: Charles R. Howell, USDA-ARS, Southern Crops Research Laboratory, College Station, Texas, phone (409) 260-9232; fax (409) 260-9470,