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Effect of glyphosate application on foliar diseases in glyphosate-tolerant alfalfa

Samac, Deborah A.
Plant disease 2012 v.96 no.8 pp. 1104
Colletotrichum trifolii, Medicago sativa, Phoma medicaginis, Uromyces, active ingredients, alfalfa, application rate, disease control, foliar diseases, fungal spores, fungi, glyphosate, greenhouse experimentation, pathogens, pesticide application, regrowth, rust diseases, stubble, transgenic plants
Glyphosate, the active ingredient in Roundup herbicide, inhibits 5-enol-pyruvyl shikimate 3-phophate synthase (EPSPS), an enzyme found in plants, fungi, and bacteria. Plants engineered for glyphosate tolerance with a glyphosate-insensitive EPSPS take up and translocate the herbicide throughout the plant. In greenhouse experiments we found that application of glyphosate at the recommended field application rate completely controlled alfalfa rust (Uromyces striatus) on 4-week-old plants inoculated with the fungus 3 days after glyphosate treatment. Also, excellent control of rust was obtained when glyphosate was applied up to 10 days after rust spores, indicating that the herbicide has protective and curative activity. Glyphosate application to stubble and regrowth provided protection for up to 21 days when plants were inoculated with rust spores 3 days after treatment or for up to 14 days when spores infected plants 11 days after treatment. Treatment afforded some control for anthracnose, caused by Colletotrichum trifolii, a hemi-biotrophic pathogen, but not for spring black stem and leaf spot, caused by Phoma medicaginis, a necrotrophic pathogen. These results indicate that glyphosate could be used to help manage foliar diseases in glyphosate-tolerant alfalfa.