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Disease Detection and Crop Losses

Leaf Infection and Yield Losses Caused by Brown Spot and Bacterial Blight Diseases of Soybean. D. J. Williams, Former graduate student, Department of Plant Pathology, Iowa State University, Ames 50011, Present address of senior author: USDA, APHIS-PPQ, Henry A. Wallace Building, Room 146, Des Moines, IA 50319; R. F. Nyvall, professor, Department of Plant Pathology, Iowa State University, Ames 50011. Phytopathology 70:900-902. Accepted for publication 7 March 1980. Copyright The American Phytopathological Society. DOI: 10.1094/Phyto-70-900.

Yield reductions caused by Septoria glycines and Pseudomonas glycinea (P. syringae) on soybeans were measured in the field on plants inoculated with either pathogen and by both in combination. The disease index based on percentage defoliation and percentage of remaining leaf area diseased on samples of 25 inoculated plants per plot ranged 65–78% for S. glycines, 60–69% for both combined, 46–62% for P. glycinea, and 4–24% of the uninoculated check plants. Yield reductions of 17.9% for P. glycinea, and 17.4% for S. glycines, and 14.1% for both organisms combined were observed. Both yield and infection of inoculated plants differed statistically from uninoculated plants.