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Disease Detection and Losses

Brown Spot Development and Yield Response of Soybean Inoculated with Septoria glycines at Various Growth Stages. L. D. Young, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607, Present address of senior author: Pfizer Genetics, P.O Box 245, Circleville, OH 43113; J. P. Ross, Research Plant Pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, P.O. Box 5397, Raleigh, NC 27607. Phytopathology 68:8-11. Accepted for publication 8 July 1978. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1979.. DOI: 10.1094/Phyto-69-8.

Brown spot (which is incited by Septoria glycines) caused 17.1% yield loss on Essex soybeans in field tests in 1976; yield and seed size were negatively correlated with percent leaf area diseased. Yield loss was due to reduction in seed size. Symptoms appeared 2 wk later in 1977 than in 1976; disease levels were lower and loss was nil. The periods for maximum symptom development for Essex plants inoculated with S. glycines at the second trifoliolate stage, at flowering, and at full-pod stage were approximately 21, 40, and 21 days, respectively. The longer incubation period of infections initiated near flowering accounted for the marked reduction in brown spot of soybean during midsummer.