Gail Ruhl, Plant Disease Diagnostician
The irregular marginal leaf scorch symptom exhibited on the lower leaves has been identified as Phyllosticta leaf spot. The infection starts at the leaf margin and progresses inward, forming an irregular, V-shaped area. Random leaf spots may also accompany the marginal necrosis.
This fungal disease occurs throughout the soybean belt in the United States. It may cause minimal premature defoliation to occur, and under certain environmental conditions may also progress from the leaf blades into the petioles and eventually into stem tissue. Infection of pods and seed is possible, however, this disease is generally considered of minor importance.
Since this fungal pathogen is seedborne, control measures include planting seeds relatively free of the pathogen, rotating soybeans with other crops and plowing under crop residues.
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Last updated: 22 September 1999/tlm.