Numerous cases of Frogeye leaf spot have been reported in fields of susceptible soybean varieties. Circospora sojina is the fungus that infects leaves, stems and pods. Warm, humid and rainy conditions favor rapid development of infection. Infection may take hold anytime during growth and development but is most commonly found after flowering and in the upper canopy. Where disease pressure is severe on susceptible varieties, yield losses of up to 30 percent may occur. Foliar fungicide application may be warranted where threshold levels have been reached or exceeded.
Brown Spot is a soybean disease that starts in the lower canopy and migrates up the plant. Different soybean varieties vary in susceptibility to brown spot. Look for yellowing leaves and defoliation in the lower canopy. Dark brown and irregular spots will spread throughout the canopy. Lesions may have a yellow halo. Stems and pod lesions may follow as the disease progresses.
Because there is a wide range of soybean development/maturity this year, determining treatment timing will take some extra consideration. Talk with your AgVenture Yield Specialist to determine optimal treatment timing.
(photos: University of Nebraska-Lincoln)