Foliar Health Basics: Brown Spot (Septoria) Control in Soybeans
Brown spot or Septoria leaf blight in soybeans is caused by the fungus Septoria glycines, which spreads from soil to young soybean plants by splashing rain and is found throughout much of the United States.
Severe brown spot infection reduces yield 8 to 15 percent when 25 to 50 percent of plant leaves drop early. Infected plants tend to produce smaller soybeans.
Risk Factors: Brown spot disease is most severe in continuously cropped soybean fields, since it overwinters on soybean residue, other legumes and certain weeds including velvetleaf.
Scout soybeans from V2 through R6, especially during warm, wet conditions. Begin scouting in low-lying fields and areas surrounded by trees.
Signs of Infection
Brown, irregular spots, often surrounded by yellow halos, begin on tops and undersides of lower leaves and work upward through the plant. Late in the growing season, infected leaves turn yellow or reddish-brown and drop. Signs can develop on stems and pods near crop maturity.
An application of DuPont™ Aproach® Prima fungicide made at R2-R3 reduces disease severity and preserves yield. Field trials in 2015 demonstrate effectiveness of an R3 application of Aproach® Prima in preserving yield, compared to other fungicide options.
Complete resistance is not yet available in soybean varieties, but some offer partial resistance. Crop rotation is an effective preventive strategy. In fields with heavy levels of brown spot, tillage promotes soybean residue decay.
DuPont™ Aproach® Prima fungicide is not registered in all states. See your DuPont retailer or representative for availability in your state.
Fortix® (FMC); Quadris®, Quilt Xcel®, Trivapro™ (Syngenta); Stratego® (Bayer).
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