Humid orwet and warm temperatures favor Cercospora leaf blight development.
- Wind and rain during the growing season can spread spores to soybean plants.
- Red, orange, or bronze colored upper leaves and a leathery appearance are symptoms.
- Purple seed stain can result if seeds become infected.
Cercospora leaf blight is a warm temperature (75 to 80º F) fungal (Cercospora
The upper leaves of infected plants that are setting seeds become dark red, orange, or bronze colored and have a leathery appearance (Figure 1).2 Very small, dark lesions develop on or near major leaf veins and on petioles, which can lead to premature defoliaton.3 Leaves that are sunburned and plants that are characterized by early senescence can be confused with Cercospora leaf blight.1
Seeds can become infected when the fungus grows into the upper vein on a pod, resulting in purple seed stain (Figure 2).1 Purple seed stain may range from tiny purplish marks to blotches covering most of the seed.2 Planting infected seed the following year can result in reduced germination, emergence, and vigor.
Fungicide applications are a potential option during the growing season and should be based on disease severity and timing. Applications for late-season diseases are generally made between growth stages R3 and R5 (pod development stages). Fungicide applications after plants reach full maturity or after the R6 growth stage
Crop rotation and tillage, which can help reduce disease inoculum, and the use of certified seed are cultural controls that should be considered when developing crop plans for the next growing season.2
Effect on Yield
The potential for the disease to reduce yields ranges from very low to substantial depending on disease onset timing, the speed of development, and environmental conditions.3 Should favorable conditions develop early in the growing season and continue throughout the growing season, the potential for a negative effect on yield increases.
1 Cercospora leaf blight. 2014. Soybean Research & Information Initiative. North Central Soybean Research Program. http://www.soybeanresearchinfo.com. 2 Yang, X.B. 2004. Soybean Cercospora diseases show up. Integrated Crop Management. IC-492(17). Iowa State University. http://www.ipm.iastate.edu/ipm/icm/2004/7-26-2004/cercospora.html. 3 Hershman, D.E. 2009. Cercospora leaf blight in Kentucky. Plant Pathology Fact Sheet. PPFS-AG-S-20.