Target Spot begins movement to Midwest

Closeup of a target spot lesion. Photo courtesy of Heather Kelly, University of Tennessee.

Farmers in the Delta and Southeast US are already familiar with Target Spot, but Midwest farmers are beginning to notice the foliar soybean disease.

Corynespora Cassiicola is the fungus that causes Target Spot, which overwinters in diseased debris and can survive in fallow soil for more than two years.i Symptoms typically are visible in mid-to-late reproductive stages or after the plants canopy. Symptoms develop in the lower canopy and appear as large circular lesions (1/4 to ½ inch diameter) with concentric rings, thus the name Target Spot. According to University of Tennessee researchers, the lesions can be confused with Septoria Brown Spot.

Fig. 2. Smaller lesions on leaflet in mid-canopy. Photo courtesy of University of Arkansas.

Excess moisture, high relative humidity (>85%) and warm temperatures over a period of 5 to 7 days cause this fungus to develop. Dry conditions should suppress disease development.ii Travis Faske, Extension Plant Pathologist for the University of Arkansas, adds that with the right conditions, Target Spot can produce smaller legions in the mid-to-upper canopy (Fig. 2) and can sometimes be confused with Frogeye Leaf Spot. Lesions can also develop on the petioles, pods and stems.

Symptoms develop in the lower canopy and appear as large circular lesions with concentric rings, thus the name Target Spot

Problem fields can be remedied by rotating to corn, grain sorghum or rice to reduce the total inoculum.iii Fungicide timing is the key to protection, according to Faske. He recommends two ways to manage the disease: suppressing target spot development ahead of its advancement up the canopy and utilizing water volume to move the fungicide into the canopy.

Discuss fungicide choices with your AgVenture Yield Specialist to determine the best disease management plan for your operation.

i University of Tennessee Institute of Agriculture.
ii University of Arkansas Division of Agriculture.
iii AgProfessional.com