Field Crops Disease Update

Alyssa Koehler, Extension Field Crops Pathologist;

Grey leaf spot is becoming more common over the past week. To scout, check how far up the canopy lesions have moved. If the ear leaf or two leaves below have 5% or more of the leaf surface covered in lesions on over 50% of plants, you may want to consider a fungicide application while we are at R1 or just beyond. Lesions from GLS tend to be rectangular in shape (Figure 1). The 2020 CDWG Fungicide Efficacy Table can be viewed at

Figure 1. Rectangular lesion of Grey Leaf Spot on corn

Foliar soybean diseases have been limited this season. We have observed Septoria brown spot on lower leaves. This fungal disease is often observed low in the canopy and while it may cause some leaves to drop, does not typically affect soybean productivity.

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