A few corn fields scouted this week were found with eyespot and anthracnose leaf blight at low incidence and severity. These fields were corn on corn (high corn residue), the rotated corn fields were mainly disease free.
Eyespot is a fungal disease caused by Aureobasidium zeae. This fungus survives on corn residue and infection is promoted by several hours of leaf wetness (from rainy weather or prolonged heavy dew on leaves). The spores are splashed onto lower leaves from corn residue or blown by wind to upper leaves. Initial symptoms appear as small round brown lesions (Figure 1). As symptoms advance, the lesions develop a tan center surrounded by a yellow halo. These can coalesce to form large yellowing lesions on the leaf.
Figure 1. Eyespot symptoms on a corn leaf. Notice the circular tan centers surrounded by a yellow halo.
Anthracnose Leaf Blight
Anthracnose leaf blight is caused by a fungal pathogen, Colletotricum graminicola. This pathogen also survives on corn residue and like eyespot, anthracnose leaf blight develops under prolonged wet weather and warm temperatures. The symptoms develop in lower leaves as irregular reddish-brown elliptical lesions (5-6 inches long) with tan centers (Figure 2). When the lesions coalesce, this can lead to early senescence of lower leaves.
Figure 2. Anthracnose leaf blight symptoms on lower corn leaves.
Eyespot and anthracnose leaf blight are considered minor diseases in corn except where the hybrid planted is highly susceptible under no-rotation and no-till conditions. These diseases can be best managed by planting resistant/tolerant hybrids, crop rotation and residue management through tillage where practical. A fungicide may be applied at tasseling growth stage if eyespot is observed in mid-canopy leaves. View Fungicide Efficacy for Control of Corn Diseases for a list of fungicides effective against eyespot.