Description and Symptoms
The initial symptoms of eyespot (Aureobasidium zeae) are small, water-soaked or chlorotic circular spots. The tissue at the center of the spot later dies and turns tan-colored with a brown ring at the margin. The spot is surrounded by a yellow “halo” that can be seen clearly when the leaf is lighted from behind. Spots may join together into large necrotic areas and the entire leaf may die. The spots remain visible even after the leaf dies. The disease is more common when corn follows corn. Cool temperatures (60s°F to low 70s°F) favor disease development, thus eyespot may appear early in the season on lower leaves and again near the end of the season on upper leaves. Resistant hybrids and inbreds are available. Crop rotation and tillage reduce survival of the fungus. Foliar fungicides labeled for eyespot are available.
Eyespot loves wet and cool weather so it is probably not surprising that the disease is especially prevalent this year. If such weather continues, we can expect the disease to spread.
The cornerstone of eyespot and GLS management is resistance. Rotation can also reduce risk of disease. Fungicides are also effective at reducing disease and protecting yield.
To determine if a fungicide application is necessary, the following factors should be considered:
• disease pressure in the field
• hybrid susceptibility
• predicted weather conditions during grain fill
• price of corn and cost of fungicide plus application
• previous crop
• field history of disease
Photo by Adam Sisson