No. 18 Article 3/August 6, 2010

Diplodia Ear Rot Making a Reappearance

Symptoms of Diplodia ear rot are apparent in some cornfields. Husks with a bleached appearance may indicate the presence of the disease. When these affected husk leaves are pulled back to expose the ear, a white mold may be growing on and between the kernels, which is diagnostic of Diplodia ear rot (see below for photos).

Discolored husk leaves--an indication that Diplodia ear rot is present on the ear.

Symptoms of Diplodia ear rot on the base of a corn ear.

Diplodia ear rot, caused by the fungus Stenocarpella maydis, was a major problem in Illinois and surrounding states in the 2009 growing season. Initial observations in 2010 indicate that the incidence may not be as high. Because the causal fungus overwinters in corn debris, fields that are corn-on-corn may be affected the most (especially where significant amounts of corn residue were left on the soil surface). Wet weather during ear development favors the disease.

The best management practices for control of Diplodia ear rot are used prior to planting, including tilling to bury infected corn residue, planting corn in fields that follow soybean, and planting hybrids with improved resistance to Diplodia ear rot. To my knowledge, Quilt Xcel (Syngenta) is the only foliar fungicide that includes Diplodia ear rot on the label; however, more research is needed to better determine the best application timing for control of Diplodia ear rot as well as the level of control that could be expected with this product.--Carl A. Bradley

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