Agronomic Crop Disease Updates – September 17, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Corn
Corn harvest is underway so be sure to check corn fields for lodging potential by squeezing the lower nodes or pushing on the stalks. A simple way to do this is to walk through the field and, keeping your hands at chest height, push stalks 8-10 inches from vertical. If 10-15% of the stalks lodge, schedule the field for early harvest before a strong wind results in severe lodging. Drought conditions during grain fill put substantial stress on corn plants. In many fields, it is likely that the corn crop responded by cannibalizing stalk reserves to fill the grain. This results in a weakened stalk and greater susceptibility to stalk rot.

Small Grain
Be sure that you plant wheat varieties with high levels of disease resistance. Select varieties with high levels of resistance to powdery mildew, leaf rust and stripe rust. Seed should be treated with Baytan, Raxil, Dividend or other labeled product to protect plants from loose smut and common bunt. Varieties that are susceptible to powdery mildew should be treated with Baytan, Dividend or other seed treatment that will protect them from early infection.

Soybeans
Do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags are available from the county Extension offices for $10/ sample bag.

Soybean Rust Update
Nothing new has developed north of the North Carolina find on August 30. Florida had its first soybean rust detection on soybeans on September 14. Needless to say, soybean rust is not going to be an issue in most of the US this season.

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