One of the most difficult planting seasons is finally over. With high soil moisture and warm temperatures, crops could grow fast but the plant diseases will grow fast too. While scouting for insects, make sure to watch out for diseases also. This will not only help you in getting prepared for foliar fungicides if needed later, you might be able to take some control measures right away for certain pathogens.
Stewart's wilt is one of those diseases that may be controlled if detected early. It is caused by bacteria carried by shiny black flea beetles, the size of a pin-head. The bacteria live in the body of the beetles during winter and if the winters are mild, more beetles will survive. They cause bacterial wilt and leaf blight in the corn plants by feeding and injecting the bacteria into the plants. The insects strip away the green tissue and inject bacteria into the leaves. If not controlled, this disease can cause wilting and seedling death. Later, the affected adult plants that survive may develop long, wavy brown streaks through the length of the whole leaves. .
Several insecticides are available that can kill the flea beetles and control the disease but it must be applied as soon as they are detected. There are several hybrids available with excellent resistance to this disease. If you have susceptible hybrids this year, check with your Seedsman to make sure you order resistant hybrids for 2012.
It will still pay to scout and see what is in the field. If you have seed corn, flea beetles and Stewart's wilt tends to be more of a perennial issue. It would definitely require checking this year.
If you have trouble identifying the beetle or the disease, ask your Extension educator fro help. Many states publish pocket-sized field guides that can help you identify this and other key, early season diseases. Two of the best are published by Purdue University and Ohio State University.
For example, the Corn and Soybean Field Guide published by the Diagnostic Training Center at Purdue features pictures of Stewart's wilts at various stages in the plant's development on page 96. It also references other seedling blights, and what to look for in scouting for these diseases. Visit
www.agry.purdue.edu/dtc or www.entm.purdue.edu/fieldcropsipm.
Scouting for the leaf blight phase of Stewart's wilt is suggested throughout June and July. You can also scout for other foliar diseases prevalent in your area at the same time.