Hot, humid weather has many corn diseases on the rise across Nebraska (and other states). Growers need to keep watch for corn disease development, says Tamra Jackson, a University of Nebraska-Lincoln Extension plant pathologist. "There are quite a few diseases out there," she says.

Gray leaf spot, anthracnose leaf blight and common rust are fungi-caused diseases developing now across the state. However, it is important to make an accurate diagnosis as some of these diseases are being mimicked by some bacterial diseases, such as Goss' wilt and blight and bacterial stalk rot.

"Making an accurate diagnosis is critical to avoid making unnecessary fungicide applications," Jackson says.

When it comes to gray leaf spot, corn growers need to look for small, gray and rectangular lesions, which will start at the bottom of the plant and work their way up.

"Some people may consider spraying a fungicide, which is especially critical on susceptible hybrids," Jackson says. "So, be sure to look at your companies' catalogs and literature so you know how they will react."

Another problem disease is Goss' wilt.

"I have seen this in several counties, even in fields that didn't get hail, but high winds," Jackson says. Ripped leaves make corn more susceptible to Goss's wilt.

Jackson says this disease could be mistaken for physoderma or corn blotch leaf miner.

Symptoms of Goss' wilt are water soaking around the edges of leaf and dark green to black flecks, or freckles, on the edge of the lesions.

This is a bacterial disease that can't be controlled with a fungicide. It is too late to do anything about this disease this growing season.

Other diseases being reported across the state include common rust and bacterial stalk rot.

Common rust should not be confused with the more aggressive southern rust disease that caused significant yield loss in 2006. Common rust spores and pustules tend to be reddish brown during this time of the growing season.

Conditions also are suitable for bacterial stalk rot to develop due to warm and flooded conditions in some areas of Nebraska, Jackson says.

Affected plants wilt rapidly and are overtaken by a slimy lesion that may begin at either the top or bottom of the plant. These plants also may have foul odor.

For more information about all these corn diseases, including pictures, visit Crop Watch, UNL Extension's crop production newsletter, or watch the July 9 edition of "Market Journal."

Diseased plants also can be submitted to the UNL Plant and Pest Diagnostic Clinic. For more information visit http://pdc.unl.edu/diagnosticclinics/plantandpest. For more information and other plant diseases or for submission forms and instructions, visit the Plant Disease Central website at http://pdc.unl.edu/.