Check now for corn leaf disease

Published 5:41 pm Thursday, May 26, 2011



In the past corn growers in Georgia have not commonly used fungicides on field corn.

However, yield loss can be minimized by using sound disease management practices and using the appropriate fungicides. Fungicide usage should be based on the presence of disease, especially southern corn rust and northern corn leaf blight.

Northern corn leaf blight can be a devastating disease in corn if it is allowed to spread unchecked through susceptible hybrids. If you do have susceptible hybrids, watch them closely for the symptoms and be prepared to make a timely application of a labeled fungicide particularly on those fields that have good yield potential. The most appropriate time is at tasseling and early silk.

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Southern rust can also be a problem when we have southerly or western winds, which bring in the spores that cause the infection. Southern rust infections at pre- or early tasseling can be very destructive and cause severe yield loss.

Bob Kemerait, a University of Georgia extension plant pathologist, says the current hot and very dry conditions we are experiencing are generally not favorable for the development of diseases of corn. However, southern rust does develop under warm conditions so far we have not seen any of it yet. Also, the extreme dryness will reduce the risk to this disease.

Kemerait says most of our corn crop has reached or will reach first tassel over the next couple of weeks.

“First Tassel” is recognized by many corn growers as the “time” to apply fungicides. The University of Georgia Cooperative Extension recommendation is that “first tassel” is the appropriate time to assess the need for fungicides.

It would be a mistake for corn growers in our state to believe that all of our corn fields should be automatically sprayed at first tassel—there are many this year that do not need to be sprayed. However, first tassel can be an appropriate time to protect the corn crop from serious disease losses.

It would be appropriate to spray now if the field has good yield potential and there is some reason to believe that the field is at increased risk to disease like corn behind corn or a disease like northern corn leaf blight is progressing within the crop or if southern corn rust is detected in sentinel plots in the area.

If a grower decides to use a fungicide, which one should he or she use?

Kemerait explains that Tebuconazole and propiconazole are less expensive and are effective fungicides but will not have the same protective window the Headline, Quilt Xcel and Stratego YLD will have.

Fungicides like Headline, Headline AMP, Quilt Xcel and Stratego YLD are more costly than tebuconazole or propiconazole; however, they are likely to have a broader spectrum of activity against corn diseases, a longer protective window and perhaps some “plant health” benefit, though this can be difficult to document.