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Gray leaf spot epidemic in the making?

Agriculture.com Staff 07/14/2009 @ 7:45am

Corn leaves at the ear and above that position have a huge impact on yields contributing as much as 70% to final bushel level at harvest. So it's understandable that Tamra Jackson is scared of what is happening in Nebraska corn fields.

The University of Nebraska plant pathologist warns that the severity of gray leaf spot, a potentially crippling plant disease, is spreading rapidly and much earlier in the year than normal.

Grey leaf spot thrives in moisture conditions when the temperature is between 70 to 90 degrees Fahrenheit. Jackson notes that 2 to 3 weeks ago there was frequent rain and several consecutive days of high humidity. This likely led to the seemingly "overnight" development of gray leaf spot lesions that has occurred in corn fields.

Making matters worse, the disease is likely to worsen after this past week's showers, overcast conditions and mild temperatures.

Jackson points out that resistant hybrids and ratings for gray leaf spot reaction are available from the majority of seed companies. Although resistant hybrids may still develop disease, resistance slows disease progression by limiting lesion development and slowing advancement up the plant. Resistant hybrids may provide enough protection to delay fungicide applications or, in some cases, to avoid them all together.

Since the ear leaf and those above it contribute the most to yield (approximately 70%), it is especially concerning that the disease has already progressed to them this early in the season, Jackson warns. It may be necessary to apply fungicide to slow disease progression, particularly if the disease has reached the ear leaf.

Fungicide application costs have increased to approximately $25 per acre (including the application), Jackson estimates. This expense requires an increase of at least 7 to 8 bushels per acre to cover the cost.

Corn leaves at the ear and above that position have a huge impact on yields contributing as much as 70% to final bushel level at harvest. So it's understandable that Tamra Jackson is scared of what is happening in Nebraska corn fields.

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