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Yield Loss from Foliar Blights in Wheat

April 26, 2002
Conditions are primed for development of foliar fungal infections in areas of the state that have had intense sustained rains, such as Tim Laatch, of Effingham Extension Unit, reports. This presents an extremely conducive environment for development of foliar fungal blights on the wheat crop. Plants already infected with virus disease can also host fungal infections. Start scouting for fungal leaf blight development this week.

How can you decide if the infection warrants fungicide treatment? With wheat at around $2.70 as I write today, fungicide application may or may not be a good economic decision for your yield potential, but it may still be a good disease management decision.

The flag and flag-1 leaves contribute the most to final yield of the plant. In general, you can expect a yield loss in the range of 1 bushel per acre for each 5% of leaf tissue infected on either of these two leaves. To make your decision whether or not to spray, you will need to determine your yield potential. A rough way to determine yield potential is to count the number of tillers per square foot and multiply by 1.5. Then consider that fungicides can generally provide yield increases of 10 to 20% in fields where diseases are economically important compared to an untreated field. Next, determine the cost of the fungicide plus application at approximately $16 to $26 per acre, depending on material and type of application. With wheat at $2.70, yield increases of 6 to 10 bushels would be needed to cover the cost of treatment. Putting a pencil to it with your own cost estimates and yield potential will help you make the decision whether a fungicide application will benefit you this season.--Suzanne Bissonnette

Author: Suzanne Bissonnette

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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