Yield Loss From Foliar Blights in Wheat

April 30, 1999
Weather conditions continue to be favorable for development of foliar fungal blights on the wheat crop. Should you apply a fungicide? With new crop wheat currently at around $2.30, it isn't likely that a fungicide application is a good economic decision, although 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 one bushel per acre for each 5 percent 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 percent in fields where diseases are economically important compared to an untreated field. Next determine the cost of the fungicide plus application (approximately around $16 to $26 per acre, depending on material and type of application). With wheat at $2.30, yield increases of 7 to 11 bushels would be needed to cover the cost of treatment. For this scenario you would need approximately a 70- to 100-bushel yield potential. Putting a pencil to it with your own cost estimates and yield potential will help you make the decision about whether a fungicide application will benefit you this season.--Suzanne Bissonnette

Author: Suzanne Bissonnette