Source: Kiersten Wise, Purdue University
Wheat is at or approaching Feekes growth stage 7 in most areas in southern Indiana. Wheat in Tippecanoe county is still at Feekes 5 to 6. The amount of time it takes from jointing (Feekes 6) until flag leaf emergence (Feekes 8) depends on temperature. Research conducted by Dr. Greg Shaner found that it takes between 12 and 17 days for wheat to progress from jointing to flag leaf emergence in Indiana. Therefore, if producers are considering fungicide applications at flag leaf emergence through boot stage (Feekes 8-10), now is a good time to review the fungicides available for foliar wheat disease management.
In Indiana, foliar fungicides are commonly applied to manage the Stagonospora /Septoria leaf blotch complex in wheat. This complex produces tan to brown, round to elliptical lesions (Figure 1) on lower leaves initially. Warm nights (over 45Â°F), and a few days of rainy, cloudy weather can promote infection and disease development. When lesions form on the flag leaf or above, the disease may contribute to yield loss.
Several factors should be considered to determine if a fungicide application is needed, including the susceptibility of the variety planted to disease and the level of fungal disease as wheat reaches Feekes 8-10. When scouting fields, examine the lower leaves of the wheat plant to see if lesions are present, and monitor weather forecasts to determine if conditions will be favorable for disease development. If there are no lesions or very few lesions on lower leaves, and the weather is warm and dry through boot stage, a fungicide application for leaf blotch management may not be necessary. If the weather becomes more favorable for disease and lesions are observed two leaves below the flag leaf, and the variety is susceptible to leaf blotch, a fungicide application may be beneficial. Economic factors such as expected yield and crop price should also be considered.
Fungicides were tested for foliar disease control in a trial in West Lafayette, IN in 2009 (Table 1). In this trial fungicides were applied to a variety susceptible to the foliar leaf blotch complex. Fungicides were applied at full flag leaf expansion through boot stage (Feekes 9 -10).
The cost of a fungicide application can range from $16.00 to $25.00 per acre, depending on the fungicide product, and application method. A break-even response calculated based on an application cost of $20.00/A, and a wheat price of $5.00/bu means that yield must increase by 4 bu/A to pay for the cost of the fungicide application. In the 2009 trial, the break-even threshold of 4 bu/A was reached in 4 of the 6 treatments tested.
There are several fungicides available for use against foliar wheat diseases. The NCERA-184 committee is composed of university wheat pathologists, and each year this group discusses how labeled fungicides products perform against wheat diseases, and post ratings in a wheat fungicide efficacy table. The 2010 version can be accessed at the following Web site. This is an excellent resource for selecting fungicide products to manage foliar wheat diseases, as well as Fusarium head blight, or scab.
Figure 1. Lesions typical of Septoria/Stagonospora leaf blotch of wheat.
(Photo Credit: G. Shaner)
|Table 1. Effect of foliar fungicides on Septoria leaf blotch management at the Agronomy Center for Research and Education (ACRE), West Lafayette, IN, 2009.|
|Treatments||Rate (fl. oz./A)||Application Timing (Feekes Growth Stage)||Septoria Leaf Blotch (% on Flag Leaf)
|Yield (bu/A)||Test Weight (lbs./bu)|