Risk of Fusarium head blight (scab) in wheat
The recent rains and extended periods of high relative humidity are increasing the risk of problems with Fusarium head blight (FHB, or scab) in wheat. We are concerned about Fusarium for two reasons.
1. The wheat crop is at or will soon reach the flowering and early grain fill stages that are most vulnerable to the disease (Figure 1).
2. Weather conditions have been favorable for the reproduction and development of this disease.
The Fusarium Head Blight Prediction Center suggests that most of the eastern half of the state is at moderate to high risk of severe FHB. You can find risk maps prediction tools at: http://www.wheatscab.psu.edu. This prediction is largely driven by extended periods of high relative humidity and frequent rainfall (Figures 2 and 3).
Growers can help reduce the risk of Fusarium head blight in their fields with fungicide applications. Choosing the right fungicide is important with FHB; much more so than with stripe rust or leaf rust. Products such as Prosaro, and Caramba are the best options because these products offer about 50% suppression of the disease. Folicur or generic tebuconazole can also offer about 35% suppression of the disease. All of these fungicide must be applied after the heads have fully emerged to be effective. These fungicides can be applied through flowering and into the grain filling stages of growth but producers must stay within the 30-day pre-harvest interval on the label. Fungicides containing strobilurin active ingredients should be avoided during high risk periods for FHB. These products are not labeled for FHB, and in some situations can actually aggravate the DON mycotoxin problems caused by this disease.
Figure 1. Estimated growth stage in wheat based on model estimated development and K-State observations of crop stage. Local growth stage may vary with planting date and variety.
Figure 2. Rainfall summary for Kansas during the week of April 21-27.
Figure 3. Hours of relative humidity greater than 80% for Kansas. These periods of high relative humidity are very favorable for the development of Fusarium head blight.
Erick DeWolf, Extension Plant Pathology
Mary Knapp, Weather Data Library
Romulo Lollato, Wheat and Forages Specialist