Frequent rainfall and extended periods of high relative humidity create an ideal environment for many wheat diseases. When these weather conditions occur around the flowering time for wheat, it increases the risk for Fusarium head blight. This fungal disease reproduces on crop residues from previous corn and wheat crops. Wet weather as wheat is heading stimulates the fungus to reproduce and release spores. These spores are moved by wind to developing wheat with infection taking place during flowering or early stages of grain fill. The resulting symptoms include large tan lesions that encompass one or more spikelet’s, or in some cases, can damage the entire head (Figure 1).
Figure 1. Wheat with symptoms of Fusarium head blight. Photo provided by Erick DeWolf, K-State Research and Extension.
Fungicide applications of products such as Prosaro, Caramba, or Miravis Ace provide the best available disease suppression. These fungicides are most effective when applied at the start of anthesis or within a few days after flowering is completed. Given the current low grain prices, it may be even more important to only apply fungicides when they are most needed.
Fortunately, there is a prediction effort designed to help growers evaluate the need for fungicides to suppress Fusarium head blight. These models target the past 2 weeks of observed weather and are most accurate as the crop approaches flowering when the fungicide decision must be made. The current risk map indicates that some areas of southeast and south central Kansas may be at risk for severe disease problems (Figure 2). The current prediction is most relevant for fields that are currently heading or flowering. With more wet weather forecasted for next week, growers in these areas should be monitoring the weather and disease predictions. Fungicides may be needed if the risk persists or increase over the next week.
The predictive models for Fusarium can be found on-line at: http://www.wheatscab.psu.edu
Figure 2. Screenshot of the current risk of Fusarium head blight in KS as estimated by the Fusarium Head Blight Prediction Center (http://www.wheatscab.psu.edu).
Erick DeWolf, Extension Plant Pathology