Wheat in Tennessee has headed out and a good majority is flowering, which is the main growth stage for applying fungicides for Fusarium head blight (FHB or scab) control.
Tennessee has continued to have weekly rain events followed by cooler temperatures. These cooler temperatures are a limiting factor for FHB development and is the reason the risk has continued to stay low for now (visit www.wheatscab.psu.edu for updates on FHB risk). As posted in an early article (Wheat Disease Update and Fungicide Considerations), weather conditions that favor severe Fusarium head blight development include 3 or more days with frequent rainfall, extended periods of high relative humidity, and moderate temperatures (65 to 80 °F). These conditions present before, during, and after flowering favor inoculum production, floret infection, and colonization of developing grains. While optimum temperatures for infection are between 75 and 85 °F, infection can occur at lower temperatures during prolonged periods of high humidity and moisture. Wheat is susceptible to FHB infection at flowering (Feekes 10.5.1) through early dough stage (Feekes 11.2).
Forecasts predict rain events at the end of this week with warmer temperatures for Tennessee, which may rapidly increase FHB risk. Therefore, fungicide applications for wheat that will be in bloom by the end of the week should be considered. Research has shown the most effective timing for controlling FHB and mycotoxin levels is at flowering (Feekes 10.5.1 – image), but applications made 5 to 6 days after initial bloom can also provide a benefit in reducing FHB and mycotoxin levels. Whereas applications made at earlier growth stages, such as flag leaf, do not provide any control of FHB and mycotoxin levels.
When considering a fungicide application during bloom make sure it is a triazole only product (see the Wheat Fungicide Table). Products that contain a strobilurin can increase the mycotoxin levels in FHB infected wheat. Products labeled for FHB include: Caramba (good control), Prosaro (good control), Proline (good control), Folicur or other tebuconazole products (fair control), and Tilt or other propiconazole products (poor control).
I have had some questions about adding tebuconazole products to Prosaro. When answering this question I ask what rate of Prosaro is being used? If the full rate of Prosaro (8.2 fl. oz./a) is being applied please keep in mind that it contains the maximum season use rate of tebuconazole (4 fl. oz. per acre) . However, when using the lower rate of Prosaro (6.5 fl. oz./a) you may spike it with 0.8 fl. oz. per acre of tebuconazole in order to apply the full labeled rate. Make sure to read and follow all current label directions.
