Figure 1. A map of South Dakota showing the varying risk levels for Fusarium head blight or scab as of 6/19/2018. The green areas indicate low risk, yellow areas, moderate risk, while the red areas indicate a high risk for scab.
With the recent frequent rains for some areas and rain in the forecast, the risk for Fusarium head blight (FHB) or scab has changed. Areas in the south central and east now (as of 6/19/2018) have a moderate to high risk for scab (Figure 1). The forecast for the next three days also shows moderate to high FHB risk these areas. Wheat in these areas that is at between heading and flowering growth stages should be protected from FHB by applying a triazole fungicide.
Fusarium head blight is caused by a fungus, Fusarium graminearum. The pathogen survives on wheat stubble as well as corn stalks and other small grains. Infection is promoted by high humidity and warm temperatures around the time when wheat is flowering. Not only does FHB lead to reduced yields but it also reduces grain quality. Infected grains contain mycotoxins mainly deoxynivalenol (DON) which is poisonous to humans and animals if contaminated grains/grain products are consumed. Grain with more than 2ppm can be docked for price or rejected at the grain elevator.
The risk for scab decreases over time once wheat is done flowering. The best timing for a fungicide is at flowering (when 50% of the plants are showing initial flowers) and recommended fungicide class is the triazole fungicides. View a list of fungicides effective against scab for more information. Growers are encouraged to keep changing on the scab prediction tool and at SDSU Small Grains Disease Forecasting Tool to determine the likelihood for scab and foliar diseases to develop and plan a fungicide accordingly.