Wheat Disease Update: Week Of May 30

 

Several winter wheat fields were scouted last week and the main diseases observed were stripe rust and wheat streak mosaic. Powdery mildew was also observed in a few fields but at low severity.

 

Stripe rust has now been confirmed in 5 counties including Brookings, Hand, Tripp, Union, and Stanley. One field in Stanley County was found to have a moderate level of stripe rust (Figure 1). For winter wheat that is at heading and has stripe rust, a fungicide may be delayed for a few days and a triazole may be applied instead at flowering to manage both the stripe rust infection and prevent Fusarium head blight from developing in areas where risk for scab is predicted to be moderate to high (Figure 3 and Figure 4). For areas where scab is predicted to be low but stripe rust is observed on leaves, a fungicide approved after boot growth state may be applied to manage stripe rust and other fungal pathogens.

 

 

Wheat streak mosaic was most frequently found in Central and West River counties. Some of the infected plants observed under the stereo microscope were found with a lot of wheat curl mites, the vectors of wheat streak mosaic (Figure 2A and Figure 2B). Wheat heads developing from infected plants were also infested with WCM (Figure 2A and Figure 2B). These mites will be the source of wheat streak mosaic virus for the following wheat crop. As the wheat plants mature and wheat grain starts to ripen, WCMs position themselves to be picked up and carried by the wind. WCMs are then deposited on nearby host crops such as corn, spring wheat or grass pasture. Some WCMs will fall to the ground and can survive on volunteer wheat and grassy weeds within the field. Future wheat streak mosaic management should include destroying volunteer wheat at least two weeks before planting, delaying time of planting, and selecting a tolerant wheat cultivar.

 

 

 

Moderate to high risk for Eastern-most counties

Most of the winter wheat is now at heading. In a few days these fields will be at flowering, a stage when Fusarium head blight (FHB) starts to develop. The FHB risk prediction tools show the Eastern-most counties and a few southern most areas to have moderate to high risk for FHB (Figure 3 and Figure 4), while the west river and central counties have low risk of FHB. Growers should continue to monitor the FHB risk prediction until wheat has completed flowering. For areas with moderate to high FHB risk, a triazole fungicide (Prosaro and Caramba are the most effective against FHB) should be applied at flowering to protect wheat against FHB.