Wheat Disease Update: Risk of Scab Increases with Rains - UNL CropWatch, May 4, 2012

Wheat Disease Update: Risk of Scab Increases with Rains - UNL CropWatch, May 4, 2012

Field of healthy wheat in western Nebraska Healthy head of wheat
Figure 1. While most western Nebraska fields surveyed this week looked healthy, on closer examination, disease symptoms were identified.  (Photos by Stephen Wegulo, unless otherwise indicated.) Figure 2. Most of the fields surveyed were at full heading or flowering.

Stripe rust in wheat

Figure 3. Stripe rust in wheat in western Nebraska

Barley yellow dwarf in wheat

Figure 4. Barley yellow dwarf disease in wheat in Gage County (Photo by Paul Hay)

Wheat streak mosaic in wheat

Figure 5. Wheat streak mosaic virus in wheat in Gage County (Photo by Paul Hay)

Loose smut

Figure 6. Loose smut in western Nebraska field

A May 3 survey of wheat fields in south central and southwest Nebraska confirmed stripe rust in Kearney, Phelps, Furnas, Red Willow, Hitchcock, Chase, Perkins, Keith, and Garden counties. (Note: On May 7 stripe rust was also confirmed in Morrill and Cheyenne counties.)

Most fields looked healthy (Figure 1) and were at the full heading or flowering (Figure 2) growth stage, with a few fields still in the boot stage. Close examination underneath the canopy revealed various diseases. Incidence and severity of stripe rust were generally low with several hot spots within a field showing high severity (Figure 3). Fields farther west had mostly trace amounts of stripe rust just starting to develop.

Symptoms of barley yellow dwarf virus (BYDV, Figure 4) were seen in all fields surveyed at varying degrees of incidence with some fields more severely affected than others. Other virus diseases, notably wheat streak mosaic virus (WSMV), were consistently observed in most fields surveyed. Back east, Extension Educator Paul Hay reported seeing a field in Gage County that had a high incidence of BYDV (Figure 4) and severe symptoms of WSMV (Figure 5). 

Loose smut (Figure 6) was observed in a few fields at trace to low levels of incidence. Other diseases observed were powdery mildew, Septoria leaf blotch, and tan spot.

Risk of Fusarium Head Blight in Wheat

Recent localized heavy rains (May 2 and May 3) in south central and southeast Nebraska are likely to increase the risk of Fusarium head blight (scab). Wheat in this region of the state is fully headed or flowering and therefore at high risk for scab infections.

Management of Fungal Diseases in Wheat

If wheat is fully headed or starting to flower and stripe rust and other foliar fungal diseases are present in the field, apply a fungicide that can control both foliar diseases and scab if the risk of scab exists based on weather conditions (recent or forecast rainfall). The fungicide table developed by the multistate committee NCERA-184 provides a list of fungicides, their efficacies on various fungal diseases of wheat, and pre-harvest restrictions. Care should be taken to observe pre-harvest restrictions when applying a fungicide to wheat.

Management of Virus Diseases in Wheat

Nothing can be done to control virus diseases during the current growing season. See the April 27 CropWatch article on wheat disease for management recommendations for virus diseases.

Stephen Wegulo
Extension Plant Pathologist