Wheat disease surveys were conducted May 12 to May 21 in the wheat-growing regions of Nebraska. Irrigated fields (Figure 1) looked healthy with normal growth and a lush green canopy. In dryland fields, the soil was very dry (Figure 2) and wheat was stunted, averaging a foot tall (Figure 3). Growth stage ranged from flag leaf emerged in the northern Panhandle to flowering or past flowering in the southeast.

In the southwest, leaf yellowing resembling barley yellow dwarf was observed in some fields (Figures 4 and 5), but it was determined that the yellowing was due to freeze injury that occurred in mid- and late April. In a previous CropWatch article, leaf yellowing in a field at the West Central Research, Extension and Education Center (WCREEC) near North Platte was attributed to barley yellow dwarf. However, a second visit to the same field determined that most of the yellowing was due to freeze injury.

An isolated case of severe wheat streak mosaic disease complex (Figure 6) was observed in a grower’s field in Colfax County. This field is adjacent to a field that had volunteer wheat that was not controlled before planting wheat last fall.

From May 18-21, leaf rust and stripe rust (Figure 7) and fungal leaf spot diseases (Figure 8) were observed in research plots at Havelock Research Farm in Lincoln, Lancaster County. Moderate to high levels of barley yellow dwarf were observed in scattered areas in research plots at Havelock Research Farm (Figure 9).

Management

Nothing can be done to alleviate damage caused by freeze injury and virus diseases. The most effective management strategy for the wheat streak mosaic disease complex is to control volunteer wheat before planting wheat in the fall. The volunteer must be completely dead at least two weeks before planting.

Barley yellow dwarf cannot be controlled once it occurs. Insecticide sprays to control the aphid vectors of the virus can reduce disease incidence and spread, but this strategy is effective only if the aphid species present in the field are known to be efficient vectors of the virus. Insecticide seed treatments can reduce spread of the virus by killing the aphid vectors.

Foliar fungal diseases (rusts and leaf spots) can be controlled by applying a fungicide to protect the flag leaf. Currently, wheat in many fields in eastern Nebraska is past the growth stage (early flowering) at which a fungicide can be applied.

Fusarium head blight (FHB) has not been observed and the Fusarium risk tool is showing a low risk in Nebraska. However, the risk has been elevated by recent heavy rainfall in localized areas.  FHB can be suppressed by applying a fungicide at early flowering.