From left: Figure 1. Tan spot. Figure 2. Septoria tritici blotch. Figure 3. Powdery mildew.

Due to fairly dry weather, wheat fields in Nebraska are largely free of foliar fungal diseases. Irrigated fields and those in which wheat was drilled into wheat stubble should be watched closely for development of residue borne diseases such as tan spot (Figure 1) and Septoria tritici blotch (Figure 2).

Figure 4: Field symptoms of wheat soilborne mosaic virus. (Photo by Paul Hay)

Figure 5: Field symptoms of wheat streak mosaic virus.

Due to dry conditions in southern states, the amount of rust inoculum (spores) blowing north this year is small, hence the risk for development of rust diseases is low.  As of May 3, there was one report of leaf rust in Oklahoma in a no-till irrigated field.  As of April 28, no rust diseases had been observed in Kansas and tan spot, Septoria, and powdery mildew were absent in most fields due to dry weather.Growers are encouraged to scout wheat fields for early detection of diseases, especially those that overwinter in Nebraska such as tan spot, Septoria, and powdery mildew (Figure 3).  If conditions (rain, irrigation) become favorable for development of foliar fungal diseases, consider applying a fungicide to protect the flag leaf.

As of now, the only virus disease that has been observed in some wheat fields is wheat soilborne mosaic virus.  This disease causes yellowing in patches or large areas (Figure 4) in the field early in the growing season and is favored by moisture and cool temperatures in the fall and spring.  As temperatures warm, symptoms of soilborne mosaic usually fade and those of wheat streak mosaic virus (Figure 5) become prominent.  Virus diseases cannot be controlled once they occur.