Figure 1. Leaf rust and powdery mildew pustules on leaves collected from a wheat field near Red Cloud in Webster County on May 4, 2007. (Photos by Stephen Wegulo and Duane Lienemann)

Figure 3. Septoria leaf blotch on leaves collected from a wheat field near Red Cloud in Webster County on May 4, 2007.

Figure 2. Powdery mildew in a wheat field near Red Cloud in Webster County, May 9, 2007.

Figure 4. Tan spot on wheat plants collected from a grower’s field near Alliance in Box Butte County on May 9, 2007.

May 11, 2007

Wheat Disease Update: Leaf Rust Confirmed in Nebraska

With the recent rains, we expect leaf rust incidence and severity in this field and other fields in south central and southeastern Nebraska to increase significantly over the next one to two weeks. We did not observe leaf rust in fields further north; however, we expect leaf rust to be widespread across the state by mid-June.

Powdery mildew (Figures 1 and 2) was present in every field visited during a disease survey this week in south central Nebraska. It was more severe in fields with dense canopies. In one rain-fed field planted with Jagalene, powdery mildew was very severe on the lower leaves and was visible on the flag -1 leaf. Other diseases we observed were Septoria leaf blotch (Figure 3) and tan spot. Wheat plant samples collected on May 9 from a grower’s field near Alliance in the Nebraska Panhandle showed heavy infection by tan spot (Figure 4).

The latest report from Kansas by Erick DeWolf, Kansas State University extension wheat pathologist, indicates that the predominant rust disease is leaf rust. In north central Kansas, susceptible cultivars are showing 100% incidence of leaf rust on the flag -1 leaf with 2% to 10% severity. The flag leaves are showing 1-2% severity. Stripe rust also has been reported in several north central Kansas counties, including Mitchell, Osborne, Jewell, Ellis and Republic.

If wet weather continues during the growing season, we expect to see higher levels of disease than we did last year. Fungicide sprays should be considered for high risk fields (those under irrigation and/or those planted with susceptible cultivars) and should be aimed at protecting the flag and flag -1 leaves.