Figure 1. Severe stripe rust in a localized area in a wheat field in Dawes County in the northern Panhandle on June 2.

Figure 2. Closeup showing entire leaves yellowed and covered with stripe rust pustules in a wheat field in Dawes County in the northern Panhandle on June 2.

June 4, 2010

A tour of wheat fields on June 2 and June 3 found stripe rust in the northern Panhandle of Nebraska. Some fields had none whereas others had trace levels. One field in Dawes County had severe levels (Figure 1) in localized areas in the field. Some leaves were entirely yellow and covered with stripe rust pustules (Figure 2).

Other diseases found in the northern Panhandle were tan spot and Septoria tritici blotch. Continue scouting fields for stripe rust and make a decision to spray based on criteria outlined in the May 19 CropWatch article. Fungicides that control stripe rust have very good to excellent efficacy on tan spot and Septoria tritici blotch. Observe pre-harvest intervals for fungicide applications. (See Table of Fungicide Efficacy for wheat.)

A few fields appeared conspicuously yellow (Figure 3) in Box Butte County. Although there was some barley yellow dwarf (which causes yellowing of flag leaves) in these fields, the major cause of the yellowing was a recent hailstorm that caused significant injury. Most of the flag leaves that appeared yellow were injured on the sheath or on the leaf blade (Figure 4). In those fields in which the flag leaf had not emerged when the hailstorm came through, it (the flag leaf) was spared and the fields look a lot better. Incidence of head trapping (Figure 4) was higher than normally observed and this may be due to frost or hail damage or both.

Further east in Holt County, there were trace levels of Fusarium head blight or scab (Figure 5) in an irrigated field. As of June 4, the Fusarium head blight risk assessment tool showed a low risk for Fusarium head blight throughout the entire state. Many fields in south central and southeast Nebraska should be past the flowering stage when the risk of scab is greatest.

Insect pests observed in surveyed fields included trace levels of the wheat stem maggot, aphids, and the wheat stem sawfly. At the levels observed, treatment is not warranted.

Stephen Wegulo, Extension Plant Pathologist, Lincoln
Gary Hein, Professor of Entomology, Lincoln