University of Nebraska-Lincoln Extension, Institute of Agriculture and Natural Resources

May 19, 2006

Figure 1. Leaf rust pustules on leaves of Jagalene from research plots at the South Central Agricultural Laboratory near Clay Center (May 19).

Wheat disease update

Leaf rust found in south central Nebraska

On Friday, May 19, we saw leaf rust for the first time this year in Nebraska winter wheat. Pustules were just beginning to appear (Figure 1), mostly on lower leaves, in research plots at the South Central Agricultural Laboratory near Clay Center. The rust was seen on both Jagalene and Millennium. Severity was very low, on average less than one pustule per leaf on infected plants. Incidence (percentage of infected plants) was very low as well, estimated at less than 0.1%. Given the current dry conditions and the fact that most of the wheat crop is already at or past the boot stage, the impact of leaf rust on yield is likely to be minimal this year.

According to the May 16 Cereal Rust Bulletin from the Cereal Disease Lab in St. Paul, MN., up to 10% leaf rust severities were noted in mid May on flag and flag -1 leaves in southeast and south central Kansas. Plots of susceptible cultivars had up to 60% leaf rust severities in south central Kansas.

Currently the major disease of wheat in south central and eastern Nebraska is powdery mildew. Infections in some fields is heavy on leaves (Figure 2) as well as on stems (Figure 3). In a field near Lincoln, infections in some spots are so heavy that the wheat is stunted (Figure 4). Symptoms of soilborne mosaic virus are fading whereas symptoms of wheat streak mosaic virus are more conspicuous now compared to mid to late April. Wheat streak mosaic has been observed in fields from the Panhandle to Nebraska City. On May 5, a heavy tan spot infection was observed in a field at the High Plains Ag Lab near Sidney.

Stephen Wegulo
Extension Plant Pathologist, Lincoln
Julie Breathnach
Research Technologist, Lincoln

Figure 2. Powdery mildew on wheat leaves in a field near Lincoln (May 14). Figure 3. Powdery mildew on wheat stems in a field near Lincoln (May 14). Figure 4. A spot in a field near Lincoln showing stunting of wheat due to heavy colonization of leaves and stems by powdery mildew (May 14). Examination of the leaves and stems revealed heavy powdery mildew infection.

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