(Clockwise from left) Figure 1. Severe stripe rust in a state variety trial in Lincoln County on June 18. Figure 2. A wheat flag leaf showing Septoria tritici blotch, leaf rust, and stripe rust in a state variety trial planted in a grower's field in Chase County on June 14. Although severity of the three diseases on this leaf is low, many fields in the state, especially those that were not sprayed with fungicide, have had high severity. Figure 3. Stem rust on triticale in research plots at the Agricultural Research and Development Center (ARDC) near Mead on June 23.

June 25, 2010

Prolonged wet conditions during the 2010 growing season favored the development of many wheat diseases. The most widespread diseases continue to be stripe rust (Figure 1) and Septoria tritici blotch (Figure 2). Leaf rust (Figure 2) also developed later in the growing season.

Stem rust has been observed on triticale (Figure 3) and a couple susceptible wheat lines. Fusarium head blight (scab, Figure 4) developed to moderate levels in isolated fields; however, incidence and severity have been low in most wheat growing areas in Nebraska.

Other diseases observed this season are Stagonospora glume blotch (Figure 5), sooty mold (Figure 6), loose smut, tan spot, soilborne mosaic virus, and isolated cases of wheat streak mosaic virus. At least two samples submitted to the UNL Plant and Pest Diagnostic Clinic tested positive for black chaff. Root diseases including common root rot also have been observed.

To date there have been no reports of common bunt (stinking smut); however, producers should be on the lookout for common bunted grain.

Harvest and Post-Harvest Precautions

Fungal diseases affecting the foliage usually result in some yield loss, but seldom affect grain quality except for low test weight. Diseases affecting the wheat head also can affect the grain, causing it to be scabby, black pointed, or infected without showing symptoms.

If you have scab in your field:

• Increase the fan speed on the combine during harvest to blow out scabby grain.
• Harvest and store grain from severely affected parts of the field separately from grain from other areas of the field.
• Test grain for vomitoxin before feeding it to livestock.
• Test straw for vomitoxin before using it as hay.
• Wear gloves and a mask when handling scabby grain.
• Do not use scabby grain as seed for the next wheat crop.
• Treat grain from scabby fields with a systemic seed treatment fungicide before using it as seed for the next wheat crop.
• Store grain at or below 12% moisture under well ventilated conditions.

If you have Stagonospora glume blotch or sooty mold in your field:

• Store grain at or below 12% moisture under well ventilated conditions.
• Treat grain with a systemic seed treatment fungicide before using it as seed for the next wheat crop.

Loose smut, common bunt, and fungal root diseases can be managed by treating grain with a systemic seed treatment fungicide before using it as seed for the next wheat crop. Due to the excessively wet conditions during the growing season, it is recommended that seed be treated with a systemic fungicide before planting in the fall.

Black chaff can be managed by avoiding the use of affected grain as seed for the next wheat crop.

Wheat streak mosaic virus and other virus diseases transmitted by the wheat curl mite, such as Triticum mosaic virus, can be managed by controlling volunteer wheat before fall planting. Soilborne mosaic virus can be managed by planting resistant varieties.

Stephen Wegulo
Extension Plant Pathologist, Lincoln
Greg Kruger
Cropping Systems Specialist, West Central Research and Extension Center
Amy Timmerman
Extension Educator, UNL Plant and Pest Diagnostic Clinic, Lincoln