Wheat Survey Reveals Low Disease and Insect Levels
|Figure 1. Loose smut. All photos by Stephen Wegulo||Figure 2. Leaf rust|
|Figure 3. (left) Tan spot|
June 12, 2009
|Figure 4. Tan spot on lower leaves of wheat planted into wheat stubble at the High Plains Ag Lab near Sidney|
|Figure 5. Severe wheat streak mosaic in a field at the High Plains Ag Lab near Sidney|
|Figure 7. Fusarium head blight was observed on June 9 in this grower's field in Morrill County.|
On June 8-9 faculty, staff, and graduate students from the University of Nebraska-Lincoln and the University of Wyoming conducted a wheat disease survey of the southern and central Nebraska Panhandle. Wheat growth stage ranged from full heading to just past flowering.
There was little disease in all growers' fields toured in the southern Panhandle on June 8. Those observed were loose smut (Figure 1) at about 1% incidence, leaf rust (Figure 2) at trace levels, and tan spot (Figure 3) at trace levels.
At the UNL High Plains Ag Lab near Sidney in a field in which wheat was drilled into wheat stubble, tan spot severity on lower leaves averaged about 30% and incidence was 100% in the areas of the field scouted (Figure 4). This field also had severe wheat streak mosaic (Figure 5) at the northwest corner. Volunteer wheat was actively growing last fall after wheat planting in an adjacent sunflower field north and northwest of this wheat field.
On June 9, the survey focused on wheat fields in the central Panhandle in Scotts Bluff and Morrill counties. Trace levels of stripe rust (Figure 6), leaf rust, and tan spot were found. In the one irrigated field in which stripe rust was found, the disease was spotty, but affected plants had pustules on about one-third of the leaves including the flag leaf. Average severity of stripe rust on affected plants was about 2%.
There was a low level (about 0.5% incidence) of Fusarium head blight (scab) in one field in Scotts Bluff County. In another field in Morrill County, scab was just starting with an incidence of 35% to 40% (Figure 7). About 1% of wheat heads were 30% to 70% bleached (Figure 8) and the rest had a spikelet or two bleached. This particular field is expected to have a significant level of scab.
Frequent rainfall in this area from about two weeks before flowering increased the risk of scab, which is "unheard of" in the Panhandle. The field is next to the Platte River. Corn stubble was observed on the soil surface, indicating that the wheat was planted after corn in this field.
Russian wheat aphids (Figure 9) were commonly seen in wheat fields but no economic infestations were observed. Other aphids, primarily greenbugs (Figure 10), were also seen but again not in significant levels. Few other insect problems (Figure 11) were noted except for the presence in some areas of slight feeding (Figure 12) from black grass bug (Figures 13). This feeding was more apparent next to crested wheatgrass borders and in no-till fields where it appeared that volunteer wheat was not being well controlled.
University of Nebraska-Lincoln
Stephen Wegulo, Extension Plant Pathologist
Gary Hein, Director, Doctor of Plant Health Program
Robert Harveson, Extension Plant Pathologist
Drew Lyon, Dryland Crops Specialist William Booker, Extension Educator
University of Wyoming
William Stump, Research Scientist
Jack Cecil, Research Scientist
Jeff Edwards, Extension Educator
Tsering Youdon, Graduate Student
Xiao Yang, Graduate Student
|(Left) Figure 8. A wheat head with about 70% bleaching from Fusarium head blight in a grower's field in Morrill County (Right) Figure 9. Russian wheat aphids|
|(Left) Figure 10. Green bugs. (Right) Figure 11. The wheat stem sawfly was among the insect pests observed during the wheat disease survey|
|(Left) Figure 12. Damage caused by black grass bug feeding. (Right) Figure 13. Black grass bug|