COLORADO WHEAT DISEASE NEWSLETTER
Thank you to all who attended the Colorado Wheat Field Days! We certainly lucked out with the weather, and it was great to see you all again.
DISEASE WATCH AND MANAGEMENT
Stripe rust has been spotted at very low incidence and severity in Kit Carson, Adams, Arapahoe, Weld, Sedgewick, Yuma, and Washington counties (Figure 1). While the weather in Colorado has been conducive to stripe rust disease development, I anticipate that the spore levels will remain low and should not cause widespread disease.
Management and Prevention
The decision to spray should depend on the susceptibility of the wheat variety to stripe rust and the growth stage of wheat. Protecting the emerging flag leaf is most important since it is the biggest contributor to grain fill. Wheat that isn’t flowering yet may benefit from a pesticide spray if susceptible varieties are affected. However, be sure to pay attention to the permitted pre-harvest spray interval for each pesticide.
Figure 1. Very low levels of stripe rust found duringWheat Field Days.
Wheat Streak Mosaic virus/Triticum Mosaic virus
Several samples have tested positive for WSMV and TriMV. These viruses are transmitted by the wheat curl mite and typically occur together. Symptoms appear as yellow streaks and mosaic, yellow and green patterns on leaves.
Management and prevention
There is no treatment for virus-infected plants, and no miticides are effective against the vector (the wheat curl mite). Controlling volunteer wheat and planting WSMV- and mite-resistant varieties are the best control measures. However, there is no resistance against TriMV available, so controlling volunteer wheat between harvest and planting is critical.
Figure 2. Symptoms of a WSMV and TriMVco-infection.
Tan spot is appearing across much of Colorado at very low levels (Figure 3). Tan spot appears as necrotic (dead, brown) diamond-shaped spots surrounded by yellow halos or borders. It is often found along with Stagonospora leaf blotch (Figure 4).
Management and prevention
Typically, as the weather warms tan spot does not continue to be a problem
Figure 3. Tan spot symptoms on wheat.
Figure 4. Glume blotch caused by Stagonospora fungus.
Growers are strongly encouraged to regularly scout wheat fields for diseases.
The Colorado Wheat Entomology Newsletter, written by Dr. Punya Nachappa, covers insect/mite pests and management tips. The newsletters are published bi-weekly during the growing season.
- The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) Fungicide Efficacy for Control of Wheat Diseases Table
- Wheat variety database with stripe rust and virus resistance ratings from field trials.
Many thanks to Tyler Benninghoven, Dr. Esten Mason, and Dr. Ana Cristina Fulladolsa, who contributed to this report.