Dr. Kirk Broders, Plant Pathologist, Department of Bioagricultural Sciences and Pest Management and RF Meyer Area Extension Agronomist, Colorado State University
Wheat field observations have been taking place throughout northeast Colorado this spring from various on-farm testing sites. We’ve been looking for wheat pest production issues and have found various pests. Evidence of Brown Wheat Mite was found at numerous locations. However, this dry weather wheat insect pest was controlled by the late March precipitation received and is no longer an issue in the current production year. One field had Russian Wheat Aphid, but it was found below economic treatment levels. Cutworm damage was not observed at locations inspected.
The wheat crop in Colorado is on average between Feekes growth stage 6-8 (jointing to second node). Much of the state has received some moisture and so the crop continues to look good, but additional moisture in some areas will be needed. The limited moisture has had a positive effect in that very few foliar fungal diseases have been reported to date in Colorado. However, stripe rust continues to be reported in additional counties in central Kansas and western Nebraska. With cool wet weather predicted for next week, it is possible that Colorado will begin to see the first signs of stripe rust in the eastern most counties. If stripe rust arrives, and there is a need for fungicide applications, on recommendation is for growers to wait until the flag leaf is fully or nearly fully emerged. Protecting the flag leaf is critical. Flag leaf emergence is a critical growth stage and it is important to protect the flag leaf from rust infection. This will only be necessary if stripe rust poses a threat to yield.
The diseases observed most frequently throughout eastern Colorado, were viral diseases. So far we have identified Wheat Streak Mosaic Virus (WSMV), Triticum mosaic (TriMV), High Plains virus (HPV) and Barley Yellow Dwarf Virus (BYDV) in several fields. Of the 15 fields surveyed to date, 11 were positive WSMV, 7 were positive for TriMV, 5 were positive for HPV and 4 were positive for BYDV. While WSMV is the most frequently observed viral pathogen, 11 of the 15 fields tested had at least 2 viruses present (Figure 1 & 2). This included fields from Adams, Arapahoe, Lincoln, Washington, Kit Carson, Yuma, Logan and Morgan counties. As the wheat continues to mature the expression of virus symptoms continues to become more evident. Many of these viral infections likely occurred last fall after the wheat germinated, and then we continued to have very mild temperatures until late November. However, we are seeing the first signs of secondary infection, where wheat curl mites became active this spring and moved to previously healthy fields and infected wheat plants in these fields with virus pathogens. Once wheat is infected with any of these viruses there is no chemical treatment that can eliminate the pathogen. In fields where virus diseases are present it will be important to ensure volunteer wheat and weeds are managed, as these represent “green bridges” for the wheat curl mite, which vectors WSMV, TriMV and HPV, to survive from one wheat crop to the next. Testing wheat plants is an option to determine if plants are infected with virus or also to identify which virus is present.
Submitted to Barn Media by:
CSU Golden Plains Area Extension, Ron Meyer, Area Extension Agent (Agronomy),
(719) 346-5571 x 305, firstname.lastname@example.org
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