The wheat crop in Colorado is on average between Feekes growth stage 8-10 (flag leaf to boot stage). As I mentioned in my last message, during the last two weeks the weather has been conducive for the development of stripe rust. That combined with ample inoculum present in Kansas and Oklahoma it was a matter of time before symptoms began showing up in eastern Colorado. In the last week, Ron Meyer from CSU extension has observed stripe rust in Cheyenne, Kiowa, Kit Carson and Yuma counties in eastern Colorado. Stripe rust was also confirmed in western Colorado near Loma in Mesa county. Stripe rust was observed in the upper canopy, but has not made it to the flag leaf. Disease incidence is very low in these fields, but given the strong wind and rain in the forecast for the coming week, spores will likely begin moving throughout the region and we may see an increase in stripe rust infection over the next couple weeks. I would strongly encourage growers to scout fields over the course of the next couple weeks, prior to making a decision on fungicide application. If stripe rust levels remain low and don’t reach the flag leaf, it may not be necessary to apply fungicides. However, in the far eastern part of the state, the forecasted rain and cooler temperatures may lead to an increase in disease, prompting a need for fungicide application.
I have continued to work with the CSU diagnostic lab to monitor the virus situation in the state. 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 28 samples received to date, 23 were positive for WSMV, 16 were positive for TriMV, 7 were positive for HPV and 4 were positive for BYDV. While WSMV is the most frequently observed viral pathogen, 21 of 28 samples tested had at lease 2 viruses present. The incidence of TriMV is much higher than in previous years, and it is still unclear why we are seeing this increase in TriMV in Colorado. Survey results included samples from Adams, Arapahoe, Baca, Cheyenne, Kit Carson, Kiowa, Lincoln, Logan, Morgan, Otero, Prowers, Phillips, Sedgwick, Washington and Yuma counties. As you can see by the list of counties, viral diseases are widespread throughout eastern Colorado. In order to understand the distribution of virus infection, the crop pathology lab at CSU will continue to cover the cost of virus diagnosis completed by the CSU diagnostic lab. If you believe you are observing virus symptoms in any of your fields, I strongly encourage you to send samples to the CSU Plant Disease Diagnostic Clinic.