Dr. Kirk Broders, Plant Pathologist
Department of Bioagricultural Sciences and Pest Management
Colorado State University
Most of the eastern part of Colorado has received much needed rainfall in the last month. However, with this moisture comes the increased risk of foliar fungal pathogens. Certainly the cool and wet condition in the northeast part of Colorado have been ideal for stripe rust infection. However, I believe that due to the limited amount of inoculum in neighboring states, such as Kansas and Oklahoma, there have been no significant stripe rust infections in the state. A recent report by Dr. Erick DeWolf of Kansas State University summarized the current status of stripe rust in Kansas as: “Stripe rust was detected several weeks ago in the SE corner of the state and the disease has moved to the flag leaves. There was also a trace amount of stripe rust found in an irrigated field in central Kansas (Edwards County). Most of the crop in western Kansas has been under considerable drought stress this year and I suspect the dry conditions continue to hold the diseases in check.”
I believe the lack of inoculum in western Kansas has prevented spores from reaching northeastern Colorado and the front range where weather conditions have been particularly ideal. I did receive one report of stripe rust from the Stratton area, but have not receive a sample to provide an absolute positive identification. Ron Meyer, CSU Extension Professional, has visit a number of wheat fields in eastern Colorado and has not seen stripe rust in this area. I therefore, think the impact of stripe rust on yield will be minimal this year. I also do not think fungicide applications for stripe rust protection are warranted at this time.
Other diseases that have been observed, include tan spot, wheat streak mosaic virus and Cephalosporium stripe. Tan spot is cause by a fungal pathogen that survives in the wheat residue. In years where there is significant precipitation and leaf moisture, the spores of the fungus will germinate and infect leaves in the lower canopy first, and if the wet weather persists, it can move to the upper canopy. All infections observed to date in Colorado remain in the lower canopy, and with the current forecast I do not expect the disease to spread to the upper canopy.
Wheat streak mosaic virus is prevalent again this year, but it does not seem to be as severe during 2017. We are still trying to gauge the severity statewide, so if you believe you have samples with WSMV, or other virus symptoms, I would encourage you to send those in to the CSU diagnostic lab.
Cephalosporium stripe is rare in the state but has been observed in a couple fields in the Burlington area. It is possible to misdiagnose this disease for stripe rust, so if you have any doubts, send a sample to the diagnostic lab, or send me a photo. I can then either provide a diagnosis, or direct you to send the sample in.