This article is by Jeanne Falk Jones:
Q: We have been getting lots of questions on wheat in the last couple weeks. They generally center on stripe rust and wheat streak mosaic. These are two different diseases- stripe rust is a fungal disease, while wheat streak is a virus.
A: Stripe rust is a fungus that blows up on the wind currents from Texas. We are currently finding stripe rust in the wheat fields throughout the area. It is being found on one to three leaves below the flag leaf, but not the flag leaf. About a week ago, stripe rust pustules were more difficult to find, but are now being found relatively easy. The stripe rust pustules are raised, orange colored, blister-like lesions on the leaf surface. If you run your thumb over the leaf surface, many times you can feel the pustules and your thumb will be orange from the rust spores. Many times the stripe rust will occur in a longitudinal ‘striped’ appearance following the veins on the leaf. As I am writing this article on Tuesday afternoon, it is cool and foggy with mist/rain. These are the conditions that stripe rust loves. It really likes cool temperatures- with overnight lows from 40 to 60 degrees- and it takes moisture for rust spore to infect the leaf. The forecast is for these types of conditions to be around for the rest of the week. How do you make a decision on treating with a fungicide? This is really a tough question with the wide variety of potential wheat fields across the area. Research done at K-State suggests that the yield response for stripe rust can be more than 20% when conditions favor disease development on susceptible varieties. Fungicides applications are most likely to result in a 10% yield response greater if the stripe rust or other disease are established on the upper leaves prior to flowering. If the disease is only present in the low to mid-canopy at these growth stages, a fungicide application will only result in the desired yield response about 50-60% of the time. This is very dependent on the weather forecast for the next 10-14 days. Additional information is available on stripe rust in a couple K-State publications -Evaluating the Need for Foliar Fungicides and Foliar Fungicide Efficiency Ratings For Wheat Disease Management. For wheat streak mosaic, it is showing up in fields this spring, especially after we caught some rain. The wheat curl mite is a microscopic insect that moves the wheat stroke mosaic virus from the summer host into the newly emerged wheat crop. We seem to be seeing more of it than normal spring. That is likely due to the long, warm, fall like we had. It allowed the curl mites to be active for longer than normal and infect more plants with the wheat streak mosaic virus. In addition, as the wheat hit its growth spurt this spring after the rain, the virus replicated quite quickly in the plant and the symptoms showed up quickly and fairly severe. For wheat streak mosaic, there are really no good control measures after the symptoms are showing up in your wheat. This is a virus, not a fungus, so a fungicide will not help. The best control measure is really prevention- and that included controlling volunteer wheat prior to drilling. The wheat streak mosaic virus shows up as mottled (intermixed green and yellow) patches on the leaf and can have a streaked appearance. This virus is like the flu for us. There really isn’t anything that can be done to stop the virus, but minimizing stress (drought, nutrients) on the plant can help the plant fight back. The only difference is that we can fight off the flu, whereas wheat cannot fight off the mosaic streak. In addition, most of the commonly planted varieties of wheat are susceptible to this disease. If you have additional questions, please contact JoEllyn Aragbright at the Rawlins County Extension Office or Jeanne Falk Jones, K-State agronomist at the K-State Experiment Station in Colby.
