Damon Smith, Extension Field Crops Pathologist, Department of Plant Pathology, University of Wisconsin-Madison
This week I scouted winter wheat in variety trials in Janesville and Arlington Wisconsin on June 11, 2013. Wheat is in full flower or completed flowering in the Janesville location while wheat just began flowering this week at the Arlington location.
In Janesville, stripe rust has become abundant (Fig. 1). A week ago when I scouted this location I had to hunt quite hard to find stripe rust. This week, there are plots with stripe rust on 25%-50% of the leaves and severity in the 20%-50% range or higher (Fig. 2). In plots where stripe rust is high, flag leaves are being affected. This will result in yield reductions in some of these plots. It is too late to apply a fungicide at this stage in this location. However, as the wheat season progresses north of this location, growers and consultants should scout frequently and be aware of the danger for stripe rust. Temperatures in the long-term forecast show moderate temperatures and decent chances for moisture, which are conducive for stripe rust epidemics.
Also at the Janesville location I found several wheat heads with symptoms and signs of Fusarium head blight or scab (Fig. 3). Wheat in this location is past the window of opportunity to apply a fungicide. However, wheat at the Arlington location, and north, is flowering now or beginning to flower and conditions in parts of the state heave been conducive for Fusarium head blight (FHB). As of this writing the Fusarium head blight risk assessment tool (http://www.wheatscab.psu.edu) is showing a moderate to high risk for FHB on flowering winter wheat in the east central portions of Wisconsin. If wheat is flowering, and in an area of risk, then a fungicide application might be considered. DO NOT use fungicides that contain strobilurin fungicides (FRAC 11) for control of head scab, as increased risk for DON (deoxynivalenol) can result. A triazole fungicide such as Prosaro, Caramba, Proline, or similar product applied during the onset of flowering to 3-5 days after will be most effective. To learn more about Fusarium head blight and how to manage the disease, visit http://fyi.uwex.edu/fieldcroppathology/.
At the Arlington location, leaf blotch is the primary disease. Find a fact sheet about leaf blotch at http://fyi.uwex.edu/fieldcroppathology/files/2013/04/Leaf-Blotch-Diseases-of-Wheat-1.pdf. I suspect that leaf blotch spread in these plots will slow as frequent rainy conditions are not as prevalent and temperatures are warming. Higher temperatures are not as conducive for the pathogens that cause leaf blotch.
Shawn Conley and his field crew observed powdery mildew on winter wheat in a variety trial in Chilton, WI this week. This is the first find of powdery mildew in the state in 2013. I provided a detailed write-up about powdery mildew in the May 30 Crop Manager publication. This can be found at https://ipcm.wisc.edu/blog/2013/05/wisconsin-winter-wheat-disease-update-may-15-2013-2/. Powdery mildew has been basically non-existent in other locations around the state that have been scouted. As weather becomes more humid, I would expect the incidence and severity of powdery mildew to increase.