Wisconsin Winter Wheat Disease Update – June 5, 2013

Damon Smith, Extension Field Crops Pathologist, Department of Plant Pathology, University of Wisconsin-Madison

Winter wheat was scouted in variety trials in Janesville and Lancaster Wisconsin on June 4, 2013. Wheat is beginning to flower, or is in full flower, in these locations in Southern WI. Risk for head scab has been low to moderate in these locations over the last week or so according to the risk assessment tool. I would expect the risk to remain moderate in these locations over the next several days with good chances of rain in the forecast and a warming trend during the late week and weekend. Farmers in Southern Wisconsin should assess their head scab risk now and make a decision on when to apply fungicide to manage head scab. 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, or similar product applied during the onset of flowering to 3-5 days after will be most effective.

In the Janesville location a single flag leaf with stripe rust was identified (Fig. 1).  I would classify the level of stripe rust as “trace” currently in Southern Wisconsin.  No leaf rust has been found in Wisconsin.  Other diseases include a moderate level of Septoria/Stagnospora leaf blotch in some more susceptible varieties.  Extremely wet weather has resulted in moderate severity on lower and mid-level leaves that may spread to the flag leaf if wet weather continues. Low levels of Barley Yellow Dwarf Virus (BYDV) were also noted in some varieties.  No powdery mildew has been found during scouting trips this season.  This is very unusual in Wisconsin.  I suspect frequent rainy conditions have prevented spore attachment and/or resulted in spores bursting due to too much free moisture.

Figure 1.  Stripe rust pustules on a soft red winter wheat flag leaf.  Photo Credit: Damon Smith
Figure 1. Stripe rust pustules on a soft red winter wheat flag leaf. Photo Credit: Damon Smith