Powdery Mildew & Tan Spot
Winter wheat fields scouted this week showed powdery mildew and tan spot increasing in severity (Fig. 1 and 2). Severe powdery mildew and tan spot early in the season can lead to reduced tillering and plant vigor. Rainfall and cooler temperatures last week favored development of both diseases.
Fig. 1. Severe powdery mildew developing in the lower canopy. Notice the old foliage which the source of inoculum.
Fig. 2. Lower wheat leaves with tan spot symptoms.
Stripe Rust
Another disease observed during scouting this week was stripe rust (Fig. 3). This rust was found at low incidence and severity on a winter wheat field in Brookings County. The pustules were developing on newer leaves indicating that there is stripe rust inoculum available in the area which could be from overwintered inoculum or blowing in from southern states. Stripe rust develops under cooler conditions and when there is at least 8 hours of leaf wetness.
Fig. 3. (Above) Stripe rust pustules on winter wheat in Brookings County.
What can be done now for developing winter wheat diseases?
The weather forecast for the next 1-2 weeks indicates limited chances of rain with warmer temperatures on average. These conditions may check the development of some of these diseases. With some of the winter wheat at jointing, scouting should continue until flag leaf emergence, where a fungicide can be applied. Research indicates that fungicide applied at flag leaf emergence is the most likely to provide profitable yield than at tillering. The threshold for applying fungicide at flag leaf emergence is 2-3 fungal lesions on the leaf below flag leaf.
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