UNL CropWatch May 21, 2010: Wheat Update: Responding to Stripe Rust
|Figure 1. A wheat field in Nuckolls County on May 18. It was planted with three varieties differing in resistance to stripe rust. The variety in the center is highly susceptible whereas the other two varieties have some level of resistance.|
May 21, 2010
Stripe rust is widespread in eastern Nebraska and has been reported in neighboring wheat producing states of Kansas, Colorado, and South Dakota. The latest report from Colorado includes multiple sightings in the southeastern part of the state.
Figure 2. Severe stripe rust in a wheat field in Nuckolls County on May 18.
Assess and Treat
Scout wheat fields now for stripe rust and plan for a fungicide treatment where necessary.
Some of the fields we scouted this week have had little rust while neighboring fields had a lot. Some fields had hot spots of severe rust while the rest of the field had none.
Be prepared to apply a fungicide to protect the flag leaf. A fungicide application will not be effective if stripe rust has already progressed to severe levels (Figure 2). If severe levels are present over most or all of the field, assess the yield potential and make a decision about the viability of planting an alternative, spring-sown crop.
The optimum timing for a fungicide application is when the disease is just beginning (trace levels of severity) or before disease symptoms are observed. If disease severity is low to moderate and the top three leaves are still green, some yield loss will be prevented by a fungicide application. Yield loss also will be prevented by a fungicide application if only small areas of a field are affected by severe stripe rust. In this case the fungicide will protect the wheat crop that is not yet affected within the field.
Planting Resistant Varieties
Resistance can make a difference in the amount of damage caused by stripe rust and other wheat diseases (Figure 1). Although it is too late this growing season to choose varieties that have resistance to stripe rust, consider planting resistant varieties (Table 1) this fall.
When choosing varieties, consider resistance not just to stripe rust but to other diseases as well. Choosing a variety resistant to rust, as indicated in Table 1, won’t guarantee complete protection, since a new race of the pathogen can overcome the existing resistance, but it can help protect the crop. That’s why we still recommend a fungicide application if stripe rust is present in a variety listed as resistant.
Extension Plant Pathologist
|Table 1. Wheat varieties with resistance to stripe rust.|