Stripe Rust Update And Reminder Of Fungicide Timing

 

Stripe rust incidence and severity have been increasing throughout several states in the upper Great Plains. Specifically, the Panhandle region of Nebraska has reported widespread and severe levels of stripe rust. The elevated levels of stripe rust in these areas may increase stripe rust risk in the North Dakota wheat crop if southerly winds continue to carry spores into ND, cool nighttime temperatures (below 70°F) occur and adequate moisture is present (i.e.: dews, rain or irrigation). Currently, stripe rust has been detected in winter wheat in the southeast, northcentral, southwestern and northeastern portions of ND (Figure 1). The hot weather projected over the next couple days will slow down stripe rust, but most likely will not stop it. Make sure to scout small grain fields in the next couple weeks for the onset of stripe rust.

 

If you detect stripe rust in a field, the decision to apply a fungicide will come into question. Research conducted at NDSU has indicated the best time to apply a fungicide in spring wheat for stripe rust management is at flag leaf. Similar studies conducted in other states on winter wheat have also indicated the importance of a flag leaf application. Winter wheat in North Dakota is heading or flowering and some areas will be applying (or have applied) a fungicide for Fusarium head blight (scab). The fungicide chemistries recommended for scab will also manage stripe rust. However, it is important to remember that fungicides work best when used preventively.

 

For example, if a fungicide is applied at early-flowering for scab and stripe rust pustules appear on the flag leaf a few days later, this doesn’t mean the fungicide application did not work. Rather, part of the reasoning could be attributed to fungicide timing and the biology of the pathogen. The amount of time for the stripe rust pathogen to initiate an infection site to pustule development is 10-14 days. Therefore, the fungicide application likely missed the opportune time to disrupt the development of the stripe rust fungus.