Stripe Rust Being Found On Flag Leaves

 

The cool, wet weather in June provided ideal conditions for the development of great looking wheat crop. However, these same conditions also promoted the development of stripe rust (Figure 1). During the past ten days, there have been several reports of stripe rust lesions on flag leaves of spring wheat on the eastern half of the state. Several questions have been asked on how to manage this disease. I will provide some insight on some of the commonly asked questions.

 

 

 

 

 

Using data from the winter wheat belt in the southern Great Plains, strobilurin (ie: Headline, Quadris and Evito) and triazole (ie: Folicur (generics), Prosaro and Caramba) based products have very good to excellent activity on stripe rust. The more important issue is the timing of a fungicide application.  Fungicides that were applied with a herbicide will help protect the leaves available at the time of the application, but as the wheat crop matured, newer leaves (especially the flag leaf) developed and were vulnerable to subsequent infection events.

 

 

The good news is fungicides that are effective in suppression scab and DON are also effective in managing stripe rust. The bad news is these fungicides will not cure infections that have already occurred. The amount of time it takes a spore landing on a leaf and causing a pustule is approximately 14 days. Therefore, when a fungicide application was sprayed at early-flowering, it will only protect the leaf tissue that has not been colonized by the pathogen. This is a perfect example of how rust diseases can appear to have increased after a fungicide application.

 

 

This past week Dr. Maricelis Acevedo and I rated a spring wheat variety by fungicide trial conducted by Dr. Joel Ransom in southeast ND. This trial had a natural epidemic of stripe rust and differences in susceptibility were observed amongst the spring wheat varieties. We found that a large majority of the spring wheat varieties were susceptible or moderately susceptible to stripe rust (Figure 2). Future evaluations will be conducted at other sites that are known to have stripe rust in them. We expect to gather more varietal information and include it in the Hard Red Spring Wheat Variety Selection guide for next year.

 

 

 

 

Continue to scout fields for the presence of stripe rust. If you have a later developing wheat crop, a flag leaf application may be needed if the weather remains cool and wet. If your area receives consecutive days of hot temperatures (close to 90˚F) and warm nights (above 60˚F) the stripe rust pathogen will “slow down” and may go into the overwintering spore stage (Figure 3).