By Robert M. Harveson, UNL Extension Plant Pathologist, Panhandle Research and Extension Center, and Stephen Wegulo, UNL Extension Plant Pathologist, Dept. of Plant Pathology, Lincoln
Wheat farmers in Nebraska should be prepared to scout their fields for rust diseases, which have already been reported in several states to the south and are likely to spread northward.
Wheat in Nebraska is affected by three primary rust diseases – stem, leaf, and stripe rust. All share some fundamental characteristics, including being favored by wet, humid conditions. They also normally arrive in Nebraska from the south on wind currents that move up through the Great Plains in the spring. Therefore we can use reports on the status of rust disease presence coming from Texas, Oklahoma, or Kansas to estimate when or if they will most likely appear in Nebraska.
Over the last week I have received word from Oklahoma and Kansas that both stripe rust and leaf rust have been detected. Stripe rust has additionally been found this week in northeastern Colorado. This is abnormally early for rust to occur, and we must be alert to these findings as spring approaches. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state.
We do not know if the same thing has occurred in Nebraska, but with the milder winter and heavy snow cover back in December and much of January it is also possible that the pathogens have survived in western Nebraska as well. Farmers should strongly consider this fact, particularly after new rust infections were identified last year in October in several locations in Banner County on fall-planted crops.
Current and projected weather conditions over the next several weeks are favorable for development and spread of rust diseases. It is not necessary to treat fields now with fungicides, but fields must be scouted and monitored for disease development.
If disease levels become moderate to severe, it may be necessary to make early fungicide applications at the jointing growth stage. However, if you make an early fungicide application, be aware that it will most likely be necessary to make a second application at 50 percent to 100 percent flag leaf emergence to protect the flag leaf.