Wheat stem rust
A pathogen that showed up in Cache Valley this year was wheat stem rust (Puccinia graminis). This pathogen can cause up to 70% yield loss in severe cases. Even though it is called stem rust it also colonizes leaf tissues and sometimes glumes and even seed. Stem infections weaken the stem and when the seed heads mature the stem may not be able to support the weight and break.
The life cycle of wheat stem rust is both complex and simple. The complex life cycle: Stem rust produces four types of spores – basidiospores, aeciospores, uredospores, and teliospores. In the spring the overwintering teliospores produce basidiospores. The basidiospores can only infect barberry not wheat. Once it infects barberry aeciospores are produced which in turn infect wheat. On wheat, the rust produces uredospores all summer long that can re-infect wheat. Both aeciospores and uredospores can only infect wheat. Once the plants mature and start to get dry, the fungus produces its overwintering spores (teliospores) that will survive until the next spring if plant debris left in the field.
Not all regions have barberry, yet they may still have wheat stem rust. What frequently happens is that stem rust shows up earlier in the season in southern states and the uredospores are blown north by wind and then colonize wheat without the need for barberries to complete the life cycle.
There are many races of wheat stem rust. We were not able to get this isolate typed and therefore do not know the race. If it becomes more of a problem in the future samples can be sent to a lab that can do race typing. Once the race is known resistant varieties can be planted. However, since the spores are blown in by wind, different races could arrive each year. Fungicides can be used but would have to be applied as a protectant once the first rust pustules develop.
In Utah, we frequently see wheat stripe rust. One way to differentiate between the two is that wheat stripe rust does not infect and colonize the stems of wheat.
- Dr. Claudia Nischwitz (Extension Plant Pathologist)
For more information, please see: https://utahpests.usu.edu/factsheets/plant-diseases.
To submit plant samples, please see: https://utahpests.usu.edu/uppdl/submit-plant-sample.