Some Issues Related to Stripe Rust in the PNW 7/8/10

July 8, 2010

Xianming Chen
Currently, there are some issues on stripe rust

The rust season has not been over yet. As hot and dry weather has finally come to the PNW, high-temperature adult-plant resistance has started working better. However, stripe rust will continue developing in fields grown with susceptible varieties as low night temperatures in many areas will still below 60oF and dew will continue forming at night for a while, which allow stripe rust infection will continue occurring. Spring crops of susceptible varieties should be sprayed if have not done so.

Grain quality has become a hot topic, partially related to stripe rust infection and partially related to high precipitation that may reduce the percentage of protein. If crops have been sprayed with fungicide on time, rust damage on both grain yield and quality should be minimal. Stripe rust definitely reduces total protein from damaged grain, but the percentage of protein may increase little bit in grain from rust damaged crops. However, such little increase is at a cost of huge yield loss. Therefore, it is not a good idea to allow rust causing plant stress in order to increase grain protein.

Another big concern is related to rust carryover. In the previous update, I mentioned that rust is not seedborne, and therefore head infection will not make rust carryover to next crop season through seed. Here, I’d like to also emphasize that rust is NOT soilborne and that stripe rust is not crop residue-borne. Therefore, fields with crops heavily infected this year may not necessarily have rust next year. Whether or not such fields will get rust next year will depend upon which varieties you will grow and the rust situation in the region next crop season. Orange rust spores will die very quickly when they stick on soil surface. Orange rust spores will also die quickly on plants after green tissue is completely gone before harvest. Therefore, straws and stubbles cannot carry viable rust orange spores to next season. Stripe rust survives from one crop season to next through surviving in the air for few days (the dryer and cooler the weather, the longer rust orange spores can survive) and to catch green plants. People may ask how about the black telial pustules on straws and stubbles. For stem rust, the black telial pustules contribute to carrying over from one crop season to next because in the PNW stem rust needs the telial stage to infect barberry next spring and later, stem rust spreads from barberry plants to wheat and barley. However, black telial stage is not necessary for stripe rust to survive from season to season, although some barberry plants can be infected by wheat stripe rust under greenhouse conditions as recently reported. If any, barberry plants play a much limited role to stripe rust epidemic in the nature, compared to wheat crops for carrying over and spreading. Therefore, burning, baling, or burying stubbles are not necessary to eliminate stripe rust. Because stripe rust is carried over from green plants to green plants, any managerial practices that eliminate volunteer wheat plants can contribute to reduction of rust spores. Appropriately (for good emergence of crops) delayed planting of winter wheat can reduce rust infection in the fall.

Related to the above issue is a question if stripe rust will be a big problem next year. We could not predict how severe stripe rust will be next year until after December. However, we can clearly say that stripe rust is a problem every year in the PNW if highly susceptible cultivars are grown, but it is just a matter of how big the problem. Therefore, select more resistant varieties to grow is always a good idea. We will update variety reactions to stripe rust as soon as we finish note-taking and summarizing the information.