Rust Update 5/20/11

May 20, 2011

Xianming Chen

We were checking wheat fields yesterday in Latah county, ID and Whitman, Adam, Lincoln, and Grant countries, WA along highways 95, 27, 271, Pine City-Malden, 23, Mohler Rd, 28, 17, 170, 21, and 26. Winter wheat crops ranged from early Jointing (Feekes 5) in the Latah and Whitman counties to boot stage (Feekes 10) in Adams county. The crops in the Latah and Whitman counties did not grown much in the past month due to the cool weather conditions. Spring crops were still being planted in these counties. Most checked fields appeared to be sprayed with fungicides together with herbicides and therefore, stripe rust was mostly under control. Some fields along highway 17 near Lind appeared not to be sprayed and stripe rust developed to 10% severity (percentage of leaf area infected) and 40% prevalence (percentage of plants infected). These fields are not too late to spray with a fungicide and are better to be sprayed to protect the crop in the fields and to reduce effect on crop in neighboring fields and even the whole region. In some sprayed fields, stripe rust started showing up in upper leaves because new infection had occurred when the previous sprayed fungicide started passing the effective duration.

The weather forecasted for the next couple of weeks will be cool and moist. Even without additional precipitation, good soil moisture in most areas in Idaho, Oregon, and Washington will create dew-forming conditions for stripe rust to infect crops. Therefore, the weather conditions in the next two weeks will continue to be conducive for stripe rust development. Since this is a very long rust season, a second spray may be necessary. Winter wheat fields should be checked immediately if they have not been sprayed. If active rust infection (producing rust powder) is observed quiet commonly throughout the field, spray should be done as soon as possible. For fields that have been sprayed, please check fields about three to four weeks after spray. When active infection is observed, consider a second spray. Areas in the western PNW and some areas in the eastern PNW, a third spray may be needed, but please read labels for restriction on crop stages. For spring crops, please check field at the time to spray with herbicide. If rust is found, it is better to spray with a fungicide with herbicide. For both winter and spring crops, please consider using a full rate as reduced rates are generally not very effective.

Barley stripe rust has been reported in California and western Washington.

Nationally, stripe rust has been reported in California, Georgia, Idaho, Indiana, Illinois, Kansas, Kentucky, Louisiana, Mississippi, Montana, Oregon, Texas, Washington, and Virginia.