Southern Idaho Strip Rust Update

Much of the stripe rust in winter wheat is starting to shut down, especially in those varieties with high-temperature adult plant resistance (HTAP). We are, at this stage, past the application window for applying fungicides to control stripe rust in winter wheat. In any case, further application in winter wheat would not be economically beneficial.  Most of the winter wheat is in or past the grain fill stage.

In our spring grain, significant damage can still occur depending upon growth stage. The preharvest intervals for most of the fungicides vary from 45 – 30 days, depending upon the fungicide. PLEASE READ AND FOLLOW THE LABEL INSTRUCTIONS. DO NOT spray past the recommended preharvest interval. Spring grains are now in grain fill in the lower elevations, flowering in the Idaho Falls region, and still at stem extension in the upper elevation areas. Some of the spring lines with HTAP are showing higher than expected stripe rust infection (UI Pettit) while HTAP in Alturas, for example, is holding. Those fields that have been sprayed with fungicides at herbicide timing did very well in reducing infection compared to those that were not sprayed, although stripe rust is re-establishing if a second fungicide application was not applied.

In barley, we can find stripe rust but any damage has been minimal. I have yet to see stripe rust in barley in commercial fields at damaging levels. Most barley is past flowering in most of the production areas, except in the higher elevation areas.

Attached is an excel file with ratings of the winter and spring wheat varieties in the extension variety trials in Aberdeen. PLEASE NOTE that the disease pressure at that location is extraordinary. While I included both the seedling and adult reaction of the spring wheat, I did not for the winter wheat, but there are two ratings in the spring/summer and I included the raw data of two replications (untreated with fungicides). The infection type is rated on a 0 to 9 scale, with 0 being immune, 1, 2, 3 resistant, 4,5,6 intermediate, and 7, 8, 9 being susceptible. A rating of 9 means the plant was heavily infected with no chlorosis, and high levels of sporulation. If you would like further information/ clarification on the definitions of infection TYPE, let me know. In addition, there is a rating on the percent leaf area affected in the entire plot. Some varieties have a susceptible reaction, with lower levels of diseased tissue. There was a tremendous amount of necrosis this year, hence the mixed reaction types. For example, one variety may have a rating of 5/8 and percent 30/5, meaning that 30 % of the plot had an infection type about 5 (intermediate resistance with quite a bit of necrosis but sporulating still) and 5 % of the plants in the plot were showing extensive sporulation with an infection type of 8, with a little chlorosis.

Please let me know if you have additional questions.

Juliet

Juliet Marshall
Associate Professor, Cereals Pathology and Agronomy

Idaho Falls R&E Center
1776 Science Drive Suite 205
Idaho Falls, ID 83402
208-529-8376 office
208-390-4859 cell

http://www.cals.uidaho.edu/scseidaho/