Stripe Rust on Volunteer Plants in Winter Wheat Fields
Stripe rust is widely occurring in spring wheat fields planted with susceptible varieties in eastern Washington and Northern Idaho. Some fields have been sprayed with fungicides. The recent dry conditions have slowed down, but could not stop rust development, because temperatures have been favorable to stripe rust. Depending upon moistures in the next two to three weeks, various severity levels of stripe rust will occur in fields grown with susceptible varieties.
Resistance in soft white winter wheat, such as Madsen, Eltan, Rod, Hill 81, and Daws, is still effective. If you grow these varieties, you do not need to wary about stripe rust. However, if you grow these winter wheat varieties in fields that were grown with susceptible varieties like Zak last year, you may have stripe rust occurring in the winter wheat fields because Zak has the shattering problem and Zak volunteer plants survived the last mild winter. About 10 days ago, there was a report in Columbia County that a field of the mixture of Madsen and Rod had 20% Zak plants that had stripe rust. On June 24, we checked a couple of fields in Spokane County, which were planted with either Madsen or Hill 81 this year in last year’s Zak fields. The fields had 20% or more Zak volunteers that had rust up to 60% severity.
The following facts can be used in the consideration of fungicide application for the winter wheat fields with susceptible volunteer plants this year and for the disease control in the future:
- Severe stripe rust occurs only and will cause damage only on the susceptible volunteer plants if the winter wheat variety is highly resistant, such as Madsen, Hill 81, Eltan, Rod, and Daws. However, if a winter variety is moderately resistant or moderately susceptible, it may get higher rust infection because volunteer plants produce more rust spores to infect the winter wheat. For most of fields with susceptible volunteers, a simple calculation can be used to estimate damage: yield loss (bushels/acre) = yield potential (bushels/acre) X the percent of volunteer plants X the percent of yield loss. In maximum, the susceptible plants in such field may get yield loss of 60%.
- A fungicide application may not be profitable for the particular field, but it can reduce rust spores, and therefore, slow down rust development in adjacent fields and the whole region.
- Generally, the more shattering during harvest, the more volunteer plants. Growing crops other than winter wheat can reduce or eliminate the volunteer problem, and therefore reduce the potential of rust epidemic.
Light stripe rust of barley was found in Spokane County and trace leaf rust of wheat was found in Grant County near Moses Lake.
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