Tuesday, November 8, 2011

Stripe Rust Fall Infection Levels

The following observations of stripe rust fall infection levels were made by Dr. Xianming Chen, USDA ARS, Pullman on November 3, 2011 in eastern Washington:

On November 3, we were checking stripe rust infection in winter wheat fields along Highway 23, Platter Rd, Doerschlag Rd, Lake Rd, Stromberger Rd, and Danekas Rd in Whitman, Adam, and Lincoln counties and the Horse Heaven Hills region in Benton County in Washington.  Wheat ranged from non-emerged to early jointing (Feekes 5).  We only check fields with big plants (Feekes 3-5) as big plants were more likely to be infected. 

We found stripe rust pustules in 6 fields out of a total of 15-20 fields that were carefully checked: two fields west of St. John and east of Sprague along HW 23 in Whitman County (Fig. 1); one field along Stromberger Rd in Lincoln County near the Adam County border; one field along Doerschlag Rd; one field along Danekas Rd about five miles east of Ritzville in Adams County and one field in Horse Heaven Hills in Benton County (Fig. 2).  We were able to found only 1 or 2 leaves with rust pustules in each of the fields. 

Fig. 1: Stripe rust, November 3, 2011 near Colfax, WA
In contrast to the big hotspots found in the Horse Heavy Hills region and other regions in Washington in early November, 2010, the rust infection level and distribution found yesterday were much lower.  This level of stripe rust infection is expected based on the dry weather conditions in September this year.

Stripe rust infection was found on volunteer wheat plants in the middle of October in Mt Vernon (northwestern Washington) as usual when our people were planting winter wheat nurseries.  Stripe rust was also reported by Dr. Juliet Marshall to be occurring on volunteer wheat plants in October in southern Idaho.  

Fig. 2: Stripe rust, November 3, 2011 in Horse Heaven Hills area, WA

The finding of stripe rust in winter wheat fields allows us to know the level of infection before the winter, which will help us to predict disease situation for the next year.  There is no action for growers to take for most of the regions in the PNW until next February or March, except for selection of spring wheat cultivars to grow in next spring (resistant cultivars should be always considered anyway).  As the weather starts getting cold, stripe rust spores on the leaf surface will be killed and the fungus will sleep as mycelium within the infected but not sporulated leaves during the winter.  Some of the sleeping rust mycelia may be killed by harsh winter and some will survive.  The level of the survival will depend on how cold and how much snow-cover during this winter.  A recent weather prediction says that this winter for the PNW will be colder than normal (http://www.weather.com/outlook/weather-news/news/articles/late-fall-winter-outlook_2011-10-24).  If, this prediction will be true, we should not have stripe rust as bad as this year.  We will wait to see how cold the winter will be and have our first forecast in February for stripe rust in the PNW next year.  People in the south-central states may need to check for stripe rust earlier as that weather prediction indicates a warmer winter.   

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