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Winter wheat is a little behind schedule this year likely due to inadequate moisture and lower than average temperatures. Much of eastern Colorado is experiencing moderate drought conditions and southern Colorado is under moderate to severe drought. However, thus far the wheat looks good and without disease symptoms, though some frost damage even before the snowstorm.
While there are currently no reports that stripe rust overwintered in Colorado this year, we do need to be on the look-out. Stripe rust has been reported in eastern Kansas. Bob Hunger, Extension wheat Pathologist at Oklahoma State University, reports stripe rust “hotspots” in central Oklahoma. Leaf rust is prevalent in Texas. Texas and Oklahoma are the locations where the inoculum builds up and could affect eastern Colorado later in the season.
Stripe rust is caused by the fungal pathogen Puccinia striiformis and is spread by wind over long distances. It can also overwinter on volunteer wheat and weedy grasses. Symptoms include small oval shaped yellow-orange pustules that form in stripes along the leaf veins When stripe rust pustules erupt, spores are released and the disease spreads. Temperatures between 50-64°F, with substantial dew periods are optimal growth conditions. The primary management practice for stripe rust is planting of resistant varieties (see CSU Variety Characteristics Table), timely foliar fungicide application (see K-state Foliar Fungicide Efficacy Ratings), late planting and control of wheat residue..
Leaf rust is caused by the fungal pathogen Puccinia triticina forming small round orange pustules that are typically scattered on the leaf as opposed to the stripe pattern formed by stripe rust pustules. Management for leaf rust is the same as for stripe rust.