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Wheat Rust Detections in ND (6/21/12)

Wheat leaf rust, caused by Puccinia triticina, was detected in winter wheat by field scouts in ND on June 18, in Cass County in the east and in Slope County in the southwest. Leaf rust was at trace levels. This is the first NDSU confirmed detection of wheat leaf rust this year. We don’t know the race of leaf rust detected; in recent years many of the leaf rust races present were ones that could defeat a wheat leaf rust resistant gene called Lr21, found in some of the most commonly grown spring wheat cultivars in our area.

Stripe rust, caused by Puccinia striiformis, continues to be observed in wheat, more frequently up to now in the eastern half of the state.  Occurrence is most common in winter wheat, but also has been detected in spring wheat cultivars such as Faller, Prosper, RB07, Rollag and Brennan, and perhaps a few others.  We have incomplete data on variety response in currently grown wheat varieties and incomplete information on stripe rust resistant genes present in current cultivars, but Dr. Maricelis Acevedo in the NDSU Dept. of Plant Pathology currently has a project on greenhouse screening of current cultivars and breeding materials.  Stripe rust resistance genes within the wheat host are designated as Yr genes (yellow rust).  Stripe rust usually shuts down with temperatures over 80 degrees.

Wheat rust thresholds: Thresholds for wheat leaf rust control in susceptible varieties, based on information from winter wheat states, are averages of 1-3 pustules of rust on the flag leaf, and 5-10 on the leaf below the flag leaf.  For stripe rust, the pustules generally are much larger than for wheat leaf rust, and it may be feasible to use one stripe rust pustule on the flag leaf as a threshold, if cool, wet environmental conditions exist, which are favorable for that rust’s development.

Fungicides, Rust, and Scab: The 2012 Wheat Fungicide Efficacy Table (compiled by plant pathologists in multiple states) indicates that a number of fungicide products provide excellent control of leaf and stripe rust, but only two (Prosaro and Caramba), also provide the best control available for Fusarium head blight (scab).  This chart is found by clicking on the link under new publications at the Extension Plant Pathology web site:  http://www.ag.ndsu.edu/extplantpath/.

The USDA Cereal Disease Laboratory in St. Paul, MN has excellent information on all cereal rusts.  Detailed information on these rusts may be found at:  http://www.ars.usda.gov/Main/docs.htm?docid=9854

Fusarium Head Blight Risk: Moderate to high risk of Fusarium head blight infection in susceptible cultivars was indicated on June 19th for Cavalier, Towner, Rolette and parts of Bottineau Counties in North Dakota, with a few scattered areas around Devils Lake and in Burke County also having moderate risk for flowering wheat.  Similar risks might exist in those areas for barley that is heading now.  Recent rains may bump the risk up in other areas, as well.

Marcia McMullen

Extension Plant Pathologist – Cereal Crops

marcia.mcmullen@ndsu.edu

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