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Despite rust increase, scientists still more concerned with scab
The incidence and severity of scab were generally minor and sporadic during the 1999 growing season, with the fungal disease taking a back seat to sprout
damage and rust as the big problems for small grain producers in the Northern Plains this year. In North Dakota, scab yield losses in hard red spring wheat averaged between 1% and 3%, and barley, 1% to 2%, with
some fields at higher levels, says NDSU extension plant pathologist Marcia McMullen. Scab was more prevalent in durum; partly because of its increased susceptibility to the disease but also because some
late-planted durum fields flowered during environmental conditions that favored infection. Leaf rust in 1999 was the most severe and concentrated problem the Northern Plains has seen in 20 years, say area crop
scientists. Abundant numbers of wheat leaf rust fungal spores moved northward from southern states on wind currents early in the growing season. Frequent rains deposited those spores on crops, and environmental
conditions favored infection. Most hard red spring wheat varieties grown in the Northern Plains are rated as resistant to prevalent races of leaf and stem rust. However, there is a tradeoff with some varieties
grown in the Northern Plains such as 2375 and AC Barrie that farmers have turned to in recent years for better performance against scab: these varieties are more susceptible to leaf rust. In field surveys this year
across North Dakota, McMullen says field scouts saw rust severities on the flag leaf ranging from 1% to 80%. Wheat leaf rust severities of 30% to 40% were common, and higher leaf rust severities were recorded in some
varieties in research plots in all districts. She estimates yield losses averaging between 4% to 8% statewide due to leaf rust. Crop scientists are monitoring this year's rust problem closely, as varieties formerly
considered resistant can become susceptible if shifts in virulence or new races of rust occur. More information on rust may be found online at www.cdl. umn.edu, the web site of the U.S. Agriculture Department's Cereal Disease Lab in St. Paul, Minn.
The good news relating to wheat leaf rust for 1999 is that fungicides continue to work. McMullen says preliminary reports from producers who used fungicides to treat leaf diseases show that the products (Folicur and
Tilt are two of the most widely used fungicide products in the Northern Plains) controlled leaf rust well and returned anywhere from 8 to 12 bushels per acre. While there are management options and crop breeding
material available to treat and research rust in small grains, there are fewer management options for scab, points out Bob Busch, who will retire as wheat breeder for the University of Minnesota and USDA next
year. That's why scab continues to be a major focus of small grains research, he says . |
