NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
November 4, 1999
Results of North Dakota's 1999 small grain survey reveal that both fungal and viral diseases attacked the state's small grain crops this year, but the most common diseases in both wheat and barley were fungal leaf-spot diseases. Barley yellow dwarf virus was also quite prevalent in wheat this year.
But severities of Fusarium head blight (scab)--the most devastating fungal disease in recent years--were quite low in both North Dakota's wheat and barley crops, says a specialist with the North Dakota State University Extension Service.
"Our greatest average yield loss on wheat due to scab was less than 3 percent," says Marcia McMullen, an extension plant pathologist at NDSU. "Rains weren't abundant at the time the crops flowered or during early grain fill. The rains and high humidities that favor scab infection occurred either too early or too late in most cases."
Similarly, the average 1999 scab severity for the state's barley crop was between 1 and 2 percent, McMullen says. Scab appeared most frequently in barley fields surveyed in North Dakota's northeast crop reporting district. No scab was observed in barley in western counties.
Working out of the NDSU research extension centers in Carrington, Minot and Dickinson, as well as the main station in Fargo, four crop surveyors monitored crop disease conditions in more than 900 small grain fields from first leaf through the hard-dough stage of kernel development, McMullen says. They surveyed fields in all of North Dakota's nine crop reporting districts and in all 53 counties, with the majority of surveyed fields being wheat. Funds from the federal Integrated Pest Management Program supported the survey.
Tan spot and Septoria, fungal leaf-spot diseases affecting wheat, were very common throughout the state, McMullen says. These diseases were most severe in the central, east central and southeast districts.
"In the worst-hit areas of the state, 30 to 45 percent of the wheat flag leaf was consumed by leaf-spot fungi by the soft dough stage of kernel development," McMullen says.
The fungal leaf-spot diseases of Septoria, net blotch and spot blotch were the most common diseases of barley for 1999. Spot blotch was the most common in North Dakota's western and southern counties while net blotch was most common in the northern counties. Septoria was most common in the southeast and east central counties, McMullen says. The combined severities of these three diseases ranged from 30 percent to 50 percent on the flag leaf in five of the state's nine crop reporting districts.
The leaves of small grain plants manufacture carbohydrates and other nutrients, and the flag leaf is a primary contributor to the nutrients necessary for kernel development. When the flag leaf becomes diseased, lower yields and reduced test weights are the result, McMullen explains.
Wheat leaf rust was much more widespread and severe than in recent years in all parts of North Dakota in 1999, except in the northwest district. McMullen says the severity of leaf rust was the greatest in the central, south central and southeast districts, where surveyors reported that, on average, a fifth of each flag leaf was consumed by the disease.
"There appears to be a new mix of leaf-rust races in the region, which would account for leaf rust occurring on varieties previously resistant to the prevalent races," McMullen says. "There was also a tremendous buildup of rust spores in the southern Great Plains states last spring. After being blown northward on air currents, those spores served as inoculum for fields here."
Barley yellow dwarf virus (BYDV) was observed extensively in wheat and barley in 1999. BYDV appeared in wheat in all districts, with a range of 4 to 24 percent of the fields within a district showing symptoms. In barley, the north central district had the highest frequency of fields showing BYDV symptoms, at 48 percent.
BYDV attacks wheat, barley and oats and is transmitted by common grain aphids, McMullen explains. The disease causes yellowed, stunted plants. Late crops are most vulnerable because the aphids that transmit the disease must migrate northward on wind currents from southern states such as Texas. Once in this region, the insects must build up populations to transmit BYDV.
"If our grain crops would have been planted early, most of them would have escaped the virus," McMullen concludes.
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Source: Marcia McMullen (701) 231-7627
Editor: Dean Hulse (701) 231-6136
Click here for a pdf version of this graphic. (47KB b&w map of ND crop reporting districts)