NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
September 16, 1999
Abundant numbers of wheat leaf rust fungal spores moved northward from southern states on wind currents during the late spring and early summer. Frequent rains deposited those spores on crops, and environmental conditions favored infection. The result was the most severe and concentrated wheat leaf rust problem the Upper Midwest has seen in 20 years.
"This year, yield losses to leaf rust are expected in both winter and spring wheats in the northern plains," says Dave Long, a plant pathologist at the USDA-ARS Cereal Disease Laboratory in St. Paul.
Long analyzes the rust samples coming to the St. Paul lab for race determination. He also prepares the rust loss report for the United States. The final 1999 report should be issued later this year.
"At this point, I would estimate that North Dakota wheat producers experienced a yield loss averaging between 4 percent to 8 percent statewide due to leaf rust," says Marcia McMullen, extension plant pathologist at NDSU. "More than 900 North Dakota wheat fields were surveyed this summer and leaf rust was found throughout the state."
In the south central and central portions of North Dakota, nearly 71 percent of the surveyed wheat fields showed some leaf rust. In the eastern third of the state, about 73 percent of fields in the survey showed symptoms of leaf rust, McMullen says. Nearly 66 percent of the surveyed fields in the southwest and west central parts of the state showed leaf rust, as did 38 percent of surveyed fields in the north central and northwest.
"Field scouts saw rust severities on the flag leaf ranging from 2 percent to 100 percent. Wheat leaf rust severities of 40 percent were common, and higher leaf rust severities were recorded in some varieties in research plots in all districts," McMullen says.
The North Dakota Agricultural Experiment Station operates rust nurseries for spring wheat near Fargo, Carrington and Langdon, in cooperation with Jim Miller, a USDA-ARS plant pathologist in Fargo. The NDSU plant pathologist involved in this project is Jack Rasmussen, who has compiled a preliminary summary of leaf-rust reactions among some spring wheat varieties. McMullen says the summary, which is based on an average of infections from all three rust nurseries, shows that the highest average severity in 1999 was on Grandin, followed by high severity values on ACBarrie, Marquis, 2398, Gunner, Forge, Reeder, 2375 and Parshall.
Reeder produced an especially high reaction at the Carrington nursery while the severity reaction for 2375 at that location was uncharacteristically low. McMullen says, "We don't know if that's because there's a different race there or if there's some other explanation."
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 returned anywhere from 8 to 12 bushels per acre.
"In my 1999 research plots, I got almost 100-percent control of wheat leaf rust with Folicur and Tilt for almost three weeks after application," McMullen says.
But with that good news come challenges. McMullen says that based on the 1998 samples from North Dakota analyzed at the USDA-ARS Cereal Disease Laboratory in St. Paul, it appears that there are more rust races developing in North Dakota than in previous years. She adds, "And there seems to be a shift in the grouping of races."
In Kansas, several popular wheat varieties growing in research plots showed significant erosion in resistance to leaf rust compared to last year, says Bob Bowden, extension plant pathologist with Kansas State University. For 1999, he estimates that loss due to leaf rust in Kansas was 3.4 percent, below the 10-year average of 5 percent but greater than last year's estimate of 2.5 percent.
McMullen says the leaf rust problem in Kansas this year likely would have been more severe, but the problem didn't surface until near harvest when the potential for yield damage is reduced. She concludes, "North Dakota's wheat leaf rust potential for next year depends on what happens in Texas, Oklahoma and Kansas. In areas where leaf rust was a problem last year, I would advise North Dakota wheat producers to consider varieties that have more tolerance and budget for fungicides up front."
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Source: Marcia McMullen (701) 231-7627
Editor: Dean Hulse (701) 231-6136