August 28, 2003

 

Soybean Cyst Nematode Reported in North Dakota

The first verified cases of soybean cyst nematode in North Dakota have been discovered in several fields in Richland County, according to Carl Bradley, North Dakota State University plant pathologist. Soybean cyst nematode is the most important soybean disease in the country. In 2002, the estimated losses from SCN in the United States were 133 million bushels.

The disease was probably imported along with soybean seed from Asia and was first discovered in North Carolina in 1954. Since then it has spread to many states and Canada. "The disease was reported in Minnesota in 1978 and in South Dakota in 1995," Bradley says. "Given that the disease was so close, we knew it was only a matter of time before it would hit North Dakota."

The nematode, a microscopic worm, attacks soybean roots causing major damage to the plant. It may take many years from initial infestation to reach damaging levels, which may be a reason the disease has not been reported in the state. "The damage caused by the soybean cyst nematode varies so it can be confused with other causes such as iron deficiency, soil compaction, chemical injury or root rots," Bradley says.

Some of the symptoms include yellowing of the foliage in July or August, stunting of plants, thin stands and slow closing of rows. A wavy pattern may be seen down the rows due to stunted or poorly growing plants. Symptoms may first occur near field entrances, vehicle and storage areas in the field, compacted headlands, along fencerows where windblown soil accumulates, on the tops of knolls or in low or flooded areas.

"Losses of 15 to 30 percent have been reported even when there are no obvious above_ ground symptoms," Bradley says. "When the nematode is abundant, losses can exceed 20 bushels per acre. In extreme cases, almost no crop will be produced."

With funding from the North Dakota Soybean Council, Ted Helms, NDSU’s soybean breeder, and Berlin Nelson, NDSU plant pathologist, are working to develop new varieties that are resistant to SCN and other soybean diseases. "It just takes time to do the breeding and pathology work," Nelson says. "We geared up 6 years ago to come up with new varieties for our area because we knew SCN would eventually get here," Helms says. "We have some cultivars that are in the experimental stage that show promise but are not ready to be released. MN_0902CN is a variety that has resistance to SCN that is commercially viable even at the moderate infestation level."

Because SCN is sometimes difficult to detect, it is not known just how extensive an area is infested. A large field survey was conducted several years ago but no SCN was found. "I don’t think it is widespread but it’s in North Dakota and it’s well established," Nelson says. "We think it could have been in the infected fields for five to seven years before we detected it because it takes awhile to build up."

Crop rotation to non_hosts and the use of host resistance varieties are the principal methods for reducing nematode populations. Examples of non_host crops are small grains, corn, sunflower, sugar beet, flax, potato, alfalfa, forage grasses, sorghum and canola. Dry beans are SCN hosts, and should not be in a rotation. "A three to four year rotation to non_host crops will reduce moderate levels of nematode populations below the economic threshold," Bradley says. "Before a decision is made to plant susceptible soybeans again, sample the soil and have it analyzed for the egg population."

Among the laboratories that can analyze soil for SCN is the NDSU Plant Diagnostic Laboratory. It can be reached at (701) 231_7854 or on the Web at http://www.ag.ndsu.nodak.edu/diaglab/

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Source: Carl Bradley, (701) 231_7056, carl.Bradley@ndsu.nodak.edu
Berlin Nelson, (701) 231_7057, berlin.nelson@ndsu.nodak.edu
Ted Helms, (701) 231_8136, ted.helms@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231_6136, richard.mattern@ndsu.nodak.edu