Soybean cyst nemotode

White to light-yellow soybean cyst nematode are seen on soybean roots. Soybean cyst nematodes interfere with nodulation on legumes and can cause early yellowing and stunting.

White to light yellow soybean cyst nematode females on soybean roots.


TWIN FALLS — Idaho farmers are well aware of the damage nematodes can cause in their fields and to their markets.

Japan suspended all U.S. potato imports after the pale potato cyst nematode was detected in Idaho in 2006. Japan later reopened the market to U.S. potatoes except those grown in Idaho. It took 11 years — and an aggressive state testing and eradication program — for Japan to lift the ban on potatoes from Idaho. Mexico still requires testing for the pest before export.

That’s why bean producers are so concerned about soybean cyst nematode finding its way into Idaho.

“I’m afraid that if we have soybean cyst nematode, we won’t be able to export bean seed,” said Bill Bitzenburg, a former member of the Idaho Bean Commission. “It could kill the bean seed industry in Idaho.”

Soybeans are included in the state’s bean quarantine law and is not legal to bring them into Idaho from regions east of the Continental Divide. However, some cover crop mixes that are purchased from out-of-state dealers have included soybeans and a couple hundred acres of feed soybeans were grown in the Magic Valley last year, said Don Tolmie, a member of the Idaho Bean Commission.

The dairy industry is interested in using soybeans as an alternative source of protein. However, significant investment is needed in processing the beans to make them palatable to dairy cows.

“Even though soy is included in the bean quarantine, I don’t think the law is well understood,” Tolmie said. Seeing the soybeans grown last year in the Magic Valley without oversight or inspection prodded the dry bean industry into seeking broader clarification from the State Legislature. Both the Senate and House Agriculture Committees heard testimony on January 30 about the dangers of soybean cyst nematode. Legislation is expected to be introduced in early February.

Nematodes are not new to Idaho, explained Saad Hafez, nematologist with the University of Idaho Cooperative Extension Service. About 5 percent of the samples from Idaho have root lesion nematode, a native species found in sagebrush regions.

Sugar beet cyst nematode is a problem in the MiniCassia area. Hop cyst nematode and cereal cyst nematode are other species that growers have learned to manage. But soybean cyst nematode is a species that has not yet been found in Idaho and Hafez would prefer not to see it.

“If we ever get it here in Idaho, it won’t be eradicated,” Hafez told growers during the University of Idaho Bean School. ‘We can manage it — I won’t use the word control — but we cannot eradicate it.”

Soybean cyst nematode interferes with nodulation on legumes and can cause early yellowing and stunting. Soybean growers have seen losses of 10 to 70 percent from the nematode. One estimate says the nematode causes up to $2 billion annually in losses worldwide.

Soybean cyst nematodes have a couple of adaptive strategies that make them a more formidable pest problem than any other nematodes.

First, this nematode has a four- to six-week life cycle which allows the pest to achieve three to five generations per growing season. A single female lays up to 5,000 eggs, Hafez said. Multiple 5,000 eggs by three to five generations and the population can quickly explode.

Fumigants can help manage populations but are not 100 percent effective, he said. Even at 90 percent control and multiple generations during the season, the population will still be higher at the end of the season than the beginning. Although he is quick to point out that 90 percent control is better than none.

This nematode is not active when temperatures fall below 57 degrees or exceed 93 degrees. Females form cysts to overwinter to provide the first generation of eggs the following season. But if a non-host crop is planted, the eggs inside the cyst will wait for many years, even decades, before hatching.

Soybeans, common beans and alfalfa are all hosts for the soybean cyst nematode. Several studies have also indicated that sugar beets can be a host for the soybean cyst nematode. Studies dating back to 1965 have shown that if both nematode species are present in a field, they can mate and the progeny will survive on both sugar beets and bean plants.

“We already sugar beet nematode in every county in Idaho,” said Hafez. “I expect that if soybeans are introduced to Idaho, some will be grown on acres where sugar beet cyst nematode is already present.”

The best defense, Hafez argues, is not to allow soybeans to be grown in Idaho at all. The nematode will not arrive in seed, but in dirt that accompanies seed. Bean seed is notoriously hard to clean because of how beans are harvested but other seed crops grown in a field contaminated with soybean cyst nematode could also carry the pest along with soil particles.

Soybean cyst nematode is not the only pest that soybeans could bring to Idaho. Soybean aphid is a vector for five of the largest disease problems in sugar beets and dry beans.

The proposed legislation is expected to prohibit soybeans from being grown in bean producing regions of the state and to provide oversight for plantings in other areas, Tolmie said.

“We don’t want to jeopardize one industry to let an unknown industry in.”

“I’m afraid that if we have soybean cyst nematode, we won’t be able to export bean seed. It could kill the bean seed industry in Idaho.” Bill Bitzenburg, Magic Valley grower and former member of the Idaho Bean Commission

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