SCN soybean cyst nematodes

The reproduction rates of soybean cyst nematodes tend to favor warm, dry conditions.

Despite an overall wet year for many parts of Iowa and Illinois, Iowa State University nematologist Greg Tylka said in this year’s Iowa State SCN-resistant soybean variety trials, extended periods of dryness helped nematodes become more prevalent.

“My perception of 2018 was that it was a dryer year overall than 2017 statewide,” Tylka said. “I don’t know if the meteorological data would support that, but that’s my perception at least.”

The 2018 trial results are included with this edition of Iowa Farmer Today.

Tylka said the southern part of Iowa tends to have more rapid SCN reproduction, but this year proved to be an exception, as southeast Iowa tended to be lower.

“Mother Nature throws us a curveball every once in a while,” he said.

He noted that Iowa had extended, alternating stretches of dry weather to wet weather, which helped jumpstart the reproduction cycles early in 2018.

“In early June, we had seen the first round of adult females earlier than ever before,” Tylka said. “Once planting started, conditions were pretty hot and dry. Soybean cyst nematodes reproduce better and cause more damage in hot, dry conditions.”

The SCN populations in all of the fields where the experiments were conducted had 10 percent or less reproduction on Peking. But reproduction of the SCN populations on PI 88788 was more than 10 percent in all fields and ranged from 11 percent to 53 percent.

Ideally, levels of reproduction should be less than 10 percent. PI 88788 is the source of resistance genes for more than 95 percent of resistant varieties in Iowa, whereas currently, Peking resistance is available only in 35 varieties.

In their nine major field plots that covered the state of Iowa, Tylka said total yields were down overall. Some varieties proved to be an exception, depending on location, giving nearly 80 bushels per acre, but the gross total was down.

Differences in yields of individual SCN-resistant varieties ranged from 10.6 to 35.6 bushels per acre in the experiments.

Even though initial SCN population densities were low in all but one experiment, differences in yield between resistant and susceptible varieties occurred in all of the experiments and ranged from 3.8 to 19.3 bushels per acre.

When picking plots for this year’s tests, Tylka said the researchers often favor areas that have a moderate SCN presence, but this year, multiple locations had low presence to begin with.

“Despite that, there were still big yield differences in every one of those experiments, even the ones that started with low number,” Tylka said. “There were big increases in nematode numbers throughout the season. What that shows farmers is even if you have a low number of SCN in your field, it can reduce your soybean yields.”

The tests are supported by funds from the Iowa Soybean Association, and Tylka said the reason for the tests is to help farmers make a more educated choice when looking at seed next year.

He suggested taking the information in the trials and combining that with local studies and seed company data. He said their results aren’t necessarily the ultimate source of information, and no farmer should rely on a single source of information.

“We are just one source of information,” Tylka said.

Another good resource for farmers to keep an eye on is TheSCNcoalition.com, he said.