Chalk up one more advantage for no-till crop production. It slows the spread of soybean cyst nematode (SCN) - the No. 1 profit thief in soybean production.

That's one take-home message from a six-state, north-central region disease study using randomized site selection, which gives it high reliability.

"We got 1,476 soil samples from randomly selected sites in five states where we also had tillage information and tested them for cyst nematodes," explains Greg Tylka, Iowa State University extension nematologist.

"As one part of the study, we were able to figure out how many of the no-till fields had SCN vs. the conventional-till fields," Tylka adds. "We found that significantly fewer no-till fields had the problem in all of the states, and of all the fields that had it, the no-till fields had lower numbers of SCN eggs."

The study was conducted by Tylka, X.B. Yang and Fekede Workneh from Iowa State University and Jamal Faghihi and John Ferris of Purdue University. They analyzed samples from sites in Illinois, Iowa, Minnesota, Missouri and Ohio.

The research was supported in part by grower checkoff funds from the Iowa Soybean Promotion Board and the North Central Soybean Research Program. The results back up two earlier studies in the South.

"SCN can be spread in several ways, but it is mainly machinery spread," says Tylka.

Machinery can spread it from field to field and area to area. It's likely the main way SCN has spread from the South, where it was discovered in North Carolina in 1954.

It's also thought to be the main way it's spread within fields, starting at field entries. Other research at Iowa State, for example, verified that logical supposition.

"We found over the course of three or four years that tillage spread it about 11' per year," Tylka notes.

There's another explanation for the higher SCN numbers in tilled fields than in no-till fields, he says.

"We know from previous studies that if you take 1,000 nematodes and spread them across a much greater distance, they will have more food per nematode than if 1,000 of them are all clustered under one plant. With a good food supply, they will reproduce much more successfully when spread out."

Researchers point out that it's possible for nematodes to spread without machinery. Windblown or water-washed soil can move it. So can migratory birds that stop to feed in a wet field, then visit another field some distance away to feed again. The culprit can be carried on their muddy feet.

So, will no-till reverse the SCN buildup we've seen? "I don't think the buildup will be reversed, or stopped, but I think it could be slowed with no-till," says Tylka.

The study suggested confirmation of one downside of no-till in the disease arena. That is, while SCN was suppressed by no-till, the plant pathologists found a higher incidence of brown stem rot (BSR) and phytophthora root rot (PRR) under no-till.

Fortunately, neither disease has as widespread an economic impact as SCN, partly because BSR is limited to more northern areas and PRR has economical seed treatments that help. And both have greater numbers of tolerant or resistant varieties than does SCN.