High standards. Or, any standard at all. That's what's on the wish list of farmers and university researchers when it comes to soybean cyst nematode (SCN) resistance.
Terry Niblack, University of Illinois SCN management professor, along with other researchers, is working on a program to standardize SCN resistance.
“Several years ago we tested many varieties and found that two-thirds of the varieties labeled as SCN-resistant were not really resistant, according to our assessment,” says Niblack. “In 2008, over 80% of the varieties that companies claimed were resistant actually were resistant. We feel that is the effect of the program.
“The standardization allows soybean farmers to compare apples to apples,” Niblack says. “With this system, farmers will know the actual resistance in SCN-resistant varieties. Seed companies can use this method to prove their resistance.”
Seed companies are also working toward resistance.
ACCORDING TO Jerry Harrington of Pioneer Hi-Bred, it uses Accelerated Yield Technology to select for SCN resistance within its soybean breeding program. This makes use of molecular marker technology to choose better SCN-resistant candidates before advancing them to field testing, increasing the efficiency of soybean variety development.
“We found (in on-farm trials) there is significant value using SCN-resistant varieties,” says Jim Boersma, Pioneer agronomist in Minnesota, who encourages growers to rotate SCN sources of resistance and varieties each year soybeans are planted.
“Rotating sources of resistance is vital to ensure one race or population doesn't become more dominant,” says Boersma.
Sources of resistance include PI88788, Peking and PI437654 (also called Hartwig or Cyst-X). However, nematodes are adapting to PI88788.
“Since 95% of varieties are from 88788, and it doesn't provide complete resistance, the nematodes have adapted to it,” Niblack says. “So, most of the nematodes now in Illinois (and other states) can attack that source of resistance. Those farmers need varieties with alternative sources of resistance in order to protect yields in the long term.”
Farmers also need to remember to rotate not only their resistance type, but also the crop.
“Thanks to rotation and management, my SCN numbers are very low,” says Ed Winkle, who farms 2,700 acres around Martinsville, OH. “My grandpa taught us crop rotation and when we do that, we do well.”
To manage his soil health, Winkle soil samples and uses no-till. The University of Wisconsin has evidence that SCN is not as damaging when no-till is used.
“Management is money. To do that you have to produce a good yield at minimum cost. For me that is no-till; continuous no-till,” he says. “I tested all of my fields, and I've been sampling every year,” he says. “It costs money, but it's worth it.”
Boersma agrees. “Soil sampling and rotating sources of SCN resistance act as a check and balance for growers,” he says. “Growers can monitor SCN management by sending soil samples to their university nematode laboratory every few years.”
SOIL SAMPLING EVERY six years in a rotated-crop environment should be sufficient, says Niblack.
“The only way you can tell if there are nematodes is by soil sampling. We recommend — unless there's a severe problem farmers already know about — to sample every six years in a corn-soybean rotation (three years of soybeans). If numbers go up, their management isn't working. If numbers are down, farmers can keep using the management techniques.”
And those management techniques are rotating resistance, rotating crops and soil sampling, something that can't be repeated and stressed enough.
“Rotation and resistance are the two biggies as far as SCN management,” Niblack says. “Our newest recommendation to management is to rotate sources of resistance.”
Boersma's advice: “Don't let SCN numbers escalate; it leads to limited cropping rotations (corn-corn). Be sure to rotate sources of resistance, use crop rotation and soil sample to monitor SCN pressure.”
To learn which varieties are doing the job, check out the following Web sites for university variety trials.