Soybean nematodes play for keeps

By Tom J. Bechman
If you think your varieties resistant to soybean cyst nematode aren’t working as well the past couple seasons, you may be right. Certain strains are overcoming specific types of resistance.
This month’s Indiana Certified Crop Advisers panel relays valuable information about the changing picture of soybean cyst nematode control.
Question: I have cyst nematodes in some fields. It seems like my resistant varieties aren’t doing the job any more. My dealer keeps changing the subject when I ask what type of resistance his varieties have. Should I keep asking, or switch companies?
Jeff Nagel, agronomist, Ceres Solutions, Lafayette: Switching companies may not accomplish anything, but your dealer should answer your questions. The three main sources of cyst resistance today are PI88788, PI 437654 and Peking. The vast majority of soybeans use PI88788, which makes it difficult to rotate sources of resistance. Each source of resistance contain several genes that confer resistance. Even if using the same source of resistance, such as PI 88788, not all varieties will have the same number or order of genes so performance can be different. There’s more evidence that some SCN populations are able to increase population on SCN varieties with PI88788. This may be due to its widespread use.
Darrell Shemwell, agronomist, Posey County Co-op: If your dealer won’t give you information, ask someone else. Most all seed companies can tell you if their varieties have cyst resistance, and to which races. Do you know which races you have? This is the first thing to find out. The best management practice is to rotate to corn for a year or if populations are high, two years. Other non-host crops are small grains, alfalfa and canola. If you’re unable to rotate, consider a seed treatment such as Votivo. My best advice is to get your fields checked so you know if you have nematodes, and which races you have. Then determine your best management practices.
Nagel: Soybean cyst management consists of multiple strategies. Consider the following options.
  • Use crop rotation, as Darrell noted, with a non-host crop like corn or wheat.
  • Control winter weeds in the fall to eliminate alternative SCN hosts.
  • Plant high-yielding SCN varieties with other disease protecting traits. If you’re in a corn and soybean rotation, avoid planting the same variety in the same field when rotating back to soybeans. Use a different SCS resistant variety.
  • Mange pH levels. SCN densities tend to be higher with increasing soil pH. Don’t over lime where soil pH levels are already in the upper 6 or lower 7.0 range. This is why some very high SCN levels are found in river bottoms.
  • If planting into fields with known high SCN levels, use Votivo or a new product, Clariva, on SCN resistant soybeans.
  • Test fields every three to four years to determine if SCN densities are relatively stable, increasing or decreasing.

Key points

  • Some varieties with PI88788 resistance to soybean cyst nematode aren’t controlling the pest well
  • Seed treatments such as Votivo and Clariva may help
  • Test to make sure you have SCN, and if so, which races are present