Sample to Detect Soybean Cyst Nematode

PRINCETON - Aug 3/04 - SNS -- North American soybean producers should be sampling fields from this point through harvest for the presence of soybean cyst nematode (SCN) to assess pest levels and develop management strategies that will help prevent yield losses in the future.

Field sampling for SCN includes looking for small, dull white-to-yellow cyst sacs on soybean roots. Female cysts are the only unique symptom of SCN.

"Female cysts that attack soybean roots are tiny, lemon-shaped structures, which are much smaller than the familiar root nodule," says Jody Gander, agronomy research manager for Pioneer Hi-Bred International, Inc., in Princeton, Ill. "Early detection of these cysts will allow you to make better soybean variety selections in the future."

Gander points out that it is important to sample fields that have not exhibited SCN symptoms in the past, as the pest continues to spread throughout all major soybean-producing states in the Midwest. Sampling fields is the only way to detect SCN before it becomes an economic problem. Once you see symptoms – leaf yellowing and plant stunting – yields can already suffer 15 percent to 20 percent reductions.

"It takes a period of years for SCN to build up in a field to damaging levels," says Gander. "Preventing the spread of SCN requires early detection and management, because SCN cannot be eradicated once it infests a field."

In fields with confirmed infestation of SCN, use a combination of strategies for effective control. In addition to prevention, rotation and resistant varieties, any management practice that promotes good soybean health and growth is important.

"Avoid conditions that can put stress on soybeans," says Gander. "Stresses like compaction, drought and other disease or insect pressures can weaken the soybean plants’ ability to withstand effects of SCN."

Since SCN cannot be eradicated from a field once it is present, prevention becomes a critical management strategy. Growers should use common-sense sanitation practices to prevent the spread of SCN from a confirmed infested field to an uninfested field.

"Clean equipment with high pressure water or steam to remove all soil particles before moving to an uninfested area," says Gander. "If possible, work in the infested fields last to reduce the chance of spreading the pest. Consider no-tilling infested fields to reduce equipment passes and water and wind erosion which also spreads the pest.

Rotation to a non-host crop also is a key strategy to reduce SCN pressure. Corn, alfalfa and small grains are the most common choices for reducing SCN numbers. SCN-resistant soybean varieties also offer significant benefits.

"Using a resistant variety can increase yield by more than 50 percent in heavily infested fields," says Gander.

Pioneer currently offers 36 SCN-resistant varieties across a wide range of maturities. This offers growers several options to choose from when managing soybean cyst nematode.

Sampling strategies for SCN vary depending on the history of SCN in a field. Sample fields with no prior history of SCN every four to six years. But, if plant symptoms begin to appear, don’t wait to collect a soil sample.

"Collect 10 or more soil core samples within the root zone of those plants exhibiting visual symptoms using a soil probe, small shovel or a trowel," says Gander. "For comparison you might also want to take a sample from an area of healthy plants. Carefully dig roots and examine for presence of SCN females (cysts)."

Send these samples to a qualified laboratory professional, so he or she can determine the number of cysts or eggs in the soil. This information will help you make decisions about next year’s crop.

In taking a sample from an SCN-infested field, remember the following:

1. Limit the area represented in a single sample to 10-20 acres to increase accuracy of results.

2. Collect soil to a depth of 6 to 8 inches in the root zone of the plant.

3. Collect 10-20 1/4-cup subsamples.

4. Collect subsamples using a zigzag pattern across the entire sample area.

5. Separately sample different soil textures and areas with different cropping histories.

6. Deposit subsamples in a bucket and mix thoroughly. Place two cups of soil in a plastic bag and label with a permanent marker. Paper bags allow soil to dry excessively and are not recommended for SCN sampling.

7. Do not store samples in direct sun or allow them to overheat. Ship as soon as possible.