The soybean cyst nematode (SCN) is a minute critter that may forever be a problem for growers fighting the yield robbers. But with a good non-host rotation program, and even sound irrigation where available, SCN control is possible.
University of Arkansas Plant Pathologist Terry Kirkpatrick encourages growers to take SCN seriously and not overlook cyst invasions while worrying about other insects or diseases.
“With soybean acreage likely up this year, and with things like Asian soybean rust making headlines, it will be easy to overlook pathogens like SCN that rob yields in a less conspicuous way,” he says, advising growers to consider rotation as well as soil sampling to manage SCN populations.
He says planting a non-host crop such as corn, peanuts, cotton or grain sorghum for one year can significantly reduce the SCN population.
“Two years of a non-host may be necessary to reduce SCN densities to levels that won't cause damage, especially in sandy soils,” adds Kirkpatrick. “Soybeans are more tolerant of SCN in heavier soils than in sandy soils, so growing soybeans every third year may be the best option on light soil.”
He says growing soybeans every other year on heavier soils may be an economical solution. However, some damage from SCN will generally occur in rotations using soybeans every third year, but at possibly tolerable levels.
The boon in corn prices has carried over into more SCN control options for Midsouth growers who may have counted on a rice rotation in the past.
Kirkpatrick isn't comfortable with a corn-wheat-soybean rotation because he's seen some heavy SCN caused yield losses in beans after wheat. And a corn-wheat-soybean-soybean rotation can certainly “result in severe damage to the second soybean crop,” he says, adding that rotation is recommended even if resistant varieties are used.
“I'd say that of the SCN populations we've seen in recent years in Arkansas, we don't have good resistance to about 90% of them,” Kirkpatrick contends. “We have created our own monster by using resistant varieties excessively. There is some new resistance down the road, but growers need to make sure they don't count on solving their SCN problems with resistance right now.”
Irrigation can help growers increase yields they might have lost from SCN, but they shouldn't use excessive irrigation just for SCN control, says Kirkpatrick.
SOIL SAMPLING IS a must. Soybean fields that performed poorly with stunted or yellow plants last year or fields where SCN has been observed previously are easy SCN targets this year — rotation should be highly considered. And soil sampling in late summer or immediately after harvest is a good way to determine if SCN is laying in wait for the next bean crop.
Kirkpatrick says one downside of rotating soybeans with corn for SCN control is the potential for increased root knot nematode.
“It can create a bigger problem,” he says. “Most Group IVs grown in the Midsouth are susceptible to root knot. They can bring you to your knees,” he says. “You need a soil sample to know what you are dealing with on the front end.”
No-till or minimum-till production has both pros and cons. Minimum tillage avoids spreading nematodes, but leaving the SCN undisturbed in the soil may allow better overwinter survival, says Kirkpatrick. “Still, the overall advantages you receive from no-till, in my opinion, outweigh the risk of enhancing an SCN situation.”
SCN SOIL SAMPLING GUIDELINES
Terry Kirkpatrick, University of Arkansas plant pathologist, says growers should carefully sample their fields for soybean cyst nematode (SCN) to locate the hot spots.
“If there are no obvious problem spots within the field, then sample the whole field as a unit,” he says. “Collect a minimum of 20 soil cores that represent the field as well as possible. If a field is large, divide it into more parts and sample each separately.
“If, on the other hand, there are obvious areas that are suspect in the field, samplethese areas along with the surrounding, apparently normal soybeans, once againusing 15-20 individual cores for each area,” he adds.
In such a case, one of the most useful tools besides the standard sampling tube is a handheld GPS unit. “Mark the areas that were sampled,” suggests Kirkpatrick. “Cores should be pulled to a depth of 6-8 in., and sampling should be random throughout the area in a pattern that will include soil from both sides, both ends and the middle.”
Soil should be mixed well, placed in a plastic bag, sealed to prevent drying and tagged for proper site identification. “Although not mandatory, including several root systems with SCN would aid in sample assays, particularly if growers want a race analysis, as well as a general assay.”