Crop rotation and planting SCN-resistant varieties are the two most important strategies for SCN management. Sample fields to determine SCN population densities -- preferably before buying soybeans for the next season, but certainly before planting soybeans.
||Soybean not next crop to be grown
||Soybean next crop to be grown
|No SCN eggs detected
|| No management strategies are necessary. However, not finding SCN in a soil sample does not prove that it is not present in the field. Follow-up sampling is recommended to check for SCN infestations in future years.
||1 - 4,000
||1 - 2,000
||If this is first discovery of SCN, follow the rotation described below starting with Year 1 the next time soybeans are to be grown. If Years 1 – 4 of the rotation described below already have been completed, continue with Year 5 of the rotation.
||4,001 - 16,000
||2,001 - 12,000
||Begin Year 1 of the rotation described below the next time soybeans are to be grown.
||Grow several years of a nonhost crop and sample field again every fall to monitor decrease in SCN population densities.
|NOTE: Egg counts are reported as eggs per 100 cm3 (about ½ cup) of soil and are only estimations of actual SCN population densities.
Recommended crop rotations to manage SCN in fields with less than 5000 eggs/100 cc soil.
Greg Tylka, Iowa State University.
Non-host crops can reduce SCN population densities each year a non-host crop is planted. Non-host crops include barley, alfalfa, corn, sorghum, sunflower, oats, barrel medic, clovers (red, white, berseem and crimson), buckwheat, canola, flax, potato, sugar beet, sun hemp and tomato.
Rotation crops to avoid are dry beans, cowpeas, common and hairy vetch.
Suggested crop rotation to decrease populations of SCN
Year 1 - SCN-resistant soybean with PI88788 source of resistance
Year 2 - nonhost crop
Year 3 - SCN-resistant variety different than the one planted in Year 1.
Note: If an SCN-resistant soybean variety with resistance from a source other than PI 88788 is not available for use in Year 3, grow a soybean variety with SCN resistance derived from PI 88788 that is different from the one that was grown in Year 1. Grow the exact same PI 88788 SCN-resistant soybean variety in Years 1 and 3 only if no other SCN-resistant soybean varieties with PI 88788 or other sources of resistance are available.
Year 4 - nonhost crop
Year 5 - SCN-resistant variety different than the ones planted in Year 1 and Year 3, or susceptible soybean.
Note: What determines whether a resistant or a susceptible soybean variety should be grown in this year? Almost all SCN-resistant soybean varieties available to north-central growers have the PI 88788 SCN resistance (“PI” stands for plant introduction). Because SCN-resistant varieties allow low level of reproduction, SCN populations can become “resistant to the resistance” as resistant varieties are repeatedly grown, especially if only one source of resistance is used.
Growers concerned about this possibility can prolong the effectiveness of a single source of SCN resistance by growing a susceptible (non-resistant) variety when SCN numbers are low. But SCN causes much greater damage and seems to reproduce at a greater rate in hot, dry growing seasons than in years with adequate to excess rainfall. So if a severe drought is anticipated, growers might opt not to grow a SCN-susceptible variety in an SCN-infested field, even if SCN population densities are low.
Year 6 - non-host crop
The popular SCN Management Guide is based on decades of research on soybean management in SCN-infested fields. It's now in it's 5th edition.
Read online (pdf)»
Order a print copy»
A checkoff-funded study was recently completed in which the ability of cover crops to serve as inadvertent hosts for SCN was investigated. Berseem clover, cowpea, crimson clover, red clovers, sweet clover, white clovers, Austrian winter peas, and field peas were grown in soil infested with SCN.After 30 days, SCN reproduction was assessed by carefully observing the roots of each plant for the presence of adult SCN females. Almost no SCN reproduction occurred on the six to 12 replicate plants of each of the cover crop plants tested in the two experiments.
The results of these experiments indicate that these legumes should not serve as inadvertent hosts for SCN if used as cover crops. Cover crops may reduce nematode population densities as an added benefit -- but the magnitude and consistency of the effects on SCN has yet to be demonstrated.
Source: Cover crops and SCN: What’s the connection?
Providing a plant the best possible growing conditions will reduce stress and yield losses due to SCN. Maintain optimum soil fertility to optimize plant growth and development.
Weed control not only reduces plant stress, but some weeds act as alternate hosts of SCN. Disease and insect control maintains plant health and minimizes damage due to SCN.
On their own, winter annual weeds and soybean cyst nematode (SCN) can cause significant problems in soybean fields. But now, researchers in Indiana have identified six winter annual weeds that act as alternate hosts to SCN:
The Purdue researchers documented SCN reproduction on purple deadnettle and henbit in the field, and noted that reproduction in the greenhouse was as efficient as reproduction on SCN-susceptible soybean.
This means that fields with these weed hosts may be increasing SCN population densities at a faster rate than fields without these weeds. A recent study in Indiana found that known SCN weed hosts were prevalent in 93 percent of the fields surveyed (Creech and Johnson, 2006), indicating the possibility of a statewide increase in nematode population densities due to weeds.
Read more in the recent full-color extension publication from Purdue University Winter Annual Weeds and Soybean Cyst Nematode Management»
Avoid spreading SCN from infested to noninfested fields. If possible, plant noninfested fields first and power wash equipment after working infested fields.
Nematicides will reduce yield loss of SCN-susceptible varieties planted in infested fields but increases the cost of production. Although nematicide will give early season protection against yield loss they do not reduce nematode population densities. Final SCN population densities are often as high as if a nematicide had not been used.
In general, nematicide use should be considered only where adapted resistant varieties are unavailable and where susceptible varieties are planted and SCN population densities are above the threshold level.
Preplant soil sampling
Sampling can be done following either soybeans or corn. If samples are taken in a soybean field, sample only the margins of affected areas, not the centers.
Sample fields to determine SCN population densities preferably before buying soybeans for the next season, but certainly before planting soybeans.
Samples for SCN can be taken anytime during the year, but soil samples taken following harvest provide the best population density estimates.
Check roots during midseason for the presence of females and cysts. Although SCN population density is only one component in soybean yield loss, it may suggest potential yield loss and is information vital for sound SCN management decisions.
The various details to consider when interpreting results of soil tests for SCN are explained in Interpreting SCN Soil Testing Results. (pdf, Iowa State University).
Creech, J. E., and W. G. Johnson. 2006. Survey of broadleaf winter weeds in Indiana production fields infested with soybean cyst nematode (Heterodera glycines). Weed Technol. 20:1066-1075.