Soybean Cyst Nematode - Management

 

Management recommendations based on soil test results

NOTE: Egg counts are reported as eggs per 100 cm3 (about ½ cup) of soil and are only estimations of actual SCN population densities.

Infestation category	Soybean not next crop to be grown	Soybean next crop to be grown	Management recommendation
No SCN eggs detected	0	0	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.
Low	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.
Moderate	4,001 - 16,000	2,001 - 12,000	Begin Year 1 of the rotation described below the next time soybeans are to be grown.
High	>16,000	>12,000	Grow several years of a nonhost crop and sample field again every fall to monitor decrease in SCN population densities.

 

SCN Management Guide

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»

Crop Rotation

Crop rotation coupled with SCN-resistant varieties are the cornerstones for the management of SCN. Non-host crops, such as corn, sorghum, sunflower, and alfalfa can reduce SCN population densities each year a non-host crop is planted.

Suggested crop rotation to decrease populations of SCN
(see Figure 1, below)

Year 1 - SCN-resistant soybean with PI88788 source of resistance

Year 2 - nonhost crop (such as corn, oats, alfalfa)

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 (such as corn, oats, alfalfa)

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 Iowa and other 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 (such as corn, oats, alfalfa). Dry beans are not a sutiable rotation crop, as SCN has been shown to develop and reproduce normally on 24 cultivars of dry bean plants.

Figure 1. Recommended crop rotations to manage SCN in fields with less than 5000 eggs/100 cc soil. Source: Greg Tylka, Iowa State University.

 

Cultural practices

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.

Weed control

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, and observed that SCN can reproduce in the field on purple deadnettle and henbit.

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»

Sanitation

Avoid spreading SCN from infested to noninfested fields. If possible, plant noninfested fields first and power wash equipment after working infested fields.

Nematicides

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.

Samples to check for SCN can be taken anytime during the year, but soil samples taken following harvest provide the best population density estimates. View a video about fall sampling for SCN» Also check roots during midseason for the presence of females and cysts. View a video on how to check roots for female SCN»

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).

Field guides and specific management recommendations for your state can be found on the SCN Resources page»