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SCN is an important pest:

  • Iowa grows 9-10 million acres of soybeans annually.
  • SCN has been found in 60 to 75% of the fields in Iowa in surveys conducted in the 1990s, the 2000s, and in 2017.
  • Yield reduction from SCN can be 10 to 30 bushels per acre or more depending on the soybean variety grown and the weather conditions during the growing season.
  • Research results have revealed that there is an increased reproduction of SCN populations in Iowa fields on PI 88788, the breeding line used to develop most SCN-resistant soybean varieties in the state.

SCN Distribution

SCN Management Recommendations

There are multiple tactics for managing SCN:

  • Scout/sample fields to know which fields are infested with SCN and what the population densities (numbers) are
  • Grow non-host crops
  • Grow SCN-resistant varieties

Other need-to-knows about SCN:

  • It is possible that cover crops may reduce SCN numbers, but this effect has not been studied thoroughly or proven in Iowa. Research on this topic is ongoing.

Soil testing tips:

  • Why?
    • To check if SCN is present in a field before planting
    • To determine if your SCN management program has been successful in keeping SCN population densities in check
    • To determine if SCN was responsible for poor soybean yields
  • How often? At least preceding every second or third soybean crop
  • Where should soil test samples be sent?
    • Iowa State University Plant and Insect Diagnostic Clinic plus numerous private soil testing laboratories (ACTS, Inc., Ag-Vise, Centrol, Midwest Labs, Minnesota Valley Testing Labs)

What to know about rotating different resistant varieties:

  • Different soybean varieties with the same source of resistance can vary greatly in yield and in the SCN control that they provide.
  • It is beneficial to select SCN-resistant soybean varieties with high yield and strong nematode suppression.
  • If using soybean varieties with only the common PI 88788 source of resistance, it is beneficial to rotate or grow different soybean varieties because SCN populations can adapt to or build up on individual soybean varieties. (This rotating of varieties will happen probably with not much effort because soybean varieties currently are sold only for a few years before they are replaced by new varieties.)

What to know about rotating different sources of resistance:

  • Farmers are advised to grow soybean varieties with different sources of SCN resistance to avoid selecting or causing the buildup of nematodes that are able to produce on a single source of resistance.
  • Growing varieties with different sources of SCN resistance is similar to using herbicides with different active ingredients or modes of action.

What to know about rotating to non-host crops:

  • Growing a non-host crop for one year can reduce SCN numbers from 5 or 10% to as much as 45 or 50% in Iowa.
  • Although the reduction in SCN numbers when a nonhost crop is grown varies from year to year, the decrease in SCN numbers is similar when the nonhost crops alfalfa, corn, and oats are grown in Iowa.
  • The reduction in SCN numbers is less in successive years after the first year of nonhost crop is grown.

What you should know about nematode-protectant seed treatments:

  • Many seed treatments are available from numerous companies.
  • Each seed treatment has a different reported mode of action.
  • Seed treatments do not provide season-long protection from SCN, but early season protection from a seed treatment can result in increased yield and reduced SCN reproduction.
  • Nematode-protectant seed treatments are not meant to be a replacement for resistant soybean varieties; instead, they should be used on seeds of SCN-resistant soybean varieties.
  • Using a nematode-protectant seed treatment may slow down the decline in effectiveness of SCN resistance.
  •  Not every seed treatment is available in every seed brand. Many seed companies offer only one choice of a nematode-protectant seed treatment.
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Iowa State University Experts

Greg Tylka | Nematologist

Iowa State University

515-294-3021