Information about the SCN Female Index

SCN Profit Checker: Information about the SCN Female Index

The SCN Profit Checker tool uses several pieces of information to estimate the yield and profit impact of soybean cyst nematode (SCN) in a farmer’s field. One of those inputs is the SCN female index of the SCN population index on PI 88788, a soybean breeding line used in about 95% of SCN-resistant soybean varieties.

To obtain a female index percentage, an HG type test must be done. HG stands for Heterodera glycines, the scientific name for SCN. The test indicates the type of SCN population in the field and provides a female index for PI 88788 as well as six other breeding lines used as HG type test indicator lines. If the female index is below 10%, it signals the SCN resistance source being used is still effective. Conversely, the higher the female index, the greater the yield and profit risk posed by SCN. 

States that provide HG type tests:

If you have not had an HG type test done, a default female index for PI 88788 was not provided for your state, or you question the default female index value for your state, here are things to consider when using the SCN Profit Checker:

  1. If a default female index value on PI 88788 for your state is not available and SCN-resistant soybean varieties have not been grown in the field for a decade or more, a reasonable female index value to use would be a whole number between 0 and 10.
  1. If a default female index value for PI 88788 in your state is not available and SCN-resistant soybean varieties have been grown in the field for numerous (six or more) soybean crops, we strongly suggest getting an HG type test done to obtain a female index of the SCN population on PI 88788.
  1. A default value of a female index on PI 88788 for a state is an educated guess based on limited information. If you believe the female index of the SCN population on PI 88788 in your field is substantially different than the default value suggested for your state, you should use a value you think is realistic. 
  1. The calculator is based on relationships between soil and environmental conditions, SCN population densities and levels of reproduction on soybean varieties possessing PI 88788 SCN resistance, and yield data from 35,000 intensively sampled soybean research plots over the past two decades in Iowa. The calculator should provide a reasonable estimate of the effect of SCN on soybean yields (in percentage yield suppression) in other states. However, local soil and weather conditions significantly influence the effects of SCN on soybean yields. Consequently, the output of the tool should be considered only an estimate of the possible effect of SCN on soybean yields in your field.

Learn more about actively managing SCN to protect soybean yields.