By Jamal Faghihi and Virginia Ferris
Soybean Cyst Nematode (SCN) has been, and continues to be, a problem in Indiana soybeans. However, this time of the year those cysts are no longer visible on mature plant roots but they are residing in the soil. They can be extracted at our nematology lab from the soil samples submitted by growers to reveal the severity of the problem.
We have been warning growers that the field populations of SCN in Indiana are changing in ways that render the most common source of resistance to SCN (PI88788) less effective. Other researchers in the region have reported similar trends. We have also reported that symptoms of the Sudden Death Syndrome (SDS) in many of the SCN infested fields are more severe when PI88788 resistance is no longer effective. Even though SDS symptoms are not caused by the SCN, the SDS severity is magnified when a resistance-breaking population of SCN is present in the soil.
We continue to emphasize the importance of soil tests as the only accurate way to know whether the numbers of SCN are changing and whether a resistant variety is still effective. We have to emphasize that genetic shifts in SCN populations are gradual, and growers should not wait for obvious yield losses before determining that a change in the SCN population has occurred. If genetic determination (HG-type or race test) has been performed for a field population in the past, you might want to repeat the test after about four soybean crops to measure any possible changes. If no genetic profile exists for a field, one must be established so future comparisons are possible. In other words, simply planting SCN varieties said to be resistant is no longer an effective solution to the SCN problem; and areas with high levels of both SDS and SCN need to managed simultaneously. The management of this highly adaptable nematode pest is an ongoing and dynamic situation that requires constant vigilance.
The best way to manage SCN over the years is to monitor your populations by sampling each field at least every four years. In fields with a history of SCN and SDS, growers should select varieties that have resistance to both the disease and nematode. You can sample the soil anytime of the year and get an accurate understanding of the cyst population. Now is the best time to sample for SCN. This is a very crucial step in SCN management and should not be neglected. We provide this service to soybean growers at the cost of $10/sample. For more information on how to sample and where to submit samples you may visit our Nematology website: https://extension.entm.purdue.edu/nematology/.
If you have any questions about plant parasitic nematodes, you can contact Jamal Faghihi at 765-494-5901 or send an email to [email protected]. Soil samples for nematode analysis can be sent to: Nematology Laboratory, Purdue University, Department of Entomology, Smith Hall, 901 W. State Street, West Lafayette, IN 47907-2089.