Fall is a perfect time to collect soil samples for testing for soybean cyst nematodes (SCN), according to Iowa State University nematologist Greg Tylka.
"Detecting SCN in fields this fall will allow growers to develop management plans to combat the nematode before next season begins," Tylka says. "If SCN numbers are not too high, SCN-resistant soybean varieties will work great for next year's crop."
Growers can save time and collect one soil sample for both soil fertility and SCN testing if the samples are sent to a laboratory that offers both services, Tylka adds.
Soil samples can be analyzed for SCN by the Iowa State Plant Disease Clinic. The fee is $15 per sample. Forms for submitting soil samples for SCN analysis by the ISU Plant Disease Clinic can be obtained from any county extension office.
SCN is an extremely damaging and widespread pest of soybean in Iowa that is thought to infest up to 75% of the fields statewide, but usually causes no obvious plant symptoms for many years after being introduced to a field. Many SCN-infested fields in Iowa have not been diagnosed.
Soil samples should consist of multiple soil cores collected with a soil probe. Fifteen to 20 soil cores, 6-8 in.s deep, should be collected in a zig-zag pattern from no more than 20 acres, and the cores should be mixed before being placed in a bag for submission. Several samples will need to be taken from large fields.
Harvested fields with corn stalks should be sampled to determine if SCN is present for next year's soybean crop. However, fields in which soybeans were grown in 2004 also can be sampled. "It is most important to sample fields in which soybeans will be planted in 2005 to know whether or not SCN-resistant soybean varieties should be grown," Tylka stresses.
If SCN is discovered in a field this fall, there are many choices of SCN-resistant soybean varieties from which growers can choose for the 2005 growing season. Most soybean seed companies have SCN-resistant soybean varieties, which generally are available with or without herbicide resistance. A listing of the SCN-resistant soybean varieties available for Iowa growers can be obtained or ordered from any county extension office and the most recent version of the list will be sent out in the November 2004 issue of the Iowa Soybean Review magazine.
More information on SCN biology, scouting and management, is available at: www.soybeancyst.info and www.planthealth.info. Results of field-testing of SCN-resistant soybean varieties in fields located throughout Iowa can be found at: www.isuscnvarietytrials.info .