There is still time this spring to collect soil samples from fields and have the soil tested for presence of soybean cyst nematode. This yield-robbing pest, which feeds on soybean roots, can be especially damaging in years when weather is dry during the growing season. And with below normal supplies of subsoil moisture going into spring this year in Iowa, that's something to think about.
"Soybean cyst nematode has the potential to cause devastating yield losses," says Greg Tylka, Iowa State University Extension nematologist. "Populations in the soil can increase rapidly within a single growing season. And dormant eggs can survive in the soil for more than a decade in infested soils, even in the absence of soybeans."
Although the soybean cyst nematode (SCN) is one of the most persistent and destructive pests of soybean in Iowa and the Midwest, the potential to underestimate the nematode's yield-reducing effects is great because damage from SCN is not readily apparent in the field during growing seasons with adequate to excess moisture. The need to take the threat of SCN seriously was recently reviewed in an ICM News article.
Fortunately, fields can be checked for the presence of SCN in the spring through soil sampling, notes Tylka.
Guidelines for checking fields for SCN this spring—how to collect a good soil sample
Soil cores should be collected from the upper eight inches of soil.
Do not collect samples if the fields are frozen or wet and muddy.
The more soil cores collected and the smaller the area sampled, the more accurate the results will be.
If corn or some other nonhost crop was last grown in the field, it doesn't matter if soil cores are collected in the previous crop row, and it is better to collect soil cores after the previous nonhost crop rows have been destroyed by tillage.
If soybeans were last grown in the field, collect soil cores from under the old crop rows.
If sampling conventionally (not grid sampling), collect 15 to 20 soil cores in a zigzag pattern from no more than 20 acres. The 20-acre parcels of the field do not need to be square or rectangular; samples can be collected from zones according to the agronomic features of the field (figure 1).
If grid sampling: collect one or two extra soil cores from every grid cell sample and combine these extra cores from the number of cells that represent approximately 20 acres.
In fields where SCN has not been discovered, high-risk areas where SCN may be first found include high pH spots, low spots, near fence lines and other places where soil from other fields may have been introduced (figure 2).
Getting soil samples tested for SCN—where to send the samples, what it will cost
Many private soil laboratories in Iowa and throughout the Midwest can process soil samples to determine SCN egg population densities. Also, soil samples can be sent to the Iowa State University for nematode testing. Mail samples to:
Plant and Insect Diagnostic Clinic
327 Bessey Hall
Department of Plant Pathology and Microbiology
Iowa State University
Ames, IA 50011-1020
The current fee for SCN analysis at the ISU clinic is $15 per sample for samples from Iowa. Call the ISU Clinic at 515-294-0581 to check about processing of soil samples from outside Iowa. Samples sent to the clinic should be accompanied by a completed Plant Nematode Sample Submission Form.
More information about SCN: Additional information about the biology, scouting and management of SCN, including many resources relating to SCN-resistant soybean varieties, can be found at www.soybeancyst.info and also at the Plant Health Initiative's website.