SCN still top pest in soybeans

Every summer we talk about management of soybean aphid and leaf diseases, yet soybean cyst nematode is still the single most damaging pest affecting soybean in Iowa. And yes, we have SCN in northeast Iowa. I’ve been in many fields with stunted plants and cysts present on the roots.

SCN still top pest in soybeans

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Every summer we talk about management of soybean aphid and leaf diseases, yet soybean cyst nematode is still the single most damaging pest affecting soybean in Iowa. And yes, we have SCN in northeast Iowa. I’ve been in many fields with stunted plants and cysts present on the roots.

The main problem with this pest is farmers will suffer declining yields for several years without knowing they even have SCN, because aboveground symptoms don’t show until the pest populations reach severe levels. To maximize yield potential, practices to manage SCN should be implemented when SCN populations in fields are still at low levels.

What to look for

Late July through August is the most common period when areas of soybean fields may show stunting and yellowing due to feeding by this tiny, microscopic worm. A field diagnosis is possible at this time by digging roots and looking for the small, white or yellow SCN female cysts on the roots. The nematodes are inside these cysts, which attach to the roots.

The SCN female cysts are small, about the size of a period at the end of a sentence on a printed page. SCN cysts are considerably smaller and lighter in color than the tan or root-colored nitrogen-fixing nodules that are present on soybean roots.

Take care digging up the plants. The cysts are lightly attached to smaller, newer roots located deeper in the soil and farther laterally from the stem of the plant. To check soybean roots for SCN females, dig roots using a spade, and then gently crumble away or shake off the soil to expose the roots for close observation. The SCN cysts are visible to the unaided eye, but a magnifying glass or hand lens might help.

For an infested field identified mid-season, there is nothing that can be done to manage a current SCN pest problem. But it is imperative to properly diagnose fields this year so management strategies can be implemented for next year’s crop. Specific management recommendations are heavily dependent on the SCN population levels found in the field. Getting a reading of the SCN population present in each field can only be done by collecting a representative soil sample.

How and where to sample

Soil samples can be collected from suspect areas of fields at any time of the season, including after harvest, and sent to a qualified laboratory for testing for SCN cysts or eggs. Soil samples should consist of 15 or more 6- to 8-inch-deep soil cores collected from no more than 20 acres.

The Iowa State University Plant Disease Clinic offers this testing service, as do several private soil-testing laboratories. The ISU sample submission form is available at your county Extension office and online at store.extension.iastate.edu/Product/Plant-Nematode-Sample-Submission-Form.

If you are scouting a field that has never been checked for SCN, consider that SCN can be in the soil in a field for many years without the tops of the plants becoming yellow or stunted. For this reason, it is a good idea to include healthy-looking plants in your scouting, root checking and soil sampling.

Need more information?

For more information about SCN, how to properly diagnose infestations and how to implement a management plan, contact your county Extension office for printed publications, or visit www.soybeancyst.info.

Lang is an ISU Extension field agronomist at Decorah in northeast Iowa. Contact him at [email protected]

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ROOT CHECK: The small white “dots” attached to the thinner roots are SCN cysts. The larger, round and tan structures are soybean nodules that produce nitrogen. The nitrogen-fixing nodules are often confused with cysts.

This article published in the August, 2014 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2014.

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