September 15, 2005
From: The Saginaw News, 13 Sep 2005 [edited]
<http://www.mlive.com/news/sanews/index.ssf?/base/news-16/1126621333107190.xml&coll=9>

Soybean cyst nematodes [SCN] are almost invisible without magnification, says George W. Bird -- but if left unchecked, they can destroy soybean farms. The SCN is a small roundworm that attacks the roots of soybeans, said Bird, a professor and nematologist with the Department of Entomology at Michigan State University Extension in East Lansing.

SCN, discovered in Japan in 1934, arrived in North Carolina in 1954. It traveled the Mississippi River to soybean country, where it flourished. The worm appeared in Michigan in Gratiot County in 1987.

SCN has now reached 39 counties in the state, which comprise more than half of the state's soybean crop, Bird said. Once present in the soil, SCN can never be eliminated. However, farmers can manage them.
Losses can range from 5 bushels an acre to the entire crop.

Each nematode can contain about 250 eggs. When they drop off, they can remain viable in the soil for up to 12 years in the absence of a host. Growers can mistake plant damage for nutrient deficiencies, drought stress, herbicide injury, or other plant diseases.

The 1st symptoms of nematode injury in the field are circular or oval areas of stunted, yellowed plants that vary in size, often showing a sharp dividing line between stunted and healthy plants, Bird said.

Scientists have tried to naturally develop SCN-resistant seeds. Bird spoke about nematodes and resistant seeds to about 30 growers and seed company representatives at the farms of Greg Mahoney in St.
Charles Township and Jon E. Oakes in Albee Township. Mark Seamon, MSU Extension agriculture agent for Saginaw County, helped coordinate the event.

In the Oakes plot, plants from resistant seeds fared much better than those from nonresistant seeds. Nematode-resistant varieties generally have 1 of 3 sources of resistance -- Peking, PI 88788 or PI 437654.
Historically, most varieties are derived from PI 88788.

In the Albee Township trials, 25 of 45 varieties were PI 88788, a "plant introduction" number the national United States Department of Agriculture designated to the variety. However, many seed companies used the PI 88788 resistance series -- a breeding line -- in a host of varieties, so no 2 were the same. The lowest counts were Pioneer's 91M80, Dyna Gro's 3221, Asgrow's AG2405, Lathum Seeds' E2611 and Midwest seeds' GR2831 -- all of which were free of SCN.

The most important factors in fighting infestation are good rotation and increasing soil organic matter, Bird said. Manure, if available, pays off well.

[Byline: Dean Bohn]

--
ProMED-mail
<promed@promedmail.org>

[_Heterodera glycines_, the soybean cyst nematode [SCN] is a major limiting factor in Michigan soybean production. First detected in Michigan in 1987, it is known to exist in almost all of Michigan's major soybean-producing counties. SCN infestations can result in poor stands, stunted plants, yellow foliage and low soybean yields. Losses can range from 5 percent to 90 percent of the yield potential.
Michigan soybean growers need to have a well-developed strategy to avoid SCN problems or to minimize impacts if SCN is already present.

It is a problem for soybean producers as well as a regulatory concern for growers wishing to export seed or plant material to other states or countries, many of which will not accept seed or plant material unless it is certified SCN-free. It is important that growers using land that has been previously planted to soybeans have their fields sampled routinely if they wish to export seed or plant material.

SCN has 3 major life stages: egg, juvenile, and adult. Juvenile stages feed on roots as they continue to develop into either adult males or females. Affected plants express above-ground symptoms such as plant stunting and yellowing. SCN females can be observed on the root systems of soybeans around 45 days after planting. They are small white spheres about the size of the head of a pin and are found attached to the roots of the host plant. As the females mature, they turn brown and become a protective cyst for their eggs that can remain viable in the soil for many years. Each cyst may contain up to several hundred eggs that will eventually hatch when a suitable host is present. SCN hosts are mainly legumes such as soybeans, dry beans, and snap beans but it has also been known to survive on some winter annual weed species.

Monitoring for SCN is an essential part of nematode management. All fields in Michigan should be routinely sampled for nematodes, preferably every fall before soybeans are planted. Early detection is critical to avoid drastic yield losses and high population densities of SCN. Sampling for SCN and other plant-parasitic nematodes is described in Michigan State University [MSU] AG Facts Bulletin E-2199, Detecting and Avoiding Nematode Problems. Samples consisting of roots, soil or both can be submitted to Diagnostic Services at MSU for nematode analyses.

Lateral movement of SCN is slow, about an inch a year on its own. However, SCN can be transported over long distances in soil associated with crop transplants (e.g., tomato, strawberry, ornamentals), on machinery, animals, and with seed. Movement of soil should be minimized. Fields without SCN should always be worked and harvested before infested fields. To minimize the spread of SCN, equipment should always be washed free of soil after working in SCN-infested fields.

Reduction of SCN is the strategy used for minimizing risks in SCN-fields. Once a field is infested with SCN it is virtually impossible to eradicate it. If SCN is present in a field, the objective in most situations is to reduce the population density. This can be achieved by growing non-host crops, maintaining good weed management, and incorporating SCN-resistant soybean varieties into cropping schemes. Currently, there are a very limited number of nematicides registered for control of SCN, and the economics of nematicide use for control of SCN in Michigan have not been justified.

Recommendations for SCN management will vary depending on population densities and the production needs of the grower. When samples are submitted to Diagnostic Services at MSU, a nematode diagnostician will provide recommendations to growers to assist them in implementing appropriate SCN management strategies. Apparently no SCN has been detected in the Upper Peninsula region of the state as of May 2004.

Information on SCN diagnostics can be obtained at <http://www.pestid.msu.edu/>

Links:
<http://muextension.missouri.edu/explore/agguides/crops/g04450.htm>
<http://web1.msue.msu.edu/msue/imp/mods1/fact9702.html>
<http://www.inspection.gc.ca/english/sci/surv/data/hetglye.shtml>
<http://www.apsnet.org/pd/pdfs/1999/1112-01R.pdf>
- Mod.DH]

[see also in the archive:
Sudden death syndrome, soybean - USA (KY) 20050811.2350 Quarantine pests, new data - EPPO 20050523.1418
2004
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Soybean cyst nematode - USA (ND) 20041101.2950
2003
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Sudden death syndrome, soybean - USA (MN) 20030328.0776 Soybean cyst nematode - USA (Arkansas) 20030709.1678 Plant pests, new data, EPPO (04) 20030915.2336
2002
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Heterodera glycines, soybean - Europe: alert 20020802.4914]