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Sign up soon for SCN sampling program: Race 2, SCN spreading in west Tennessee

You're already paying for it through checkoff funds, so you might as well use the service. That what University of Tennessee plant pathologist Melvin Newman says about a sampling program to detect the presence of soybean cyst nematode in west Tennessee soybean fields.

The sampling program is made possible through an ongoing grant from the Tennessee Soybean Promotion Board. The grant covers all costs including labor, four-wheelers and laboratory screening. The sampling will take place this fall after harvest.

Farmers can take soil samples themselves or sign up to have the UT Extension Service do the sampling. If you do it yourself, the samples can be dropped off at a local county Extension office to be sent away for screening. Extension will provide 1-gallon plastic bags. Place a quart of soil in each bag from every 25-acre block.

If you want Extension to do the sampling, you need to provide aerial maps of your farms, circle the fields that need to be sampled and provide your county agent with the maps during the growing season. Be sure to do this well before fall to insure your fields are included.

“Tell the county agent you want to participate in the free sampling program and the county agent will line it up with us,” Newman said. “When it's time to hit the road, we set our own schedule. We don't ask anybody; we just go out and do the sampling.”

The producer should have the results by the last of February or the first of March, according to Newman.

Newman stressed that growers shouldn't base their decision to sample on whether or not they see symptoms of soybean cyst nematode or SCN. “Even a moderate infestation will show undetectable symptoms other than yield less.”

When asked if every soybean producer should get his soybean acreage sampled, Newman said, “Yes. In big, bold letters and underlined. We've been trying to stress this in our winter meetings and agent training sessions.”

About half of west Tennessee soybean fields are now infested with SCN, according to Newman. To manage SCN, farmers can rotate to another crop, plant a resistant variety or go with Temik in-furrow at 5 pounds per acre. “If the level of SCN is well above 100 cysts per pint of soil, and you're not using a resistant variety, it is advisable to go with the Temik,” the pathologist said.

The sampling program has also revealed that about 60 percent of SCN-infested soybean acreage in west Tennessee is race 2 — a race new to the region for which there are no resistant commercial varieties.

The emergence of SCN race 2 is proof positive that planting resistant varieties should not be the only way to manage SCN, Newman stressed.

“When we put any resistant variety out there, there will be some nematodes in the population that will thrive and all the other races will decline. The reason we have so much SCN race 2 is because we've been planting resistant varieties (to races 3 and 14) for so long. Our producers need to rotate to other crops as well as to susceptible varieties to cut down on the pressure.”

The only variety with resistance to SCN race 2 is Anand, a public variety from the breeding program at the University of Missouri. The Group V Anand is not available in a Roundup Ready version.

Newman noted that farmers who have planted Anand, “have upped their yields 10 to 20 bushels per acre. Anand is resistant to several other diseases such as SDS, stem canker and frogeye, so that helps too.”

An example of a good plan for impeding the development of new SCN races would be to go with Anand one year, followed by a year of corn or grain sorghum, and then a year of a susceptible variety, before going back to Anand or corn.

“We could stretch it out for 20 years before we get another race. But if producers plant Anand (or lines developed from it) over and over, it'll be short-term before we have another race.”

Part of the problem with detecting and dealing with SCN is that today's symptoms are masked by better overall management and fertility of the crop, as well as better genetics. “Some of the older soybean farmers will remember the yellowing of the beans we had in race 3,” says Newman. “We hardly see that any more and we don't see much stunting.”

Nonetheless, there is a moderate amount of damage taking place resulting in 5-bushel to 10-bushel decreases in yield, according to Newman. “That's profit skimmed right off the top of your income.”

Newman says university researchers are using the sampling program's two four-wheelers, which are equipped with GPS units, to collect additional research on the development of new races. In the four years of the program, over 100,000 acres have been sampled.


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