As the 2019 soybean crop nears maturity, Tennessee growers should look for signs of nematode damage. If they see symptoms, they may want to take samples before harvest to assess population density.
After harvest, producers should definitely sample for nematodes, says University of Tennessee Institute of Agriculture associate professor and Extension specialist Dr. Heather Kelly.
From samples collected last year, “we found a lot of nematodes,” says Kelly, who works out of the West Tennessee Ag Research and Education Center in Jackson.
Based on just under 200 samples from Tennessee and western Kentucky, surveys noted 42 percent had soybean cyst nematode populations. “In sampled counties, 85 percent, all but three, had soybean cyst nematodes. In almost any county with more than one field sampled, we found nematodes,” Kelly says.
“They are out there. Most samples indicated low numbers, but some pushed into the moderate or high range. We’re still in a good position to manage nematodes without significant yield loss.”
Kelly emphasizes the importance of sampling in a UTIA publication, What’s your type: (https://bit.ly/2ZdkJHW).
“Typical yield loss with severe symptoms (yellowing leaves and stunting) can be 50 percent or more based on the difference between growing a SCN susceptible variety and SCN resistant variety. Even with no symptoms, one can expect typical yield loss of 10 percent.
“So, when it comes to planting soybean in an SCN infested field, it should be a no brainer decision to plant a resistant variety. The bargain of the century is that the seed of a resistant variety doesn’t cost any more than the seed of a susceptible variety – it’s free.
“On top of getting the yield benefit from a resistant variety, there’s a second payment in the nematode control that it will provide.”
Kelly says soil labs test to determine SCN HG Type (the new way to say race of SCN) in the lab show reproduction on some resistant varieties.
“We try to type HG (Heterodera glycines) to identify the virulence of populations (what use to be called the race). We’re measuring how well it reproduces on resistant sources. We have found populations that can reproduce on indicator lines with the main source of resistance, that’s the resistance that 90 to 95 percent of all commercial varieties contain. Reproduction is not as high as on fully susceptible varieties, though.”
Breeders and researchers are looking for more resistance to breed into soy cultivars, she adds.
Tests are free
Another reason to sample for nematodes is that the tests are free.
“SCN testing has and will continue to be free to Tennessee farmers due to the state board support (Tennessee Soybean Promotion Board) and to increased support from USB (United Soybean Board),” Kelly says.
“Also, this year, with additional TSPB and USB support, we are screening for over 12 pathogenic nematodes for free, as well as HG Type testing (old race test) of SCN for free (around a $150 test otherwise). In 2020 will go back to only SCN free.”
Kelly says soybean growers also get free testing for charcoal rot.
She recommends that producers with SCN populations rotate with corn and monitor populations to determine if they need nematicide seed treatments.
Sampling for nematode populations requires a technique different from pulling nutrient samples. Timing is also important.
Kelly says it’s okay to sample before harvest, especially if symptoms are apparent. “It’s easier to get into the field after harvest. Sample before first frost, before nematodes move deeper into soil profile.
Sample in rootzone
“Sample in the rootzone, not between rows. Sample at a 45-degree angle to target the rootzone. Provide 1 quart of soil with each sample.” (See https://bit.ly/33WIVNs)
Sampling was delayed last year. “We had a wet fall and sampled into December. We couldn’t get in fields.”
She adds that sampling after a rain is good but not “when soppy wet. We want to get 6 inches to 10 inches deep to pull nematode samples.”
The point, she adds, is to know what’s in the field, determine species, population density, and HG Type. With that data, producers have enough information to devise a management strategy and reduce yield losses.