By Emily Unglesbee
DTN Staff Reporter
MIAMI (DTN) -- Companies and scientists are looking beyond SCN-resistant soybean varieties for control of the troublesome soybean cyst nematode.
On the second day of the SCN conference in Miami, Florida, this week, much of the sessions were devoted to alternative control options, such as seed-applied nematicide products and cover crops.
That shift in focus is a telling one. The continual use of one single source of genetic resistance (PI 88788) in soybean varieties has eroded that trait's value and future SCN management strategies will have to include new tools, scientists told growers.
According to state surveys of nematode populations, 88% of nematode populations in Illinois have adapted the ability to reproduce on soybean varieties with PI 88788 resistance, as well as 72% of nematode populations in Minnesota, 78% in Missouri, 56% in Iowa, 56% in Indiana, 93% in Tennessee, 55% in Nebraska and 100% in Kentucky.
This situation is the natural result of 97% of SCN-resistant soybean varieties using only the same source of resistance, but many farmers are likely unaware of the problem, noted United Soybean Board farmer-director Thomas Oswald, who farms near Cleghorn, Iowa. "These PI 88788 SCN-resistant varieties have lulled people into a sense of security that is not warranted," he said.
In the meantime, companies have been busy developing microbial nematicide seed treatments, two of which are already on the market. Syngenta sells Clariva Complete beans, which include a nematicide active ingredient in addition to fungicides and a neonicotinoid insecticide. Bayer's ILeVO seed treatment is designed to target the SDS fungus, but it also has activity against the soybean cyst nematode.
At the conference, Syngenta scientist Dale Ireland showed growers company trial results showing a 2.7-bushel-per-acre (bpa) bump from SCN control in Clariva Complete Beans. Bayer scientist Breann Bender displayed company trial results showing ILeVO producing up to a 94% decrease in nematode numbers on treated soybean roots (compared to an untreated check), as well as an 81% decrease in nematode development. No yield results were provided for the ILeVO treated soybeans.
Valent USA presented a third nematicide seed treatment, called Aveo EZ, designed to be added to their Intego Suite soybeans. So far company data shows a modest yield increase of 0.68 bpa from Aveo, which is expected to be registered and available by the fall of 2017.
Some growers in attendance voiced disappointment in the modest yield results of the nematicides. "I don't know what they cost, but I have a feeling they're going to be a hard sell to farmers," said Daryl Cates, a farmer-director with the Illinois Soybean Association, who farms near Columbia, Illinois.
Farmer reluctance to invest in these seed treatments, particularly in the current farm economy, will definitely be a major obstacle, Ireland acknowledged. "Farmers are not adopting nematicide seed treatments, because they simply haven't had to pay for SCN protection for the last two decades," he said. "And because they've never had to spend money on it, it doesn't feel like it's an important disease."
Cover crops are also a growing focus of some SCN researchers, after growers have expressed both interest in using them to control the pest, as well as concern that some species may serve as a host for it.
Krishna Acharya, a Ph.D. plant pathology student from North Dakota State University, presented the results of a study he conducted on 21 cover crop species and their interaction with SCN.
Most of the crops he tested proved to be non-hosts for the soybean cyst nematode, with the exception of Austrian winter pea, field peas, forage peas, crimson clover, hairy vetch and turnips. Researchers did find female SCN on these cover crops' roots, ranging from just one (crimson clover) to 173 (forage peas). However, only forage peas and field peas actually increased the sampled field's starting population of SCN; all the other cover crop species decreased populations.
For more information on the SCN conference and its presenters and topics, see this link: http://bit.ly/….
Emily Unglesbee can be reached at Emily.unglesbee@dtn.com
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