In Arkansas, three soybean nematodes cause problems: soybean cyst, root-knot, and reniform. “Normally, we see problems with soybean cyst and root-knot in our regular rotations,” says Scott Monfort, Arkansas Extension plant pathologist.
“Soybean cyst nematodes typically show up more in fields where soybean has been in consistent rotation with other crops.”
Root-knot is “spotty in different places” depending on rotations employed. “It has nailed some fields rather severely where we had large acreage of monoculture cotton going into soybeans. Many farmers were coming out of cotton systems where root-knot has been awful. In those situations, when you go into soybeans, the nematode problems are even more severe because soybeans are more susceptible and can’t take the damage as well as cotton can.”
Some farmers saw “dramatic problems in fields where the nematodes were actually killing the soybean plants,” says Monfort. Even from an airplane the damage “was very evident.”
Researchers in the state had already ratcheted up their studies of nematodes in soybeans. But when the current situation developed, “root-knot came to the forefront and proved to cause much more damage than the other two nematodes. Soybeans on cotton ground really took a hit from root-knot.”
At that point, Monfort and colleagues began trials looking at everything available for controlling nematodes in soybeans. Also, “we wanted to study things that have potential in soybeans but are labeled for other crops. We’re trying to find anything that might work and we can go after a label on in the future.”
This is necessary because, right now, “we’re probably more limited in managing nematodes in soybeans than any other crop. The major nematicide we’ve used for many years, Temik, lost its label on soybeans in 2009. That chemical loss is huge.”
Have any other promising products been identified?
Monfort says they have. The big question is whether or not companies will be able to secure labels for soybeans.
“One of the products is Vydate, which is used in cotton pretty heavily for nematode suppression. Vydate seems to do very well but it depends on the chemical company whether or not we can get an exemption, or label, from the Environmental Protection Agency for soybeans. It would be great to have Vydate available because it’s a relatively low-cost management tool compared to high rates of Temik or Telone.
Chances of getting a label or exemption?
“Right now, they don’t know. We haven’t heard any great news. We’re trying to get the chemical company to really consider this, though. We need options like this and other potential nematicides for when beans drop to $5 or $6 per bushel.”
Researchers have also been checking all the seed treatments available. “Also, we have some biologicals — seed treatments and in-furrow products — coming down the pipeline we’ll look at to see if they have any good activity.”
Some seed treatments don’t work well in severe infestations of root-knot. However, “if you plant moderately resistant varieties with the seed treatments, they look pretty good.
“It just depends on the situation. We have so many problematic fields — some hit severely, some with light-to-moderate root-knot infestation — we have to mix and match the management strategies to exact problems within a field. There’s no prescription that fits all.”
Asked to describe affected fields a bit more, Monfort says in light-to-moderately hit fields, “farmers experience anywhere from 5 to 10 bushels per acre losses. Those fields make 50 bushels, normally.”
In severely hit fields in northeast Arkansas, “we’re seeing 50-plus percent losses from root-knot. In other words, where we made right at 60 bushels with our best treatment (Telone), the untreated check yielded 26 bushels.”
In 2009, Arkansas researchers had “some seven trials dealing with root-knot, two or three cyst fields and one or two reniform. We hope to increase our trial work with reniform and cyst this year.”
The researchers knew that with susceptible soybean varieties in root-knot-infested fields they’d have to add “something stout” like Telone for control. But “we’ve also been looking at the little resistance available — and there are only a few root-knot-resistant varieties available in the maturity groups we grow — in combination with a seed treatment.”
On a susceptible variety that approach would normally provide little control. But such management tied to a resistant variety would provide good control.
“We’re just looking at different scenarios with an eye towards providing recommendations. The first step is to find options for growers — looking at the chemistries labeled for other crops. Growers should know we’re working on this but it’s a slow process.”