Northern nuisance

at one time nematodes were considered a regional problem. They first became an issue in the Southeast where they thrived in the sandy soil prevalent in the region.

“Some of the more damaging nematodes are found in sandy soil,” says Dr. Billy Crow, a landscape nematologist at the University of Florida who has been researching nematode control options for 15 years. “Down here in Florida we have sand everywhere so nematodes are a problem on greens and tees, and fairways, and roughs, and athletic fields and lawns. Some of the more damaging nematodes, for example, sting nematodes, really have to have a lot of sand to survive. They aren’t going to be a problem in heavy soils but will be in sand-based greens.”

Dr. Nathaniel Mitkowski, who chairs the University of Rhode Island’s Department of Plant Science and Entomology, is seeing increased nematode populations in his section of the country along with attendant turf damage. Changes in weather patterns are one reason why.

“Climate change and increased temperatures are going to have an effect on nematode biology,” Mitkowski says. “Nematodes are going to reproduce more quickly when the temperatures are warmer. With longer seasons they’re going to have more opportunity to attack roots and potentially have more generations.”

And while human activity – such as contaminated sod or maintenance equipment – is responsible for some of the spread of nematodes, he says at the heart of the issue is the prohibition on Nemacur. “People that may have had a (nematode) issue and just dealt with it don’t have the tool to deal with it the way they did,” he says.

Alternatives to Nemacur are coming on line, but none of them are as versatile as Nemacur was, Mitkowski says. “Some are better on some nematodes than others and (more effective) under some conditions than others,” he says.

Turf management practices also contribute to the nematode problem. “We’re constantly lowering mowing heights, which makes nematode problems more severe because the grass is under more stress,” Crow says. “[In Florida] we’re using the ultradwarf Bermudagrasses which tend to be more susceptible (than older strains of Bermuda).”

Modern green complexes, built to USGA specifications have been shown to be more susceptible to nematodes than old-style pushup greens. “USGA-spec greens are an ideal habitat for nematodes,” Crow says. “The move to sand-based greens makes nematodes more of an issue.”

In his part of the country – lower New England and upper Mid-Atlantic – the microscopic, non-segmented round worms are especially problematic on putting greens, Mitkowski says. They feed on root systems any time the ground is not frozen. To compound the matter, nematodes, at least in New England and the Northeast, are most active during the summer when the turf is most stressed. Their presence leads to additional stress, decreased disease resistance, and decreased response to water and fertilizer. In extreme cases, nematodes will kill plants.

“All golf course putting greens have populations of plant-parasitic nematodes,” he says. “But for reasons that are still not well understood, theses nematodes do not always reach problematic levels on every course.”

There are several options for dealing with nematodes. If a club has limited resources, then it may deal with the issue the way it would with something like heat stress. The turf will feel the effects during the summer months and recover in the fall, Mitkowski says. Heavy overseeding, beginning in late August, will be required to replace lost turf.

Raising cutting heights on the greens (to 0.135 inch or higher) and reducing the number of mowings or reducing the number of rounds to reduce foot traffic is another option. The downside is golfers may become frustrated with slower green speeds but the turf will be healthier.

A story on finding “the right balance” in situations of this sort would likely fill this entire magazine.

As far as chemical controls are concerned, Mitkowski says there aren’t as many proven options available for nematodes as there are for other turf issues. “There isn’t a lot out there that’s effective,” he says, “and for the most part what we’ve seen is that superintendents who use other organophosphates for insects will get some pretty good nematode control out of that. If the superintendent makes a Dylox (trichlorfon) application for white grubs or a Dursban (chlorpyrifos) they will likely have success with nematodes because they all affect the same systems.

“Unfortunately, Dursban is currently in registration review. There was supposed to be an announcement in December, and I think they’ve pushed it off so we don’t know what the fate of chlorpyrifos is going to be. Dylox I don’t believe is facing a re-registration concern.”

But Mitkowski is quick to point out that Dursban and Dylox aren’t labeled for nematodes, although there is usually a drop in the nematode population when those chemicals are used to combat other pests. “You can’t really go in and say, ‘I’ve got a nematode problem. I’ve got to drop seven ounces of Dylox on it,’” he says. “That’s an illegal approach. Experimentally yes, we’ve seen it work.”

Crow has seen other products have a positive impact further South. “In costal and southern states we have Curfew, a soil fumigant,” he says, “which works very, very well on sting nematodes. Less so against some of the other ones but it’s like magic on sting nematodes, which is the most damaging one.”

“We have abamectin which is an insecticide that also controls nematodes. There’s a formulation of abamectin called Avid, which is currently labeled in a number of states for nematodes, but just on greens. It doesn’t move in soil very well, but it’s effective against root-knot nematodes because they stay up in the thatch. It’s not as effective against some of the other ones but it works really, really well on root-knot nematodes.

“There should be a new formulation of abamectin coming out this year that we’ve work with. It has a little bit better soil movement than Avid does. So there will be a new abamectin formulation that will have a national label as opposed to the current 24(c) special-local-needs labels, which are state by state.”

Some wonder why no broad-spectrum replacement for Nemacur was in the pipeline. Mitkowski says it’s a matter of cost and return. “The cost of developing any of these materials is incredibly high and the return from golf courses is very low,” he says. “Almost all the products we have in golf turf were originally developed for agricultural purposes because that’s where all the acreage is. Then, after they’ve been successful in that arena, they (make them available) to the turf world.”

Rick Woelfel is a Philadelphia-based writer and frequent GCI contributor.