While superintendents prepare for diseases like dollar spot or Pythium root rot, nematodes often go unnoticed as they making meals out of the vulnerable roots of turf recovering after winter. When turf starts underperforming all other possibilities are checked off, says Richard Buckley, director of the plant diagnostic lab and nematode detection service at Rutgers.
“Usually with nematodes, it’s not uncommon for them to be the last thing the superintendents think about when the grass isn’t performing well,” he says. “They’ve got dry spots they have to hand water a lot more, or poor nutrient uptake.”
Affected turf starts to thin and yellow in areas that otherwise seem healthy, and even when fertilizer is applied, the turf doesn’t respond. “Very often in those situations, when they’ve exhausted every other possibility, that’s when the sampling happens, and then maybe they count nematodes,” Buckley says. “At that point, you’re in a curative or reactionary mode, and there’s not a lot you can do until you recover some root biomass.”
Instead, it pays to be proactive, starting with regular sampling once temperatures start to warm up for the season, says Dr. Billy Crow, landscape nematologist for the University of Florida. Though each kind of nematode is different, most aren’t too active below 50 degrees.
“Then, from soil temperatures of about 50-80 degrees, they’re going to be more active,” he says. Once temperatures move past about 80 degrees, nematode activity should fall back again.
The length and intensity of the winter plays a part in nematode activity as well, as a long, difficult winter potentially meaning fewer nematodes than a milder winter, he says.
If there’s been a history of nematode issues on a course, a superintendent should sample occasionally, possibly about once each year, says Crow. For courses without a history of heavy nematode pressure, it can be helpful to track totals, but less necessary to do an annual check-in. With or without, if turf is showing root loss without a direct cause, that’s a signal that nematodes might be the culprit.
If superintendents have never made an accurate count of nematodes before, it’s a good way to establish a baseline, says Dr. Lane Tredway, Syngenta senior technical representative. “It’s the first step, and really one of the most important,” he says.
Buckley prefers sampling before the season starts, as the turf is growing most vigorously and the nematode counts will be highest. “I like to know what you have coming out of winter,” he says. “Then you can use the nematicide that’s most effective. You can knock the stress off the grass, and it’s one thing you can put to bed before you go into the heat of the summer.”
Getting a head start on nematodes might help control turf stress later in the season with a more proactive approach, says Tredway.
“You used to be able to wait until the nematodes got out of control, then go throw out the Nemacur and walk away for a year,” he says. “Those days are gone. To me, treating a nematode now is a lot like managing a fungal disease. You want to be preventive. You want to have a program that controls them before they get out of control.”
Don’t rely on eyesight to see nematode populations on the turf itself. Nematodes won’t be visible on the turf’s roots, at least without a powerful hand lens or a microscope, says Crow.
“Samples are the only way you’ll really know you’ve got an issue. You have to get those to a lab,” he says. “The biggest thing that sampling is going to do for you is let you know what kind of nematodes you’re dealing with.”
When taking samples for analysis, don’t pull only from a single area in affected turf, and try to avoid just taking a cup cutter, Buckley says.
“I had a guy send me 10 cup cutters from a single green, and we did every sample individually. The variability from plug to plug was remarkable,” he says. “Literally from samples two feet apart, one will be well above threshold, the other won’t.”
Using plugs, if a superintendent sent samples to Buckley’s and other labs, they’re likely to come back with varied counts, he says.
Buckley recommends using a 1-inch soil probe and taking about 25 cores from around the affected area and collecting them in a bucket and using the composite for testing instead.
“If you have a composite, [results from different labs] should all be relatively similar. We all came out of the same bucket, so there’s less of a margin of error,” he says.
Superintendents can focus on problem greens or send samples from around the course if they’re looking for a broader baseline to start with, says Buckley.
“Nematodes on a golf course are going to be present across the entire property, really,” Tredway says. “But you can have hot spots where the populations are particularly high. You’re going to see symptoms of the issue where there are other stresses being imposed on the turf, whether that’s drought, shade or traffic.”
It’s just a number
The results will give a superintendent a rough idea of whether particular nematode populations are potentially causing a problem on the course, says Tredway. Each population total can be compared to threshold totals, established for a course’s particular region and turf species. But those numbers aren’t a definitive ruling on whether nematodes are to blame for turf damage. “Comparing to the threshold really isn’t the final answer for a lot of reasons,” he says.
One major reason is that the thresholds only consider individual nematodes, but in most cases, in reality, “you’ve got a combination of four or five or six different nematodes all present at the same time,” Tredway adds. “If all four of them are below threshold values, they could still be acting together to cause a significant issue.”
Buckley uses thresholds from “The Turfgrass Disease Handbook” by Houston Couch because they have peer review behind them.
“If you search for nematode thresholds, you’ll find that everyone’s got different numbers,” he says. “If you’re in the northern climate, my numbers are probably too low. If you’re in the southern climate, they’re probably too high. But I would take all the thresholds and treatment recommendations with a grain of salt. They’re guidelines.”
Even with high numbers of nematodes, they might not be actually doing damage to the turf itself, says Crow.
“One thing I’ve been trying to get people to focus on, is they get so caught up in nematode counts,” he says. “You’re not trying to manage nematode numbers. You manage the health of your grass. That should really be your focus. You want to take samples to get an idea of what you’re dealing with, but guys get obsessed with these counts.”
If a superintendent has a high lance nematode count, but the turf looks healthy and the roots look strong, those nematodes aren’t something to worry about right now, Crow says. Once the turf starts fading, then it might be time to consider those high counts.
“You’re not going to kill all these nematodes,” he says. “They’re a component, but they’re not the whole story.”
Once nematodes are identified, superintendents should do everything possible culturally to help turf rebuild root biomass.
“Always the first thing we recommend is changes to the culture: Raise your height of cut, do whatever you can to grow new roots. Fertilize, water more,” Buckley says. “Which, all this may be contrary to what you want to do to maintain playability. In some cases, if you do that and become permanently proactive that way, that might be all you need to do.
“I always tell guys to look in the mirror and ask themselves, ‘What do my clients want from this golf turf?’ If it doesn’t have to Stimp well every day, then what are you doing? Find your sweet spot with your clientele, and maybe that’s all it takes.”
As a superintendent gets a nematicide program started, look for products that cover the types of nematodes that seem to be the most prevalent on the turf, says Buckley. He looks to Bayer’s Indemnify, Syngenta’s Divanem or Quali-Pro’s Nimitz Pro G. For each, the label’s recommendations are for preventive applications, so he recommends getting a count in spring and then using the products according to the label.
Though there aren’t any cases of true resistance in root-feeding nematodes, the possibility definitely exists, says Tredway.
“For example, intestinal worms in animals: Those are nematodes. And they’re known to become resistant to dewormers that are used in agriculture and in companion animals as well,” he says. “That’s another great reason to use a program approach incorporating multiple products during the season to hopefully prevent or at least delay resistance.”