Not just a warm-weather nemesis

Features - Pests & Disease

Permanently losing a venerable control option continues to raise numerous questions about nematodes on golf courses.

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May 1, 2019

Dr. N. Lange | adobe stock

October 6, 2017 marked the start of a new era in nematode control. On that date, the protocol for dealing with nematode issues dramatically changed when an EPA ban on the use of Nemacur took effect. Ever since, superintendents have employed a variety of chemistries to deal with nematode concerns.

At this point, we’d like to dispel two nematode-related myths. Some believe that nematodes are an issue only in warmer climates, but Dr. Axel Elling, a turf specialist for Bayer, says that’s not the case. “Nematodes are a problem all over North America,” he says, “and I would go one step further and say nematodes are a problem worldwide. So, nematodes are not something superintendents should ignore.”

Some have suggested that nematodes are migrating northward in response to warmer temperatures but Dr. Lane Tredway, a field technical manager for Syngenta, says that really isn’t so. “Certainly, nematodes can be moved in soil and in plant material,” he says, “but we don’t tend to move those things long distances, just because of the expense, so most of our soil and turf is distributed more locally.”

Dr. Nathaniel Mitkowski at the University of Rhode Island is one of the nation’s foremost authorities on nematodes. “We have always had the nematodes in the North,” he says, “and we have always had damage. When I was an undergraduate (at the University of Massachusetts under Dr. Robert Wick) in 1994, we were actively counting and studying damaging nematodes in New England, and Wick had been working on it since the mid-1980s.”

One issue that is problematic for turf professionals is that nematode issues are not necessarily easy to identify.

Examples of nematode damage on turf maintained at various heights.

“The symptoms are very nondescript,” Tredway says. “Basically, you end up with turf that has very weak and shallow root growth and as a result of that, the top growth is weak and very prone to a variety of stresses. And so, of course, there are a lot of different issues that can essentially cause those same exact symptoms.”

Those “different issues” might include excessive foot or cart traffic, soil issues or the weather.

Tredway notes that the pressures, real and implied, to produce faster greens, are also contributing to the problem. “We’re putting more stress on our turf, it seems like, year in and year out,” he says, “with lower mowing heights and the ever-increasing demands for fast putting greens.”

Mitkowski believes that warmer temperatures have contributed to an increased nematode presence in a post-Nemacur world.

According to the Northeast Regional Climate Center, which analyzes weather data in 12 states from Maine to Maryland, the mean March temperature in Rhode Island for the whole of the 20th century was 36.1 degrees. Over the last two decades however, the average March temperature in the state was nearly two degrees warmer at 37.8, and over the last 10 years (from 2009 through last year) it increased to 38 degrees. For the entire region, the mean 20th-century March temperature was 33.5 degrees. For the past two decades, the region’s average March temperature was 34.64. Over the last decade, it was 34.8.

“With cooler temperatures, (nematodes) are less aggressive and have fewer generations,” Mitkowski says. “My personal feeling is that while nematodes are becoming a bigger issue on northern turf because of increased temperatures and climate change, we would be much less concerned if we had Nemacur.”

Mitkowski notes nematodes tend to be more aggressive in warmer locales. “Nematodes are creatures of temperature,” he says. “Their rate of feeding and reproductive rate are directly correlated with temperature. The warmer the soil, the more nematodes produced and the more feeding that happens. In northern locations, we have a shorter growing season and a frozen winter, which slows the nematodes down and controls their populations.

Examples of nematode damage on turf maintained at various heights.

“But with climate change, the nematodes will be more successful. Sting nematode cannot survive northern winters, but it is likely to start showing up farther north as the climate warms.”

With Nemacur no longer available, superintendents must utilize other chemistries. Divanem (active ingredient: abamectin), Indemnify (fluopyram), Nimitz Pro G (fluensulfone) and MultiGuard Protect (furfural) are among the nematode control products available to superintendents.

Divanem was first approved for mite and insect control. It was first utilized as a nematicide in 2011 via a local-needs label (under the brand name Avid), then registered in October of 2016 before being introduced at the Golf Industry Show the following February.

Originally developed for mite and insect control, it has proved effective against a broad spectrum of nematodes — including sting, lance and root knot — but has been less effective against Anguina nematodes.

Indemnify was developed as a crop fungicide but interest in its effectiveness as a nematicide picked up in 2013 when it appeared that Nemacur would be banned the next year (the ban was eventually postponed). It was officially introduced as a nematicide in August of 2016 and has proved effective against sting, root-knot, ring, stunt and Anguina pacifica.

Mitkowski offers an overview. “The most effective turf nematicide currently on the market (based on his research and that of others) is Indemnify,” he says. “Unfortunately, Indemnify does not work on all nematodes. It generally provides no control of lance nematodes. That said, it is extremely effective against stunt and sting nematodes, and I have seen it be active against stunt populations for more than 60 days.

“Divanem and Todal (both abamectin) have a very broad spectrum of activity against most nematodes but getting them to the nematodes is sometimes difficult.

Examples of nematode damage on turf maintained at various heights.

“These products are reported to bind to the thatch and positive results can be hit-or-miss. A number of superintendents are using both Indemnify and abamectin and getting good control, but this approach is usually cost prohibitive.

“Other products are also available, namely Nimitz and Multiguard, but our research results using these materials is variable. Sometimes we see positive results and sometimes we don’t see any result. We are never quite sure why the discrepancy. We have yet to see any nematode resistance to any material.

“When Nemacur stopped working, it was typically because the bacteria in the soil was consuming the material so quickly it never makes it to the nematode. That happened occasionally in northern states but was much more common in the South.”

Nemacur was not only extremely effective as a nematicide, but it was cost effective; one application per season would often take care of the problem. Tredway says superintendents must now develop a multi-faceted approach to nematode control, as they do with their fungicide programs.

“They have their own strengths and weakness so, depending on the spectrum of nematicides you have … maybe you incorporate multiple products into a program,” he adds. “I tend to think of nematode management in the same way as disease control, because the products we do have available to us today are just so different.”

If a superintendent suspects they may have a nematode issue, Tredway suggests they first take a good look at their turf. “Observe the symptoms and the distribution of the symptoms across the turf,” he says. “You want to compare the depth and quality of the root systems in affected vs. unaffected areas. And if you see a drastic difference, or any distinct stunting or abnormal growth on the affected roots, then that could be a good sign that you might be dealing with nematode issues.”

Mitkowski notes that nematodes are not necessarily easy to detect. “Nematodes attack roots,” he says, “so anything that resembles root damage could be nematode-induced. Unusually shallow rooting is a common symptom, as is wilt, loss of vigor and being unresponsive to watering and fertilization. Other pathogens also attack roots however, so these symptoms are not exclusive to nematodes.

“If a superintendent suspects nematode damage, they should contact a diagnostic lab to figure out the best way to test. Different labs have different procedures and depending upon the time of year, the lab may not be open. Most labs can get results back to the sender in a day or so and then a management plan can be devised if necessary.”

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