Golfdom • June 2022 • Strong rootzones a last line of defense

Experts advise that strong roots could be the difference between nuisance and disaster

Nematodes and their effects on turfgrass are springing up in areas that used to be largely free from infestation, an outcome fueled by warm weather stretching into the latter parts of the year, according to industry experts.

Also known as roundworms, nematodes are among the most abundant animals on Earth. They can build populations as parasites in animals and plants or as free-living forms in soil, freshwater and marine environments. They’ve also been known to make themselves at home in vinegar, beer malts and water- filled cracks deep within the ground.

When symptoms of infestation begin to show on golf courses and other turfgrass areas, it’s usually well after nematodes began wreaking havoc on underground roots.

Keeping those rootzones healthy is invaluable in combating nematode problems and can often act as superintendents’ last line of defense, says Joe Roberts, Ph.D., assistant professor, Clemson University.

“With nematode damage, it is associated with the nematode numbers, but there’s also a cor relat ion with plant stress,” he says. “With nematodes, they’re feeding on the roots, and if there’s damage to the root system already present, that stress is going to make it easier for them to cause the damage. In drought conditions, where a root system has been fed on and is drastically compromised, those plants aren’t going to be able to withstand the drought conditions when compared to an area with no (nematode) problem.”

A strong rootzone pathogen protection program is part of any successful and long-lasting nematode treatment regiment, Roberts adds.

“Kabuto, as a fungicide, is going to help with some of those diseases we see in accordance with nematodes,” he says. “Particularly some of the diseases we’re seeing in bermudagrass right now like spring dead spot, we do see some relationships with nematode feeding. That goes for cool- and warm-season turf. Having a well-designed fungicide program to make sure you’re preventing those pathogens from impacting the root means those roots are going to hold up much better with nematode feeding.”

Nematodes were first identified in 1758, and there are around 25,000 known species. However, in particular, two stand out to experts when it comes to an infestation of U.S. turfgrass areas.

The sting nematode seen traditionally throughout Florida and the Carolina coasts manages to stay relatively strong year-round, with its peak occurring in the fall and winter. At the same time, root knot nematode populations can show up essentially anywhere in the country with its peak season lining up with summer and warmer months, says William Crow, Ph. D., landscape nematologist at the University of Florida.

“Warmer conditions and the warmer season grasses are heading further north, and they’re bringing the nematodes along with them,” he says. “They’re moving around a lot compared to what we’re used to seeing. Nematodes have a great deal of interaction with fungi, so, typically, we get much better turf response when there’s nematicides and fungicides working in combination, not just one or the other.”

Roberts says he and colleagues are still working to determine whether nematode feeding can lead directly to pathogens that negatively affect turfgrass.

“We’re trying to design research to test some of these hypotheses and sort out these correlations that we’re seeing with the high nematode numbers and diseases that we’re seeing,” he says. “We’re not sure if it’s just a lack of vigor with the root systems or the actual feeding of the nematodes creating an infection. Again, if you’re in an environment where both fungal diseases and nematodes are an issue, having a robust fungicide program is going to go a long way toward promoting turfgrass survival. You’re still going to have to go back in and eliminate the nematode issues, as well.”

Crow said a strong root system can sometimes overwhelm nematode infestations before they become a problem.

“A more competitive root system may be able to outcompete these nematode populations, in certain cases,” he says. “The sting nematodes tends to do most of their reproduction in the spring and a little more in the fall, so that’s when it’s best to target your management for. With root knot nematodes, you’re typically applying treatments around May, June, July and August.”

According to Encyclopedia Britannica, 35 nematode species have been identified in human body infestation, but most live in the top 15 centimeters of soil.

The most famous species, Caenorhabditis elegans, is found in compost and was the first organism to have its entire genome sequenced. It made headlines in 2003 when specimens were found to have survived the Columbia space shuttle disaster and remains the only organism to have its neuronal wiring diagram completed.

Nematodes are also essential in the nitrogen cycle and for regulating the decomposition of organic matter.

Populations are usually concentrated near their prey groups. Bacterial-feeders perpetuate near roots where bacteria congregate, fungal-feeders are near fungal biomass, and root-feeders are concentrated around roots of stressed or susceptible plants. Predatory nematodes are more likely to be abundant in soils where other nematode species are already present.

Because of their size, nematodes tend to be more common in coarser-textured soils, according to the U.S. Department of Agriculture.

Roberts says that taking soil samples and other proactive measures are arguably just as important in combating nematode damage as treatment once symptoms arise.

“To really identify the problem you’re dealing with, you have to sample,” he says. “There can’t be a lack of sampling. You may have an area that has a potential high population of nematodes but you have to identify what species you’re working with, because they can impact grasses in different ways. Knowing the nematode population you’re dealing with is a key first step because we have certain nematicides and products available to combat them, but sampling is going to do nothing but make you better prepared to set up a defense plan.”

Echoing Roberts’ sentiments, Crow adds that strong rootzones can be the difference between disaster and a short-term nuisance.

“If I have 25 sting nematodes and a really good root system, I’m not going to be that worried about it,” he says. “If I have a compromised root system, 25 sting nematodes are enough to keep any roots from ever developing again. The (nematode) counts need to be taken into context with the overall root health, always. Otherwise, numbers can lack a lot of the meaning they need.”

Crow urges turfgrass supervisors to be aware of which pest management products also act as fungicides and to plan their treatments accordingly.

“Some of your new nematicides that have come out are also SDHI (succinate dehydrogenase inhibitor) fungicides as well as nematicides,” he says. “You need to be aware of that with your fungicide planning. Others don’t have fungicide activity, and they don’t have the SDHI chemistry. You have to be aware of all those things if you want to stay on top of any problem.”