You cannot see them, you cannot spray for them in any straightforward way, and they are in nearly every sandy lawn between Monticello and the coast. Plant-parasitic nematodes are microscopic roundworms that feed on turf roots, and on the sandy soils south of town they are one of the most common reasons a lawn looks stressed for no visible reason.
What they do
Nematodes feed on root tips and along root surfaces. The grass above ground does not die outright; it just has fewer functioning roots than it should. That shows up as a lawn that wilts faster than its neighbors in dry weather, greens up slowly in spring, responds poorly to fertilizer, and thins gradually in irregular patches, especially in full sun on the sandiest ground. Weeds move into the thin areas because the turf has no vigor to compete.
The species that matter in the Big Bend are sting nematode, which is the most damaging on sand and hits all warm-season grasses, lance nematode, root-knot nematode, and a few others. Sting in particular likes exactly the soil we have south of Monticello: coarse, well-drained sand.
Recognizing the damage
- Irregular patches of thin, off-color turf that look like drought stress but do not respond to water.
- Roots that are short, stubby, dark or swollen when you pull a plug and rinse it, compared with the long white roots on a healthy plug from a good area.
- Worst in the sunniest, sandiest parts of the yard and less bad under shade or on heavier ground.
- No insects visible, no fungal rings or lesions, and fungicide and insecticide applications change nothing.
The look-alikes are ground pearls, which you can find by sifting soil, and plain drought or compaction. Our post on diagnosing lawn problems walks through ruling them out.
Confirming it
The only way to know is a nematode assay. Take soil samples from the edge of damaged areas, where roots are still alive, and from a healthy area for comparison, keep them cool and moist, and send them through your county extension office to the UF/IFAS nematode assay lab. The report gives counts by species and says whether they are above damage thresholds for your grass. Sample in late spring or summer when populations are active; a winter sample can read low.
Chemical options are limited
For home lawns, nematicide options are few and change over time; most of what works is restricted to professional applicators or is not labeled for residential turf. Ask your extension office what is currently labeled before buying anything, and do not assume a product sold for "soil pests" does anything to nematodes. In practice, management on a home lawn is cultural.
Managing a lawn that has them
The goal is to grow more roots than the nematodes eat. Everything below points that way:
- Water deep, less often. Deep roots are less affected than shallow ones. Cycle-and-soak on sand so the water gets down.
- Mow high. More leaf supports more root. Centipede at two inches, St. Augustine at four.
- Feed lightly and often rather than heavily and rarely, with slow-release nitrogen and adequate potassium. Damaged roots cannot take up a big dose and the rest leaches.
- Build organic matter. Compost topdressing after aeration improves water holding and supports the soil life that keeps nematode populations in check. Our topdressing post covers it.
- Do not add stress. Herbicides on stressed turf, scalping, and heavy traffic all hurt a nematode-damaged lawn more than a healthy one.
Choosing a more tolerant grass
No warm-season lawn grass is immune, but tolerance varies. Bahia is the most tolerant of sting nematode, which is one reason it persists on the poorest sandy ground. Some Zoysia and Bermuda cultivars hold up better than others. Centipede and St. Augustine are both susceptible. If you are re-sodding an area that assays high for sting, it is worth asking the sod supplier which cultivars they have seen do well on sandy sites.
Expectations
Nematodes are not eliminated; they are managed. A lawn with a moderate population and good cultural care can look fine. The same lawn with shallow watering and a short cut looks terrible every July. The difference is entirely in the management.
FAQ
Are lawn nematodes harmful to people or pets?
No. They feed only on plant roots.
Can I bring nematodes in with new sod?
Yes, and it is a common way they arrive. Buy from a reputable farm and ask.
Do beneficial nematodes help?
Products sold as beneficial nematodes target insects, not plant-parasitic nematodes. They do not control the ones eating your grass.
Can you manage a lawn like this?
That is most of what a good maintenance plan is: height, water and feeding set for the ground you have.
If your sandy lawn wilts by noon and never fills in, reach out and we'll help get a sample tested and set the program to suit. We maintain lawns on the sandy soils around Wacissa, Crawfordville and across the southern half of the county.