Nematodes in Florida Lawns: The Pest You Cannot See

If a lawn in Central Florida is thin, weak, and slow to recover no matter what goes on it, and every obvious cause has been ruled out, nematodes belong on the list. They are microscopic roundworms that live in the soil and feed on grass roots. Florida's deep sandy soils suit them better than almost anywhere in the country, and because nobody can see them, they get blamed on everything else.

What nematode damage looks like

• Irregular patches of thin, weak, off-color grass that do not have a defined edge.
• Grass that wilts quickly in dry weather even when the rest of the lawn is fine, because the damaged roots cannot take up water.
• Poor response to fertilizer and water. The lawn is being fed and watered but cannot use it.
• Short, stubby, sometimes knotted or darkened roots when a plug is pulled. The root system is a fraction of what it should be.
• Weeds moving into the thin areas, because the grass cannot compete.
• Symptoms worst in the hottest, driest periods and in the sandiest parts of the lawn.

It resembles drought, take-all root rot, and grub damage, and it can coexist with any of them. What distinguishes it is the pattern: damage concentrated in sandy, sunny areas, roots stunted rather than rotten black, and no insects to be found.

How it is confirmed

Nematodes are confirmed by a soil sample sent to a lab that counts them. It is the only reliable way, and it matters because the management is expensive enough that guessing is not a good idea. Samples are taken from the edge of damaged areas, where the population is active, not from the dead center. The lab reports which species are present and roughly at what level, and that decides whether nematodes are the main problem or a minor contributor.

Why there is no easy spray

The products that used to control lawn nematodes cheaply are no longer available to homeowners, and the ones that exist for professional use are limited. Management is mostly about making the lawn strong enough to live with a nematode population rather than eliminating it.

What actually helps

• Raise the mowing height. More leaf means more root, and a bigger root system tolerates more feeding damage.
• Water deeply and infrequently. A damaged root system in dry sand fails fast; a deeper root zone gives it a chance.
• Add organic matter. Sandy soil with almost no organic matter is nematode heaven. Topdressing with compost over time improves water holding and supports the soil life that competes with nematodes.
• Feed carefully. Frequent light feeding rather than heavy doses, with attention to potassium and micronutrients.
• Consider the grass. Some grasses and cultivars tolerate nematodes better than others. On a lawn with a confirmed severe population, choosing the right grass at re-sod time matters more than any product.

Nematodes and new sod

Laying new sod on a lawn with a heavy nematode population without changing anything else usually produces a lawn that looks good for a season and then declines exactly as the old one did. If the sample confirms a severe population, the re-sod plan should include organic matter worked into the soil, a tolerant grass, correct irrigation from day one and a feeding program that supports roots. Our guide to new sod care covers the establishment period, which is when a nematode-prone site is most vulnerable.

When to call

If a lawn has been thin and weak for more than a season and nothing has worked, we will pull plugs, look at the roots, and arrange a lab sample if the pattern points to nematodes. Request a visit and we will tell you what we find, or see our lawn restoration services if the lawn is past saving.