Grub Worms in Florida Lawns: Signs, Damage and Control

Grubs are the larval stage of scarab beetles — June beetles, masked chafers and others — and they live in the soil eating grass roots. In Polk County they are less common than chinch bugs, but when there is a real infestation the damage is dramatic and fast.

The signs

• Irregular brown patches that expand over a few weeks, usually starting in late summer or early fall.
• Turf that lifts like loose carpet. This is the giveaway. Grubs sever the roots, so the sod has nothing holding it down.
• Spongy feel underfoot in the affected area.
• Animals digging. Armadillos, raccoons and birds tearing up the lawn are hunting grubs. In Polk County armadillo damage is often the first thing homeowners notice.
• Grass that does not respond to watering — because there are no roots left to take it up.

The tug test

Go to the edge of a brown patch where damaged turf meets healthy turf. Grab a handful of grass and pull firmly upward.

Healthy turf resists. Grub-damaged turf peels back in a sheet, and underneath you will see white, C-shaped larvae with brown heads and visible legs, typically half an inch to an inch long.

Count what you find in a square foot. A handful of grubs in a healthy lawn is normal and does not need treatment. Six or more per square foot in St. Augustine is where damage becomes likely and treatment is justified.

Grubs versus chinch bugs

These get confused constantly, and the treatments are different, so the distinction matters.

• Chinch bugs damage in full sun, in the hottest, driest part of the lawn, often along driveways and sidewalks. Damage looks like drought stress. Insects are tiny, black-and-white, and found at the soil surface among the blades.
• Grubs damage anywhere, most often in irrigated turf, and the turf lifts freely. Larvae are large, white and below the surface.

If pulling the grass does not lift a mat, you probably do not have a grub problem. Check our Lakeland pest guide for the full comparison.

Timing treatment

Grubs are only vulnerable at certain life stages, which is why poorly timed applications fail.

• Adult beetles fly and lay eggs in late spring and early summer.
• Small, newly hatched grubs in mid to late summer are the easiest to kill — they are near the surface and small enough that a modest dose works.
• Large grubs in fall are much harder to control and doing the most feeding damage.
• In winter they move deeper and treatment is largely wasted.

Preventive products go down before or during the egg-laying window. Curative products go down when you find active young grubs. Applying a preventive product in October, after the damage has appeared, is a common and expensive mistake.

Watering it in

Grub insecticides need to move through the thatch layer to reach the soil where the larvae live. Irrigating after application, typically half an inch, is what carries the product down.

Skipping that step is the most common reason a treatment appears not to work. Similarly, a heavy thatch layer intercepts the product and stops it reaching the root zone — another reason to keep thatch under control.

Repairing the damage

Grub-killed turf does not recover, because the roots are gone. Once the infestation is controlled:

1. Rake out the dead material.
2. Small patches will fill in from the edges if you keep them watered and lightly fed.
3. Larger areas need resodding. Do not lay new sod until the grubs are actually controlled or you will feed them a fresh meal.
4. Follow the 30-day establishment schedule on anything new.

Prevention

A healthy, deeply rooted lawn tolerates a grub population that would wreck a stressed one. Deep infrequent watering builds the root depth that gives turf a buffer. Correct mowing height, sensible fertility and controlled thatch all contribute.

Excessive night lighting also attracts adult beetles to the property, which is a small but real factor worth knowing if you have extensive landscape lighting.

Not sure what is eating your lawn?

Misdiagnosis costs a season. Luxury Lawns USA will identify the actual pest, treat with the right product at the right time, and get the damaged areas back. Call (863) 279-7724 for a free estimate in Lakeland and Polk County.