How to Get Rid of Grubs in Your Lawn

Texas A&M AgriLife Extension describes white grub damage as irregular patches of weak or dying grass. The turf has lost roots, so it lifts by hand or rolls back like loose carpet. In the top few inches of soil, in the root zone, you should find C-shaped white larvae with a brown head. Sandy soil may put them a little deeper. They do the most damage once they are about 1/2 to 1 inch long. Depending on where you are in Texas, that damage can show from June into October.

Dig before you buy anything. AgriLife says to check several plugs, at least 3 to 4 inches across and about 4 inches deep, including the edge of the weak area. A practical sample is up to one square foot of plugs for every 1,000 square feet of lawn. Finding more than five white grubs per square foot justifies treatment. Some lawns show no damage even with more than that, so a number without symptoms is not an automatic spray, and symptoms without grubs are not grubs.

Take-all patch can look similar and is easy to blame on insects. AgriLife says it shows more in spring and early summer, the roots look rotted, and the dead spots may stick around into summer. If you do not find grubs, stop and reconsider. Chinch bugs are the other summer mix-up on St. Augustine: the grass stays rooted, and the insects are in the thatch, not the soil. Large patch is a cool-season circle, not a carpet you can roll up in August.

Green June beetle larvae are a different animal. AgriLife says they feed mostly on decaying organic matter, crawl on their backs, and leave small mounds. They are common near compost and fruit. Do not treat them with the same plan you use for the June beetle and the southern masked chafer, which are the grubs that actually eat Texas turf roots. Bermuda, zoysia, St. Augustine, and buffalograss are all on the menu for those two.

Most of the turf-feeding grubs in Texas finish a life cycle in one year. Adults, the June beetles and masked chafers, emerge, lay eggs, and the tiny larvae start feeding. AgriLife says the useful treatment window is while those larvae are small, less than about 1/2 inch, ideally within about six weeks of egg laying. In South Texas that is early to mid-June. In Central and North Texas it is early to mid-July. After they reach the third instar, the large grub you find under a dead patch in late summer, the preventive products lose their grip.

Spring is the wrong season to treat. Larvae pupate then, and a pupa is not feeding. AgriLife says a grub treatment during the pupal stage does nothing useful. Beetles at the porch light from March into June are often other scarabs that do not damage the lawn. Seeing them is not a threshold.

It is early summer and this lawn dies in the same spots every year. AgriLife says a preventive application can make sense if you have confirmed grubs in past years. The products it discusses for that early window are imidacloprid and the insect growth regulator halofenozide. Both need to be down while grubs are small. Imidacloprid is strongest on small and medium grubs. Halofenozide misses larvae that are already in the last stage. South Texas: early to mid-June. Central and North Texas: early to mid-July. If you live outside Texas, egg hatch moves with the local beetles. Use your state extension's window rather than assuming Houston's June is Charlotte's June.

The lawn is already brown and the grubs you dig are large. Switch products. AgriLife says trichlorfon or carbaryl are the choices once damage is visible and the grubs are bigger. Pyrethroids, including bifenthrin, permethrin, and similar ingredients, bind near the surface and do a poor job on grubs, especially in clay. Do not buy a general bug spray and water it in hoping for the best.

You have not dug. Do that first. Five grubs per square foot is the AgriLife line for justifying a treatment. Under that, you may be looking at drought or disease. The brown lawn guide is the sorting step.

Whatever you apply, water it into the root zone. AgriLife wants 1/2 to 1 inch of water immediately after a liquid, and irrigation within 24 hours for granules. If the soil is dry, put down 1/4 to 1/2 inch the day before so the spray can move and the grubs are closer to the surface. Thatch thicker than about 1/2 inch ties the insecticide up before it reaches the soil. Check with a straight-sided can or a rain gauge so "I watered it in" is a measured half inch, not a guess.

If you would rather not use an insecticide, AgriLife discusses beneficial nematodes in the genera Steinernema and Heterorhabditis. With enough moisture they can cut grub numbers by half or more. They need about 1/4 inch of water before you apply them and another 1/4 inch after. Milky spore, which is sold for Japanese beetles in other parts of the country, has not been shown to work on the white grubs that infest Texas turf. Do not count on it here.

• Treating in April because beetles hit the window screens. Many of those beetles are not lawn pests, and pupae in the soil will not respond.
• Spreading a preventive imidacloprid or halofenozide product in September on grubs that are already an inch long.
• Using a pyrethroid and expecting it to move down to the roots.
• Skipping the water-in step, or watering so hard it runs off the yard.
• Treating the whole property off one grub, or treating with no sample at all.
• Confusing chinch bug damage, which stays rooted, with grub damage, which rolls up.
• Buying milky spore for a Texas lawn and treating that as the control plan.