Grubs are a common nuisance in Texas, and one of the hardest lawn pests to deal with. They feed on grass roots, and if left unchecked, can severely damage your lawn.
Grubs — What are They?
In Texas, white grubs are the larval stage of scarab beetles, also known as May or June beetles. Their larvae have creamy-white, C-shaped soft bodies, 1/2 to 1 inch long, with three pairs of legs near the head.
Other common names for the May/June beetles include “May bug” and “June bug”. They’re the small reddish-brown or black insects that are attracted to your porch lights and fly into your windows and screens at night during the late spring and early summer.
Over 100 species of May/June beetles live in Texas, but only a few cause damage to turfgrass. The most prevalent white grubs in Texas are the June beetle (phyllophaga crinita), and the southern masked chafer (cyclocephala lurida). Both types attack warm-season turfgrasses, such as St. Augustine grass, bermudagrass, zoysia grass, and buffalo grass, feeding on the roots and other underground portions. Most of this damage is caused during the summer and fall months.
Cool season grasses, such as the bluegrasses, ryegrasses, and fescues are also harmed by the June bug and chafer but are attacked more often by the May beetle (phyllophaga congrua). The damage from May beetles often appears in the spring and early summer, before damage from other types of white grubs becomes noticeable.
Another type of June beetle found in Texas is the green June beetle (cotinis nitida). Their larvae are about 2 inches long when mature. They aren’t often found curled in the C-shape as most white grubs are. They’re easily distinguished by their habit of crawling on their backs.
The green June beetle grubs normally don’t injure turf, feeding mainly on decaying organic matter. However, lawns can be damaged because of their burrowing. You’ll find them mostly underneath fruit trees, in manure and compost piles, and in heavily mulched gardens and flower beds with soils high in organic content. Their daytime resting places are usually near such sites, and telltale signs are small mounds of soil on the surface of nearby lawns.
Another type of damaging beetle, the Japanese beetle (Popillia japonica), was introduced into the northeastern United States in 1916, and has since migrated west and south. It has been detected in some Texas counties, and is particularly destructive, destroying turf in golf courses, parks, and lawns. The larvae can be identified by their off-white color, C-shape, and a V-shaped row of spines beneath the abdomen.
Where do Grubs Come From?
White grubs go through a four-part life cycle that includes egg, larval (grub stage), pupal, and adult phases. The June beetle and southern masked chafer emerge from the soil from late May (south Texas) to early July (north Texas). Their mating flights occur at night, and it’s the male beetles that are mostly attracted to lighted windows and outdoor lights.
After mating, the females tunnel into the soil to lay their eggs, which hatch into small white grubs in about two weeks. These newly-hatched grubs immediately start feeding on grass roots. The larvae will pass through three stages, increasing in size and appetite.
It’s during their third stage that the grubs do the most damage. Large numbers feeding on the lawn can quickly destroy the root system and prevent the proper uptake of food and water.
The larvae continue attacking the roots until the cool weather in the fall, at which time they move about a foot below the ground and become dormant until the following spring. In the spring they move closer to the soil surface and feed for a brief period, before going into the pupal stage.
The pupal stage lasts about three weeks. During this stage the white grub doesn’t feed or move through the soil while it’s transforming into an adult beetle, which eventually emerges to mate.
Life cycles for the June beetle and southern masked chafer take one year to complete, while in north Texas it may take two years. The green June bug and Japanese beetle also have a one-year cycle. The May beetle, however, has a life cycle of two years.
What are the Signs Your Lawn is Under Attack?
- You’ve seen large numbers of adult beetles attracted to outdoor lights or lighted windows in the late spring and early summer.
- In the spring, your lawn has brown patches that never turn green. These dead grass patches could be damage from grubs the previous fall.
- In the summer, your grass loses its strength, wilts, doesn’t grow quickly, and is susceptible to weeds and drying out.
- In the late summer or early fall your lawn has irregularly-shaped dead patches, despite being well-irrigated. At least one of those patches peels away easily from the soil with no roots holding it down.
- Before the dead patches appear, your lawn feels spongy when walked on, as if it were freshly-laid sod.
- Birds, skunks, raccoons, moles, or armadillos are digging up your lawn, looking for large, mature grubs. They’ve stripped away your grass or dug tunnels looking for their favorite food. However, these animals will also dig up your lawn looking for earthworms, so confirm you have grubs before applying any treatment.
How do You Check for Lawn Grubs?
- Dig several sections of sod one-foot square by four inches deep (deeper in sandy soils) in different parts of your yard and peel them back.
- Treatment based on number of grubs found per square foot:
- 0-5 grubs — no treatment needed
- 6-9 grubs — no treatment needed for healthy lawn, but you may have to treat for a stressed lawn, especially if animals are digging up the grass
- 10 or more grubs — you need to treat, and your lawn is probably showing visible damage
When do You Treat White Grubs?
The best time to inspect for grubs and apply treatment occurs approximately five to six weeks after the heaviest June beetle flights. This will prevent future grub problems by eradicating the newly hatched generation. Keep in mind that peak flight times vary in different parts of Texas as much as two months from year to year because of rainfall variations.
There are also May or June beetles in some areas that don’t attack turf, but are attracted to lights, making it difficult to know when to inspect or treat. Contact your local county Extension office to confirm the ideal inspection and treatment periods.
September or October, and in the spring before early May, are also good times to inspect and treat if your lawn has visible signs of grub damage. You want to kill the grubs in their late larvae stage and before they pupate.
What are Your Treatment Options?
- Chemical preventative products containing active insecticides. These products kill grubs over a longer period of time and are more effective for newly hatched grubs if applied 5-6 weeks after peak June beetle flights but can also be applied late in the season.
- Curative insecticides are short-lived products that kill all life stages of grubs. Apply them late in the season (September or October), and in the spring before early May.
- Organic options include beneficial nematodes (microscopic worms) of the Steinernema and Heterohabditis genera, used to attack white grubs and other soil-inhabiting insects. Milky spore (a microbial pesticide, Bacillus popilliae) can be used against the white grub of the Japanese beetle, but has not been found to be effective against other types of white grubs.
Before selecting any particular product to use, please consult the Texas A&M guide.
Irrigation is essential for both chemical and biological treatments before and after application. The irrigation beforehand helps the insecticide penetrate the soil and brings the white grubs closer to the surface. The post-application moves the treatments down into the root zone where the grubs feed.
What Else Can You do to Keep Lawns Healthy?
- Test your soil every 2-3 years and follow the fertilizer and amendment recommendations.
- Keep your grass mowed high, 2-3 inches or more to give it a healthy root system that can tolerate some grub feeding.
- Overseed bare or sparse areas in the spring and fall.
- Irrigate effectively to maintain a healthy lawn and root system. Grubs love moisture, and overwatering encourages grub development and population growth.
Sound irrigation practices are indispensable to a healthy lawn. Call the licensed irrigators at Smart Earth Sprinklers at (512) 694-1147 or contact us online to keep your sprinkler system operating optimally.