Got Grubs? by DeAnna Hambly
Dry wilted grass or areas where grass has disappeared completely could be signs of a grub infestation in the lawn. Another sign, holes in the soil, may indicate that crows or gophers are digging for grubs. Grubs are the most destructive insects to a lawn, and if left untreated they can destroy an entire lawn very quickly.
Grubs are the immature stage (larvae) of the adult beetle (Japanese, June or others). They are white or cream colored, have a C-shaped body and vary in length between 1/2 and 1-1/2 inches. Six legs and a brown head are distinguishing features. Grubs live two to three inches below the soil surface where they feast on the root systems of grasses and plants.
It is important to understand the lifecycle of this insect in order to eliminate and control it. The female beetle begins laying her eggs in the warm summer grass around mid July. The eggs hatch, and grubs are present in early August. It’s during this time that grubs are most destructive. They feed on grass roots; eating as much as possible in order to build up their body fat in preparation for overwintering, and they can quickly annihilate an entire root system.
In November the grubs go down four to eight inches into the soil to hibernate, and in the spring (March) they return to the top two inches of the soil and begin feeding again. The damage isn’t quite as destructive during the spring because larvae are not preparing their bodies for hibernation. Instead, they are preparing for the transformation into adulthood (pupation) which takes place in June. This period lasts about two weeks, after which the adult beetle emerges from the soil to begin the next round of mating, feeding and laying eggs.
It is relatively easy and inexpensive to control grubs if the correct treatment and proper timing are used. The ideal time to treat the lawn is during the larvae stage–early August through September. Grubs are young, small, and feeding close to the surface of the soil at this time. If your grub problem is severe, you may also need to apply treatment in the spring.
Grub control includes chemical, biological and preventative treatments. Chemical treatment requires the use of insecticides. Look for products that contain the words, “Season Long Grub Control”. You can treat your lawn for grubs as early as May, but it’s best to start in mid July.
In spring, use a 24-hour grub control application if necessary. Since most of the damage will be done in the fall, the goal at this time is to prevent the larvae from pupating. Both of the above products need to be watered into the soil before they are effective; be sure to read the application instructions for maximum benefit. Some chemicals are toxic to birds, animals and people. Please read all warning labels before beginning any type of chemical treatment around your home.
Biological control involves the use of Milky Spores. Milky Spore is a bacterial infection that infects white grubs. It does not infect other insects, earthworms, birds, animals, people or plants. This type of treatment is more expensive than using insecticides, and the results are not as rapid. However, treatment can last 15-20 years.
Preventative controls include maintaining well drained soil, thatching and aerating the lawn, and cutting your grass higher in the summer. You should also inspect your lawn in March and August for the presence of grubs. Cut a one-square-foot piece of sod, three to four inches deep. Roll it back, breaking up the soil to expose any grub activity. Do this in several areas of the lawn. An average of six or more grubs per square foot warrants treatment.
For more information on controlling grubs, visit the Texas A&M AgriLife Extension office at 2217 Washington Street in downtown Greenville.