Pest Identification: White grubs are the larval stage of several different types of beetles. They can all devastate a lawn if left untreated. In fact, these pests are considered by many to be the most damaging turf insect in the U.S. White grubs can be identified by their whitish color with dark areas near their rear-end, C-shaped bodies with a total of six legs, and a distinctly brown head. They tend to spend most of their lives under the ground. The grub stage of this insect can last anywhere from two months to three years, depending on the species.
The only sure way to discover if you have a white grub infestation is to examine the soil under the grass. Fall is the best time to do this. In order to examine the soil, take a spade and cut a roughly one foot square area of lawn, only on three of the sides, approximately three inches deep. Then, by forcing the spade under the sod, pull back the grass, using the uncut side as a kind of hinge. Finally, use a trowel or some other instrument to dislodge some of the soil from the exposed roots of the grass. Look for any signs of white grubs. When you are finished, carefully replace the sod, making sure the roots can re-establish contact with the soil. It is recommended that you repeat this process in several areas of your lawn.
Damage Identification: These pest live under the ground by eating the roots of grass. Although damage usually occurs most severely in mid-to-late summer, the actual symptoms may not become apparent until early fall, when it is too late to do anything to minimize the damage. The main symptom that appears due to a relatively minor white grub infestation is irregularly-shaped patches of brown, dying grass. If an area becomes heavily infested, it can take on a gray-green color, wilt quickly in the sun, and be easily rolled up since the roots have become weakened or are missing altogether.
Control/Treatment: There are many options for how you treat a white grub outbreak. These can be easily broken down into three distinct categories:
- Cultural Modifications
- Some of the insects that produce this larva are attracted to certain plants. For instance, Japanese beetles like roses, grapes, and lindens while May/June beetles prefer oaks and fruit trees. Thus, it would be to your lawns benefit to avoid these plants in regions where these insects are common.
- Careful water management can also help control a major outbreak. Almost all the white grub species need moist soil in order for their eggs to hatch. Larva also tend to be very susceptible to dry conditions. So, if your lawn can withstand some drought stress, it is best to avoid watering as much as possible during July and early-August.
- Biological Control
- There are several biological methods for dealing with a grub infestation. Parasitic wasps, which attack grubs, as well as parasitic nematodes, can be very effective in controlling the population on these insects.
- Another biological option is to use a strain of bacterium, known as Bacillus popilliae (or, more commonly, Milky Disease). This works particularly well against Japanese beetle grubs. This bacteria infects the grubs as they feed and causes their body fluids to turn a milky-white. This eventually leads to their death. If you are considering this option, know that it is a more long-term treatment/prevention tool than many others. The bacterial preparations should be applied every year for three to five years to provide lasting results.
- There are several pesticides available for treatment as well. Depending on the type you choose to use, they can be applied as a preventative measure, an early response to infestation, or a late-season response to damage. All three types of pesticide can be very effective, but the earlier you can identify a white lawn grub worm infestation and apply treatments, the less damage your lawn will suffer.
Grass Types Most Susceptible to Infestation:
- Centipede Grass
- Fescue Grass
- St. Augustine
- Zoysia Grass