Facts About White Grubs
Adult June beetles eat leaves and flowers of broadleaf plants.
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4 Know If You Have Grubs Eating Your Grass
If you have a lawn as part of your landscape, it has the potential to harbor scarab beetle larvae called white grubs that feed on the grass roots. Several kinds of beetles lay eggs in turf areas, and brown patches of dead grass can occur. Healthy lawns can tolerate a low incidence of white grub infestation and there is no need for insect control measures unless grubs reach a level of six grubs per square foot of lawn.
Kinds of White Grubs
White grubs of scarab beetles have a characteristic C-shape. Masked chafers (Cyclocephala hirta) have a large, 1-inch-long grub with brown head and legs and a patch of bristles at the end of the abdomen. Adults are golden brown beetles with a dark head and hairy undersides. May and June beetles (Phyllophaga spp.) have smaller 1/2- to 5/8-inch-long grubs. There are more than 100 different kinds, with adults light to dark brown and attracted to lights at night. The small black ataenius beetle, 1/4 inch long, has the smallest grub, also 1/4 inch long. It is most common in highly fertilized and watered cool season grass areas such as golf courses.
Most white grub species have an annual life cycle. In the spring, female beetles burrow into the soil and lay eggs in the grass root zone. After hatching, the first two larval stages actively feed in the root zone for about three weeks. The third larval stage feeds through the summer, when lawn damage is most likely to occur, and then overwinters deeper in the soil. Pupation occurs in pupal cells 3 to 6 inches underground in the spring and early summer, with adults emerging after about three weeks. The black ataenius beetle can complete two to five generations per year.
Monitoring Grub Levels
To monitor the level of grub infestation, dig through the grass root zone, roll back a 1-foot-square patch of turf and count the number of white grubs you see. Do this in several different parts of the lawn. If there are fewer than five or six grubs per sample, control isn't necessary. Some indications that you need to sample for grubs are dead or dying areas of grass or wildlife such as crows, racoons or skunks digging in your lawn to harvest grubs. To decide on treatment options, figure out what kind of grubs you have, whether you can use preventative or biological control and how to time the control for the insects that are present.
Keeping your lawn healthy helps prevent your lawn from becoming stressed under minimal white grub infestation. Aerating the lawn and removing thatch is also helpful. Biological control agents such as a parasitic tiphiid wasps can help manage but not control grub populations. Pathogenic nematodes may control early stages of white grubs. Since damaging levels of white grub infestations are not common, treatment with chemical insecticides is usually not needed.
University of California Integrated Pest Management Program: UC Pest Management Guidelines: Turfgrass: Masked Chafers (White Grubs)
University of California Integrated Pest Management Program: How to Manage Pests: The UC Guide to Healthy Lawns: Masked Chafers (White Grubs) -- Cyclocephala Spp.
Texas A&M AgriLife Extension: June Beetle
Texas A&M AgriLife Extension: Masked Chafer
University of California Integrated Pest Management Program: UC Pest Management Guidelines: Turfgrass: Black Turfgrass Ataenius
University of California Integrated Pest Management Program: How to Manage Pests: Pests in Gardens and Landscapes: Lawn Insects
Carolyn Csanyi began writing in 1973, specializing in topics related to plants, insects and southwestern ecology. Her work has appeared in the "American Midland Naturalist" and Greenwood Press. Csanyi holds a Doctor of Philosophy in biology from the University of Wisconsin at Madison.
Csanyi, Carolyn. "Facts About White Grubs." Home Guides | SF Gate, http://homeguides.sfgate.com/white-grubs-85256.html. Accessed 16 July 2019.
Csanyi, Carolyn. (n.d.). Facts About White Grubs. Home Guides | SF Gate. Retrieved from http://homeguides.sfgate.com/white-grubs-85256.html
Csanyi, Carolyn. "Facts About White Grubs" accessed July 16, 2019. http://homeguides.sfgate.com/white-grubs-85256.html
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