Pests & Diseases

What to Do About White Grubs

White grubs can be a problem in home lawns. How can a gardener get rid of the grubs? First it helps to know what type of grub is in the lawn. That may require digging down into the lawn to identify the grubs. Most can be found in the top three to four inches of soil and grass roots.

It would make life so much easier if there was only one type of white grub. However, larva (immature stage) of several different beetles are called white grubs. These include Japanese beetle, green June beetle, southern masked chafer, northern masked chafer and Asiatic garden beetles.

Most of these beetles have a very similar life cycle. They emerge from the ground in late spring or early summer. They fly around for a few weeks feeding, mating, and laying eggs. The eggs hatch in late summer or early fall and feed on the roots of grass or on decaying organic matter in the soil. When the soil gets cold in the fall and winter they burrow down deep to wait for the weather to warm so they can finish fattening up before pupating into adults and beginning the cycle again.

Now that we know how our enemy lives we can learn how to get rid of the problem.

Biological
In our changing world there are many people who would rather not use chemicals. There are a couple options when it comes to biological control. These may fall under the category of the solution is worse than the problem, but birds, moles, skunks and raccoons all feed on white grubs to some extent. In reality, I get about as many phone calls on how to get rid of moles as I do on how to get rid of grubs.

If you are certain the only grubs you have are from Japanese beetles, then you may be in luck. There is a disease called milky spore disease that can be purchased and applied to the soil to control the grubs of Japanese beetles. It takes a few years to get the disease established, but once it’s established it kills the grubs as they ingest the fungal spores and the fungus grows in their gut until it kills them.

Chemical
There are many chemicals on the market that are effective against white grubs. To help with the effectiveness of these chemicals it is beneficial to water the lawn a day or two before the chemicals are applied. This moisture in the soil will bring the grubs closer to the surface. With most chemicals you will then want to spread the granular product on the ground and then water the chemicals in to get them down into the soil where the grubs are. The grubs of most beetles are small and near the surface in August and September, making August the perfect time to apply grub control products. There are a number of grub control products on the market, including Bonide’s Annual Grub Beater.

The extremely large green June beetle grubs have a behavior that is a little different from the other grubs. They will come out of the ground at night and move across the soil surface on their backs before burrowing back down into the soil. An option available for killing these grubs is to spread granular Sevin in the area where they are found and let them crawl across the chemical all night. The next morning there will be large, dead grubs all over the area. This is one way to know for sure the grubs are dead.

When using chemicals read and follow directions for use including safety pre-cautions. More specific chemical recommendations can be found in the North Carolina Agriculture Chemicals Manual or by calling your local county cooperative extension office. www.turffiles.ncsu.edu/Insects

Photo: Pictured left to right, Japanese beetle, Popillia japonica; European chafer, Rhizotrogus majalis; Junebug, Phyllophaga sp.
David Cappaert, Michigan State University, Bugwood.org

Byline:
Shawn Banks is the Consumer Horticulture Agent with NC Cooperative Extension in Johnston County. You may reach him at [email protected]