For anyone who has a lawn, pests can be a major concern. One of the most common turf pests is actually a group called “white grubs.”

White grub mouth
Grubs have large chewing mouthparts.
Photo Credit: ©2004 Buglady Consulting
Grub lawn damage
This turf damage was caused by grubs.
Photo Credit: ©2007 Buglady Consulting
White grub
Grubs can make a feast out of turf roots.
Photo Credit: ©2004 Buglady Consulting

These white grubs are the immature life stage of many different Scarab beetle species. Most of the time people blame Japanese beetles, but in actuality, they’re just a small part of the grub population. The reason they get blamed is because the adults are out during the day, where most of these other beetle species fly at night, not to be seen.

Identifying Characteristics

White grubs can vary greatly in size, depending on species, from a ¼ inch to the size of your thumb. They tend to stay curled up in a “c” shape and are white to cream in color. They have brown heads and six legs.

Biology

Depending on the species, most adult beetles come crawling out of the lawn in late spring/early summer. The adults mate and deposit their eggs back into the soil. Some of the adults, like the Japanese beetle and green June bug, feed on plants. Others, like the European chafer, don’t feed at all as adults.

Once the eggs hatch, they start to feed until cooler temperatures drive them down into the soil profile so they can overwinter.

Plant Injury Symptoms

Most of these grubs feed on the roots of grass, cutting off the plant’s ability to take up water and nutrients. This results in yellowing or browning of the turf , making the grass easy to pull up. Additional damage can occur when mammals like skunks, birds or even moles dig up the lawn looking for these grubs to feed on.

Control Methods

Before you treat, be sure grubs are the actual cause of the problem and not a lack of water, chinch bugs or disease. The only way to determine this is by digging. The best way is to cut three sides of a 1-foot square and roll the grass back. If you find high numbers of grubs, you may need to treat. If only a few are found, then treatment isn’t necessary. Once done assessing the situation, roll the grass back, and it’ll continue to grow.

Here’s a general rule to follow:

White Grub Turf Thresholds / 1 foot2
0-5 grubs Don’t worry.
6-9 grubs Watch the population, it may go down naturally.
10 or more Treatment may be necessary.

Sprays

There are many granular and spray on products available for the treatment of white grubs. Make sure you read the label and apply the correct rate. MORE IS NOT BETTER, and you could damage your lawn. Spot-treating will also help conserve your native beneficial insects that could be feeding on your pests. Only treat where needed.

Biological control

More work has been done in recent years on using beneficial (entomopathogenic) nematodes for white grub control. These can be purchased from many suppliers on the Internet and are an organic way to control lawn pests. They’re safe to use around humans and pets.