Common Grub Control Questions

Masked Chafer Adults - Center photo
Masked Chafer Adults - Center photo

By Sarah Browning, Extension Educator in Lancaster County

WHAT ARE GRUBS?
Almost every gardener has seen grub larvae in the soil while installing new plants or tilling the vegetable garden. The term “white grub” actually encompasses the larval stage of several scarab beetles, the most common, and most damaging, being the June beetle or masked chafer and the Japanese beetle. Less well-known are the May/June beetle and green June beetle. All have a grub larval stage that can cause damage to turfgrass. The grubs are off white, with six legs located just behind their reddish-brown head and are usually found curled into a “C” shape in the soil.

Adult June beetles are stout bodied, oval-shaped insects, about 1/2-inch in length and dark yellow to light brown in color. They are most active at night and, unlike other scarab beetles, do not feed on plants as adults. Japanese beetle adults are slightly smaller, only 3/8-inch in length, with a dark-metallic-green head and coppery-brown body. (See https://go.unl.edu/japanese_beetle.) They also have five tufts of white hairs on the sides of their abdomen. Both masked chafers and Japanese beetles have a 1-year life cycle.

Unlike June beetles, Japanese beetles do feed as adults, and can cause severe damage to a wide range of landscape plants.

DO ALL LAWNS HAVE GRUB PROBLEMS?
No. Newly established lawns and low-maintenance lawns usually have few problems with grubs. Turf-type tall fescue lawns also have few problems and seldom need preventive treatment. Kentucky bluegrass lawns maintained at a high level with frequent fertilizer and water applications are most prone to attack.

DO ALL LAWNS NEED GRUB PROTECTION?
No, only those with a history of problems.

I FOUND A COUPLE GRUBS IN MY LAWN. DO I NEED TO APPLY CONTROL?
No. Masked chafers are Nebraska native insects, so a few white grubs are natural and common in the spring lawn or landscape during planting. At this level, control is not needed.

The damage threshold for turfgrass by masked chafer larvae is 8–10 white grubs per square foot of lawn; for Japanese beetle larva, it's 10 grubs per square foot.

WHAT DOES GRUB DAMAGE LOOK LIKE IN MY LAWN?
White grubs feed on turf and ornamental plant roots and other organic matter in the soil. They damage grass by destroying roots and eliminating plants’ ability to pull up water from the soil. Damage is usually at its worst in late-July and early August if high insect numbers are present and not controlled.

Initially, small patches of grass turn brown and die. Damage may appear to be drought injury, or even a disease such as summer patch. But close inspection of affected areas show turf can be pulled back easily, like a carpet, and numerous white grub larvae are found.

Later in the season, September and October, birds and other types of wildlife can cause further damage as they rip up turfgrass to find juicy, fat, mature grubs.

WHEN IS THE BEST TIME TO APPLY CONTROL IF MY LAWN HAS A HISTORY OF GRUB DAMAGE?
Apply control in mid- to late-June. Imidacloprid (Merit, Bonide Grub Beater, BioAdvanced Season Long Grub Control + fertilizer), chlorantraniliprole (Scotts GrubEx, Acelepryn) and halofenozide (Mach 2) provide excellent control.

In addition to the products mentioned above, commercial lawn professionals may use clothianidin (Arena) or thiamethoxam (Meridian) for control. All products are very effective against young grubs.
Do not use products containing ONLY bifenthin, deltamethrin, cyfluthrin, permethrin, lambda-cyhalothrin or gamma-cyhalothrin for soil-applied grub control. These chemicals bind with organic matter at the soil surface and will not move down into the soil to provide effective control.

YIKES! IT’S AUGUST, I MISSED THE JUNE WINDOW FOR CONTROL, BUT NOW HAVE DAMAGE APPEARING.
If grub control is needed in August or September, carbaryl (Sevin) or trichlorfon (Dylox, BioAdvanced Grub and Insect Control) provide the best control due to their higher kill rate against mature white grubs.

ANY TIPS FOR MAKING MY GRUB CONTROL APPLICATION?
White grub infestations tend to be localized to preferred locations in the landscape — a sunny, irrigated slope or turfgrass underneath a yard light — instead of being uniform. Spot applications of grub control products made only to areas with a history of problems, and not applied to the entire yard, is a more environmentally sensitive strategy.

Be sure to water-in grub control products after application for best control.