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 inches in length, with a dark metallic green head and coppery-brown body. They also have 5 tufts of white hairs on the sides of their abdomen. Both masked chafers and Japanese beetles have a 1-year lifecycle.
Unlike June beetles, Japanese beetles do feed as adults, and can cause severe damage to a wide range of landscape plants. Roses, oaks and cherries are a few of their preferred plants and can suffered significant defoliation.
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.
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 to protect my lawn?
If your lawn has a history of grub problems plan to apply control in mid to late June. Imidacloprid (Merit), chlorantraniliprole (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.
Yikes! It’s August and I missed the June window for grub control but now have damage appearing. What can I do?
If grub control is needed in August or September, carbaryl (Sevin) or Dylox 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 also tend to be localized to preferred locations in the landscape, such as a sunny, irrigated slope or turfgrass underneath a yard light, instead of being uniform. Spot applications of grub control products can be made to areas with a history of attack and not applied to the entire yard if the homeowner prefers.
Be sure to water-in grub control products after application for best control.
Images
- May/June beetle larvae. Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
- May/June beetles Adult - Photo University of Nebraska, Department of Entomology