Dealing with Grubs in Lawns

Grubs are the most serious and destructive lawn insect pest in Illinois. While not all lawns will get grubs and the extent of grub damage varies from year to year, there are some important points to consider concerning managing grubs in lawns.

Grubs are typically white, with a characteristic "C" shape body when found in the soil feeding on lawn roots. Grubs are the larval stage of beetles.

A common grub species in our soil is the larval stage of the Japanese Beetle. Eggs are laid in the soil in mid-summer, primarily on low-cut, well-watered lawns in full sun, often near pavement. Damage from grubs typically starts in mid-August and may continue until early October. Other species may damage lawns but are becoming less common than the Japanese Beetle. Monitoring and control of these species is the same. The true white grub (May or June beetle), for example, typically has a 3-year life cycle, meaning it could potentially damage lawns throughout multiple seasons. Adult Japanese beetles can be a serious problem on many crops and ornamental plants. Additional information on adult Japanese beetle.

Since grubs feed on the roots of lawn grasses, damage will appear as browning of the lawn. Consider that this also could be due to problems such as drought, poor soil, and diseases. However, grubs are easy to find by lifting sod in damaged areas and checking the root zone for the whitish grubs. Don't treat for grubs that don't exist! Typically a population of about 12 grubs per square foot can cause lawn damage that requires control. You can monitor this yourself by cutting up a square foot of sod at the margins of damaged areas. Peel back the sod and count how many grubs are in that square foot. Replace the sod, firm it up against the soil, and water to reestablish the roots. Healthy lawns can typically outpace the damage caused by grubs under the 12 per square-foot threshold. Skunks and raccoons may tear up lawns in search of grubs, even when grub numbers are relatively low.

Late June to mid-July is the peak egg-laying time for beetles. Make your lawn less attractive to female beetles by not watering your lawn. Allow it to go dormant during the summer. Plant more trees. Adult beetles lay fewer eggs under tree canopies.

Lawns showing damage from grubs may be treated with an insecticide. Insecticides available for homeowners include:

  • Imidacloprid (various trade names)
  • Chlorantranilprole (GrubEX)
  • Trichlorfon (various trade names) for control of white grubs
  • Heterorhabditis bacteriophora nematode is an example of an alternative product for white grub control that is available.
  • Bacillus thuringiensis galleriae is a soil-dwelling bacteria that specifically targets grubs.

For all products, read and follow all label directions, then apply to damaged areas. Water the insecticide into the soil immediately. If treating a large area, stop after a portion has been treated and water the material in, then complete the rest of the lawn area needing treatment. Only treat in and around affected areas; grubs may only be in a small part of the lawn. Imidacloprid is suggested to be applied before grub damage appears. An example of a way to use this product would be to apply in July to irrigated lawns that are surrounded by dry lawns, especially when adult beetle flight is high in areas with a history of grub damage.

Spring treatment for annual white grub is not suggested since the grubs feed for a short time in spring and are reaching maturity and thus are not controlled easily. In addition, turfgrasses are actively growing at that time so usually don’t show damage.