University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

White Grub Concerns in Lawns

August 3, 2000

White grubs are the most serious and destructive lawn insect pests in Illinois. The time period from late August through September is typically when grub damage shows in northern 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 white in color, with a characteristic "C" shape body when found in the soil feeding on lawn roots. Grubs are the larval stage of beetles. Species that fed on lawns in northern Illinois include the annual white grub, true white grub, and Japanese beetle.

The most common grub species in our area is the annual white grub, of which the adult is a tan chafer beetle. Eggs are laid in the soil in July, primarily on well-watered lawns in full sun, often near pavement. Damage from annual white grubs may start as early as mid August and may continue even into early October. Japanese beetle grubs also occur in northern Illinois and have timing very similar to annual white grub.

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 other problems such as drought, poor soil, or diseases. However, grubs are easy to find by lifting sod in damaged areas and checking the root zone for the whitish grubs. Skunks and raccoons may tear up lawns in search of grubs, even when grub numbers are relatively low. Usually a population of about 10 to 12
grubs per square foot cause lawn damage that requires control; whereas lower populations may not damage the grass, they may attract skunks and raccoons.

Lawns showing damage from grubs may be treated with an insecticide. Insecticides suggested for lawns being damaged include diazinon (liquid or granular); trichlorfon (Dylox) (granular); bendiocarb (Intercept), and Heterorhabditis bacteriophora nematode. Imidacloprid and halofenozide (GrubEx) are suggested for application before grub damage appears.

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.

 

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