Looking Ahead to White Grub Control

Perhaps the major lawn concern of summer is white grubs, in particular if they affected the lawn in the past. Grub damage can be difficult to predict. Lawns that have seen heavy damage last year may or may not see a problem this year. Likewise, the 2000 season could be the first time a particular lawn shows damage from grubs.

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. The most common grub species in our area is the annual white grub (adult is masked chafer beetle). Eggs are laid in the soil in mid-summer, primarily on well-watered lawns in full sun, often near pavement. Damage from annual white grubs typically starts in mid August and may continue until early October. Japanese beetle grubs also occur in northern Illinois, with timing very similar to annual white grub. Adult Japanese beetles are serious defoliators of many ornamental plants. A third species, the true white grub (May or June beetle), typically has a 3-year life cycle which means it could potentially damage lawns throughout the season. Both annual white grub and Japanese beetle go through their life cycle in one year.

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, diseases, etc. 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! Skunks and raccoons may tear up lawns in search of grubs, even when grub numbers are relatively low. Typically a population of about 8 to 12 grubs per square foot causes 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 available for homeowners to use for white grub control include diazinon (25% EC [liquid] or 5% granular); trichlorfon (Dylox) (6.2% granular); bendiocarb (Intercept), halofenozide (GrubBGon, GrubEx), or imidacloprid (Merit, formerly GrubEx). Heterorhabditis bacteriophora nematode is an example of an alternative product for white grub control that is available. 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.

Many questions are asked about preventing grub damage with GrubEx (halofenozide, formerly imidacloprid). Imidacloprid and halofenozide are suggested to be applied before grub damage appears, but don’t apply them too early. An example of a way to use these products in northern Illinois 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. Adult beetles will lay eggs in areas with adequate soil moisture, so if July is dry but your lawn is watered, it is a target for egg laying to occur. Look for Japanese beetles flying during the day and annual white grub (masked chafer) beetles flying shortly after sundown.

For the other insecticides listed, wait until grubs actually start to show up before applying them to the lawn. Monitor the lawn starting about mid-August and if any brown areas start to show, look for the grubs in the soil below. If they are found to be causing the damage, then treat them with an insecticide.

June - July 2000: Gardening with Hebs - Part 2 | Chlorosis of Landscape Plants | Looking Ahead to White Grub Control