Environment Task Force Newsletter
Ohio State University Extension
Summer, 1997, v1 #2

Too Many Grubs Spoil the Grass

Pete Lane, Montgomery County Agriculture and Natural Resources Agent

Grubs can make a yard look gross.

White grubs are easy to find, and the damage they do to a lawn is more noticeable than that of other pests. When large areas of grass die in the late summer or fall, grubs are the prime suspect.

Grubs eat grass roots, so dead turf can be lifted just like new sod. Underneath, the grubs are plainly visible until freezing weather sends them deeper into the soil. The following spring they return to the surface but feed little before starting their transformation into adult beetles.

If adult beetles frequent an area, chances are there will be eggs laid there for another generation of grubs. They're most often found on property with dense turf, full sun and good drainage.

The best way to ensure that grub controls are applied only when needed is to lift the sod and look for newly hatched grubs in August and September. Their c-shaped, cream-colored bodies with brown heads may only be a quarter-inch long, but if unchecked they will grow more than an inch in the next couple of months. Healthy turf can tolerate five to 10 grubs per square foot, but populations of 40 or more are common.

Homeowners who've experienced a grub infestation are inclined to "shoot first and ask questions later." Even those who've never suffered grub damage are more aware of grubs than other pests that are more common but less obvious. Lawn services time their insect controls for maximum impact on these other pests, not for grubs. The same is true of four- or five-step packages for do-it-yourself gardeners. The packages' typical June date for general insect control misses grubs, since they've either departed as adult beetles or are sealed up as pupae transforming into adults.

Timing is everything

Grubs discovered during spring planting often trigger an insecticide application that is mostly futile. At this time, mature grubs feed little and are larger, so it is difficult to expose them to lethal doses. Also, grass that survived grub feeding the previous season is unlikely to succumb in spring's cooler, wetter conditions. It's better to hold off in the spring and wait to see whether the beetles that come from those grubs choose to stick around and start another generation.

The ideal time to control grubs, if numbers warrant, is late summer when they're young and hungry and turf is vulnerable. One of the newest grub controls will work only on immature grubs. Imidacloprid is marketed as Merit or Grub-X, and while it's not effective when applied late, an application as early as late May can control billbugs and the next crop of grubs.

Regardless of the product used, irrigation or rainfall after an application is essential, so the insecticide sinks deeper into the soil where it's needed.