To see if you have grubs and how bad the infestation is, you have to dig. Some turf insects, such as caterpillars, can be forced to the surface with salt or soapy water solutions. This won't work with white grubs. Use a bulb planter, shovel, or golf course cup cutter to examine soil cores for grubs in the root zone. Depending on the species, eggs and first instars (first developmental stage of the larvae) are relatively difficult to see, while the larger second and third instars are relatively easy to pick out of the soil.
The best time to sample is early August in southeastern NY and mid-August upstate. Egg hatch and grub development, however, may be delayed by cool or dry weather and may also vary from species to species.
Where you sample should be based on identified problem areas, susceptible areas, and areas that otherwise require better protection (e.g., front lawns, fairways). Increase the number of samples in high priority and high-risk areas to reduce the chances of overlooking a damaging infestation.
Watch our video to find out if your lawn needs treatment.
How many is too many?
The question of how many is too many depends on the grub species. Typically, the larger the grub, the fewer grubs per square foot can be tolerated by the turf before damage is visible. Threshold levels have been established for each species as outlined in the Cornell Guide for Commercial Turfgrass Management.
|White grub treatment thresholds|
|Number of grubs per|
|Asiatic garden beetle||18-20||2|
|Black turfgrass ataenius||30-50||3-5|
|Green June beetle||5||Any|
|Northern masked chafer||8-12||Any|
|May and June beetle||3-4||Any|
|14.25-inch diameter soil core of a standard golf course cup cutter|
If several sampled areas are at or above the threshold, intervention may be warranted. Remember, turfgrass with a healthy root system will tolerate higher numbers of grubs than the suggested thresholds. Extensive research in upstate NY shows that insecticide treatments are needed only 20% of the time on home lawns and golf course fairways.