I am wondering what the best way to get rid of grubs in a lawn? I have skunks that are coming in my backyard and I assume they are eating the grubs. Not sure how else to get rid of the skunks.
In Kentucky, the grubs that cause the most damage to turfgrass are the larvae of the Japanese beetle and the masked chafers. You may also encounter grubs from the green June beetle. There are several methods for attempting to control grubs, and to explain them all would take up considerable room. I will give you a short summary and provide links to Kentucky Cooperative Extension Service publications that outline control strategies in great detail.
While the fact that skunks are visiting your yard to dig up grubs may be an indication that you have an infestation, we recommend that you sample your turf in several spots to get an idea of the extent of the infestation. Cut out a square-foot piece of sod in several areas and search the roots and soil to a depth of about 2 inches for grubs. Finding a few grubs is normal, but if you’re averaging eight or more per sample, you might want to consider treatment.
One possible approach, if you have Kentucky bluegrass or perennial ryegrass, is to renovate your lawn with tall fescue. Fescue is more tolerant of grubs than the bluegrass or ryegrass.
The grubs have natural enemies in the form of parasitic wasps, ground beetles and some ants, but they are generally not available commercially for purchase. The naturally occurring individuals while beneficial generally aren’t present in sufficient numbers to provide complete control of the grubs.
There is a milky disease spore dust commercially available that has been advertised for controlling Japanese beetle grubs, but these products have not been shown to be effective in University of Kentucky research trials.
Insect-parasitic nematodes are also available, but results have been less consistent than those utilizing pesticide applications.
There are basically two pesticide strategies: curative and preventive. The curative approach utilizes pesticides that have a relatively short residual effectiveness in the soil, so timing of the application is very important. In Kentucky, the optimum time of application is early to mid-August when the grubs are still small. Later, in late August and September, the grubs are still somewhat susceptible to the pesticide, but as they grow larger they become harder to control. By late September, depending on the temperatures, grubs usually start to dig deeper into the soil and leave the treatment zone.
In the preventive approach, pesticides that have a much longer residual effect are utilized and optimum time of application is mid-June to mid-July, approximately one month prior to the hatching of the beetle eggs. This is basically an insurance approach, and is implemented before you have a problem.
While you may still be able to apply curative approach pesticides, the fact that we have passed the optimum application time, may limit your control results.
If you decide to utilize pesticides, please make sure you follow all label directions.
Here are some links to some excellent Kentucky Cooperative Extension publications I believe will explain everything in greater detail:
Controlling White Grubs in Turfgrass:
Insecticides for Control of White Grubs in Kentucky Turfgrass: http://www2.ca.uky.edu/entomology/entfacts/ef441.asp
Improving Turf through Renovation:
These last two publications are referenced in the first one.
Assuming you have a grub infestation, if you get them under control, this should reduce the skunk visits. Until then, you may want to try using a motion activated sprinkler (sometimes referred to as scarecrow sprinklers) in the area where the skunks are visiting. These can be somewhat expensive, so I would just purchase one to try first.
Hope this answers your question, and thank you for using Ask an Expert.