How to Identify (and Kill!) White Grubs

If you are a gardener, chances are you have been out digging or rototilling and have noticed white specks standing out against the dark brown of the soil: the hated white grub. And if you're not a gardener, chances are you have seen a June bug repeatedly knocking its head against your porch light on a warm summer night. This seemingly unintelligent guest was also a white grub weeks prior.

White grubs belong to the Scarabaeidae family, and are usually referred to as scarabs. Though some scarabs are not destructive during their beetle stage, they all wreak havoc on the roots of turf grass and ornamental plants in their larval stage. Their damage can sometimes be overlooked, especially if the turf is watered and mammal pests like moles, possums, skunks and raccoons don't start showing up to dig up your lawn and feed on the grubs.

So, you know you have white grubs, but why do you need to know which white grubs you have? If you plan on treating naturally it can be helpful to know what specifically you are dealing with, or you may wish to know for your general edification. For instance, milky spore will kill Japanese beetle larvae, but if you have a yard full of European chafer you are probably wasting your money treating with milky spore. Sending specimens off to a lab usually takes a week or two for results, and then they charge you for something you could have done with a little knowledge and a magnifying glass or field microscope.

If you decide to treat with beneficial nematodes (which kill all types of white grubs) we recommend Heterorhabditis bacteriophora (Heteromask), but Steinernema feltiae (Scanmask) will also work.

Identifying white grubs

First you will need some type of magnification; we recommend just a normal magnifying glass. You will also need tweezers or forceps to hold your specimen still. You will be looking at the raster pattern on the grub, located on the underside right above the anus.

Then use these drawings of the five most common white grubs in North America to identify your grub.

Japanese beetle

May/June beetle

European chafer

Oriental beetle

Asiatic garden beetle

Here is an actual example of the Asiatic garden beetle.

It is important to compare what you are seeing against all of the drawings before making a determination. Or, if you don't feel like taking the time, or have difficulty determining whether you have Japanese beetles or one of the other four varieties, you could just treat with Heteromask. We recommend about 25,000 nematodes per square foot. The "How much do I need?" calculator on the Heteromask Spray page shows which size fits your lawn. It is best (and most economical!) to treat just the areas affected by the grubs and the immediate surrounding areas. Without a source of food (aka pests) the nematodes will die off and the treatment will be wasted. There are two windows to treat for white grubs: early in the spring, or late summer and early fall. As always, if you have any questions please contact us!

Happy gardening.