Harmful insects

How to Get Rid of White Grubs in Your Lawn?

Who hasn’t seen grubs in their lawn? These large “C” shaped worms eat the roots of the grass to the point where the lawn can be removed in large patches. But it’s the raccoons and skunks that do even more damage by digging under the grass to eat their favorite food! Grubs are the larvae of various species of chafer and beetle.

White grubs.Photo: Stéphanie Boucher.

European Chafer

The grubs that have been doing the most damage to our lawns for the past few decades in Quebec are the larvae of the European chafer. Since they are particularly active in the spring and the damage is very visible now, it is very tempting to intervene right away. However, this is not the best time and, in any case, these large white worms turn into pupae around mid-May and do not feed again until they metamorphose into flying adults around mid-June, depending on the weather and the region where you live.

Damage due to grubs.Photo: Edith Smeesters.

It is therefore useless to spend large sums of money on all kinds of products at this time or to strip the entire lawn to get rid of them, because they will emerge without your intervention. On the other hand, at the end of May, it’s time to over-seed the bare spots with a low-maintenance grass seed mix with endophytes. Take advantage of this time to topdress with a small layer of compost (0.5 cm) and keep the surface moist until emergence. You have until the end of August to revitalize your lawn before the new grubs start doing real damage! You can also plant species they don’t like as much – clover, birdsfoot trefoil, creeping thyme – or install a ground cover other than a lawn.

The adult chafer eats the leaves of various tree species, but does not do much damage like its Japanese cousin. They will mostly mate and lay eggs that will turn into small white worms in your lawn by the end of July and grow until the cold weather arrives when they will descend deep into the soil.

European chafer. Photo: René Limoges, Montreal insectarium.

To reduce the number of grubs next year, you should consider preventing the chafer from laying eggs in your home from mid-June to mid-August! Since the chafer is a nocturnal insect, it is very important to limit outdoor lighting at night. However, you can make a lighted trap to catch a lot of them: hang a sheet or a white curtain over a trash can filled with soapy water. A fun way to start a nocturnal insect collection! There are also pheromone traps that are easily found in hardware stores today.

Intervene in August and September

Once the beetles have laid their eggs, it is the best time to intervene while the grubs are small, i.e. in August and September, before the first frost. You can treat the lawn with nematodes or with BTG (Bacillus thuringiensis galleriae): a new product on the market for only a few years that seems to be quite effective.

All these methods will not eliminate grubs 100%, but a vigorous lawn can survive a substantial presence of grubs. So, the ideal is to combine several strategies if there are grub problems in your area or if you have had grubs in the spring.

As for the common chafer, it has a 3-year cycle and will do most of its damage in its second year, but the same treatment can be applied as for the European chafer.

The cycle of the Japanese beetle is a bit different from the European chafer, but this species does most of its damage in the adult stage on certain trees and shrubs.

I will talk to you about it again this summer when the time comes to intervene.

Edith Smeesters is a biologist and a pioneer in ecological horticulture in Quebec. She has given countless conferences and workshops and written several books on the subject for over 20 years. She founded and has been president of several environmental organizations, such as Nature-Action Québec and the Coalition for Alternatives to Pesticides. She was a key figure in the creation of the Pesticide Management Code of Quebec, which has been in effect since 2003. She has received several awards for her involvement in the environment and is a member of the prestigious "Cercle des Phénix".

4 comments on “How to Get Rid of White Grubs in Your Lawn?

  1. Mary L Discuillo

    I occasionally find grubs in my compost pile. I think they are one of the most disgusting creatures and squash them everytime. I don’t have a lawn but perhaps they get in there from grass clippings from
    the neighbors that I collect.? In any case if I am disturbing the balance of nature so be it. Does anyone know if scrub jays eat them ? They’re pretty big I

    • Different species eat different things. Some species of beetle larvae (indeed many)consume exclusively detritus and decomposing matter. As adults they provide an important food source for birds and small mammals so yes, you can be disrupting ” the balance of nature” or simple be detrimental to the food Web.

  2. I just looked this strain up.

    Conclusion: This study supports efficacy of Btg strain SDS-502 for reducing defoliation by adult JB in urban landscape settings. Granular formulations, however, failed to control JB grubs in turfgrass soils. Btg should not be used in gardens with larval host plants of the monarch butterfly or other non-pest Lepidoptera, especially species of conservation concern. © 2019 Society of Chemical Industry.

    Doesnt sound too good!

  3. marianwhit

    A non-selective way to kill every insect to maintain a perfect monocrop of a species of grass not native to here and a magnet to an introduced insect. Hmmm. I wonder what would happen if we turned to using native grasses, small plants, and diminutive sedges and rushes instead? What if instead of lawns, we thought about growing grasslands of mixed species mowed maybe once a year, or one third a year instead? Chafers would probably still be there, but in lower numbers…clearly native animals find them a valuable food source (most likely in the face of a lack of their natural food sources). Small owls, and raptors, for example need large beetles for prey. A diverse planting would lessen the visual impact of the damage these insects make, and reduce the tendency to reach for the nearest non-selective “obliterate all the insects” answers. Much work is needed to supply seed mixes that meet this need, but we need more to disengage from thinking our yards should aesthetically look the same as the floor in our living room or a golf course. We need to stop “keeping up with the Joneses and really looking at and take responsibility for the consequences of our actions.

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