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Dealing with white grubs

Last time, I left you with the gloomy image of my lawn devastated by White Grubs. Small excavations and torn up turf were interspersed with bare patches, coupled with the tell-tale purple seed stalks of the intrusive Crabgrass. Since then I have planted, watered and nurtured bags of grass seed to try to help my lawn recover before winter. All is going reasonably well, but now it seems that I have the largest sparrow feeder in the world as these little migrants seem to love freshly planted (but not yet sprouted) grass seed. Sigh! So let’s look at some solutions to the White Grub issue. Short of pesticides, there are no easy options. One that can be successful, but takes some effort, is to take advantage of the affinity of the adults to be attracted to lights. So if you have a porch light and are willing to spend some time you can catch and kill them at the lights in the evening. Every one you take will mean that 10 to 30 eggs won’t be laid! The small beetle carcasses can be tossed on the ground and something will eat them so there is no waste. Now this may not sound environmentally friendly, but you have to weigh the economic loss of your lawn against the lives of a few bugs. If you have to replant your lawn, because the damage is so severe, you should carefully consider the type of grass seed you plant. Kentucky Bluegrass or Perennial Ryegrass lawns are less tolerant to White Grub damage than some other varieties, but Tall Fescue is generally more resistant to them. It reportedly also provides better drought and disease resistance and shade tolerance. Locally you can mix your own grass seed at some bulk outlets like Canadian Tire. Do not use only one type of seed as varieties give differing benefits to your lawn and respond differently to environmental conditions. Some Tall Fescue and Perennial Ryegrass cultivars (which are desirable in lawns) contain endophytes (i.e. symbiotic fungi) that provide resistance to certain insect pests such as sod webworms, which are found in our area. Rainfall and soil moisture are critical factors that determine the extent of seasonal White Grub damage. Watering, although beneficial to the lawn, can attract egg-lying White Grubs to your property, particularly if water is scarce elsewhere. High soil moisture likewise increases egg survival. If lawns are irrigated during June and July, you may very well have a grub problem later in the summer. On the other hand, enhancing soil moisture through frequent light watering in August and September can help lawns recover or tolerate relatively high concentrations of grubs (e.g. 200+ grubs/square meter). Moderate fertilization in late fall can be beneficial to developing strong roots, but the opposite occurs if applied in spring and summer. Natural controls such as predators and parasites can help keep White Grubs in check. Predators such as skunks, raccoons and moles are effective at controlling large numbers of White Grubs. The latter are very common in our area and can consume hundreds or thousands of the grubs in a season. The raccoon and skunk aren’t as tidy when they eat and they leave tell-tale evidence of their passing in the form of small holes and torn up turf. However, each hole represents a dead grub! Certain species of wasps parasitize White Grubs by laying their eggs on them. These wasps are sometimes seen hovering over the turf in late summer searching for the grubs. The wasp larva feeds externally upon the grub, eventually killing it before spinning a fuzzy, brown, jelly bean-size cocoon in the soil. Other, less conspicuous, species of wasps and some other beetles and ants will also take eggs and small grubs, but their influence is minor. None of these are available to buy commercially so we have to rely on nature to let them find your lawn – but rest assured they will if the grubs are bad enough! The effort I’ve expended is showing benefits, is environmentally friendly and in the end I will have a healthy lawn again next spring.

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line at and on LinkedIn and Facebook.

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