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White Grub

 

What is white grub?

White grubs are the larvae of certain scarab beetles, such as June bugs, European Chafer and others.  The larvae feed on roots of grass or various plants, depending on the species. In a healthy lawn, having up to 4 or 5 per square foot is normal.  However, once the number of grub exceeds 10 or even 20 per square foot, the lawn is considered infested, and the grass gets severely damaged or destroyed by having its roots eaten.  The lawn then turns yellow and feels spongy when we walk on it. Raccoons, skunks and birds tear up an infested turf to find the white larvae.

European Chafer grub <===>  European Chafer beetle

Lawn infested with white grubs

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What species of grub is invading Beaconsfield?

In the last few years, lawn owners in countless Canadian towns and cities, from Vancouver to Halifax, have been struggling with grub infestations caused by various beetles.  The white grubs currently infesting Beaconsfield lawns are the larvae of the European Chafer.  This insect has a one year life cycle:  The adult beetle, resembling a June bug, lays eggs around the end of June and beginning of July, which subsequently hatch into baby white grubs.   The grubs feed on grass roots from August to November.  The grubs burrow deep in the soil when frost arrives.  After spring thaw, around May or June, they come up to the surface again to devour more grass roots (and this time they are big and even more voracious). Finally, they change into beetles and emerge from the ground in mid-June.  They mate and lay their eggs over a period of about 3 weeks - end of June, beginning of July.

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Why do I have white  grub in my lawn and my neighbour doesn't?

Partly, it's "luck".  However, the beetles who are ready to lay their eggs generally choose a lawn where it is easy for them to land, lay the eggs and take off flying again.  So, they like

  • bare ground patches
  • loose, sandy, dry soil
  • lawns which are mowed short  (shorter than 3 inches) where landing and take-off is easy
  • light at night - they are attracted to light ornaments, lanterns, etc.

They will generally avoid:

  • thick lawns mowed high (more than 3 inches) where landing and take-off is difficult
  • non-grass ground covers
  • eating clover in their larval state

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How do I treat my lawn which is infested with white grub?

Grubworm damage on lawnTo protect human health, synthetic pesticides are banned in Beaconsfield.  A natural alternative exists, and that is an application of "nematodes" on the damaged lawn area and up to a meter around its perimeter.  Nematodes are microscopic worms which are parasitic to the grub, that is they enter the grubs' bodies and eat them.  Once they run out of grubs they die out.  Nematodes can be purchased at most West Island nurseries and garden centres.  The time to apply nematodes is when the white grubs are close to the lawn surface and ideally when they are small and vulnerable (August or beginning of September).  In May and June the grub are also close to the surface, but they are big and more resistant, so a nematode application is less effective.   Applying nematodes means keeping them refrigerated until application time, choosing an evening (they become ineffective if exposed to light) and  spraying them over the affected lawn area using a hose-end sprayer.  The area then needs to be kept soaked for 5-10 days to allow the drought-sensitive nematodes to live and "swim" through the soil to reach their prey for as long as possible.   The cost of nematodes comes to around $40 for covering a 2000 square foot area.

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 What if my lawn is ravaged by racoons, skunks and birds (eating the grub)?

Nature's useful predators such as raccoons and skunks have yet to be trained to tidy after themselves!   If the grub-infested area is not huge, covering the yellowed grub-infested area with chicken wire will prevent predator access until the grubs mature, change into beetles and fly away in June.  

If the area is too large to cover with chicken wire, you can try some of the following options to chase pests off your lawn:

  • Raccoons don't like getting wet.  A motion detector sprinkler available at Lee Valley Hardware can be set to spray water when anything moves within its field of view.
  • "Scent-a-gone" and "Fiche le Camp" are 100% natural products (cayenne pepper, etc.)  that can be sprinkled all around your garden and should repel many of the pests for up to 30 days.

You may alternatively choose to wait for the beetles to emerge in June, re-cover and re-seed the area and then treat again with nematodes in August (see above) so that the new lawn doesn't suffer the same damage in the fall and next spring.

Rather than completely rebuild a very damaged lawn it may be a good time to consider replanting with alternative ground cover which won't be attractive to the grub in the next season.  Some excellent hardy plants include hostas or ferns (under trees), white clover (sprinkled throughout the lawn or on its own) and periwinkle, to mention some of the most popular plants.

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How do I prevent white grub from (re-)infesting my lawn? 

We want to make our lawn 

  1. not attractive to the beetles who want to lay their eggs at the end of June and beginning of July and also 
  2. somewhat resistant to the ravages caused by their larvae, the white grub.

In general, try to 

  • replace a vulnerable monoculture of one type of grass by a mixture of different grasses and white clover.  A healthy mixed grass lawn can tolerate up to 60 grubs per square foot!
  • aerate, fertilize (preferably with compost) and reseed your lawn yearly or bi-annually to keep it lush 
  • Mow high at minimum 3 inches (so mower set at 4 inches) 
  • water infrequently but deeply if desired  to ensure the turf develops deep and healthy roots, more resistant to any root-feeding larvae. 
  • do not install small garden lamps, or at least avoid turning them on from mid-June to mid-July, when egg-laying beetles are attracted by them

Refer to our organic lawn care page for more detailed directions.

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More info about grubs

 

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