What to know about white grubs, tips to avoid them, and how to deal with them!
To know
In Quebec, white grubs are actually the larval stage of the common chafer, European chafer, or Japanese beetle. It is also important to know that the presence of a few white grubs on a healthy lawn is not problematic and is even normal. Kentucky bluegrass has an astonishing ability to regenerate thanks to its rhizomes. There is also a higher risk of white grubs when winters are milder.
Damage usually appears in the fall and then the following spring when full-sized larvae feed on the roots of the grass at the soil surface. The lawn then begins to wilt and turn brown in places and pulls up easily. It is then easy to turn over the turf to observe the white grubs. There may also be secondary damage caused by skunks, raccoons, or starlings attracted by the white grubs.
Some tips
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A healthy lawn will recover more easily from an insect attack thanks to its more developed root system.
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Keep the lawn high (3-4 inches), as adult insects prefer to lay eggs in short grass, and long grass will have a longer and more abundant root system to resist attacks.
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Irrigate as needed during dry periods to keep the lawn strong and healthy.
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Fertilize adequately with compost and/or fertilizer and ideally practice grasscycling to keep the lawn healthy.
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Aerate as needed if the thatch is too thick on old grass.
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Reseed as needed if the lawn is bare after spreading some compost or topsoil.
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White grubs prefer to feed on Kentucky bluegrass if given the choice. Fine fescues will therefore generally be less affected. Some studies tend to show that adding clover to the lawn is recommended to prevent infestations. Be aware that in the event of a major infestation, all species can be attacked by white grubs.
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Avoid leaving outdoor lights on during mating season (June to mid-July), as this attracts adult chafers.
In case of a severe infestation, the best solution will be to renew the lawn, ideally in the spring once the white grubs have finished causing the most significant damage to the lawn (around mid-May to late May). You can lay Groupe Richer, opting for a variety containing fine fescues such as Low Maintenance or Fescue, or reseed after raking dead grass and applying a thin layer of compost or soil.
Biological treatments (nematodes) are harmless to the environment and to humans. However, to be effective, they must be applied only from mid-August and in September when soil temperatures reach 20-25°C and the larvae are still relatively small and vulnerable. If the soil is too cold, the treatment will not be effective. The application should not be done in direct sunlight, and the soil must be drenched before and after treatment and kept moist for several days. As these are living organisms, the challenge is to keep them alive! These products are available at garden centers. Their effectiveness varies, generally around 50% in the best-case scenario. This treatment can be used preventively every year.
Before treating, it is recommended to consult a specialist to ensure that you are actually dealing with white grubs and, ideally, to identify the species in order to choose the best (and most environmentally responsible) strategy for your situation.
Found white grubs in your new sod?
First and foremost, know that according to entomologist Dave Shetlar, PhD, white grubs do not survive sod transplantation! Gauvreau Terre de surface and Groupe Richer cannot guarantee that no white grubs are present on their land, as we work with nature in an open environment. However, rest assured that we conduct regular screenings on all our farms to ensure that populations are kept at acceptable levels, otherwise, we would carry out the necessary treatments. As our product is dense and in perfect health, the presence of white grubs detected on our rolls will not be significant enough to affect the establishment of the lawn. Furthermore, the larvae do not multiply among themselves! They will soon transform into adults (if it's June) and fly away from the lawn!
