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Japanese beetle and white grubs

Scarabée japonais

The Japanese beetle is an invasive exotic insect native to Japan. It was detected for the first time in North America in 1916 on the east coast of the United States. It was then introduced into Canada in 1939 through Nova Scotia, arriving in a tourist’s car from Maine. During that same year, three other adult insects were captured in Lacolle in southern Quebec.

The adult Japanese beetle attacks more than 250 species of plants, several tree species and many fruit and vegetable plants. Examples include the elm, maple, grape vine, peach, apple, apricot, cherry, plum, rose, zinnia, corn, asparagus, soybean, blueberries, raspberries and blackberries. 

The larvae of the Japanese beetle, commonly called “white grubs,” are a real scourge for lawns. In the larval stage, the beetle feeds mainly on the fibrous grass roots, leaving behind brown patches of dead grass. 

The Japanese beetle has no known predator and is difficult to control. There is no effective technique for eradicating it. 

Biological cycle

The biological cycle of the Japanese beetle has 4 stages: egg, larva, pupa and adult. The adult beetles are very active for six to eight weeks during the summer. They prefer to feed on hot, humid days and to rest on rainy days. 

The females lay their eggs about 8 cm beneath the turf surface. The larvae hatch from the eggs and feed on the grass roots, as do June bugs. The larvae develop and spend the winter in the form of pupae

The adult emerges at the end of June or in early July and feeds on the flowers and foliage of many plants, including vegetable plants and certain tree species. 

What does it look like?

The insect has different looks during the various in its biological cycle:

Photo credits: Research Branch, Agriculture & Agri-Food Canada, Ottawa

The eggs are small and white (about 1.5 mm long). They are laid roughly 8 cm below the soil surface.

The larva is a white, C-shaped grub with a yellowish-brown head and measures less than 2.5 cm at maturity. 

The pupa is similar in size to the adult. It hides about 5 to 8 cm below the soil surface. 

The adult’s abdomen, head and thorax are a metallic green and the wings are coppery brown.

Small white tufts of hair are visible along its sides and the back of the abdomen.

The adult beetle is nearly 1 cm long and 6 mm wide.

Scarabée japonais - stade 1Scarabée japonais - stade 2Scarabée japonais - stade 3Scarabée japonais - Stade 4

Vers blancs dans la pelousePredators

Skunks, racoons, and some bird species such as starlings and blackbirds are natural predators of white grubs. Certain species of insects also help control white grubs by feeding on them. 

What can you do to prevent white grubs?

As a general rule, the key to successful prevention is having a healthy, vigorous lawn. It is also the most effective long-term solution. 

In the spring and fall

Even if a lawn has been scavenged by skunks or racoons looking for the little insects they love, various prevention measures can be taken, depending on the condition of the turf.:

  • Aerate the soil using a carrot-type aerator; 
  • Add organic matter (commercial compost);
  • Diversify the plant species that make up the lawn by including ryegrasses with endophytes (microscopic fungi that live inside some plants and produce substances repellant to certain insects), fescues and forage plants like white clover;
  • Reduce nitrogen fertilization (particularly chemical); 
  • Choose 100%-natural fertilizers whose nitrogen, phosphorus and potassium (N-P-K) content is less than 10 for each element;
  • Keep your grass tall: mow the grass to a height of not lower than 3 inches (7.5 cm); 
  • Leave grass clippings on the lawn (slow-release fertilizer);
  • Reduce watering in early June to allow the earth to harden; 
  • Keep the soil’s pH level between 6.5 and 7.0.

During the summer

  • Keep the grass long and dry during the egg-laying period, from July to August (minimum three weeks). Dry soil partially hinders the development of the eggs and larvae;
  • Turn off the lights on your property because they attract the adult beetles.

At the end of the summer

The application of nematodes (parasites) is effective from mid-August to mid-September. This is the time when the white grubs are often found at the soil surface feeding off the turf roots. Follow this procedure:

  • The soil temperature must be between 15oC and 30oC (preferably around 20oC). It’s useless to apply nematodes in May because the soil is not the right temperature. Also, in May and June, the larvae turn into pupae. At this stage, they are no longer feeding.
  • One of the most effective nematodes against European chafer larvae is the Heterorhabditis bacteriophora. It’s best to do the treatment during a long rainy period. Never apply the treatment when it’s sunny because the UV rays are fatal for nematodes. 
  • Remove the filter from the sprayer or make sure that the holes in your watering can are big enough to let the nematodes through so they reach the soil. 
  • Shake the solution of water and nematode powder regularly to make sure the nematodes don’t die due to lack of oxygen.

How to fight an infestation of Japanese beetles? 

  • Remove as many adult Japanese beetles as possible by hand and put them in soapy water to kill them. It’s easier to capture them in the early morning because the dew makes it harder for them to fly. Some people use a small vacuum.
  • Attract birds by putting out a birdhouse and food.
  • Plant toxic plants in your flower beds. Examples are fescues, ryegrasses, cultivated geraniums, larkspur, castorbeans, and horse-chestnut flowers.
  • Spread compost, because white grubs prefer sandy soils.
  • Crush the dead Japanese beetles in a little water and spread them around plants. This acts as a natural repellant. 
  • Spray the patches of infested lawn with a nematode solution. These microscopic small grubs are parasites that feed on white grubs. They are already present in the soil, but you want to increase their density.
  • Install light traps, because they attract insects.
  • Pheromone traps (controversial for small spaces). According to one study, the female beetles are attracted to the general location of the trap rather than to the trap itself. The waste of the females on adjacent plant leaves then becomes more attractive than the trap for the males looking for mates. See this link for more details:

Beware about using pesticides or insecticides
You are strongly advised NOT to use chemical pesticides in your vegetable garden. First, the insecticides are never effective in the long term because the next generation of insects becomes resistant. As well, you risk killing beneficial insects like ladybugs and staunch warriors like aphids and flower thrips. 

The application of pesticides is also subject to By-law 2006-14 concerning the use of products containing pesticides. For more details, consult the pesticide by-law. 

Information resources

We invite you to visit the website of the Canadian Food Inspection Agency as well as the Government of Canada website.