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Niagara Falls
Saturday, July 13, 2024
Growing Together: Japanese beetle season is upon us
Because the Japanese beetle is an introduced species here in Canada, there are no (or very few) natural predators that keep the beetle population in control.

It is that wonderful time of the summer — that’s right: Japanese beetle season. Everyone’s favourite insect … actually, I don’t think it would be on anyone’s top ten list.  

No one ever said that gardening is without its challenges. It is the challenges that keeps us invested in our gardens, keeps us learning and keeps us persevering while trying to conquer all that nature has to throw at us. 

If you have been gardening for any length of time, you have probably come across these colourful insects at some point or another.   

The Japanese beetle (Popillia japonica) is a species of scarab beetle. If you haven’t seen them yet in your garden this summer, you will see them in the next couple of weeks. 

The beetle has an iridescent, copper-coloured body and a green thorax and head. The adults measure about 15 millimeters (half an inch) in length and 10 millimeters (0.4 inches) in width.  

The Japanese beetle adults start emerging from the soil late June and July. At this stage, they come out to mate and to store up with food. 

The adult beetles are known as “skeletonizers” meaning they eat away all the leaf tissue with just the veins remaining (leaving a skeleton of the leaf). 

They feed on more than 300 species of plants with some favourites being roses, grapes, lindens, birch, cannas, hibiscus, rhubarb, and Virginia creeper. 

This insect will never kill the plants, but it does make them unsightly. 

Once the adults have mated, they go back into the soil and the next stage of their life cycle begins. The grubs (larvae form) can play havoc with your lawns.  

If you have ever had a lawn to look after before, you will be familiar white grubs, which is the larvae of the Japanese beetles. They feed on the roots of grass, killing patches of your lawn.

The larvae overwinter deeper into the soil and will then pupate four to six weeks after breaking hibernation. The adult beetles typically appear mid-to-late June and will be visible for 30 to 45 days.  

The key to winning the battle over any insect problem is to be constantly monitoring your plants at least on a weekly basis.  

If you can catch the problem early on (nipping it in the bud, so to speak), it is much easier to get ahead of the insect before they become too much of a nuisance. 

By catching it early, it also means that you can possibly treat the problem without the need of resorting to the use of strong chemicals, which should never be your first method of control.

The best and most environmentally friendly method of controlling the adult beetles is to hand pick them or shake them off the plant and put into a soapy pail of water. 

At least, by putting them into the soapy water, they die with a clean conscience.  

Never squish the beetles with your fingers. When you do, they emit pheromones that will attract more beetles to that area.  

Another way of controlling the adult beetle form is by hanging Japanese beetle traps in your yard. These hanging bags uses a food and pheromone attractant to lure the beetles into the bag where they cannot escape and disrupts their mating cycle.  

Make sure that you hang the bags at least ten feet away from the plants that are on feeding on or it may attract beetles to the foliage if placed closer. 

There is much debate as to whether the traps are an effective control of beetles.

While studies show that they do attract nearby beetles, they also show that it results in heavier feeding in that area due to the increase in beetle numbers. Some studies show that the traps are 75 per cent effective. 

Using an insecticide on the beetles is a hit-and-miss deal. In order for the insecticide to work it has to hit the insect directly.

Using an insecticide also means that you are killing beneficial insects at the same time. So, hand-picking is the safest and most effective control of the beetles. 

Because the Japanese beetle is an introduced species here in Canada, there are no (or very few) natural predators that keep the beetle population in control.

The best control of the grubs is applying nematodes to the lawn. Nematodes are microscopic organisms already present in the soil that feed on and reproduce inside the white grubs.  

The best time to treat your lawn with nematodes would be late August to early September (about a month after the Japanese beetles have disappeared).

This is the time that the white grubs begin to feed on the roots of your lawn.

Remember, not every bug in your garden is a bad bug. Take some time to learn about them before resorting to sprays that will kill beneficial insects as well as harmful insects.

Joanne Young is a Niagara-on-the-Lake garden expert and coach. See her website at joanneyoung.ca

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