Fighting with Japanese beetles

This week, Japanese beetles showed up in the garden. They are the ones with the green heads and copper bodies, about a half-centimetre long. They are quite beautiful in the abstract; the problem is they have a taste for flowers, leaves, and fruit in gardens. We found them on our hibiscus, on our Rose of Sharon, and on our Stargazer Lilies. They are ravenous and eat through several layers of petals to the point where blooms look like Swiss cheese. They are known as skeletonizers, meaning they eat the most tender part of a plant, on both blooms and between leaf veins. A friend reported that Japanese beetles were feasting on his ferns. They are known to love raspberry plants, cannas, roses, and maples. Here is a comprehensive list of plants that Japanese beetles feast on.

Their life cycle as adults is about 6 to 7 weeks, from mid-June to about the end of August. Strangely enough, they are attracted to each other, so if you have a few in your garden, you’ll soon have an infestation. They prefer plants that are in direct sunlight, so check those first. They are easiest to try to catch in the early morning and early evening; they are most active in the hottest part of the afternoon where they will take flight if they sense danger.

To control them at the grub stage, where they spend 10 months of their lives, try nematodes. You can get these at garden centres and Canadian Tire as well.

Japanese beetles arrived in North America more than a century ago. In Japan they are part of the food chain of birds, frogs, and lizards, but here they have no natural predators. We prefer to pick them off and crush them rather than using chemicals. Yes, you have to crush each one because their shells are quite hard. If you don’t crush them, you will be surprised at the number that just fly away.

You can use mix dish soap, garlic powder, and cayenne pepper dissolved in water in a spray bottle and apply it to your plants. Japanese beetles will find your plants less appealing with this mixture. You can also try baby powder sprinkled directly on your plants.

Here is good information about their lifecycle, from the University of Kentucky.

Here is information on methods of controlling Japanese beetles.