It is early July, customers are bringing in leaves that have been chewed to pieces and phone is ringing asking what is stripping all the flowers off their roses. Over the last few years plants in south western Ontario have been infested by the Japanese beetle.
The adults are easily indentified as a beetle about 15 mm long and copper and turquoise in colour. They are clumsy flyers. The adults spend most of their time feeding on soft plant tissue. The infestations start in late June and last till about the beginning of August. During this time the females lay eggs continuously. The females like to lay their eggs on open turf areas. These eggs hatch into white grubs that feed on the tender roots of grass plants leaving ugly bare patches.
As the name suggests they originated in Japan and there they pose no problem because they are controlled by native predators. Accidently introduced into eastern north America they have spread over a wide range. So far there are no native predators to eat them.
There are some plants that they prefer to be sure. They love tropical and perennial hibiscus, rose of Sharon, canna lily, fruit trees and other members of the rose family. When one beetle flies to a plant they produce pheromones that attract more beetles.
Dealing with the Damage
What can be done? There are traps you can buy that meant to attract and trap adults. I have found this ineffective, they are poor flyers and land on a choice plant before they make it to the trap, Japanese beetle traps just seem to attract more pests to your property. Keep an eye on which plant they favour, because they like to congregate, take a dish of soapy water and simply knock them into water. You need to do this on a regular basis because they are attracted to each other.
As for the grubs we are not legally able to buy pesticides to kill them. Nematodes are becoming more popular but with only mixed results. Nematodes must be applied at exactly the right time in the grub’s life cycle and the conditions have to be perfect. Remember and an individual nematode only lives for a few hours and has to re-introduced with every new infestation. If you irrigate your lawn regularly during the hottest part of the summer the grubs will thrive, letting your lawn go dormant at this time will deprive them of their food source.
Most importantly we should be trying to minimize the beetle problem, eradicating them at this time isn’t an option. Use trap plants, plants they seem to gather to, and use the soapy water on them (one part dish washing liquid to 19 parts water). As for grubs you could try an alternative ground instead of traditional grass, they really thrive in open turf. Since the pesticide ban and watering restrictions you might have to change the way we garden. As for Japanese beetle adults they are finished in 5 to 6 weeks and then most plants quickly recover.