Japanese beetle season is beginning in Maine, and you are likely to see plenty of shiny green scarabs on your plants and in your lawn again this summer.
Populations have been increasing over the past few years, helped by mild winters. While they won’t kill your crops, the leaf- and grass-eaters are still an unwelcome sight to Maine gardeners and can be deterred through several simple methods.
“Based on the last two years, this could be a banner year for beetles,” said Jim Dill, pest management specialist for the University of Maine Cooperative Extension.
It’s too early to say for sure, because they could still be affected by fungi, bacteria or other killing factors. But the expectation is that it could be bad, Dill said.
The beetles spend the winter underground, and without periods of snow cover or below-zero temperatures, fewer of them die off each year. The adults are coming out now in early July and will soon lay their eggs in grass.
When grown, the beetles eat more than 300 types of Maine crops.They’re most likely to harm fruit plants by nibbling raspberries or grapes, and also have a taste for roses, apples, stone fruits, corn and beans.
They leave damage to plant leaves that looks scary, but they won’t kill your plants. They do not spread disease, either, Dill said.
It’s another story in your lawn, where beetles eat grass roots in their young grub stage. If you’re having turf problems, though, it’s now more likely from other species such as chafer beetles.
Ten or 15 years ago the Japanese beetle was probably the biggest culprit destroying turf, but other species of white grubs that thrive in warmer conditions have pushed them out to more weedy grasses.
Watering nematodes into your lawn for several years can make a difference on all types of white grubs. Milky spore is a popular treatment in other states, but Maine soil is too cold for it to be your most effective choice, Dill said. It also only targets the Japanese beetle.
Traps have become a popular option for managing beetle populations, but be careful how you use them. They include pheromones that attract beetles ready to mate. Not all the beetles will make it in the trap, so Dill recommends placing them from 50 to 100 feet away from the plants you want to protect instead of right near them.
In the morning or evening, you can take a walk with a bucket of soapy water and knock the beetles into it. When they’re cold, as they are at these times, they are likely to fall in rather than fly and perhaps swarm you.
A handheld vacuum dedicated to beetle removal is another good option, Dill said, and can be a fun chore for kids.
Insecticides are also an option, but they might not be worth it when compared to the amount of damage beetles do.
Some gardeners spray neem oil on foliage, which will kill the next generation of larvae when adults ingest it. Kaolin clay spray is another deterrent.
Or, instead of a bucket of soapy water, put the mixture in a spray bottle to target-shoot beetles. One tablespoon of soap to one cup of water will work, and you can also try the mix with a traditional soap instead of a dish detergent. A sprayed mix of cedar oil and water will also repel them.
In future seasons, consider adding plants less attractive to the beetles, such as lilacs, forsythia or magnolia.
Whatever you do, it’ll be more effective if you can coordinate with your neighbors to control the beetles too. That way they will be less likely to fly in from nearby properties, Dill said.
