They’re here. Those shiny green and copper invaders. They land on our roses, our apple and cherry trees, any choice plant that we love. They eat everything in their path, but favor the flowers.
The scourge and bane of the New England gardener in July is a small, 6-legged creature. Popillia japonica, or Japanese beetles, showed up in the US around 1916, and have been bugging us ever since. They do not have any largely effective natural predators, so we are treated to hordes of them descending upon our gardens every summer.
All is not lost, however. There are ways of controlling these pests. The most effective and surefire way to eliminate the threat without further damage to the plant is to take a jar of soapy water and flick the beetles into it. It is time consuming, but if one has only a few rosebushes or other host plants, a few minutes in the morning is well worth it. Some swear by leaving the beetles to marinate in the jar, and spraying the affected plants with the resulting dead beetle wash. It smells quite unpleasant, but those that do it say it keeps other beetles from flying in.
Sprays are effective for killing beetles that are already on your plants, but more will quickly in to replace them, so it is not the best way to treat the problem. Pheromone trap bags actually do more to attract beetles to the area, so while effective, they must be placed far away from the plants you wish to protect, preferably downwind.
There are trials for some biological controls; there are a few parasitic wasps and flies that will lay their eggs inside the larva or the adult beetle, but it is not truly effective in stopping their munching until the eggs hatch. If you see a beetle with white dots on its head, it has been visited by one of these predatory insects. It’s a toss-up on whether to dunk that particular beetle in the soapy water bath or to let it live and hatch more predators…
Milky Spore is another biological control. It is a bacteria that lives in the soil and attacks the larval stage of the insect. It is entirely pet- and child-safe, and remains in the soil for up to 10 years. There have been dramatic decreases in beetle populations observed in the season following application, which has the added bonus of reducing the mole and burrower population, keeping your lawn healthier.