June 27, 2018

Japanese Beetles Return, Threatening Local Plants

THE BEETLES ARE BACK: Leaf skeletonization is the telltale sign of Japanese beetles. Over-the-counter anti-grub pesticides can be an effective way to prevent the invasive species from laying eggs, but by the time they reach adulthood, the best and most effective form of protection is removing them by hand. (Photo by Lamba)

By William Uhl

As the summer weather heats up, Japanese beetles have been emerging across trees and gardens around Princeton. First spotted in 1916 at a New Jersey nursery, the bronze-bodied beetles have become a major problem for East Coast plant life.

“In the U.S., there’s about 200 plants that they will feed on,” said Taylor Sapudar, Princeton’s arborist. “They have a vast variety of plants that they consume and, unfortunately, they really don’t have a major natural predator here in the states.” Though they consume most kinds of plants, roses and crepe myrtles are particularly at risk.

Keeping a garden clear of Japanese beetles is no simple task. Pheromone traps tend to attract more beetles than they catch, and insecticides can hurt other harmless or beneficial insects. According to Sapudar, by the time leaves appear skeletonized — reduced to just their veins — the grubs have already become adults and prevention efforts are too late. The most effective approach is hand-picking them. Doing so in the early morning, around 7 a.m., will catch them when they are sluggish — shaking beetle-infested plants at that time will knock them off the plant and make collection easier. Once removed from plants, they can be safely drowned in soapy water.

While Japanese beetles have threatened American gardens for nearly a century, Sapudar mentioned a new threat to look out for: spotted lantern flies. “It’s another invasive species that, at this time, isn’t seen here, but I know it’s over the bridge in Pennsylvania,” said Sapudar. Spotted lantern flies have first been recorded in America in the past five years, and are known for the danger they pose to trees. If you spot the red and black-bodied adults or the mud-like eggs, report them to the New Jersey Department of Agriculture at ContactAg@ag.state.nj.us.