UNION COUNTY, NJ — In and around the county residents are quite used to seeing creatures like white-tailed deer, squirrels and fireflies as the temperature warms. One common insect is often overlooked despite its prevalence and pronounced ecological effects; the Japanese beetle.
With July upon us, it’s time to start looking for them, according to arborist Bob O’Rourke, who has worked for the Davey Tree Expert Company in New Jersey for 30 years.
“When we do have a bad year, they severely damage about five or six species of tree,” O’Rourke said. “They can devastate and literally strip all the leaves off the tree.”
The Japanese beetle is an invasive insect that feeds on various forms of plant life. They were first discovered in the state in the early 20th century, and have since spread throughout most of the United States.
While their activity in recent years has dwindled, the beetles’ presence in large numbers can have an enormously detrimental impact on the local environment, O’Rourke said.
According to O’Rourke, there has not been a local outbreak of these insects in several years. Although the specific causes of an outbreak are unknown, he credits the reduced beetle problem to successful containment efforts and favorable winter weather.
“About five years ago it was really, really bad,” O’Rourke said. “A lot of people set traps and put grub control down, enough to the point that we may have decreased the population.”
Adult Japanese beetles usually emerge in July. They feed on tree leaves, consuming the plant matter between the stems and leaving the leaf with a skeletal appearance. According to O’Rourke, damage to the leaves will create a “stress factor” for the tree, which leaves it vulnerable to diseases.
“When the leaves are compromised by any insect, it decreases the vigor in the tree,” O’Rourke said. “After feeding on the trees, the beetles go into the lawn and lay eggs. Those eggs hatch in August, and the larva damage the lawn.”
Japanese beetle larvae grow by feeding on the roots of grass, so beetles often lay eggs in lawns. According to O’Rourke, this can seriously damage the lawn that hosts the larva.
“In severe years, you can have whole lawns wiped out to where the lawn peels up like a carpet,” O’Rourke said.
Simple and inexpensive traps exist for the purposes of catching these insects, but according to O’Rourke, they are often improperly used. The traps contain a pheromone that attracts the beetles, which are then caught inside a container and unable to fly out.
“A big mistake people make is they will buy the trap and put it by their tree, and often the beetles will feed on the tree a great deal before they wind up going in the trap,” O’Rourke said. “It’s recommended that traps are put in a far corner of the property, at least 50 feet from the tree, to try to draw the beetles away and into the pheromone.”
When an infestation is too extensive for traps, arborists like O’Rourke create treatments using systemic soil insecticides to efficiently kill any beetles feeding on the treated vegetation. O’Rourke said it is easy to tell when such measures should be taken.
“If you go a year and you barely see a Japanese beetle, then you don’t have to worry about a grub problem,” O’Rourke said.
Though it has been a slow year for Japanese beetles, it is important to pay attention to the amount of beetles seen in the summer months, as to not let it get out of control.
“They’re above ground for maybe six weeks, and that’s your opportunity to control them with a treatment,” O’Rourke said. “It’s a short-lived cycle of feeding, but if there’s a lot of beetles it can be a devastating one.”