Penn State experts weigh in on the threat posed by box tree moths

Identifying box tree moths

Most adult box tree moths are primarily white, with a border of brown along the edges of their wings. Around 5% are completely brown. Skvarla says they bear a slight resemblance to melonworm moths, which are native to North America, but are otherwise distinctive for our area.

By the time you’re noticing moths, however, the damage may already be done.

“The caterpillar stage is the most damaging stage,” Skvarla said. “It’s the almost mature caterpillars that are doing the majority of feeding. It can kill boxwoods quickly. There are some reports that boxwoods will die within a year of heavy feeding. Part of the problem is the caterpillars, especially in heavy infestations, will strip all of the leaves off of the boxwood. Once they strip the leaves, if they’re still hungry, they’ll start chewing on the bark.”

Boxwoods may be able to recover from damage to their leaves, but once the caterpillars start stripping the bark, entire branches can die off — which can mean death for the plants.

“Even if they do recover, the shape of the bush is often lost,” Skvarla said. “So there goes the aesthetic value of having them in ornamental planting.”

The caterpillars are lime green with yellow, white and black stripes running along each side.

But the easiest way to identify them, Skvarla says, may be simply to keep an eye on your boxwoods.

“There are no other caterpillar pests on boxwood in North America,” Skvarla said. “So if you find a caterpillar on boxwoods, it’s a pretty good guess that it’s going to be a box tree moth.”

Dealing with box tree moths

Unlike with spotted lanternflies, Skvarla doesn’t recommend stomping any and all caterpillars or moths that you think might be box trees.

“Most times, private homeowners are going to be aware of infestations because of the damage they see to their boxwoods, not because of the moths that they’re seeing flying around,” he said. “So if your boxwood is really damaged, that’s the time to start going, ‘Well, maybe this is a box tree moth. I should look further, look for caterpillars, maybe look for moths.’”

The first step for anyone who suspects they might have an infestation is to monitor their boxwoods, says Patricia Prade, an entomologist with Penn State Extension who specializes in controlling pests and invasive species.

“You need to know if you have this insect,” Prade said. “So you need to constantly check if you see any larvae.”

One way to confirm whether or not you have an infestation is to purchase pheromone traps geared specifically toward box tree moths.

Prade says there are a few options for curbing box tree moths. Her first suggestion is to simply pluck them off, or trim away the infested areas.

“If you’re a homeowner, for example, and you see some caterpillars, you can handpick them and kill them easily,” she said. “It can be challenging if you have a lot of plants infested, but if you have just a couple, you can cut a branch or something like that. That’s very targeted, right? It’s a very good way to control them fast and not to just spray chemicals on the environment.”

Because box tree moths are so new, Prade says, studies are still being done to find out what chemicals are most effective against them while being the least damaging to other life. In the meantime, she says, homeowners can seek out pesticides targeted toward caterpillars, which are likely to kill box tree moths.