This pesky critter is destroying your boxwood shrubs. How to stop it

Throughout the year that I write these articles, I try to avoid repeating information because I prefer to continue to offer you different and new information. Sometimes I have to make exceptions. This happens when something happens that poses a potential threat to plants that might be growing in your landscape.

The boxwood moth is an insect that certainly fits this description. This insect causes significant damage to most varieties of boxwood shrubs. Boxwoods are the most common evergreen shrubs used by most landscapers.

This insect has spread very quickly in parts of southwest Ohio. It was first detected in Loveland, on the border of Hamilton and Clermont counties, in 2023. Last year, in 2025, it was spreading and appearing in many other communities. These were primarily on the east side of I-71.

Most people don’t notice the damage until it’s too late. Insects are difficult to detect. There are no insecticides available that you can spray to prevent damage. I want to help you prepare a strategy so you can be prepared to protect your boxwoods.

First you need to understand the life cycle of this insect. The insect when it comes to a moth is not the problem. These butterflies lay their eggs in boxwood bushes. Then the eggs hatch into caterpillars. That’s when the damage is done. They are lime green with black stripes. They are very well camouflaged and big eaters. This is why you don’t see them until the damage is severe enough.

Then they form cocoons and then hatch again as moths. This life cycle occurs quickly, leaving the possibility of 3 to 4 generations of this insect in one season. Once you have them, you need to continually monitor your plants on a weekly basis.

They become active when the weather starts to warm up. You will need to start monitoring your boxwood around mid-May. This would be especially true if you had them last year or if they were present in your neighborhood.

You can start the monitoring process by getting a trap to catch butterflies. Garden stores are starting to sell them. You will hang this trap near your boxwoods. They are baited with a lure to attract the butterfly. The trap will serve two purposes.

The first is to hopefully catch the butterflies before they can lay their eggs. However, there is no way to know if they have laid eggs or not. The second purpose of the trap is that it alerts you that it is time to start monitoring your boxwoods for worms. You need to gently spread the branches with your hand to look inside the plant. The eggs are usually buried deep in the plant and feeding begins inside.

When you see the first worm, it’s time to start treating the plants with an insecticide. In the short time we have been fighting these insects, products containing Spinosad have proven to be the most effective. Spinosad works on contact with the caterpillars. It also has a residual effect when on foliage, allowing caterpillars to ingest it.

This Spinosad will only stay on the foliage for 3 to 7 days. The spray strategy is to spray once a week for three weeks when you see the butterflies and/or caterpillars. After a three-week spray cycle, you will need to repeat spraying 3 to 4 weeks later. It is then that a new generation could hatch. You will have to continue this as long as it is warm in the fall.

It’s understandable that this is a challenge you don’t want to accept. If you choose not to spray, you will need to consider replacing your boxwoods with alternative shrubs.

This article originally appeared on the Cincinnati Enquirer: This Insect Is Killing Your Boxwood Shrubs. Here’s how to protect them