BTM was first identified in Canada in 2018 and then moved into Michigan. It has moved into Ohio, and within the last two years, the population has expanded. ODA has male-attracting pheromone traps around the state. During the most recent inspection of the traps, adult males were found.
This invasive pest, which only feeds on boxwood, has some people removing boxwood as well as not planting them at all in the landscape. But “don’t throw the baby out with the bathwater,” as the say.
It can be controlled. The future for boxwoods is still good in Ohio.
BTM currently has two generations in Ohio and emerges from the overwintering pupae in May and June. The moth lays her eggs on the boxwood plant, eggs hatch into larvae, and they feed, going through seven molts (growing out of old skin) until they pupate and then become adults.
The second-generation adult moths lay their eggs, and the same happens again. However, currently, they pupate and overwinter as pupae. In warmer areas, literature suggests that there could be up to five generations in a year. Right now, Ohio has two.
What do you do if you have boxwoods in your landscape? The first thing is to monitor your plants. Now and next spring, look closely. The newly hatched caterpillars tend to start feeding on the inside of the plant where you aren’t looking. By monitoring and getting them early, you can spray Bt, or Bacillus thuriengensis, a very safe biological control. It won’t work, however, on larger caterpillars.
There are numerous sprays available that can be used. The key is to kill out the entire first generation if possible. The theory is that there might not be a second generation. However, if others in the area don’t kill them, there may be moths laying eggs again in the summer. Monitor.
What do you do if you live in areas where your boxwoods look dead? You can rejuvenate them by pruning them back to about a foot or so in height. Keep in mind, the larger the plant, the longer it will take for them to come back since they store their food in their leaves.
Credit: CUSTOM/Joe Boggs
Credit: CUSTOM/Joe Boggs
This caterpillar can completely defoliate boxwood in up to 10 days. We have very few insects that can do this. As they grow, they eat the entire leaf. An important note: BTM is different than boxwood blight — there will be no leaves on the ground since they are consumed.
There is not enough room in this column to write about the details of BTM. Go to go.osu.edu/BTM and review our new fact sheets that Joe and others created to help navigate the management of this pest.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
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