Boxwood plants are a foundation staple in many landscapes

Boxwood shrubs were all over the news last fall and will likely be in the news this spring in the region. The boxtree moth is one of the biggest challenges for those with boxwood in the landscape.

Boxwoods are also affected by boxwood blight, a disease that has been confirmed in the Cincinnati area, and Volutella leaf blight, boxwood leaf miner, and boxwood psyllids. Of all of these, BTM is the one to worry about now.

In a few weeks, the overwintering caterpillars will emerge from diapause. Diapause is an arrested state of growth or suspended development that allows them to overwinter. BTM overwinters as a small caterpillar.

These caterpillars will begin to grow, pupate, become adults, mate, and lay eggs. As they grow, the larger caterpillars can defoliate boxwoods quickly. Also important, know that they start in the center of the plant, hidden from predators.

Inspection is your first step. If you had BTM last year, or if you are near a known infestation, start checking the internal growth of your boxwoods for caterpillars. They will be very small in the beginning and are greenish yellow with black stripes and black dots.

As they feed in the beginning, they leave an odd “curlicue” shape to the leaf. They chew the entire leaf except for the outside edge. You may see webbing eventually, and frass or bug poop on the ground.

Pesticide sprays that are effective on caterpillars and have either boxwoods or ornamental plants on the label can be sprayed. Preventive sprays are not recommended. If you can knock down the first generation of caterpillars early, you won’t have as many later in the season.

That said, it’s suspected that we will likely have three generations in Ohio, so continue monitoring your boxwoods. I will also be monitoring boxwoods in Clark County and alert you to their status.

We have three fact sheets that help you with identification and management decisions, including which pesticides can be used. Go to go.osu.edu/BTMOhio for more information.

I also see winter injury to boxwoods in the area. This is common after a winter like the one we experienced. The foliage dries out and turns brown. If significantly damaged, it will eventually fall off. You can also prune out the dead foliage.

I am not seeing much Volutella or boxwood blight currently. However, it’s a good idea to learn about these two diseases and to be able to distinguish between them.