Nature abhors a vacuum. For years, viburnums have been carefree shrubs. They flower consistently each year, some with fragrant blooms, and produce colorful berries in fall for beauty and for the birds. Viburnums have few pests or problems, until now.
Over the last 10 years, a new bug has been in town. The viburnum leaf beetle. If you've noticed the leaves on your viburnums are skeletonized, check on the leaf underside. You'll often see a small, yellowish caterpillar feeding. While the damage from this viburnum leaf beetle caterpillar won't kill the plant, it does make it look like a mess until the plant leafs back out. Repeated defoliations can harm the plant over time.
It all starts in summer and fall. The adult beetle creates cavities on the undersides of the branch tips and lays eggs. They cover the eggs with a mixture feces and bark. The eggs overwinter and hatch in mid-May. The larvae start feeding soon afterward.
The simplest solution is to plant viburnum species the beetle doesn't like. Resistant species include the Korean spice, Doublefile, and the Japanese snowball viburnums. You'll find the most damage on the Arrowwood, American cranberry, and European cranberry viburnums.
This time of year, if the caterpillars are still present, a single spray of insecticidal soap is effective in killing them. You can also spray horticultural oil in late winter, before leaves emerge, to kill the overwintering eggs.
This winter, look for the raised bumps on the branch twigs, and prune those branch tips off and discard. This will prevent the eggs from hatching and starting the whole damage cycle.
Next week on the Connecticut Garden Journal, I'll be talking about historic gardens. Until then, I'll be seeing you in the garden.
