Info about Pest Control
Viburnum Leaf Beetle
The viburnum leaf beetle, of VLB, is an insect that is native to both Asia and Europe. It has, however, been a North American garden pest since it was first spotted in Canada’s Ottawa-Hull region in 1978.
The viburnum leaf beetle is a relative of the elm leaf beetle and is capable of quickly stripping away the leaves of viburnum plants. This is because both the adult beetle and the larva enjoy eating the leaves of these plants. Although an initial infestation of the viburnum leaf beetle will not completely kill the plant, it will eventually die if it is defoliated by the insect for two to three consecutive years.
The viburnum leaf beetle has a fairly bland appearance and, therefore, is easy to overlook. The adults, which measure about ¼ inch in length, are dull brown. In addition, their eggs are very tiny. The larvae of the viburnum leaf beetles grow to about ½ inch long and are a greenish-yellow color, which helps them to blend into the foliage.
During the winter, the viburnum leaf beetles remain in egg form on the branches of the plant. In May, they hatch and the larvae feed on the new leaves that have developed on the plant. New larvae are very tiny and, therefore, are easy to overlook when they first emerge.
Similarly, the damage they cause to the plant may initially go unnoticed. This is because the holes can be as tiny as a pinhole. After about a month of feeding on the plant, however, it is hard to miss the damage they have caused.
In June, the larvae will descend to the ground. Here, they will pupate and the adults will emerge in late July. The adults then continue eating the plant. In all, it takes the larvae about eight to ten weeks to become an adult.
In late summer and through to the first frost, the female lays her eggs, which may be as many as 500 in just one season. To do so, she chews holes through the new growth in the plant and lays her eggs within each of the holes. She then covers the holes with excrement and chewed twigs in order to disguise and protect them. Although it can be difficult to spot these holes, you should be able to find them if you look at the underside of the twig. The holes will be found here and they will be in a straight line.
To avoid an infestation of the vibernum leaf beetle, it is best to plant varieties of viburnum that are resistant to these pests. You can get an updated list of the varieties that are the most resistant, as well as those that are most effected, by viewing Cornell University’s Vibernum Leaf Beetle Citizen Science list at
www.hort.cornell.edu.vlb.suspects.htm.
If you decide to plant viburnums in your garden, be sure to keep a close eye on them. Closely inspect the small twigs in the early spring before the eggs have a chance to grow in May. Look at the growth from the previous year to see if you can find any scars or holes from egg laying. The warmer temperature of the spring will cause these holes to swell, which can cause the caps to fall off and make them easier to spot. Prune and destroy any infested wood before the eggs have a chance to hatch.
When the leaves on the plant begin to open, check both sides for larvae and prune and destroy any that are infested. If you choose to use chemical pesticides, it is best to apply them while the larvae are still in their early stage. This is because adults will simply fly away or they will drop to the ground to avoid the spray. Your local Extension Office should be able to recommend the best pesticides for your area.