Viburnum leaf beetle
Viburnum leaf beetle, Pyrrhaltaviburni (Paykull), is a chrysomelid
beetle, aptly named, as it feeds on leaves of viburnum. The damage potential
from the beetle is quite extensive, if not managed.
DESCRIPTION OF THE PEST
Viburnum leaf beetle overwinters in the egg stage. Eggs are
inserted into pits chewed into the stems, generally in a straight line. Larvae
hatch from the eggs in the spring mid-late April. There are three larval stages
(instars). Larvae eventually drop or crawl down the trunk of the plant to
pupate in the soil. Pupae remain in the soil for about 10 days. Adults are
found in the summer in July. Both larvae and adults feed on leaves. Adult
females begin laying eggs in the late summer and fall. She can lay up to 500
eggs during her lifetime. There is only one generation per year.
Look for oviposition scars on current year`s
growth. Look for holes in leaves in the spring by the larvae. They usually feed
on the leaf undersides. Like many leaf beetle larvae, they superficially
resemble a caterpillar but lack crochets (hooked appendages) on the prolegs.
The newly hatched larvae are very small, around 1/8" long and are light
yellow to tan. Their feeding damage tends to be leaf skeletonization. Larger
larvae are light to dark green with black spots.The adult beetles are
bronze-brown color and similar in size to an elm leaf beetle. Feeding by the
adults tend to show up as larger holes in the leaves. Dieback from oviposition
can also lead to terminal dieback on stems.
The most effective means of control for small scale plantings is
pruning and destroying infested twigs after egg laying has ceased in the fall,
anytime from October to April. When pruning is not practical, a number of
pesticides may be effective in controlling VLB.
Home gardeners may use acephate, carbaryl, cyfluthrin,
imidacloprid, or malathion. Spray when larvae first appear in early May for
best results. If damage from adults is excessive, a second application in mid-
to late-summer may be helpful.