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Over the Fence

Where gardeners come to find out what's happening out in the yard.

The New Guy in Town

Posted by Richard Hentschel -

Reports have been scattered, but throughout Cook and DuPage counties, homeowner's have discovered unfamiliar insects feeding on their viburnums in the landscape. This turns out to be yet another pest from a foreign land, the Viburnum Leaf Beetle. Like many of the insects that are not native to the United States, the source for this beetle happens to be Europe (the Emerald Ash Borer originated in Asia). The viburnum leaf beetle has established itself in the northeast and began to show up in Illinois in the last two years.

The viburnum leaf beetle feeds on foliage leaving irregular shaped holes, while the larvae stage feed much more heavily as they develop into larger versions before they pupate. Heavy feeding leaves the leaf nearly skeletonized. Additional damage is done by the female beetle by chewing into the current season's twig or branch growth to deposit the eggs which will hatch in 2016. Once the egg laying activity is spotted, in a general way it will resemble the damage done by the female cicada. The adults are not winter hardy and will perish at our first killing frost of the fall. Reports are that heavy feeding and subsequent egg laying can cause plant death if left untreated in as little as 2- 3 years.

The Viburnum Leaf Beetle favors those viburnums that have a smooth shiny leaf. In our area, Viburnum dentatum (Arrowwood Viburnum) seems to be the favorite viburnum of the beetle so far. Those viburnums that have "hairy" leaves do not seem to be attractive to the beetle. Other smooth leaved viburnums common to our area include American and European Cranberry Bush. Next in line for the beetle is Viburnum lantana (Wayfaringtree viburnum) which is also frequently planted. Down the list further for being moderately susceptible is Viburnum lentago (Nannyberry viburnum), another one planted in our area.

The best management practice is to look for and remove any twigs with evidence of the female egg laying activity. This will drop the population of larvae down significantly. The next best practice would be to treat the newly emerging larvae as soon as possible. Like all insects, controlling them when they are young is much easier, plus less feeding damage to the plants too! If you suspect that your viburnums in your landscape have been fed upon by the Viburnum Leaf Beetle, the Illinois State History Survey would sure like to know so a map can be developed to track the spread. Contact Kelly Estes at kcook8@illinois.edu or

Other insect pests in our area from foreign lands include Gypsy Moth which is monitored by various state and federal agencies and treated when their numbers rise significantly. Treatments for Gypsy Moth have occurred the last two years in Kendall, Kane and DuPage counties. Already mentioned is the Emerald Ash Borer. The Emerald Ash Borer is now responsible for killing well over 25 million trees in the Midwest. At this time, nearly the entire state of Illinois is in quarantine and the ongoing efforts of the Illinois Department of Agriculture is to slow the spread.



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