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Viburnum Leaf Beetles

Some Viburnums are more susceptible than others

By: Sandy Feather ©2011
Penn State Extension


Q. The new growth on my arrowwood viburnum looks like something is eating it, but I do not see any insects. Even very tiny new leaves appear to be damaged. Do you have any idea what is causing this and what I can do about it?

A: There is a good chance the damage you are seeing is caused by viburnum leaf beetle  (Pyrrhalta viburni) larvae. They overwinter as eggs laid in the twigs of susceptible viburnum species, and they have hatched out in the last week or so.

When they first hatch, they are tiny (under one-eighth inch) and feed on the underside of leaves. You would not notice them unless you were looking for them. In my observations, their hatch appears to coincide with arrowwood viburnum (Viburnum dentatum) leafing out.
 


Insect Origins

These European natives were first identified in Canada in the late 1970ís, and are now established throughout New England, New York, Pennsylvania and Ohio. According to entomologist Dr. Paul Weston from Cornell University, viburnum leaf beetles are only known to infest plants in the Viburnum genus. The good news is that some species of viburnums are more susceptible to attack than others. The bad news is that most of our native viburnums are highly or moderately susceptible to attack.


Susceptible Plants

Westonís list of susceptible species includes arrowwood (V. dentatum); possum-haw (V. nudum), European cranberrybush viburnum (V. opulus); Rafinesque viburnum (V. rafinesquianum); Sargent viburnum (V. sargentii); and American cranberrybush viburnum (V. opulus var. americanum). Left untreated, viburnum leaf beetles can kill susceptible species in two or three years by repeatedly defoliating them.

viburnum blossoms
Doublefile Viburnum is moderately susceptible

Weston also lists moderately susceptible species, including mapleleaf viburnum (V. acerifolium); linden viburnum (V. dilatatum); wayfaring tree (V. lantana); hobblebush (V. lantanoides), nannyberry (V. lentago); doublefile viburnum (V. plicatum x tomentosum); Prague viburnum (V. x pragense); blackhaw viburnum (V. prunifolium); and Wright viburnum (V. wrightii). Although the beetles feed on these species, the plants seem to survive even when attacked by large populations of this pest.

 


Resistant Plants

Finally, Weston lists species that are resistant to Viburnum leaf beetle. They include Burkwood viburnum (V. x burkwoodii); fragrant viburnum (V. x carlcephalum); Koreanspice viburnum (V. carlesii); Judd viburnum (V. x juddii); lantanaphyllum viburnum (V. x rhytidophylloides); leatherleaf viburnum (V. rhytidophyllum); tea viburnum (V. setigerum) and Siebold viburnum (V. sieboldii). Species with thicker leaves and Koreanspice viburnum parentage seem most resistant to the beetles.
 


Insect Description

Adult viburnum leaf beetles are small (4.5 to 6.5 mm long), roughly the size of a matchstick head. They are yellowish-brown to light brown in color. They resemble their close relatives, the elm leaf beetle, but are smaller and less brightly colored. Young larvae are off-white to greenish-yellow. Mature larvae develop uniform black spots on their bodies. Viburnum leaf beetles overwinter as eggs laid in the twigs of host plants. Larvae hatch in mid-spring and feed voraciously on the underside of the newly expanding leaves.

They skeletonize the foliage, leaving only the midrib and major veins intact. Mature larvae drop to the ground to pupate in early summer Adults emerge mid- to late July and resume feeding on viburnum foliage. Plants often put on a second of flush of growth to compensate for the foliage destroyed by the larvae, only to have it devoured by the adults. Adults feed, mate and lay eggs until the first frost. Adult females chew holes in small branches and twigs to create cavities where they lay their eggs. Afterwards, they seal the cavities with a mixture of excrement, chewed bark and bits of shredded wood to protect the eggs and maintain a humid environment to ensure their survival.

viburnum blooming
Doublefile Viburnum blooming in spring


Control Options

Control options include pruning infested twigs after egg laying is finished in the fall, from October through March. Burn infested twigs to avoid moving this pest into new areas. Hand destruction of larvae and adults can provide effective control in small plantings, but would be impractical with large ones. Insecticides labeled to control viburnum leaf beetles in Pennsylvania include organic-approved materials such as horticultural oil, Captain Jackís Deadbug Brew (spinosad), and BioNeem (azadirachtin). These products are most effective on small larvae. Complete coverage of the undersides of the leaves is important for good control. Better control of mature larvae and adult beetles will be obtained with Bayer Advanced Garden Dual Action Rose & Flower Insect Killer (cyfluthrin and imidacloprid) or Bayer Advanced Garden Tree & Shrub Insect Control (imidacloprid).
 


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