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Viburnum Leaf Beetle

Some Viburnums have resistance to this insect

By: Sandy Feather ©2009
Penn State Extension


Q. Last year I noticed some small, yellow “worms” eating holes in the leaves of my arrowwood viburnum (Viburnum dentatum). I also have Koreanspice viburnum (Viburnum carlesii) and ‘Mohawk’ viburnum (Viburnum x burkwoodii ‘Mohawk’), but they do not seem to bothered. Can you tell me what they are and how I can get rid of them? They made the leaves look like lace by mid-summer.

A. There is a new pest in our area called the viburnum leaf beetle (Pyrrhalta viburni). These European natives were first identified in Canada in the late seventies, and are now established in southern Maine, western New York, Erie County in Pennsylvania and northern Vermont. I have seen them feeding on native viburnums along the Youghiogheny River bike trail for the last four years or so. Their arrival in Pittsburgh is not surprising.
 


According to an Entomologist

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.


List of Susceptible Plants

Weston’s list of susceptible species includes arrowwood (V. dentatum); European cranberrybush viburnum (V. opulus); Rafinesque viburnum (V. rafinesquianum); Sargent viburnum (V. sargentii); and American cranberrybush viburnum (V. trilobum). Left untreated, viburnum leaf beetles can kill susceptible species in two or three years by repeatedly defoliating them.

doublefile viburnum
Doublefile Viburnum

Moderately Susceptible

Weston also lists moderately susceptible species, including mapleleaf viburnum (V. acerifolium); linden viburnum (V. dilatatum); wayfaring tree (V. lantana); 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.
  

Fragrant flower of Judd Viburnum
The fragrant Judd Viburnum is resistant

Adult viburnum leaf beetles are very 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 May and feed voraciously on the underside of the newly expanding leaves.

'Lacey-like' Leaf Damage

They skeletonize the foliage, leaving only the midrib and major veins intact. Mature larvae drop to the ground to pupate early to mid-June. 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 she lays her eggs. Afterwards, she seals 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.

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: horticultural oil (larvae only), BioNeem (azadirachtin), Bayer Advanced Garden Dual Action Rose & Flower Insect Killer (cyfluthrin and imidacloprid), Bayer Advanced Garden Tree & Shrub Insect Control (imidacloprid), and pyrethrins & piperonyl butoxide.


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