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
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.
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
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.
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
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.
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.
Doublefile Viburnum blooming in spring
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).
Renovating Privet Hedges