of Rhode Island GreenShare Factsheets
The white pine weevil, native to North America, is a very
serious pest of white pines in the forest and can also stunt
and disfigure trees grown for ornamental purposes.
The trees which bear the most serious attacks are white
pine, Norway spruce and jack pine. Other trees which are commonly
attacked are pitch pine, Japanese red pine, western white pine,
limber pine, foxtail pine and red spruce. Scotch pine, western
yellow pine, mugho pine and black spruce sustain occasional
attacks. The conifers which are rarely attacked include red
or Norway pine, Himalayan blue pine, white spruce and Douglas
The adult white pine weevils are reddish-brown snout beetles
about a quarter-inch long which are marked irregularly with
patches of brown and white scales. The adults overwinter in
litter on the ground and resume activity in April. The weevils
prefer small trees 3 to 15 feet in height and seldom attack
trees growing in the shade of other trees.
The weevils feed on the bark tissue of the terminal shoots.
They then chew small pits in the leader and lay their eggs
there in May. The eggs hatch in 7 to 10 days and the legless
grubs feed on the inner bark and tissues that produce tree
growth. When several larvae are feeding, the shoot is soon
girdled and dies. The grubs mature and pupate inside the leaders.
Adult beetles emerge from late June to early September. Since
spring egg-laying lasts more than a month, one shoot can contain
larvae in various stages of growth. There is only one generation
a year. After emergence, the beetles spread to new areas by
The first sign of attack ranges from small, glistening
droplets to resin oozing from tiny holes in the leader. This
is caused by adult weevils that are feeding before egg-laying.
As the terminal is girdled, the new shoot of the current year's
growth withers and the tip bends over and turns brown. This
stage of damage usually becomes noticeable about mid-June.
Examination of the dead shoots will show the white larvae or
pupae beneath the bark or in the wood and pitch. That year's
growth is always killed, but two or three years of growth is
commonly killed. The result is forked and crooked trees.
Preventive Pruning of Infested Leaders:
At low infestation levels, prompt removal and disposal
of infested leaders before the weevils emerge reduces the chance
of population buildup. Prune infested leaders at a point below
the tunneling grubs, at least including some green bark at
the base of injury. Immediately burn, chip, or deeply bury
cut leaders to destroy the larvae and pupae. Wilting leaders
may be detected in June and July, but be sure to prune by mid-July
to prevent emergence of adults.
Pruning infested leaders early in the season before completion
of new shoot growth promotes establishment of a new dominant
branch and correction of the stem form. Early pruning also
prevents the grubs from penetrating the node of the first whorl
of branches, reducing the amount of weevil-induced damage.
Cultural Control Methods:
One alternative for preventive pruning is to avoid planting
white pine or spruce in areas of high weevil hazard. Heavy
clay soils and densely sodded fields might increase the chance
of weevil attack as well.
Partial shade (45-50%) helps protect the leaders from
weevil attack by encouraging less preferred bark thickness
and bark temperature. White pines can be planted beneath hardwoods
or other conifer species. These trees then can be removed when
the young white pine trees are 16 to 18 feet high. However,
the disadvantage of partial shade--reduced rate of growth--must
be kept in mind.
Placing tanglefoot or other sticky substances on the wrapped
leader, or wrapping tape with the sticky side out around the
leader, may also prevent infestation. Never place sticky materials
directly on the tree, as injury may result.
Some homeowners report success in controlling larvae by
pinching terminal leaders. Because larvae feed just beneath
the thin bark, it is possible to squish the larvae within the
stems before they severely damage the shoot. This approach
is best used in early June on short trees with shoots that
show the resin from adult feeding and oviposition.
If it is necessary
to use chemicals against this insect, it is best to use materials
with moderate residual activity or systemics which are absorbed
by the plant. Call the URI Gardening Hotline or check your
gardening center for currently registered insecticides. To
spray effectively, thoroughly spray the top half of leaders
before the buds open in the spring, before May 1 in most years.
The leaders and especially the buds must be sprayed to the
point of runoff. An extended sprayer rod that reaches leaders
of taller trees helps speed up treatment.
Corrective pruning of injured tops should remove all but
a single shoot (one of the smallest) at the topmost healthy
whorl. This promotes healing, resumption of vertical growth
and straightening of stem form. Corrective pruning may be postponed
until the year after weevil injury to ensure that at least
one lateral branch survives ice and snow damage or repeated
weevil attacks the following year.
Adapted from the
University of Connecticut Integrated Pest Management Program
the University of Maine Cooperative Extension, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program