White pine weevils are becoming an increasing problem
in Indiana landscapes. Figure 1 shows how the top of a mugho pine can
be killed after weevil larvae tunnel into stems. Figure 2 shows the
holes left in the stems after adult weevils have left the shoots. These
weevils are known to attack all species of pines, Norway spruce and
Colorado blue spruce.
Adults winter in leaf litter and fly to tree tops to mate when
the weather warms in the spring. Females lay many eggs in terminals that
hatch into grubs that bore into shoots. Legless larvae continue to feed
until July when they pupate in chip bark cocoons. Adults emerge in August
and chew on twigs.
In early spring (April) applications of broad spectrum insecticide
to tree tops should be timed to kill adults gathering on twigs. Prune
and destroy damaged leaders that contain larvae or chip bark cocoons before
adults emerge in August. Mixed species plantings of pines are less likely
to build damaging numbers of this pest than pure stands of susceptible
species.
--Cliff Sadof, Department of Entomology, Purdue University |
Figure 1. Top of a mugho pine
after weevil larvae tunnel into stems
Figure 2. Holes left in the stems
after adult weevils have
left the shoots
|
