Controlling
Borers on Pines
Cliff Sadof Department
of Entomology
Purdue University
11/1/00
Borer
symptoms include sawdust on the limbs, holes in the bark and the exudation of
gummy sap.� In this article I will talk
about two groups of borers: those not requiring dead pines to breed, and those
rquiring dead pines and stumps to breed.�
Pine shoot beetle and other shoot borers will not be discussed.
Identify
members of this group by the size of the hole, the kind of sawdust and the pattern
of boring in the wood.� Some of the more
commonly encountered borers include several species of bark beetles, pine
sawyer beetles, and Zimmerman pine moth.��
����������� BARK BEETLES� are among the most common boring problems
detected in declining pine in urban and rural areas.� These and other related bark beetles attack trees that are under
environmental stress, due to weather, too much or too little water, or
construction injury. One of the pine engravers, Ips pini� is frequently collected from declining
stands of white pine.� Symptoms include
holes as thick as a pencil lead along on the main trunk and major limbs.�� The small black bark beetles are about 3-4
mm long and have visible spines along the edge of the indentation near the hind
end of their wings.� Once beneath the
bark, adults lay eggs that hatch into small grubs that bore beneath the
bark.� Grubs eventually hatch into
adults that re-infest the declining tree.�
Large numbers of bark beetles (>100 per square foot of bark) can
emerge from declining trees carrying a blue staining fungus that attacks the
plant vascular system.� This fungus� can�
be passed to new trees when attacked by the adult bark beetles. BARK
BEETLES on pines have several generations of adults from mid April through mid
September.� Many bark beetles, including
Ips pini ,feed on PINE and SPRUCE.
����������� �Healthy trees can often withstand attack from small numbers of
disease-infested bark beetles.� The
fungus trips on a chemical switch that causes the trees to produce large quantities
of toxic compounds called monoterpenes that kill beetles and fungi.� A healthy tree can succumb to beetles when
repeated attacks by the beetles deplete its energy reserves and reduce its
capacity to defend itself.�
����������� PINE SAWYER BEETLES (long horned
beetle) are often reported on white and Scotch pine.� Infested trees have holes about 3/8" wide that exude a
tremendous amount of finely shredded wood shavings and brown grainy excrement.
Peeling back the bark IN the spring and fall should reveal 3/4" long white
round headed borers with strong brown mandibles.� These beetles will girdle trees and can transmit PINE WILT
NEMATODE, a round worm that clogs the vascular system of pines, killing them so
fast that their needles yellow and wilt before they brown.�� Like bark beetles and blue-staining fungi,
healthy plants are able to withstand some attacks.� The pine sawyer beetles winter as larvae and emerge as adults
from mid-May through July.
����������� ZIMMERMAN PINE MOTH, is a common
pest of Austrian and Scotch pines and�
Norway spruce that can kill tree limbs and tree tops.� It is usually found boring into the trunks
of trees near where the branches meet the main stem.� Unlike the previously mentioned pests, these insect causes the
tree to produce a large amount of gummy sap and sawdust pellets that are most
apparent from late June through early August.�
Adults emerge from trees from late July through August and lay eggs in
wounds. Young caterpillar feed in bits of bark until they dig their shallow pit
where they spend the winter.� When the
weather warms in early April the caterpillar crawls out of its resting place
along the exposed bark surface to either the tip of the leader, or to where the
branches join the central trunk.� When
it bores to where branches join the central trunk it produces the gummy wounds,
sometimes girdling or killing limbs or tree tops.
����������� You can reduce the chances of
successful borer attack by maintaining tree health.� This includes proper mulching and watering. �When you spot a half dead tree with one of
these pests, remove it and destroy the whole tree.� Heavily damaged trees are difficult if not impossible to save.� When you remove these trees between October
and April you kill boring pests inside and reduce breeding material. Treat
adjacent healthy trees the following April with a long lasting insecticide,
like Astro (Permethrin), Talstar T&O(bifentrhin) or Sevin XLR (carbaryl) or
Lindane, to kill bark beetles, and Zimmerman pine moth entering trees in the
spring, and in May to kill pine sawyers.�
A second spray in August- can kill Zimmerman pine moth caterpillars as
they hatch from eggs and bore into trees.�
����������� A somewhat related group of pine
pests are those that breed in dead trees and stumps.� These mainly cause problems in Christmas tree plantations and
windbreaks and street plantings where young trees are planted near stumps.�� These include the PALES WEEVIL, NORTHERN
PINE WEEVIL,� and PINE ROOT COLLAR
WEEVIL.
����������� The pales and northern pine weevil
are two closely related species that chew the twig surface in the fall and
spring, causing twigs to ooze sap and turn brown in early summer.� Adults are black snout-weevils. Pales weevil
is about 1/2" long with small gold spots.�
Northern pine weevil is somewhat smaller with white patches on the end
of its hind wings.� Larvae of both
species are white and legless.� Adults
are attracted to cut pine and mate on pine stumps when the weather warms in
spring.� Females burrow to roots of cut
stumps to lay eggs. Larvae feed on these roots until they pupate in chip bark
cocoons and emerge as adults in September.�
During the summer adults spend days in leaf litter and nights feeding on
the twigs.�� Adults live for two years
and lay eggs during both summers.�
����������� Pine root collar weevil is less common in the landscape, but can readily kill trees. Adults feed on the bark near the soil surface and young feed on root and root collar.� Injured plants produce large amounts of darkened sap at or near the feeding sites that are clearly visible at the soil line.� Partially girdled plants become weak and are subject to bark beetle attack.� Completely girdled plants die and turn brown.� Adults are black snout-weevils. Larvae are white and legless. Adults live for two years and lay eggs both summers.� They then chew into bark of live trees and lay eggs in injured sites from May to September.� Eggs laid in spring become pupae or adults by September.� Eggs laid in summer winter as larvae and become pupae the following July.�� Larvae feed on root and are present all months of the year.�
CONTROLLING
BORERS ASSOCIATED WITH DEAD PINE
����������� Control of these three pests involves
removal of breeding sites (stumps of host plants), or spraying with residual
insecticide can reduce the chances for tree injury. Improve timing of sprays by
monitoring for the emergence of adults in spring.�� Place freshly cut disks of pine�
( 2" thick) on the soil surface in a discrete area near an infested
site and check upper and lower surfaces for adults.� When adults are found, apply a long-lasting broad spectrum
insecticide like like Astro (Permethrin), Talstar T&O(bifenthrin) or Sevin
XLR (carbaryl) or Lindane to stumps to kill mating weevils and on live trees to
kill adults attempting to feed on twigs.�
Spray stumps in the fall to kill emerging adults. Entomophagous
nematodes have been used to pine root collar weevil.� Best results are likely to occur in early June� after soil warms, and most beetles are in
the larval stage