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Controlling Borers on Pines

Cliff Sadof Department of Entomology

Purdue University




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. 



            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