Weevil in Spruceby Robert C. Wilson and Edward J. Bechinski - PDF document

CIS 1133 Weevil in Spruceby Robert C. Wilson and Edward J. Bechinski University of Idaho Extension ¥ Idaho Agricultural Experiment Station The white pine weevil, Mechanical controlsWithout intervention,weevils reinfest the same tree fromwhich they emerged or disperse to nearby trees and expandthe infestation.Removal and destruction ofinfested shootswhile larvae or pupae are still present is an effective way tobreak the damage cycle.However,because adults can liveseveral years,and especially because adults can invadeuninfested areas by flying from nearby infested trees,it isnecessary to monitor for and prune-out infested leadersevery year until trees exceed a susceptible size (30 feet).Examine often.Examine trees at least every other week forevidence ofwilting in the terminal leader (Fig.5) throughJune and July to identify infested trees.Closer examinationby peeling back any soft bark will reveal ifweevil larvae arepresent.Pruning.Make pruning cuts in sound wood below the pointofweevil damage but immediately above the next uppermostundamaged whorl ofbranches.Remove all but the singlemost vigorous side shoot immediately below the cut termi-nal;this lateral branch will regrow as a replacement leader..Once the terminal has been removed,some correc-tive work is needed to prevent the tree from developing acrook in the trunk or forming multiple leaders.A stiffrod orstake can be tied to the tree top.Then bend a strong lateralbranch up and tie it to the rod.The earlier in the season thisis done,the straighter the trunk ultimately will be.Remove competing branches.Other branches may try togrow upwards naturally.Or,ifno action is taken,several newtops may develop.These should be cut offto leave only onestrong terminal.This will preserve the structure ofthe treeand ensure healthy growth.Note that these new leaders canbe attacked by white pine weevil in subsequent years.Oncetrees exceed 30 feet,they are rarely attacked by the white pineweevil (Turnquist and Alfaro 1996).Destroy pruned shoots.Destroy pruned shoots by burningor by burying;otherwise grubs will continue development toadult weevils within the pruned tree material.Ifemergenceholes are present,the pest already has escaped as adults,andremoval ofthe terminals will not provide any pestBand with sticky tape/paint.Another mechanical controlthat contributes to pest suppression is banding the base ofmain top shoots with sticky tape.This tactic can reduceegg-laying by entrapping female weevils as they crawl onleaders.Painting the base ofthe trunk with a sticky materialhas been practiced in southern Idaho.This can trap weevilsthat crawl up the trunk in the spring,although overallimpact ofthis treatment has not been evaluated.Horticultural controlsAvoid drought stress.Although egg-laying weevils seem toprefer vigorously growing trees,healthy,strong trees alsohave some natural capacity to kill young weevil grubs byincreased pitch flow at the feeding site.When only a fewgrubs are present,a well-watered tree can drown insect lar-vae in resin.Do not allow trees to become drought stressed,because this especially reduces their ability to Òpitch-outÓinsects.Large transplanted spruce in residential settingsespecially are susceptible to injury.Only a limited number ofinsecticides are available for whitepine weevil control (Table 1).Insecticides labeled forapplication on spruce trees to control bark beetles orwood-boring beetles probably also would kill white pineweevils,but it is University ofIdaho policy only torecommend products that specifically include both the targetplant (spruce trees) and the target pest (white pine weevil). 3 Figure 4: Emergence holesare left by adult weevils chewingout of the stems, usually in August. The l/8-inch exit hole isvisible to the naked eye. Ten to 20 adults may emerge froma single stem. Photo by Dave Overholser, USDA ForestService, www.forestryimages.org Figure 5: Wilted topof Colorado spruce is an indicator thetree is infested with white pine weevil. Photo by WhitneyCranshaw, Colorado State University, www.forestryimages.org small containers ofgrain alcohol (ethyl alcohol,not iso-propyl rubbing alcohol) and turpentine.These solvents arebelieved to mimic the natural scents ofpine trees and soattract weevils to traps where they can be counted.Trap counts simply show that weevils are present;they donot capture enough insects to reduce damage from subse-quent grub infestations.We have no experience in Idahowith the modified Tedders trap.Nursery operators who wantto try Tedders traps can purchase them from Great LakesIPM,online at http://www.greatlakesipm.com.Specific detailsabout trap use in the eastern U.S.are described by thePennsylvania Department ofAgriculture,http://ctrees.cas.psu.edu/pdfs/whitepinewvtraps.pdf.No sexpheromone has yet been identified for the white pine weevil.Table 1 shows that a few white pine weevil insecticides(acephate,avermectin and oxydemeton methyl) have sys-temic killing actionÑthey move internally in the tree withthe sap flow.Systemics not only kill adult female weevils asthey chew egg-laying punctures in the bark,they additionallycan control pre-existing larval infestations.Acephate systemic insecticide is formulated as tree-implants,small cartridges that contain dry concentratedinsecticide;these are designed to be permanently placedwithin a hole drilled into the tree trunk.Avermectin systemic insecticide is available to professionalarborists as the Tree Tech microinjection system,a plastic con-tainer prepacked with liquid insecticide that is temporarilyplaced via a feeder tube within a hole drilled into the treetrunk.Both ofthese products are best suited for individual high-value trees in landscapes rather than large-scale plantings incommercial nurseries or tree plantations.Oxydemetonmethyl is the only systemic suited for widespread use incommercial nurseries.Health hazards With the exception ofdiflubenzuron,all ofthe insecticides inTable 1 are neurotoxins,chemicals that kill by interferingwith the normal functioning ofthe nervous system.As nervepoisons,these insecticides pose at least some hazard tohuman health and non-target wildlife via accidental expo-sure.The relative risks ofany pesticide to human health canbe judged by the label signal words,where ÒwarningÓdesig-nates products that are at least 10-fold more toxic than thoselabeled Òcaution.ÓNone ofthe white pine weevil insecticidescarry the Òdanger Ð poisonÓsignal words that designate themost highly acutely toxic category ofpesticides.In contrast to these neurotoxins,diflubenzuron insteadinterferes with the ability ofinsects to form a normalexoskeleton;it poses reduced hazards to animals exceptinsects and related arthropods that have exoskeletons.Whitepine weevil adults treated with diflubenzuron produceabnormal eggs that do not hatch into larvae.Remember:When using pesticides,always read andfollow the label.FOR FURTHER READINGFurniss,R.L.and V.M.Carolin.1977.Western Forest Insects.USDA Forest Service.Misc.Pub.No.1339.Turnquist,R.D.and R.I.Alfaro.1996.Spruce Weevil inBritish Columbia.Canadian Forest Service Forest PestLeaflet.