Common Insect Pests And Diseases Of Sitka Spruce On The .
Common Insect Pests and Diseases ofSITKA SPRUCEon the Oregon CoastJ. Reeb and D. ShawEM 9105J AN UA RY 2 01 5
Common Insect Pests and Diseases ofSitka Spruce on the Oregon CoastE M 9105 Jan uar y 2015J. Reeb and D. ShawSitka spruce (Picea sitchensis) (Figure 1) is oneof the most prominent trees along the PacificNorthwest coast of North America. This species’ range extends from northern California toAlaska. The Oregon coast is at the southern limitof the range of Sitka spruce, and the tree there hasmany problems that are distinct from the ones itfaces in British Columbia and Alaska.Background on Sitka SpruceSitka spruce is also known as tidewater spruce,coast spruce, and yellow spruce. It is found near thePacific Coast, where mild winters, moist maritimeair, and cool summer fog maintain the humidconditions that are necessary for its growth (Figure2, page 3). It is most often associated with westernhemlock (Tsuga heterophylla) in dense standswhere growth rates are among the highest in NorthAmerica. Along Oregon’s central and north coasts, itcan be found with western red cedar (Thuja plicata),Douglas-fir (Pseudotsuga menziesii), Pacific silver fir(Abies amabilis), grand fir (Abies grandis), red alder(Alnus rubra), bigleaf maple (Acer macrophyllum),and black cottonwood (Populus trichocarpa). Onthe southern Oregon coast, it associates with coastredwood (Sequoia sempervirens) and Port Orfordcedar (Chamaecyparis lawsoniana).Figure 1. Sitka spruce in coastal Oregon. Note thedrooping branchlets and the associated maximization offoliage display.tolerant as its most common associate, westernhemlock.Sitka spruce is among the world’s fastest growingtrees. It is the largest of the world’s spruces. Itcommonly reaches heights of 180 feet (55 meters),with diameters of 5 feet (1.5 meters). The largestknown Sitka spruce in the country grew in KlootchyPark southeast of Seaside, Oregon. Before a 2006windstorm, the Seaside spruce stood 216 feet(65.8 meters) tall and over 18 feet (5.5 meters) indiameter. The windstorm caused a large amount ofrotted wood to break free from the tree at the siteof an old lightning scar. One year later, a secondwindstorm snapped the trunk about 80 feet fromthe ground. In February 2011, the Oregon Parksand Recreation Department removed 40 feet of theSitka spruce is more tolerant of salt spraythan associated tree species, and often occupiesa prominent position on exposed headlands andbeaches along the Oregon coast. It often followsshore pine (Pinus contorta) in succession on coastalsand dunes as they become stabilized by vegetation.On highly disturbed sites, it frequently becomesestablished with red alder or Sitka alder (A. sinuata),gradually overtopping the alder. Sitka spruce growsbest on deep, moist, and well-aerated soils with highamounts of calcium, magnesium, and phosphorus.Growth is poor in poorly drained, swampy areas.Sitka spruce is shade tolerant, although not as shadeJim Reeb is an Extension forester and David Shaw is anExtension forest health specialist, both of Oregon StateUniversity.2
woods, its strength-to-weight ratio is very high,and consequently it is used for ladders, aircraftshells, racing shells, garage doors, boat oars, sailboatmasts and spars, planking, folding bleachers, andother uses where light but strong wood is needed.It is especially known for its outstanding resonantqualities in pianos, organs, and violins. Sitka spruce’slong wood fibers make it ideal for making paper.Abiotic and Human-Caused Problemsof Sitka SpruceAbiotic means nonliving or nonbiological. Abioticproblems often look like insect or disease damage,or one might find a biotic agent on a tree because itis stressed by abiotic factors. Most insects and bioticdiseases affect a particular host tree species or groupof tree species. Abiotic problems will often affectall or many of the trees, shrubs, and herbaceousspecies growing near each other. However, differentspecies of trees, and trees of the same species butof different ages and vigor, often vary in theirsusceptibility to this type of damage. It is not alwayseasy distinguishing abiotic causes of stress frombiological causes (Figure 3).Figure 2. Range of Sitka spruce in the Pacific Northwestof North America. Note the very narrow range along theOregon coast, at the southern limit of the tree species.By Alexander Karnstedt (Alexrk2) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commonsremaining snag due to concerns about decayingwood falling and putting visitors at risk. Sitka spruceand western hemlock are nearly equal in heightgrowth during the period of most rapid growth,but spruce grows more rapidly in diameter. Sprucecontinues to maintain height growth longer thanwestern hemlock, and it lives longer. Few westernhemlock live more than 500 years, but Sitka sprucecan live to 800 years. Eventually, old spruces assumea dominant position in old-growth, hemlock-sprucestands.The 2005 Oregon Coast defoliation andShoot-Blight EventIn the late spring and early summer of 2005,Sitka spruce along the entire coast of Oregon hadMost Sitka spruce trees do not begin cone bearinguntil after 20 years. Sitka spruce is monoecious; thatis, it has both male and female flowers on the sametree. Female cones are usually found at the endsof primary branches near tops of trees, and malestrobili are usually found at the ends of secondarybranches lower in trees. Sometimes, both are foundon the same branch. Cones are 1 to 4 inches (2.5 to10 centimeters) in length, hang down from branches,and have very thin scales with jagged edges. Needlesare about 1-inch long (2.5 centimeters), often flat incross-section, yellow-green in color, stiff, and usuallyvery sharp.Figure 3. These Sitka spruce trees in a picnic areaestablished on “nurse logs” of the rainforest. The logs havesince rotted away, and surrounding forest vegetationhas been cleared. The compaction and root disturbanceassociated with heavy human use may eventuallycompromise the health of these trees.Throughout much of its range, Sitka spruceis a commercial timber species used for lumber,pulp, and many special uses. Compared with other3
an unusual defoliation event, especially noticeablealong roadways. No biotic agents were found to bedirectly linked to the event. Oregon Departmentof Forestry forest entomologists and pathologistsinvestigated the problem, which included currentyear foliage dying and then some apparentolder-foliage dying with subsequent small-twigdying. This was most intense in the lower crowns,but appeared to progress upwards. Scientiststheorized that an extreme weather event of very highdaytime temperatures exceeding 90o F in late Mayset the stage for the foliage loss. They also thoughtthat spruce aphids (Elatobium abietinum) may haveexacerbated the situation by injecting toxins intoneedles, although this was not proven. The followingyear, there were no indications of a similar problem,Shade and EpicormicBranchingSitka spruce’stolerance for shade liessomewhere between thatof Douglas-fir, a shadeintolerant species, andwestern hemlock, ashade-tolerant species.It can grow in theshade but does better insunlight. Sitka spruce isone of the few conifersthat develop epicormicbranches (Figure 5).Epicormic branchesFigure 5. The epicormicare shoots arisingbranching of these Sitkaspontaneously from an spruce is associated withadventitious or dormant exposure to sunlight whenbud on the stem of athe adjacent stand waswoody plant. Epicormic harvested.branching is related to light intensity, and occurswhen the tree’s trunk is newly exposed to sunlight.Thinning, windthrow, and road building can leadto more sunlight reaching the trunk. Epicormicbranching can decrease the quality of the logs forsuch high-value products as molding, siding, ormusical instruments. However, little to no value islost if the logs are destined for pulp production orfor structural lumber.An abiotic agent might be suspected when thelower limbs in Sitka spruce die. However, in deepshade, it is natural for the lower limbs to die, decay,and break off. Small, often resinous, branch stubs canremain on the trunk for many years. Occasionally,large dead branches are shed under live trees as anormal part of shade pruning.Figure 4. The abiotic needle loss on these trees isassociated with 2005 weather events.leading scientists to conclude that the extremeweather event led to the defoliation (Figure 4).Salt DamageSalt spray can damage and kill a wide variety ofplants along the Oregon coast. Sitka spruce is ableto withstand salt winds and harsh conditions alongthe central Oregon coast better than other associatedconifers, such as western hemlock and shore pine.Sitka spruce normally grows in mixed stands, butbecause of its high tolerance of salt, it can be foundin pure stands in tidewater areas. Salt damage is veryuncommon for this species.As with salt spray, shade isn’t typically a majorcause of stress for Sitka spruce.Trenching and Construction DamageThe architecture of a given tree is a balancebetween the crown and the roots. The size of thecrown is related to the size of the root system. Eachindividual leaf has a direct connection to certainroots due to small capillary water streams. Althoughtrees have some ability to compensate when a majorportion of the root system is severed, the entire4
crown cannot be sustained, and a portion of theleaves and branches are shed (die). Butt woundingand root damage, especially roots severed bytrenching, can cause a tree to die or to lose someportion of its crown. This is the same stress causedby drought (lack of water to the foliage), and mayappear as drought damage. Wounding also allowsroot diseases and wood rot to access the tree, andencourages insects and pathogens that can furtherweaken the tree. Consequently, trenching andconstruction can cause major damage to Sitka sprucein landscape and housing areas. Expect damagedtrees to have a wide range of health problems.coast. A recent example is the November 2007 stormalong the north coast. Although this is not oftenconfused with insect damage, heavily broken treesare often attacked by insect pests that can later infeststanding trees.To differentiate between windthrow and rootdisease, look for a central area that has the longestdead trees. Think of this as the mortality center.Look for trees that are showing fewer symptoms ofdisease, or have been dead a shorter period of time,as you move away from the mortality center.This is how root disease progresses. Centersof mortality from bark beetles, lightning, andwindthrow won’t look like this. If the fallen trees arealigned in the same direction, then the likely culpritwas windthrow (Figure 6). If the trees are lying inall different directions, then the cause is likely tobe a root disease. If the tree broke off rather thanbeing uprooted, check the characteristics of thebreak. Wood that was nondiseased when it brokehas jagged, splintery breaks, whereas wood that wasdecayed when it broke has “brash” breaks, wherefailure is across the grain and less splintery.Off-Site PlantingTrees that are not genetically suited to an areaare called off-site. As with other tree species havinglarge ranges, a tree grown from stock originating along distance from the planting site has less chanceof survival than a locally grown seedling. Off-siteplantings are often more susceptible to insect attack.WindthrowWindthrow of Sitka spruce can occur duringviolent windstorms, which often strike the OregonFigure 6. Windthrow of coastal forest exposed by clear-cut near Newport.5
Insectssevere stem deformations. The tree usually survivesattacks by this weevil, but with repeated attacks,growth is reduced and the tree becomes crooked orbushy as one or more lateral shoots try to replacethe killed, terminal growth. Sitka spruce located inthe heavy fog zone within 2 miles of the coast areless influenced by the white pine weevil than treeslocated farther inland.Beetles: Weevils, Bark Beetles, AmbrosiaBeetles, and Wood BorersWeevils, bark beetles, and ambrosia beetlesare in the same family of beetles (Curculionidae).The typical weevils have a distinct snout-shapedface and feed on a variety of plant parts. Bark andambrosia beetles refer to specific group of beetles(subfamily Scolytinae) that feed in the bark andwood of trees. The term “wood borer” refers toa broad range of potential insects that bore intowood. The term often refers to two families ofbeetles—long-horned wood borers or round-headedwood borers (Cerambycidae), and flat-headed ormetallic wood borers (Buprestidae). Bark beetles andambrosia beetles are related to each other but differsignificantly in their life history. Bark beetles are theonly group that can cause significant mortality ofmature trees.The adult weevil is about 0.18 of an inch (5mm) long, dark colored with splotches of lightcolored scales, and has a pronounced snout typicalof weevils. In spring, it makes feeding puncturewounds on the previous years’ leader below the bud.The female lays eggs just below the terminal leaderbud, and these puncture wounds may have resinflowing from them. When the eggs hatch, the grubsbore into the inner bark and descend along theprevious years’ growth. The grubs feed on the innerbark until constructing a cocoon of chips by August,within which the grub pupates into an adult beetle.The adults emerge in autumn, chewing an exit holevisible to the eye, and overwinter in forest litter. Theleader that did develop in spring above this activitydies midway through the summer, often forminga J-shaped “shepherd’s crook” (Figure 7).White Pine Weevil (Sitka Spruce Weevil)The white pine weevil (Pissodes strobi)(Coleoptera: Curculionidae), also locally known asthe Sitka spruce tip weevil, is the most importantinsect pest of Sitka spruce in forest plantations.The weevil repeatedly infests and kills the leader ofthe tree and therefore slows growth and producesThe beetles specialize in attacking leaders ofexposed, open-growing, vigorous trees from aboutFigure 7. Effect of Sitka spruce (white pine) weevil on the terminal leader of Sitka spruce.6
3 feet tall (1 meter) to about 60 feet tall (18 meters).The plantation size-class considered most susceptibleto heavy damage is from about 5 to 30 feet tall andat low density. Two primary plantation-managementideas have been put forward. One is to plant Sitkaspruce at high density and delay precommercialthinning until age 25 or so. This changes themicroclimate around the leaders, crowds the crownsso that secondary leaders can easily take over fromkilled primary leaders, increases height growth,and improves the chances that not every leader willbe attacked. Then, at age 25 or so, the stand can bethinned, removing lower-quality trees. The secondoption is to grow Sitka spruce intermixed with redalder. The canopy of alder has a general effect on thelight environment (shade, speckling) and lowers theprobability of weevil attack. This is a silviculturallychallenging strategy, but some may find it practicaland economical.include ornamental varieties of white and blackspruces, which are reported to be rarely infested withthe white pine weevil. On landscape trees, it may bedesirable to prune and burn the infested terminalleaders in August to lower weevil populationnumbers. Pruning all the lateral shoots but onein the whorl just below the infested terminal mayimprove stem form, allowing a secondary branch totake over.Contact insecticide sprays (bifenthrin,esfenvalerate) are effective only on adult pests; allother life stages occur under the bark. Apply tothe leader and upper branches in spring as adultsbegin to feed and lay eggs. Systemic insecticides(abamectin, imidacloprid) can also be used tokill larvae feeding within the leader. Consult thecurrent year edition of the Pacific Northwest InsectManagement Handbook (available at http://insect.pnwhandbooks.org/ or http://extension.oregonstate.edu/catalog/) for specific recommendations. Alwaysconsult and follow labels.Some Sitka spruce trees in British Columbia areresistant to white pine weevil damage. This indicatesthat resistant mechanisms exist in this host-insectsystem. In the future, the use of weevil-resistantplanting stock may again make Sitka spruce a viableand important commercial species along Oregon’scoast.Ambrosia BeetlesAmbrosia beetles (Coleoptera: Curculionidae:Scolytinae and Platypodinae) are relatives of barkbeetles, but they bore into sapwood directly. Theyinoculate the sapwood with an ambrosia fungus,which they carry into the tree on specialized bodystructures called mycangia (Figure 8).The larvae eat the growing fungus thatlines the larval cavity. The beetles donot kill trees but attack freshly deador strongly declining trees. They arethe first invaders of a dead tree! Whitedust may appear at the entrance hole asthe adults bore into the sapwood. Thisis in contrast to bark beetles, whichbore into the inner bark and create areddish boring dust.In a western Oregon landscape setting, Sitkaspruce is likely to be attacked. Alternatives mayFigure 8. Pinhole borer (ambrosia beetle) galleries in sapwood. Someholes are stained with ambrosia fungi.7Along the Pacific coast of Oregon,ambrosia beetles can be significantpests of Sitka spruce logs that areleft in place, or stored on landingsor mill yards with the bark still on.The pinholes created by the beetlescause a defect in the lumber. Logsare particularly susceptible in springand summer. Trypodendron lineatum
and Gnathotrichus spp. are considered the mostimportant ambrosia beetles in coastal-log storage.Quick movement of logs out of the forest and intothe mill is the best strategy for tree growers to reducedamage by these insects.will have boring dust around the base of the treefrom excavation of the bark by the beetles. This willlook like reddish-brown sawdust, which can alsocollect in bark fissures. The beetles attack the treeby directly boring into the bark, where females layeggs in a distinctly patterned gallery near the woodbark interface. The galleries are visible on the insideof the bark after removing it from the tree. Larvaeexcavate away from the main vertical egg gallery andmine the inner bark, eventually crisscrossing eachother and melding together into large communalfeeding areas. Larvae pupate in the inner bark andadult emergence is likely in spring or early summerof the year following the initial attack. Distinctivewoodpecker feeding on large trees attacked bybeetles appears from the flaking activity of the birdsthat are harvesting grubs out of the bark, not thewood.Spruce BeetleThroughout the West, the spruce beetle(Dendroctonus rufipennis) (Coleoptera:Curculionidae: Scolytinae) is capable of large-scalemortality of mature and older trees, includingSitka spruce in British Columbia and Alaska.Although the beetle is present in Oregon, it is notconsidered a threat to the Sitka spruce forests inthe state. The beetles appear to focus on very weaktrees, or recently dead and down large trees, afterwinter storms. In other regions of the West, sprucebeetle epidemics usually occur after a large-scale,windthrow event. The beetles colonize the downedwood in the late spring or early summer followingthe windthrow, and populations build to a degreethat allows them to mass attack nearby healthyspruce in the following years. Again, this behaviorhas not been observed along the Oregon coast.Aphids, Adelgids, Scale Insects, andMitesAphids, adelgids, and scale insects are smallinsects with piercing-sucking mouth parts. Thereare numerous types, although aphids are usuallynaked, while adelgids and scales often have sometype of covering or form a gall. The spruce aphid isthe most important and influential of these insectsfor Sitka spruce along the Oregon coast. Mites arean unrelated group of arthropods, not insects. Theyhave eight legs, are very small, and are an incrediblydiverse group. Only one, the spruce spider mite, iswidely known to cause problems in spruce.Depending on location, the spruce beetle canhave a life cycle of one to three or more years. InOregon, the beetle is reported to have a two-yearlife cycle. The beetle is dark brown to black and verysmall—4 to 7 millimeters (1/4 inch) long(Figure 9). Wing covers are reddish, and the beetleshave hair-like projections. A recently attacked treeCooley Spruce Gall AdelgidThe Cooley spruce gall adelgid (Adelges cooleyi,Homoptera: Adelgidae) is a fascinating insect thatmay cycle between two host trees: Douglas-fir andSitka spruce. On Sitka spruce, the insect creates aswollen, cone-shaped gall on the new growth ofspruce twigs (Figure 10, page 9). When these dry,they look much like brown cones on the terminalsof the branches. Adelgids feed on succulent newgrowth at the base of developing needles. Thisstimulates the development of the gall. On closeinspection of the maturing gall when fresh (notdried), the adelgids can be found inside chamberscreated by the gall. On Douglas-fir, the insect settlessingly on new needles and covers itself with waxyexcretion that looks like a cottony tuft. FeedingFigure 9. Spruce beetle.Photo from OSU Integrated Plant Protection Center.8
newer needles. The insect populations, which aregregarious, usually peak during late winter, andthe needles that were fed on may be lost during thefollowing growing season as new foliage emerges.The lower and inner crowns are typically mostseriously affected. A tree crown in summer may haveunaffected new needles and the remainder of thecrown may be thin and lack needle retention.The spruce aphid is thought to be influencedprimarily by weather, with mild winters favoring theinsect. Populations can flare up into epidemics, butthese typically last only a few years. Mortality eventsin Sitka spruce are often associated with spruceaphid, but it is thought to be only one of a complexof factors observed.Figure 10. Branchlet tips deformed by Cooley spruce galladelgid.Control of spruce aphid is mostly influenced byweather. Ornamental spruce may be treated withinsecticides if the landowner is very concerned.Sprays must be applied in late March or early Aprildamage is usually slight on young Douglas-fir,causing needle spotting or loss. However, this insectcan reduce visual quality of Christmas trees, andgrowers concerned about Cooley spruce gall adelgidshould not have any spruce species growing mixedwith Douglas-fir. The adelgid is common on allspruce tree species throughout the West but is rarelyconsidered a major problem.Spruce AphidThe spruce aphid (Elatobium abietinum)(Homoptera: Aphididae) causes foliage loss andcrown thinning on trees of all ages and sizes(Figure 11). Continued infestations can cause treedeath. It is common on Sitka spruce and ornamentalspruces (especially blue spruce, Picea pungens) onthe Oregon coast. The spruce aphid is thought to bea nonnative invasive from Europe and is a problemacross North America on several spruce species. InNorth America, the insect is parthenogenetic (canreproduce without mating) and consists of femalesonly.On Sitka spruce, the insect is present year-roundbut rarely found in the drier seasons. It is most easilyseen during late fall through early spring, when itcan be very abundant. To find the insect, tap or beatthe branches while holding a white sheet of paperunder the branch. If the green (or olive-green)aphids are common, they will fall on the paper andbe easily observed, despite their small size (1/16inch or 1.5 mm long). Winged individuals are rare.Figure 11. Symptoms of spruce aphid include foliagedecline and loss of the lower and inner crown on Sitkaspruce.The spruce aphid sucks sap primarily on theundersides of older needles, rarely affecting the9
Figure 12. Spruce spider mites. Note webbing.to be effective. Formulations that are registered foruse on ornamental spruce include insecticidal soap,bifenthrin, acephate, and imidacloprid. Follow alldirections and cautions when applying pesticides.tree may have poor foliage retention. Spruce spidermites are very small and may require magnificationto see. Tapping branches while holding a white sheetof paper will cause the mites to drop out, and onecan observe the tiny creatures.Spruce Spider MiteLeaf-Eating DefoliatorsThe spruce spider mite (Oligonychus ununguis)(Acari: Tetranychidae) is an 8-legged arthropodnot related to insects. It is a common conifer peston Christmas tree farms and intensive nurseryproduction areas. The spruce spider mite prefersspruce, but can be found on most conifers(Figure 12). Sometimes, the mite populations canerupt in forest settings. Spruce spider mites feed onplant juices and can cause a stippled or bronzingappearance on foliage, which may eventually turnyellowish to brown and fall off. Webbing is oftenpresent among the foliage and around the twigs. Thegeneral appearance is one of off-color gray, and theDefoliating insects that eat spruce needles andcan cause significant loss of foliage in the entirecrown are not particularly common on Sitka spruce.The damage is done by the moth caterpillars, orperhaps by sawfly larvae, which are actually relatedto bees and wasps. There are many insects that canfeed on Sitka spruce needles; some are specializedto spruce, while others are generalists that may eat anumber of different conifers. Table 2 (pages 17-20)lists many of the leaf-eating insects known on Sitkaspruce, but defoliation of Sitka spruce by leaf-feedinginsects is reasonably rare. The spruce bud moth,10
Figure 13. Silver spotted tiger moth caterpillars on Sitka spruce.Photo by Bryan BlackZeiraphera spp. (Lepidoptera: Tortricidae), may killdeveloping buds. But perhaps the most recognizabledefoliator is the silver spotted tiger moth.Handling these insects can cause skin reactions. Thepatchy defoliation caused by these insects is mostnoticeable in late-winter to mid-spring, unlike mostother tent caterpillars that develop afterspring arrives.Silver Spotted Tiger MothThe silver spotted tiger moth (Lophocampaargentata, Lepidoptera: Arctiidae) feeds primarilyon Douglas-fir but also is found on Sitka spruce(Figure 13), western hemlock, and grand fir alongthe coast. The adults fly in the fall, when the femalelays eggs on the sunny side of the tree crown. Eggshatch in fall, and the caterpillars feed together insocial groups. The caterpillars form a loose tent andmay spend time in it, though they are not restrictedto the tent. The caterpillars are active all winter,aggregating to bask in sunshine (thermoregulate).The caterpillars feed socially until mid-spring, atwhich time they disperse throughout the crown.The social feeding creates patches of defoliation on atree crown, but rarely is the entire crown defoliated.Initially, the caterpillars are dark colored and have afew hairs, but as they grow, they develop hairy tufts.Diseases Caused by FungiDisease is a broad term that refers to abnormalplant growth and development. This can be causedby abiotic agents, such as weather, soil nutrients, andherbicides (Table 1, page 17) or biotic agents, suchas fungi, bacteria, viruses, and parasitic plants. Incoastal Oregon Sitka spruce, fungi are the primarydisease agents of concern (Table 3, pages 21-24).Root, Butt, and Stem RotsRoot, butt, and stem rot diseases are caused bywood decay fungi that colonize and decay the woodof live trees. They can cause significant losses intimber production, especially in older, multi-entrystands of Sitka spruce and western hemlock. Thefungus can enter the tree wood via root, butt, and11
Figure 14. Conks indicating Heterobasidion root and butt rot is present in the stand.stem wounds; root-to-root contacts; grafts betweeninfected and noninfected trees; dead branches; andsmall, dead branch twigs.Heterobasidion (Annosus) Root and Butt RotHeterobasidion root and butt rot, caused by thefungus Heterobasidion occidentale, is an issue inmanagement of western hemlock and Sitka sprucealong the coast of Oregon (Figures 14 and 15). Thefungus is a prolific spore producer that can colonizeroots and butts (even the stem) of wounded trees. Italso can grow from one tree to another across rootgrafts and contacts. Heterobasidion is known for itsability to colonize freshly cut stump surfaces. It cangrow down through the stump and infect nearbytrees that have roots in contact with the stump roots.However, this is most important in drier habitats,such as white fir forests of California and grand firforests in the Oregon Cascades. Along the coast, thisdoes not appear to be a major form of tree infectionFigure 15. This windthrow is associated with butt rotcaused by Heterobasidion occidentale. Note the whiterot. This picture is of western hemlock, but decay in Sitkaspruce will look very similar.12
in thinned stands ofwestern hemlock. Ourknowledge of Sitkaspruce is limited by thelack of any plantationmanagement.Heterobasidionroot and butt rot ismost important inlandscapes aroundpeople, cars, and houses,and recreational areasalong the coast, whereheavily decayed, largetrees may pose a hazard.Butt-scarred trees arelikely infected with thefungus, and the whiterot, with occasionalblack specks, can beextensive. The sporesemanate from a bracketshaped conk that isfound in protected sites,underneath the butt ofdowned trees, or insidethe heavily decayedheart or butt of the tree.The conks may forminside hollow stumps.The conk is dark aboveand creamy below, witha thin, sterile margin.Conks on the outsideof a tree indicatesignificant internaldecay.Figure 16. Armillaria mushrooms grow out of a recently dead red alder tree. There arenumerous species of Armillaria that are difficult to tell apart. However, when fruiting fromthe base on the lower bole of a tree, it is likely the fungus played a part in tree death.Armillaria Root Rotfungus that grows from tree to tree across rootcontacts.Armillaria root rot is caused by a numberof Armillaria species. Any given site may haveseveral Armillaria species, but only one will likelybe pathogenic. Although Armi
The architecture of a given tree is a balance between the crown and the roots. The size of the crown is related to the size of the root system. Each individual leaf has a direct connection to certain roots due to small capillary water streams. Although trees have some ability to compensate when a major
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