Tree Problem Identification Guide

Medium

Adelgids

Adelges abietis, A. cooleyi, A. tsugae

Adelgids are soft-bodied, aphid-like insects that create characteristic galls on spruce and woolly masses on hemlock. These insects have complex life cycles that often involve alternate host species and can cause significant damage to conifers.

High

Ambrosia Beetles (Including PSHB)

Various species including Polyphagous Shot Hole Borer

Ambrosia beetles are weevil subfamily beetles that live in nutritional symbiosis with ambrosia fungi. They excavate tunnels in trees where they cultivate fungal gardens as their sole source of nutrition. The Polyphagous Shot Hole Borer (PSHB) is causing very serious concern and damage in California.

High

American Plum Borer

Euzophera semifuneralis (Lepidoptera: Pyralidae)

A cambium-feeding moth pest that bores into trees, creating reddish orange frass and gum pockets (gummosis). The major borer pest of stone fruits and ornamental trees, causing up to 33% decline in life span of cherry trees. Most damaging to scaffold crotches and graft unions of young trees.

Medium

Aphids

Various genera including Aphis, Microsiphum, and Myzus

Small, soft-bodied insects that feed by sucking plant juices from leaves, stems, and shoots. Adults are 1/8 to 1/4 inch long with two elongated projections from the abdomen. Often found in clusters on undersides of leaves and may be coated with white, cottony wax.

High

Asian Cycad Scale

Aulacaspis yasumatsui (Hemiptera: Diaspididae)

An exotic invasive armored scale insect that forms devastatingly dense populations on cycad plants. The scale creates white coverings that can completely coat plants, appearing like snow. Unique among scales for its ability to infest both foliage and root systems.

High

Asian Longhorned Beetle

Anoplophora glabripennis

A highly destructive invasive wood-boring beetle from Asia that attacks and kills healthy hardwood trees. This pest poses a severe threat to North American forests and urban trees.

Medium

Birch Leaf Miner

Fenusa pusilla

A small sawfly whose larvae mine between the upper and lower leaf surfaces of birch trees, creating distinctive brown blotches. While healthy trees can tolerate infestations, repeated attacks over several years can significantly weaken trees.

Medium

Black Turpentine Beetle

Dendroctonus terebrans

A bark beetle that attacks the bases of pine trees, creating large cavities between bark and wood filled with resinous fluid. While primarily attacking stressed or injured trees, they can also infest healthy pines under certain conditions.

High

Black Vine Weevil

Otiorhynchus sulcatus (Coleoptera: Curculionidae)

The most destructive and widespread weevil species, also known as Taxus weevil due to its preference for yew. This flightless weevil feeds on over 100 plant species and has populations consisting entirely of females in North America.

Medium

Black Vine Weevil Adult

Otiorhynchus sulcatus

The most destructive and widespread of weevils, black vine weevil adults are flightless beetles that feed on leaf margins of over 100 plant species. Found throughout northern North America, these nocturnal pests are particularly damaging to yew, rhododendrons, and other broad-leaf evergreens.

High

Black Vine Weevil Larvae

Otiorhynchus sulcatus

Off-white grubs with brown heads in characteristic C-shape, black vine weevil larvae are the most damaging stage of this widespread weevil. They tunnel through soil to feed on roots and can cause significant damage including plant death, especially in spring before pupation.

High

Bronze Birch Borer

Agrilus anxius Gory (Coleoptera: Buprestidae)

A destructive wood-boring beetle that attacks stressed birch trees. Adults are deep green-bronze beetles, with females about 1/2 inch long. Larvae create feeding galleries that girdle trunks and branches, leading to tree decline and death.

High

California Oakworm

Phryganadia californica

A defoliating moth whose larvae can cause severe damage to oak trees, particularly in the San Francisco Bay area. Young larvae feed by removing leaf surfaces while older larvae completely consume leaves, potentially defoliating entire tree crowns. Repeated annual defoliation may kill trees.

Low

California Tent Caterpillar

Malacosoma californica

A moth whose larvae construct characteristic silk tents around twig tips and feed on terminal leaves for about 6 weeks. While they can cause heavy defoliation, the resulting damage is usually of little importance since trees recover readily, especially if fertilized.

Medium

Cedar Bark Beetles

Phleosinus species

Small bark beetles that attack weakened or stressed cedar and related coniferous trees. Adults are red-brown to black, shiny beetles ranging from 1/8 to 3/8 inch long. They create characteristic short, longitudinal egg galleries with little branching that become confused under heavy infestations.

High

Citrus Longhorned Beetle

Anoplophora chinensis

An extremely destructive invasive beetle from Asia that poses an unprecedented threat to North American trees. This pest attacks healthy trees and has no natural enemies, threatening urban landscapes, forests, orchards, and wildlife habitat. Each female can lay up to 200 eggs in tree bark.

Medium

Citrus Mealybug

Planococcus citri (Risso) (Hemiptera: Pseudococcidae)

A small, soft-bodied insect that appears to have been rolled in flour due to its white, waxy coating. A pest of citrus and ornamental plants since the 1800s, it damages plants by sucking sap and secreting honeydew that supports sooty mold growth.

Medium

Clearwing Borers

Sesiidae family (various species)

A family of moths whose larvae bore into wood and plant roots, causing serious damage to fruit trees, timber, and ornamental plants. Adults have transparent wings and wasp-like appearance, enabling daytime activity through Batesian mimicry. Many species are significant pests of cultivated trees.

Medium

Cottonwood Longhorned Borer

Plectrodera scalator

A large longhorned beetle that attacks cottonwood, poplar, aspen, and willow trees, primarily at the base or below ground line. Adults are 1-1.5 inches long, shiny black with cream-colored markings. Extensive larval mining can girdle young trees and create structural weakness.

Low

Cynipid Gall Wasps

Cynipidae family (various species)

Small wasps that create distinctive galls on oak trees through their feeding and development activities. They produce two types of galls: spherical corky galls from asexual generations and smaller wheat-kernel-like galls from sexual generations. While generally not seriously damaging, numerous galls can be aesthetically disfiguring.

Medium

Cypress Bark Beetle

Phleosinus species

Small bark beetles that primarily attack weakened or stressed coniferous trees, especially during drought conditions. Healthy trees can usually resist attack through sap production, but stressed trees become vulnerable to infestations that can result in tree mortality.

Medium

Dogwood Twig Borer

Oberea tripunctata

A longhorned beetle whose larvae cause severe twig dieback in dogwood trees. Adults are distinctive yellow beetles with three black spots on the thorax, and larvae bore through the center of twigs, often cutting off portions from within and creating characteristic round holes with frass exudation.

Medium

Douglas Fir Cone Moth

Barbara colfaxiana

A moth whose larvae infest Douglas fir cones, potentially destroying seed crops. Adults are silvery gray moths about 1/2 inch long, and larvae create resinous tunnels through cone bracts, feeding on scales and seeds, which can prevent cone opening and seed release.

Medium

Douglas Fir Cone Moth Larvae

Barbara colfaxiana

The larval stage of the Douglas fir cone moth, representing the most damaging phase of this pest. Larvae are initially yellow-white with black heads, later becoming pink to yellow with brown heads. They create tortuous resinous tunnels through cone bracts and feed directly on scales and seeds.

High

Douglas Fir Gall Midge

Contarinia pseudotsuga

A small midge considered the most significant pest of Douglas fir seed orchards, capable of destroying up to 70% of seed crops. Orange maggots cause galls around seeds, killing them or fusing them to cone scales so they cannot be shed or extracted.

Medium

Eastern Tent Caterpillar

Malacosoma americana (Lepidoptera: Lasiocampidae)

One of the most widespread defoliators of deciduous shade trees in eastern North America. Larvae create distinctive silk tents in limb crotches during spring feeding, distinguished from Fall Webworm which forms tents terminally on branches in late summer.

High

Elm Leaf Beetle

Pyrrhalta luteola (Coleoptera: Chrysomelidae)

A destructive beetle pest affecting all elm species and Japanese zelkova. Adults chew circular holes in leaves while larvae skeletonize foliage from underneath. Multiple generations per year can cause significant defoliation and tree mortality.

High

Emerald Ash Borer

Agrilus planipennis (Coleoptera: Buprestidae)

An invasive wood-boring beetle from Asia that attacks all species of ash trees. Adults are bright metallic green, larger than native Agrilus species, and highly destructive to North American ash forests.

High

Engraver Beetles (Pine Bark Beetles)

Ips spp.

Small bark beetles that create characteristic curved, S-shaped, or Y-shaped galleries under the bark of conifers. They primarily attack weakened or stressed trees and can cause rapid tree mortality through their tunneling activities.

High

Eucalyptus Longhorned Borer

Phoracantha semipunctata, P. recurva

A large longhorned beetle that bores into eucalyptus trees, creating extensive galleries in the inner bark and cambium. Adults have distinctive long antennae and shiny, dark brown wing covers with yellow markings.

Medium

European Elm Scale

Gossyparia spuria

A scale insect that feeds on elm branches, producing copious honeydew that leads to sooty mold problems. Often first noticed when honeydew becomes a nuisance on cars and outdoor furniture beneath infested trees.

High

European Pine Sawfly

Neodiprion sertifer

A defoliating sawfly whose larvae feed in groups on pine needles, causing significant aesthetic damage and potential tree mortality with repeated defoliation. Adults resemble large flies but are actually primitive wasps with serrated ovipositors for slitting needles to lay eggs.

Medium

Fall Web Worm

Hyphantria cunea (Lepidoptera: Erebidae)

A native North American moth whose larvae create distinctive white silk webs on terminal branches. Has two distinct races (blackhead and redhead) that vary in appearance and habits. While capable of significant defoliation, damage is typically more cosmetic than life-threatening to trees.

High

Flatheaded Borer

Chrysobothris californica

Small metallic beetles whose larvae create irregular tunnels in the inner bark and cambium of stressed trees. Adults are flattened in appearance, and larvae have distinctive broad, segmented heads that are three times wider than their bodies.

Medium

Gouty Gall Wasps

Callirhytis punctata

Tiny cynipid wasps that create yellowish, irregularly round galls on oak twigs. These wasps have a complex two-year life cycle with alternating generations creating different types of galls.

High

Gypsy Moth

Lymantria dispar (formerly Porthetria dispar) (Lepidoptera: Erebidae)

A highly destructive defoliating moth introduced to North America in 1869. Larvae are voracious feeders capable of completely defoliating trees over large areas. Adults show strong sexual dimorphism, with flightless females and smaller flying males.

Low

Hackberry Nipple Gall Psyllid

Pachypsylla spp. (Hemiptera: Psyllidae)

Small jumping insects that create distinctive nipple-shaped galls on hackberry leaves. Adults emerge in fall and become household nuisances when seeking winter shelter. The insects resemble miniature cicadas and do not cause serious harm to host trees.

Medium

Hackberry Psyllid

Pachypsylla spp.

Small jumping plant lice that feed on hackberry trees and cause various types of galls on leaves, twigs, and bark. These insects complete their development inside protective gall structures.

High

Hemlock Woolly Adelgid

Adelges tsugae (Sternorrhyncha: Adelgidae)

A destructive invasive pest native to East Asia that feeds by sucking sap from hemlock and spruce trees. In eastern North America, it gravely threatens eastern hemlock and Carolina hemlock populations through its feeding damage and hypersensitive tree response.

High

Japanese Beetle

Popillia japonica Newman (Scarabaeidae, Coleoptera)

A highly destructive invasive beetle with a metallic green body and coppery wing covers. Adults are voracious feeders on foliage and fruit, while larvae damage turf root systems. First introduced in 1916, they have become established across much of eastern North America.

High

Juniper Bark Beetles

Phloeosinus serratus, Phleosinus sp.

Small bark beetles that attack weakened juniper and cedar trees, particularly during drought stress. Healthy trees can usually resist attack through sap production, but stressed trees are vulnerable to infestation and death.

Medium

Lacebugs

Corythucha ciliata, C. ulmui, C. arcuata, Stephanitis sp., Kalmia sp.

Small piercing-sucking insects with distinctive netlike wing patterns that feed on the undersides of leaves. They cause characteristic yellow spotting on upper leaf surfaces and produce brown varnish-like droppings.

Medium

Leaf Miners

Fenusa pusilla (birch), F. ulmi (elm), various species

Small sawfly larvae that tunnel within leaf tissues, creating distinctive brown blotches or blisters on leaves. While healthy trees can withstand infestations, repeated attacks over several years can significantly weaken trees, making them vulnerable to secondary pests and diseases.

Medium

Leafhoppers

Edwardsiana, Empoasca, Erythroneura, Alebra spp.

Small, slender sap-sucking insects that feed on the undersides of leaves, causing speckled and pale foliage. There are hundreds of species affecting ornamental trees and shrubs, and they move rapidly when disturbed.

Medium

Lepidoptera (Moths and Butterflies)

Order Lepidoptera

An order of insects including moths and butterflies with over 180,000 described species. While many are beneficial pollinators, some species can cause serious damage to trees by feeding on bark, leaves, and stems during their larval (caterpillar) stage.

Medium

Lerp Psyllids

Glycaspis species, G. brimblecombi (redgum lerp psyllid)

Plant juice-sucking insects that create protective crystallized honeydew covers called 'lerps' during their nymphal stage. High populations can cause severe leaf drop and extensive defoliation, weakening trees and increasing susceptibility to wood-boring pests.

Medium

Lesser Peach Tree Borer

Synanthedon pictipes

A clearwing moth borer that is an important pest in peach and cherry orchards. Adults are day-flying moths resembling wasps, and larvae create tunnels in trunk and limbs, causing characteristic gumosis. Problems are typically associated with Cytospora canker and tree wounds.

Medium

Mimosa Webworm

Homadaula anisocentra

An introduced pest from China that feeds primarily on mimosa and honeylocust trees, creating characteristic webs around foliage. First reported in Washington D.C. in the 1940s, this pest can cause complete defoliation by early September if left untreated.

High

Mountain Pine Beetles

Dendroctonus ponderosae, D. brevicomis (Western Pine Beetle)

Native bark beetles of western North America that have caused unprecedented forest destruction, possibly the largest forest insect blight ever seen in North America. Climate change has contributed to outbreak severity, with millions of acres affected and significant impacts on forest ecosystems.

Medium

Nantucket Pine Tip Moths

Rhyacionia frustra

A moth pest whose larvae kill the tips of terminals and lateral branches by boring into needles, buds, and twigs. Young pines can be seriously deformed and occasionally killed, with some trees killed back to a foot below terminal growth.

Low

Oak Gall Wasp

Amphibolips confluens (and 717 other species in North America)

Small cynipid wasps that create distinctive large, shiny, round galls on oak leaves through growth-regulating chemicals. While causing no apparent damage to trees, fallen galls can damage lawn mowing equipment. Part of a diverse complex of 717 gall wasp species attacking oaks in North America.

Medium

Obscure Scale

Melanaspis obscura

An armored scale insect that forms dense, clustered colonies on bark and twigs, sometimes creating layers of individuals. Adults are approximately 1/25 inch diameter with gray to tawny coloration, often with a distinctive black nipple in the center.

High

Pine Bark Beetles

Ips spp., Dendroctonus spp.

A complex of bark beetle species that attack pine trees, including mountain pine beetle, southern pine beetle, and various engraver beetles. These insects bore through bark and can kill trees through direct feeding damage and vectored fungal diseases.

High

Pine Engraver Beetles

Ips spp.

Specific bark beetle species within the Ips genus known for their characteristic 'engraved' gallery patterns under bark. These beetles target weakened conifers and are named for their distinctive tunneling patterns that resemble engravings in the wood surface.

Medium

Pine Needle Scale

Chionaspis pinifoliae

A key armored scale insect pest of pines in landscapes, nurseries, and Christmas tree plantations. Females develop white waxy covers with yellow tips while feeding on needle fluids, causing yellowing and potential dieback of infested branches.

High

Pine Tent Caterpillars

Thaumetopoea pityocampa

A destructive moth pest of the family Thaumetopoeidae that attacks pines and cedars in Central Asia, North Africa, and southern Europe. The caterpillar larvae have urticating hairs that cause harmful reactions in humans and other mammals.

Medium

Pine Tip Moth Larvae

Rhyacionia frustra

A destructive moth pest whose larvae bore into pine terminals and laterals, causing tip kill and deformation. Most commonly known as the Nantucket tip moth, these pests can seriously damage young pines and occasionally kill trees.

Medium

Pit Scale

Asterolecanium variolosum

Small soft scale insects that create characteristic sunken pits in the bark of oak trees where they feed. These scales can cause dieback of twigs and branches, and heavy infestations may kill trees.

Medium

Psyllids

Pachypsylla spp.

Small jumping insects with piercing-sucking mouthparts that feed on plant juices. Includes both gall-making species (like hackberry nipple gall maker) and non-gall-making species. Adults resemble tiny cicadas with jumping hind legs.

High

Red Turpentine Beetles

Dendroctonus valens

Destructive bark beetles that attack the bases of pine trees, creating irregular longitudinal galleries filled with resinous frass. Both red and black turpentine beetles target healthy, dying, injured, or felled trees and stumps.

High

Redwood Bark Beetles

Phleosinus spp.

Bark beetles that attack redwood, cedar, and cypress species. Adults attack all upper parts of weak, dying or dead trees, and construct egg galleries after feeding on healthy twigs and branches, girdling them until nutrient flow stops.

Medium

Roundheaded Borers (Excluding Asian Longhorn Beetles)

Cerambycidae family

Wood-boring larvae of longhorned beetles (Cerambycidae family) that tunnel through trees. Adults are called longhorned beetles due to their long antennae. These pests primarily attack damaged, dying, or recently-killed trees where they lay eggs on bark.

Low

Royal Palm Bug

Xylastodoris luteolus (Hemiptera: Thaumastocoridae)

A very small, specialized pest that feeds exclusively on royal palm. Adults reach only 2.5mm in length and cause scattered yellow spots on leaf surfaces. While rarely fatal to palms, heavy infestations can damage large portions of the crown.

Medium

Rugose Spiraling Whitefly

A large whitefly with a broad host range affecting palms, woody ornamentals, and fruit trees. Creates distinctive spiral egg patterns and extensive white waxy material on leaves. Closely related to giant whitefly but more docile.

Medium

Sawfly

Neodiprion sertifer

Non-stinging wasps (not flies) with over 100 species attacking conifers and some broadleaf trees. Larvae feed on needles, preferring older needles which they consume entirely, leaving partially eaten needles looking like fine straw.

Medium

Scale Insects

Including Melanaspis tenebricosa (Gloomy Scale) and Lepidosaphes ulmi (Oystershell Scale)

Small, immobile insects that attach to bark, twigs, and leaves, feeding by sucking plant juices. Adult females are oval, reddish-brown with waxy fringe along body margin. They remain stationary for most of their adult life after initial settling.

High

Southern Pine Beetle

Dendroctonus frontalis

One of the most economically important bark beetles in southern United States forests. Small reddish-brown to black beetle about the size of a grain of rice that attacks many pine species, creating characteristic S-shaped galleries under bark.

Medium

Spider Mites

Various species including Bryobia, Eutetranychus, Oligonychus, Panonychus, Schizotetranychus, and Tetranychus

Tiny arachnids ranging from 0.25-1.0 mm in size that feed on plant cells by piercing and sucking. Colors vary from pale yellow and green to dark green and red. Most active at temperatures between 54-100°F, with rapid reproduction in hot, dry conditions.

Medium

Spittlebug (Froghopper)

Several species including Aphrophora, Clastoptera, Philaenus, and Prosopia (Hemiptera: Cercopidae)

Small jumping insects also known as froghoppers that create distinctive white frothy masses ('spittle') on foliage. Nymphs feed on plant sap and are completely enclosed in protective foam secretions during development.

High

Spotted Lanternfly

Lycorma delicatula

An invasive planthopper recently introduced to the United States from Asia. Native to China, India, and Vietnam. Adults are about 1 inch long with distinctive greyish-brown forewings with black spots. High populations can cause significant damage to ornamental, forestry, and agricultural crops.

High

Spruce Budworm

Choristoneura fumiferana

One of the most destructive native insects in northern spruce and fir forests of Eastern United States and Canada. Periodic outbreaks are part of the natural cycle associated with maturing balsam fir, resulting in loss of millions of cords of timber.

Medium

Sycamore Borer

Ramosia resplendens

A clearwing moth that attacks Western sycamore and coast live oak in California. Larvae bore into inner bark creating twisting tunnels, causing bark to slough off. Prefers older trees under drought stress and those with wounds.

Medium

Sycamore Lace Bug

Corythucha ciliata

Small insects with netlike wing patterns that feed on the undersides of leaves with piercing-sucking mouthparts. Adults are 3-6mm long with brown and black dotted wings, while nymphs are smaller with spines. They attack sycamore, birch, elm, and many other deciduous trees.

Medium

Thrips

Frankliniella occidentalis

Tiny, slender insects from Order Thysanoptera with rasping mouthparts that scar leaf and fruit surfaces. Adults are small and tend to feed in buds, furled leaves, or other unexposed plant areas. Their damage is often observed before the insects can be seen.

High

Western Pine Beetles

Dendroctonus brevicomis

Destructive bark beetles that attack ponderosa and Coulter pines from Baja California north to western Canada. Larvae are white, curved, rice grain-sized and feed in inner bark. Adults create winding, crossing egg galleries forming network patterns under bark.

High

Western Spruce Budworm

Choristoneura occidentalis

The most widely distributed and destructive defoliator of coniferous forests in Western North America. Adult moths are 12.7mm long with 22-28mm wingspread, gray or orange-brown forewings with distinctive white dots. Larvae develop through six stages, becoming 25-32mm long.

Medium

Whiteflies

Tetraleurodes stanfordi

Small insects from family Aleyrodidae, related to psyllids and aphids. Not true flies despite the name. Adults have wings covered with waxy powder, while nymphs resemble scale insects after molting. Many species attack landscape plants in mild-winter areas.

High

Winter Moth (Operophtera brumata)

Operophtera brumata

An introduced European moth whose larvae are pale green caterpillars or loopers with two pairs of prolegs and white stripes. Often misidentified as cankerworms. Female moths are gray and cannot fly (brachypterous), while males can fly and are attracted to lights.

Medium

Alder Ceratocystis Canker

Ceratocystis fimbriata

A serious vascular disease that affects alder trees, causing cankers, branch dieback, and eventual tree death. The fungus blocks water transport and creates characteristic canker formations.

Medium

Anthracnose

Apiognomonia veneta, A. quercina, Gleosporium aridum (fungus)

A fungal disease affecting many tree species, considered a transition between leaf and stem disease. Most severe on sycamore, oak, and ash trees. The disease causes progressive necrosis along leaf veins and can move into twig tissues, forming cankers that may girdle branches.

Medium

Apple Scab

Venturia inequalis, V. asperata

A fungal disease that causes olive-green to dark spots on leaves and fruit of apple, crabapple, and related species. The disease is favored by cool, wet weather and can cause severe defoliation of susceptible varieties.

High

Arborvitae Branch Canker

Seiridium unicorne

A serious fungal canker disease that affects members of the cypress family, particularly Oriental arborvitae. The disease causes elongated, flattened cankers that can girdle branches and stems, leading to dieback and potential tree death.

High

Armillaria Root Rot

Armillaria mellea (also known as Oak Foot Fungus, Oak Root Rot)

A widespread fungal root disease attacking most tree species worldwide. Often associated with stressed trees, it spreads through root contact and can survive for decades in infected stumps. The disease causes gradual decline and can predispose trees to bark beetle infestation.

High

Ash Yellows

Phytoplasma (formerly mycoplasma)

A phytoplasma disease that affects ash species throughout northeastern and midwestern North America. The disease causes progressive decline with reduced growth, abnormal branching patterns, and eventual tree death.

Medium

Bacterial Blight

Xanthomonas spp.

A bacterial disease caused by Xanthomonas species that enters plants through wounds or natural openings. The bacteria move systemically through the plant, causing severe leaf blight with characteristic water-soaked lesions and yellow borders.

High

Bacterial Leaf Scorch

Xylella fastidiosa (bacterium)

A bacterial disease affecting multiple tree species, caused by a bacterium that invades xylem cells and disrupts water transport. The disease causes characteristic marginal leaf browning and can lead to chronic decline and death over multiple years.

High

Birch Melanconium Dieback

Melanconium betulinum

A serious fungal disease affecting all birch species, causing progressive browning of foliage and dieback of twigs and branches. The disease is often associated with environmental stress factors and can lead to significant tree decline.

High

Botryodiplodia and Oak Decline Complex

Multiple fungi including Botryodiplodia querci, Fusarium solani, Cephalosporium diospyri, Pestalotia macrosporum, Diplodia quercina, Phialophora sp., Dothiorella querci, Verticicladiella sp., Fusarium oxysporum, Verticillium albo-atrum

A complex of fungal pathogens causing oak decline, often following drought stress and root damage. The disease can cause rapid death in 2-3 months or gradual decline over 3-8 years. Infection typically occurs through roots from soil-borne phases of the fungi.

High

Botryosphaeria Branch Canker

Botryosphaeria species

A serious fungal disease affecting all redwood species, causing twig cankers and needle blight. Cool, damp spring weather favors spore spread, while hot, dry weather accelerates internal fungal growth and twig girdling. Trees grown outside their native environment are most susceptible.

High

Cedar Branch Canker

Seridium cardinale, Coryneum berckmanii

A serious fungal disease complex affecting cypress, cedar, and arborvitae species. Multiple pathogenic fungi cause branch cankers and twig blight, with disease development closely tied to environmental stress and weather conditions.

Medium

Cedar Coryneum Blight

Coryneum berckmanii, C. thujina

A fungal leaf and twig blight disease affecting cedar and cypress species, also known as Cedar Leaf Blight, Cedar Twig Blight, or Berckman's Blight. The disease causes progressive dieback starting from small branches and can lead to tree mortality through repeated infections.

Medium

Cephalosporium Ulmi (Dothiorella Ulmi)

Dothiorella ulmi (formerly Cephalosporium ulmi)

A vascular wilt disease affecting American elms, now classified as Dothiorella ulmi. This fungal pathogen causes wilting, yellowing, and dieback symptoms that resemble other wilt diseases. Stress factors significantly increase susceptibility to infection.

High

Ceratocystis Canker

Ceratocystis fimbriata

A serious fungal canker disease affecting a wide range of hardwood trees. The pathogen causes characteristic lens-shaped cankers that can girdle branches and stems, leading to wilting above infection sites and potential tree mortality.

High

Ceratocystis Dieback (Oak Wilt)

Ceratocystis fagacearum

A devastating vascular wilt disease of oak trees caused by Ceratocystis fagacearum. The disease causes rapid mortality in red oak group species and chronic decline in white oaks, spreading through root grafts between adjacent trees and by insect vectors.

High

Ceratocystis Fagacearum (Oak Wilt)

Ceratocystis fagacearum

Oak wilt is one of the most serious diseases affecting oak trees, caused by the fungus Ceratocystis fagacearum. This vascular pathogen disrupts water transport, causing rapid mortality in susceptible oaks and spreading through underground root connections.

High

Ceratocystis Ulmi (Dutch Elm Disease)

Ophiostoma ulmi (formerly Ceratocystis ulmi)

Dutch Elm Disease is one of the most devastating tree diseases in North America, caused by the fungus Ophiostoma ulmi and spread by elm bark beetles. This vascular wilt disease has killed millions of elm trees and continues to threaten remaining elm populations.

High

Coryneum Blight

Coryneum berckmannii, C. thujina (fungus)

A fungal blight disease also known as Cedar Leaf Blight, Cedar Twig Blight, or Berckman's Blight. Affects Oriental arborvitae, Italian cypress, and Monterey cypress in the Western Coastal United States, causing branch death and eventual tree mortality.

Medium

Coryneum Canker

Coryneum berckmanii, C. thujina

A fungal canker and blight disease affecting cedar, cypress, and arborvitae species, also known as Cedar Leaf Blight, Cedar Twig Blight, or Berckman's Blight. The disease causes progressive branch death and can lead to tree mortality through repeated infections.

Medium

Crab Apple Scab

Venturia inequalis, V. asperata

A fungal disease affecting apple, crabapple, pear, and related species throughout North America and Europe. Cool, wet weather favors severe infections that can cause significant defoliation and reduce tree aesthetic value.

High

Cypress Cedar Branch Canker

Seridium cardinale, S. unicornie, S. cupressi

A serious canker disease affecting Leyland cypress and related species, particularly damaging in landscape plantings and Christmas tree operations. Disease development is closely tied to hot, dry summer weather conditions, and can kill considerable portions of affected trees.

High

Cytospora Canker

Valsa kunzei (Cytospora kunzei), V. nivea, V. sordida

A widespread fungal canker disease affecting numerous tree species throughout North America. The disease typically attacks trees weakened by wounds, improper pruning, or environmental stress, causing irregular cankers that can girdle trunks and large branches.

Medium

Diplocarpon Theumenii (Hawthorn Leaf Spot)

Diplocarpon mespili

A fungal leaf spot disease affecting hawthorn, photinia, and related plants. The disease is favored by cool, wet weather and can cause severe defoliation, reducing landscape screening value and increasing plant susceptibility to cold injury and other stresses.

Medium

Diplodia Tip Blight

Sphaeropsis sapinea (formerly Diplodia pinea) (fungus)

A fungal disease primarily affecting pine species, causing tip blight and cankers. Most severe on trees planted outside their natural range and under stress conditions. The disease is rare in normal forest conditions but common in urban environments.

Medium

Dothiorella (Elm Wilt)

Dothiorella ulmi

A fungal wilt disease affecting elm trees, particularly American elms. The pathogen causes yellowing, wilting, and gradual dieback through vascular disruption. Stress factors such as drought, malnutrition, and wounds significantly increase susceptibility to infection.

Medium

Douglas Fir Phomopsis Canker

Phomopsis lokoyae

A fungal canker disease specifically affecting Douglas fir trees throughout California and Oregon. The disease causes long, narrow cankers that can girdle entire branches in one season, particularly targeting saplings on poor sites and stressed mature ornamental trees.

Medium

Douglas Fir Phomopsis Canker

Phomopsis lokoyae (fungus)

A fungal canker disease affecting Douglas fir trees throughout California and Oregon. Most commonly attacks saplings on poor sites but may also affect individual branches of mature ornamental trees under stress conditions.

High

Dutch Elm Disease

Ophiostoma ulmi (formerly Ceratocystis ulmi)

A devastating fungal disease that has killed millions of elm trees across North America. The disease is spread primarily by elm bark beetles and through root grafts between adjacent trees.

Low

Elm Dieback (Vermicularia)

Vermicularia ipomearum

A fungal disease causing small, girdling cankers on elm twigs that lead to limited dieback. While not highly significant, it creates aesthetic concerns with its characteristic black fruiting structures.

High

Elm Phloem Necrosis (Elm Yellows)

Phytoplasma (bacteria-like organism)

A systemic disease of elms caused by a phytoplasma, also known as elm yellows. Formerly called elm phloem necrosis in the U.S. and witches' broom in Europe. The disease causes degeneration of phloem and cambium, resulting in tree death.

High

Elm Phloem Necrosis (Elm Yellows)

Phytoplasma sp.

A fatal systemic disease of elm trees caused by a phytoplasma organism, formerly known as elm phloem necrosis in the U.S. and witches' broom in Europe. The pathogen destroys phloem tissue, disrupting nutrient transport and causing rapid tree death.

High

Elm Wilt

Dothiorella ulmi

A serious fungal wilt disease that affects elms, causing progressive yellowing, wilting, and dieback. The fungus enters through wounds and moves through the vascular system, plugging vessels and creating characteristic cankers.

High

Fire Blight

Erwinia amylovora (bacterium)

A devastating bacterial disease affecting many species in the rose family. Infected areas appear water-soaked initially, then quickly turn brown to black as if burned by fire. The disease can progress rapidly and kill entire branches or trees if left untreated.

High

Fusarium Pine Pathogen

Fusarium subglutinans f. sp. pini

An important pine pathogen that causes pitch canker in mature trees and root rot and damping-off in seedlings. This fungus can be spread by both infected seedlings and seeds, and is synonymous with Fusarium circinatum.

High

Fusarium Wilt

Fusarium oxysporum

A soilborne vascular wilt disease affecting a wide range of tree species. The fungus colonizes the root system and moves into the vascular tissue, causing progressive wilting and eventual tree death.

High

Fusarium Wilt

Fusarium oxysporum

A soilborne fungal disease affecting a wide range of tree species, causing vascular wilt through vessel plugging. The pathogen survives long periods in soil through specialized resting spores and typically causes death within 18 months of infection onset.

High

Fusarium Wilt (Mimosa Wilt)

Fusarium oxysporum f.sp. perniciosum

A common and lethal vascular wilt disease of mimosa (Albizia julibrissin), also known as Persian silktree. The soil-borne fungus colonizes and clogs the tree's vascular tissue, interfering with water and nutrient movement and resulting in relatively rapid tree death.

Medium

Hawthorn Leaf Spot

Entomosporium mespili

A fungal leaf spot disease affecting hawthorns and photinias during cool, wet weather. The disease causes distinctive bright red spots that can merge into large maroon blotches, leading to early defoliation.

Medium

Kabatina Branch Canker

Kabatina juniperi, Phomopsis juniperovora, Sclerophoma pithyophila (imperfect fungi)

A fungal disease complex affecting young conifers, causing progressive branch dieback and eventual tree death. Most evident in seedlings and transplant beds on trees less than 4 years old. Multiple fungal species work together to girdle conducting tissues.

High

Leptographium Canker (White Pine Root Decline)

Leptographium procerum (formerly Verticicladiella procera)

A serious root and canker disease affecting various pine species, originally described as White Pine Root Decline. The disease manifests as both root decline and wilt symptoms, and can reach epidemic proportions in Christmas tree plantations and susceptible pine stands.

Medium

Melanconium Dieback

Melanconium betulinum

A fungal disease affecting all birch species, causing progressive browning of foliage and dieback of twigs and branches. The disease is typically associated with stress factors such as borer infestations, drought, poor drainage, and extreme temperatures.

High

Mimosa Wilt

Fusarium oxysporum f.sp. perniciosum

A lethal vascular wilt disease of mimosa trees caused by a soilborne fungus that colonizes and clogs the tree's water-conducting tissue, resulting in relatively rapid tree death.

Medium

Nectria Canker

Nectria cinnabarina, N. coccinea, N. galligena

A fungal canker disease affecting numerous hardwood species, characterized by distinctive target-type cankers with raised, calloused edges and salmon-red pustules. The disease is perennial and can eventually girdle branches or stems, particularly problematic on recent transplants.

High

Oak Decline Complex

Multiple fungi: Botryodiplodia querci, Fusarium solani, Cephalosporium diospyri, Pestalotia macrosporum, Diplodia quercina, Phialophora sp., Dothiorella querci, Verticicladiella sp., Fusarium oxysporum, Verticillium albo-atrum

A complex syndrome involving multiple fungal pathogens that attack oak trees, typically triggered by stress factors such as drought, high temperatures, and root damage. Tree mortality can occur rapidly (2-3 months) or gradually over 3-8 years depending on conditions.

High

Oak Wilt

Ceratocystis fagacearum

One of the most devastating diseases of oak trees, causing rapid mortality in red oak group species and chronic decline in white oaks. The fungus disrupts water transport, spreads through root grafts between adjacent trees, and can be transmitted by insects feeding on fresh wounds.

High

Palm Bud Rot

Penicillium vermoeseni

A fungal disease affecting palm trees, particularly problematic in coastal areas with cool, foggy weather. The disease causes terminal bud death and leafstalk base rot, eventually leading to tree mortality if infection becomes established in the crown whorl.

High

Palm Bud Rot

Penicillium vermoeseni

A serious fungal disease affecting palm trees, particularly in coastal areas of central and southern California. This pathogen attacks the terminal bud and crown area, causing progressive rot that leads to tree death. Favored by cool, foggy weather conditions.

High

Palm Lethal Yellows

Phytoplasma (formerly mycoplasma)

A devastating phytoplasma disease that causes rapid mortality in coconut palms and other susceptible species. The disease progresses through distinct stages from premature coconut drop to characteristic yellowing of fronds, ultimately resulting in death within 3-6 months of first symptoms.

High

Peach X-Disease

Phytoplasma sp.

A lethal phytoplasma disease that affects peach trees throughout North America, transmitted by leafhoppers feeding on infected trees and wild chokecherry reservoirs. This systemic pathogen moves through phloem tissue causing progressive tree decline and death.

High

Pestalotia (Oak Decline Complex)

Pestalotia macrosporum

A fungal pathogen that contributes to Oak Decline Complex, working alongside multiple other fungi including Botryodiplodia, Fusarium, and Diplodia species. This soilborne pathogen primarily infects through roots, causing progressive vascular damage and tree decline.

Medium

Phomopsis Blight

Phomopsis juniperovora, Kabatina juniperi, Sclerophoma pithyophila

A fungal blight disease affecting numerous coniferous species, caused by multiple related fungi. Most severe on young trees and transplants under 4 years old, causing tip dieback, branch cankers, and progressive decline. Favored by cool, moist conditions.

Medium

Physalospora Bleeding Canker

Physalospora obtusa

A fungal disease causing bleeding cankers, twig dieback, and various blights on numerous tree species. Most notable for wet, bleeding cankers on alder stems and branches. The pathogen causes fruit rot, cankers, cone and seed rot on conifers, and twig blights.

High

Phytophthora cactorum

Phytophthora cactorum

A soilborne water mold pathogen causing crown rot, collar rot, root rot, and stem rot on numerous tree species. This aggressive pathogen can kill trees in one growing season or cause chronic decline over multiple years. Favored by cool, wet conditions and poorly drained soils.

High

Phytophthora cinnamomi

Phytophthora cinnamomi

A devastating soilborne water mold pathogen known as one of the world's most aggressive root rot pathogens. Causes crown rot, collar rot, root rot, and stem rot, often leading to rapid tree death. Particularly destructive in Mediterranean climates and areas with wet, poorly drained soils.

High

Phytophthora palmivora

Phytophthora palmivora

A devastating water mold pathogen that causes root rot, stem cankers, and crown rot in palms and many other tropical and subtropical plants. This oomycete thrives in wet conditions and causes rapid plant decline.

High

Phytophthora Root Rot

Phytophthora spp. including P. ramorum, P. cactorum, P. cinnamomi, P. palmivora, P. citricola, P. nicotianae, P. ramora

A soil-borne oomycete pathogen causing crown rot, collar rot, root rot, and stem rot. The pathogen survives in soil for several years and is particularly problematic in poorly drained soils. Trees may die in one season or linger for multiple growing seasons.

High

Phytophthora spp.

Phytophthora spp.

A genus of water mold pathogens that cause various diseases including root rot, crown rot, cankers, and leaf blights on many plant species. These oomycetes thrive in wet conditions and cause significant agricultural and forestry losses.

High

Pine Atropellis Canker

Atropellis apiculata, A. arizonicum, A. pinicola, A. piniphila, A. tingens

A serious fungal canker disease affecting numerous pine species throughout the continental United States. Multiple Atropellis species cause perennial cankers with characteristic blue-black wood discoloration and 'target' canker formations. Young trees are most severely affected.

High

Pine Pitch Canker

Fusarium moniliforme var. subglutinans

A serious fungal disease affecting pine trees, causing resin-soaked lesions and perennial cankers that can girdle branches and main trunks. Often transmitted by insects and through wounds.

High

Pine Pitch Canker

Fusarium circinatum

A devastating fungal disease affecting pine trees worldwide, causing resinous cankers, shoot dieback, and tree mortality. This disease is particularly severe on Monterey pine and other susceptible pine species.

High

Pine Pitch Girdle

Cunninghamella meinickella

A soilborne fungal disease that affects pine trees in California, particularly Jeffrey, Monterey, and ponderosa pines. The fungus causes pitch exudation at the root collar and can predispose trees to bark beetle infestation.

High

Pine Wilt Nematode

Bursaphelenchus xylophilus

A parasitic nematode that causes pine wilt disease, transmitted by pine sawyer beetles. The disease can quickly kill pine trees within one to two years, with Scots, Austrian, and Japanese black pines being most susceptible.

Medium

Pink Bud Rot

Nalanthamala vermoeseni

An opportunistic fungal pathogen that primarily affects stressed or weakened palms. While it can attack all parts of a palm, it is most problematic in growing tips (apical meristem) where new leaves are produced and in newly emerged leaves.

High

Plum Non-Bearing Leaf Scald

Xylella fastidiosa

A bacterial disease that clogs water-conducting xylem cells and causes leaf scald symptoms. The bacterium is spread by leafhoppers and affects flowering fruit trees, causing them to bloom earlier and hold leaves later in fall.

Medium

Redwood Branch Canker

A fungal disease affecting all redwood species (Sequoia, Sequoiadendron, Metasequoia) that causes purple spots on needles and cankers that girdle twigs. Most susceptible are trees grown outside their native environment.

High

Sudden Oak Death

Phytophthora ramorum (oomycete plant pathogen)

A devastating disease caused by an oomycete plant pathogen that kills oak and other species of trees. Has had catastrophic effects on oak populations in California and Oregon, and is also present in Europe. Known for causing rapid tree mortality in previously healthy oak forests.

High

Thielaviopsis Decline

Thielaviopsis basicola

A soilborne fungal disease that causes root rot in elm and madrone trees. The fungus lives saprophytically in soil and typically enters roots through wounds caused by nematodes. Most problematic in heavy, cold, slightly acid to alkaline soils well supplied with humus.

High

Verticicladiella (Oak Decline Complex)

Verticicladiella sp.

A complex of fungi that causes oak decline throughout the continental United States. Predisposed by drought stress, root damage from construction or transplanting, and soil compaction. Can kill trees in 2-3 months or cause gradual death over 3-8 years.

High

Verticillium Wilt

Verticillium albo-atrum, V. dahliae (fungus)

A soil-borne fungal disease affecting a wide range of tree species. The fungus invades the vascular system, causing wilt symptoms that can range from sudden collapse to chronic decline. Disease can be acute with rapid death or chronic with slow dieback over multiple seasons.

Medium

Iron Deficiency

Nutrient disorder (Fe deficiency)

A common nutrient deficiency affecting trees in alkaline or neutral soils where iron becomes insoluble and unavailable for plant uptake. Iron is essential for chlorophyll production and proper tree health.

Medium

Magnesium Deficiency

Nutrient disorder (Mg deficiency)

A nutrient deficiency affecting the chlorophyll molecule and phosphorus transport. Magnesium is the key element in chlorophyll and functions as a carrier for phosphorus. Most abundant in regions of rapid growth such as stem and root tips. Commonly occurs in wet soils due to magnesium's high solubility.

Medium

Nitrogen Deficiency

Nutrient disorder (N deficiency)

A common nutrient deficiency that affects plant protein production and overall growth. Nitrogen is essential for forming proteins critical for all plant growth processes. Plants take up nitrogen as ammonium or nitrate ions from soil.

Medium

Phosphorus Deficiency

Nutrient disorder

A nutrient disorder affecting trees when phosphorus content in soil is insufficient for proper plant metabolism. Phosphorus normally represents 0.2%-0.8% of plant dry matter and is essential for metabolism, protein formation, and root development. Often associated with poor mycorrhizal activity.

Medium

Potassium Deficiency

A nutritional disorder caused by inadequate potassium availability in soil. Potassium is essential for carbohydrate formation, starch formation, and meristematic activity in plants. Shows different symptoms on broadleaf plants versus conifers.

Medium

Zinc Deficiency

A nutritional disorder most common in the Gulf States and California, especially in calcareous or sandy soils. Zinc is essential for chlorophyll production and acts as a catalyst with copper and manganese. Together with copper, zinc aids in enzyme development for nitrogen reduction.