Tree Diseases

There are over 20 common tree diseases that contribute to health decline and death of most of the trees in the United States. This list of tree diseases cause most tree health problems and death. These diseases are the cause of significant replacement expense of yard trees and the commercial expense of future losses of forest products.

Brown Spot Needle Blight

(Mycosphaerella dearnessii)

Hosts

The most important host of this fungal disease in the South is
longleaf pine (Pinus palustris).

Symptoms and Signs

Symptoms are most noticeable on low growing branches and
small seedlings. Look for needle lesions from May through
October. There are two types of lesions to look for, one starts
out a straw yellow color and develops brown margins, the
second type is a brown spot with a yellow band. Diseased
needles often times have brown tips. Both needle spots increase
in size over time, resulting in needle death. Killed needles
turn reddish brown before dropping off. Longleaf pine
seedlings often die while still in the grass stage after repeated
defoliations.
Both sexual and asexual spores, which are produced
in fruiting bodies on needles throughout the year in the South,
are the most common signs to look for. Boat -shaped spores
can be collected from the gray to black spots on first -year
needles for positive identification using a microscope.

Life-Cycle

M. dearnessii survives the winter in lesions on dead needles,
either still attached to the plant or in fallen needles. New infections
occur from spring through summer as spores are
spread from these infected needles via splashing and wind
driven rain. Young succulent needles are more susceptible to
infection than older needles and needles need to be wet for
infection to occur. Warm, wet weather favors this disease and
infection in longleaf pine is highest during wet periods when
day and night temperatures are about 30°C and 21°C, respectively.

Management

Plant resistant pine species and only use healthy nursery
stock.. Eliminate and destroy small infected trees. In longleaf
pine plantations managed with fire, burn during the dormant
season in order to eliminate infected needles that have
fallen on the forest floor. Fungicide sprays can be effective in
nurseries, but are not recommended for homeowners. Both
chlorothalonil or Bordeaux mixture provide excellent disease
control. Begin spraying in the spring when new needles are 1
to 2 inches long.

Needle Casts

(Ploioderma spp. & Lophodermium spp.)

Hosts

All southern pines are susceptible with the exception of longleaf
pine (Pinus paultris). Needle cast fungi are often very
host-specific.

Symptoms and Signs

Needle cast is a general term for a group of foliar diseases on
pine which cause small spots or lesions on needles, needle
browning, needle death, and premature needle drop. Most
needle cast fungi infect young, newly formed needles in the
late spring or early summer, however symptoms do not begin
to develop until the following winter or early spring. The first
symptoms of infection are small yellow spots on needles less
than one year old. Yellow spots begin to turn brown and expand
to form bands that surround the entire circumference of
the needle. In spring, the bands may turn pale yellow or grayish-
brown. Tips of the needles and tissue between multiple
bands will then turn brown and die; the base of the needle will
often stay green however.
Infected needles (especially needles with completely
dead tips) will begin to prematurely drop in the late spring
and throughout the summer. On severely diseased trees, all
needles from the previous growing season may be lost, leaving
only new growth. Heavily defoliated branches and shoots
may not grow very much, therefore new needles produced
will be very close together around the shoot tip, giving it a
tufted appearance.

Life-Cycle

In late spring (April-May), sticky spores (sexual spores) are
produced on lesions from the previous year’s infections. The
spores are spread by splashing rain or may be carried by
strong winds for short distances. Infection can only occur
during wet and preferably cool weather. The fungus grows
slowly, and the first symptoms of infection will not be visible
until the following spring. The fungus eventually expands to
surround the entire needle, at which time small black fruiting
bodies form within the lesion and produce sexual spores.
There is only one disease cycle per year.

Management

Management for needle cast is usually not necessary as it
causes no serious harm to the tree; however aesthetic concerns
may warrant an attempt to reduce disease severity.
Plant pines on a wide spacing and keep the area clear of vegetation
to improve air circulation. Destruction of diseased needles
that have fallen is ineffective because these needles have
already released their spores before falling to the ground.

Passalora Needle Blight on Leyland

Cypress (Passalora sequoia)

Hosts

Eastern red cedar (Juniperus virginiana), bald cypress
(Taxodium distichum), and most commonly Leyland cypress
(x Cupressocyparis leylandii) are all susceptible to this fungal
disease.

Symptoms and Signs

Symptoms usually appear during summer months and typically
the disease only affects one -year old foliage. Common
symptoms include browning of needles and eventual needle
drop. Passalora needle blight symptoms start on lower
branches near the trunk and then spread outward toward
branch tips. The loss of foliage spreads upward and outward
from year to year. In severe cases, the entire tree will turn
brown except for the new growth at the tips of the branches.
Brownish spores develop during late spring to summer
on infected foliage.

Life-Cycle

This pathogen overwinters in diseased leaves on living plants.
Spores are produced throughout the growing season, most
abundantly during wet weather in late spring and summer.
Spores are dispersed primarily by rain, overhead irrigation,
and wind. Once a spore lands on wet foliage it will germinate
and enter the leaves through the stomata. Infections occur
throughout summer and symptoms appear 2 -3 weeks after
infection from mid-summer to late fall.

Management

Plant trees at their proper spacing in order to allow adequate
air flow between foliage, to reduce prolonged periods of leaf
wetness, which is prone to infection. To reduce the spread of
spores, avoid overhead irrigation or restrict it to early morning
hours. Since spores can be spread via pruning tools, it is important
to sterilize tools with a 10% bleach solution following
the pruning of diseased limbs. Fungicides are available, however
they are usually not practical for homeowners and are
therefore not recommended. Encourage homeowners with
diseased Leyland cypress hedge rows to consider replanting
with a diversity of plants. Evergreen plants to consider interplanting
Leyland cypress with include hollies ( Ilex spp.), waxmyrtle
(Myrica cerifera), Eastern red cedar, and thuja `Green
Giant’ (Thuja (standishii x plicata) ‘Green Giant’).

Anthracnose

(Caused by Several Fungi)

Hosts

Anthracnose is a general term for a group of diseases on hardwoods
that cause lesions on leaves, twigs, and fruits. The
fungi responsible for anthracnose are Gloeosporium spp.,
Gnomonia spp., and Apiognomonia spp. Hosts include a wide
variety of hardwoods. Common hosts include oak, maple,
sycamore, ash, walnut, and dogwood.

Symptoms and Signs

Symptoms vary with species, but in general the most obvious
symptoms are the leaf lesions produced in the spring and expanding
throughout the summer. Lesions often begin as pale
green or greenish-grey blotches, but then turn yellow, tan,
reddish-brown, or brown.
Lesions tend to begin along leaf veins (because the
depressions along veins hold water for a longer period of time
and spores tend to collect there), but often rapidly expand.
Severely infected leaves may have a scorched appearance,
becoming almost completely brown, wilted, or cupped.
(Note: drought symptoms and/or leaf scorch differ because
the browning and wilting of leaf tissue begins at the leaf tips
and leaf margins and progresses inward ).
Some trees respond to infection by prematurely shedding
leaves (e.g. sycamore and ash), but others retain their
leaves until normal leaf drop in the fall (e.g. oak). In sycamore,
the fungus is able to grow out of leaves into adjacent
twigs where it causes small cankers, shoot dieback, and
witches brooms or deformed twigs.

Life-Cycle

Most anthracnose fungi infect their hosts during the spring,
just as the first new leaves begin to expand, and continue
through the summer while environmental conditions are suitable.
Spores are released from last year’s diseased tissue
(most commonly from fallen leaves). Spores can be spread
by wind or rain-splash, and can only infect soft, succulent
tissues such as new shoots, flowers, and fruits, but leaves are
the most severely infected. The fungus obtains nutrients from
plant cells, and in turn the cells are killed creating the leaf
lesion. The lesion expands as the fungus spreads. During
periods of sustained wetness and cool temperatures, spores
are produced from leaf lesions which can re -infect the same
leaf or neighboring leaves. New infections usually do not
occur after mid-summer because conditions are too warm and
dry. Most anthracnose fungi over -winter on the ground in
fallen leaves, but some (e.g. sycamore anthracnose) can also
spread from the leaves into adjacent shoots and over -winter in
the twigs where they directly infect new leaves in the spring.

Management

Management for anthracnose is usually not necessary as it
causes no serious harm to the tree; however aesthetic concerns
may warrant an attempt to reduce disease severity.
Plant trees on a wide spacing, keep the surrounding area clear
of vegetation, and prune properly to improve air circulation
within the crown.

Powdery Mildew

(Caused by Several Fungi)

Hosts

Powdery mildew is caused by numerous fungi ( Erysiphe spp.
Phyllactinia spp., and others). Powdery mildew has an extremely
wide host range; trees most commonly affected include
crapemyrtle (Lagerstroemia indica) and flowering dogwood
(Cornus florida).

Symptoms and Signs

Symptoms usually appear late in the growing season during
periods of high relative humidity. Injury commonly seen on
infected plants includes stunting and distortion of leaves,
buds, growing tips, and fruit.
The presence of white to gray fungal growth over leaf
surfaces is the most common sign of the disease. Powdery
mildew begins as circular, powdery white spots and expands
to coat the entire leaf surface. In most cases this fungal
growth can be removed by rubbing the leaves.

Life-Cycle

The fungi that cause powdery mildew are spread by wind
blown spores that blow from infected leaves to new hosts
throughout the entire growing season. Powdery mildew fungi
are generally host specific, for example the fungus species
infecting lilacs will not cause powdery mildew on oak. During
the winter the fungus survives on infected plant parts and in
fallen leaf debris. During this time it may produce resting
structures known as cleistothecia, which appear as tiny black
`pepper-like’ spheres on the underside of leaves that can survive
harsh environments. In spring, spores are released from
the cleistothecia and carried by wind to susceptible leaves.
Once a spore finds a suitable host it reproduces asexually,
leading to an increase in the spread and infection of the disease
throughout the growing season.

Management

Plant resistant cultivars. Lagerstroemia indica x fauriei hybrids
are resistant to powdery mildew. These include, but are
not limited to, `Apalachee’ and `Fantasy’. Flowering dogwood
cultivars `Appalachian Joy’ and `Appalachian Blush’
are very resistant to powdery mildew.
The fungi that cause powdery mildew can overwinter
on dead leaves so it important to keep the surrounding area
clear of diseased vegetation. Plant trees on a wide spacing
and prune properly to improve air circulation within the
crown. The use of fungicides is rarely warranted in a landscape
situation.

Fusiform Rust

(Cronartium quercuum f. sp. fusiforme)

Hosts

This fungal disease attacks several southern pine species, but
is most damaging on slash pine (Pinus elliottii) and loblolly
pine (Pinus taeda). Oaks, such as water oak (Quercus nigra),
willow oak (Q. phellos), and southern red oak (Q. falcata),
serve as important alternate hosts for this disease, but do not
sustain any damage.

Symptoms and Signs

On pine, the most obvious symptom of infection is the formation
of a spindle-shaped gall on a branch or main stem. The
gall may be pitch soaked and occasionally exude sap. During
cool spring months, bright orange spores are often produced
on the gall surface. These aeciospores are blown off by the
wind and serve to infect oak leaves.
On oak, symptoms are limited to small leaf spots that
may be chlorotic or necrotic. A key diagnostic characteristic
on oaks are the bright orange spores (urediospores) produced
on the underside of the leaf.

Life-Cycle

Cronartium quercuum f. sp. fusiforme has five spore stages
and takes two years or longer to complete its life -cycle. Starting
in the spring (February-April), orange aeciospores are
produced on gall surfaces. These aeciospores are dispersed
by wind and infect the leaves of susceptible oaks, where they
cause leaf spots. After one week, bright orange urediospores
are produced on the underside of the leaf, which serve to re –
infect the same leaf or nearby oak leaves in order to build up
the pathogen population. A week following, urediospore production,
small brown teliospores are also produced on the
underside of the leaf. These spores can survive for several
months, until conditions are just right (60 -80F, 95-100% RH),
at which time they germinate and produce basidiospores. The
basidiospores are also blown by the wind, back to nearby
pines where they can infect needles. The fungus grows into
the branch or stem, forming a gall. Aeciospores are produced
on the gall during the next spring, thus completing the life
cycle.

Management

Plant resistant pine species. Shortleaf pine (P. echinata) is
highly resistant and longleaf pine (P. palustris) is relatively
resistant. Avoid planting susceptible species in areas with
historically high incidence of fusiform rust. Prune out galls
within 8 inches of the main stem. Avoid practices that over –
stimulate growth such as fertilization, as this has been shown
to increase the incidence of rust.

Cedar-Apple Rust

(Gymnosporangium juniperi-virginianae)

Hosts

Cedar-apple rust is caused by the fungus Gymnosporangium
juniperi-virginianae.The primary host is apple (Malus domestica)
and the alternate host is eastern redcedar ( Juniperus virginiana).

Symptoms and Signs

The fungus forms galls on the branches of eastern redcedar.
Branches with galls experience some dieback, but otherwise
cause little harm to the tree. Once galls are mature, bright orange,
gelatinous, spore-producing telial horns emerge from
the gall. Telial horns are most commonly seen following a
warm, spring rain. Telia gelatinize and dry several times in
response to intermittent rains. The galls eventually dry and
die, but remain attached to twigs for a year or more.
Yellow or orange leaf spots form on the apple host in
the spring. Powdery, yellow-orange spores are produced on
the undersides of the apple leaves. The leaf spots turn necrotic
as the disease progresses, causing premature defoliation and
crop reduction in apple.

Life-Cycle

Rusts spend the winter on redcedar as stem galls. In the
spring, bright orange telial horns emerge from the galls in
response to warm, wet weather. Basidiospores, are released in
the spring from these gelatinous galls, to infect the young
leaves and fruit of apple trees. Spores called aeciospores are
produced on the underside of apple leaves that infect redcedar
from midsummer to early autumn. Galls form on redcedar the
next year, and telia are produced on galls 21 -22 months after
infection. The cedar-apple rust life-cycle takes two years to
complete

Management

Galls can be picked and destroyed from redcedar. Use resistant
apple and Juniperus cultivars. Apple cultivars that normally
show good to excellent resistance to cedar -apple rust
include `Red Delicious’, `McIntosh’, `Arkansas Black’, and
`Winesap’, just to name a few. Removing redcedar trees
growing near apple orchards may reduce the occurrence of the
disease on apple, however spores can travel several miles. In
apple orchards, fungicides can be used to prevent spring
basidiospore infections. Refer to the publication FDIN002
(Disease and Insect Management in the Home Orchard), for
spray schedule information.

Fire Blight

(Erwinia amylovora)

Hosts

Fire blight is a disease caused by the bacteria Erwinia amylovora.
There are more than 100 species of plants known to be
susceptible to fire blight; all are in the Roseaceae family.
Trees susceptible include apples, hawthorns, pears, and mountain-
ash. The disease can also occur (but is far less common)
in the stone fruits: peach, cherry, and plum.

Symptoms and Signs

Blighting flowers is usually the first symptom to appear in
spring. Flowers will darken, droop, shrivel, and turn black.
The tips of infected shoots will also droop and turn black and
bend over into a shepherd’s crook shape. If many shoots are
infected, trees will appear to be burned or scorched, hence the
name “fire blight”.
Cankers may form when branches and stems are infected
by the bacteria. Bark on cankers may appear raised
and slightly blistered, especially when cankers are actively
expanding during the growing season. Cankers can eventually
girdle and kill branches or the entire tree. Bacteria may
be visible oozing from or near infected plant parts during
warm, humid weather.

Life-Cycle

Bacteria overwinter in diseased plant parts including cankers,
twigs, and buds. When warm humid weather returns, small
drops of bacteria ooze from infected plant parts and can be
transmitted to new growth via rain-splash, wind-driven rain,
irrigation water, insects, birds, and pruning tools. There are
many insects known to vector the fire blight bacteria, but the
most common are pollinators such as bees and flies. Once the
bacteria enters the plant through small wounds or openings
populations can double once every hour and spread through
plant tissue at rates of up to 10 inches a day. As bacteria
spread, they release enzymes that kill and dissolve plant cells;
symptoms begin to appear a few weeks after infection.

Management

Prune off infected plant tissues as soon as they are observed;
be sure to prune 8 inches or more from the nearest symptomatic
tissue. Prune trees regularly to increase air circulation
in the crown. Make sure to sanitize pruning tools with a 10%
bleach solution after use to prevent spreading the disease.
Most new infections start on flowers; removal of flowers on
small trees can prevent infection. Bactericides are available,
but proper timing of applications is critical and is difficult to
accomplish effectively. Examine trees thoroughly 1 -3 weeks
after warm wet periods in the spring for symptomatic tissue
and remove.

Bacterial Leaf Scorch

(Xylella fastidiosa)

Hosts

Bacterial leaf scorch is caused by a bacterial infection of a
tree’s water conducting tissue. The pathogen is Xylella fastidiosa.
There are hundreds of known hosts of bacterial leaf
scorch. Trees include maple, buckeye, hackberry, dogwood,
sweetgum, sycamore, plum, oak, and elm.

Symptoms and Signs

Infection is perennial; bacteria are able to survive from year to
year in the host vascular system. Bacteria interfere with water
transport in the xylem, therefore symptoms closely resemble
those of drought and other vascular diseases. Leaf margins
turn red or yellow; then leaves will wilt and turn brown especially
during the summer months. A red or yellow band often
separates brown from green tissue. Older leaves are usually
scorched first, with symptoms progressing towards shoot tips.
Scorched leaves are retained on the tree into the fall.
Trees may have decreased fruit production, delayed
bud break, reduced growth, stunting, branch dieback, and
eventually death. Leaves usually expand normally each year;
then symptoms begin to appear in late spring and progress
throughout the summer. Hot droughty weather makes symptoms
worse. Symptoms may initially appear in isolated
branches or sections of the crown, but eventually spread
throughout the tree. Symptoms can fluctuate in severity from
year to year.

Life-Cycle

Bacteria must be introduced into a tree’s vascular system by
insects in order for infection to occur. Common insect vectors
include spittlebugs and sharpshooter leafhoppers; insects
pick up the bacteria from infected trees and transmit it during
feeding to healthy trees. Bacteria multiply rapidly in the xylem
and are carried faster upward in the transpiration stream ,
but also spread downward. Symptoms develop within a few
weeks to a year depending on tree health and species. The
bacteria overwinter in roots and stems and each year they
spread to new xylem vessels. The bacteria produce enzymes
that dissolve cell wall components and plug the vascular system.

Management

There are currently no effective treatments for bacterial leaf
scorch.

Alcoholic Slime Flux

(Caused by Bacteria)

Hosts

Slime flux is not a serious disease of trees, but is very common
and often of great concern to homeowners. Found very
commonly in elm (Ulmus Americana). Also found in maple
(Acer spp.), oak (Quercus spp.), sweet-gum (Liquidambar
styracifula), sycamore (Platanus occidentalis), willow (Salix
spp.), hemlock (Tsuga spp.), and fir (Abies spp.).

Symptoms and Signs

Symptoms usually appear during the spring or summer, but
can occur in the fall. Alcoholic slime flux is usually noticed
when fluid pressure builds up and breaks through the outer –
sapwood and bark. The fluid will have a sour smell, and
leave grey, brown, or black streaks down the bark. Alcoholic
slime flux will always be associated with an old crack,
wound, or cavity. The flux is colorless (though may be frothy
white under pressure) and has a fermented odor. It will also
discolor bark. Alcoholic slime flux is highly attractive to insects
such as bees, wasps, ants, butterflies, and moths. Fluid
darkens when exposed to air and may be produced so excessively
as to flow or pool on the ground below. Various fungi
and bacteria colonize the fluids once exposed to oxygen, and
therefore the ooze may become slimy and bad smelling.

Life-Cycle

Alcoholic slime flux occurs when microorganisms (fungi and
bacteria) invade cracks, wounds, or cavities and begin to ferment
sap and dead wood. Ethanol and gases are produced
during the fermentation process, which cause pressure to
build. Excess pressure is relieved when liquid and gas is expelled
through the surface.

Management

There are no preventative measures for slime flux. Fluids can
be washed from the bark surface with a mild soap solution.
Do not attempt to cut into or drain pockets of wet -wood; introduction
of oxygen into these cavities will allow wood rotting
fungi to invade, and severe decay can occur.

Laurel Wilt

(Raffaelea lauricola)

Hosts

Discovered in 2003, laurel wilt has rapidly become a disease
of serious concern in the southeast. The laurel wilt fungus
(Raffaelea lauricola) can kill mature trees very quickly, is
vectored by a small ambrosia beetle (Xyleborus glabratus)
from Asia, and is spreading through the southeast at approximately
20 miles per year. It affects plants of the laurel family;
most commonly red bay (Persea borbonia). Also susceptible
are sassafras, avocado, swamp bay, silk bay, pondberry
(endangered-U.S.), pond spice (threatened-NC), Northern
spicebush, and California laurel.

Symptoms and Signs

Symptoms of the disease may be similar to drought. Leaves
begin to turn olive grey, then reddish -brown, and begin to
droop before wilting completely and turning brown. Leaves
are retained on dead trees for a year or more. Symptoms may
start in an isolated branch or in the top of the tree, but will
spread throughout the entire tree rapidly. Most trees wilt and
die a few weeks or months after symptoms first appear.
Dark staining in the outer sapwood is clearly visible
in dead or dying trees. Staining will be dark purplish or
black, and be easily seen by looking at wilted branches in
cross section or removing the bark to expose the xylem.
Staining in dead trees extends through the roots to all
branches and twigs.

Life-Cycle

The red bay ambrosia beetle is a “fungus farmer”. It creates
galleries in dead or dying trees to grow the fungus on which it
feeds. The beetle carries the fungus with it from tree to tree,
and coincidentally, the fungus that the red bay beetle farms is
highly pathogenic on the beetle’s preferred host tree. This
creates a symbiotic relationship in which the fungus kills trees
for the beetles to invade, and the beetles farm and carry the
fungus to new trees. It may only take one or a couple of beetles
to infect a tree. Beetles cannot attack healthy trees, so it
is likely that the fungus is introduced to the tree during failed
attempts by beetles to enter. Only after the tree is dead or
dying can beetles return to infest the tree and farm the fungus.
Once introduced into the tree’s vascular system, the
fungus rapidly spreads in the sapwood throughout the entire
tree. The tree responds by plugging its vascular system to
prevent spread of the fungus, but this also cuts off the tree’s
supply of water. Therefore, trees wilt and die rapidly after
infection.

Management

There are currently no effective control options. Research is
being conducted on systemic insecticides and fungicides.
Human movement of infested wood is responsible for the diseases
rapid spread through the southeast; without human assistance
the disease can only spread approximately 20 miles
per year. Although laurel wilt has not been reported in NC
yet, any suspected incidence of laurel wilt should be reported
to NCDFR Pest Control staff immediately (919 -731-7988).

1000 Cankers Disease

(Geosmithia morbida (proposed))

Hosts

Thousand cankers disease is caused by a pathogen vectored
by the walnut twig beetle (Pityophthorus juglandis) and is
caused by the fungus Geosmithia morbida (proposed). The
walnut twig beetle can feed on multiple walnut species, but
black walnut (Juglans nigra) is the beetle’s preferred host.

Symptoms and Signs

The most obvious symptoms are dieback and mortality.
Black walnut trees in the final stage of thousand cankers disease
will often times have large areas of foliage that rapidly
wilt. Small, round entry/exit holes may be present along infested
branches or stems and adult walnut twig beetles may be
present at certain times of the year. Some resin weeping may
also be seen around beetle entry holes. Infected trees will
have walnut twig beetle galleries and associated cankers can
be found under the bark.

Life-Cycle

Thousand cankers is an insect -disease complex. This disease
was first confirmed east of the Mississippi River in Knoxville,
TN in July 2010, so little is known about the life -cycle in this
area. In the west, adult walnut twig beetles spend the winter
within insect cavities in the bark of the host trunk.. Adults
become active again in April, at which time they fly to new
hosts, mate, and create new egg galleries. During the construction
of egg galleries, the fungus Geosmithia is introduced,
where it begins to grow around the tunnels. The Geosmithia
fungus causes a small brownish-black canker under the
bark and around the beetle’s entry hole. Walnut branches and
stems may be attacked by many beetles, resulting in numerous
small cankers which eventually overlap and girdle the tree.
Trees are often killed within three years after initial symptoms
are noted. The walnut twig beetle produces a second generation
from mid-July through late August. In the fall, adult beetles
begin hibernation until the following spring.

Management

There are no known management tactics at this time. Any
walnut trees suspected of being infected with thousand cankers
disease should be immediately reported to the N.C. Department
of Agriculture Plant Industry Division in Raleigh
(919)733-3933, or to one of the two North Carolina Forest
disease Pest Control Branch offices in Goldsboro (919)731 –
7988 or Morganton (828)438-3793 for confirmation. Do not
move wood suspected to be infected with thousand cankers
disease, this includes firewood.

Armillaria Root Rot

(Armillaria spp.)

Hosts

Armillaria root rot is a general name for a group of diseases
caused by fungi of the genus Armillaria; most commonly A.
mellea and A. ostoyae. In general they are pathogens of the
roots and lower stems of both hardwoods and conifers and are
important decomposers of dead trees.

Symptoms and Signs

The symptoms of Armillaria root rot often resemble many
other diseases and disorders of trees such as drought, decline,
Hypoxylon canker, Annosus root rot, and Phytophthora root
rot. Growth reduction, chlorotic or scorched leaves, early fall
coloration and/or premature leaf drop, branch dieback, wind –
throw, and tree death are common above -ground symptoms.
Conifers may produce large crops of undersized cones during
decline. Trees are often affected in groups.
Armillaria causes cankers (lesions) on the inner -bark
and outer-sapwood on the root-crown and lower stem. Cankers
may expand slowly and eventually kill large roots; entire
stems are not usually completely girdled, but large lesions
may cause dieback or death. After a tree dies, the fungus
colonizes and decays sapwood.
There are some very distinct signs of the Armillaria
fungus used to confirm its presence. White mycelial fans
(sheets of white fungal tissue) are often visible beneath the
bark of cankers of rotted wood. Black or brown branched
rhizomorphs (also fungal tissue) that resemble fine roots or
shoe strings may also be visible beneath bark, on root surfaces,
and may even extend into the soil. Rhizomorphs may
be flattened when found beneath bark, but are cylindrical (<1/32 inches in diameter) when found on the bark surface or inthe soil. Golden-yellow mushrooms may be produced arounddead or diseased trees in the fall. Many species of Armillariaare bioluminescent.

Life-Cycle

Stressed trees are highly predisposed to Armillaria root rot.
Armillaria spreads via rhizomorphs, root to root contact, and
airborne spores. Rhizomorphs are made up of densely packed
fungal hyphae to form fine root-like structures. Rhizomorphs
can grow through the soil (up to 8 feet per year) feeding on
organic matter as they go, until they reach the roots of new
trees. Rhizomorphs attach to tree roots and penetrate the bark
by mechanical force and enzymatic degradation. Airborne
spores are produced from golden-yellow mushrooms (honey
mushrooms) that grow around the base of infected trees.
Spores infect dead stumps and wounds on lower stems and
exposed root tissue. The hyphae of a single fungus can spread
great distances through the soil.

Management

Prevention is difficult; no practical treatment options are
available. It is critical to maintain proper tree health. Select
the proper tree species for the site; provide adequate water
and fertilization if necessary. Remove diseased trees and infected
root systems if possible.

Seiridium Canker

(Seiridium spp.)

Hosts

Seiridium canker is a destructive fungal disease on Leyland
cypress. In the southeast, this disease is caused most often by
the fungus Seiridium unicorne.

Symptoms and Signs

Branch dieback and foliage discoloration is one of the first
noticeable symptoms of this disease. Chlorotic and necrotic
foliage is most likely to appear in spring; however it can be
seen at any time of the year. Upon close examination,
branches exhibiting discoloration will have dark, elongated
lesions called cankers. Seirdium cankers form on stems,
branches, and in branch axils. They may be discolored dark
brown to purple and are often accompanied by an extensive
flow of resin.
Spore producing structures can be seen on the surface
of cankers, as small, black dots with the aid of a 10X hand
lends. These black fruiting bodies open during wet weather to
release spores, called conidia.

Life-Cycle

The pathogen overwinters in cankers on diseased trees. Fruiting
bodies with conidia are present throughout the year. Environmental
stressors, like drought or ice injury, predispose
Leyland cypress to infection. Most infections are thought to
be initiated during wet weather by conidia. Spores can be
spread via rain, overhead irrigation, and pruning tools. Twig
and branch wounds are the common places for infections to
occur. Following infection, canker development and dieback
can take several years to develop, depending on environmental
conditions. It is important to note that spore production
is interrupted during hot, dry weather.

Management

Proper tree care is the best defense against seirdium canker in
residential landscapes. Plant Leyland cypress trees at a minimum
of 12 to 15 feet apart to ensure good air circulation between
trees. Provide trees with adequate water (at least 1 -2
inches per week below the entire drip line), and avoid over –
fertilization. To reduce the spread of spores, avoid overhead
irrigation or restrict it to early morning hours. Prune out
branch cankers by making pruning cuts 3 to 4 inches below
diseased tissue. Since spores can be spread via pruning tools,
it is important to sterilize tools with a 10% bleach solution
following the pruning of diseased limbs. Fungicides provide
no control once an infection has taken place.

Pine Wood Nematode

(Bursaphelenchus xylophilis)

Hosts

This disease occurs mostly on non -native species of pine. In
particular, Japanese black pine (Pinus thunbergii), Japanese
red pine (Pinus densiflora), and Austrian pine (Pinus nigra)
are highly susceptible.

Symptoms and Signs

The first symptom is wilting foliage. Wilted trees will turn
yellow to brown within three months after becoming infested.
The pine wood nematode can only be identified under
microscope magnification. Symptomatic branches will
need to be sent to the NC Department of Agriculture Nematode
Assay Section. Do not let samples dry out and submit
them as soon as possible.

Life-Cycle

Longhorned beetles in the genus Monochamus have been
shown to transmit the pine wood nematodes. These beetles
are known as sawyers. The pine wood nematode is transmitted
to new pine hosts during beetle feeding. In April and
May, adult sawyers emerge from nematode infested trees,
carrying hundreds of nematodes in their bodies. As the adult
beetles feed on healthy pine shoots, the nematodes leave the
sawyers and enter the new pine host through beetle feeding
wounds. The pine wood nematode first colonizes the resin
ducts of the tree and then moves into the water -conducting
tissue, xylem. The nematode reproduces rapidly in the xylem,
which leads to wilting and tree death.
Sawyers are attracted to dying or dead trees in which
they can lay their eggs. The nematodes, by killing trees, are
providing breeding areas for the sawyer beetles. Pupal chambers
are created in the dead wood, where the sawyer beetles
complete their life-cycle. In the pupal chamber, juvenile
nematodes enter the bodies of young adult beetles just before
they emerge from their chambers. These young adults fly
away from the dead host carrying the nematodes in their bodies
in search of healthy pine trees to feed on, repeating the
life-cycle.

Management

Do not plant susceptible, non-native pine species. Remove
and discard all diseased trees by burning, burying, or debarking.
There are no chemical control options available

Hypoxylon Canker

(Hypoxylon spp.)

Hosts

Hypoxylon canker is a secondary disease of many hardwood species that affects trees that are already severely stressed by some other cause. Hypoxylon canker is caused by many Hypoxylon fungi, most commonly H. atropunctatum and H. mediterranea. Most common hosts are oaks (especially red oaks). Also found in hickory, maple, beech, sycamore, birch, elm, walnut, and many others.

Symptoms and Signs

Symptoms may initially resemble those of oak decline. Bud break may be delayed, leaves may be undersized, foliage may be chlorotic, scorched or wilted, and branches may begin to dieback from the top of the tree downward.
The easiest way to identify Hypoxylon canker is by the large spore-bearing mats (stromata) produced beneath the bark of infected trees. These stromata usually appear the year following drought (or other severe stress), but may appear within a few months. Stromata will grow in size and eventually rupture the bark; patches of sloughed off bark range from a few inches to many feet in size. In severe cases, almost the entire tree will lose its bark and be covered in the fungal mats. Stromata can vary in color from tan, brown, black or grey depending on the species. Trees die quickly if not already dead at the time of stromata production.

Life-Cycle

Spores of Hypoxylon fungi are everywhere. Even when little or no disease is present in the forest, the fungus is present as a wood-rotter and feeds on dead wood. Trees are most often infected at a very early age through small wounds and natural openings. It is believed that most oaks and other susceptible species have Hypoxylon infections, but disease does not develop until trees become severely stressed. When trees become water stressed, the Hypoxylon colonies begin to grow rapidly in the water-depleted sapwood and inner bark. The fungus attacks these tissues, forms stromata, and the bark is sloughed off. With little or no remaining functional vascular system, trees die quickly once the invasion begins. The fungus then invades the remaining wood; initially turning sapwood brown, it causes a yellowish-white decay with black zone lines.

Management

Few management options are available. Proper tree care is critical. Provide trees adequate water (at least 1 -2 inches per week below the entire drip line), fertilizer (avoid nitrogen rich fertilizers), and room to grow with little competition from neighboring trees or understory. Add a thin layer of mulch (1-3 inches) around the drip line. Avoid planting susceptible species on dry sites.

Mistletoe

(Phoradendron spp.)

Hosts

Mistletoe is a perennial, broad-leafed, evergreen plant that parasitizes many species of hardwood trees; most commonly oaks and hickories.

Symptoms and Signs

Heavily infested trees may be reduced in vigor, stunted, or even killed, especially if they are stressed by other factors.
The presence of green stems and thick oval shaped mistletoe leaves is the only reliable sign of an infestation. Identification of an infestation is easier to observe in the winter when all the leaves are off the host plant. Leafy mistletoe has opposite evergreen leaves, rounded growth habit, and reaches approximately 2 feet in width. Inconspicuous flowers produce small, sticky, whitish berries in the fall.

Life-Cycle

Mistletoe plants are either female (produce berries) or male (produce pollen). After fertilization, female plants produce sticky berries that are dispersed either by birds or by falling to lower branches. Mistletoe seeds germinate anywhere if environmental conditions are right, but they can only initiate infection if they stick to the bark of a suitable host. Once the mistletoe seed lands on a suitable host and germinates, it grows through the host bark and into the tree’s water – conducting tissues, where root-like structures called haustoria develop. The haustoria absorbs both water and minerals from its host tree. Mistletoe leaves are capable of photosynthesizing their own food; this food is not shared with the host. As the mistletoe plant grows, the haustoria gradually extends up and down the inside of the infected branch. Female plants will eventually bloom, produce seed, and infect new hosts, repeating the life-cycle.

Management

Control is usually not necessary. Pruning out mistletoe is the most effective method of control. Infected branches need to be cut at least one foot below the point of mistletoe attachment, in order to remove all the haustoria. Mistletoe infecting a major branch or trunk where it cannot be pruned may be controlled by cutting off the mistletoe flush with the limb or trunk. Then wrap the area with black polyethylene to exclude light and prevent photosynthesis. It is important to remove mistletoe before it produces seed and spreads to other limbs or trees.

Pine Beetles

(Dendroctonus ponderosae)

Hosts

Pine Betlees will infest and kill all species of pine within its distribution (Thatcher et al. 1980). In the southern United States, the preferred hosts are loblolly pine, shortleaf pine (Pinus echinata Mill.), pond pine (P. serotina Michx.), and Virginia pine (P. virginiana Mill.) (Thatcher and Barry 1982). In Florida, SPB will also readily attack and kill spruce pine (P. glabra Walter), and sand pine (P. clausa (Chapman ex Engelm.) Vasey ex Sarg.) (Chellman and Wilkinson 1975). Slash pine (P. elliottii Engelm.) and longleaf pine (P. palustris Mill.) are generally considered to be more resistant to SPB attacks, but during outbreaks even healthy trees of these species can be successfully colonized (Belanger et al. 1993, Belanger and Malac 1980).

Symptoms and Signs

Often the first noticeable indication of SPB attack is foliage discoloration. Crowns of dying pines change color from green to yellow to red before turning brown and falling from the tree. The time it takes for these changes varies seasonally. Frequently, by the time crowns are red the beetles have already vacated the tree. The earliest signs of possible SPB-attack is the presence of brownish-orange boring dust and tiny white pitch pellets accumulating at the base of the tree, in bark crevices, in nearby spider webs, and on understory foliage. A more noticeable indication of SPB attack is the presence of multiple popcorn size lumps of pitch (i.e., pitch tubes) on the outer bark of pine stems. These pitch tubes may occur from near ground level up to 60-ft. (18-m) high, but may not develop at all on trees severely weakened before beetle attack. The most diagnostic sign of SPB activity is the presence of the winding S-shaped galleries that cross over each other and are packed with boring dust and frass. These can be found by exposing a portion of the inner bark beneath pitch tubes or by removing a section of bark. Another sign of possible SPB activity is the presence of clear shot-like holes (ca. 1 mm in dia.) on the exterior bark surfaces where SPB have emerged (Billings and Pase 1979, Thatcher and Conner 1985). SPB infestations typically kill groups of trees, which allows for prioritizing investigations of suspect mortality.

Life-Cycle

Beetles develop through four stages: egg, larva, pupa and adult. Except for a few days during the summer when adults emerge from brood trees and fly to attack new host trees, all life stages are spent beneath the bark.
In low elevation stands and in warm years, mountain pine beetles require one year to complete a generation. At high elevations, where summers are typically cooler, life cycles may vary from one to two years.
Female beetles initiate attacks. As they chew into the inner bark and phloem, pheromones are released, attracting male and female beetles to the same tree. The attacking beetles produce more pheromones, resulting in a mass attack that overcomes the tree’s defenses, and results in attacks on adjacent trees.
Natural predators of the mountain pine beetle include certain birds, particularly woodpeckers, and various insects.

Management

Management techniques include harvesting at the leading edges of what is known as “green attack”, as well as other techniques that can be used to manage infestations on a smaller scale, including:
  • Pheromone baiting – is luring beetles into trees ‘baited’ with a synthetic hormone that mimics the scent of a female beetle. Beetles can then be contained in a single area, where they
  • can more easily be destroyed.
  • Sanitation harvesting – is removing single infested trees to control the spread of beetle populations to other areas.
  • Snip and skid – is removing groups of infested trees scattered over a large area.
  • Controlled, or mosaic, burning – is burning an area where infested trees are concentrated, to reduce high beetle infestations in the area or to help reduce the fire hazard in an area.
  • Fall and burn – is cutting (felling) and burning beetle-infested trees to prevent the spread of beetle populations to other areas. This is usually done in winter, to reduce the risk of
  • starting forest fires.
  • Pesticides – Biopesticides such as chitosan have been tested for protection against the mountain pine beetle, and pesticides such as carbaryl, permethrin, and bifenthrin are used for
  • smaller area applications. The concept of natural plant defense holds hope for eliminating pine beetle infestation. Beneficial microbial solutions are being researched and developed that work with the plant to activate and enhance its resistance mechanisms against insects and disease.