Agricultural Research Service • U.S. Department of Agriculture
Contents

Paee

Leaf and flower diseases and control methods - 1

Fungus and bacterial diseases — -- 1

Anthracnose - — 1

Phyllostieta spot — 2

Tar spots - 2

Bacterial spot -— - - 4

Leaf blister - -- - 4

Shoot droop_ - - - - 4

Bulls-eye spot - - - — 5

Gray mold spot - 5

Leaf scab 6

Bigleaf brown spot- — 6

Septoria spot - — "?

Powdery mildews - - ''

Flower blight - '

Noninfectious disorders _ — ''

Leaf scorch "^

Leaf distortion and dwarfing ^

Premature reddening or yellowing _ 8

Gas poisoning 8

Abnormalities of unknown cause - 9

Spray materials and schedules - — 9

Cankers and other damage to woody parts - 10

Eutypella trunk canker ..„ - 10

Nectria canker 10

Bleeding canker_ 11

Basal canker „ - IS

Schizoxylon canker 14

Other cankers - — - 14

Trunk splitting, frost beaks, and bark freezing 14

Sapsucker damage 15

Root diseases— — - — 16

Root-knot nematode 16

Root rots____ _ 16

Root damage from adverse soil conditions 16

General infections _ .— 17

Slime flux and wetwood 17

Verticillium wilt 18

Red stain of boxelder 19

Sap streak_ __ 19

Silver leaf- — _ _ 19

Wood decay ___ _. 19

Common and scientific names of maples _ _. __ 22

Washington, D.C. Issued December 1961

For sale by the Superintendent of Documents. U.S. Government Printing Office

Washington 25. D.C. - Price 1.5 cents
By CURTIS MAY,

plant pathologist.

Crops Research

Division, Agricultural

Research Scrvicf

Diseases F^ ^

of Shade

and Ornamental

Maples

Pathogenic organisms attack

shade and ornamental maples and

cause diseases of the leaf and

flower, woody parts, and root.

Leaf scorch, a noninfectious disorder, often seriously damages

foliage of sugar, Norway, and

sometimes other species of maple.

Air pollutants may adversely affect maple and limit its usefulness

in some localities.

LEAF AND FLOWER DISEASES

AND CONTROL METHODS

Leaf blights and spots of maple

sometimes damage large trees and

frequentljr are serious on small or

recently transplanted trees or

trees growing under adverse conditions. Leaf diseases mar their

appearance and detract from their

landscape value.

FUNGUS AND BACTERIAL

DISEASES

Anthracnose

Anthracnose is caused by Gloeosporiuvi apocryptum Ell. & Ev.

This fungus invades and kills the

leaf tissue, producing small to

large circular to irregular spots

or necrotic areas, which turn light

brown, purplish, or black. If the

spots are numerous, they may

merge until the whole leaf is affected. Usually they appear from

late May until August. Affected

leaves of Norway maple have

purple to brown diseased tissue

along the veins (fig. 1, A). On

sugar maple large green- or redbrown anthracnose lesions occur

along or between the veins, and

often they extend to the leaf margin (fig. 1, B). On Japanese maple

the disease may aff'ect the entire

young leaf, which often becomes

blackened and shriveled. Trees

are not always seriously damaged

by anthracnose.

Spores of the anthracnose fungus are produced in acervuli on

the diseased leaves and are spread
AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

FIGURE 1.- -Leaves affected by anthracnose: A, Nonvay maple (/TíÍ); B, sugar

maple ( X % ).

by spattering rain and wind.

These spores are 5 to 12 by 21/2

to 5 microns and are oblong to

narrowly elliptic.

Anthracnose can be controlled

by spraying with a fungicide (see

p. 9). This measure will help

prevent disfiguration and loss of

leaves. It will benefit weak and

recently transplanted trees and

trees that are diseased year after

year. An application of fertilizer

will usually improve the vigor of

trees that are weakened by repeated severe attacks of anthracnose.

Phyllosticta Spot

Phyllosticta spot is caused by

the fungus Phyllosticta minima

(Berk. & Curt.) Ell. & Ev. This

disease is widespread and sometimes serious. On difl:erent maple

species the spots vary considerably. On sugar and Rocky Mountain maples the spots commonly

have a narrow purplish border.

The diseased tissue often falls

out, and holes are left in the leaf.

On Japanese maple, which may be

severely damaged by the disease,

the spots are straw to tan colored

with a definite margin. The central part of the spot may be somewhat transparent. Usually the

spots are small, irregularly circular, and reddish brown with narrow to broad purplish borders

(fig. 2, A).

The spots have minute black

fruiting bodies, or pycnidia, of the

causal fungus. Not all the spots

produce the fruiting bodies.

Spores are .5 to 6 by 8 to 9 microns.

A closely related fungus, Plujllosticta negundinis Sacc. & Speg.,

causes a similar leaf spot on boxelder. The fungus Septoria aceris

(Lib.) Berk. & Br. attacks leaves

of the bigleaf maple and also

causes leaf spot (fig. 2, B). Small

reddish-tan to brown spots develop with a narrow yellow

border. On other maple species

the margin is usually irregular

and indefinite.

Spraying with a fungicide

should reduce damage from phyllosticta spot (see p. 9).

Tar Spots

Black spots on the leaves are

the conspicuous symptom of tar

spots. The fungi Rhytisma acerinmn (Pers.) ex Fr. and R. punctatum (Pers.) ex Fr. cause the
DISEASES OF SHADE AND ORNAMENTAL MAPLES

or '^

',/

FIGURE 2.~A, Maple leaf affected by phyllosticta spot (X li;) ; B, bigleaf maple

leaf attacked by the fungus Septoyia aceris i^-, Vz).

disease. When first invaded the

leaves develop minute watersoaked spots. Soon small dark

dots appear on the upper leaf

surface between the veins. The

dots enlarge and soon coalesce,

and the entire spot becomes black

and thickened.

R. acerinum (fig. 3, A) is likely

to produce one or more relatively

large black spots, whereas R.

imnctatum (fig. 3, B) produces

numerous small ones that often

do not coalesce. R. acerinum, the

cause of common tar spot, attacks

many species of maple, but seldom

the Norway and sycamore maples.

It is rare on the Pacific coast. R.

pu.nctatum, the cause of blackspeckled tar spot, has been reported on many species, especially

silver, mountain, and striped

maples. It is abundant on bigleaf

maple on the Pacific coast. It is

not so frequently encountered in

i:

<

%.m,

^

FIGURES.—Maple leaves with tar spots caused by the fungi (A) Rhytisma acerinun

and (B) R. punctatum. (X Vz-)
AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

the Eastern United States as R.

acerin^tm.

First infections of tar spots in

the spring are from ascospores,

which are produced in the blackened areas on fallen overwintered

leaves. Rod-shaped conidia are

produced in the spots on leaves on

the tree. They are spread by

wind and rain in the summer.

For information on control

measures for tar spots, see page

9.

Bacterial Spot

Bacterial spot is caused by

Pseudomonas aceris (Ark) Starr

& Burkh. This bacterial disease

afï'ects bigleaf maple in California. It was found on nursery seedlings and on wild tree leaves

hanging close above water. The

disease seems to be relatively unimportant economically.

Japanese and vine maples and

boxelder are reported to be susceptible to bacterial spot. Affected

leaves develop pinpoint to onequarter inch water-soaked spots

with yellowish margins. Later

the spots become brown. Lesions

develop on the petioles.

One outbreak of the disease on

seedlings growing under humid

conditions was controlled by

aeration.

Leaf Blister

Several species of fungi of the

genus Tapkrina cause leaf blister.

These fungi are closely related to

those causing peach leaf curl and

leaf blister of oak.

The following species have been

reported on maple:

FIGURE 4.—Maple leaves affected by leaf

blister. ( Vi.)

Domed blisters—convex as seen

from the upper leaf surface—and

curling, twisting, and dying of the

leaf are characteristic symptoms

of leaf blister (fig. 4). This is

not a common disease.

Leaf blister can probably be

controlled by applying a fungicide

while the trees are dormant. The

spray must be used before the

bud scales separate and the buds

open.

Shoot Droop

Shoot droop, a disease of the

leaf and shoot of trident maple in

Japan, is reported to be caused by

the bacterium Pseudomonas acernect Ogawa. Irregular spots appear along the midrib. They enlarge and become gray or black.

Affected leaves wither, turn black,

and finally dry. The following

maples are said to be susceptible

Taphrina species Maple

bartholomaei Mi-^ (synonym: aceris (Dearn. & Barth.) Mix) biertooth

carveyi Jenkins -. ____ silver

darkeri Mix -- _____ vine

deai-nessii Jenkins red

letífera (Pk.) Sacc _ red and mountain

sacchan Jenkms sugar and black
DISEASES OF SHADE AND ORNAMENTAL MAPLES

FIGURE 5.—Norway maple leaf affected

by bulls-eye spot. (X 1-)

midal conidiophores, which are

repeatedly trichotomously or dichotomously branched. The spores

are hyaline, globose, 2 to 4 microns in diameter, and easily detached from the conidiophore.

The fungus produces sclerotia

sparingly in culture on Leonian's

medium and also forms eightsided crystals, as described by

Bowen ^ for the closely related C.

depraedans (Cke.) Hoehn. Sclerotia have not been found in nature.

Gray IMold Spot

Cristulariella depraedans (Cke.)

Hoehn. causes gray mold spot.

The spots are separate or confluent, irregular, and grayish without a definite margin or concentric circles (fig. 6). This fungus

to shoot droop: Acer shirasaioanu)n Koidz., amur, devil, hawthorn, Japanese, redvein, siebold,

silver, and boxelder.

Bulls-Eye Spot

Bulls-eye spot is caused by the

fungus Cristulariella pyramidalis

Waterman & Marshall. The disease is characterized by the development of numerous targetlike

spots on the foliage of boxelder

and silver, sugar, Norway, and

sycamore maples (fig. 5). The

spots are yellowish gray with

light-brown concentric rings on

the upper surface of the leaf.

Spots vary in size and may coalesce. On the lower surface of the

leaf the spots are brown and

without the concentric rings. The

spots commonly are larger on

leaves of the sugar maple than on

those of other species. The disease has not been adequately studied to determine its damage potential. It occurs sporadically and

may appear in midsummer.

Spores are produced on pyraFlGURE 6.—Gi-ay mold spot on sugar

maple leaf. (X 1.)

" BOWEN, P. R. A MAPLE LEAF DISEASE

CAUSED BY CRISTULARIELLA DEPRAEDANS.

Conn. Agr. Expt. Sta. Bui. 316: 625-

647, illus. 1930.
AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

produces sclerotia in culture, but

they have not been found in nature. Very little is known about

this disease. It appears late in

the summer and apparently is not

serious, but it can cause some defoliation.

Leaf Scab

The fungus Cercospora negundinis Ell. & Ev. causes leaf scab.

Small brownish-red spots with

indefinite margins appear on

leaves of boxelder (flg. 7). Under

a hand lens the spots appear

scabby or cracked. They have numerous whitish areas with minute

black fruiting bodies on the older

parts. Spores of the fungus have

FIGURE 7.- -Boxelder leaflet

scab. (X 1.)

with leaf

FIGURE 8.—Bigleaf maple leaf affected

by bigleaf brown spot. (X V¿-)

indistinct septa, are long and narrow, and vary from 5 to 6 by 50

to 110 microns. The disease has

been reported from Nebraska and

Wisconsin. It has not caused serious damage.

Bigleaf Brown Spot

On bigleaf maple the fungus lUosporium mactdicola Sacc.

causes bigleaf brown spot (fig. 8).

A large brown spot up to 3 inches

in diameter develops. It usually

is rather concentrically zoned and

has an indefinite margin. The diseased area frequently spans main

veins. Older parts of the spot

break out and leave ragged holes.

The spots are dark on the upper
DISEASES OF SHADE AND ORNAMENTAL MAPLES

leaf surface and lighter on the

underside. The fungus Cercosporella aceris Dearn. & Barth, causes

a similar spot on bigleaf maple.

Further study may prove that the

two fungi are identical. No study

has been made of control measures for bigleaf brown spot.

Septoria Spot

The fungus Septoria aceris

(Lib.) Berk. & Br. causes septoria spot on leaves of several

maple species. The spots are commonly small and reddish tan to

brown. On bigleaf maple the

spots have a narrow yellow margin, but on other species the border is usually indefinite and irregular. The fungus also attacks immature fruits and causes

browning. The extent of damage

caused by this fungus cannot be

estimated.

Powdery Mildews

The mildews commonly found

on maple are Uncinida circinata

Cke. & Pk., Microsphaera alni DC.

ex Wint., and Phyllactinia corylea

Pers. ex Karst. These fungi

have distinguishing characteristics, which enable a specialist to

identify them.

Powdery mildews often produce

a whitish superficial growth on

maple leaves, particularly near

the end of the growing season.

The mycelia of the fungi cover the

leaf, but they feed on the interior

through absorbing hyphae, which

penetrate the leaf cells. Black

roughly spherical fruiting bodies

of the mildews commonly are

abundant on the surface of infected leaves in the autumn. The

powdery mildews overwinter as

ascospores in the black fruiting

bodies on fallen leaves. They

usually do not seriously damage

maple.

Powdery mildews generally may

be controlled by spraying with a

fungicide after they develop on

the leaves, but no research has

been reported on their control on

maple.

Flower Blight

The fungus Ciboria acerina

Whet. & Buchew. causes flower

blight, a disease of the inflorescences of red and silver maples.

It has been reported from New

York. The flowers are killed and

seed formation is prevented, but

the disease is of minor economic

importance.

NONINFECTIOUS DISORDERS

Leaf Scorch

Leaf scorch is a physiological

disease affecting particularly sugar and Norway maples. Margins

of the leaves or the tissues between the veins of affected trees

turn brown in the summer, particularly during or after hot, dry

periods. Maples in poor condition

are predisposed to develop this

disease. Maintenance of vigor by

controlling pests, applying fertilizers including minor elements

when needed, and watering during hot, dry weather will prevent

or alleviate leaf scorch on many

trees.

Leaf Distortion and Dwarfing

Maples are sensitive to many

herbicides. 2,4-D and 2,4,5-T

cause twisting, curling, cupping,

browning of margins, and dwarfing of developing leaves (fig. 9).

Abnormally narrow lobes are

common and give a shoestring effect. Phenyl urea herbicides

cause somewhat similar symptoms. Leaves affected by sodium

arsenite usually turn black and

fall. Since the fallen leaves contain arsenic, they should be gathered and destroyed.

In soils that drain quickly,

flooding may help to reduce damage from 2,4-D and 2,4,5-T. Un-
AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

FIGURE y.—Effect of 2,4-D on red maple

leaves. ( / V2.)

fortunately the danger from herbicides generally is not recognized

until after damage appears. Trees

that receive weak dosages may

eventually recover from the effects of 2,4-D or 2,4,5-T, but

damage may persist for 2 years.

Incorporation of activated charcoal, sludge, or other organic materials into soil on which the

phenyl urea herbicides have been

used may reduce their damage to

trees. However, research is needed

before such treatments can be

recommended.

Poisons may be absorbed

through the roots, leaves, or

buds. Toxic vapors are formed

by some herbicides. The vapors

can damage trees at considerable

distances from where the herbicides are applied.

Premature Reddening or

Yellowing

Young, recently transplanted

trees that fail to grow and have

small leaves that turn red or yellow prematurely may have defective root sy.stems. Poor internal

soil drainage can cause oxygen

deficiency. Low oxygen in the

soil prevents normal root development (see p. 16).

Gas Poisoning

If leaves die suddenly, one

should consider the possibility of

gas leaking into the soil from

underground pipes. Leaves may

wilt and turn brown suddenly or

affected trees may decline slowly

with top dieback as the most

prominent symptom. The bark

sometimes cracks. Roots may become bluish black.

Some types of gas contain toxic

chemicals and others can kill or

injure trees by displacing oxygen

from the soil in which the roots

are growing.

Usually oxygen-deficient soil

has a sour, disagreeable odor.

Dig a hole a foot or more deep,

remove some soil, and smell it, or

smell the air in the hole after a

few minutes. The sour, foul odor

is readily detectable if oxygen deficiency is serious.

Gas also may contain substances that have a characteristic

odor, which can be detected by

smelling soil removed from the

hole. Gas companies usually will

test for leaks if notified that one

is suspected.

To treat trees affected by gas

poisoning, first stop the leaks.

Sometimes aerating the soil will

save trees that would die if not

treated. Thorough aeration may

be accomplished by injecting

compressed air or by flooding in

soils that drain quickly. Some-
DISEASES OF SHADE AND ORNAMENTAL MAPLES

times replacement of soil may be

practical.

ABNORMALITIES OF

UNKNOWN CAUSE

Tatter-leaf, an irregular, shothole condition of maple leaves

(fig. 10, A), has been observed in

Logan, Utah, Orange, N.J., New

Britain, Conn., and Wisconsin.

The cause has not been determined. However, frost damage to

the leaf before it unfolds from the

bud is suspected.

A silvery scablike condition

has been observed on leaves of

the Crimson King variety of Northe northern Sierras, the drainages of the Sacramento and Klamath Rivers, and throughout the

coastal mountains of northern

California.

The cause of puckering of some

Norway maple leaves (fig. 10, B)

has not been determined. This

condition may be due to a genetic

factor or possibly a virus.

SPRAY MATERIALS AND

SCHEDULES

Bordeaux mixture, dichlone,

Puratized Agricultural Spray

(phenyl mercuri triethanol ammonium lactate), and zineb have

FIGURE 10.- -A, Tatter-leaf of maple (X Vz) ; B, puckering of Norway maple leaf

(X %).

way maple. Neither the cause nor

the significance of the abnormality is known.

The causes of dieback of maple

in Wisconsin and of a recently

reported dying of sugar maple in

New York are not known.

Also, the cause of a viruslike

disease of bigleaf maple in the

West has not been determined.

This disease has been found in

eff'ectively controlled anthracnose,

phyllosticta spot, and tar spots.-

Two or three applications with a

2- to 3-week interval between

them often give satisfactory results. The first application for

anthracnose should be made when

the new leaves are about half de-

- Mention of a trade product does not

imply its endorsement by the U.S. Department of Agriculture over similar

products not named.
10 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

veloped and the second about 2

week.s later. If rains are frequent

or violent during the early part

of the growing season, a third

application may be needed and

the interval between applications

shortened. In wet seasons an extra

application may be needed in midsummer to control anthracnose

and phyllosticta spot.

Spraying maples with an organic mercury or copper fungicide

is recommended to prevent tar

spots. The first spray should be

applied when the leaf buds are

opening. In wet seasons one

to four additional applications

should be made at 10- to 21-day

intervals, depending on the frequency and amount of rain and

how much of the fungicide is

washed from the leaves.

Bordeaux mixture sometimes

causes a marginal drying of leaves

of sugar and Norway maples.

Black flecking of leaves of Norway maple after spraying with

Bordeaux mixture has been reported, but extensive damage to

maple from this spray has not

been common. Puratized Agricultural Spray sometimes causes a

yellow spotting of leaves of Norway and silver maples and russeting of sugar maple.

No research information is

available on the effectiveness of

spraying to control leaf diseases

other than anthracnose, phyllosticta spot, and tar spots. Research

is needed to determine which

spi'ay materials and schedules

will control most effectively the

maple leaf diseases.

CANKERS AND OTHER DAMAGE TO WOODY PARTS

EUTYPELLA TRUNK

CANKER

The fungus Eutijpella parasítica Davidson & Lorenz causes

eutypella trunk cankers of sugar

and red maples and boxelder.

Trunks of young trees may break

at the canker. On older trees decay may start at the cankers and

gradually weaken the trunk.

Characteristics of the canker

are swelling and distortion of the

trunk, firmly attached bark, heavy

white to buif mycelial fans under

the bark at the margin of the

canker, slightly raised concentric

rings or ridges of callous tissue,

and long-necked, black beaks of

the fungus fruiting bodies in

older parts of the canker (fig. 11).

The fungus penetrates the sapwood, which becomes brown and

brittle. Cankers usually are 2 to

8 feet aboveground, but they may

occur at 30 feet.

In culture on malt agar the

fungus may produce spores in 4

to 6 weeks on white mycelium. In

old cultures mycelium may develop light-bufl: to cream-colored

patches. The long, slender, curved

conidia are pointed at the ends

and 26 to .34 microns by 1 micron.

Ascospores are slightly curved,

irregularly two or more seriate,

dark brown, slightly attenuated

at the end, and 8 to 11 by 2 to

2.3 microns.

No control measures are known

for eutypella trunk canker on

shade trees.

NECTRIA CANKER

Nectria cankers develop on

trunks and other woody parts at

the top of both young and old

trees. They have been reported

on mountain, red, silver, sugar,

Norway, sycamore, bigleaf, Japanese, and striped maples and on

boxelder. The cankers resemble

superficially those caused by Eutypella. However, the bark falls

from older parts of nectria cankers and dry wood is exposed,
DISEASES OP SHADE AND ORNAMENTAL MAPLES 11

FIGURE 11.—Maple disfigured by eutypella trunk canker. (X Ys.)

whereas the bark usually clings

to the central part of eutypella

cankers.

On larger woody parts nectria

cankers are characterized by

roughly concentric ridges of callous tissue (fig. 12, A). Rough

excrescences or overgrowths commonly form on affected limbs and

branches. The fungus invades

the bark through injuries. Dead

branch stubs also afford a point

of entry for the Nectria. The

fungus grows in the bark and kills

it while the tree is dormant. When

the tree resumes active growth, a

ridge of callus forms, which is

killed when the tree again becomes dormant in the autumn.

The alternate killing and formation of callus account for the socalled target or catface configuration of the canker.

Infection by Nectria often takes

place through injuries in tender

bark of twigs. During the growing season the fungus may invade

cambium and wood through injuries in the bark. Wood invaded

by Nectria is streaked with olivaceous green, but the fungus does

not penetrate deeply (fig. 12, B).

The cankers are entrance points

for wood-decaying fungi.

The cankers are commonly

caused by the fungus Nectria galligena Bres., but other closely related species of Nectria may also

be involved. N. galligena produces two-celled elliptic ascospores. They range from 12 to 20

by 4 to 6 microns.

The microconidia are formed in

the summer and early autumn in

cream-colored pustules of recently

killed or dying bark. Later brightto dark-red globose perethecia

may form in these pustules (fig.

12, C). Ascospores may be forcibly expelled from the perethecia.

Affected smaller woody parts

may be pruned, but usually trunk

cankers are incurable. Trees in

low vigor often bear numerous

nectria cankers, but the relationship between the vigor of maples

and the damage by nectria cankers has not been adequately

studied.

BLEEDING CANKER

The fungus Phytophthora cactoriim (Leb. & Cohn) Schroet.

causes bleeding canker of maple.

Circular to elongated cankers are

found in the trunk or branches of

infected trees. On young smoothbarked trees the cankers cause

sunken or depressed areas in the

bark. On older thick-barked trees

the diseased bark is usually
12 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

FIGURE 12.—A, Nectria canker (X Vz) ; B, wood invaded by Nectria (X %); C,

perethecia of Nectria galligena in recently killed or dying bark (X 4).

not sunken. Moist areas in the

bark commonly secrete a bloodred or black fluid (fig. 13). Beneath the surface of the canker

the bark tissue is reddish brown,

surrounded by an olive-green

border at the transition between

healthy and diseased tissue. A

dark discoloration occurs in the

wood beneath the canker and may

extend several feet upward from

the canker and downward into

the roots.

Leaves of trees affected by

bleeding canker are often small

and foliage may appear to be
DISEASES OF SHADE AND ORNAMENTAL MAPLES 13

FIGURE 13.—Bleeding- canker of maple.

(X Vi.)

sparse. Dieback of tops may occur, and the trees may produce

excessively heavy crops of seed.

Bleeding canker has been reported on black, Norway, red, sugar, and sycamore maples. Trees

are especially susceptible to bleeding canker if they have been damaged or weakened by earth cuts

or fills, frosts, wind, or soil compaction. These cankers commonly

develop around bark injuries produced by frost, storms, or mechanical impact.

Control measures for bleeding

canker are not always successful.

Excising diseased bark and correcting adverse conditions under

which the affected tree may be

growing are recommended. In

excising the diseased bark remove

all discolored tissue plus a narrow

margin of healthy bark around

the edge of the canker. Then shape

the resulting wound so that it is

oval or elliptic and the margin is

smooth and regular, with the bark

adhering tightly to the wood. Disinfect wounds by swabbing or

brushing several times with denatured alcohol and then paint

with shellac. After the shellac has

dried, coat the wound once or

twice with an asphalt tree-wound

dressing. However, excision or

treatment of the cankered area

often fails to control the disease

unless adverse growing conditions

are corrected and the tree is

brought into good vigor. Young

diseased trees have recovered

without treatment of the cankei-s

when the trees were exposed to

full sunlight.

BASAL CANKER

A canker developing at the base

of the trunk and caused by the

fungus Phytophthora cambivora

(Petri) Buis, was reported on

Norway maple in New Jersey. In

the United States the fungus has

not been found elsewhere or on

any other host. It is widespread

in Europe and is the cause of the

serious ink disease of chestnut.

Basal canker is characterized

by reddish-brown discoloration

of the bark, cambium, and outer

sapwood near and below the soil

line. No pink or red exúdate is

present. Crowns of affected trees

are thin. Diseased trees may die

within a year or two.

No control measures are known

for this canker disease.
14 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

SCHIZOXYLON CANKER

Schizoxylon canker is caused

by the fungus Schizoxylon microsporum Davidson & Lorenz. This

disease occurs in the Lake States

on suppressed red and sugar

maples less than 3 inches in diameter. It is of little economic importance. The catface cankers resemble those caused by Nectria.

The cankers are shallow and

sunken. The wood is often exposed in older areas and often

partly decayed. White mycelial

fans form beneath the bark at

the margin of the canker.

The fungus grows on 2Vä-percent malt agar, in which it produces a white mycelial mat with

occasional light-brown patches in

older cultures. This mat is tufted

and wavy with numerous globose

bunches of mycelium, which appear to be pycnidial primordia.

The margin of the mat is thin and

irregular.

The light-gray globose pycnidia

are embedded in shallow, cuplike

depressions. The spores are rod

shaped and 2 to 5 microns by 1

micron. Ascospores are filiform,

multiseptate, 1 micron in diameter, and up to 170 microns long.

They finally break into slightly

curved segments or short rods

from 2 to 3 or 4 to 8 microns

long.

OTHER CANKERS

Fungi of the genera Hypoxylon

and Diatrype cause cankers, particularly on winter-injured trees.

The cankers are frequently elongate and have callous beaks, or

ridges. They probably are produced annually. They are of relatively minor economic importance

on maple.

Weakened boxelder and other

maples are attacked by weakly

pathogenic canker fungi belonging to the genera Sphaeropsis,

Leptothyrium, and Phacidium.

Pruning affected parts, fertilizing, and maintaining good cultural conditions will often control

these parasitic fungi.

TRUNK SPLITTING, FROST

BEAKS, AND BARK

FREEZING

Deep winter cold may freeze

fluids in the wood. Trunks may

crack vertically, sometimes with a

loud report. The cracks serve as

entrance ports for fungi and bacteria. Callous tissue forms on

both sides of the crack and may

develop into frost beaks, or ridges,

commonly seen on maple (fig. 14).

In some areas frost cracks are

common on Norway maple.

Treatment consists of cleaning

and smoothing the bark along the

frost crack and covering with antiseptic asphalt paint. Split trunks

may be drawn together with bolts.

Bore one or more holes through

the trunk. Use washers on both

ends of each bolt. Countersink

the washers and bolt head and

tap into the wood. Cover the bolt

ends and surrounding exposed

wood with an antiseptic asphalt

paint.

Bark may be killed by freezing,

often in small patches on upper

or exposed surfaces of small limbs

or branches. Damage becomes

evident in midsummer, when the

killed or weakened bark dries.

Leaves on parts distal to the injured bark may suddenly dry.

Weakly pathogenic or saprophytic

fungi soon appear on the damaged

parts, and the presence of their

fruiting bodies confuses the diagnosis of the cause.

Exposure to full sunlight by

pruning previously shaded limbs

predisposes to freezing damage
DISEASES OF SHADE AND ORNAMENTAL MAPLES 15

FIGURE 14.—Frost beak on silver maple.

(X 1/15.)

and sunscald of thin bark. To

minimize this damage, avoid extensive pruning of the crowns of

heavily shaded trees, such as

those in woodlands. Gradual thinning of crowns reduces danger of

damage from both freezing and

sunscald.

SAPSUCKER DAMAGE

Sapsuckers sometimes seriously

injure maple. The birds peck

roughly horizontal rows of holes

in the bark (fig. 15). Transfer of

food materials downward in the

bark is reduced. Injured bark

dries and dies, and the injuries

serve as entrance ports for fungi.

FIGURE 15.—^Section of maple branch

severely damaged by sapsuckers.

(X 1/2.)
16 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

ROOT DISEASES

ROOT-KNOT NEMATODE

Root knot, caused by Meloidogyne sp.," was reported on bigleaf

maple in Oregon. Roots swell, become stubby, and produce galls

when attacked by this nematode.

No cure is known, but soil in nursery seedbeds may be disinfected

before planting if previous experience indicates that root knot

is likely to be a serious problem. Under experimental conditions Meloidogyne incognita

Chitwood produced galls on roots

of Japanese maple."*

ROOT ROTS

The fungus Phymatotrichum

omyiivorum (Shear) Dug. causes

a serious and often lethal root

rot of many species of plants. It

has been reported on silver maple

in Texas and on boxelder in Texas

and California. No cure is known.

Avoid planting maples on sites infested with this fungus.

Armillaria mellea Vahl ex Fr.

may cause a root rot. It is sometimes called shoestring root rot

because of the long, commonly

flattened strands of mycelium that

the casual fungus produces beneath the bark of affected trees.

The fungus is also known as the

honey mushroom from the color

of its fruiting bodies. A. mellea

may kill weakened trees. The

fruiting bodies of the fungus are

usually produced in clusters at

the base of dead or dying trees or

on the ground from infected roots.

The stalk of the fungus is 3 to 10

inches tall with a broad, honeyyellow to brown cap with scales.

" Reported as Heterodera marioni

(Cornu, 1929) Goodey, 1932. This species has been divided and placed in

Meloidogyne,

' Personal communication from R.

Schindler, Crops Research Division.

Gills of the lower surface are

whitish and attached to the stalk.

The fungus Ganoderma lucidum (Leyss. ex Fr.) Karst, causes

a root rot of maple and decay of

the bole. The corky fruiting

bodies develop annually at the

base of affected trees or later on

stumps. The upper surface of

new conks is red and shining as

if varnished. The fungus can

enter through wounds. Avoid /

wounding roots and the base of

the trunk.

No practical method of control- ,

ling the root rots caused by A.

mellea or G. lucidimi is known.

However, they are more likely to

aifect trees in poor vigor. The

following practices should help

prevent these root rots : Applying i

fertilizer, correcting unfavorable

soil conditions, watering during

droughts, and treating wounds on

exposed roots at the base of the

trunk.

ROOT DAMAGE FROM

ADVERSE SOIL CONDITIONS

Young, recently transplanted

trees that fail to grow and have

small leaves that turn red or yellow prematurely may have defective root systems.

Poorly drained soil is a common cause of poor root development and defective root systems.

Roots need oxygen. In clay soil

retention of too much water excludes air. In such soil water may

collect in a planting hole filled

with porous soil. Even though the

site may be on a slope, it is advisable to check drainage in the

hole. Dig a hole 10 to 15 inches

deep. Fill it with water in the

spring or fall. The water should

drain from the hole overnight. If

it does not, provide drainage or

slightly elevate the planting site.
DISEASES OF SHADE AND ORNAMENTAL MAPLES 17

In sandy or gravelly soil or in

areas with low rainfall maples

may need to be watered during

droughts. Wilting of leaves and

drying and browning of their

margins are symptoms of water

deficiency. The sugar maple is

particularly sensitive to drought.

Maples that grow slowly and

have light-green or small leaves

or leaves with various abnormally

colored spots may need fertilizer.

A standard garden fertilizer is

satisfactory. A minimum dosage

is 2 pounds per diameter inch of

trunk measured at breast height.

GENERAL INFECTIONS

SLIME FLUX AND WETWOOD

The characteristic symptom of

slime flux is a persistent or intermittent flow or oozing of sap from

cracks or other injuries in the

bark and wood of maple. This

infection is usually associated

with a water-soaked and more or

less discolored condition of the

wood known as wetwood. Often

the fluid exuding from wetwood

is so copious that it will flow down

the trunk to the ground in a glistening stream, particularly in the

spring. Often less fluid may be

exuded. It may gradually seep

down the trunk or limbs and

evaporate before reaching the

ground. However, moist streaks

or whitish deposits remain on the

bark. The exuded fluid frequently

thickens until it becomes viscous

and sticky. If the flux dries, a

light-gray to brown deposit may

be left in a more or less vertical

streak on the bark (fig. 16).

The clear sap that runs for a

short time from fresh wounds is

similar to the sap obtained when

maples are tapped for sirup and

should not be confused with slime

flux. However, if injuries do not

heal, slime flux may develop later

in them.

The cause of slime flux of elm

is a bacterium, Erwinia nimipressuralis Carter. Although the cause

of slime flux of maple has not been

investigated thoroughly, it is

probably caused by a bacterium.

FIGURE 16.- -Slime flux on maple trunk.

(X 1/4.)

Invasion of the wood by bacteria may be limited to relatively

small areas or may be extensive

in the trunk and ¡branches. The

infected wood becomes more or

less discolored and water-soaked,

and considerable gas pressure
18 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

may develop in it. The pressure

is instrumental in forcing fluids

out of the affected tissues.

Injurious compounds are produced in affected trees. They

spread to the smaller branches

and may discolor and wilt the

leaves and cause dieback of twigs

and small branches. Bark over

which the toxic sap flows may be

killed, and wound healing often is

retarded or prevented. Badly affected trees may eventually lose

most of their smaller branches

and become stag headed. Healthy

sapwood of Norway maple is

slightly acid ; diseased sapwood is

alkaline.

Not all trees with wetwood release toxic sap through injuries,

pruning wounds, or other channels from the interior to the outside of the trunk. IMany such

trees grow poorly and show symptoms of decline, such as small

leaves, dying leaf tissue, and dieback of shoot tips.

Control or alleviation of slime

flux and wetwood can often be

obtained by inserting drain pipes

into the infected wood. This procedure does not cure the disease,

but much of the toxic fluid is removed from the wood and often

the tree benefits.

Drain pipes should be inserted

into the trunk and branches near

where the flux issues. Sometimes

a single pipe installed near the

base of the trunk is sufficient.

Galvanized pipes with a driving fit should be inserted into each

hole to a depth of 2 to 4 inches.

A tight fit is necessary to prevent

the pipes from becoming loose

and falling out. Sometimes it may

be desirable to run the pipe down

the trunk to the ground or to a

surface drain. Other times the

pipe may extend from several

inches to a foot or more out from

the trunk. The pipe always should

be long enough to conduct the

toxic sap away from the trunk

and the base of the tree. The sap

will sometimes kill grass when it

drops on it. Pipes one-half to 1

inch in diameter may be used.

After the gas pressure is reduced and the flux has ceased except for drainage through the

pipe, the wounds from which the

flux issued can be cleaned and

painted with a wound dressing.

Sometimes the wood around the

flux point remains so wet that

paint will not adhere to it.

As a supplementary treatment

apply fertilizer to help keep affected trees vigorous.

VERTICILLIUM WILT

Verticillium wilt affects Norway, sugar, red, hedge, silver,

Japanese, bigleaf, and sycamore

maples and boxelder. Characteristic symptoms of this fungus disease are dying of one or more

limbs and progressive dying of

the crown. Sometimes trees wilt

suddenly, but more often the

disease develops slowly. Leaves

wilt and dry, sometimes remaining on the twigs and sometimes

dropping. Wilting and dying are

more prevalent in late than in

early summer but may occur at

any time. Affected trees are predisposed to winter freezing and

slime flux is common on them.

Maples affected by this wilt often

have sparse foliage throughout

the crown.

Diseased ti'ees develop a greenish discoloration in the infected

sapwood. The green streaks may

be found in leaf petioles, twigs,

and larger woody parts, especially

in the lower trunk. Maples also

develop greenish stains in wood

around wounds in the absence of

this fungus disease. Such a lo-
DISEASES OF SHADE AND ORNAMENTAL MAPLES 19

i. calized stain development is conÎ fusing in the diagnosis of verti- Î cillium wilt.

1 Trees with a trunk diameter of

s 1 to 2 inches may be killed in a

Id year by the disease. Larger trees

may live many years after symp-

, toms appear, but they may decline

i progressively or remain unattraci tive.

t Maples can be inoculated by in-

¡_ serting the causal fungus Vertir cillium albo-atrum Reinke &

Í. Berth, into holes bored into the

; wood and into wounds. The fungus commonly invades through

the roots.

,; The recommended treatments

for maples affected by verticillium

wilt include pruning the dying or

dead parts, pollarding severely

affected trees, improving soil fertility, using fertilizers containing

ammonium sulfate as the nitrogen

source, and watering during

drought periods.

Pruning tools should be sterilized with wood alcohol or other

disinfectant after use on such

trees. These treatments are not

always effective, but they are the

best known. No method is known

of treating trees internally for

this internal disease. Some affected trees recover without treatment.

RED STAIN OF BOXELDER

Red stain of wood of living boxelders is caused by the fungus

Fusarium reticulatum Mont. var.

negundinis (Sherb.) Wr., which

grows in heartwood and to a less

extent in sapwood of all woody

parts. The light- to dark-red

stain is commonly present in boxelders, but very little is known

about its relationship to tree

growth. The fungus probably is

a weak pai-asite.

SAP STREAK

Sap streak is caused by the fungus Endoconidiophora virescens

Davidson. This disease of sugar

maple occurs in a national forest

in North Carolina. The fungus

also causes a sap stain of hardwood lumber throughout the East.

Leaves of affected trees are

smaller than normal and often

slightly chlorotic. The foliage appears to be sparse because of the

small leaves. Dieback of the

crown progresses until some trees

die after 3 or more years. Occasionally affected trees in full

foliage die suddenly, but the dead

leaves usually do not fall. Sapwood of affected trees appears

water-soaked and has green

streaks at the margins of the

water-soaked areas. The watersoaked sapwood has a pH of about

8.5, whereas normal maple sapwood has a pH of about 5.5.

SILVER LEAF

The fungus Stereum purpureum Pers. ex Fr. has been reported as the cause of silver leaf

of maple in South Dakota. The

fungus invades woody parts. Diseased trees have small leaves and

are stunted. Very little is known

about this disease.

WOOD DECAY

All species of maple are subject

to damage by wood-decaying

fungi. Some of these fungi decay sapwood, some heartwood,

and some both. Those causing

sapwood decay attack the smaller

limbs and branches as well as the

trunk. Fungi causing decay of

heartwood invade the older and

larger limbs and the trunk, eventually weakening them so seriously that they may break in
20 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

FIGURE 17.—Wuod-decaying fungi on maples: A, Sporophores of Fames applanatiis

I Va) ] B. soft, creamy-white svorophore of Stecchei-inuiyi septentrionale (Xyio).

wind, snow, or ice storms. In general, heartwood decay is more

serious than sapwood decay.

Some of the fungi causing decay of maple are as follows :

Fungus Decayó

Armilîaria 7nellea (Vahl ex Fr.)

Kumm S-H-W

Collybia velutipes (W. Curt.

ex Fr.) Kumm . ... S-W

Corticinm vellereum Ell. & Crag . W

Daedalea miicotor (Bull.) ex Fr H-W

Fomes applanatiis (Pers. ex

S. F. Gray) Gill H-W

Fomes connatus (Weinm. ex Fr.)

Gill - ..H-W

Fomes everhartii (Ell. & Gall.)

Sehr. & Spauld.. H-W

Fomes fomentarius (L. ex Fr.)

Kickx H-W

Fomes fraxineus (Bull, ex Fr.)

Cke - H-W

Fomes igniarins (L. ex Fr.)

Kickx ___H-W

Ganodermu applanatum (Pers. ex

S. F. Gray) Pat..... H-W

Ganoderma lucidum (Leyss. ex

Fr.) Karst ...... ...S-W

Gymnopilus spectahilis (Fr.) Sing H

Fungus Decay'

Hericittm erinaceus (Bull, ex Fr.)

Pers H-W

Hericium laciniatnm Leers ex

Banker .. -W

Peniophora sp B

Pholiota adiposa (Fr.) Kumm H-B

Pleurotiis ostreatus (jacq. ex

Fr.) Kumm ._. S-W

Plenrotns nbnarius (Bull, ex

Fr.) Kumm S-H-W

Polyporu.s adustus (Willd.) ex Fr. S-W

Polyporas glomeratiis Pk S-W

Polyponis hirsutns (Wulf.) ex

Fr S-H-W

Polyporus pargamenus Fr H-W

Polyporus pubescens (Schum.)

ex Fr S-W

Polypoi'HS resinosits (Schrad.)

ex Fr .....S-H-W

Polyporus suiphureits (Bull.)

ex Fr _ H-B

Polyporus tulipiferus (Schw.)

Overh ....... S-W

Polyponis versicolor (L.) ex Fr S-W

Schizophyllum coniviune Fr S-W

Steccherinum septentrionale

(Fr.) Banker H-W

Stereunimurraii (Berk. & Curt.)

Burt W

Ustiilina vulgaris Tul W

Valsa leucostomoides Pk S

sapwood, H — heartwood, W = white or light colored, B ^ brown.
DISEASES OF SHADE AND ORNAMENTAL MAPLES 21

Identification of fruiting bodies

of the wood-decaying- fungi requires specialized knowledge. The

sporophores, conks, or other

spore-producing structures may

be sent to your State agricultural

experiment station or to the U.S.

Department of Agriculture for

identification.

The spore-producing structures

may be hard and woody (fig. 17,

A), corky, leathery, or fleshy like

a mushroom (fig. 17, B). Some

persist for years, some are annuals, and some last only a few

days or weeks.

Recognition of the fruiting

bodies of some fungi is useful in

estimating the extent of probable

decay in a diseased tree. The

fruiting bodies of Fomes connatus

indicate limited decay of not more

than 3 to 4 feet, and often less,

above and below them. Those of

Steccherinum, septentrionale suggest extensive decay from 6 feet

below to 13 feet above them.

Conks of Fomes igniarius indicate that decay may extend 5 feet

below and 9 feet above them.

Fruiting bodies of Ustulina vulgaris indicate that decay may extend about 9 feet above them.

This fungus enters through the

roots or at least at the base of

the tree. On the other hand, fruiting bodies of Pleurotus ostreatus

suggest that decay may extend

only a short distance from them.

Older trees are more likely to

be attacked by wood-decaying

fungi than young trees. One investigator in Canada reported "'

that decay occurred in 67 percent

of sugar maples 81 to 120 years

old and in 85 percent of trees 121

" NORDIN, V. J. STUDIES IN FOREST

PATHOLOGY. XIII. DECAY IN SUGAR MAPLE

IN THE OTTAWA-HURON AND ALGOMA EXTENSION FOREST REGION OP ONTARIO.

Canad. Jour. Bot. 32: 221-2.58, illus.

1954.

FIGURE 18.—Decay starting at a pruning wound on sugar maple. (X %.)

to 160 years old. Increasing diameter of the trunk is associated

with increased decay. In the

Canadian study sugar maples 10

inches in diameter at breast

height had one or more decayed

areas and 80 percent of the trees

were infected, whereas those

more than 10 inches in diameter

had decayed wood and 90 percent

of the trees were infected.

Wounds that break through the

protective bark and expose wood

are points of entry for fungi

causing sapwood and heartwood

decay. Frost cracks, pruning

scars, lightning scars, sapsucker

punctures, dead stubs of branches,
22 AGR. HANDBOOK 211, U.S. DEPT. OF AGRICULTURE

cankers, fire scars, broken tops,

and the parent stump of sprout

reproduction serve as invasion

routes for wood-decaying fungi

(fig. 18).

One investigator in Canada

stated " that in sugar maple, frost

cracks were the access points for

about .35 percent of the decay organisms, and branches and stubs

for 3.3 percent. Armillaria mellea,

Ustulina indgaris, and Pholiota

usually enter through the roots.

In the Canadian study Polyporus glomeratiis, Corticiiim vellereum, Armillaria mellea, and

Fom.es connatus accounted for

slightly over 65 percent of the infections and 62 percent of the

volume of decay of sugar maple.

Ustulina vuUiaris, although present in only 3.8 percent of the infections, caused 13.1 percent of

the volume of decay. P. glomeratiis was present in 36 percent of

the infections. It should be noted

that sugar maple is reaching its

northern limits in Ontario.

Valsa leucostomoides is reported ' to be the principal cause

of decay and discoloration associated with tapping of sugar

maple. The fungus fruits during

July and August in Vermont. The

discolored zone the fungus produces in the wood is light yellowish green in the center and deep

olive or greenish black at the

margin.

The cause of a black stain in

the heartwood is not known.

Decayed wood can sometimes be

gouged out of limbs and large

branches, but if it is extensive,

removal of the member may be

necessary. Decayed wood can also

be removed from tree trunks. The

resulting cavity may be filled with

concrete or left open. Cavity fillings are usually unsatisfactory in

silver and red maples and boxelder.

COMMON AND SCIENTIFIC NAMES OF MAPLES

Acer ginnala Maxim.

- — _ macrophyllum Pursh

- - grandicJp^^frifiim Nutt.

nigrum Michx. f.

— - _ negundo L.

diabo^icJim Blume ex K. Koch

_. crataegifo^hfm Sieb. & Zuce.

camnesfre L.

palmatuw Thunb.

spicatum Lam.

plafanoides L.

- )ïib)nm L.

rufinerve Sieb. & Zuce.

- - - - glabnim Torr.

sieboldianitm Miq.

__ saccharinimi L.

pensylvanicum L.

saccharum Marsh.

- pseudo-platauus L.

-- - hnergerianinn Miq.

-— _-. circinatnm Pursh

'^ See footnote 5, p. 21.

' SPROSTON, T., JR., and SCOTT, W. W. VALSA LEUCORTOMOID^.S, THE CAUSE OF

DECAY AND DISCOLORATION IN TAPPED SUGAR MAPLES. PhvtopatholoR-V 44: 12-13,

illus. 1954.

amur

bigleaf ____

bigtooth._ ,

black

boxplder.___

devil

hawthorn

hedge

Japanese —_

mountain ^

Norway

red __

redvein

Rocky Mountain _

siebold

silver

striped

sugar

sycamore. ___

trident

vine

S-V U.S. GOVERNMENT PRINTING OFFICEi