Anthracnose. A Fungal Disease of Shade Trees.pdf

Virginia

Cooperative

Extension

Plant Disease

Fact Sheets

2000

PUBLICATION 450-604W

Anthracnose-A Fungal Disease of Shade Trees

R. J. Stipes and M. A. Hansen*

Anthracnose is a name for a group of diseases caused

by several closely related fungi that attack many of our

finest shade trees. It occurs most commonly and severely

on sycamore, white oak, elm, dogwood, and maple.

Other host plants that are usually only slightly affected

include linden (basswood), tulip tree, hickory, birch, and

walnut. Each species of anthracnose fungus attacks only

a limited number of tree species. The fungus that causes

sycamore anthracnose, for example, infects only

sycamore and not other tree species. Other

anthracnose-causing fungi have similar life cycles, but

require slightly different moisture and temperature

conditions for infection.

killing of single leaves or leaf clusters may occur as the

leaves expand. The disease continues to develop later

in the season, resulting in irregular brown to nearly

black, dead areas between or along the main leaf veins

and extending to the margin (Fig. 1). Infected leaves

fall when the

petiole is girdled

or when several

lesions enlarge

and coalesce to

form large, dead

blotches. After

defoliation from

spring infections,

the tree may

appear bare

except for tufts

of leaves at

branch tips.

Regrowth

appears by

midsummer.

Sunken cankers

form on larger

twigs during

cooler weather

in fall, winter,

and spring (Fig.

2). Twigs may die

as a result of

canker

formation.

When terminal twigs are killed, lateral twigs take over

as leaders. Thus, repeated twig dieback results in the

formation of crooked branches.

• On oak , small scattered brown spots or large light

brown blotches form along veins. The leaves look

scorched.

• On maple , purplish brown areas form along the veins

or larger, irregular, light to dark brown spots form

along or between veins (Fig.3), extending to the leaf

Symptoms

Anthracnose fungi may cause defoliation of most maple,

oak, elm, walnut, birch, sycamore, and hickory species

and, occasionally, of ash and linden trees. Damage of this

type usually occurs after unusually cool, wet weather

during bud break. Single attacks are seldom harmful to

the tree, but yearly infections will cause reduced growth

and may predispose the tree to other stresses. Damage

may be in the form of:

Fig. 1. Blighting of leaf tissue caused by the

sycamore anthracnose fungus.

(Photo by E. Dutky-U. Md.).

• killing of buds, which stimulates the development of

many short twigs or “witches’ brooms;” these may spoil

the shape of the tree

• girdling and killing of small twigs, leaves, and branches

up to an inch in diameter

• repeated early loss of leaves, which over several

successive years weakens the tree and predisposes it

to borer attack and winter injury

• premature leaf drop, which lessens the shade and

ornamental value of the tree

Fig. 2. Twig canker caused by the sycamore

anthracnose fungus.

(Photo by E. Dutky-U. Md.).

Specific symptoms of anthracnose vary somewhat

depending on the tree species infected:

• On sycamore, leaves and growing tips of the twigs may

die as they emerge from the bud. This damage is often

confused with late frost injury. Sudden browning and

*Professor of Plant Pathology and Extension Plant Pathologist, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, respectivel y

VIRGINIA POLYTECHNIC INSTITUTE

AND STATE UNIVERSITY

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national origin, disability, or political affiliation. An equal opportunity/affirmative action employer. Issued in furtherance of

Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department

of Agriculture cooperating. J. David Barrett, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg;

Lorenza W. Lyons, Administrator, 1890 Extension Program, Virginia State, Petersburg.

VIRGINIA STATE UNIVERSITY

margin.

• On ash , large,

irregular, light

brown spots

appear, most

often along leaf

margins (Fig. 4).

• On linden , large

brown areas with

black margins

appear, especially

along main leaf

veins. The areas

are small to

large and

circular to

elongate.

• On birch , small,

irregular,

circular, brown

spots with dark

brown margins

are apparent.

• On hickory , large, irregular, reddish brown spots

appear on the upper leaf surface and a dull brown

area is apparent on the lower leaf surface.

• On walnut , irregular, circular, dark brown to black

spots are visible on leaves.

• On dogwood , two different anthracnose diseases may

occur. Symptoms of spot anthracnose include tiny

leaf and bract spots, about the size of a pinhead, with

whitish centers and purplish borders. Symptoms of

Discula anthracnose (dogwood anthracnose)

include irregular, small to large brown blotches with

purplish borders on leaves and bracts, lower branch

dieback, and trunk cankers that culminate in death of

the tree.

Control

Disease control measures for different trees vary slightly

because the period of infection is different depending on

the fungal species involved. If fungicides are used, sprays

must be applied on a preventative basis, beginning before

infection takes place. Spraying large trees for many

anthracnose diseases may be impractical and

unnecessary, especially in dry springs. Sanitation is

important in reducing the amount of fungal inoculum

available for new infections. For large, high-value

sycamore

trees,

injection

with the

fungicide,

thiabendazole

hypophosphite

(e.g.

Arbotect

20-S), on a

3-year basis

is also an

option

(Fig 5).

Fig. 4. Anthracnose on ash.

(Photo by Virginia Tech Photo Lab)

Fig. 5. Two trees on right showing symptoms of

sycamore anthracnose compared to tree injected with

Arbotect 20-S fungicide on left.

(Photo by R. J. Stipes)

For effective anthracnose control of most anthracnose

diseases:

• Rake up and remove infected leaves in the fall. Leaves

may be shredded and composted or burned.

• Prune out and burn or bury dead twigs and small

branches. Prune to thin the crown. Thinning will

improve air movement and promote faster drying of

the leaves.

• If fertilizer is needed, fertilize in the fall about a month

after the average date of the first frost or in early spring

about a month before the date of the last frost to

increase tree vigor.

• If chemical control is desired, spray with a fungicide

containing mancozeb (e.g. Manzate 200, Dithane M-45)

at budswell and twice again during leaf expansion (in

most years, this would be at 10-14 day intervals).

Follow label rates or refer to the current Virginia Pest

Management Guide for Home Grounds and Animals (VCE

Publication 456-018), http://www.ext.vt.edu/pubs/pmg,

for details on fungicide application. For information on

the proper use of pesticides and fungicides, refer to

any current VCE pest management guide.

• Because Discula anthracnose is often fatal to the tree,

control of this anthracnose disease on dogwood is a

special case and is described in VCE Publication 450-

611W, Foliar Diseases of Dogwood.

Disease Cycle

Anthracnose fungi overwinter in infected leaves on the

ground. Some canker-causing anthracnose fungi, such as

the sycamore anthracnose fungus, also overwinter in

twigs on the ground or in cankered twigs that remain on

the tree. Microscopic spores of most anthracnose fungi

are produced in infected tissues during April and May.

The spores are blown and splashed to the buds and young

leaves and, with favorable moisture conditions, penetrate

and infect the swelling buds and unfolding leaves. Long

rainy periods help the fungus to spread rapidly.

Disclaimer

Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does

not endorse these products and does not intend discrimination against other products which also may be suitable.

Fig. 3. Leaf symptoms of anthracnose on

sugar maple.

(Photo by M. A. Hansen)

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