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| ANTHRACNOSE
OF TREES AND SHRUBS |
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Introduction
Anthracnose diseases are caused by fungi that are capable of
infecting stems, branches, leaves and fruits of a wide variety of
deciduous trees and shrubs. Sycamore, ash, maple, oak and
privet are especially susceptible. The disease can be found
throughout the eastern United States. The symptoms of the
disease are more severe in years of extended cool, wet spring
weather.
Symptoms
Symptoms vary according to the plant part and
the host attacked. Leaf infections may show necrotic
spots, irregular dead blotches or necrotic lesions that
associate with large leaf veins. Infections on new shoots
may kill them entirely or cause severe tissue distortion.
Defoliation may occur early in the season followed by a
second growth of leaves in early summer. Buds are often
invaded and killed. Twig lesion often expands and may
girdle the twig entirely, causing death of the parts
beyond the lesion. Repeated twig dieback may alter the
form of the tree, causing crooked branches and "witches
brooms" (a development of
clusters of twigs around a common point on a branch).
Cankers form on the branches as a result of the death of
buds and twigs. Cankers may remain active beyond one
dormant sea son, girdling and killing branches. Cankers
may also be inactivated by callus formation near the
margins. Large trees that sustain repeated attacks by the
pathogen are severely weakened showing loss of vigor,
dieback of large branches and increased susceptibility
to insect borers and winter injury.
Figure 1: Symptoms
of twig damage on Sycamore . (provided
by Dr. Wayne Sinclair, Cornell
University) |
Figure 2: Foliar symptoms of vein damage
and leaf blotching. (provided by
Dr. Wayne Sinclair, Cornell
University) |
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Disease
Cycle
Anthracnose pathogens overwinter in leaf
debris. In spring they produce spores that are carried by
air currants to young buds of the host. Spores germinate
under moist conditions and infect leaf tissue. If moist
conditions persist the first generation of new spores is
produced in the infected leaf tissue. There are dispersed
by rain to cause new infections. The death and loss of
many leaves greatly weaken the host plant. The fungi that attack both stems and leaves overwinter in infected
buds and twigs, in branch cankers and in debris on the
ground. They contain spores that are dispersed by air
currents and raindrops and remain in contact with the
host plant throughout the year. The fungus spreads from
the infected leaves into the twigs, where it overwinters.
It resumes growth before any tree growth occurs in the
spring and kills buds and twigs. If a prolonged period of
cold weather retards tree development after bud break,
the fungus kills new shoots. The fungus than reproduces
on those dead buds, twigs and shoots, and in cankers.
Cool moist conditions favor infection and epidemic
development of anthracnose diseases. Prolonged cool
weather before bud break favors bud and twig blight and
canker phases of the anthracnose by retarding tree
development more than fungus growth. Cool moist weather
after bud break favors shoot blight and leaf blight
phases by retarding host growth and providing conditions
necessary for dispersal and germination of spores.
Management Strategies
Good control of some anthracnose diseases can be
obtained by destroying plant material and debris in which
the fungus overwinters. Gathering and destruction of
leaves or composting them under several inches of soil
and pruning out infected twigs reduces the amount of
available inoculum and reduces the severity of the
disease. When planting trees and shrubs that are normally
susceptible to anthracnose disease, preference should be
given to resistant varieties. Control of many anthracnose
diseases can be accomplished through properly times
sprays of fungicides. Current recommendations include copper,
thiophanate-methyl, and chlorothalonil applied according to label
directions.
Created, KLS, 1/01
This publication contains pesticide recommendations.
Changes in pesticide regulations occur constantly, some
materials mentioned may no longer be available, and some
uses may no longer be legal. All pesticides distributed,
sold, and/or applied in New York State must be registered
with the New York State Department of Environmental
Conservation (DEC). Questions concerning the legality and/or
registration status for pesticide use in New York State
should be directed to the appropriate Cornell Cooperative
Extension Specialist or your regional DEC office. READ
THE LABEL BEFORE APPLYING ANY PESTICIDE.
__________________________________________________________________________________
The Plant Disease Diagnostic
Clinic at Cornell University is located at 334
Plant Science Building, Ithaca, NY, 14853. Phone:
607-255-7850, Fax: 607-255-4471, Email: kls13@cornell.edu
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