 |
| ANTHRACNOSE
OF TREES AND SHRUBS
|
|
 |
|
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. These diseases can be found throughout the eastern
United States. The symptoms of these diseases 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 associated with large leaf veins (Fig.
1). Infections on new shoots may kill them entirely or
cause severe tissue distortion (Fig. 2).
Defoliation may occur early in the season followed by a second growth
of leaves in early summer. Buds are often invaded and killed. Twig
lesions often expand 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 season, 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: Foliar symptoms
of vein damage and leaf blotching. (provided
by Dr. Wayne Sinclair, Cornell University) |
Figure 2: Symptoms of twig damage
on Sycamore . (provided by Dr.
Wayne Sinclair, Cornell University) |
|
Disease Cycle
Anthracnose pathogens overwinter in leaf debris. In spring they
produce spores that are carried by air currents 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 may then reproduce 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
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 these fungi overwinter.
Gathering and destroying 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 diseases,
preference should be given to resistant varieties. London Plane (Platanus X. acerifolia) may be planted in place of susceptible sycamore. Control of many
anthracnose diseases can be accomplished through properly timed sprays
of fungicides. If needed, landscape trees in New York State may be treated with Kop-R-Spray, Prescription Treatment Camelot, Protect DF, or with some products containing the active ingredient chlorothalonil. Note: Although registered for use on landscape plants, not all of these products listed may be suitable for use by homeowners. Kop-R-Spray is registered for Home Garden use in New York State..
Be certain any formulation(s) of pesticide(s) you purchase
are registered for the intended use, and follow
label directions. If large trees require treatment, consider hiring a commercial
applicator. Commercial applicators should refer to the appropriate
commercial pest management guidelines, or contact your local Cooperative
Extension Office for more information on other currently registered products.
Created, KLS, 1/01 ; Updated, SLJ, 3/08
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
or slj2@cornell.edu
|