Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001670
11/12/99
Anthracnose
Symptoms: The leaf symptoms of anthracnose are dead areas
of the leaf that develop along main veins (Vis. 1), often in
a V-shape from the margin of the leaf. If infection occurs
before and during bud break, anthracnose can cause buds
and young expanding leaves (Vis. 2) to turn brown and die.
Cause: Several trees -- including sycamore, maple, white
oak, ash and dogwood -- are very susceptible to
anthracnose. A number of fungi can cause anthracnose. When
the disease becomes severe, it deforms the plants, making
each one an unsightly addition to a landscape. Susceptible
plants are distorted by the death of shoots and buds, which
causes the plants to grow asymmetrically. Affected
branches may look crooked and angular. Often clusters of
shoots -- "witches'-brooms" -- grow from one area of a
branch. When the fungus grows through the bud or down the
leaf petiole into the wood, it kills the branch. In the
wood, the fungus grows as a canker (Vis. 3). Each year's
new buds, shoots and leaves may become infected by spores
produced on the cankered wood in early spring. The disease
is most severe when springs are cool (average temperatures
less than 60 degrees F) and wet.
Control: The most effective control is to replant using
resistant trees as substitutes. For anthracnose, planetree
is a good resistant substitute for sycamore and most oaks
are less severely affected than white oak.
Keeping trees healthy with applications of nitrogen
fertilizers will enhance the plant's ability to regenerate
leaves and shoots.
Thinning the crown will allow better air circulation through
the foliage. As the anthracnose spores require moisture to
germinate, improved air will help speed drying of the
foliage.
Fungicides are available and should be applied during leaf
and shoot emergence. The expense of spraying can be avoided
through the use of resistant trees.
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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