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Introduction
Maple
decline affects primarily sugar maple (Acer saccharum), Norway
maple (A. platanoides) and red maple (A. rubrum) in the
Northeast. The problem is not a new one; stagheaded maples were described
as early as 1917 in Massachusetts. At that time, dieback was attributed
mainly to drought and to the poor conditions for tree growth afforded by
the urban environment. However, reports of the incidence and severity of
maple decline have increased markedly in recent years to include urban,
sugarbush, and forest environments.
In forests, maples usually
begin decline after several successive years of defoliation by insects.
Affected trees not only lose their first set of leaves to these insects,
but will often use up valuable food reserves to produce a second set.
During and after "refoliation", chemical changes occur in the tree that
increase its susceptibility to secondary pathogens. Armillaria
mellea (root rot), Nectria cinnabarina (branch canker) and
Steganosporium ovatum (twig blight) are three fungi that
frequently attack and may kill trees weakened by defoliation and
refoliation.
In sugarbushes, predisposing stresses include
drought, heavy grazing, over-tapping, and/or heavy traffic by farm
machinery. Seriously affected trees are often over-mature and have been
heavily tapped for many years. Tapping holes, animal-damaged roots, and
machine-damaged roots are all routes for entry of wood decay organisms. If
this scenario is followed by insect defoliation as previously described,
the result is often mortality of the stressed trees.
In urban
sites principal stress factors in maple decline include drought, de-icing
salts and/or road and sidewalk construction. These stresses also
facilitate invasion by secondary organisms including root rots, decays and
twig blights which greatly reduce chances of recovery from original
stress(es). No matter which of the three environments maple decline occurs
in, the sequence of events is similar. Healthy trees are stressed
repeatedly, the stresses alter the tree's internal chemistry to allow
repeated attack by secondary organisms, and the trees ultimately die.
Symptoms
Figure 1: |
Figure 2:
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1. Reduced twig growth. Yearly twig
growth varies considerably between trees and even within the canopies of
individual trees. If the distance from bud scar to bud scar is less than
or equal to five cm on a non-shaded twig, the tree may be in trouble.
2. Reduced foliage growth. Keep in mind the
normal, healthy appearance of the particular maple species' foliage.
Foliage that is sparse, light green and/or scorched signals that the tree
may be declining.
3. Early fall coloration.
Maples normally begin showing fall color after the first frost or in
mid-to-late September. When fall color develops earlier than normal, in
late July or early August, the maple is suffering from decline.
4. Dead branches in upper canopy. Small dead
branches seen in tree tops in late spring or early summer are indicative
of decline. Over time, larger, more visible branches and limbs will
dieback. The more numerous the dead twigs or branches are, the more severe
the decline condition.
5. Poor root condition. If
roots can be examined, look for reduced occurrence of small feeder
rootlets; dead, brittle roots; and decaying buttress roots.
Control
Strategies
Treatment for
declining urban maples includes watering, fertilizing, pruning dead
branches, and reducing salt-laden spring water runoff over the roots.
Thoroughly water trees every week or two during extended dry weather.
Trees should be watered with a slow stream from a hose. Move the hose
periodically to soak the entire soil area under the tree's branches to a
depth of six or more inches. Fertilize trees with a complete fertilizer in
the spring and/or late fall. The general recommendation is 2 to 4 lbs
fertilizer per inch of tree diameter (0.35 to 0.7 kg per cm of tree
diameter at 1.5 m above ground). Broadcast the fertilizer over the surface
of the ground. Some risk of burn on nearby turf may occur at the higher
rates. Prune dead branches as well to possibly stimulate renewed, vigorous
shoot growth. Pruning is best done in the early spring, prior to budbreak,
to promote healing of the pruning cuts. Road salt impact can be reduced by
placing a barrier (curb, burm, ditch, etc.) which will catch and/or divert
the spring runoff water which often contains copious amounts of salt. If
soil and foliar analyses have been run and high sodium or chloride
concentrations were found, then leaching the soil with fresh water or
applying gypsum to improve the soil structure or texture may be useful.
By the time symptoms are noticed, the tree may be beyond being
restored to its original splendor. However, at this time another tree may
be planted which will eventually replace the declining maple. In this way
the newly planted tree will have a few years to grow prior to the removal
of the declining maple. Plant young maple trees away from roads to avoid
de-icing salt problems.
The success of treatment to declining
maples depends primarily on early detection of maple decline, the health
of the tree prior to treatment, and/or its ability to respond to
treatment. Positive diagnosis will often depend on "on the spot"
examination or the amount of information obtainable from the person
submitting a sample. However, the prescribed treatments of fertilizing,
watering and pruning will not damage healthy trees.
Created, KLS, 8/99
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 |
