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University
of Rhode Island GreenShare Factsheets
Maple
Tree Decline
Maples grown in urban areas experience stresses that trees
in a forested situation seldom encounter. They are often planted
in disturbed soils and are continuously subjected to salt and
air pollutants. The repercussions of these stresses are evident
in smaller leaves, leaf browning and death of branches or limbs.
This collection of problems is often described as maple decline.
Maple decline is not a disease per se, and is certainly not contagious--it
is instead a general term used to refer to the collection of
problems found on maple which result in a decline in tree vigor.
Many of these problems are not specific to maple trees, and suggestions
for prevention or care would be the same for other, similarly
affected shade trees.
Maple leaves often show a browning or drying at the outer
margin of the leaf or in the areas between the veins in mid to
late summer. The areas near the veins generally remain green;
however in extreme cases the entire leaf may dry and fall prematurely.
This may lead to scorch caused when leaves lose water more rapidly
than moisture can be replaced from the soil. This can be caused
by too little water in the soil or a physical restriction of
the root.
The symptoms of leaf scorch usually appear during hot,
dry, windy weather. Trees growing along streets or in areas where
the roots are restricted seem to suffer most. Scorch itself seldom
kills a tree, but may weaken it to the point where insects or
disease can further injure it. Leaf scorch is best controlled
by deep watering during dry periods.
See GreenShare Factsheet on leafscorch for
more information.
If a tree shows symptoms of poor vigor such as small leaves,
death of small limbs, top dieback or leaf scorch, the condition
could be due to a girdling root. This problem occurs when a root
entwines around another large root or the base of the tree and
prevents or hinders water and nutrient movement. Often the girdling
root occurs below ground level, indicated by a lack of root flare
at the base of the trunk, but can only be confirmed by careful
digging around the base of the tree. Norway maple is often affected
by girdling roots.
Not all girdling roots need correcting. Only if the tree
shows a decrease in vigor should action be taken. Remove the
portion of the root that is girdling the tree; the open wound
can then be treated with wound paint prior to covering with soil.
Fertilization of the tree after root removal will help recovery.
The use of proper planting techniques, especially making the
hole large enough to accommodate the roots, will minimize the
likelihood of girdling roots.
Damage to streetside maples can often be attributed to
the use of de-icing salts. Symptoms can vary from marginal leaf
browning (similar to scorch) to yellowing of leaves to branch
dieback. The problem is often more severe on sugar maple than
the other maples. Trees near intersections or on major streets
where greater amounts of salt are applied or low areas where
run-off water collects will often show the most injury.
Salt damage results from two sources. Windblown spray from
passing automobiles causes most damage to the lower branches
of the tree, while salt uptake by roots from run-off water is
usually evident in the upper portion of the tree. Soil tests
seldom show excessive salt concentrations, as salt leaches readily
from the soil. The best indicator is chemical analysis of the
foliage where excessive chloride concentrations will usually
be associated with de-icing salt injury.
Salt damage on existing trees is difficult to control as
long as the practice of applying salt to the roadway continues.
Future plantings made 30 feet away from the roadside will have
less injury. The use of sand and the more judicious use of salt
is the best long-term solution.
Street and yard trees often grow in soil that has been disturbed
by construction. Such soil may not contain the proper nutrients
necessary for tree growth, or the pH of the soil may not allow
nutrients to be taken up by trees. Likewise, leaves are often
removed from the soil each year, giving the tree little chance
to change the soil conditions. The trees may look fine for years
and then suddenly show the effects of lack of growth nutrients.
A characteristic symptom of nutrient problems is a yellowing
of the leaf while the areas along the veins remain green. Other
symptoms can be marginal leaf browning, smaller leaves and reduced
twig growth.
Nutrients lacking in the tree are often present in the soil
but are not readily available to the plant because of high soil
pH. Application of soil amendments such as sulfur to lower the
pH often gives promising results, but is difficult and expensive
over a large area. Improvement has also been found with the application
of foliar nutrients; however, when the leaves fall, most of the
fertilizer falls, too, and the application must be repeated yearly.
Trunk implantation of fertilizer capsules has also given excellent
results, although this too is probably a short-term solution.
As with most tree problems, proper care and maintenance of a
tree throughout its life will lessen the likelihood of nutrient
problems. When planting in poor soil, use trees tolerant of a
wider variety of soil conditions.
Maple tree decline can often be attributed to soil compaction
and paving. Areas around driveways and along non-curbed streets
are often used for parking, causing considerable soil compaction
beneath trees. If a tree is completely surrounded by a paved
area, there is little room for water and air exchange in the
soil, resulting in a buildup of carbon dioxide. This condition
is especially critical if the paving was done after the tree
had already established its root system. Symptoms of soil compaction
and paving include marginal browning of leaves, twig dieback,
summertime yellowing of leaves and smaller leaf size. These symptoms
are often similar to girdling roots and construction damage.
Frequently, more than one of these conditions exist on an individual
tree. The effects of pavement are difficult to correct without
removing the pavement for a distance of at least 8 feet from
the base of the tree. Sidewalk and curb construction damage can
be decreased by fertilization prior to root damage so that the
tree is growing vigorously when the roots are cut. If soils are
compacted, aeration and fertilization will help the tree recover.
The source of compaction must be eliminated for long-term recovery.
In addition to the most common environmental problems already
discussed, there are additional factors that can stress trees:
A. Grade Changes
Soil fill on top of root systems of living trees
can cause serious damage. As little as 4 to 6 inches of fill can
be damaging to some maples and other tree species. The typical
symptoms of fill damage are yellowing of foliage and branch dieback.
These symptoms may not be expressed until several years after the
grade change was made. There are ways to fill around trees without
causing serious damage, such as using coarse gravel for the lower
fill under the topsoil. The use of a well around the trunk can
be helpful to the tree as well. Soil removal around trees is also
damaging because very little soil can be removed without root destruction;
delayed symptom expression is again common. Terracing is one way
to avoid removing large quantities of soil.
B. Frost and Wind Damage
Leaves can be damaged in late spring by frosts. Young leaves may suddenly turn
brown or black several days after a frost, or the edges of the leaves may
curl. If the leaves are not killed, they often are left with jagged open
spaces similar to feeding holes made by certain insects.
Wind damage may also appear on young leaves, especially
on newly transplanted trees. Symptoms of wind damage are also
jagged, torn leaves not unlike some insect damage to leaves.
Little can be done to control wind and frost injury. Most trees
will recover if they have been well maintained and are in good
health.
C. Herbicide Damage
Trees in lawns occasionally show a leaf curl and distortion from indiscriminate
use of herbicides. Combinations of fertilizers and weed killers, or weed
killers alone, should be avoided under the canopy of trees, as they can
cause serious damage or defoliation of trees. In some circumstances, misuse
of herbicides can kill trees. If damage is already evident, a thorough
watering and fertilization is the best way to promote recovery.
D. Diseases
There are several maple diseases that may cause symptoms similar to those caused
by adverse environmental conditions. Verticillium wilt, a fungal disease,
can cause a sudden wilting and dying of branches; in a mild form the only
symptoms may be poor vigor and sparse growth. The wood of affected plants
often shows gray to olive-green streaks when the bark is peeled from recently
affected limbs. Positive identification, however, can be made only by laboratory
tests.
Anthracnose is distinguishable from scorch because the browning
occurs along the veins or in irregular areas on the leaf, while
scorch occurs along the leaf margin. Anthracnose occurs during
cool, wet spring weather, and scorch generally occurs during
hot, dry summer weather.
There are several root and butt rots that can cause branch
dieback and leaf browning. There may be loose bark at the base
of the tree under which strands of a fungus can be found, or
there may be fruiting bodies (mushrooms) or a fungus present
at the base of the tree. Once infected, little can be done to
control these rots, but trees kept in a healthy, vigorous condition
are less likely to be infected. Care should be taken to avoid
wounding trees, which provides openings where rot fungi can enter.
Maples, like all trees, have many problems that are not
easy to categorize. An individual tree may exhibit symptoms caused
by a combination of factors. One stress may make a tree more
susceptible to another stress, disease or insect problem. Not
all tree problems can be corrected or controlled, but most can
be prevented or avoided by selecting the tree species or variety
best suited to a planting site, followed by giving the tree proper
care and maintenance.
Adapted from M.J. Walterscheidt,
Michigan State University Extension, 2000
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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