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.
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
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.
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.
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
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.
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
In addition to the most common environmental problems already discussed,
there are additional factors that can stress trees:
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.
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.
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.
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.
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.
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.
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.
from M.J. Walterscheidt, Michigan State University Extension, 2000