Learn what you can do about the common tree issues and concerns that you might have.

Leaves falling in eavestrough or on property

Deciduous or broadleaf trees produce large leaves that produce energy for the tree during the summer and then fall off during the autumn as the tree enters dormancy. 

Coniferous, or softwood trees produce thin needles in the spring and retain them throughout the year (except larch trees). Mature trees will lose needles throughout the year, but not in large amounts.  

Leaves can be difficult to rake, but this event usually only happens for a very brief period of the year. They can also enter eavestroughs, or rain gutters, on roofs. We reccommend installation of fine meshes that prevent entry of the leaves into the troughs. The leaves will then be blown off the mesh by wind, reducing the liklihood of backup and the need for cleaning. Leaves are an aspect of nature and are not considered a nuisance. 

Sap dripping from tree branches

Have you found drops on your car after you've parked it under a tree? You might be dealing with aphids or scales. These common insects occur on many trees and shrubs.

Aphids and scales

Aphids and scales are small, sap-sucking arthropods. Their population can vary in size through time. A large population one year does not mean there will be an equally large or larger population the following season. They can be found on many different trees, including:

  • Ash
  • Elm
  • Apples
  • Maple
  • Oak
  • Rose
  • Willow


While aphids and scales often go unnoticed, their waste, called honeydew, can cause issues. It looks a lot like sap and is clear and sticky. It coats bark and leaves, and lands on objects beneath the plant. The best way to remove this is to use soap and water in small amounts, or wash your vehicle at a desingated wash station, such as a commercial wash bay. Washing your car in your driveway is not recommended, as storm drains divert water directly into waterways.

What you can do

The first option is leaving them alone. Their populations are regulated in many ways, including natural enemies like ladybugs and weather, such as heavy rainfalls. Remember that leaving aphids alone generally causes little damage to the plant. This has the added benefit of giving natural enemies the chance to lower their number.

Don't over-fertilize

Too much fertilizer promotes growth that attracts aphids. Organic fertilizers release nutrients slowly and ensure that plants receive appropriate amounts of fertilizer. Adequate water and light will help produce unstressed plants that can fend off aphids and scales. For completely infested trees, you can use dormant oil as a means of control.

Trees losing leaves in spring

 Ash trees, maples, oaks and other species can succumb to hardwood leaf diseases known as anthracnoses.


Anthracnoses are one of the most visible of the hardwood diseases but isn’t very damaging. There are different fungi that cause anthracnose in different species of trees. The fungus hibernates in infected twigs and fallen leaves. Infection on newly emerged leaves and shoots begins in early spring during cool and wet weather.


Symptoms range from:

  • Leaf spots
  • Blotches and blights of leaves and shoots
  • Cankers and diebacks of twigs and branches

Irregular water-soaked spots appear on young shoots and leaves shortly after infection. As the disease develops, leaflets can has brown to black blotches or spots, usually from the margins toward the center. The leaves tend to curl. Infected leaves often drop prematurely. Older leaves are more resistant and may only appear spotted. The disease usually infects the lower portion of the canopy first and then spreads upward.

Often doesn’t cause permanent damage

A tree may lose a large part of its foliage, but produces a new flush of leaves later in the spring. The disease does not usually cause permanent damage to the tree; however, repeated leaf loss year after year can weaken trees and can lead to pest problems or environmental stresses.

What you can do

Rake and remove leaves as soon as they fall so that they do not re-infect healthy leaves remaining on the tree. Do not compost those leaves but dispose of them in garbage bags. Removing leaves in the fall will help reduce the over-wintering population of anthracnose fungi. Avoid watering the canopy of the tree.

Problematic tree roots

Most people know that tree roots are required to stabilize a tree in a vertical position, especially those roots that grow horizontally from the base of the trunk or stem. However, that is only part of their job. They absorb oxygen, water and nutrients (such as nitrogen, potassium and phosphorus) from the soil, are then sent to the rest of the tree. All of these elements are essential for the tree’s growth and overall health. Tree roots also store starches produced during the growing season. They are essential for growth and survival. If a tree’s roots are damaged, it will become stressed and its health will decline and could lead to death.

Surface Roots

Surface roots are common in some species of tree once they reach maturity. At this stage in the tree's life there are many benefits to the homeowner such as

  • Shade,
  • Habitat for wildlife,
  • Reducing noise pollution,
  • Increasing neighbourhood safety,
  • Improving home value,
  • Reducing heating costs,
  • Absorbing carbon dioxide and producing oxygen, and
  • Preventing soil erosion and flooding.

Cut tree roots and grass

If tree roots are cut, the tree could be in danger of infection, instability and death. If roots are covered with too much soil, roots can become smothered which will affect the health of the tree. Grass can also compete with the tree for nutrients, making the tree weak and a likely host for infection. The tree is also likely to have roots that resurface again.

Caring for your tree’s health

The best way to care for your tree's health and continued success, as well as address on-the-ground situations is to mulch over the tree roots. Put down enough mulch to even the level with the top of the roots so that you can walk without tripping. You can also install decorative rocks or boulders to complement your naturally beautiful lawn.

Roots in sewers

Tree roots do not crack intact pipes. They will invade and clog pipes that have pre-existing openings or cracks and cause leakage. Sewer connection pipes are usually 1.4 to 2.5m below ground level, while tree roots often grow in the upper meter of soil. To survive, roots require both water and oxygen, which decrease in deeper soil. Leaking pipes provide oxygen and nutrient rich water, which draws tree roots deeper into the soil than they would normally be, allowing them to get into pre-existing openings. If you think you might have roots in your pipes, please contact the City's Environment Division.

Bumps on maple and linden leaves

If you see red bumps on your maple or linden's leaves, your tree probably has gall mites.

Maple bladder galls are small, red, round wart-like bumps about 1.5 mm to 3 mm in diameter. They can cover the upper surface of the foliage on silver and red maple trees. Galls can appear every year, though their number varies greatly from year to year and from tree to tree.  A small mite, vasates quadripedes, causes these galls. 

There are also red fuzzy growths that can appear on maple leaves. These are called velvet erineum mites.

On lindens, eriophyid mites cause pointy galls to appear and can cause the leaf to curl and become distorted.


You might first notice these bumps in May, about the time leaves fully expand. At first, the galls are green but they turn pink to red and eventually black. A severe infestation may cover leaves with so many galls that they twist out of shape and drop early. Adult mites spend the winter under the bark and other protective places on the trees.

In the early spring, the adults move to developing, unfolding leaves and begin feeding. The leaf responds to the small irritation by rapidly producing extra cells that form the abnormal growth at the feeding site. The gall encloses the mite, which continues to feed and lay numerous eggs inside. Reproduction is prolific and as the new mites mature, they leave the gall and move to other newly emerging leaves to repeat the process. Only new leaves are capable of producing galls. Mite activity continues until mid-summer when it starts to decline. Adult mites leave the foliage in the fall and move to the over-wintering sites.

No permanent damage

Leaf galls seldom cause permanent injury to a tree.  Most commonly, the galls only cause aesthetic damage and possible early leaf drop. Following a mild winter, damage from these leaf galls can be excessive but affected trees often send out new leaves to replace the damaged ones.

What you can do

It is important to keep your tree well watered and healthy so that it can build up its own defenses to fight infestations. You cannot cure galls after they have formed. Sprays or systemic insecticides will not remove the galls or improve the condition of the trees. Preventive treatments, such as dormant oils applied at the time of bud break in early spring are a possible option. The galls are not significant to the trees and don’t really justify massive pesticide use as it has little effect.

Black clumps on tree branches

If you see black clumps on your tree’s branches. Your plum, cherry or choke cherry tree may have a disease known as black knot.

Black knot

The characteristic feature of black knot is the presence of thick, black, irregular swellings on twigs and branches. These can be seen in the winter when leaves are not present. The disease is difficult to notice during the early stages of infection. The disease initially appears as small light brown swellings on current or previous season’s growth.

Following year

The following year, the swellings appear olive green with a velvety texture. By the end of the season, knots darken and harden. Numerous knots may be present on one tree. Often the branch beyond the knot will fail to leaf out or will suddenly wilt.

Apiosporina morbosa

The fungus Apiosporina morbosa causes black knot. It infects trees in the spring, about the time buds emerge. Spores are released following a period of warm, wet weather. They can disperse after only a few hours of rainfall. Temperatures between 16 and 27°C are ideal for dispersal, germination and infection. Spores spread by splashing water, wind, insects and birds. The gall has a corky texture and becomes hardened and black. The black knot fungus overwinters in the knots, but gall enlargement ceases over the winter and resumes in the spring when knots may then enlarge rapidly. Old knots enlarge every year and may range from 2 to 30 cm in length. Duration of the disease cycle is usually 2 years.

It can spread

Fungus in old knots may invade other tissues to form new knots. The fungus can spread internally. Branches stop moving water and nutrients. This can lead to dieback. A branch may survive, but may have a large canker with a sunken center serving as an invasion point for other insects and diseases. Succulent new growth or wounded tissue is more commonly infected.

What you can do

In order to control black knot, prune infected branches at least 15 to 20 cm past the gall. Prune trees when they are dormant, before March 1, or after they have finished flowering. Sterilize tools between each cut using chlorine, bleach or alcohol. Knots are capable of producing spores after removal so you need to burn, bury or remove infected branches from the area.

Birch tree appears to be dying

The most threatening of the birch tree pests is the bronze birch borer (Agrilus anxius). Evidence of borer infestation is a progressive thinning of the crown of the tree beginning at the top. Trees often die after two or three years of infestations by the borer’s larvae.

Bronze birch borer

As an adult, the borer is a small bronze coloured beetle up to 5 cm in length. Its larvae bore into the phloem and cambium layers of the tree after emerging from their eggs on the bark. The borers' tunneling weakens and kills trees by interrupting the flow of sap. The entire lifecycle of the borer is one year from egg to beetle.

What you can do

Prune out and destroy all dead or dying branches. If you catch it early enough, there are insecticides that can prevent new infestations. Trees with advanced crown loss will not benefit from insecticide use and you should remove them. The good news is that healthy, well-situated, well-maintained birches are more resistant to the borer. Female borers prefer to lay eggs in the sunlight and are less attracted to trees whose trunks are shaded.

Take care of your tree

Tree wounds attract borers, so you should take care to avoid damaging the bark of trees. Finally, trees under stress are more likely to be targets for borers, so ensure that birch trees receive adequate water and proper fertilization.

Newly planted tree doing poorly

Do not worry if your tree doesn’t grow quickly right away. Trees can take years to establish. They need to create a good root system underground before you’ll see lot of new growth above ground.

What you can do

What the tree needs most from you is regular and frequent watering throughout the 5-year establishment period.

Avoid weed trimmers

Please do not use a weed trimmer to cut grass around the base of your tree. Instead, re-apply mulch so that grass doesn’t grow near the trunk. Weed trimming damage is one of the leading causes of death to trees in urban environments. Once you create a wound, it disturbs the trees physiology and makes it difficult to heal and also provides an entry point for insects and disease. If the damage extends around the circumference of the trunk, the tree will die.

Remove the stakes and cloth supports after one year

After one year, ensure that you remove the tree’s stakes and cloth supports. The wooden stakes are beneficial in the beginning to prevent breakage of newly initiated roots when the tree sways.  Removing the stakes after one year allows the tree to start swaying naturally and efficiently relocating photosynthates. If you are unable to remove the stake yourself, or if you notice many street trees in your area that are still staked after a year, contact us.

Soil compaction affects trees

Soil compaction occurs when vehicles or heavy equipment are placed or travel under the crown of a tree. This reduces the number of air pockets in the ground and decreases the availability of air and water that trees need to stay healthy. Roots in compacted soil are unable to supply these essential elements to the rest of the tree, resulting in the tree stress and a decline in health.

Leaves in autumn

Deciduous or broadleaved trees need to prepare for the oncoming cold winter temperatures or else soft leaf tissue and the fluids inside leaves will freeze. In autumn, a layer of cells forms at the base of each leaf that blocks the veins that convey the fluids into and out of the leaf. As a result, the leaves slowly die then drop off. This protects the rest of the tree from the effects of the cold.

Coniferous or evergreen trees

Coniferous or evergreen trees, such as pine and spruce, retain their needle-like leaves in winter due to a protective waxy covering and substances inside their leaves that resist freezing. Their needles stay on the tree for about two to three years before they drop off.

Identifying insects

Use BugGuide to identify insects on your tree. It is a great online resource for information on insects, spiders, and more in Canada. There are dozens of detailed photographs and drawings of bugs from the U.S. and Canada for identification and research.

Invasive pests

Visit the Invasive Species Centre to report and find out more about common invasive pests. 

Bark splitting on young tree

Southwest injury or trunk scald often causes maple tree trunks and bark to split in winter. The problem is more prevalent in thick-barked maples and in younger trees. The low angle sunlight in winter warms the trunk tissues, activating dormant cells and making them prone to cracking and splitting during cold nighttime temperatures. Trees can often recover from this bark splitting quickly. You can manage southwest injury by covering the lower trunks with burlap or jute during winter. This material can be re-used every winter while the tree is still young and the bark is thin.

Winter browning of conifers

Winter browning is most severe on younger trees up to about 25 years old, although some older trees or older stands also have some browning. Trees in plantations and trees on the edges of forest stands are severely affected. It affects the upper parts of the trees while lower portions are often still green.


Winter browning causes the needles on conifer trees to dry out and turn brown. In some species, the needles may appear red, yellow, or grey, or purple in blue spruces. In most cases, the buds are still alive. Damage is more severe on younger, smaller trees, on the south or west side of trees, and edge trees with westerly or southerly exposures.


During periods of increased sunlight, strong winds, and warm temperatures, conifers lose water from their needles faster than they can replace it. This is common in February and March. Dormant roots and the frozen ground prevent the tree from replacing lost water, causing the needles to dry out and die.

It affects smaller trees more severely

It can affect smaller trees more severely because larger trees have more moisture to replenish the water lost to drying conditions. Smaller trees also have more foliage closer to the ground, where sunlight reflected from snow or ice can increase temperatures and cause increased drying of needles. Foliage below the snowline is protected from the drying conditions, and will survive the event and remain green. If there is no snow, heating of the ground by the sun warms the surrounding air, which in turn warms the parts of the tree closest to the ground, making smaller trees more susceptible to drying.

Needle damage

The damage to needles worsens when warm temperatures and sunlight cause the needles to break dormancy and begin photosynthesis (using energy from the sun to convert water and CO2 into carbohydrates). Active needles lose their cold tolerance and can freeze if cold temperatures return. If one or more thaw/freeze cycles occur after sunlight, strong winds, and warm temperatures, the needles can dry out, freeze, and die.

Spring of 2012

This is likely what occurred in northwestern Ontario in the spring of 2012. Record-breaking high temperatures in March (10 - 22) were followed by an extended period of cold temperatures and winter weather. Cold days were followed by short periods of warm temperatures, setting up a cycle of thawing and freezing of the needles. Initial drying of the needles caused cells to lose moisture, damaging the needle tissues. The needles may have been able to recover from this but thaw/freeze cycles in May caused further damage to the tissues before they could repair themselves from drying. Trees would have appeared healthy in March, but cold weather in May killed the damaged needles, resulting in rapid death and browning.


In most cases, the warm weather in March did not last long enough for trees to break bud and start growing and producing new shoots. Buds have likely survived with little damage. Trees may look heavily damaged, but if buds are still alive then the trees can recover from the loss of needles. Existing buds will break dormancy in response to warm spring weather growing into new shoots with a new crop of needles. Ground checks May 10 to 14 in 2012 showed good bud expansion and healthy growth, indicating the trees were recovering. A better growing season (i.e., ample rainfall and moderate temperatures) the following years, provided a better the chance for trees to make a full recovery.

Damaged needles            

Damaged needles drop from the trees during the summer, leaving the older sections of the branches bare of needles. Within one to two years, the damage should no longer be visible. It is important to note that dry, flammable needles, are an increased fire hazard.

What you can do

Watering trees with a low spraying sprinkler system is the best way for these browning Conifers to overcome the stress.

Webbing in tree

The fall webworm (Hyphantria cunea) is a small defoliating caterpillar that produces a web nest in trees that it is consuming. The web nest protects the insects from predators and provides a nice environment for them to eat leaves. Often the caterpillars are visible and their excrement (frass) is left at the bottom of their nest. These caterpillars, though their nest can be unsightly, are not a harm to the tree.

 Forest tent caterpillars

Forest tent caterpillars (Malacosoma disstria) defoliate trees, and do cause them stress, particularly if the outbreak lasts for more than three years. The caterpillars defoliate:

  • Aspen,
  • Oak,
  • Ash,
  • Maple, and
  • White birch trees.

These trees weaken from the repeated defoliation, which makes them more susceptible to stresses such as drought or other pests. However, the trees generally do not die. Population outbreaks occur every 10-12 years in the boreal forest and last about three years. Forest tent caterpillars weave a silky sheet where they lie together during molting.

Friendly flies

Once the caterpillar outbreak slows down, expect another pest: friendly flies. They are native parasites that attack forest tent caterpillars and follow their populations. As the fly population increases, the caterpillar population decreases. Friendly flies do not bite humans.

What you can do

 You can take a few steps to control the tent caterpillar.

  • Scrape off and discard overwintering egg masses, and tear the protective tents out by hand before the larvae start to feed.
  • Use Sticky Tree Bands or Tanglefoot Pest Barrier to control their movement and restrict access to feeding areas (the band should only be on the tree for a short time to avoid constricting the tree).
Apply Bacillus thuringiensis, var. kurstaki (Bt-k) to the leaves to kill feeding caterpillars if it’s your privately owned tree.

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