Learn to Identify Common Tree Diseases in Alberta

HEART ROT DISEASE – ASCOCORYNE SARCOIDES

  Location: Centre of tree

  Season: Summer and fall (after pruning)

  Causes: Fungus

  Effects: Causes tree to decay over time, which leads to branch breakage

  Signs: Presence of mushrooms and other forms of fungi around the roots or trunk of the tree

  Tree species: Maples and oaks

  Management: Minimize pruning wounds that expose heartwood and shape trees at an early age so major branch removal isn’t necessary later

LARCH DWARF MISTLETOE – ARCEUTHOBIUM LARICIS

  Location: Trunk and branches

  Season: Summer

  Causes: Parasites

  Effects: Reduce wood quality, diameter and height growth and sometimes kill the tree because it provides entrance points for stain and decay producing fungi

  Signs: Branches and stems are often swollen at dwarf mistletoe infection sites

  Tree species: Lodgepole pine among others

  Management: Prune infected branches; when the trunk is infected clearcut harvesting of infected trees is necessary to ensure parasites cannot spread to other trees

PINE NEEDLE CAST – LOPHODERMELLA CONCOLOR

  Location: Needles on conifers

  Season: Moist summers

  Causes: Fungus

  Effects: Defoliation of needles, dieback and death of branches and mortality after repeated epidemics (especially in young trees); they only affect new foliage

  Signs: Red-brown needles that eventually turn straw coloured with concolourous, oval-shaped fruiting bodies 

  Tree species: Lodgepole pine

  Management: Ensure efficient air circulation around trees and maintain good weed control; apply fungicides to protect healthy new foliage

RED HEART ROT – STEREUM SANGUINOLENTUM

  Location: Trunks

  Season: Summer

  Causes: Fungus

  Effects: Most often leads to destruction of tree but can be responsible for heartwood stains and terminal dieback of branches

  Signs: Fruiting body forms a crust-like layer that is cinnamon brown with a wavy edge; it turns blood red when rubbed

  Tree species: White spruce, balsam poplar, tamarack larch, pines and firs

  Management: Once established it cannot be effectively treated; prevent by avoiding unnecessary damage or injuries from pruning

BRONZE LEAF DISEASE – APIOPLAGIOSTOMA POPULI

  Location: Leaves

  Season: Spring/Summer

  Causes: Fungus

  Effects: Without proper management, an infected tree can die within 3-5 years

  Signs: Infected leaves turn orange-brown to reddish-brown with colouration starting at the edges of the leaf and moving inward toward the base. A defining characteristic of the disease is the way that the leaf veins and petiole often remain a bright green in stark contrast to the rest of the leaf.

  Tree species: Poplars

  Management: Bronze Leaf lives inside a tree and, once established, cannot be eradicated. The only treatment is containment, which is accomplished by removing affected branches or, at last resort, the tree itself.

ELM SCALE – GOSSYPARIA SPURIA

  Location: Smaller limbs that are higher on the tree

  Season: Spring

  Causes: Insects

  Effects: Heavy infestations may kill weakened trees and cause branch dieback in healthy trees

  Signs: A sooty, grayish/black mould on leaves, as well as honeydew that can spread to coat nearby structures and vehicles

  Tree species: Elm, hackberry

  Management: European Elm Scale is easily treated with soil-applied insecticides, as well as systemic products that are applied at the base of the tree and distributed through the root system. By law, Elms in Calgary should only be pruned between October 1st and March 31st in order to prevent the spread of Dutch Elm Disease.

FIRE BLIGHT – ERWINIA AMYLOVORA

  Location: Limbs, trunk, root system, flower clusters

  Season: Spring

  Causes: Bacteria

  Effects: Fire blight can destroy limbs and even entire trees

  Signs: Early indications of fire blight include a light tan to reddish, watery ooze coming from an infected branch, twig, or trunk cankers. Flowers wilt and turn brown, twigs shrivel and blacken, and in advanced cases, cankers begin to form on branches.

  Tree species: Fruit trees: Apple, pear, quince, crabapple, etc.

  Management: There is no known cure for Fire Blight; the only effective treatment is regular pruning to remove infected stems and branches, although spraying of bactericide chemicals can reduce the bacteria’s ability to survive and reproduce. Pruning can also be a means of transmission; it is critical that you sanitize your tools as you prune.

OYSTERSHELL SCALE – LEPIDOSAPHES ULMI

  Location: Bark on trunk and limbs

  Season: Spring

  Causes: Insects

  Effects: Heavy Oystershell Scale populations on limbs and twigs are not only unattractive but will also weaken the tree and make it more susceptible to further disease and damage.

  Signs: Oystershell shaped bumps on branches, leaves that are turning yellow, branch dieback

  Tree species: Fruit trees, lilac, ash, maple, dogwood, poplar, and willow

  Management: This pest reproduces only once per year, during a period of approximately 10 days occurring in early to mid-June. Horticultural oil can be applied at this time in an effort to suffocate the pest inside its permanent shell. Natural remedies include the introduction of natural predators of oystershell scale, such as ladybugs or lacewings. Pruning is often the most effective remedy.

DUTCH ELM DISEASE – OPHIOSTOMA NOVO-ULMI

  Location: Leaves, branches, roots

  Season: Summer

  Causes: Fungus spread by elm bark beetles

  Effects: Starvation of the tree roots

  Signs: Withering and yellowing of leaves on the upper branches during the summer months that spreads and causes branches to dieback

  Tree species: Elms

  Management: Because elm bark beetles represent the primary mode of Dutch Elm Disease infection, insecticides such as Arbotect are often used to provide ongoing control. An alternative and less effective method involves the injection of a fungicide into the base of the tree, using specialized equipment. Disinfect any tools used on diseased trees.

OAK WILT – BRETZIELLA FAGACEARUM

  Location: Starts at the crown and spreads to lower branches, limbs, and roots

  Season: Spring/Summer

  Causes: Fungus

  Effects: Wilting of leaves and limbs and eventual tree death

  Signs: An oily green appearance in sections of the tree’s canopy, which rapidly turns a tan or red colour

  Tree species: Oak

  Management: There is no permanent cure for Oak Wilt, so prevention offers the most likely method of control. Do not prune oak trees in the spring and summer months; take care to protect susceptible trees from injury during this period and use tree paint to cover any wounds that might occur. Injections of propiconazole, a fungicide, into the roots can help prevent transmission, as well.