Black Knot Fungus
Is your Mayday, Chokecherry or Lilac showing a black, lumpy growth on its branches? It may be infected with black knot fungus - a disease that affects Prunus family trees. Although the fungal disease is rarely fatal, if left unchecked it will affect the health of your tree.
This fungal condition infects only Prunus species of plants, and may be recognized by the clumpy-looking, black masses of abnormal growths on the branches of your cherry trees.
What You Can Do
To manage black knot fungus, it’s essential to prune off infected branches 2-4 inches below each "knot” and dispose of them in a land fill. Between each cut, sanitize your tools with a bleach-water solution (25% bleach, 75% water).
The best time to prune is during late winter, as the fungus is dormant and the abnormal “knotty” growths are easy to see. Avoid pruning in the spring when the fungus is active. The fungus is transported by spores so the proper sanitization of pruning tools is very important to limit its spread from plant to plant.
For the health of the tree, we recommend citizens educate themselves in proper pruning techniques or hire the services of a certified arborist. Pruning a tree or shrub leaves a wound, requiring the tree to heal itself, and correct pruning provides the tree with optimal conditions for healing properly.
Bronze Leaf Disease (BLD)
Bronze leaf disease is a fungus that infects various poplar species and hybrids, including Swedish columnar aspens and tower poplars.
Symptoms of bronze leaf disease typically appear in late summer or early fall and may only be on a few branches or leaves.
- Infected leaves turn orange-brown to reddish-brown; colouration starts at the edges of the leaf and moves inward toward the base.
- Dieback may occur on infected branches.
- Browning may be observed under the bark of diseased branches.
- Leaf veins often remain a bright green in stark contrast to the rest of the leaf.
What You Can Do
- Prune out affected branches 20-30 cm into healthy wood while still attempting to maintain the tree's shape. Often, this is back to the trunk. Between each cut, sanitize your tools with a bleach-water solution (25% bleach, 75% water). Removal of dead and or dying trees is important as they will infect nearby trees as well.
- Pick up leaf litter from under the trees as soon as they drop. Fallen leaves and pruned wood should be bagged and disposed of in the garbage only. Do not bring infected leaves and wood to Leaf and Pumpkin Composting drop-off locations. Dispose of it in the garbage or take directly to the landfill.
- If you are unsure about how/where to prune, we recommend hiring an International Society of Arboriculture-certified arborist.
- If you suspect bronze leaf disease in a City-owned tree, contact 311.
Good sanitation is the best method of controlling the disease. Early detection and treatment is important.
European elm scale (EES) is a pest that normally attacks fruit and ornamental trees. Elm scale feeds by piercing leaves and bark and sucking juices from the tree. The eggs begin to hatch in late June and start feeding on leaves in mid-July. By autumn, the pest moves onto branches and twigs where they prepare to overwinter.
Damage symptoms are not readily apparent on Elm trees unless the infestation level is extremely high. Damage consists of:
- Leaf discoloration and premature leaf drop.
- Twig and branch dieback.
- Sticky honeydew material falling as fine droplets from the tree canopy.
What You Can Do
The easiest way to prevent pests and diseases is to keep your trees healthy. One way to do this is to give your trees a deep watering on a monthly basis, beginning when the tree leafs out and ending when the tree drops its leaves in the fall.
If you detect an infestation, homeowners are encouraged to first gently hose the tree down with water. Another option involves applying dormant or horticultural oil in order to suffocate the pest. Early season control is applied shortly after tree bud-break, prior to the production of elm scale adults and crawlers. Late season control is undertaken just prior to leaf drop as elm scale move back to the branches. During peak crawler numbers, apply a soap and permethrin mix known as Trounce® to significantly reduce the infestation.
The City of Calgary is conducting an injection program to treat select, highly infested Elm trees with a systemic insecticide. This control approach permits the control of all parts of the pests lifecycle.
Elms in Calgary should only be pruned between October 1 and March 31 by law to prevent the spread of Dutch Elm Disease.
Fire blight is a serious bacterial disease affecting trees and shrubs in the rose family. It can ravage Calgary’s urban forests during humid and warm summer weather conditions. Generally, fire blight is very rare in Calgary since our summers are usually too cool and dry for disease development. However, severe thunderstorms and hail can lead to an outbreak of fire blight.
Fire blight affects primarily the rose family of trees and shrubs. Common members of this family include apple and crab apple, pear, mountain ash, cotoneaster, raspberry, flowering almond, and saskatoon.
Fire blight bacteria can spread a number of ways, including insect transmission, use of contaminated pruning tools and strong winds and rain. Hailstorms help spread the disease by wounding the bark and making the tree vulnerable to infection.
- Diseased leaves appear red and fire-scorched. Blighted leaves eventually brown and die but remain attached to the tree.
- New growth exhibits a dramatic downward wilting at the tips.
- Clear amber liquid may be found oozing from diseased twigs. This liquid is highly charged with the bacterium, which causes the disease. Transferring even a small amount to healthy trees can generate new infections.
- Some trees may develop secondary infections indicated by bark cankers, which appear as indented, discoloured areas on the branches and trunks. Bark cankers are usually more serious infections and can kill the tree.
What You Can Do
The first step to controlling the disease is to prune, remove and destroy all diseased wood. However, pruning can also be a means of transmission. It is critical that you sanitize your tools as you prune. After each and every pruning cut, the cutting blade must be sanitized with a 25% solution of bleach and water (1 part bleach + 3 parts water).
Take diseased branches and other wood to the landfill to prevent re-infection. Do not use fire blight-infected wood in mulch, compost or store as firewood or compost materials. Infected branches will continue to harbour the disease and serve as a potential source of re-infection.
Bacteria blight: A similar disease
Not all dead leaves and branches are caused by fire blight. A disease known as bacteria blight is commonly mistaken for fire blight. The symptoms of bacterial blight are somewhat similar to fire blight but can also affect lilacs, cherries, apricots, and other types of flowering trees. Treatment for bacterial blight is the same as for fire blight.
Oystershell scale is an introduced pest in Calgary. It has the appearance of small clusters of oyster-shaped “shells” that cover bark on shrubs and trees.
This pest only reproduces once per year, with the egg hatch occurring in early to mid June over an approximate ten day period. Once hatched, the “Crawlers” feed on fluids found in the twigs and branches; they then permanently attach to the branch, developing a hardened shell that protects them from predators, the elements and most pest-control methods.
Plants At Risk
Fruit trees, lilac, ash, maple, dogwood, poplar, and willow. Oystershell scale is considered a serious pest on Cotoneaster shrub- which is a popular choice for hedges in our city.
Symptoms of infestation don’t usually show up until your shrub or tree is heavily infested, making this a difficult pest to fight. Inspecting plants that are prone to Oystershell is a good preventative measure. Look for branches with oyster-shell shaped bumps, leaves that are turning yellow, and branch dieback or gaps in your hedges.
It's important to act early in the infestation progression as once you can easily notice it, the infestation is usually quite severe. The best defence is to keep up on yard maintenance and inspect your plants for any signs of pests on a regular basis.
What You Can Do
Keeping your garden, including all plants, shrubs and trees healthy, watered and happy is your best first defence. A healthy plant can fight off many pests and rebound from infestations more easily.
When Oystershell scale eggs hatch in early June and become “crawlers”, they are most vulnerable to treatment methods. This stage only lasts for a week to ten days, so it’s important to act quickly:
- Apply a Horticultural Oil (this helps suffocate the “shells”).
- Natural pest control: ladybugs (lady beetles), lacewings and other natural predators are helpful in controlling outbreaks.
- Once dead patches are easily spotted, pruning out affected stems or cutting the entire hedge to ground level is the most effective control. Cotoneasters with healthy root systems will quickly re-grow.
Dutch Elm Disease
Since Dutch Elm Disease (DED) was first introduced to North America from Europe in 1930, it has destroyed millions of elm trees. Alberta is one of the last geographic areas in North America to be free of DED – let’s keep it that way.
Signs of Dutch Elm Disease
Dutch Elm Disease is caused by a fungus (ophiostoma ulmi or ophiostoma nova) that spreads from one elm tree to another by elm bark beetles. Signs of the disease vary depending on the season:
- In the spring, trees will have a few branches with smaller leaves than the rest, or no leaves at all.
- In the early summer, green leaves on some branches will wilt or droop. Some leaves will be shrivelled and brown, and they’ll cling to the branch.
- In the late summer, leaves may be yellow and drooping, a distinct characteristic that is known as flagging. Yellow leaves will also drop prematurely, and succulent branches on the trunk will wilt and turn brown.
What You Can Do
Homeowners in Calgary should be aware of Dutch Elm Disease and take the following steps to help prevent this disease from ravaging our elm trees:
- Adhere to the Provincial elm pruning ban between April 1 and September 30. Pruning should be done when beetles are not active, between October and March. All tools used on diseased trees should be disinfected.
- Elm materials should be disposed of at City landfills – stored elm firewood is an ideal breeding ground for elm bark beetles.
- All trees should be watered every two to three weeks from April to mid-August, then again in the fall before freezing. Trees need much more water than lawns do.
Keeping Alberta Free of Dutch Elm Disease
The province has no native elm trees but; many thousands of elms worth millions of dollars have been planted in Alberta cities, towns and rural landscapes because of their stately beauty, rapid growth, good regenerative capacity, extensive life-span, and ability to survive extreme climate conditions. The City takes several steps to prevent introduction of Dutch elm disease to Alberta, including promoting elm health, promoting awareness of the disease, monitoring elm beetle populations and testing trees for DED symptoms. Sticky panel traps with lures are placed at sites throughout Calgary and checked every 30 days during the summer to monitor beetle populations.
The Alberta Society to Prevent Dutch Elm Disease (STOPDED), in cooperation with Alberta Agriculture, Food and Rural Development, promotes public awareness of DED through media events and trade shows. DED Awareness Week is recognized annually throughout the province from June 24-30.