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  • Writer's pictureAaron Cull

Common Tree Diseases in Calgary

Updated: Apr 5

The Arborists at Evergreen Lawn Services Ltd. have noticed a significant increase in the prevalence of disease on trees this year. The extreme drought this summer has put considerable stress on the variety of cultivars leading to an increase in sickness. Outlined are 4 common tree issues and treatment to consider.

1. Black Knot Fungus on Schubert Cherry & Mayday Trees:

Tree Diseases in Calgary

Often this problem is referred to as ‘poop on a stick.’ Scientifically it is referred to as black knot fungus and the spores infect other trees of the same species primarily Prunus virginiana & Prunus padus. The spores are carried airborne or on the claws of birds who land in close proximity to a branch infected with it. How to Limit? The Best treatment is to cut it out immediately. Pruning it off at the trunk or where a branch forks out is the best method to prevent the spread. However, once a tree is infected, the fungus is harbored within and will be susceptible to further outbreaks. If the Fungus is left for too long, structural damage will result and the entire tree may need to be removed. Our Arborists at Evergreen are qualified to tackle any job with Black knot. All cutting tools are cleaned before & after use to prevent the spread. As well, specialized tree paste is used to seal up any open wounds which may result from cutting the portions out.

2. Aphids on Poplar & Aspen Trees:

Aphids are a common pest which infect a variety of tree species in Calgary including Birch, Willow, Maple, Mayday & Poplar trees. They are pear shaped and the ones usually seen here are black or grey. A tell-tale sign are 2 tiny colorful appendages protruding from the back known as cornicles. Majority of clients have been surprised by the abundance of aphids on Poplar trees coming into the fall months. Let’s explain! When Poplars/Aspen trees are stressed most often due to extreme heat, cankers form on the trunk where the sun is most highly concentrated. This causes an initial sunburn to form and if persists leads to a full blown open wound (canker). Once an open wound is present sap starts to ooze and run down the bark. Sap contains carbohydrates which aphids of the genus Chaitophorus or Periphyllus are attracted to and feed on. Due to the abundance of sap & the inability of aphids to fully digest it, an amount flows out onto their backs. In-turn yellow jacket wasps feed on this substance called ‘honeydew’. One of the reasons why there are swarms of wasps around Poplars/Columnar Aspens. Extra sap can also buildup on the leaves leading to their shiny appearance and sticking together. How to control an outbreak? First line of defense to prevent aphids from congregating is to be proactive and keep trees healthy. An organic fertilizer is best to be applied in the Spring to promote healthy growth and fall to protect the roots from overwinter temperature fluctuations. However, if you notice an open wound, it is important to seal it with a variety of natural sealants you can purchase at a specialized garden store and then wrap it. If Aphids do begin to congregate in numbers, spraying the tree with a mixture of a tablespoon of soap and 1 liter of water. Insecticidal soap can be used or dormant oils can be applied over winter to suffocate any eggs and preventing their life cycle from continuing. If left untreated, nutrients in the sap cannot pass up through the vascular system of the tree leading to structural integrity being compromised & eventual demise. Consult our team at Evergreen to assess an effective treatment plan for higher canopy trees

3. Leaf Miner on Birch Trees:

Birch Trees

Leaf Miner have been decimating Birch (Betula) trees in Calgary and Flowering Crab Apple’s to a lesser extent. The most common sign a tree is infected is the presence of a tunnel on a leaf or the leaf being half green half yellow. Leaf miner larvae are pale green, stubby, translucent & approximately 1/8”. The adults molt into black or black-yellow flies 1/10”. Adults emerge from overwinter cocoons in early spring & lay eggs on leaves. Leaf miner larvae tunnel/mine leaves of many vegetable crops and trees, predominantly Birch for 1-3 weeks. They drop to the soil to pupate for 2-4 weeks. This life cycle usually continues for 2-3 generations per season. How to restrict an overabundance? The most effective way to prevent an overabundance is to spray with dormant/neem oil around the base of the tree. This needs to be applied in early Spring before the adults emerge and lay eggs. Sticky traps can also be used to trap a portion of the airborne adults but is not a long term solution. If there is an infestation, a consultation with an Arborist/pest control expert will be able to address an application plan and protect your tree from decline

4. Dutch Elm Disease on Elm Trees:

Dutch Elm Disease on Elm Trees

Healthy Elm trees are sadly becoming infected & dying at a significant rate here in Calgary. This stems from the Elm bark beetle which blocks water from flowing up through its vascular system. The beetles creep up the new growth on trees where it will suck sap and drip out a honeydew excrement. A secondary host, sooty mold fungus feeds off the excrement causing a characteristic black stain on the outer sapwood layer. This leads to an ‘oozing drip’ onto anything underneath the canopy in the summer months. As the disease persists leaves wilt and vegetation becomes thinner. Solutions: High pressure washing multiple times with an Insecticidal Soap or Water in the Summer Application of Dormant Oils prior to leaves falling this will suffocate the eggs & prevent re-infection in Spring A Proper Deep Root Fertilization Schedule will help ward off Infestations; we use Organic mixture which is high in Phosphorous & Potassium supporting Root System & throughout Prune Dead portions out ONLY Between October 1st & March 31st to prevent the pheromone release by the beetle that can attract further beetles carrying the disease Water regularly throughout the summer & before a killing frost hits Calgary (-2°C), to encourage sufficient soil moisture in the Spring

Evergreen Lawn Services has arborists and tree experts ready to help you prevent, treat, trim, or if required, safely remove trees impacted by disease or other unhealthy issues. We care about your trees and will do everything we can to restore them to health. Contact us today for a free quote or to discuss your tree questions or concerns.

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