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Guide for Bronze Leaf Disease Treatment

trees affected by bronze leaf disease

Bronze leaf disease (BLD) is a fungus that infects various poplar species and hybrids; specifically trembling aspen, Swedish columnar aspen and tower poplar. BLD is relatively new to Calgary, Edmonton and Western Canada, and can kill an infected tree within three to five years of initial infection. Taking preventative actions, early detection, and understanding treatment options can save trees and mitigate the risk of widespread infection. Here’s what you need to know.

Bronze leaf disease, also called BLD, is an emerging threat to Alberta trees. The fungus infects and kills various poplar species, including:

  • Trembling aspen
  • Tower poplar
  • Swedish columnar aspen
  • Balsam poplar
  • Eastern cottonwood

There are currently no known chemical controls for bronze leaf disease, so early detection and treatment are essential.

Symptoms of Bronze Leaf Disease

Knowing the warning signs of BLD is crucial for early detection and treatment. Here are some of the symptoms to watch for.

  • Diseased leaves often first show up in the lower two-thirds of the tree. They may sometimes be scattered throughout the crown or isolated to a few branches.
  • Leaves become dark reddish-brown, chocolate brown or bronze, although the veins and the leaf stem may remain green for some time.
  • Infected leaves remain on the tree through winter.
  • Once the disease spreads, browning may be observed under the bark of diseased branches.
  • New leaves on infected branches may appear underdeveloped in subsequent years.

How Does Bronze Leaf Disease Spread?

Bronze leaf disease is one of many aspen and poplar tree diseases caused by a fungus. It spreads from one tree to the next via airborne spores. The spores survive the winter inside structures attached to overwintering leaves. The spores are released from their pods between April and June when rainfall is present and daily temperatures average 18 degrees Celsius. The spores land on and infect a tree and move into its vascular system, which is why bronze leaf disease treatment is so challenging.

Bronze leaf disease can also spread from one tree to another via infected debris and branches.

How to Prevent and Manage Bronze Leaf Disease

There’s no chemical treatment for BLD. That’s why it’s vitally important that you remove infected branches immediately and dispose of them properly. Follow these steps at the first sign of infection:

  • Sanitize your tools between every cut. Soak them in a 10% bleach or 70% rubbing alcohol solution for one minute.
  • Collect materials from diseased trees and take them to a municipal landfill.
  • Do not compost, chip or use this material for firewood. The spores can easily spread to other trees.
  • Carefully clean all tools and remove all debris from the ground.

Tree tip: Regular maintenance and tree care will strengthen your trees to resist disease and fight infections. Routine care goes a long way to ensuring good tree health.

Does My Tree Have Bronze Leaf Disease?

Below are the typical symptoms of bronze leaf disease during all four seasons. This information is for reference only. If your tree displays any of these symptoms, it may be infected. Contact your local tree care professional for diagnosis and treatment information.

  • Leaves will remain on an infected tree. They’ll have a brown or bronze colour.
  • Already-infected branches may grow new, stunted leaves. These leaves may appear underdeveloped, but their colour will have a normal green colour.
  • An infected tree will produce regular-sized, healthy green leaves that will become infected by spores from previously infected leaves on the same tree. After it becomes infected, the stem and leaf veins of the regular-sized leaves will remain green while the rest of the leaf progressively turns brown or bronze. Eventually, the infected leaf will turn colour.
  • A localized infection will be evident. The tree will display a combination of both healthy and infected branches. Healthy leaves will fall, and infected leaves will remain on the tree.

Be aware that the colour of infected leaves varies from very bronze to chocolate brown to dull brown.

How Do I Report a Confirmed Case of Bronze Leaf Disease?

Phone 311 or 403-268-CITY (2489) if calling from outside Calgary, complete the 311 Online Contact Form or contact ArborCare® at our Calgary (403-273-6378) or Edmonton (780-413-9319) offices, or toll-free at 1-800-645-6533.

Collaboration between municipal governments, citizens and tree care professionals is required to make sure BLD does not become widespread. Parks officials want to know about all confirmed cases of BLD in privately owned trees.

Please help us understand the scope of BLD in Calgary and help keep our urban forests healthy. Report any confirmed cases of BLD.

Tree Disease Management in Calgary and Edmonton

At ArborCare, our trained and experienced arborists can identify bronze leaf disease, plus other poplar and aspen tree diseases, and then recommend the best treatment. Contact us today to book an appointment.

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