Weeds, pests and diseases

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The Town of High River uses an Integrated Pest Management system to control weeds and pests throughout the community. This is a decision making model used to prevent and manage pest problems using a variety of methods to manage infestations.

Cosmetic Weeds (Dandelions)

Dandelions are considered a cosmetic weed. Typically, the Town controls dandelions in the cemetery, sports fields and high profile parks and greenspaces. Thresholds of dandelions are monitored in all parks and greenspaces and controlled accordingly. Many municipalities are eliminating or reducing the spraying of cosmetic weeds. Tree Canada has issued a statement asking residents not to spray dandelions to help increase bee populations. The Town of High River uses best management practices when determining areas of control.

Noxious Weeds

Noxious weeds must be controlled and Prohibited Noxious weeds must be destroyed, under the Alberta Weed Control Act. The Agricultural Pests Act and Regulations empowers municipalities to appoint inspectors to carry out the requirements of the Act and regulations. The Town of High River has a Municipal weed Inspector as appointed by Council and enforcement is carried out through the Towns’ municipal bylaw services.

For common pests please visit the Alberta Invasive Species Council website for fact sheets and other resources. If you suspect an infestation please contact the Town of High River.

For information on Dutch Elm Disease see the urban forest tab and visit: www.stopded.org

Fact Sheets

European Elm Scale

What is it?

It is a soft scale insect which feeds on Elm species. Feeding damage from this insect includes stunted, chlorotic foliage, premature leaf drop and branch dieback. Black sooty mold growth on honeydew on tops of branch gives trees an overall black appearance.

Signs and symptoms

Often first noticed on urban Elms when honeydew produced by feeding scales becomes a nuisance on parked cars or outdoor furniture. Branches on infested trees are typically blackened by sooty mold growing on the honeydew. Closer examination reveals female scales, which appear as grey or reddish brown discs surrounded by a white waxy fringe.

What to do

Keep your Elms healthy:

  • Water regularly especially during drought times(includes mature trees)
  • Protect roots from damage (i.e. compaction)
  • Mulch area around the tree

*If your tree is showing signs from European Elm scale, contact an ISA Certified Arborist. Severe infestations may require a chemical application.

What is it?

Black knot is caused by the fungus Apiosporina morbosa and is a very common disease in various species of Prunus. This includes both ornamental and fruit bearing species such as the Mayday tree, Amur Cherry, Schubert Choke-cherry etc.

Signs and symptoms

  • Early stages are a small olive-green gall or swelling on the new growth of a tree.
  • Swelling will grow until mature after 2-3 years and will result in black, tar-like swellings (galls).
  • Mature galls produce and release a vast amount of spores during the bloom period, resulting in a rapid increase in infections. These spores are spread by wind and rain.
  • If the knot circles the entire circumference of the branch, the branch will die. In addition, if a tree is severely infected the disease can eventually kill a tree.
  • One diseased tree can contaminate an entire neighborhood

What to do

  • Prune any infected branches during winter or very early spring when plants are dormant and the disease is easy to see.
  • Prune branch 15-20 cm below any visible swelling.
  • As a precaution ensure pruning tools are disinfected between cuts.
  • Diseased wood must be destroyed immediately (burned, buried or removed from site)
  • Diseased knots can produce and release spores for up to 4 months after removal.
  • Ensure plants are healthy and free from stress (not a guarantee from disease)
  • If caught early enough, Black Knot can be controlled by regular monitoring, pruning and destroying the affected branches.

What is it?

DED is caused by a fungus that blocks the water conducting vessels of an Elm. The fungus is spread by an Elm Bark beetle which comes in contact with infected wood and then feeds and overwinters on a healthy elm.  Alberta is currently Dutch Elm Disease Free.  No cases have been found in our Province.

Signs and symptoms

The leaves of an infected Elm will wilt, turn yellow then curl and turn brown. Brown leaves will remain on the tree throughout winter. Infection later in the summer can cause leaves to turn yellow and fall prematurely.

What to do

Keep your Elms healthy:

  • Water regularly especially during drought times(includes mature trees)
  • To help keep Alberta free of the disease, Elm pruning is not permitted from April 1 to September 30. Elm bark beetles (EBB), the vectors of DED are active between these dates and can be attracted to the scent of fresh cuts, possibly infecting a healthy tree. Once an elm is infected with DED it will die within a year.
  • Keep your Elms free of deadwood and broken branches
  • Proper pruning techniques performed by qualified personnel are essential in maintaining a healthy Elm population. Topping or removing an excessive amount of live wood is not recommended on any variety of trees and will weaken a tree’s structure. Disinfecting tools and properly disposing of Elm wood either by chipping or landfill is an important practice that will also aid in preventing this disease.
  • Do not transport, use or store Elm firewood