Alnus glutinosa

Alder

Also known as:

Common alder

Family: Betulaceae

Origin: Eurasia, North Africa

A cluster of cones on an alder tree that stands next to a lake.
Female catkins, once pollinated, develop into woody green cones.
Photo credit: Paul Wray, Iowa State University, Bugwood.org

Regional Pest Management Plan (RPMP) status

  • Whole region — Sustained control
  • Hauraki Gulf Controlled Area Notice pest

View more about the RPMP statuses

General description

Deciduous tree < 15 m tall. Bark is fissured. Leaves are toothed and oblong. Buds and young leaves are slightly sticky with resinous gum. Male catkins are borne in clusters. Female catkins are also borne in clusters, and they mature to cones and persist on the tree following dehiscence.

What you need to know

To help protect our environment, from 1 September 2022, you:

  • will not be allowed to breed, distribute, release or sell alder within the Auckland region.
  • will not be allowed to plant alder within the Auckland region, unless you are transferring an existing plant on your land to another location within the boundaries of the same property.
  • must destroy any alder on land that you occupy if it has been planted in breach of the above rules and you are directed to do so by an authorised person.

Habitats

Wetlands, riparian areas, open and disturbed areas, damp ground.

Dispersal

Seed dispersed by wind and water. Vegetative spread from suckers.

Impact on environment

Restructures riparian and wetland plant communities. Nitrogen fixer. Leaf litter in waterways can alter oxygen and nitrogen levels and affect stream invertebrate communities. Dense stands may restrict access to waterways. Pollen may be allergenic.

Control

Site Management

Always treat standing plants, do not cut down as all stems will regrow. Allow to fully die before felling if required.

Recommended approaches

Physical control

Method: Dig out.

Plant parts requiring disposal: All parts.

Disposal options: Remove to greenwaste or landfill.

Biocontrol

Biocontrol is currently not available for this species.

Community agrichemical control recommendations

Certified Handler/Experienced agrichemical user: Drill and inject trees with 750ml glyphosate green and 10ml penetrant per 1L of water, if safe to do so. Drill 18mm holes (tangentially angled downwards) in a spiral up the trunk.

For 50mm stems drill one hole. For 100mm stems drill two holes. For larger stems drill holes 150mm apart. Foliar spray seedlings with 200ml glyphosate green per 10L of water and 20ml penetrant.

Safety notes

Large trees must not be drilled that are closer than 1.5 times the height of the tree from paths, walkways and property.

Trees over 4 metres in height should be treated and then removed by a qualified arborist.

Caution: When using any herbicide or pesticide please read the label thoroughly to ensure that all instructions and safety requirements are followed.

Long catkins on an alder tree.
Alders have narrow yellow male catkins that are made up of many flowers and dangle from branches.
Photo credit: Paul Wray, Iowa State University, Bugwood.org
A catkin hanging from the tip of a branch with other little buds of the alder tree.
Alders are deciduous and moderately fast growing.
Photo credit: Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database