Grey willow

Deciduous shrub or small tree around 7m tall with petal-free flowers. Grey willow displaces native species and alters waterways by blocking or flooding.

Description

• Stems are grey/green and hairy or red/dark purple and smooth.
• Leaves are oval-like and narrower at the base, less than 7 x 3.5cm.
• Flower clusters with no petals (catkins) are cylindrical and appear before leaves.
• Seed is wind dispersed. Vegetative spread from stem fragments and suckers, dispersed by water.
• Human-mediated dispersal through deliberate plantings.
• Habitats include wetlands, water bodies, water body margins, swamps, and wet areas behind coastal dunes.

What you need to know

Grey willow replaces native vegetation in riparian sites and grows into dense (often pure) stands. Thick canopies can reduce light penetration and limit the growth of understory species. It can also cause blockages, flooding, and structure changes in waterways.

Management approach

Grey willow is declared an unwanted organism by the Ministry for Primary Industries (MPI) because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.

These species pose a high risk to our environment, economy, recreation, and cultural values.

Rules

Any species declared a pest, including unwanted organisms, cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread.

Consider removing these invasive species from your property and consult your local council for appropriate disposal. Consider lower-risk alternatives for your garden, such as native plants.

Control

Site management

Follow up treated areas three times per year. Encourage natural regeneration of native plants or replant treated areas where possible after two to three treatments to establish dense ground cover and minimise reinvasion.

Physical control

Dig or pull small plants out.

Plant parts requiring disposal: all parts.

Contact your local council for appropriate disposal locations.

Chemical control

Cut plant close to the ground and immediately treat the stump with herbicide gel containing glyphosate or picloram.

Basal spray with X-Tree Basal - apply from the ground to a height of six times the diameter of the tree, ensure the base is thoroughly covered at ground. Suitable for trees up to 20cm in diameter.

Drill downward sloping holes around the circumference of the trunk about 8-10 cm apart. Fill with neat glyphosate, 250ml glyphosate (120g/L) or 20g metsulfuron-methyl (10g/L) per 1L of water.

Foliar spray with 20ml glyphosate plus 2ml penetrant per 1L of water.

Foliar spray with 0.5g metsulfuron-methyl plus 3ml penetrant per 1L of water.

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