Boxthorn

What does it look like?

Boxthorn is a densely branched, erect, evergreen shrub that grows to 6 metres tall. It has tough, woody stems alternately branched at square angles, forming a box-like pattern, with rigid spines. Hairless, fleshy, bright green leaves (40 x 12 mm) are narrow, oblong and clustered along the stems. White to pale mauve flowers (10-13 mm) are produced from July to March, followed by tear shaped orange red berries (5-12 mm) in autumn.

Why is it a problem?

Boxthorn is weedy as it forms dense, tall, long-lived stands, excluding most other vegetation. It tolerates a wide variety of soil types (sand to rocky cliffs), drought, salt, wind, and hot to cold temperatures. It’s poisonous (usually not grazed). It aggressively colonises high light areas, particularly sand dunes, estuary margins, other coast areas, and limits access for recreation.

Control methods

Physical control
Hand pull seedlings, winch out larger plants (all year round). Plant material can be left on site to rot down.

Herbicide control
Stump swab (all year round) using glyphosate (200ml/L) or a product containing 100g picloram+300g triclopyr/L (200ml/L). Or, Injection method: Drill holes sloping into the sapwood at regular intervals around the tree. Inject glyphosate (250ml/L) or a product containing 100g picloram+300g triclopyr/L into holes, undiluted. If necessary, wait until the liquid subsides then apply the remainder. Or spray (all year round) using glyphosate (10ml/L + penetrant). Preferably treat coastal sites after rain to lessen effect of salt on herbicide. Total coverage is needed.

CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and safety requirements are followed.

More information

Boxthorn is widespread in Hawke’s Bay, particularly in coastal areas.

Related links

• New Zealand Plant Conservation Network - Boxthorn
• Weedbusters