Lesser knotweed
Persicaria campanulata, Polygonum campanulatum.
Polygonaceae - Aconogonon campanulatum

What does it look like?

Lesser knotweed is a perennial herb that can grow to 1m tall. The leaves are 8-15cm long and 3-5cm wide and are hairy on both sides. The tips of the branches are also slightly hairy towards the tip and are grooved. The flowers are pinkish or white and grow in bunches.

Why is it a problem?

Lesser knotweed spreads readily from rhizome (root) fragments. In Britain it is a vigorous coloniser that grows in dense patches and suppresses other plants. Lesser knotweed can be propagated from stem cuttings and dividing the underground rhizomes (roots). Its ability to produce viable seed in New Zealand is unknown.In the UK, lesser knotweed is spreading from discarded rhizome (root) fragments. It may be spread inadvertently in soil of garden waste or intentionally, for ornamental purposes.

Control Methods

Physical control

  • Dig out and bury all plant material at least 6 m deep

Herbicide control

  • Stump swab (all year round):   at 250ml glyphosate (360g/l) + penetrant per 1L water or 5g metsulfuron-methyl (600g/kg) per 1L water or 200ml triclopyr (600g/l) per 1L water.
  • Stem injection (all year round): 5ml per stem of 50g metsulfuron-methyl (600g/kg) per 1L water. 
  • Spray (spring-autumn): 200ml glyphosate + penetrant per 10L water or 5g metsulfuron-methyl (600g/kg) or 6ml Tordon Brushkiller per 1L water or 6ml triclopyr (600g/l) per 1 L water. Add penetrant.

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

Related Links