Buddleia

Scientific name: Buddleja davidii
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Fast growing, multi-stemmed, deciduous woody shrub up to 3 m tall
  • Mauve to purple flowers (occasionally white) in large, showy, spike-like panicles about 30 cm long
  • Flowers attractive to butterflies
  • Individual flowers about 5 mm across, mauve or purple, with orange colour inside the petal tube
  • Leaves lance-shaped, up to 20 cm long and 8 cm wide, green and hairless on top, whitish and hairy underneath.

Other similar species present in New Zealand

  • Four other naturalised species are found in New Zealand, the commonest being Buddleja globosa, which has globe-shaped inflorescences and is found in forest remnants near habitations.

Origin

  • Native to China
  • Commonly grown in gardens for its decorative and butterfly-attracting flowers
  • First found growing wild (that is, naturalised), before 1940
  • Now a common shrub in hedgerows, along roadsides, in forests, on river banks and in waste places throughout the country; less common in southern South Island
  • Subject to Pest Plant Management Strategies in several regions.

 Life cycle

  • Small, light seeds dispersed by wind and water
  • Plant can reach maturity and flower within one year
  • Grows quickly and aggressively, and can reach 4 m high after two years; infestations rapidly form dense thickets that out-compete other vegetation
  • Plants are relatively short-lived with infestation densities peaking within 10 years
  • By about 15 years plant densities are reduced, and native trees, if present, eventually dominate again
  • Tolerates frosts and grows well under a wide range of environmental conditions.¬†

Benefits

  • The flowers are attractive to butterflies and gardeners.

Impact on plantation forests 

  • Most important weed in central North Island plantation forestry
  • Reduces growth of plantation species
  • Costs the forestry industry about $2.9 million a year in control and lost production.

Impact on native forests

  • Readily colonises disturbed sites such as slips and stream beds, outgrowing native colonising species
  • Changes plant communities, hinders access and shades rivers
  • Difficult to control where access is difficult and because plants grow rapidly.

Impact on other natural areas

  • In riverbeds, buddleia can change water flow, divert streams, cause silt to build up, and can cause flooding problems
  • Interferes with the regeneration of native species.

Grazing management

  • Leaves are palatable to cattle and goats but not, apparently, to deer.

Physical control

  • Small plants can be pulled or dug out and then mulched
  • Plants that are cut will regrow
  • Shoot or root fragments left on the ground can root and regrow.

Chemical control

  • Painting cut stumps or stems with herbicides like picloram (Tordon), triclopyr or metsulfuron-methyl kills the whole plant
  • Plants with larger stems can be killed by frilling (making deep cuts into the sapwood around the stem) or drilling holes into the wood and then applying appropriate herbicides like glyphosate (250 ml/L) or undiluted Tordon Brushkiller
  • Basal stem treatments with X-tree Basal or triclopyr/diesel mix
  • Weed wiping foliage with glyphosate at 333 ml/L (in February-April) is effective on smaller shrubs
  • Spraygun application in February-April with glyphosate (10 ml/L), metsulfuron-methyl 600 g/kg (5 g/10 L), or Tordon Brushkiller at 90 ml/15 L (knapsack) or 250 ml/100 L gives effective control of larger bushes and infestations.

Biocontrol

  • Buddleia leaf weevil (Cleopus japonicus) was released in New Zealand in 2006
  • Adults and larvae feed on the leaves
  • Leaves with extensive damage become silvery-brown, curl and drop to the ground.

Integrated control

  • Oversowing cover grasses such as Yorkshire fog (Holcus lanatus) can effectively prevent or limit establishment of buddleia seedlings.

  • Popay I, Champion P, James TK 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.
  • Weedbusters, 2016, Buddleja davidii Factsheet (accessed 14 October 2016)