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Protecting our precious places

Tradescantia control

By Charlie Palmer & Philip Lissaman

Tradescantia fluminensis (wandering willie) is a serious weed in lowland conservation areas throughout New Zealand.

The succulent, ground-hugging stems can form extensive and thick layers on forest floors, even in deep shade. This inhibits regeneration of ferns and seedlings.

The invasion of Tradescantia can be very rapid to the point where no vegetation other than canopy trees and a ground cover of Tradescantia exist. After the eventual demise of the canopy trees there are no seedlings available to replace the forest.

Eradication of this species by hand is possible but even very small fragments either not removed, or dropped during removal can re-establish the infestation. Except for small infestations the use of herbicides is the most effective technique for Tradescantia control in conservation areas.

Research in 1988 in an open space covenant near Hikurangi indicates that Grazon was the most effective herbicide against Tradescantia (Grazon is a trademark of Dow Agroscience (NZ) Ltd).

The research commissioned by the Science and Research Division of the Department of Conservation tested five herbicides or mixtures of herbicides. Grazon had a greater kill and did not require as many follow-up treatments to achieve control as the others.

This research confirmed work by the Department of Conservation on Stephens Island in Cook Strait where Grazon with a penetrant chemical proved to be the most effective of four herbicides trialled at various concentrations, with and without penetrant chemicals.

Several precautions need to be taken to achieve safe and effective results using Grazon against Tradescantia.

  • Deep mats of Tradescantia require a good coverage of herbicide to reach the lower layers. Alternatively spray the top layers; wait for these to die, then treat lower layers.
  • Grazon does not kill rank grass. Where is growing amongst rank grass, it can be beneficial to control the rank grass first with a glyphosphate herbicide.
  • Native species including kaikomako and possibly matai can be very susceptible to Grazon. As with all herbicide use suitable care and attention to reducing spray drift needs to be given.
  • The use of a penetrant appears to increase the effectiveness of Grazon.
  • While most applications of herbicides should be applied during the actively growing period for plants, Grazon in the two trials reported here was effective year-round. This could be a consequence of the mild climates here. Application in spring is recommended in colder southern climes.

Appropriate applications rates vary for different situations, 6ml of Grazon per litre of water (with 20ml of penetrant/15l) has been found reliable in most situations.

Rates as low as 3.3ml/l have been successful in the Stephens Island trial.

Open SpaceTM Magazine No. 46, December 1999 © QEII National Trust

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