New Weapon Targets Weeds in Sensitive Sites

Forest and Bird, Issue 299, 1 February 2001, Page 8

New Weapon Targets Weeds in Sensitive Sites

— Helen Percy.

ortResearch scientists have developed a new weapon in the arsenal for anyone battling invasive weeds in ecologically sensitive areas. The herbcide is in the form of a gel which is applied directly onto the cut stem of the weed, thus avoiding problems of spray drift and the contamination of soil and adjacent plants. In trials funded by the Department of Conservation, close to a 100 percent kill rate has been achieved on old man’s beard Clematis vitalba, Japanese honeysuckle Lonicera japonica, climbing spindleberry Celastrus orbiculatus, and grey willow Salix cinerea. No regrowth was detected when the plants were reassessed two years after the first application. Just as importantly, no damage was observed on surrounding native trees.

Subsequent HortResearch trials on a wide range of other weed species (including kahili ginger, gorse, Darwin’s barberry and elaeagnus) are showing equally promising results. Known commercially as Vigilant, the gel contains five percent picloram as the active ingredient — a level that ensures effectiveness yet is of low toxicity. Department of Conservation staff and volunteers were equally successful in obtaining the high kill rates using the gel technology, which does not require a special licence to use. Stems and vines are cut with secateurs or pruning saw some 50-100 millimetres above the ground. The gel is then applied directly from the bottle to cover the entire surface of the cut. The gel can be used throughout the year, although

effectiveness may drop off slightly in colder months and cooler climates. On fine warm days the gel is absorbed into the treated plant over two to four hours. In cooler locations of New Zealand, for example, Stewart Island, the gel may take up to two days to be absorbed by the cut stem. The gel is not totally rainfast, so application during rain is not recommended.