The Eradication of Cannabis sativa L. with Herbicides in the Hunter River Valley, N.S.W., Australia

Abstract

The presence of Cannabis sativa L. as a naturalized plant in New South Wales was first reported in 1963 when it was found in the Hunter River Valley. Infestations, ranging from isolated plants to dense populations (covering as much as 8 hectares) were scattered over about 3,000 hectares extending for 64 kilometres along the flood plain of the Hunter River.

Details

Author: N. W. VANE
Pages: 49 to 50
Creation Date: 1973/01/01

The Eradication of Cannabis sativa L. with Herbicides in the Hunter River Valley, N.S.W., Australia

N. W. VANE By , B.Sc., Agr.
Regional Supervisor of Agriculture, Department of Agriculture, Mid Coast & Hunter Region, Maitland, N.S.W.

The presence of Cannabis sativa L. as a naturalized plant in New South Wales was first reported in 1963 when it was found in the Hunter River Valley. Infestations, ranging from isolated plants to dense populations (covering as much as 8 hectares) were scattered over about 3,000 hectares extending for 64 kilometres along the flood plain of the Hunter River.

The Department of Agriculture immediately began an attempt to eradicate the plant using the upstream limit of the infestation as starting point for a systematic " search and destroy" operation. A major search was undertaken in mid-summer each year followed by at least one autumn search to locate plants previously missed and late seedlings. Individual plants were pulled by hand, while larger areas were treated with a herbicide mixture.

Time did not permit experiments to be conducted to determine the most efficient herbicides to kill cannabis plants. Accordingly, herbicides which gave a quick kill coupled with some control of emerging seedlings were selected from available commercial formulations.

Initially the following herbicide mixtures were used:

0.1 per cent of 2,4-D * as the dimethylamine salt, or 0.2 per cent of amitrole * with ammonium thiocyanate; and 0.2 per cent of atrazine,* or 0.2 per cent of simazine.*

A granular herbicide was applied where cannabis plants were located alongside agricultural crops susceptible to the above spray mixture. This was also used for small patches as the searchers were able to carry a small bag of granules more readily than a sprayer. Initially this was the commercial product Chlorea (R) which consisted of a mixture of 1.2 per cent bromacil,* 30.1 per cent sodium borate, 38 per cent sodium chlorate and 0.1 per cent 2,4-D as sodium salt.

In 1969 residual herbicides were omitted from the spray mixture and the standard treatment adopted was 0.2 per cent amitrole made from a commercial formulation of 25 per cent amitrole and 22 per cent ammonium thiocyanate. A wetting agent was added to the spray mixture at the rate of one part in three hundred. In the mild climate of the Hunter River Valley cannabis plants persisted through the winter. Plants sprayed during this non-growing season were much more difficult to kill especially with 2,4-D.

* Standard common names are used for herbicides; their chemical names are:

2,4-D - 2,4-dichlorophenoxy acetic acid.

Amitrole - 3-amino-1,2,4-triazole.

Atrazine - 2-chloro-6-ethyl amino-4-isopropylamino-1,3,5-triazine.

Simazine - 2-chloro-4,6-bisethylamino-1,3,5-triazine.

Bromacil - 5-bromo-6-methyl-3-(1-methyl-N-propyl) uracil.

The Hunter River discharges into the South Pacific Ocean at Newcastle, New South Wales

Full size image: 28 kB, The Hunter River discharges into the South Pacific Ocean at Newcastle, New South Wales

Amitrole was more effective as well as safer to use near crops, hence the switch to it as a spray. Also in 1969, the granular herbicide was changed to one containing 2.4 per cent bromacil only.

During the early stages of the campaign, power spray equipment including both boom sprays and spray pistols was used. It was soon found that adult plants were only killed after being thoroughly wetted. When the infestations became smaller, knapsack sprayers were used exclusively and found to be effective. In 1971 and 1972 very few plants were found and it has been possible to remove all by hand.

Within a period of nine years the systematic eradication campaign to control cannabis in the Hunter River Valley of New South Wales has resulted in a reduction of the infestation to the occurrence of only a few seedling plants annually. This campaign has been based primarily on the herbicides amitrole and bromacil. Success was achieved by careful documentation of the infestation and immediate destruction of established plants by the application of effective herbicides, followed by at least two inspections and re-treatments in each season.

The destruction of young plants proved to be an essential ingredient in achieving a satisfactory control of the naturalized cannabis. The major cost in achieving this result has been that involved in locating the plants. Constant surveillance by reliable staff proved to be an essential ingredient for the control of a cannabis outbreak.