Methyl Bromide - the Alternatives for Horticulture
The New Zealand horticulture industry will use about 60 tonnes of methyl bromide during 2001. It is an effective broad-spectrum pesticide that has been used for many years in the agricultural industry, yet globally its use is being phased out. Jim Maud looks at why methyl bromide is a problem and what pesticide alternatives are being developed to replace it.
Horticulture in New Zealand is dependent on soil sterilisation to control pests and weeds. Of the total methyl bromide used in horticulture, approximately 65 percent is consumed by the strawberry industry and lesser amounts by the apple, tomato and cut flower industries. In total, New Zealand will use about 130 tonnes of methyl bromide this year (including the 60 tonnes used in horticulture), a fraction of the world consumption, estimated to be around 63,000 tonnes per annum.
Methyl bromide is considered to be the most effective general use broad-spectrum pesticide available. When used as a soil fumigant, methyl bromide is injected into the soil at a depth of about 20 to 30cm before the crop is planted. Covers may be used to retain the gas. Row or blanket fumigation techniques can be used depending on the crop to be planted. This application will effectively sterilise the soil, killing the vast majority of soil organisms. Over the first few days following fumigation 50 to 95 percent of the methyl bromide escapes into the atmosphere.
As a result, it has come under scrutiny from environmental scientists in the last 15 years because of the damaging effect it has on the ozone layer. It has been grouped with fluorohydrocarbons as one of the most ozone-destructive gases (although recent studies in the US have tended to lower its ozone-depleting potential rating compared with original assessments). These gases can rapidly escape into the upper atmosphere where they remove ozone and contribute to the formation of ?holes? in the ozone layer. Damaged parts of the ozone layer let in harmful radiation, which significantly reduces the burn times of skin exposed to direct sunlight. Agricultural crops can also be affected by this radiation.
There are natural sources of methyl bromide release including net releases from oceans, soil and plants. It is however generally agreed that methyl bromide added to the atmosphere as a result of human activity can significantly upset the delicate environmental balance in the stratosphere.
Because of its ozone-depleting properties, methyl bromide is being phased out under the Montreal Protocol - an international treaty established in the late 1980s with over 160 countries signed on as parties. New Zealand is a signatory and meets its treaty obligations through the Ozone Layer Protection Act 1996. The Protocol controls the manufacture and phase-out of all ozone-depleting substances on a global basis. The phase-out process for general use is being undertaken in a step-wise fashion with the 2001 consumption level now down to 60 percent of what was consumed in 1991. The figure for 2003 will be 75 percent of the 1991 consumption, with a complete phase-out by 2005. Methyl bromide use for pre-shipment and phytosanitary purposes is presently exempt from the phase-out programme, although capped at 1996/98 usage. General use by developing countries is controlled by a longer phase-out programme.
There is considerable concern among general users, including horticulturists, that a cost-effective and environmentally acceptable replacement for methyl bromide will be difficult to find before the end of the phase-out period. Research is underway, however, to find alternatives. Soil sterilisation trials using steam have proved just as effective as methyl bromide and reportedly at less cost. Fumigators in New Zealand are mixing chloropicrin with methyl bromide in an effort to minimise methyl bromide consumption. Possible chemical alternatives include 1,3-dichloropropene, basamid®, chloropicrin, metam sodium, selective contact insecticides and fungicides. Organic amendments, crop rotation, plant extracts, changed management practices, changed cultural practices, heat, biological controls, and plant breeding are all possible non-chemical alternatives. However depending on the crops to be treated and the pests requiring control, alternatives will most likely involve a combination of both chemical and non-chemical controls.
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Jim Maud Senior Policy Analyst, MAF Policy Information Group Rotorua Jim is a professional forester with over 40 years experience in forest management, processing and marketing. His experience includes the use of methyl bromide for structural, phytosanitary and preshipment treatments. He has worked in both private enterprise and government forestry organisations. |
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Amber Duncalfe
Editor - RM Update
Ministry of Agriculture and Forestry
PO Box 2526
Wellington
NEW ZEALAND
Tel: +64 4 894 0710
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