Alternatives for banned substances…adhere to adequate ratios, otherwise pests become resistant


IN 2015, as part of efforts to preserve the ozone layer, countries under the Montreal Protocol agreed to reduce the use of global warming hydrofluorocarbons (HFCs).
Last month, the country joined the world in celebrating the ‘International Day for the Preservation of the Ozone Layer’ with stakeholders calling for the continued phase-out of methyl bromide and methyl chloroform in developing countries.
It has been two years since the implementation of the phase out of methyl bromide and methyl chloroform and efforts continue to be made to ensure the use of alternative methods and chemicals.
HFCs were widely used in agriculture, but they proved harmful to the ozone layer.
Locally, methyl bromide was primarily used in the agriculture sector for soil fumigation, grain storage, cut-flower and tobacco production.
Methyl bromide is a broad spectrum pesticide used in the control of pests, insects, nematodes, weeds, pathogens and rodents.
It was also used for commodity, quarantine treatment, structural fumigation and in shipping.
In Western countries, methyl bromide was used to treat commodities such as grapes, asparagus, logs and other imported goods to prevent the introduction of pests
Methyl bromide is a toxic substance because it dissipates rapidly into the atmosphere.
Human exposure to high concentrations of methyl bromide can cause nervous and respiratory system failures and can harm the lungs, eyes and skin.
In the atmosphere, methyl bromide depletes the ozone layer and allows increased ultra-violet radiation to reach the earth’s surface.
Methyl bromide is a Class 1 ozone depleting substance (ODS) as defined by the Montreal Protocol on substances that deplete the ozone layer.
The amount of methyl bromide produced or imported was reduced incrementally until it was phased out on January 1 2005.
Environment Ministry Ozone Project manager George Chaumba said the country had managed to implement the phase-out.
“We have engaged various stakeholders to help raise awareness on the alternative chemicals or methods that can be used by those in the agriculture sector following the phasing out of methyl bromide,” said Chaumba.
In maize production, methyl bromide was used in grain storage.
“Methyl bromide was used to fumigate grain after harvesting as it was effective in preventing the grain from being destroyed by pests such as the large grain borer,” said Chaumba.
“Farmers are encouraged to use alternatives such as aluminium phosphate found in the form of tablets.
“The tablets are placed where the maize is stocked and they release phosphoric gas which is poisonous and it kills the pests.”
Chaumba said grain treated using this method was not to be used or consumed before seven days.
“Methyl bromide-treated grain could be used after two days,” he said.
“The downside of using aluminium phosphate tablets is that farmers have to adhere to the adequate ratios of administration as failure would mean that the pests become resistant and if the same method is to be used, say after delivery to grain depots, it becomes ineffective.
“If farmers decide to use this method they should do it thoroughly or not treat the grain and leave it for the depots where it will be treated by those with the know-how.”
In tobacco production, methyl bromide was used in seedbed preparation.
“Tobacco seedlings are very fragile and sensitive to pests, so before the ban of methyl bromide it was used to fumigate soils before preparing seedbeds,” said Chaumba.
“Following the phasing out of methyl bromide there was the introduction of float trays for seedbeds where soils are replaced with pine bark treated by other ozone friendly methods. Since no soil is involved, there are no pests.”
In cut-flower production, methyl bromide was used for pest control.
“Flowers continue to be produced in areas such as Juliasdale, Goromonzi and Banket for export to Europe, so farmers have to adhere to the new regulations for their product to meet the set international standards,” said Chaumba.
“As an alternative, farmers have been using steam blown into greenhouses to kill pests. However, this method has proved to be high-cost as it requires a farmer to invest in boilers and pipes for steaming.
“Fuel is also needed to heat the boilers and this has increased production costs. However, efforts continue to be made to find a low-cost and effective alternative to control pests in cut-flower production.”
In Zimbabwe, signs of global warming caused by the depletion of the ozone layer are noticeable, with changes in rainfall patterns.
The rain season used to stretch from early October to the end of March.
These global environmental problems are so closely intertwined that solving one without due consideration for the others would result in catastrophy for the entire planet.
Since Africa does not produce the HFCs, there is need for assistance to phase out consumption and developed countries must take the lead.


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