Methyl Bromide: its use in keeping Australian strawberries clean

Yes, methyl bromide is a very effective fumigant and ozone depleter, but it’s playing a big role in keeping Australia’s strawberries disease-free.

“The strawberry fruit industry has absolutely nothing to do with methyl bromide. Absolutely nothing,” says George Weda, managing director of Toolangi Certified Strawberry Runner Growers Cooperative in Victoria.

“We are strawberry plant propagators; we grow strawberry plants and as part of that production cycle, we use a fumigant called methyl bromide. We use that under a Critical Use Nomination, from the United Nations, The Montreal Protocol,” Weda says.

Recent attention on the use of the fumigant in the Toolangi region has led some to assume that the strawberries, too, must be toxic.

But the gas is being used to fumigate the soil and is not used on the strawberry fruit.

“Methyl bromide is only used to fumigate the soil prior to growing the strawberry mother plants that produce the runners, which are then bare rooted and transported to another site to replant, which will, some 6 months later bear marketable fruit, the whole process takes over 18 months from the time of the soil fumigation,” says Kevin Bartolo, Australia/Pacific Region manager for Mebrom. Mebrom is one of the companies that imports methyl bromide into Australia for Quarantine and Pre-shipment use only, which is exempt from any bans or restrictions under the Montreal Protocol.

“So there’s no connection between methyl bromide used under the Critical Use Exemption to fumigate the soil for runner production and the fruit itself. Absolutely none,” he says.

“Under normal circumstances, methyl bromide doesn’t taint food. There are set Maximum Residue Limits (MRLs) and technically those limits should never be breached because we’ve found that you would probably have to treat at relatively high dose rates, three times, before you even start approaching those MRL limits. Realistically, you only have to treat once with methyl bromide.”

In the case of the Toolangi certified strawberry runner growers, Weda says licenced contractors are brought in for the fumigation around April/May.

Once the gas is injected into the soil, it is immediately covered in plastic, trapping the gas. The gas then kills off soil pathogens and breaks down. After a week or so, the plastic is removed.

“To be absolutely on the safe side, within two or three weeks you could plant stuff in and it would grow, but if you were to pull the plastic off and plant immediately afterwards, there’s still residues in the soil and it would kill your plant,” Weda says.

The soil is then left until about August/September, when the strawberry “mother plant” is planted.

Those plants then grow and produce strawberry runners. One mother plant might make 100 “daughters” (the plants that come from strawberry runners) and those daughters are harvested the following April. Those plants are then sold to the fruit growers, who plant them in April/May and they will then get fruit from those anywhere from two months later.

Methyl bromide and the environment

Methyl bromide is an extremely effective broad spectrum fumigant which is used to treat against pests and diseases such as bacteria, fungi, nematodes and insects.

But is also very effective in destroying stratospheric ozone. In fact, it is 60 times more effective than the other major ozone depleter, stratospheric chlorine.[1]

Under the Montreal Protocol, Australia agreed to phase out methyl bromide. From 1 January, 2005, all uses of the chemical, other than for quarantine and pre shipment (QPS) or feedstock applications were prohibited in Australia. However, some 'critical use exemptions' have been allowed by the Montreal Protocol on Substances that Deplete the Ozone Layer and can be granted to sectors where there are no technically or economically feasible alternatives to methyl bromide.

And that’s where the strawberry runner growers at Toolangi, in Victoria's Yarra Valley come in. Each year the strawberry runner growers have to apply for critical use exemption.

The strawberry runners in the Yarra Valley are planted in a very heavy soil and according to Bartolo, “to date, there are no registered fumigants out there that have proven to be totally effective. It’s used on the soil only, to control macrophomina and fusarium and other fungal diseases primarily, plus if there happens to be nematodes there and exerts good control on those diseases which, if not controlled, they would literally decimate the industry.” 

The remainder of methyl bromide use in Australia is under quarantine direction on items such as imported or exported grains, imported fruit and timber, where there is deemed to be a quarantine risk.

Why not phase it out completely?

While there are alternatives to methyl bromide, they are not as effective.

“A lot of countries around the world are signatories to the Montreal Protocol so they’ve undertaken to phase out methyl bromide when a suitable alternative for each industry can be identified and used,” Weda says.

“We’ve been looking for over 15 years now…all around the world the strawberry fruit growers and the strawberry runner growers have been looking for alternatives and there isn’t one out there which is as good as methyl bromide, so we can still use it under this critical use nomination.

“If they were to take it away from us tomorrow, we just would not be able to produce the healthy plants that we do now, which means yields would go down, which means we couldn’t supply the fruit growers with a top class, A-grade, healthy plant. It would have some disease on it because there’s nothing else to control the disease like we’re doing now.

“The fruit grower would get those plants already with some level of disease in them so therefore their production would go down, and there’s potential we would get more imports from overseas. Fruit would have the potential to come in from overseas and ironically, most of those strawberries would have been grown on fumigated soil with methyl bromide.”

One alternative to methyl bromide for soil fumigation doesn’t work in heavy soils.

“For the strawberry runner producers there’s not much point in applying a chemical if it’s not going to work in heavy soils,” Bartolo says.

“You’ve got to balance the good with the bad. It’s no good looking at something and saying ‘that’s toxic’ and it’s a dangerous chemical. Well unfortunately, if you want to kill bacteria, diseases, insects and nematodes, you’ve got to have something that does kill. At this stage there isn’t much of an option. People are looking at other options but over the 20 years there have been lots that have come and gone…but the reality is, sooner or later along the line, resistance raises its head. Once you have resistance issues for a given chemical, it ceases to be fully effective.

“At the current stage, without there being a viable alternative, which the chemical industry have been looking for a viable alternative for 20 years now, [a complete phase out] would probably lead to an outbreak or spread of macrophomina and fusarium, wilt diseases in strawberries, which would literally decimate the industry. It basically would take them to the point where they would lose viability and probably end up destroying the industry.

“It’s a matter of balancing the good that methyl bromide has done against the environmental consequences. We know now that the environmental consequences are minimal,” he says.

According to a CSIRO report (Methyl Bromide: Past, Present & Future Impacts on Stratospheric Ozone) provided to Food Magazine by Bartolo, future regulation of the remaining methyl bromide production/consumption in fumigation will have little impact on ozone recovery.

The report suggests that if as of 1 January, 2015, there was zero production or emissions of methyl bromide from fumigation, the ozone would recover to 1980 levels just one year earlier than predicted if the QPS levels remained constant.

Historically, the largest man-made source of methyl bromide is from fumigation, where about 50,000 tonnes per year were emitted to the atmosphere between 1995 and 1998 from non-quarantine/pre-shipment (non-QPS) methyl bromide use (80 percent of which was largely from soil fumigation) and QPS use (20 percent: largely grain and wood products fumigation at pre-shipment). But since the introduction of the Montreal Protocol restrictions on the consumption of methyl bromide for non-QPS use, this total fumigation source reduced to about 10,000 tonnes by 2012.

While reductions in future total emissions of all ozone depleting substances could significantly hasten ozone recovery, methyl bromide will play a minor role.

It has both man-made and natural sources and according to the report, the scientific understanding of the global methyl bromide budget is not balanced, with current identified sinks (which absorb or break down the chemical) exceeding current identified sources by over 30,000 tonnes – nearly 40 percent of all identified sources. This imbalance has persisted from pre-Montreal Protocol phase-out to recent times (2012), implying there are unidentified, probably natural methyl bromide sources.

“Methyl bromide traditionally, and continues to be the mainstay and one of the most potent weapons against exotic disease incursions, so in other words they’re protecting Australia and Australia, like America and like New Zealand are relatively young countries that don’t have a lot of the diseases that exist in some of the more well-established continents…so we’ve got a lot more to protect,” Bartolo says.

“Virtually all the ozone depletion gains have been courtesy of the reduction of fumigation using methyl bromide but now we’re down the stage where it nearly makes no difference.

“It doesn’t make sense, especially when people’s livelihoods and Australian trade [is on the line]. Our image is clean and green because we haven’t got a lot of diseases and insects and organisms that they have overseas, if we didn’t have methyl bromide, we wouldn’t be able to make that claim.”

[1] P. Fraser FTSE, N. Derek, P. Krummel & Dr P. Steele. (2014). Methyl Bromide: Past, Present & Future Impacts on Stratospheric Ozone, CSIRO Oceans and Atmosphere Flagship.



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