2 April 1999

Phosphine care needed to avoid bug resistance

PHOSPHINE must be used more carefully if it is to remain a valuable fumigant for controlling pests in grain stores, delegates to last weeks Pest-Ventures seminar heard.

Phosphine and methyl bromide are the only fumigants approved in the UK. The latter is rarely used in farm stores, though it is widely used in flour mills. But its withdrawal in 2005 under the Montreal Protocol to protect the ozone layer will leave phosphine as the sole choice here for at least another five years.

Phosphine is a broad spectrum fumigant regarded as a useful backstop to kill insects, mites and rodents when other controls fail. Some suggest its good reputation with grain users means it has a role as a routine on-farm treatment rather as a fire-brigade option when things go wrong.

But already some insects in developing countries have become resistant to phosphine through faulty application by badly trained operators, noted Bob Taylor of the Natural Resources Institute.

Mike Kelly of pest specialist the Acheta Partnership was concerned that without due care the same might soon occur in the UK. "Phosphine will be our standby for years to come. But we need to use it much more carefully." The gas takes time to work, especially in cooler conditions. There were good guidelines from HGCA research to assist operators, but they were largely ignored, Mr Kelly claimed.

Until easier means of topping up the gas to maintain lethal concentrations become available, such as cylinder supplies, sealing remains a big problem, especially in farm stores. "As far as I know no grain is stored on farms in anticipation of fumigation. And phosphine can pass through 2in thick timber in 10mins."

Much more monitoring to detect leaks and insect survival is required. But MAFFs latest guidance notes on using phosphine made no mention of monitoring, said Mr Kelly. "If we do not monitor gas concentrations we are relying on guesswork." &#42

Methyl-bromide

Withdrawal of methyl bromide in 2001, as originally proposed, could have cost the UK milling industry £67m, according the NRIs Chris Collinson. Philip Greenwell of Campden and Chorleywood Food Research Association believes he has identified a viable alternative in NABIM-backed work. "The main problem is going to be lack of funding to take it forward for registration."

PHOSPHINE POSERS

&#8226 Wider use after methyl- bromide ban.

&#8226 Useful back-up when on-farm control fails.

&#8226 Insect resistance widespread overseas.

&#8226 Practical application difficulties.

&#8226 Call for more monitoring of results.