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West Coast weed faces onslaught of new enemies

West Coast weed faces onslaught of new enemies

A new attack is being launched on the noxious weed ragwort, which is proving difficult to control on the West Coast. The programme will in time have applications for other parts of the country where the weed is responding poorly to control efforts.

Ragwort (Senecio jacobaea) is prevalent in dairy pastures and on uncultivated land from Karamea in the north to Haast in the south. It can cause fatal liver damage if eaten by cattle and horses. Biocontrol agents like the ragwort flea beetle and cinnabar moth have been released nationwide to attack ragwort plants. But although the beetles and moths have destroyed significant amounts of ragwort elsewhere in New Zealand, they appear not to have made an impact on the West Coast.

The West Coast Ragwort Control Trust was set up by local dairy farmers because they want to improve the control of ragwort. The Trust was successful in getting funding from MAF's Sustainable Farming Fund to further investigate the poor performance of the ragwort flea beetle, and to import two new biocontrol agents from Australia. Both moths are originally from Europe, and their larvae kill ragwort plants by feeding on their roots.

Landcare Research weed researcher Hugh Gourlay says that in the last two years, the amount of ragwort on many farms on the West Coast has increased noticeably, creating an urgent need for better controls.

"The ragwort flea beetle is not adequately controlling ragwort. We think that the beetles do not like the West Coast's wet conditions, but we can only confirm this by finding out how many have survived, and where.

"So far we have found good numbers of beetles at just three of thirteen original release sites on the West Coast."

Mr Gourlay says the next, and most important stage of the work, is to apply to the Environmental Risk Management Authority (ERMA) to import the two new moths, 'host test' them to make sure that they will only eat ragwort, and send them into the field. Farmers who have contributed to this project will be among the first to have the new agents released onto their properties. The final stage of the project will be to make large-scale releases of the moths on a number of sites on the West Coast.

The two moths are known to be better adapted to wet soils and wet climates.

"One of them normally feeds on marsh ragwort, and the other is a prolific breeder, and may build up damaging populations more quickly than the ragwort flea beetle or cinnabar moth.

"The moths are well established and proving to be effective in Tasmania and Victoria in Australia * two states that have similar climates to wetter parts of New Zealand."

Mr Gourlay says subject to ERMA approval, the moths will be introduced into containment in New Zealand by June next year.

"If the moths do well on the West Coast, they will be released into other parts of the country where the ragwort flea beetle has not thrived, in particular Southland, and parts of Otago, Nelson, and Hawke's Bay."

This community project is partly funded by the West Coast Development Trust, the West Coast Regional Council, West Coast farmers, Westland Milk Products, the Department of Conservation, Forest & Bird (West Coast branch), and the New Zealand Landcare Trust.

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