6 April 2011

As large patches of buddleia are reduced to bare stems throughout the region, forest growers and biosecurity managers are applauding the miniature culprit responsible for the damage.

The Chinese weevil, Cleopus japonicus was released in 2006 by Crown Research Institute Scion as a sustainable weed control measure.

Scion identified the Cleopus weevil as a suitable candidate for biological control because it eats buddleia and nothing else.

Since their release, the weevils have proceeded to strip buddleia bushes of their leaves.

Scion scientist Michelle Watson says this is exactly how biological control is supposed to work.

“The weevils are achieving similar damage to herbicides in late summer to autumn, but without the need to spray,” she says.

“We are getting reports from all over the Bay of Plenty that the weevil is spreading naturally and doing a great job of defoliating buddleia."

Michelle says the most enthusiastic reports are coming from forest managers.

“Buddleia (Buddleja davidii) is one of New Zealand’s worst forestry weeds, costing the forest industry an estimated $3 million annually in lost production and control costs, so the weevil is very welcome.”

Not only is the weevil helping forest growers, it is also helping managers of public land.

Bay of Plenty Regional Council’s Land Resource Manager (Rotorua), Greg Corbett, says weevils are spreading widely throughout the region and causing significant feeding damage to buddleia plants on roadsides and riverbanks.

“This is very promising - if the weevil continues to thrive, buddleia may cease to be such a serious and costly weed in New Zealand.”

Buddleia was originally introduced to New Zealand as an ornamental plant and became a virilent weed due to its rapid growth rates and ability to colonise bare soil.

People who have various species of buddleia growing in their garden are likely to notice weevil damage.

These plants can be protected using standard pesticides if people want to retain them for ornamental purposes.

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