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Willow Threat

The willow sawfly, Nematus oligospilus, which damages tree willow, is spreading south at 200-300km per year.

HortResearch scientist John Charles says the sawfly was first found in Auckland in February 1997, and could reach the Wellington region by 2000 and Invercargill by 2003/04.

The sawfly lays eggs in tree willows, including all hybrids and clones, and the insecticide Btk has no effect on the larvae. The threat is serious, particularly where willows are used in river control and erosion-prone hill country,though conservationists may welcome its effect on invading willows in Waikato wetlands.