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Funding soars as sawfly spreads

Media Release 02/04/01

Funding soars as sawfly spreads

The fight against a pest threatening the country's multi- million dollar willow resource has been significantly boosted by a major funding increase.

Sawfly Larva

Adult Sawfly

Since its discovery in New Zealand, HortResearch scientists have been working on ways to control willow sawfly. A decision by many of the country's regional councils to triple funding for the scheme to $200,000 for the 2000/2001 financial year has meant a more in-depth scientific research programme is now underway.

"This new funding allows us to devote more time to researching the sawfly and it is likely funding will increase again in the next financial year. If this is the case, we will be able to obtain results even sooner," said Tree Breeder Lindsay Fung.

The willow sawfly feeds on the leaves of willows, eventually killing the trees by stunting their growth. It has flourished since being discovered in Auckland in early 1997 and now threatens New Zealand's willow trees which are used for soil conservation, riverbank protection and as horticultural shelterbelts.

Entomologist John Charles is researching the biology of willow sawfly to discover factors that limit the pest's development. He said he hopes to find willow species with chemicals in their leaves that slow down larval feeding, or minimise the numbers of offspring from the adults. Once these chemicals are identified, the aim will be to incorporate them into new varieties of willows.

The sawfly thrives in New Zealand's climate. In four years the pest has infested all of the North Island and Mr Charles predicts it will be established in Invercargill by 2004.

This is the first season where there has been large-scale die back of willows in the worst affected regions of Waikato, the Bay of Plenty and eastern Hawke's Bay. The hot, dry climate in these places means the insect develops quickly. Mr Charles said willow sawfly populations could complete seven generations in a warm year in Gisborne, but would probably only complete two generations at the southern end of the South Island.

While Mr Charles said eradication of willow sawfly is unlikely, a management solution is possible in the long term. "The most likely scenario is that we find a chemical in willow leaves that sawfly don't like. We will then see if this can be used to create a more resistant willow variety."

The use of insecticides as a control agent is impractical because large numbers of willows line riverbanks. This would mean the spray would have to be administered aerially which would poison fish in the rivers. Furthermore, Mr Charles said introducing a sawfly predator as a biocontrol mechanism would be costly, time- consuming and unlikely to be very effective.

Dr Fung is working on breeding a willow variety resistant to sawfly. As well as this he will be looking for new species of plants which could replace, or complement, willows as a river protection resource if the sawfly proves unstoppable.

Dr Fung said he is compiling a list of willow varieties preferred by sawfly. "It is unlikely that we will be able to breed a totally resistant willow variety that is also good for riverbank protection. However if we can breed a willow which is partially resistant it could replace soil protection willows in areas where sawfly is less of a problem. In areas devastated by the pest, using alternative plant species might be the answer."

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For more information contact: Dr Lindsay Fung HortResearch Palmerston North Tel: 06 356 8080 ext 7754 Fax: 06 354 6713 Email:

John Charles HortResearch Mt Albert Tel: 09 815 4200 ext 7094 Fax: 09 815 4210

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