Same Criteria Applied to Painted Apple Moth and Northland Grass Webworm

12 May 1999

The swift response of the Ministry of Agriculture and Forestry to the discovery of the Painted Apple Moth in Auckland has led some Northland farmers to ask why the same response was not forthcoming when grass webworm was discovered in Northland.

Northland farmers have questioned the MAF decision to move to control and eradicate the painted apple moth in Glendene, and not to undertake control work on the grass webworm, which is destroying kikuyu grass on Northland farms.

MAF's Chief Forestry Officer, Dr Ruth Frampton, said the Ministry follows the same initial procedures and policies when dealing with all unwanted exotic plant pests. "MAF applied the same criteria to the painted apple moth in the West Auckland suburb of Glendene as it did to the grass webworm in Northland," Dr Frampton said.

"Decisions about on whether or not to try to eradicate unwanted pests are based on an assessment of the probability of success," she said. "The first step in assessing this is to carry out what is known as a delimiting survey to establish the extent of spread of the pest."

In the case of the painted apple moth, the survey is almost complete, and results indicate that it is confined to a handful of properties clustered together in an industrial area, with another site about 300 metres away. The total area involved in Glendene - including the outlying site - is less than one square kilometre.

In the case of the grass webworm, the delimiting survey found that it was spread 15 kilometres to the north of the original find site, and 28 kilometres to the south. The likelihood of achieving effective spray coverage over such a large area was extremely low, meaning attempts at eradication would be almost futile. A similar decision resulted from January's discovery of blackbutt leafminer on eucalypts in a number of Auckland suburbs.

A further factor in the decision not to intervene in the Northland situation was that Northland grass webworm infestation is believed to be the result of a natural introduction, with the insect having been blown across the Tasman. Grass webwom moths have been recorded in New Zealand on several occasions over the last 15 years.

The insect is therefore constantly 'knocking at the door' of New Zealand. Further natural introductions of the grass webworm are likely to occur, and an eradication programme embarked on today may have to be repeated tomorrow. Grass webworm, being a tropical insect is unlikely to be a problem throughout New Zealand. Learning how to manage this insect in the north when it is likely to be a problem, is better sooner rather than later.

For example, research may be undertaken into identifying types of grasses which are resistant to the grass webworm.

Media inquiries to:
Dr Ruth Frampton, Chief Forestry Officer, Ministry of Agriculture and Forestry (025) 350 801
Debbie Gee, Director, Corporate Communications, Ministry of Agriculture and Forestry (04) 474 4258



Last Updated: 10 September 2010

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