P.C.N. policy priorities underlined

Press, 9 December 1983, Page 23

P.C.N. policy priorities underlined

New Zealand’s policy on potato cyst nematode (P.C.N.) is at a critical stage and must not be sacrificed for short-term financial gain, according to a paper presented to the National Growers P.C.N. Committee. The paper’s authors, Dr John Hedley and Mr Gavin Harper of the M.A.F., said the long-term objective was to contain and control P.C.N. by eradication. The P.C.N. population in New Zealand soils must be reduced to non-detectable levels, they said, and any review of control policy should follow these basic principles. “Potential yield loss and the disruption of cropping patterns that would arise from the increased incidence of P.C.N. are strong reasons why the pest should be contained if at all possible,” the paper says. High populations of nematodes in the soil debilitate plants and may reduce yield

by 50 per cent. The nematode is extremely difficult to eradicate. Nematicides, long rotations and resistant cultivars must be used, and all affect farm practice and economics.

“Once P.C.N. is present in an area, the farmer is virtually assured of loss — either directly by yield loss, or indirectly by restriction of management options.” The paper also points out that the management of widespread P.C.N. involves the constant monitoring of nematode population levels. This would take time, staff and expensive facilities. The authors argue that present P.C.N. policy will avoid these future problems.

Effective control of P.C.N. would also have an important effect on New Zealand agricultural exports. Exports of potato tubers and nursery stock to any country must be accom-

panied by certification that they come from P.C.N.-free land.

“Recently potato exports to Australia were held up because of the lack of P.C.N. documentation,” the paper says.

These import restrictions could become more severe. Onions, root crops and even non-soil-touching plant material exports could be affected.

A programme of P.C.N. control would also help convince importers of New Zealand produce that we are effective in quarantine matters.

The paper says in the United Kingdom and on the European continent large areas of land are affected by P.C.N. Here a “live with it” policy has been adopted for economic potato production, with a stricter policy for seed production. In countries where only small areas are affected, a policy of containment and

eradication is adopted. New Zealand’s policy reflects practice in Israel, Canada, Northern Ireland and South Africa.

P.C.N. was first identified at Pukekohe in 1972. Further findings were made near Christchurch in 1975, and in Dunedin a year later. P.C.N. was also found in seed areas near Christchurch during 1975. “Seed areas require special protection because if infected with P.C.N. they would provide the means of dissemination of the pest throughout New Zealand’s potato cropping land,” the paper says. When nematodes are identified on farm land the Potato Cyst Nematode Regulations (1974) are applied. The land is quarantined over a large area, and treated to eliminate the nematodes.

“It has taken just 10 years to reduce the population below the detectable level on many infested paddocks.

“However, after 10 years and at these sub-detectable levels the population density hovers ready to increase rapidly if a mistake occurs in ’ the management strategy.

“At this stage there is also a reasonable chance of further dispersal and at

worst a reinfestation of the seed areas.” The paper says policy review will recommend a firming of the regulations but with the introduction of a new rotation option for growers. At the moment only one potato crop in four years

can be grown on infested land. The new option will allow growers two potato crops in successive years, followed by four years without potato production. This rotation cycle will allow growers greater flexibility within the restrictions of the P.C.N. policy.