Asian moth poses serious threat to stone fruit

Press, 18 July 1979, Page 11

Asian moth poses serious threat to stone fruit

An Asian invader poses a significant economic threat to New Zealand’s stone fruit crops. The enemy is the Oriental fruit moth, which has already conquered much of the Auckland district and is now poised to attack orchards throughout New Zealand. The officer in charge of the Ministry of Agriculture’s plant health diagnostic station at Auckland, Mr P. S. Dale, says that the recently arrived fruit moth is “the biggest threat ever to New Zealand’s stone fruit crops." The moth probably arrived in Auckland by aircraft, because it was first seen south of the city, around Auckland Airport at Mangere. It is how solidly entrenched in Auckland in a 70km area from Albany in the north to Pukekohe in the south, and some solitary moths have been seen as far away as Whangarei and Te Kuiti. The Oriental fruit moth (Cydia molesta) • is regarded as a particularly serious pest because it can completely destroy the fruit of peaches, pears, quinces, plums, and apricots. It also attacks the yoijpg shoots of these fruit trees. It has no effective natural enemies in New Zealand and has been known to wipe out 90 per cent of the fruit on trees in South Auckland. Instead of making one hole into and out of a fruit, the caterpillar wanders around inside, carrying fungus spores which eventually cause the fruit to collapse from the inside.

Another disconcerting aspect of the pest is that the caterpillar frequently enters the fruit through the stem. Thus its presence is not easily detected when the crop is picked and the fruit can collapse after packing. As it is not unusual for the fruit moth to destroy most of the terminal buds on a young tree, its effect on subsequent growth and fruit production can be drastic. Young trees may be permanently misshapen and, if control measures are not applied, the bulk of the crop from late varieties of peaches and pears can be destroyed. The moth, which breeds in four to seven generations a year, could be expected to be equally damaging in orchards throughout the North and South Islands right down to Bluff. “Cold weather doesn’t worry it,” Mr Dale said. “It’s a serious pest in the eastern and central United States and in Canada. The moth is also found in southern Europe as far east as the Black Sea.” The most imminent danger is that the moth will be carried to rich fruit growing areas such as Hawke’s Bay, in cases or bags of infested fruit. “While few people are likely to send peaches or pears to Napier or Hastings, the fruit moth could be carried by an Auckland resident taking a few quinces to relatives in Hawke’s Bay,” said Mr Dale. He said that the Auckland public should not take fruit out of the province under any circumstances. The fruit moth could just as easily be transported to the South Island by some well-meaning relative from the north. Mr Dale said that an eradication campaign to destroy the moth would cost at least SIM initially, and up to $250,00 a year for at least five years. “Even then we could not guarantee total eradication of the pest, although we might have stood a better chance while it was confined in the Auckland district, because its natural spread seems relatively slow.” An infestation of the Oriental fruit moth in Western Australia in the early 1950 s appears to have been successfully

eradicated by a swift campaign. Mr Dale envisages a campaign of intensive chemical control, with a follow-up biological control scheme involving the breeding and release of sterile male moths and imported parasites as the most promising approach to eradication. He said that the problem was that few commercial orchards had been hit by the fruit moth yet — home gardeners in Auckland’s suburbs made up most of those worse affected at present — so there was little public concern. “If it was foot and mouth disease, or scabies, extreme measures would be taken 'to confine the outbreak, but the agricultural community is more apathetic about insect pests,” said Mr Dale. Overseas experience has shown that chemical control can give adequate protection provided it is applied thoroughly. Three sprays of carbaryl, maldison, azinphos, or parathion at 10-day intervals, beginning at petalfall, will prevent injury to shoots from first-brood larvae and may give control for the entire season in orchards free from reinfestation. Otherwise fruits can be protected with sprays seven to eight weeks and three to four weeks before harvest. The leaf roller spray schedule normally recommended for New Zealand orchards may also offer satisfactory control. The infested area in the Auckland district is tiny, but several obstacles exist to a successful eradication campaign. Most of the affected areas are closely settled with small residential sections, on which peach and other fruit trees are popular. Eradication would involve a large number of trees and would inconvenience a great number of people. Because most of the infested properties are residential, little owner expertise in spraying or pruning can be drawn on. To have any chance of success, the treatment

would have to be done by trained personnel — either staff of the Ministry of Agriculture and Fisheries, or employees taken on and trained specifically for the purpose. New Zealand may not be able to afford an allout eradication campaign, but Mr Dale is hopeful that public awareness will prevent the spread of the

fruit moth to big fruitgrowing areas for as long as possible. “Exports of fruit and vegetables were worth more than S76M last year, and keeping this new pest out of important fruit growing districts for another two or three seasons could mean a significant difference in overseas earnings,” Mr Dale said.