Omokoroa kiwifruit grower Neil Brough fears the thousands of insects crawling over the support structures, vines and fruit on his orchard may represent yet another serious threat to the industry.

'We've identified them as giant willow aphid and since we first noticed them on willow shelter in the orchard on Monday, they have moved, in big numbers, to the kiwifruit,” says Neil.

Hundreds of giant willow aphids are crawling over fruit and kiwifruit support structures on Neil Brough's gold kiwifruit orchard near Omokoroa.

Neil believes they are a new pest for kiwifruit and understands they were first identified in New Zealand in 2013.

'My concern is that they will cause sooty mould to grow on the fruit which may see it rejected for export.”

Neil says he and his staff first became aware of the insects when they noticed the trunks and stems on the willow shelter turning black with mould. Sooty molds are caused by Ascomycete fungi which grow on the sugary honeydew secreted by insects such as aphids, scales, and cicada.

'There's no sooty mould on the fruit yet but you can see the on the leaves where the aphids have excreted honeydew and they are crawling on the fruit so I expect areas of the leaves and the fruit to turn black,” says Neil.

Neil has notified Kiwifruit Vine Health, Zespri and the Ministry of Primary Industries.

KVH reports the organisation and Zespri are in discussion with MPI about the insect. This week's KVH bulletin says both entities are working to determine the scale of the problem and develop best practice recommendations.

The insect is found in most countries New Zealand exports to and is not considered a quarantine pest.

'It is quite common for aphids to develop to very high numbers very quickly then collapse again equally rapidly,” says the bulletin.

Giant willow aphid (Tuberolachnus salignus) was first reported in New Zealand in December 2013 and has since been discovered throughout the North Island and in the Tasman Region.

The KVH bulletin says that MPI conducted an incursion investigation when it was first reported and concluded that GWA are a known pest to willow and poplar trees and kiwifruit is not a known host (initial reports indicate the aphids are not feeding on kiwifruit).

However, horticultural industries could be impacted given the use of willow trees in orchard shelter belts.

Neil is still waiting for advice from Zespri and KVH on what sprays he can use to control the insects as this time of the year, very close to harvest, the kinds of sprays available to growers are restricted.

'Oils might control them, but killing them won't stop the sooty mould problem they have probably already caused.”

More than that, he is concerned that yet another new pest has apparently arrived in New Zealand.

Like virtually every other kiwifruit orchard, his has been infected with the bacterial disease Psa first identified in New Zealand in 2010. He removed both green and gold vines and the giant willow aphids are on a block of the orchard grafted to the new G3 variety which is carrying a promising-looking export crop.

Two weeks ago two white peach scale insects, a species which has caused significant problems for the industry in Italy, were spotted by a Plant & Food Research scientist on imported Italian fruit in a Tauranga supermarket.

'New Zealand needs tougher controls at our borders. These pests and Psa are bad enough but if foot and mouth disease arrived it would just about bankrupt our country,” says Neil.

Foot and mouth disease seriously affects livestock including dairy cows and an outbreak would see thousands of livestock slaughtered and countries closing their borders to most of our exports.

Giant willow aphids have an unusual lifecycle, with only wingless female born in spring, followed by several generations of egg-laying females with no males produced until finally more females with wings are hatched which return to the host willow trees in autumn when one batch of eggs hatch as males and females. These mate, the females lay eggs which over-winter, with wingless females emerging in spring.