More Natives Under Attack

Forest and Bird, Issue 291, 1 February 1999, Page 11

More Natives Under Attack

disease organism which has caused the widespread death of native cabbage trees in recent years is now suspected of killing native pittosporums and coprosmas. The disease may also be affecting other native species, including the puriri tree and the black tree fern, mamaku. Recent DNA research reveals that a phytoplasma, which also makes flax turn yellow, may be the cause of the die-back. "Yellow leaf disease’ was a major factor in the demise of the Manawatu flax industry earlier this century, and the cabbage tree disease has had a major impact, particularly in the North Island and northern South Island, during the past decade. The symptoms vary between species but usually the leaves show unusual yellowing or reddening, and fall off prematurely, leaving bare branches. These branches die back from the tip and plants rarely recover. Researchers have discovered the disease in other native trees is very closely related to, if not identical with, the disease organism which killed the cabbage trees. The Biosecurity Minister, John Luxton, has requested Government agencies to work together to find out more and decide on a course of action.

A research team led by Dr Ross Beaver of Landcare Research and Dr Richard Forster of HortResearch, suspects that one or more introduced planthoppers are involved in spreading the disease betweeen different species of plants. More work is needed, however, to confirm eaxctly which planthoppers are the culprits. There are also some 20 native planthoppers which could be involved. The spread of disease among New Zealand plants, such as cabbage trees and corprosmas, has become widespread since the mid 1970s. The extent of the disease in New Zealand, throughout the North Island and the top half of the South Island, matches the distribution of the passionvine hopper, an Australian insect which became established here about a century ago. Introduced planthoppers are already implicated in the spread of disease among horticultural crops. In Australia, a possibly identical phytoplasma is associated with diseases of strawberry, papaya and grape. Research in New Zealand is to be co-ordinat-ed with Australia because of the common problem caused by similar disease-causing phytoplasma.