Californian Grapes Present Low Risk

27 November 2000

Californian Grapes Present Low Risk Of Hosting Diseased Insect

There is a very low probability of Pierce's Disease making it into New Zealand, via the glassy winged sharp shooter, in Californian table grapes, says the Ministry of Agriculture and Forestry. The insect, the glassy winged sharp shooter (Homoalodisca coagulata) can be a carrier of the bacteria, Pierce's Disease (Xylella fastidiosa) which kill grapevines. Pierce's disease is widespread in California.

Representatives from the New Zealand Wine Institute and the Grapegrowers Council have called for a ban on Californian table grape imports in fear of this disease entering New Zealand Kevin Nalder, MAF's National Adviser for International Operations (Plant Imports) said that Californian table grapes were a very low risk pathway by which the sharp shooter insect could enter New Zealand.

He said there had never been an interception in New Zealand of the sharp shooter, or any related species, in Californian table grape imports. Nor had there been any interceptions of the insect during pre-export inspections in California.

"Sharp shooters lay their eggs on the underside of a vine leaf, in a very easily detectable egg mass. We only import the grapes. The packing and grading process takes out all the vine leaves. Very rarely is a leaf found in a packed container of table grapes. "The sharp shooter feeds on the leaves, not the grape, and if present, any leaves would dry out very quickly over the three to four week sea trip to New Zealand. For the sharp shooter to vector Pierce's disease it must eat fresh infected grape leaf. An egg mass must hatch and feed on suitable food within a short period of time to survive. With only dry leaves, the risk is very low."

Californian table grapes present a very low risk pathway and are unlikely to be the method by which Pierce's Disease ever makes it into New Zealand. A higher risk pathway is the importation of nursery stock. MAF imposes more stringent measures for the importation of grapevine plant propagation material (e.g. grapevine bud wood). Illegal smuggling of grape nursery stock would present the highest risk of introducing Pierce's Disease into New Zealand, he said. New Zealand requires pest control activities, inspections and post-harvest fumigation for Californian grapes as mitigating measures for a number of pests.

New Zealand imports approximately 400,000 cartons of Californian table grapes a year.

For further information contact: Kevin Nalder, National Advisor, International Operations (Plant Imports) Phone:04-474-4243 Gita Parsot, Communications Advisor.

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