If we needed any confirmation of that fact, think back to the emergence of Psa in kiwifruit. A disease that was known to have devastated industries in Japan, Korea and Italy, first appeared in New Zealand in 2010. In August of this year, 75 percent of the country’s kiwifruit hectares are on an orchard associated with Psa. How it came here isn’t entirely clear, but the fact it did is a frightening reality check for all our primary producers.
Dr Jim Walker from Plant&Food Research in Hawke’s Bay says there have been other bio-security threats in the past few decades, the Painted Apple Moth in 1999 in particular.
“That incursion and the eradication programme that followed cost this country $62 m with some estimates saying the cost was as high as $90m. Would we get away with that again in terms of cost, or the whole reaction to aerial spraying of Auckland should another similar unwanted pest arrive? Despite the success of the programme, there was a lot of flak and public concern about that strategy, so we need to be very vigilant in terms of our biosecurity awareness and strategy.”
What is knocking at the door of the New Zealand Wine Industry?
Walker says there are three main areas we need to be concerned about; the phytoplasmas and bacteria, fungal pathogens and insects.
In terms of phytoplasmas and bacteria, the big ones to worry about are Flavescence dorée which is an insect vectored disease of grapes. Another is black wood, an organism which is also insect vectored. Both kill vines.
Black rot is a fungal pathogen, Walker says and pathogens are often extremely difficult to eradicate once present in the country.
“To prevent the establishment of important vine-damaging diseases we need both a secure front and back door. As we have learned from the Psa experience, it is very difficult to eradicate it, once it is established. So it’s a case of being very careful around the movement of plant material when it comes to pathogens.”
Then we come to insects – which he says provide a completely different challenge.
“They break borders more often, they have a diversity of life stages from the eggs to larvae and adult. Their behaviour is cryptic, they are mobile and they fly! They have resistant stages, so they can survive adverse conditions. And they are the perfect hitchhikers, which means they have got so many inanimate pathways (into New Zealand) from suitcases to shipping containers.”
Key Insects To Look Out For
Glassy-winged sharpshooter (GWSS)
This is large leafhooper, native to south-eastern America. The reason it is such a danger, is because as a vector it can transfer Pierce’s disease. Already it has decimated vineyards in California. A xylem feeder, it has a huge range of host plants, such as pittosporum, eucalyptus and citrus. The GWSS is an extremely strong flyer and an equally strong vector for disease. While not present in New Zealand, there have been numerous reportings of GWSS in the Cook Islands.
Admittedly, you need both the GWSS and Pierce’s disease in the same country to impact on vineyards. But as Walker pointed out, we have no idea whether Pierce’s which is a bacterium (Xylella fastidiosa) is already present in New Zealand.
“The thing with xylella is there are more than 300 host plant species and many of those are asymptomatic hosts. We don’t know if we have the bacterium but not the vector. But if the vector comes in, it could complete the whole cycle and cause major problems.”
Dealing with the disease isn’t an easy task. In countries already under siege, the Integrated Pest Management practices (IPM) have been undermined, as growers have had to take serious measures to counter the disease.
“If you think about our pest management programme in NZ Winegrowers, it is a very low input programme. Would we be able to deal with this disease and retain that low input?”
There is an egg parasitoid that has been effective in killing the GWSS biologically, but Walker says it is not suited to cool climates, such as New Zealand.
Spotted-winged Drosophilia
Walker describes this insect as a very nasty one. It is a vinegar fly, that lives for up to two weeks. The females can lay up to 300 eggs and there can be up to 10 generations in a season.
“It attacks earlier, as the fruit begins to mature. It has many hosts including berry fruit, grapes, stone fruit, kiwifruit and it has spread like wildfire through Europe and North America. While it is not found in the Southern Hemisphere yet, potentially via a fruit tray it may not be far away.”
The spotted-winged Drosophilia has a serrated ovipositor that is like a chainsaw, used to great effect on maturing fruit. The consequent wounds then expose the fruit to other pathogens and fungal diseases such as botrytis.
“If this entered New Zealand it would change our pre-harvest insecticide programmes as we would have to protect to prevent berry or reduce berry damage. If we get this here, it is a game changer for everyone, from the home gardener to the commercial exporters, and to you as grape growers.”
Brown Marmorated Stink Bug
Very like a shield bug in shape, this was first found in the US in the late 1990s. Now it is present in more than 35 states, with extremely high population densities. It feeds on a wide range of host plants, from apples to citrus, figs to grapes.
When they feed on grapes, they damage berries, which impacts on the ensuing wines. What is worse, is if they are collected with the grapes at harvest and crushed with the fruit. In this case the wine taint could be significant.
They are the classic hitchhiker Walker says, easily transported in suitcases, or shipping containers.
There have already been five identifications of this bug in New Zealand. It is not easy to get rid of either.
“In apples in the US, up to 13 pyrethroid insecticides are required to control this. And even with those 13 treatments there was 10 percent fruit damage. It has completely destroyed IPM programmes.”
European Grapevine Moth
Native to Italy, this moth has spread throughout Europe. In 2008 it was found on grapes in Chile and in 2009 it was discovered in the Napa Valley, California.
Hosts include olives, apples, kiwifruit, cherries, persimmons and grapes.
Larvae feed inside berries, hollowing them out and leaving only skin and seeds. The risk to fruit health and potential botrytis epidemics are obvious.
Walker says it is an insect that could easily be introduced via fruit imports.
Vine Mealy Bug
This is of considerable concern to winegrowers throughout New Zealand. Originally emanating from Europe, it has now spread to California, and South Africa. It is spread via budwood and equipment. With a broad host range, it has four to five generations per year.
“And the damage – whole bunches literally shrivel and eventually it kills the vine. It is a significant vector of grape leafroll virus, so we need to be vigilant.”
While Walker admits the large number of devastating diseases waiting around the corner is a bleak message, there are ways we can combat the threat.
Everyone needs to be vigilant, surveillance programmes need to be optimised, and early detection is paramount for an eradication programme to be successful.
As a grower you need to be aware of what to look for. If you discover something you are unsure about, don’t just kill the insect, capture it, and get professional advice.
The following is a number all growers should have in their workplace – Exotic Pest and Disease Emergency Hotline – 0800 80 99 66. Don’t be afraid to use it. ν
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