New Zealand Treecrops Association

News - Guava Moth - Coast & Country article

By Lesley Board

The guava moth, another unwelcome insect pest from across the Tasman, is likely to spread quickly from Northland to the rest of New Zealand, causing yet another headache for fruit and nut growers.
And members of the New Zealand Tree Crops Association are unhappy at the slow reaction of authorities to the pest.
According to Karyn Froud, a HortResearch scientist at the Mt Albert Research Centre, there is no record yet of the moth damaging avocados or kiwifruit, but with its wide host range it could happen. She says Hawkes Bay growers will be anxious about its potential impact on summer fruit crops.
"The moth is now widespread in Keri Keri and other parts of Northland and I predict it will be all over New Zealand in the next 2-3 years. Because of the transportation of commercial and backyard fruit to major centres, Auckland and Whangarei will probably have it within a year. Unfortunately it is too late for eradication - the horse has bolted."
This season, commercial feijoa and macadamia orchards in the north have been severely affected by the moth (Cosinoptycha improbana), but it has also attacked plums, nashi, citrus, loquats and guavas.

Nuts Totally Destroyed

With plums and feijoas, there is little external evidence of infestation in the early stages and it's not until someone bites into a fruit that the damage is discovered. Sharp eyes may detect pin prick holes when the caterpillar first enters the fruit, later the fruit is discoloured and you can see 1mm holes where the mature grub has exited.
But with organic macadamias it acts as a boring insect and can totally destroy the nut.
The larval form is small, growing to about 8-10mm and turning pink as it matures. The moth probably has a short life of just a few days before laying eggs, offering only a short period for control, but multiple cycles of the moth are likely to occur in northern regions. The small exit holes have detritus similar to codlin moth.

According to Dr Gordon Lees, chairman of the northern region branch of the New Zealand Tree Crops Association, the moth first began to attack crops in Northland about 3 years ago. Members have been calling for action since last August when they sent macadamias to Karyn Froud for identification. They point out that the procrastination which occurred over the varroa bee mite and the painted apple moth, demonstrates the danger of failing to act in time.
"Organic orchards are at particular risk, due to the lack of chemical spray programmes," says Dr Lees. "This moth threatens the newly developing macadamia industry in New Zealand, because one of its biggest advantages over its larger Australian and Hawaiian counterparts, is its ability to grow macadamias organically."
He's disappointed that although HortResearch has identified the guava moth pheromones which could be used as lures, there appears to be no plan at present to use these for control, only for monitoring the spread of the moth.
Two years ago MAF's assessment of the problem was that the guava moth was 'unlikely to be a commercial risk' to New Zealand crops.

First Moths Not Acted Upon

The first moths were reported in 1997 but MAF didn't become involved until 1999. Karyn Froud says it's unfortunate they weren't alerted earlier, but even then, the Australian experience suggested the moth was 'no big deal.' In Australia it is considered a backyard pest only, not a threat to commercial orchards.
"We now know that this moth has the potential to be a very major pest to emerging subtropical crops in New Zealand," she said. "It has definitely had a devastating effect on macadamias, but a suspected infestation of a northern apple orchard was possibly not the moth but a virus. So far it has only affected backyard citrus and not commercial crops."
Gordon Lees, however, says commercial organic mandarin orchards in Northland have been affected and these crops have been shipped around New Zealand, though not exported. He claims about 50 percent of the Northland orchards inspected by BioGrow this year showed some degree of infestation.
Karyn says she can understand the frustration of tree croppers but she can also understand why MAF made the decision not to go for eradication on the information available at the time.
"HortResearch now hopes to get funding for bio-control research but it may take 6-10 years before an agent can be introduced. Collecting infested fruit at harvest and removing it from the orchard is another control possibility. The guava moth pheremone is also available from most grower suppliers."
The Tree Crops Association concedes that the guava moth is just one of 20-30 new plant pests reaching New Zealand each year, but claims there are defects in the response of MAF Biosecurity that need to be addressed. Members are particularly concerned at the response time over this moth and the huge increase in eradication costs for the painted apple moth because of delays in implementing that programme.

Coast & Country - May 2002 - Issue No 21

Earlier articles and their updates - Read more...

http://www.treecrops.org.nz/news/news02q2/guavacoast.html
Launched: 29/May/2002 - Updated: 2007 August 11