Moth caterpillars are inflicting serious damage to grape crops in vineyards in Western Australia, leaving growers unsure of what to do. The pests are larvae of the apple looper moth, a native of Australia and New Zealand. They are not known ever to have attacked grapes before, puzzling viticulturists and entomologists alike.
"It's difficult to guess how this will effect production," said Jim White, viticulturist at Cape Mentelle Vineyards in Margaret River. "It's come as a surprise to everyone in the regions and seems fairly widespread from north to south. Damage seems to be quite sporadic."
According to Stewart Learmonth, an entomologist with the Western Australia Department of Food and Agriculture in Manjimup, some Margaret River vineyards have sustained little or no damage, while others have lost 70 percent to 80 percent of their fruit.
Leeuwin Estate Winery, a famed Chardonnay producer in Margaret River, has suffered no apparent damage and is currently harvesting, according to staff members. White speculates that production might be down 10 percent to 15 percent at Cape Mentelle thanks to poor fruit set region-wide this season and the appearance of the apple looper, but he isn't sure of those figures at this time.
While the apple looper (aka Phrissogonus laticostata Walker) has done little damage to agricultural crops in the past, it appears to have jumped to grapes this spring in Margaret River and Manjimup. The pest is difficult to detect; because it does little harm to vine foliage, the usual visual signs of insect blight aren't present. Rather, the larvae appear to be boring into the berries and eating them from the inside, leaving them susceptible to botrytis and other forms of rot and mildew.
The experts are unsure why the pest has developed a taste for grapes, how far it will travel and how much carnage it is capable of inflicting on the harvest and subsequent wine production.
"People are nervous because they have no idea what's going to happen for the rest of the season," said Learmonth. "It seems to be a spring insect, but because it's never been seen in grapes before, we don't really know what it will do."
While there are a few insecticides that are effective in the earliest stages of infestation, they cannot be applied after the grapes have reached a certain size, about that of a pea. Growers are spraying BT (Bacillus thuringiensis), a bacteria that kills caterpillars when they ingest it but that is harmless to humans.