Up to a third of Margaret River vineyards in Australia have been attacked by apple looper caterpillars, Decanter reports.
The caterpillars — previously unknown in grapevines in the region — have caused yield losses by feeding on small berries, preventing them from developing.
But the extent of further damage is proving difficult to estimate because the caterpillars are feeding inside grape berries and becoming increasingly difficult to detect as bunches close. There has been no significant foliage damage.
“It’s a new issue. It has never been seen before,” said viticultural consultant and Margaret River Wine Industry Association President Leah Clearwater.
Clearwater estimated that 10 to 30 percent of vineyards throughout the region were affected by the caterpillars, which were between 5-mm and 2.5-cm long.
Insecticides have been used, but most are no longer able to be sprayed because of a ban between bunch closing and harvesting.
Grape growers have now begun biological control measures, using sprays containing Bacillus thuringiensis, a bacterium that acts against caterpillars.
Other control measures included thinning vine canopies to increase spray penetration of the insecticides into the fruit zone.
Stewart Learmonth, an entomologist with the Western Australian Department of Food and Agriculture, said the pest was native to Australia, Norfolk Island and New Zealand, but “not a lot was known about it.”
He said he believes that seasonal conditions had probably caused it to emerge from the bushland that it usually inhabits.