Up to a third of Margaret River vineyards have been attacked by ‘apple looper’ caterpillars
The caterpillars – previously unknown in grapevines in the region – have caused yield losses by feeding on small berries, preventing them 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’s never been seen before,’ said viticultural consultant and Margaret River Wine Industry Association president, Leah Clearwater.
Ms Clearwater estimated that 10-30% of vineyards throughout the region were affected by the caterpillars, which were between 5mm and 2.5cm long.
Insecticides have been used but most of these are no longer able to be sprayed because of a ban between bunch closing and harvesting.
Grapegrowers 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 believes that seasonal conditions had probably caused it to emerge from the bushland in which it usually existed.
There was concern that the infestation could lead to the development of botrytis as affected berries dried.
Written by Chris Snow in Adelaide