VICTORIAN and South Australian citrus growers fear for their crops as citrus gall wasp makes a move.
Citrus gall wasp is an Australian native species believed to have spread from Queensland to NSW with the expansion of citrus production throughout the 1900s.
But now the pest is a problem for parts of Victoria and Riverland in South Australia.
It has even made its way to residential Melbourne.
The wasp lays eggs in new growth, which causes woody galls to form, reducing fruit yield and killing branches.
Citrus gall wasp does not directly affect fruit, but is considered a quarantine pest by a number of countries.
Department of Primary Industries NSW entomologist Jianhua Mo said responsibility for management resided with the states because it was an endemic pest.
Dr Mo is currently conducting research into the spread of the pest to the southern states.
He said the pest started to pop up in the Sunraysia area in the mid 1990s.
"More recently it has spread into the Riverland area in South Australia, which is the first time it's crossed the border into South Australia."
Dr Mo said metropolitan treatment involved cutting off and burning branches affected by galls before the wasps emerged from October to December, peaking in November.
"They're easy to identify because after a year the galls are as big as sausages," Dr Mo said.
Another solution is the introduction of native parasitic wasps, which lay their eggs into the eggs of the citrus gall wasps, killing them.
The parasitic wasps have no effect on foliage and are a cheap option.
A large number of growers turned up at a recent workshop in the Murray Valley to discuss a new chemical alternative.
Currently, Supracide is the only registered chemical for gall wasps and the use of such a broad spectrum pesticide can upset the delicate balance of natural enemies in citrus orchards.
Dr Mo has been trialling several chemical alternatives, including petroleum spray oil.
The oil must be applied three times during the season, starting from two weeks after the first sign of the wasps emerging, and then at 10-day intervals until all the adult wasps have emerged.
