THE manufacturer of the locust biological control agent, Green Guard, is hoping there will be enough supplies to stretch to farm use this spring.

Becker Underwood national sales manager Dale Skepper said the company had the "capability to fulfil demand at the moment".

"But no one has got experience in the volumes (of locust-control agents) we're facing," Mr Skepper said. "This is a once in a 40-year phenomenon."

Victorian farmers have become concerned about the supply of Green Guard to spray on sensitive areas of their properties, such as near dams and waterways.

The control agent has no maximum residue levels and is suitable for organic farms.

"Everyone wants it to use around their dams," Birchip Cropping Group research agronomist Simon Craig said.

Heightening the concern is a Victorian Government push to use the biological control agent in vast areas of national parks and around waterways on public land.

Victorian plague locust commissioner Gordon Berg told the recent Birchip Cropping Group expo the State Government estimated it had about 600,000ha of public land to spray when locusts emerged in spring.

Mr Berg said government agencies would only be using Green Guard on public land because the control measure had no adverse effect on other insect species.

Green Guard is the only commercial biological control agent specific for locusts. It contains spores of a natural fungus, Metarhizium anisopliae var acridum, which infects the locust through its skin.

Consultant entomologist David Hunter, who helped develop Green Guard, said the fungus penetrated the gut of the locust, spilling its intestines into the body cavity.

Mr Hunter said the infected locust took from about seven to 10 days to die, depending on whether cool weather prevailed.

He said, because the fungus was a living organism, cool days slowed its growth, so it might take up to two weeks to kill locusts.

Mr Hunter said Green Guard should generally be sprayed about two weeks from the second "instar", or stage of development, to allow for variation in the hatching of nymphal insects.

He said growers should factor in a period for "cloudy days" when the Metarhizium fungus was inactive.

Cooler weather would also correspond with a slow down in hatchings, he said.

Mr Hunter said locusts could be sprayed as late as the fourth instar before they reached their damaging stage of crop destruction.

"If they are infected at the fourth instar, even though they are alive, they will be eating a lot less because they are sick," he said.