GOVERNMENT authorities will have the power to enter Victorian farms and spray locusts even without a farmer's permission, under measures to combat a ''perfect storm'' of conditions now threatening south-eastern Australia.

This spring and summer, locust swarms in Victoria could be bad enough to destroy crops, disrupt sporting events and possibly cause temporary closures of Melbourne and regional airports, the Victorian Plague Locust Commissioner warned farmers yesterday.

Gordon Berg said locusts would be declared an ''exotic pest'' under state legislation, boosting the powers of authorities to act.

''The reason for doing this is so that we can, in extreme situations, control locusts on land, even without landholder permission,'' Mr Berg told a farming expo in Birchip.

''We don't want to do that, but there may be some occasions where … a person does not want any spraying at all on their property.

''And we will have the ability to enforce that spraying, either by forcing the landholder to do it, or by coming in and doing it ourselves and billing the landholder. It's an extreme last resort, but we need to have that power available to us.''

Mr Berg said the density of some locust egg beds in Victoria was ''extremely high''. An inspection on a property at Serpentine, near Bendigo, on Wednesday revealed eggs at a density of 1000 per square foot, he said.

''We've had our mapping groups within DPI look at the spread of egg beds and where people have seen locusts. We estimate there's probably an area of something like 9.6 million hectares that is affected by locust infestations to some degree. We reckon that 2.4 million hectares may well require some sort of control treatments,'' he said.

The costs of chemicals for spraying locusts will be rebated under the Victorian Government's locust package.

Farmers were also told that a ''perfect storm'' of wet and warm weather over the past six months had created an environment that allowed locusts to breed, spread and band together in massive numbers across large areas of eastern Australia.

The ideal conditions for locusts this year have lifted survival from the normal rate of about 20 per cent to as much as 80 per cent, ensuring that a much greater than normal number of female locusts have survived into adulthood and laid eggs.

Chris Adriaansen, director of the Australian Plague Locust Commission, said about 200,000 hectares in north-west New South Wales and south-west Queensland had been sprayed in March.

''We reckon we took out somewhere in the order of 8 billion locusts. If we hadn't have done so the population that subsequently drifted south during autumn would have been much, much larger,'' he said.

Mr Adriaansen said that while a lot of work had been done, locusts were spread over a massive area in large numbers. ''It's almost the perfect storm for locusts,'' he said.

Urging farmers to keep a close eye on the commission's website, he said it displayed crucial information such as anticipated hatching dates for eggs and when locusts would be ready to fly.

Mr Adriaansen said the estimates would be modified as new weather data was included. He urged farmers to check the dates to determine when to spray.

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