GOOD timing and the right chemical weapons are critical in achieving a successful strike rate against hoppers.
The most effective way for farmers to treat Australian plague locusts is to use chemical sprays when the locusts are in the "hopper" phase, in concentrated groups known as bands.
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There are a number of insecticide products available for treating locusts and these fall into four main categories - biological insecticides, organophosphates and carbamates, phenylpyrazoles and synthetic pyrethroids.
Department of Primary Industries Chemical Standards Program manager Alan Roberts said each of these insecticide groups had different characteristics.
Mr Roberts said farmers should carefully consider which one suited their own needs.
DPI has provided a "ready reckoner" tool on its website to help farmers make informed decisions on the best use of chemicals in treating locusts.
However, Mr Roberts said farmers should also consult with agronomists and resellers when choosing their chemicals.
He said farmers should target locusts at the third instar hopper phase, when hoppers began forming thick bands on the ground - from about two weeks after hatching.
"The timing of spraying is absolutely critical," Mr Roberts said.
"Farmers must monitor early and they must monitor regularly."
He said because hoppers may not hatch and form bands all at the same time, farmers might have to spray more than once.
"If farmers do a good job of spraying, they may get a 90-95 per cent kill rate," Mr Roberts said.
"But as there may be multiple hatchings, they need to go back to check for other hoppers that need to be cleaned up.
Mr Roberts also said that, when spraying, it was critical farmers made sure their water rate per hectare was enough to ensure the locusts were sufficiently covered by the insecticide.
"A reasonable water rate for most of the chemicals for ground-based hopper band spraying is around 60-80 litres a hectare, which would be sufficient to provide adequate coverage," he said.
"But farmers should monitor their spraying and may need to adjust the rate depending on the density of the band."
He also said the area that needed to be sprayed may only be a fraction of the overall size of a farm.
"Farmers may only need to spray 20-30 per cent of their property, depending on the scale of the bands," Mr Roberts said.
He said chemical selection was critical to locust treatment, but "this whole issue is not just about killing locusts".
"It’s also about making sure you don’t leave unacceptable residues in crops and other agricultural produce," he said.
"It’s as much about market access as it is about having commodities to market."
Ensuring that crops did not exceed permissible chemical residues depended on farmers observing withholding periods and export intervals for spraying.
Mr Roberts said withholding periods differed according to individual chemicals, crops and markets and farmers had to pay particular attention to product specifications.
He said chemical product labels contained directions for use that had been assessed by the Australian Pesticides and Veterinary Medicines Authority.
If the chemical was used according to these directions, any residues would be below the maximum limits.
Mr Roberts said DPI expected all farmers to use chemicals according to good agricultural practice.
- For more information on chemicals for treating locusts, go to dpi.vic.gov.au/locusts