Victorian farmers have again been warned to take care when using zinc phosphide to kill mice.

A late autumn break has delayed sowing in many areas of the state's northwest and grain growers are still lining up to buy zinc phosphide to combat mouse infestations.

Longernong College lecturer Russell Venn, who has organised 20 zinc phosphide user courses for 600 farmers since May, said requests for courses were still being lodged.

He will travel to Jeparit next week to instruct growers on zinc phosphide safety and effective use of ground and aerial baits.

"The feedback from farmers is that while they want to be able to kill mice with zinc phosphide, because it is working, they want to make sure they don't hurt themselves, their family, neighbours or any wildlife," Mr Venn said.

"For people used to handling chemicals there are no new problems as long as they realise it is one of the most dangerous chemicals they will use."

Zinc Phosphide emits a poisonous gas called phosphine, which builds up inside containers before they are opened.

Users of the bait must wear a respirator to protect themselves against the gas.

Skin should also be protected from the chemical covered wheat.

Zinc phosphide has the potential to cause organ failure in humans, as it does in mice, and death.

Initial poisoning symptoms include nausea, vomiting and diarrhoea.

Farmers wanting to use zinc phosphide have to successfully complete a Farm Chemical Users Permit, hold a valid Agricultural Users Permit and attend a zinc phosphide safety training course.

They should use a full-face respirator for aerial baiting and a half-face cartridge respirator for ground baiting, both complying with AS 1715 standards.

Overalls and nitrile gloves must be warn and first aid kits with eye wash facilities should be available.

Neighbours should be notified of any intentions to bait, the type of bait used, the areas to be baited and of the dangers to wandering pets.

Natural resources and Environment Department mouse program operations manager Ken Dowsley confirmed the National Registration Authority had extended the ground and aerial permits for mouse baiting with zinc phosphide until October.

This is because the late season has delayed sowing and Mallee and Wimmera farmers need to use zinc phosphide to kill emerging mice populations.

Mr Dowsley said 62,640 kilograms of zinc phosphide had been sold in Victoria so far - 71 per cent of which was for ground baiting.

Fears of widespread mice plagues in the Mallee were earlier dispelled and NRE officers said infestations had been "patchy".