Australia approves emergency permit for double-strength mouse baits amid plague

Australia's chemical regulator has approved an emergency permit for double-strength mouse baits for grain paddocks amid mouse plagues in Western Australia and South Australia's farming regions.

After what farmers and rural community leaders have described as an anxious and expensive wait, the Australian Pesticides and Veterinary Medicines Authority (APVMA) has conditionally allowed the manufacture and sale of bait containing 50 grams per kilogram of zinc phosphide (ZP50).

Mice have invaded homes and sheds and are causing health concerns in some communities, with damage already evident in emerging winter grain crops.

Destroying crops before germination

At Northampton in WA's Midwest, grain farmer Scott Bridgeman said access to the stronger bait would help him "sleep better at night", knowing mice would die quickly.

He said mice had been very destructive in paddocks where he was not running his livestock.

"You can just see the amount of holes, and they're like a rabbit warren, some of them. There's holes everywhere and they've pulled a huge amount of dirt out of the ground, it's amazing how much dirt a little animal can move,"

Across WA, growers have reported mice eating planted seed before it even had a chance to germinate, and damage to emerging crops is also evident.

Independent Rural Northampton retail manager Ben Lang said the store was struggling to meet demand for bait and traps.

"If I'm not ordering 100 mouse traps then there's something wrong, same with the Ratsak, I'm ordering the same amount … it's just crazy,"

"Farmers driving around at night-time, I've heard of them popping hundreds and thousands at a time, and that's just the ones they're seeing."

Problem began months ago

A study earlier this year by the CSIRO estimated there were 8,000 mice per hectare in parts of WA's northern grain belt.

Farmers began sounding the alarm months ago, but mice numbers continued to grow, and the rodents moved into towns surrounded by grain paddocks.

Community leaders such as Morawa shire president Karen Chappel have been frustrated at the time it has taken to approve stronger baits, which kill mice after eating one poisoned grain.

"The APVMA is completely tardy and irresponsible in their delay in responding to the request to have this bait increased to 50 grams [of zinc phosphide],"

"I feel very strongly that the APVMA is considering wildlife as a priority over human life."

Light at the end of the tunnel

The grain industry, through Grain Producers Australia (GPA), had been lobbying the APVMA to approve an emergency permit application to give farmers access to the double-strength zinc phosphide mouse bait.

GPA's Andrew Weidemann said the approval would be greeted with relief by farmers.

"While grain growers have had ongoing access to 25g/kg zinc phosphide (ZP25) mouse bait, it's not strong enough to tackle the level of mice issues that we're seeing at the moment, so we are incredibly grateful for this permit,"

"This is a time-sensitive issue and GPA have been dedicated to working with the APVMA to establish practical permit conditions that balance access to stronger pesticides with safety, environmental and trade considerations."

He said farmers would need to be trained and accredited in using the bait before they could buy it.

The national emergency permit is designed to be flexible, helping farmers with moderate or high levels of mouse activity — identified through a national rapid assessment monitoring network, established by the Grains Research and Development Corporation — to access ZP50.

Farmers needing more information and links to training should go to the GPA website.

Worst plague on record

While help is on the way for farmers, people in rural communities in regional WA have been living with what they say is the worst mouse plague on record for months.

Northampton resident Erika Brown said mice had eaten the cables in one of her fridges and chewed the cushions in her new couch.

"It's disgusting, it stinks, it's filthy and horrific,"

Ms Brown prefers not to use poisons on her property, and has been relying on bucket and cage traps for control.

"I've got chooks and they can't even get through them all,"

In a statement, the APVMA said the permit had been approved with specific use instructions and controls designed to support effective mice management while reducing risks to people, wildlife and the environment.

It said these include clear permit directions on application to minimise exposure to non-target animals.

Long road to approval

The APVMA had previously rejected an application for the higher-potency baits, stating the research provided "is not of sufficient regulatory quality" to issue a permit.

Some of that research included data from the CSIRO, which has published four papers examining zinc phosphide efficacy.

All found that the 50g/kg rate of zinc phosphide was more effective than 25g/kg in controlling mice.

CSIRO research officer Steve Henry co-authored the papers and said he stood by the research.

"Effectively, all four studies have shown exactly what farmers were telling us, that the 25g/kg bait doesn't work consistently,"

So far, Mr Henry said, there was no indication a stronger rate of zinc phosphide increased the risk of secondary poisoning of birds, but scientists were continuing to study this area.