Double strength of mouse baits for best results: CSIRO

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Mice are less sensitive to zinc phosphide baits than previously reported, CSIRO finds, so a higher concentration is needed

Double strength of mouse baits for best results: CSIRO
Grain treated with 50g Zinc Phosphide per kilogram is more effective as a mousebait, new research finds


Farmers had voiced concerns to the CSIRO for years, saying they felt the mouse baits they used were not as effective as they needed to be – particularly when mouse numbers were high.

And now new research has vindicated these suspicions, with researchers now finding mouse populations can be reduced significantly by doubling the amount of zinc phosphide (ZnP) in grain baits used for broadscale agriculture.

The research, funded in part by the Grains Research and Development Corporation (GRDC), has seen three papers published in serious academic journals – and represent the first efficacy studies done in Australia since the baits were registered for agricultural use.

The publication of the reports comes after the Australian Pesticides and Veterinary Medicines Authority granted an emergency use permit to increase the concentration of ZnP from 25g ZnP/kg to 50g ZnP/kg grain bait products during the height of the 2021 mouse plague.

CSIRO researcher Steve Henry said the first study published in Pest Management Science found that bait consisting of grains coated with 25 g ZnP/kg grain did not always provide a lethal dose to mice, and the mice that didn’t die from an initial feed of this bait became bait averse. 

"We followed up with a second study, now published in Integrative Zoology, that re-assessed the sensitivity of mice to ZnP. The results showed that mice were significantly less sensitive to ZnP than previously reported," Mr Henry said.

"These results highlighted the importance of every bait grain needing to be a lethal dose as there is no guarantee that mice will find and consume more than one baited grain, and consumption of a sub-lethal dose leads to aversion."

The key, Henry says, is to double the strength of those baits – shown in a third study published in Wildlife Research

"The final study conducted near Parkes, NSW, took the findings of our laboratory tests into the field and confirmed that 50 g ZnP/kg grain bait is required to consistently reduce mouse populations," he says.

"The findings confirmed that the 50 g ZnP/kg grain bait was able to achieve more than an 80 per cent reduction in mouse populations more than 90 per cent of the time."

GRDC Pests Manager Dr Leigh Nelson says the three studies provide a solid body of evidence for the superior efficacy of the 50 g ZnP/kg grain bait, which will give growers a more effective tool to manage mice and protect their crops. 

"The use of 50g ZnP/kg grain baits should reduce the need for repeat baiting which is costly," she says.

"Any savings on the bottom line from mouse damage would be welcomed by farmers."

That said, Dr Nelson added that she would still encourage farmers to implement a range of tactics to deal with mice, rather than relying on baits alone.

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