Even after last year’s massive mouse plague and the floods, the farmers and residents of Victoria are not out of the woods yet, although diminished populations of the voracious vermin are low in numbers over the whole of the state, there are still pockets of sizable mouse populations that continue to keep farmers from resting soundly. When a wave of rodents can take up to 20% of your crop and cost thousands of dollars to control the last thing you want to hear is the pitter-patter of thousands of pestilent paws.
The recent warm winter (2011) has allowed the mice to thrive in their niche habitats and can easily swell into plague like proportion. Although historically mouse plagues only occur once every three to ten years, recently plagues have become more common place. Some speculate that this is due to poison baiting which farmers use to mitigate the damage of the rodents; the theory implies that killing the mice before they hit their peak population is actually allowing them to survive in higher numbers. Usually a mouse plague will die off in the winter when their population “pops” and the mortality rate is normally around 97%. This poses a major quandary as baiting is necessary when plague populations quickly eat through the wheat belt devouring and gnawing on anything in their way.
Mice pose a health and safety risk as properties are susceptible to damage from the constant gnawing that these vermin exhibit, the constant growth of their incisors makes them instinctively chew on anything and everything from wiring (which can start an electrical fire) to wooden structures, and even metal. This constant gnawing is also of concern to poultry raisers, pig farmers, cattle ranchers and shepherds. Mice in plague like situations will gnaw on the livestock and may even begin to eat them as they start to inhabit sheds and barns. The faeces and urine of the mice may also carry the dangerous leptospirosis bacteria which can be potentially life threatening to both humans and domestic animals.
Mice are a highly capable and voracious invasive species, the fecund creatures have little to no competition from the local fauna and the population of predators is not large enough to keep the mouse populations in check. When the conditions are suitable for the mice they can easily multiply into large hordes granted they have proper shelter and food.
The most effective way of keeping mouse plagues at bay is the proper care and attention to the food and shelter that the mice seek, if large numbers of mice have taken up residence in burrows beneath a field or in the grasses in the perimeter it is time to use baited poisons to be applied. The conservative use of baiting in necessary areas is more than enough to keep the mouse population down. The real challenge is catching it early on as a small difference of mice in the spring can make a big difference when their populations continue to grow especially in summers that allow for the mice to continue breeding. The most cost effective way of keeping the mice in check is by adhering to good agricultural hygiene, cleaning up spilt grain and eliminating rubbish piles will deny mice shelter and food. Without shelter and food it is difficult for a mouse population to explode.
The most widely used poison bait is zinc phosphide which is mixed with grains and applied within the paddock. The zinc phosphide is non reactive in dry air but when ingested the zinc phosphide reacts with the stomach acids which produces poisonous phosphine gas.