Farmers prepared in South Australia for a probable mouse plague that was likely to be as bad as last year’s case as mice populations have been reportedly been at the same numbers or more as last summer. A swell in their population threatens millions of dollars worth of crops and the livelihood of the farmers. The voracious pests are normally nothing more than a nuisance in small numbers, however when conditions are favourable their population can quickly multiply at exponential rates creating a true pestilence. A single mouse consumes around 3-4 grams of food daily in laboratory conditions, In the wild with more activity each mouse may be compelled to eat more as long as the food source is available. In plague situations a large number of mice can eat 12 kilograms of food per effected hectare per day. In the end if left unmitigated the horde will consume a half tonne of crop per hectare, this does not include the crops that are ruined by the mice which can no longer be brought to market.
Mice can quickly multiply being able to breed at 5 weeks of age and each female has 6 offspring per litter and can repeat the process in another 5 to 6 weeks. As long as the climate and conditions are right their populations can easily grow especially when there is a lack of predators to thin their numbers. Although breeding in the wild usually occurs during the spring and fall, during reasonably mild summers it is not uncommon for mouse populations to continue breeding. It is during these summers when their numbers can steadily grow as they have around 8 months of breeding which can equate to around 5 gestation periods.
The key to managing mouse populations is by mitigating their starting numbers in the spring and summer, the more mice during this period the more likely a plague will occur. For farmers this means a more stringent practice of farm hygiene, the removal of rubbish piles and spilt grain as well as trimming the verges and keeping weeds in the periphery in check. Eliminating the amount of food and habitat available to the mice is the best way to keep their population in check. Using approved poisons in troublesome areas such as hedgerows and other places where burrows are seen is the best way of limiting their numbers from exponentially growing as dense populations well entrenched in their habitat with ample food sources will quickly grow.
In South Australia the most effective way of eliminating large hordes of mice is with zinc phosphide a poison that releases deadly phosphine gas when it comes in contact with the digestive fluids inside the stomach. It is often commercially sold already mixed into grain, 1 kilogram of baited feed is needed for every hectare. It is very safe and can be applied at any time during the growing process until 2 weeks before harvest and can be applied as necessary every 14 days. Zinc phosphide can only be applied to crops by S7-Chemcert registered landholder’s and commercial operators either by ground or air. The only major drawback is the price of 10-15 dollars per hectare without the cost of labour for applying the bait. The availability of the bait is also a concern as limited stocks are only released in an emergency licensed policy. For farmers who are on a tight budget 4 Farmers offers a zinc phosphide coating service which allows your own grain to be coated with the pesticide to cut down on costs. There are around 11 suppliers in South Australia which are licensed to treat farmer’s grain with the chemicals.