Gauging Mice Numbers In Paddocks

Did you know that if there are high numbers of mice in your paddocks, they could cause up to 5% damage a night to your crop?…
April 13, 2021Agronomics Back to All

Did you know that if there are high numbers of mice in your paddocks, they could cause up to 5% damage a night to your crop? Our current farming systems of no-till and stubble retention could be why we are seeing high mice numbers each year. With massive mice numbers across Australia that are already causing damage on the east coast, it’s vital to monitor numbers and be ready to act if issues do arise. So, how do you gauge mice numbers in your paddocks? There are a couple of ways.


1. Getting a quick, rough idea:

To get an idea of what is going on in paddocks, we suggest starting by walking a transect of 100 metres across a paddock, counting the active holes in a 1-metre wide strip. Do a few strips across the paddock in different sections to get the most accurate idea.
One burrow per walk would be equal to 100 burrows per hectare.
Damage is likely when there are 1 to 2 active burrows per 100 m transect.

However, note that hole counts will vary by soil type. For instance, in sandy soils, mice can dig many holes while they search for food, but in hard-setting soils, there may be fewer holes but may contain more mice per hole. Not to mention that spotting holes in cracking soils is much more difficult again.

The problem with this method is it’s hard to gauge how many mice are in each burrow, and whether they are still there or moved on. Numbers can vary from 1-4 per hole to up to 40 per hole during plagues.
But you get the idea, if you’re consistently counting 1 – 2 holes every 100m strip, it could pay to investigate further and perhaps bait.


2. Getting a good read of activity levels:

To get a good gauge of mice numbers, this is the method we suggest. There are two ways to get a read on activity levels: The Powder Method, and The Chew Card Method.

The Powder Method is easy.
Grab a tin of talcum powder and go to a section of holes in the paddock and sprinkle the powder around the holes. Then, go back the next day to check the disturbance levels.

The Chew Card Method
The test which we like is using mouse chew cards. This is done by cutting some strong paper or light card into 10cm x 10cm squares, where each square is marked with a 1cm grid. Cut these squares out, and then soak them in canola or linseed oil. Next, place the cards randomly across a paddock and peg them to the ground. Go back the next day and count the 1cm squares which have been eaten. If more than ten x 1cm squares are eaten per card overnight, considerable mouse populations are emerging. If more than 20 squares per card are eaten, then there is a significant problem. 

Below are pictures of how chew cards work and the activity levels we found a couple years ago in She-Oak Log, Saddleworth, and Agery. 


So, you’ve got mice. When should you bait?

If mice levels are found to be high, we recommend spreading a zinc phosphide bait*. The best

practice is to bait at the time of sowing or within 24 hours to protect the recently sowed crop. Mice damage will be the most severe for about two to three weeks after crop emergence and again around seed set.

See us today for our range of mouse baits, chew cards, as well as traps and baits for around the house or any other information on monitoring mice levels and when to bait.
*Reminder that you’ll need a current chem cert to be able to purchase as this is an S7 poison.


Key tips:

1. Actively gauge numbers by going into the paddock.

2. Try to remove residual food. The best practice is to bait when there is as little alternative food as possible.

3. Bait six weeks out from sowing if pressure is excessive (as this allows enough time to overcome sub-lethal doses/aversion).

4. If mice are still present at sowing you can bait off the back of the planter to prevent damage to the freshly sown crop. 

5. Baiting at sowing is most effective if no other food sources are available.

6. Obviously, crop type will come into decision-making when baiting. If unsure, call us to chat with an agronomist.