Okay, we admit, it’s getting confusing. Sterile mouse bait. Non-sterile. Pellets. And now there’s double strength.

So, should you use normal strength sterile? Double strength sterile? Normal strength non-sterile? Or double strength non-sterile?

First, why is there now a double strength? In 2021, the APVMA approved an emergency use permit to increase zinc phosphide mouse bait rates (from 25g ZnP/kg to 50g ZnP/kg) in response to the mouse plague on the east coast. Farmers were struggling to control mice numbers with bait, finding that the standard strength mouse bait was not strong enough to kill mice in a single feed.

In light of this, the CSIRO conducted research on the potential new double-strength formulation. The research found the new dose to be lethal to 100% of mice studied, compared to only 50% for the standard dose. They also found that the mice that lived rapidly developed a disliking for zinc phosphide treated grain – (understandably) – which is why it’s crucial that mice get a lethal dose from the first treated grain they consume. 

In response to this, multiple manufacturers began producing double strength mouse bait, and the results for farmers have been far superior to single strength bait. 

The downside? Well, it costs more. Obviously, double strength mouse bait comes with an increased cost due to the higher level of active ingredient in each grain. And unlike ag chem, you have to use it at the same rate as the standard strength. To be effective, you need to cover the same area with the same density.

So, what should you use? With single and double strength bait now available in both sterile and non-sterile forms, it can be difficult to decide what’s best for your farm. And this season, it looks like if you haven’t already, you’ll need to make a choice. The GRDC Mouse Update indicates there are high mice numbers on the Yorke Peninsula and Adelaide Plains, which will peak at seeding time and have the potential to cause widespread damage if not controlled properly.  

If you are applying bait onto a paddock going into a legume or oilseed crop, then the option to use non-sterile bait is there. However, you must be prepared for grains to sprout and become a weed issue. When applying to paddocks intended for cereals – go sterile. Any non-sterile grain applied to cereal crops is likely to germinate and will be tricky to control post sowing, hence why we recommend using sterilised bait. 

Whether you should use 25g/kg or 50g/kg strength depends on your individual situation, mice activity and budget. Remember, unlike ag chem products, double-strength mouse bait is still applied at the same rate – they are just more efficient at being lethal.

If you’d like some advice tailored to your farm, or need bait put aside, give one of our agronomists a call.