May 25, 2012 – Mice In The Food Source
QUESTION:
We have a tomato greenhouse account where the major pest is mice. Recently they also started growing spices and herbs. The basil is very popular and the mice population has exploded. We had control with bait stations in the four corners and at a work station. Now the desision has been made to place bait stations on the exterior of the greenhouse. My question is how do I determine how many bait stations I need? Is there a formula?
ANSWER:
No, there really is no formula for how many stations or traps to place, nor for how far apart they should be. Dr. Corrigan made this point at an NPMA conference recently, challenging the ages-old formula that we should place mouse stations 10 feet apart and rat stations 20 feet apart, which was sort of the industry standard for them for many years. This was based on the presumption that mice were real homebodies and might not venture further than 10 feet from their harborage, and rats no more than 20 feet. The reality is that both of these resourceful animals will travel as far as necessary to go from available harborage to available food, so you need to carefully evaluate these two circumstances and place your stations and/or traps based on what you find. You also need to think "vertically" as well as horizontally, as both rats and mice are excellent climbers, and the harborage could be overhead with the food directly below.
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We have a tomato greenhouse account where the major pest is mice. Recently they also started growing spices and herbs. The basil is very popular and the mice population has exploded. We had control with bait stations in the four corners and at a work station. Now the desision has been made to place bait stations on the exterior of the greenhouse. My question is how do I determine how many bait stations I need? Is there a formula?
ANSWER:
No, there really is no formula for how many stations or traps to place, nor for how far apart they should be. Dr. Corrigan made this point at an NPMA conference recently, challenging the ages-old formula that we should place mouse stations 10 feet apart and rat stations 20 feet apart, which was sort of the industry standard for them for many years. This was based on the presumption that mice were real homebodies and might not venture further than 10 feet from their harborage, and rats no more than 20 feet. The reality is that both of these resourceful animals will travel as far as necessary to go from available harborage to available food, so you need to carefully evaluate these two circumstances and place your stations and/or traps based on what you find. You also need to think "vertically" as well as horizontally, as both rats and mice are excellent climbers, and the harborage could be overhead with the food directly below.
In the case of exterior baiting you may not have a reason to place many stations along lengthy sections of the exterior walls if there is no reason. There may be no entry points for long distances, and your preferred station placements may be near entrances that you are unable to permanently seal. You want them where you have the best likelihood that the wandering rodents are going to stumble upon them, at which point they are likely to enter the station, perceiving it as a momentary secure place as they wander around exposed to dangers. Once inside they will find food available and hopefully accept it at that time.
Interesting that you were achieving good control in the past with placements at only those 4 locations. Perhaps this tells you something about the dynamics of this problem. Perhaps the interior harborages were centered near those places, and this may still be the situation if nothing else has changed. Perhaps it was at the corners where the most convenient entrances were for the mice, or that immediately outside those points there was some harborage resource that was feeding the mice to the greenhouse. It might be of value to take a careful look around the exterior to see what can be changed to upset the routines that these rodents have gotten into. The further you can push them away from the greenhouse the more likely you will get them into stations you place on the exterior, causing them to have to travel further to get to the food resource and in that process to be more exposed to predators and other hazards.
Another suggestion made by an industry consultant years ago is NOT to skimp on stations. Use lots of them initially until you determine how large the population is and where you are getting the best results. You can always remove stations that show zero activity, but leave those that are clearly being visited by the mice. Use a combination of snap traps, multiple-catch traps, and even glue traps within stations designed for them. And, do take a good look at ways to exclude the mice from the structure as well as eliminate contributing conditions outside.
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