Last fall and winter was one that I’ll always remember. The rodent population went NUTS and we had a lot of feeding damage on nursery and landscape plants. This year, we haven’t seen as many rodents around. Low precipitation levels and tough growing conditions have diminished food sources that would support large populations of rodents. Natural predators seem to be on the rise again. Mice and voles travel in tunnels under the snow or under the cover of fall foliage and feed on the bark and phloem of several tree and shrub species. The longer the winter, the more damage they can do and so far, climatologists seem to be predicting a more typical and cold winter. Bye bye El Nino, Hello El Freezo. Late summer is the time of year when voles and mice breed heavily in expectation of the significant seed/fruit source that can be harvested and stored. By putting out rodent bait in nursery production areas in September, you can help prevent populations from getting out of control.
Use bait stations to extend the life of the bait and create a safe haven for rodents to feed. Place bait stations in areas known to be infested such as grassy fence rows, weedy patches and walkways between containers and polyhouse frames. Try to have about 10 bait stations per acre (25 per hectare) of production area. Remember to rotate zinc phosphide baits with other baits (e.g. bromidialone, brodifacaum, defethalone) since the voles will become bait shy with repeated use of zinc phosphide. Where large areas of field production exist, broadcast application of baits may give some management where tunnels and past damage are evident, but its not as effective as bait stations.
Rodent bait stations will also help keep local populations down in the landscape, but to be sure, protective tree guards should be placed around young trees (diameter less than 15 cm). You can either use traditional coiled tree guards or corrugated drainage pipe. Be sure that the tree guard extends at least 75 cm above the stem. For areas that receive a lot of snow, you might want to make that 100 cm.
Mulching or mounding soil up around the outside of the tree guard may also keep herbivores from getting in under the tree guard.
And there’s always good, old-fashioned predation to keep rodent numbers down. Be sure to avoid rodent bait applications where predation pressure is heavy. The toxins in rodent bait can also be toxic to predators.
Research on the predatory habits of the domestic cat have found that 1/3 of a cat’s day is spent trying to find and kill small mammals. I think the other 2/3 is spent sleeping or staring……..:)