THE PEST: Field Mice, Gophers, and Baby Rabbits
Field mice, gophers, and rabbits present a serious threat to orchard health. Mice feed on the bark at the base of the trees, and gophers and rabbits feed on their roots. They are particularly a threat to younger trees, as they can girdle and kill the tree quickly, but they can cause extensive damage to older trees as well - to the point of slowly killing them also. Gophers may also chew through irrigation lines, causing water loss and misdirecting irrigation water through their tunnel systems.
It may take some time to see the damage done by rodents, but stunted or yellowing trees and thin leaf growth are noticeable signs, as is bark missing near the base of the tree or 2-3 inches below ground. Root rot can also develop from gophers eating the roots, leaving them open to any bacteria in the soil. Eating through the bark disrupts the flow of nutrients throughout the tree, weakening it, and eventually killing the tree.
THE TRADITIONAL METHOD: Traps, Baits, Fumigants, Gas Explosives, Flooding, Vegetation Management
Traditional methods of killing mice and gophers involve setting traps along their tunnel systems, using herbicides to kill off the field grasses that they feed on, releasing fumigants such as aluminum phosphide into the tunnels, using a probe to place toxicant baits into their lateral tunnels, flooding their tunnels with water, or using the concussive force of a propane/oxygen explosion to knock them out and collapse their tunnels.
There are many pros and cons to each of these, and while they are effective, there is a better alternative.
OUR IPM METHOD: Owls
For about every 24 acres, you build an owl box - about 24 x 24 x 24 inches with a 6x6 inch opening - and attach it to a 20 foot pole. Around December to January, barn owls will select their nests near good food supplies. Throughout the spring and summer, the owls will then swoop through the fields, eating up the rodent population. A family of owls can consume over 1000 rodents per year. They will routinely hunt a 1 mile radius from their nest, but are known to fly up to three and a half miles from the nest to find food. It can also be helpful to place 10 foot perches around the ranch, as they are also known to hunt from a perched position. Barn owls are not territorial, so you can have as many clutches in an area as the rodent population will support.
There are typically 3-7 young per clutch, and full grown males require 3 rodents per day, females 2 per day, and young 4-5 per day.
Owls produce more young when rodent populations are higher.
Owls return to their nest sites each year.
Once you have the box up, the only labor required is to clean the boxes out twice a year.
Con: They will never completely eliminate their food supply and they do not hunt the area directly surrounding their nest. This is not ideal, but also not horrible, as rodents do provide a level of soil aeration, bringing minerals from the lower levels to the top soil and increasing water penetration.
Bonus: Owls will also eat insects.