In addition to the damage they do to crops, rodents and other pests are blatant opportunists that wreak havoc on irrigation lines, machinery wiring and vehicle upholstery. “Mice love to chew up drip tubing and tape and get into all kinds of places and chew up wiring,” Jill Kenagy of Ernst Irrigation in St. Paul, Ore., said. “We’ve had skunks, squirrels and other critters hole up in aluminum pipes. We had a guy with a hornet’s nest in his hardnose reel and when he lit it up the nest came blowing out the other end of his big gun and bent the heck out of it — and then he got stung.”
Javier Fernandez-Salvador, Oregon State University Extension small farm and berry assistant professor for Marion and Polk counties, has heard of berry farmers with full-time crews dedicated to checking and repairing drip irrigation where rodent damage is severe.
Drip tape, used for annual crops, is most susceptible to pest damage, and voles are often the culprit. Whether buried or at ground level, the slightest bit of damage will tear the thin polyethylene. Soon water will be splashing everywhere.
Drip tubing, used for perennial crops, is much thicker, but when buried underground a leak is hard to detect.
There’s a third option Fernandez-Salvador likes: Running the drip tubing along an additional trellis wire through orchard rows, 1-4 feet high, depending on the crop and machinery used.
“Running the elevated drip tubing is the only way to avoid any damage to the tubing and be sure irrigation is working adequately,” he said.
Large aluminum handlines are an attractive nesting area for rodents and can keep clogging sprinkler heads as the nesting material works its way through the system. All lines should be flushed prior to running the irrigation at the start of the season.
“One time I saw a hand line system that was so clogged you could literally see the guts of one of the rodents coming out at the sprinkler heads because of the high pressure,” Fernandez-Salvador said. “The opening in the sprinkler heads are around an eighth of an inch.”
In the field, underground, and in the shop, vehicles parked for a couple of months can emerge with chewed-up wires and smelly nests of mice in the upholstery.
Preventing and controlling such an onslaught requires a multi-pronged approach that involves removing things rodents want, excluding them physically, setting traps and then, where appropriate, using poison.
“If you have a vehicle make sure there aren’t McDonald’s wrappers in there, or nesting materials like Kleenex or a jacket; try to make the inside as inhospitable as possible,” Rose Kachadoorian, Oregon Department of Agriculture pesticides program manager, said. “If I had a piece of equipment or a truck that I used mostly for a farm-related activity, I’d be really careful where I stored it; I wouldn’t want it to be by any kind of brush or drainage ditch that would harbor rats or mice.
“Something out in the open, either on bare dirt or gravel, is best,” she said. “Rodents, particularly rats, are pretty smart and they’re not going to be wandering around haphazardly out in the open where birds of prey can spot them. They actually have a path that’s safe and will just stick to it, maybe along a building where the grass is really tall or there’s a bunch of stuff laying around.”
Exclusion is the key in keeping rodents out of buildings: simply make sure all doors and windows close adequately. The critters can squeeze through surprisingly small spaces.
Next, think about trapping, but from a rodent’s perspective.
“Peanut butter is a universally attractive rodent bait, but it won’t be as appealing when other food sources are abundant,” Kachadoorian said. “Try putting something out there that they could use for nesting material, something really nice and fibrous or soft that a would-be mother rat would look at and think, ‘That would be great for my nest.’
“At certain times of the year rodents want certain things,” she said. “If it’s hot and dry they’re looking for water; if it’s cold, they’re looking for warmth and if they’re going to be reproducing, they’re looking for nesting material. And then all year long, of course, they’re looking for food.”
Fernandez-Salvador agrees that you can’t beat the old mechanical trap and a dab of peanut butter.
“They were going off all the time in our strawberry patch,” he said. “We caught at least 25 field mice in our quarter-acre organic strawberry patch this season.”
If cleaning up, locking up and regular trapping aren’t enough and if other animals or people aren’t at risk, some rodenticides not allowed to the homeowner can be used inside farm buildings. Even better, some pesticides can be used in the perimeter outside a building.
“You don’t want them dying somewhere inaccessible; it could be a very unpleasant situation,” Kachadoorian said. “Seal off the structure or the vehicle and kill them outside of it.
“Poison alone is not going to work; there are thousands and thousands if not millions of rodents,” Kachadoorian said. “We just really have to look at ‘How do I make this less attractive to them and, if I know they’re out there, how do I physically exclude them from the places I want protected?’”