“They ruined the fan, intercooler, hydraulic cooler and radiator – 15,000 dollars.” “Had that happen on a 2388. Insurance would not cover it.” “Just before harvest this year, two took out the radiator core; 1,700 dollars and about 16 man hours to replace.”

Jaynes lynn
Emeritus Editor
Lynn Jaynes retired as an editor in 2023.

What are these folks talking about? These producers from an online ag forum had one thing in common – critters nesting in combines, choppers and tractors. A surprising number of invading critters were raccoons, although cats, rats, foxes, mice and skunks also had caused their share of problems.

According to the forum chatter, it usually only has to happen once before the farmer makes dang sure he’s checked under the hood before starting up a chopper, combine or tractor. There’s something about a $15,000 repair bill that tends to keep one focused.

It’s not an uncommon problem. And while you might not eliminate the problem, there are several things that can be done to prevent their invasion.

Clean the machine

Whatever it is – hay, wheat chaff, silage blowback – it creates food and bedding for critters. If you can clean out the equipment, you effectively eliminate an animal’s basic needs for food and shelter. Otherwise, you’ve just created their bed-and-breakfast (B&B) suite. When you’re cleaning, don’t forget the engine compartment and the top of the rear axle.


The pencil test

If you can take an old wooden pencil (you know, those things with lead that are nearly obsolete now) and fit it into a hole of any size on your equipment, then a mouse can squeeze in. Fill the hole with putty, steel wool or a silicone foam filler.

Remove cover from travel routes

Those weeds around your equipment aren’t just an eyesore; they provide travel cover for rodents and varmints. If you eliminate weeds from your landscape surrounding barns and equipment (along with that equipment you know you’re never going to use again), it exposes varmints to the all-seeing eyes of predators. They’re much less likely to invade if the risks of getting there outweigh the benefits.

As part of removing easy travel routes, take care to not park equipment beneath tree branches or overhangs. Rodents climb like nobody’s business and can “drop in” on your equipment from the protection of a tree or a building overhang.

The firewood stack or lumber pile has to go

A stack of wood isn’t a B&B; it’s more like the old YMCA boarding bunkhouses. But it’ll pack ’em in. Varmints don’t even have to work that hard to create a nest here; you’ve already created the holes for them. The suggestion is to elevate the firewood or lumber stacks at least 18 inches off the ground. Let’s at least make varmints “work for it.”


I’ve heard of soaking a rag in peppermint and putting it in a ventilated container to deter varmints. Some use other strong-smelling oils like citrus, cedar or eucalyptus. There are plenty of high-pitched squealers on the market that claim efficacy for deterrents. And a host of folks claim mothballs (which stink as bad as mice in my opinion) work, as well as dried orange peels and fabric softener sheets. They’re all unproven, but some swear by them. Some say predator urine scents (bobcat, for instance) work, although it can be pricey.

I’m not sure whether to classify cats and dogs as deterrents or “traps.” Either way, both can be effective in rodent and varmint control. (I must warn you, however, that my previous rat terrier did absolutely nothing to chase away raccoons – the coward. It took my son and his .22 to “deter” them. But I had a lot fewer problems once we got rid of the chicken house.)

Baits and chemicals

You’ll find a host of rodenticides prepared in block form, loose bait or laced in cereals. The most common rodenticide contains an anticoagulant. Its effectiveness depends on regular and continuous feeding over several days, so if you choose that route, just make sure you’re checking and replenishing bait points at least weekly. One fellow drilled a hole through bait blocks and screwed them to the building rafters to control mice (he says he learned the trick from a pest control guy).

Just be aware there can be secondary poisoning to a natural predator who may eat a treated rodent, and there can be a risk to pets. Take care where these are placed and how they’re used.

No approach is a one-and-done proposal. No matter the bait or deterrent used, you’ll need to check on it periodically through the winter (weekly for rats and mice) to make sure it’s available.


Live-capture traps, sticky boards, electromagnetic devices and killing traps are techniques that can assist with physical control – each with pros and cons. For any trap to be effective, it should be placed along rodent runs and protected against access by non-target species.

Let’s be clear here – I’m not recommending any of these suggestions; I’m just presenting them to you as things others say have worked. Check local laws regarding baiting and pest control. And one last note: Whether using baits, chemicals or traps, always collect and dispose of rodent bodies. They carry diseases than can be transmitted to humans.  end mark

Lynn Jaynes

PHOTO: Illustration by Philip Warren.


A male rat typically travels about 1/2 mile each night; females travel about 1/4 mile per night. They can jump about 32 inches vertically and can produce about eight young every 24 days in favorable conditions.

A house mouse, on the other hand, feeds at nearly 200 feeding points each night. Due to its inquisitive nature, it can range from 35 to 7,000 cubic feet per night. They out-populate rats by three days, producing about eight young every 21 days in favorable conditions.

Rodents love to chew wiring, insulation, pressboard, straps or pretty much anything else because their teeth never stop growing. If they didn’t chew, their upper incisors would eventually grow right down through their lower jaws.

Raccoons are the “goat” of the varmint world and eat indiscriminately. Raccoon males travel 3 to 20 square miles, while females travel 1 to 6 square miles. Once a year, the females have a litter of one to six kits.