Rat control on farms

Rodents destroy stored feed, damage crops, infest buildings, and chew through wires, plastic pipes and irrigation lines. They can be troublesome in barns, fruit groves and packing houses. Rodents can carry diseases and parasites that can be transmitted to wildlife, pets and people. The most common rodent pest in Osceola County is the roof rat (Rattus rattus). Roof rats have 8-inch-long bodies, and because they are mostly active at night, their presence is often unnoticed. Hollowed-out fruit and ¼-½” black, banana-shaped droppings are probably the most obvious evidence of roof rats. Roof rats use fences, utility lines, vines, and tree branches to reach food and buildings. They prefer nesting above the ground in buildings, piles of debris, or hollow trees. They eat fruit, seeds, animal feed, and garbage. If rats are a problem on your property, there are multiple options for controlling them.

The problem with poison

Rat poison is a common solution to rats, but rodenticides pose a high risk for accidental poisoning of people and animals. They are toxins designed to kill mammals, so humans can suffer similar toxic effects from these poisons. Rodents, pets, harmless wildlife and people often share environments so the risk of accidental exposure is always possible. U.S. National Poison Control Centers received over 73,000 calls for accidental human exposure to rat poison in 2015. Deer, ducks, turkeys, dogs, and children have suffered illness or death from eating bait directly. Some baits also kill wildlife like owls, eagles, hawks, and bobcats when they eat rodents that have been poisoned. Rat baits with newer “second-generation anti-coagulants” are particularly dangerous for non-target wildlife like birds of prey because they kill slowly and rodents keep eating them long after they’ve ingested a lethal dose. By the time rodents die, their bodies contain many times the lethal dose and are deadly to anything that may eat them.

Using rodent bait

Poison baits must be placed where they are inaccessible to children, pets, livestock, and wildlife. Where rodent runs are exposed, and in all outdoor situations, tamper proof bait boxes should be used. This means that the box cannot be opened and bait cannot be shaken out. Rats visit the boxes and eat the bait, and may die far away from the poison source, even days later. Bait blocks should be used in bait stations; pellets and powders should be avoided because they can be distributed out of bait stations, exposing other animals or humans, or contaminating crops. Bait blocks must be secured inside boxes, and boxes must be secured to the ground or a structure so a child or animal couldn’t move it. Bait stations should be placed near rat nesting areas or on travel routes. Bait boxes are labeled to be used outdoors, indoors, or either. Only place a bait station in an area that it is intended to be used. Bait stations should never be placed in locations that may become flooded (i.e. under roof eaves without gutters and low areas), as the poison could contaminate fields, packing areas, or irrigation sources.Some rat baits are toxic to humans even if they contact skin; read and follow all label directions.Rat baits available for commercial/agricultural use:

Pesticide Class Active Ingredient What it does Risk of Primary Poisoning
if poison is eaten
Risk of Secondary Poisoning
if poisoned rat is eaten
Bromethalin Nerve toxin- shuts down the body’s ability to produce energy. High (humans/mammals, birds, fish) Low (mammals, birds)
Cholecalciferol (Vitamin D3) Causes too much calcium to be released into blood, causes kidney, liver, heart failure. High (humans/mammals)
Moderate (birds)
Low (mammals, birds)
Sodium Chloride (salt)(efficacy unknown) Causes dehydration, blood thickening, kidney dysfunction, coma. Low (humans/mammals, birds) Low (mammals, birds)
1st Generation anti-coagulants Chlorophacinone Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, fish)
Moderate (birds)
High (mammals)
Moderate (birds)
Diphacinone Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, fish)
Moderate ( birds)
High (mammals, birds)
Warfarin Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding, causes human birth defects. Moderate-High (humans/mammals) Low (birds, fish) Low (mammals, birds)
2nd Generation anti-coagulants Brodifacoum Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, birds, fish) High (mammals, birds)
Bromadiolone Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, birds, fish) High (mammals, birds)
Difethialone Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, birds Moderate (mammals) High (birds)
Difenacoum Prevents blood clotting, inhibits Vitamin K1, causes internal bleeding. High (humans/mammals, birds, fish) High (mammals, birds)


Alternatives to poison

Trapping rats eliminates the chance of poisoned rats dying in machinery or crawl spaces, where they are difficult to retrieve, and cause odor for months. If you don’t want to deal with snap traps, electronic traps are an easy option for indoors. Bait traps with nuts or raisins; never bait with poison. Don’t use snap traps outdoors where they can harm wildlife like birds. Roof rats are cautious of new objects; leave traps in place for at least a week. Protect and encourage snakes, hawks, and owls that help control rodents naturally.

Preventing rats

If you kill rats without reducing habitat, new populations of rodents will find their way to your property. Preventing rat nesting, access, and food will help you achieve long-term control:

    • Keep lids on garbage cans.
    • Don’t keep animal feeds out at night and store it in metal cans with lids.
    • In buildings, use rodent-proof materials like metal hardware cloth or concrete over openings they could enter (ie- holes where pipes/wires enter structures)
    • Keep trees/vines from touching fences, buildings, wires.


What not to use

There is no evidence that ultrasonic or electromagnetic devices repel rodents. Ultrasonic devices cause hearing loss in dogs. Cats and dogs cannot usually control roof rats, as rats will stay above the ground to avoid predators. Avoid sticky traps, which catch other wildlife like lizards and birds. Rodent repellents are usually ineffective, and often cannot be used on human food plants.


Posted: February 6, 2018

Category: Agriculture, Crops, Farm Management, Livestock, Pests & Disease, Wildlife

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