The non-chemical approach consists of: (1) rodent proofing, (2) sanitation, and (3) traps.
Rodent-proofing or exclusion is the process of denying rodents entry into buildings by improving the building's structural integrity. Coupled with effective and ongoing environmental sanitation programs, these two practices provide the best long-term and cost effective component of any rodent IPM program. Fundamentally, exclusion involves the elimination of dead spaces, cracks, crevices, and other openings so that pests cannot hide in, enter, or leave a specific building, room, or piece of equipment (Scott 1991). Regardless of the cost or thoroughness, rodent-proofing programs require continuous vigilance.
Seal cracks and openings in building foundations and any openings for water pipes, electric wires, sewer pipes, drain spouts, and vents. No hole larger than 1/4 inch should be left unsealed, in order to exclude both rats and house mice. Make sure doors, windows, and screens fit tightly. Their edges can be covered with sheet metal if gnawing is a problem. Coarse steel wool, wire screen, and lightweight sheet metal are excellent materials for plugging gaps and holes. Norway and roof rats are likely to gnaw away plastic sheeting, wood, caulking, and other less sturdy materials. Because rats and house mice are excellent climbers, openings above ground level must also be plugged. Rodent proofing against roof rats, because of their greater climbing ability, usually requires more time to find entry points than for Norway rats. Roof rats often enter buildings at the roofline, so be sure that all access points in the roof are sealed. A common avenue of entry for rodents, especially roof rats, into the open eaves of an attic is via a tree limb touching the roof of the structure. Such tree limbs should be pruned back a minimum of 6 feet. If roof rats are traveling on overhead utility wires, contact a pest control professional or the utility company for information and assistance with measures that can be taken to prevent this. Circular rat guards of galvanized metal should be placed around vertical wires and pipes to prevent rats from climbing upward. Rats may wedge themselves between a drain and the wall and thus reach the upper floors of a house; a circular rat guard on the drain will prevent this.
Sanitation is fundamental to rat control and must be continuous. Based on the biology of rodents, it should be obvious that the overall health of a rodent, and the growth of rodent populations, heavily depends on the availability of food, harborage, water, and nesting materials. When these resources are scarce or lacking, rodent populations cannot proliferate. If sanitation measures aren’t properly maintained, the benefits of other measures will be lost and rats will quickly return. Good housekeeping in and around buildings will reduce available shelter and food sources for Norway rats and, to some extent, roof rats. Neat, off-the-ground storage of pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods will help reduce the suitability of the area for rats and also will make their detection easier. Collect garbage, trash, and garden debris frequently, and ensure all garbage receptacles have tight-fitting covers. Where dogs are kept and fed outdoors, rats can become a problem if there is a ready supply of dog food. Feed your pet only the amount of food it will eat at a feeding, and store pet food in rodent-proof containers.
For roof rats in particular, thinning dense vegetation will make the habitat less desirable. Climbing hedges such as Algerian or English ivy, star jasmine, and honeysuckle on fences or buildings are conducive to roof rat infestations and should be thinned or removed if possible, as should overhanging tree limbs within 3 feet of the roof. Separate the canopy of densely growing plants such as pyracantha and juniper from one another and from buildings by a distance of 2 feet or more to make it more difficult for rats to move between them.
Trapping is the safest and most effective method for controlling rats in and around homes, garages, and other structures. Because snap traps can be used over and over, trapping provides a quick knockdown of the population and is less costly than baits but more labor intensive. Traps can be set and left indefinitely in areas such as attics where rats have been a problem in the past. The simple, wooden rat-size snap trap is the least expensive option, but some people prefer the newer plastic, single-kill rat traps, because they are easier to set and to clean. Snap traps with large plastic treadles are especially effective, but finding the best locations to set traps is often more important than what type of trap is used. Generally, young rats can’t be trapped until they are about a month old, which is when they leave the nest to venture out for food.
The lure baits used on the snap traps should be varied. The success of any bait usually depends largely upon how much other food is available and what the rodent is accustomed to eating. Nutmeats, dried fruit, bacon, or a piece of kibbled pet food can be an attractive bait for traps. Fasten the bait securely to the trigger of the trap with light string (dental floss), thread, or fine wire so the rodent will spring the trap when attempting to remove the food. Even glue can be used to secure the bait to the trigger. Soft baits such as peanut butter and cheese can be used, but rats sometimes take soft baits without setting off the trap. Set traps so the trigger is sensitive and will spring easily.
The best places to set traps are in secluded areas where rats are likely to travel and seek shelter. Droppings, gnawings, and damage indicate the presence of rodents, and areas where such evidence is found usually are the best places to set traps, especially when these areas are located between their shelter and food sources. Place traps in natural travel ways, such as along walls, so the rodents will pass directly over the trigger of the trap. Traps are effective when set next to a wall beneath a board leaning against the wall. This creates a shadowy runway, one of the most preferred types of areas for rats and mice.