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Food plants, especially processing and manufacturing facilities, are subject to varying levels of “rodent pressure.” This is because food plants generate copious amounts of food odors, often on a 24-hour basis, for up to 365 days a year. They also generate tremendous amounts of heat and sometimes water. Naturally, these resources are highly attractive to any rodents that may be exploring the areas around the grounds or immediate exterior wall areas of a plant.

Food warehouses and distribution centers, although not producing the same amount of heat, water, and food spillage as a manufacturing plant, still remain vulnerable to rodent entry because their shipping and receiving doors typically are open for prolonged periods.

The amount of rodent pressure from one food plant or warehouse to another may vary considerably, even for facilities located within the same general area. Rodent pressure depends on the immediate exterior environment and the local mouse or rat populations nearby. Some plants, especially those that employ comprehensive IPM programs, experience low rodent activity (e.g., 0-10 mice captured indoors) year after year. But other plants are subject to combating large numbers of rodents on a monthly basis due to the plant’s location and proximity to natural favorable rodent habitats. Plants located within or nearby high rodent populations must employ maximum control efforts.

RODENT IPM. Rodent integrated pest management programs in food plants are no different in principle than rodent IPM programs for all other accounts. They differ perhaps only in scale. Thus, components of a food plant program include: 1) sanitation; 2) rodent proofing; and 3) rodent prevention and elimination programs via a two- or three-line defense system.

What follows is a brief description of sanitation and rodent proofing measures as they specifically relate to food plant environments.

SANITATION. Considering the rodent pressure in food plants it must again be emphasized that sanitation and rodent proofing must comprise the majority of a food plant’s rodent IPM program. As mammals, rodents require much more food, shelter, and water than insects. Thus, their populations will be dramatically affected by sanitation efforts. In other words, sanitation is rodent control.

Exterior areas of food plants must adhere to the highest sanitation standards possible. Allowing old equipment, conduit lines, food transfer shafts, old screw conveyors, and the like to accumulate on the ground adjacent to exterior walls is virtually installing “rodent magnets” to the plant exterior. And allowing weeds and landscaping areas to grow unmanaged can virtually result in “rearing” rodents directly on the premises.

All exterior food spills and residues should be cleaned up as frequently as possible and any large odiferous food spills should be eliminated immediately. Exterior (and interior) out-of-sight and hard-to-reach areas such as dock leveler pits, dumpsters voids, bone yards, roof vent blow outs, and all other such areas are especially important to keep clean.

These and any other shadowy, protected areas, should they also contain fermenting food residues, will serve to attract rodents directly next to or into the plant. Roof areas are also critical. Both rats and mice can and will readily scale many types of walls following odors of fermenting food lying about on roofs.

On the inside of food plants, the maintenance of a clean and unobstructed continuous sanitation line — also called an inspection aisle — along the entire interior side of the plant’s or warehouse’s exterior walls is one of the most important aspects of sanitation relative to rodent control. The sanitation line allows for regular inspections and the installation of rodent control traps.

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In warehouse areas, adequate space of 18-24 inches should also exist between rows of stacked product. This allows for easier inspections and cleaning, and rodents cannot as easily remain undetected and cause significant destruction of product. The spaces between the rows are especially important in seed warehouses.

Remember, sanitation is rodent control.

RODENT PROOFING. With effective rodent proofing efforts, fewer rodents can enter a building. Even small openings allow mice into food plants. Rodents foraging along walls of buildings tend to investigate many different types of nooks and crannies. But those openings from which currents of warm air or food odors are channeled and leaking are particularly prone to rodent invasion. And once a particular opening is used, it often is marked with rodent pheromones, attracting more rodents thereafter.

A few of the most rodent-vulnerable areas of food plants include the following: rail doors; rail pits; ramped bay doors; shipping and receiving docks/levelers; doors with improper threshold closures; open doors; unsealed utility lines entering the plant; and the obvious unrepaired structural faults and openings in the plant.

As mentioned previously for sanitation, inspections for identifying rodent entry areas should not be restricted to ground level because rodents will readily climb various conduits, building corners, and drainage gutters to gain entry from roof areas. All systems located on roofs such as ventilation fans, air-handling systems, and associated screening, stack flashing, etc., must be pest proofed. This is especially important in the roof rat regions of the U.S.

Despite good rodent proofing, some rodents are bound to gain entry to any food plant over the course of a year. Still, the difference between 20 mice versus 200 mice entering a facility each year is strongly tied to: (1) the quality and thoroughness of the facility’s rodent proofing and (2) the attitude of plant employees to cooperate in keeping the doors closed as much as operationally possible.

Dr. Robert Corrigan is author of Rodent Control: A Practical Guide for Pest Management Professionals. To order a copy of this reference book, visit www.pctonline.com/store.