warfarin and other anticoagulants, may be required for effective control of warfarin resistant rats. These one-shot baits can be used more effectively by prebaiting. When rodents, especially rats, are well-fed and not especially hungry, prebaiting for 6 to 8 days gives better control than prebaiting for shorter periods. Warfarin and other older anticoagulant rodenticides are self-prebaiting, thus eliminating the need to change from unpoisoned to poisoned bait. The optimum mix for zinc phosphide is 0.2 ounces (7.7 g) to 1 pound (.45 kg) of bait. Carefully follow the label directions for Maki.

It is frequently necessary and desirable to supplement poisoning with trapping. The wood-base spring trap is the most effective type and should be used in adequate numbers. Traps should be tied to overhead pipes, beams, or wires, nailed to rafters, or otherwise secured wherever black greasy marks indicate runways. On the ground rodents normally run close to walls; consequently, the traps should be set at right angles to the rodent runways, with the trigger pans toward the bulkhead. Boxes and crates should be positioned to create passageways where rodents must travel over the traps. Although unbaited traps with the trigger pan enlarged with a piece of cardboard or lightweight metal may be used in narrow runways, trapping is usually more effective when accomplished with baited triggers. Preferred trap baits vary with the area and the species of rodents involved and include bacon rind, nuts, fresh coconut, peanut butter, raw vegetables, and bread or oatmeal dipped in bacon grease. Service all traps regularly to remove dead rodents and replace the bait. Use chain or wire to anchor the traps and to prevent a live rodent from dragging it away.

Fumigation will effectively destroy rat populations in their burrows and other hiding places. This procedure is carried out only when burrows are away from buildings. Where the fumigant can be confined, this method of control will also kill ectoparasites infesting the rats. After the fumigant is applied, the burrow openings should be tamped shut with dirt or sand. Fumigation for rat control should be conducted only by trained certified applicators.

Rat guards are used by naval vessels berthed in ports where plague is endemic to prevent rodents from entering the ship. After a ship leaves a plague-infected port, rat guards should be used at other foreign ports of call en route to the United States. Rat guards are not required but are recommended at foreign ports of call and in U.S. ports. When the conveyance and cargo have been issued a quarantine preclearance in a retrograde cargo inspection program, rat guards are not required by quarantine even though the shipment may originate in a plagueendemic area.

Rodents are basically nocturnal. Therefore, gangways and landing ramps should be well lighted at night to discourage rodents from moving aboard. Gangways and other means of access to the vessel shall be separated from the shore by at least 6 feet unless guarded to prevent rodent movement. Cargo nets and similar devices extending between the vessel and shore will be raised or removed when not in use.

Inspection of all subsistence items and cargo for sign of rodents, such as droppings, hair, gnawing, is essential in maintaining a rodent-free ship.

A current Certificate of Deratization or a Deratization Exemption Certificate is required for naval vessels. Requirements for this certificate are detailed in BUMEDINST 6250.7 series.