Introduction
In general, baiting rodent burrows can be done relatively easily, quickly, and inexpensively – and it is a hugely effective method of rodent control. But because burrow baiting appears so easy, the procedure can also lead to some problems if the appropriate precautions are overlooked. There is much more to correctly baiting rat burrows than stuffing a packet or pouring meal bait down a rat hole and then caving in the burrow.
The correct baiting & monitoring of rat burrows is important for three reasons: 1) to maximize safety to people and non-target wildlife; 2) to maximize the eradication of the rats living within the burrows; and 3) to allow for accurate follow-up and monitoring of the burrow system long term, which in turn provides a guideline for timely follow-up treatments.
From a safety aspect, it must be kept in mind that people walk dogs; inquisitive children play in parks, yards, and empty lots; and millions enjoy watching city urban wildlife such as possums, bandicoots and birds of all kinds. All of these animals inhabit parks as well as the smallest yards and gardens. Incorrectly baited burrows can potentially harm all of these non-target groups and the environment. Finally, from an operational standpoint, incorrect baiting does not allow for the necessary monitoring post-baiting in order to determine whether or not the burrow is still active, and results in a waste of time and money, and an unnecessary introduction of pesticide in the environment.
The following is a best practices procedure for safely and correctly baiting rat burrows to achieve maximal effect.
Bait formulation
Technically, each of the rodenticide formulations (pellets, packets, blocks, meals, seeds) can provide good rat control. But certain bait formulations are better suited for burrow baiting efforts and non-target safety than others. In general, rodents have more of a tendency to translocate (i.e., carry away and move the bait) a bait back out of their burrow if the bait is large in size and easily movable.
Importantly, packet-style baits and whole bait blocks can be easily moved, carried, or pushed about by rats. Bulk loose pelletssuch as Ditrac offer both small size, and good “weatherability.” Some professionals crumble their bait blocks into smaller sizes, and then pour these into burrows, which can, with some effort, achieve the same goal as using the pellets.
Considering the dampness of the ground associated with burrows, some believe that the packet-style baits and “waxy” blocks offer the best resistance to weather and moisture. But loose pellets when inserted correctly into a burrow are likely to be consumed by rats long before they would be subject to deterioration from the ground moisture found within an active burrow.
Applying bait to burrows
The key to successful burrow baiting is to deliver the bait with as little disturbance to the rat’s home as possible. This is because both Norway and Roof rats are sensitive to changes in their environments. Often they react towards changes by avoiding or rejecting new items that are associated with any disturbances to their daily routine.
Thus, perhaps the most effective way to bait a rat’s burrow is to mimic Mother Nature. In the rat’s natural life in fields and open areas the wind blows seeds, berries, nuts and other edible items across the ground. These items tend to roll into and down the burrows. Thus, carefully placed bait pellets inserted directly down into a rat’s burrow system are rarely translocated out of the burrow compared to packets or big bait blocks.
The following steps are recommended:
1. Burrows should be baited with pellets using a long-handled (about 1m) scoop applicator or via a hose-and-funnel technique.
2. For the hose and funnel technique, a plastic funnel can be attached to a 1m. section of any type of plastic flex hose, or garden hose (18mm to 25mm diameter to allow for good pellet flow). This technique allows for a quick pour and ensure good penetration of the bait into the burrow. The hose and funnel technique also helps to save on the physical exertion of constantly bending over when many burrows need to be treated.
3. To provide adequate protection against non-target animals gaining access to bait, all baits should be placed down into the burrow so the bait is not visible from the entrance. Depending on the construction of the burrow, this will mean the bait will be inserted down from about 30cm – 1m into the burrow.
4. The amount of bait applied should be done according to label directions. For severe infestations, use the maximal amount of bait recommended. Use the minimal dosages for minor infestations.
5. After baiting a burrow, do not cave in the burrow with soil or paper. Correctly baited burrows should remain open and undisturbed for at least one—and preferably two—weeks. There are several reasons for this. First, it usually takes about 5-7 days for bait to kill a rat so there is little use of caving in the burrow immediately after baiting. Active rats will continue to come and go from the burrow system for several nights, conducting their daily forays for water, food or to conduct other behavioral routines. Second—and most important from a hazard exposure point of view—is that with a rat’s re-opening of their “disturbed” burrow, any object that is new and unfamiliar to the rat that arrived with the cave-in (i.e. your bait) may be pushed back out on top of the ground along with the soil they are excavating. This allows for potential exposure to humans and wildlife from bait that is pushed back above ground. This has been documented in countless instances around parks, zoos, yards and farms throughout the country. In summary, when pest control professionals cave burrows in immediately after baiting in an attempt to protect against unintended bait exposure to non-target animals, they are unwittingly creating a situation that increases the chances of exposure.
6. On data sheets, record the location, day, and time the burrows were treated.
Monitoring and Closing the Burrow
1. One to two weeks after the initial baiting fill the burrow opening using wads of paper.
2. Re-inspect the closed burrows 1-3 days later.
3. Re-opened burrows demonstrate that the burrows are still active and should be re-baited. Re-bait any reopened (i.e. still active) burrows. The applicator should assume that there are fewer rats per burrow, so about one-half as much bait as was used on the initial baiting can be used per burrow for the follow-up baiting.
4. Again, 7-14 days later, repeat the process until control of the rat colony is complete.
Using this procedure, especially revisiting infested areas repeatedly until the local rodent population is eliminated (or very nearly so)ensures that you are not simply reducing the population by a few rats after a single baiting, but are effectively knocking down and eliminating the population and preventing it from rebounding quickly. A single baiting in an infested area may reducethe population by as much as 40% of the rodents. However, that is not nearly enough to eliminate it. A 40% reduction after a single baiting, without follow-up baiting in still-active burrows, can allow the population to rebound to its original size (or greater) in a matter of weeks.
Done properly, repeat bait application can eliminate or reduces the target population by 90-95 percent. This means it might take any surviving rats many months to rebound to original numbers, or they may never be able to rebound at all (Of course, this is where the importance of good sanitation in the target area, reducing all of the rodents’ food sources, will ensure that the population elimination is maintained.)
Just as it is important to leave the burrows open during the baiting program, it is equally important to stress that all burrows following successful control should be filled in as best as possible with soil. In this way, community-level rat infestations can be monitored for any new or surviving infestations. Additionally, old rat burrows are attractive harborage sites for any incoming new rats, as well as for stinging yellow jackets and other ground-nesting pests to build their nests.
Using this Best Practices Procedure will provide for fresh attractive bait to be delivered directly to the rats while simultaneously reducing exposure to non-targets animals. With pesticide applications, everyone has a responsibility towards the environment and non-target animals.
