Prebaiting: To Kill Or To Monitor?

Prebaiting rodents with a nontoxic bait such as Census Bait Blocks, from Zeneca Professional Products, is being considered by some pest control operators as an innovative IPM strategy. But prebaiting is a technique that has been promoted and used in the pest control industry for decades.

It is also a Myth Conception that the use of Census is a conventional prebait procedure. According to consultant Robert Corrigan, Census should be used to determine the presence of rodents only before toxic bait is used. "Why waste 20 pounds of bait when a quarter pound will take care of the one spot showing activity?" Corrigan points out.

Conventional prebaiting has been widely practiced in the pest control industry for a long time. Rex Marsh, a biologist with the University of California-Davis, suggests using clean, untreated cereals in bait stations. In the Seventh Edition of the Mallis Handbook of Pest Control, Dr. William Jackson recommends prebaiting of the chemosterilant alpha chlorohydrin for best results.

In Rats & Mice, A.P. Meehan reported that in the 1940s, the widely used rodenticides Antu and 1080 were more effective following a prebait program, and that bait shyness with zinc phosphide could be overcome by prebaiting. In the First Edition of the Mallis Handbook, which was published in 1945, Meehan noted that prebaiting is important if previous efforts to destroy rats have been unsuccessful.

(Because few people have a copy of the First Edition, here is a sample of Mallis' humor: "PCOs are reluctant to use bait because rodents may die on the premises; their souls departed but their fragrance lingers on!")

Prebaiting for other pests is a widely accepted practice. Birds have long been enticed to feed on Avitrol by first feeding them untreated seeds. Prebaiting for ants with peanut butter, honey, Karo corn syrup and other foods is welldocumented and practiced.

Some pest control professionals question the legality of placing nontoxic bait in a bait station marked Poison. Dr. Eric Smith, co-author of the NPCA Field Guide, suggests covering the word Poison with duct tape.

OUTDOOR MONITORING. Placing nontoxic bait blocks outdoors is an ideal way to monitor the presence of rodents. A line of bait stations against the outside wall and another line at the edge of the property would most certainly be the first line of defense against nearby rodent populations.

Eric Smith suggests the use of 8- to 10-inch sections of 2- or 3-inch-diameter PVC (polyvinyl chloride) pipe. The PVC pipe has two holes drilled through it to suspend and anchor the bait in a bait station. Select the color black, green or white which best blends in with the background. The pipe should be stenciled Nontoxic Bait to avoid legal complications.

But placing a nontoxic bait inside may not be acceptable to some jurisdictions for various reasons. One reason is that the nontoxic bait block could still be mistaken for a toxic block by someone who could claim they were poisoned. Perhaps the use of a Nontoxic Bait label would avoid the ordeal that would follow such an event. (The manufacturer is planning to furnish Nontoxic Bait notices to be placed inside bait stations.) In places where the label permits, a puff of plain diatomaceous earth into the tube would take care of insects that could feed on the bait or seek shelter.

The bottom line: Conventional prebaiting may be useful where rodents are known to exist. The nontoxic bait block monitor tells you where to place the bait.

Robert Corrigan considers conventional bait placement in all possible sites equivalent to baseboard spraying with no evidence of infestation.

According to Eric Smith, in sensitive accounts where frequent monitoring is not feasible, it may still be desirable to use toxic bait in perimeter bait stations.

William Jackson agrees, but he believes an exception should be made in extremely critical situations where absolutely no rodent intrusion is permitted. In such cases, according to Jackson, management has no choice but to incur the extra expense of placing two or three perimeters of interception lines with Census blocks and then monitoring as frequently as needed.

Now we see why PCT Contributing Author Stoy Hedges has written that IPM should stand for Intelligent Pest Management.

CALLING ALL PCOs. I've been asked to write/revise the chapter on clothes moths for the Eighth Edition of the Mallis Handbook of Pest Control, which will go to press this summer. I need an immediate reply from readers from across the U.S. who can report an increase in calls for the control of clothes moths. Please specify webbing or casemaking species. Information on dermestid damage is also welcome. I need to know whether it is a Myth Conception that the fabric pest business is really moribund.

To reply, please call or fax me at 954/427-9716. (Call first before faxing.) The deadline for the Eighth Edition of Mallis is fast approaching.

Harry Katz is a PCT contributing editor.