PROBLEMS AND SOLUTIONS: Answers To Your Toughest Pest Questions

Q. What is the residual life of rodenticide active ingredients? (G.L., Ohio)

A. The formulated bait products we use have a long shelf life. That is, they retain their effectiveness and attractiveness to the rodents over a long period of time. We have to follow storage rules, though, keeping them isolated from other pesticides that may impart odors on them. Rodenticides should also be kept in dry, relatively cool conditions (but remember that cool is relative). These products are remarkably sturdy under a variety of conditions. In rodent acceptance, palatability is one of the most important objectives of a product manufacturer. Anything that affects this will affect acceptance of the bait.

As for the active ingredients (AI) themselves, they are also remarkably stable. Most important, unlike some of the earlier rodenticides we used (like warfarin), the new generation rodenticides remain active in the rodent’s body for many days, weeks or perhaps even months. This is especially important to remember if you are baiting around non-target animals. This is one of the main reasons that labels have information about using tamper-resistant stations. These actives are effective in small amounts to rodents. However, other warm-blooded animals, if they eat the bait, could also be affected, but not until after several doses. Since the AI stays active in the liver of the consuming animal, if a non-target animal consumes several doses over a period of time (possibly weeks), then the rodenticide can have the same effect on it as it does on rodents.

Q. I am doing more and more perimeter work. I am perplexed by the number of materials we have to spray on the perimeter and I wonder just how long these really last? (W.T., Va.)

A. There are many formulations and active ingredients available today. Most researchers and pest control companies would agree that wettable powder and encapsulated formulations hold up best because of the many porous surfaces we have to treat during perimeter treatments. In addition, the newer formulations of the pyrethroid actives have long residual on surfaces. But, just because something has a long residual on a surface does not mean it will be effective for that length of time. Before this causes any panic phone calls, let me explain.

The question is this: are you trying to stop insects or repel them? If the answer is both (it usually is) then there are a lot of things to consider (including what pesticide to use and what pest you’re controlling).

All pesticides on exterior surfaces will break down. More pesticides break down in areas that are often exposed to sunlight, temperature extremes and moisture. In addition, most insects we deal with do not sit on exposed surfaces. They crawl across surfaces or are holed up in a crack or crevice. True, the more they cross this surface the more likely they will pick up the amounts needed to kill them. Most pyrethroids are applied at small rates and because they are active compounds with long residuals, their activity makes up for the fact that they will break down over time.

Also, do not forget that perimeter sprays to surfaces like wood mulch or ground surfaces may be disrupted by a variety of factors. These include animals moving through the mulch, tunneling animals like voles disturbing the mulch, pets sleeping or digging in the area, and sprinkler systems. I believe the pest control operator has to evaluate all of these factors and select materials that fit the pests or control program. (This sounds like an IPM program to me).

The author is president of George Rambo Consulting Services, Herndon, Va. Fax questions to him at 703/709-9637 or via e-mail at grambo@pctonline.com.