QUESTION:

How long do fipronil (Termidor) and Imidacloprid stay active in wall voids? I have read through your archives and in one response on the length of residual chemical sprays have outside on a foundation you said they may last 30 days. If this is true is quarterly spraying really a value to customers? I only do monthly spraying, as here on the coast of Washington with our extremely wet weather I consider quarterly spraying a poor choice and a financially poor value to my clients.

ANSWER:

I always apologize for dancing around a specific answer to the question of "how long does it last", regardless of the active ingredient. The fact is that the residual length of any active ingredient varies wildly depending on where you put it, and thus the varying conditions that active ingredient will face. The chlordane we used to apply to the soil under a structure might have lasted over 30 years, with enough a.i. still there to kill termites that entered the treated soil. That same chlordane applied to a hot asphalt driveway in the sunshine in July might be destroyed within a couple of days, a victim of the UV light and heat beating down on it. Add some errant sprinklers or a rainfall and the a.i. takes a further beating.

So, according to what we were initially told when imidacloprid (Premise) first came on the market, within a few months after application for termites there was a dramatic drop in the amount of a.i. remaining in the soil. BUT, after this initial drop the residual sort of settled down and over the next 4 or 5 years it dissipated slowly until there was no longer a level that would kill termites. So, in the protected soil (cool, shaded, dry-ish) under a home the imidacloprid lasted a few years. That same active ingredient placed around a shrub or tree for aphid control gives "season long" control, and is no longer there the following year. That same a.i. applied around a foundation outside for ant control is likely gone within a few weeks, falling victim to sunshine, water, pH factors, heat, etc.

Thus, it is very difficult to put a definite number on how long something lasts at a level high enough to kill insects that crawl on the treated surface over the coming days and weeks. However, at a seminar some years ago one of our industry's noted experts stated that he would be surprised if ANY of our current products (mostly pyrethroids then) would give more than 2 weeks of effective residual when used for occasional invader pest insects outside. I recognize that this contradicts what some manufacturers tell us about their products, but I reserve the right to be suspicious. Perhaps some of them could last up to a month, especially where temps are lower and intense sun does not beat down on the treated surface. But, expecting the a.i. to last for 3 months would be wonderfully optimistic.

However, quarterly treatments certainly provide benefit, particularly if you combine them with the appropriate other steps in an overall pest management approach, meaning IPM - exclusion, source reduction, habitat modification, sanitation, etc. All of these steps minimize the ability of an arthropod pest to move into an environment and to breed and thrive there. The insecticide application is best viewed as a way to knock down the existing population so that it cannot recover quickly, and if your non-chemical steps have made life miserable for the pests in the landscape it will take them much longer to rebound and repopulate that area. If nothing is done other than treating around the foundation with a 2 foot band of chemical you may kill encroaching bugs for the next couple of weeks, and after that the constant pressure from areas beyond that 2 feet will be able to cross the treated zone and find a way inside.

I hope this answers the question without offending too many people, but we need to accept that a total reliance on pesticides is not the best approach to pest management, and customers of yours need to understand that changing the environment so that it is not conducive to pests living there is an important part of the program. Exclusion, in particular, should be explored, as our overall goal is not to eliminate all living things on the property, but to keep unwanted bugs and other animals out of the home.

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