There’s no simple answer for this question. Probably at least two years.
The name of the product won’t help you as much as reading the label to find out what the main chemical “the active” is. Some older chemicals, like chlorpyrifos, can degrade very quickly, maybe in just a few months. (Apologies for using the chemical names rather than product names – see later). Others such as bifenthrin and fipronil will generally last longer. Fipronil is effective for a disturbingly long time in the environment. Imidacloprid is somewhere in between but may wahs away or be picked up by plants. Chlorantraniliprole is a bit less known but should last at least as long as imidacloprid.
The rate at which a poison degrades varies enormously over surprisingly short distances.
The main factors are:
- How much was applied (the initial or starting dose).
- The temperatures. Most chemicals break down more quickly in the heat.
- Rainfall and wet-days.Water aids degradation, can wash the product away or can assist it to slowly disperse.
- Soil type. Soils that are basic (alkaline) or acidic can ‘eat up’ a chemical. Sandy soils with little organic matter tend not to hold on to a chemical.
- The presence of plants. Plants make just take up a chemical (imidacloprid is good for aphids, Elm Leaf Beetle and killing bees).
- Applicator skill. This distribution is never perfect and gaps can develop.
- The chemical’s properties. Some aren’t particularly stable molecules (like chlorpyrifos, deltamethrin or permethrin in the soil).
Then there’s disturbance from floods, gardeners and burrowing animals. The chemicals will nearly always last a lot longer under your house than around it. With a chemical, you might get ten years or more service life under the house but find it fails in two to five years around the outside. There’s always a risk the poisoned-soil zone mightn’t last as long as you’d hoped.
–You’ll note I used the chemical names rather than product names. There’s likely to be some variation between products that rely on the same chemical poison (=termiticide or ‘active’) but have slightly
different formulations or origins. Even the difference in the size of the tiny particles of poison can make a big difference. You can get your soil tested to see what’s there or you can rely on the experience of your pest manager to tell you when another dose is needed. Try not to over do it with applications as more is not necessarily any better but usually carries higher risks. Some pest managers will push for reapplications that may not yet be necessary. Be an informed consumer. Where chemical is applied by refillable pipes, it is common to get it replenished every 3 to 5 years. This may be a warranty requirement, so don’t miss if it means you lose cover . . .