Why one spray never clears an infestation

Almost every callback we get after a competitor’s treatment has the same shape: it worked for a fortnight, then it came back. The customer assumes the product was weak. Usually it was fine. The problem was timing.

The eggs are the point

Most residual products and baits kill adults and nymphs on contact. What they do not do is reach an egg inside its case. A cockroach ootheca, a bed-bug egg, a blowfly batch — these are sealed, and they hatch on their own clock, days to weeks after the adults are gone.

So a single visit clears the visible population and leaves the next generation loaded in the walls. When those eggs hatch, they walk out onto a barrier that — if it was laid properly — is still there and still lethal. If it was a one-off spray with nothing residual behind it, they walk out onto a clean floor.

Two things have to be true

For the follow-up to matter, two things have to hold from the first visit:

• The barrier is still there when the eggs hatch. That means a residual laid at the right rate, not a knock-down spray that is gone by the weekend.
• We come back inside the hatch window. Too early and the eggs have not hatched; too late and the new adults have already bred again. The window is specific to the pest, which is why we book the follow-up when we book the first visit, not “if it comes back”.

What that looks like on a job

On a German cockroach job in a kitchen, the first visit is gel bait at the harbourages and a residual band across the runs. The second visit, timed to the ootheca hatch, catches the nymphs before they reach breeding age. Two visits, planned from the start — not one visit and a hopeful wait.

It is less dramatic than a fogging machine and it is the reason the problem does not come back. The barrier does the work; the timing decides whether it gets the chance to.