[Richmond]

As previously stated red mite does not produce dirty vents. True it is the season for red mite but first see if you actually have it. A cigarette like ash coating inside corners of houses, joints in the wood and ends of perches are a definite sign. The ash like substance is mite droppings.

A perfectly safe treatment is copious application of diatomaceous earth (trade name Diatom). Puff in every crevice and rub all over perches liberally. You can also apply it directly to the birds. Birds affected by red mite appear listless, with pale combs and will almost certainly have stopped laying. If you can keep them outside for a few nights (in a covered pen) while the house is treated the birds will pick up.

However back to the original question of dirty vents.  Are they still mucky despite worming? Are they still on the same ground therefore could have reinfected?