Most colonies that die in winter were killed in August. Mites raised through summer
wreck the winter bees before you ever see a problem — so the plan matters more than the product.
Here's a dated one for your climate.
Dates are shifted for your zone from a south-central Pennsylvania baseline. Treat
them as the week to act in, not the day.
—
The year
Why August is the one that counts. The bees that carry a colony through winter are raised
from about mid-August to early October. They're physiologically different from summer bees — fat,
long-lived, built to last six months instead of six weeks. A mite feeding on one of those larvae
produces an adult that doesn't make it to February, and the viruses mites carry do the rest. Treat
in November and you've saved a colony of bees that were already damaged before they emerged. The
August treatment isn't about the mites you can see. It's about the bees that aren't born yet.
Don't skip the follow-up wash. Every treatment has a realized kill well below its label
number — wrong temperature, capped brood shielding mites, a strip that fell into the bottom board.
The only way you know it worked is to wash again two to three weeks later. A treatment you didn't
verify is a treatment you didn't do.
Rotate what you use. Amitraz resistance is real and spreading, and fluvalinate (Apistan)
has been largely useless in most of the country for years. Alternating between unrelated chemistry
— an acid one round, a synthetic the next — keeps both working longer. Using the same product
every time for five years is how you find out the hard way.