Hi. You should ask your vet as they are most familiar with winter conditions and prevalent vectors in your area. Like here in Maryland, I have personally witnessed flying mosquitos when it was 17 degrees Fahrenheit outside. I use it year round, just because of that. Depending on the size of your Yorkies, I would maybe look into a decreased dose (more exact) if they are on the smaller side, and/or treat them every other month, but do ask your vet. |