The best time to do this is before the start of mosquito season in your area. (oregonvma.org)
You can use a preventative during peak mosquito season in areas that have cold winters, or you can keep your dog on heartworm preventative all year long in warmer climates. (dogs.lovetoknow.com)
Because climate change is warming winter, and mosquitoes season starts earlier and stays later each year, timing is getting too difficult to predict. (animalcafe.co)