Sevin dust - is it harmful?

It says on the bag that it's harmful if swallowed so I personally wouldn't put it on anything I was going to eat. It's fine for killing ticks on the lawn though. You shouldn't have a problem washing it off just make sure you don't eat any of the berries straight off the bush. For future reference, it's better not to use that kind of stuff on your garden because it's a broad spectrum insecticide which means it kills the good bugs as well as the bad. Usually if you just leave your garden alone the good bugs will balance out the bad ones barring any non-native species invasion. Also if you see spiders in your garden don't kill them or knock down their webs because they are there to eat the bad bugs that would ruin your berries. They won't be poisonous (assuming you live in North American and not Australia) if they are hanging on webs, the poisonous species hide out in crevices (and your closets).