Hi

I need someone to help me understand this strange behavior my dog has.

Whenever I dust him with Harts flea and tick powder, halfway through the dusting he goes BESERK

Snapping and biting everything and running. Takes forever to finish dusting him.
And when I'm done, he is as calm and as relaxed as ever.

Please help IT IS frustrating

I think you mean Hartz - OTC flea stuff. I would never use a flea powder as it becomes airborne & causes choking & breathing problems, & burns the eyes. there have been numerous cases of dogs dying from the use of Hartz as well as other OTC fleas products.

the only thing you should use IMO is something from the vet. throw that stuff in the trash