D-lemonene is a great natural flea killer that is used in many all-natural flea shampoos. You can easily extract it from a lemon to make tonic for your pet’s flea problems or mange. It is so mild that it can be used daily, if the problem is severe.
1 organic lemon
1 pint water
Thinly slice a whole lemon, including the peel.
Add the lemon to 1 pint boiling water.
Let steep overnight.
The next day, sponge the solution onto your dog’s coat. You may also strain out the lemon pieces and decant the liquid into a spray bottle for frequent application.
Source: Corbett Marshall and Jim Deskevich-“Eco Dog”