Aggression toward other dogs

Question
I have a 2 1/2 year old male jack russell and recently got a 5 month old female jack russell.  There was some dominance issues at first but they seem to have figured it out.  However the male has now become aggressive toward other dogs he meets on walks-he never behaved this way before the new puppy arrived.  He behaves aggressively toward other dogs when walking with the puppy and alone.  He growls and even has begun to lunge at the other dogs.  Please help!  What can I do to stop this behavior?

Answer
Hi Anna,

If your dog is not neutered, do so promptly.

It appears your male is being protective toward his puppies (you and the other jack russell).

Teach your male to walk at a heel. Emphasis obedience training with him and control his behavior with training. Stop being a puppy and give your male firm rules and boundaries. His protectiveness/aggression can easily turn toward humans unless you exert control.

Good Luck!
Sandy