Five England goals in Rooney's last three appearances have followed, after nearly a year without an international strike.
"Wayne is confident, playing well - and being honest, one of the reasons I was happy that Berbatov signed for United was that I knew it would inspire other players in the team to step their game up another level," said United centre-back Ferdinand.
"It's not just the forwards but the other players as well - because when a new player comes in that's what happens.
"Everyone wants to impress that player and show them why they are playing for Manchester United. I think 'Wazza' has taken that on board and gone from strength to strength.
"I think they can be a great pairing - but what I'm getting at is Berbatov's arrival will help him become a better player individually and go to another level.
"'Wazza' scored 15 goals last season, and made 15 'assists'. That was a great season, and yet he wants to keep on improving and keep on getting better - and he's doing that.
"Some players go into their shells and can't handle it.
"They think 'I can't do this'. They either end up playing rubbish, or you get others like Wayne who take on that battle head first - and he's doing that."
Rooney is in the type of form that makes Ferdinand thankful he is not defending against him - even in training.
"He's normally on my team in training, so I don't get to face him," he said.
"But when he's playing he's normally causing problems for the opposition, working hard and scoring goals - and that's a danger for any defender.
"He's a nightmare to play against, and that's why I'm delighted he's at United - so I don't have to play against him.
"Someone who works that hard, scores goals and he's up there with the best in the world when it all comes together."