Rooney made it 101 goals for Manchester United with a double in the 5-0 drubbing of Wigan.
And United boss Ferguson says the England striker, 23, can only gain in confidence from reaching the landmark
He said: "It is a great achievement and he is only a young lad.
"Some players have been at the club for many years and not reached that total yet. It will do him a world of good.
"Strikers have to score - that is their mantra. If they are not scoring they think the world is at an end.
"When they are scoring they think they will never finish scoring. But that is what they are."
Fergie also saw Michael Owen break his duck with a clever finish for United's fourth, while Dimitar Berbatov and Nani also chipped in.
The Old Trafford chief added: "That is what Owen needed, he needed a goal.
"It is what he is made of. All his career has been about goals. He is one the best finishers this country has ever had. Today can only help him.
"I was so pleased for him and Dimitar Berbatov. If the strikers keep doing that it gives us a big chance."
Ferguson was delighted with the way his side responded after their midweek defeat at Burnley.
He added: "You have got to react to defeat and it is always a challenge. But we got a really good response today.
"When you are making chances and don't take them it is a worry. We made six chances in the first half and did not take any.
"But the important thing is to have the patience to keep playing and keep believing and we did that."