If you target him, you could end the haste effect that is currently on him, but he could then re-activate the boots on his next action.
If you target the boots, you can shut them down for 1d4 rounds, during which he would not be hasted. (Although he might remain hasted until the beginning of his next action. It's not entirely clear how this would work.)
An area-affect dispel could end the haste effect on him, but would not affect the boots themselves.