i think you should take him inside
do you have any other pets?
and make sure he has enough space, i.e. the space should be a little wider than thrice his wingspan, and 2 feet tall (60 cm/0.6 m).
budgie mix is good enough for him, but try as much as possible to get designated pigeon feed for him.
even seeds would be good for him (corn, some fruits, cereals (and dont worry, pigeons do NOT explode when they eat rice), etc.)
and about the disease itself, check everyday if the growths have spread on to the bill and nostrils (pigeons' nostrils are a little above the beak, covered with feathers that have bigger gaps between the small barbules.)