Take it off, probe with a surveyors pin to find the top most root and be certain that it is within 2" of the top of the root ball, and use a mycorhizia starter pack. We are in the final phase of a streetscapes project that has included approximately 160 6"cal+ nuttall oaks planted in two phases. Three different contractors were used in the project. Contractor 1 in phase 1 had 30% mortality. contractor 2 in phase 1 had about 43% mortality. Neither of the first two contractors removed baskets although they did remove burlap from the top of the ball, and granted, both plantings occurred very late in the planting season and were followed by extremely hot and dry summers. Contractor 2 did water weekly throughout the summer and ended watering in November. Contractor 3 has had 0 mortality. They have had the benefit of a cooler and wetter than normal summer. They removed the baskets and burlap completely and used mycorhizia. Personally I hate to have to go back and re-do a less than acceptable job and would much rather spend a few ore $ and time doing it right. Researchers in our university's work hard to do the research and we pay top dollar to go to conferences to get the latest info on how to do the best job, and then we try to short cut ourselves. Doesn't make any sense to me at all.