The link below is to the USGA Green Section Record magazine site. The article that is presented relates to the importance of timing of aerification. I think you may find it interesting. With the short golfing season in Chicago and the need for Golf Course Managers to make the golf course available to golfers for their enjoyment quite often the necessary practices such as aerification are delayed or omitted and course conditions can decline. I place a high priority on balancing member access to the course and still accomplishing necessary turfgrass management programs.