Its my experience that deer are vocal to a point all season long. Once the days start shortening and the first cold front moves in they then begin to respond to calls better. I take a grunt call with me always but sometimes the conditions aren't favorable, such as wind or rain that would dampen the sound. Also a decoy helps for that buck that hangs up just out of sight or range, and is the deal sealer to bring him in to get a closer look. Mature bucks will almost always circle downwind of a call they hear and try to identify the source. With a decoy in place and if the timing is right they almost cant resist.