A windrower has a crop merger attachment with a conveyor configured to receive crop material from a crop conditioning mechanism and direct the crop material to a side of the windrower, the crop merger attachment being mounted for adjusting movement between a lowered and a raised position. The windrower has a swathboard mounted for adjusting movement between a fully raised position in which the crop material passes beneath the swathboard for engagement with the merger attachment and a lowered position in which the crop material down to the ground under the merger attachment under the windrower. A control system automatically adjusts movement of the swathboard when movement of the merger attachment is detected.