Abstract: A folding boom for a tri-fold row marker for an agricultural implement. The boom comprises three segments, an inboard segment pivotally coupled to the toolbar, a middle segment pivotally coupled to the inboard segment, and an outboard segment pivotally coupled to the middle segment. Control of the boom during folding and unfolding is maintained by a toggle link mechanism having a cam a cam follower and a system of pivots and linkages. Dynamic forces are dampened at both ends of the folding and unfolding by use of a cushion hydraulic cylinder with flow limiting structure at each end of the cylinder stroke.