A few minutes east of Islip the Connetquot widens past Great River, where the tall old plantings of the Bayard Cutting Arboretum go copper and rust every October. Green Horizon Landscaping & Design Inc. carries a little of that eye into ordinary yards — mowing and edging right through the season, holding the trim lines clean, then clearing leaves once the color starts coming down. Autumn on this island is generous with leaves and unhurried about dropping them, so cleanup is a series of visits rather than one long afternoon. Done properly, a lawn goes into the cold even and clear, with nothing left waiting.