The Cornell Cooperative Extension of Westchester is offering a session titled “Flourishing Gardens vs Plant Disease,” led by plant pathologist Margery Daughtrey. She will discuss ways to battle the new diseases that affect ornamental plants, including boxwood, impatiens, and roses. It will be held April 16 from 10 am to noon at the Scarsdale Library on Olmstead Road; $15 in advance, $18 for walk-ins.