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Iris borers and botrytis blight on peony can overwinter in plant debris and old foliage left through the winter . Flowers often fail to develop color , remain green and distorted , and seeds or fruit never develop . Although other leaf spot and leaf streak diseases do occur on daylilies , it is unclear whether any of these problems are caused by fungi . The soil water level should be at least 1 foot below the soil surface or roots will suffocate . These numbers are bound to grow as populations swell and are increa-singly concentrated along coast lines and mountain ranges , which often represent tectonically active plate boundaries zones ( Bilham , 1991 ) . If larger numbers are present , treat plants with one of the following insecticides : diazinon , carbaryl ( Sevin ) , methoxychlor , or rotenone .