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Leaf Rollers

(Nov. 2008)

QuestionEvery year now we get something rolling itself up in young canna leaves in our six-year-old canna bed. We've noticed black specks, and the tightly rolled leaves never open, but become lacy. In previous years we've just kept clipping them off as they occur, but this year I'm more aware of butterflies and beneficial insects in all their stages of life. I don't want to be tossing away something that will be a butterfly or be helpful someday. None of the butterfly books I have mention cannas as a host plant. Just to be sure, can you please tell me what affects cannas this way?


AnswerThe problem is an insect called the lesser canna leaf roller (Geshna cannalis) and seems to be getting worse all the time. The adult of this insect is a small, light brown moth. She lays eggs in groups of 6-15 on the upper surface of the canna leaf starting soon after the cannas have emerged in the spring. When the eggs hatch, the larvae tunnels into the leaf leaving behind the droppings or frass as they feed. When they get to be about one week old the larvae initiate the leaf rolling, which helps to protect them from predators and insecticides. The insects overwinter in a pupal form in the dead canna leaves. Good sanitation this fall, removing all the old leaves and replacing with a fresh layer of mulch can help you start the season out clean. The moths won't get active until the cannas emerge next spring, but there can be several generations of the insects each season. If you still see symptoms next season, at the first sign--either leaf rolling or the frass or droppings, spray BT (Bacillus thuriengiensis) into the rolled leaf and the surrounding foliage. Cutting off heavily damaged leaves and destroying them, is also helpful.

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