Well-known across the South, cannas are grown for their showy, large flowers and banana-like leaves. Canna stalks normally stand 6 to 8 feet tall and feature a variety of colors from deep green to striped. They're perennials, so many leaf problems don't occur for more than one season. Leaf issues can be caused by insects, diseases or other environmental conditions.
Two types of caterpillars commonly attack cannas in two different ways. The yellow woolly-bear caterpillar chews holes between leaf veins. The holes appear in a straight line. Pluck these caterpillars off of the plant when noticed. Insecticides will control woolly-bears as well.
Canna leaf rollers curl the large foliage around themselves and feed inside. They're also protected from chemicals within their hiding places. Destroy the leaves and stalks after cutting them back in the late fall to prevent the leaf rollers from overwintering and reappearing in the spring.
A bacterium known as Xanthomonas cannae creates large spots on young leaves. The spots may begin as whitish blemishes, but soon become black. Flower buds blacken and never open. Older leaves may be affected as well, showing yellow spots. No chemical solution is available for the disease. Infected plants should be dug up and destroyed.
Canna Mosaic Virus
Pale yellow stripes along leaves that appear wrinkled or curled are likely caused by a virus spread by aphids. Yellow bands will show around flowers and stems. Control the aphids with strong bursts from a water hose, or with insecticide sprays.
Often canna leaves will become torn in parallel lines. Such a symptom may not be caused by insect feeding, but by infrequent watering. The tears appear when cannas survive a period of drought, and then receive a heavy dose of water. Keep the plants watered regularly during hot dry spells to keep leaves intact.