Canna lilies are popular garden additions, prized for their tropical appearance, large leaves, and vibrant flowers. Their broad foliage makes them a frequent target for various garden pests. When clean, circular holes appear in the leaves, it signals a chewing insect has been actively feeding. Identifying the specific pattern of damage is the first step toward effective management.
The Canna Leaf Roller
The primary culprit for distinctive canna damage is the larva of the Brazilian skipper butterfly, Calpodes ethlius, known as the canna leaf roller. This caterpillar is pale green with a dark orange head and can grow up to two inches long. The newly hatched larva uses silk strands to tie or stitch unfurled, young leaves together, creating a protective, rolled tube where it feeds in seclusion. The larva consumes the leaf tissue from the inside, pushing out small, dark frass pellets. This feeding behavior causes the unique damage pattern visible after the leaf completely opens.
Identifying Damage Patterns
The tell-tale sign of a canna leaf roller infestation is a series of uniformly spaced, circular holes running in a straight line across the leaf width. These holes appear because the caterpillar chewed through the tightly rolled leaf layers while the leaf was still a closed spike. A leaf that is partially rolled and tied with silk threads further confirms the pest’s presence. Damage from other chewing insects lacks this symmetry. Slugs and snails, which are nocturnal feeders, leave large, irregular holes, often near the edges, along with a silvery, dried slime trail. Beetles and grasshoppers create ragged, asymmetrical holes or chewed edges, sometimes leaving a skeletonized appearance.
Other Common Chewing Pests
Slugs and snails are common pests attracted to moist environments where cannas thrive. They hide in damp mulch or debris during the day and emerge at night to rasp away at the leaves, creating significant tears and non-uniform gaps. Reducing moisture around the plant base helps deter these mollusks. Japanese beetles are another generalist garden pest that feeds on canna leaves. These pests often cause skeletonizing, chewing the softer tissue between the veins and leaving a lace-like pattern. Other caterpillars, such as the wooly bear, may also chew large, irregular chunks out of the leaf margins. Identifying the specific pest by the damage pattern helps select the correct control method.
Effective Pest Management
For canna leaf rollers, manual removal and destruction of the rolled leaves is the most direct control. Inspect young, unfurling leaves for signs of silk or a tightly bound appearance, then gently crush the rolled section to eliminate the larva inside. For heavy infestations, apply Bacillus thuringiensis (Bt), a naturally occurring soil bacterium. Bt is a targeted insecticide that must be ingested, so spray it directly into the rolled leaves where the larva is feeding. For slugs and snails, cultural control involves clearing debris and reducing excess moisture around the plants. Iron phosphate baits are an effective, pet-safe option for controlling these mollusks. Maintaining a clean garden bed by cutting down and disposing of all foliage at the end of the season prevents leaf roller larvae from overwintering.