Although referred to as the Canna Leaf Roller, there are actually two different creatures that go under that name. Cannas are largely free of pests but in the USA plants sometimes fall victim to Calpodes ethlius, the larval state of the Brazilian skipper butterfly, which cuts the leaves and rolls them over to live inside while pupating and eating the leaf. In addition, the Lesser Canna Leaf Roller, Geshna cannalis, a moth larvae, will sew the leaves shut before they can unfurl, by spinning a silk thread around the leaf. The resultant leaf damage can be most distressing to a keen gardener. Gardeners in the rest of the world are free from this particular problem, at present.
There are several ways to manage infestations of the Leaf Roller caterpillars. Since there can be three or more generations of the butterfly in a single season, re-treatment should be anticipated.
- If the infestation is light, then affected leaves can be cut off and destroyed or unrolled and cleaned (removing the caterpillar). It is not wise to compost infected leaves, burning is the surest way to avoid re-infection.
- If there is extensive damage, a further measure to consider is Bacillus thuringiensis (BT) which is sold in the USA under various trade names including Dipel and Bio-Worm Killer. Applied as a spray, particular care should be taken to ensure that the underside of the leaves is wet. After applying BT the caterpillars will stop feeding on the leaves, although it may take them a day or two to expire. If BT is applied early enough in the growth of the caterpillars, little damage to the leaves will be evident.
- Another alternative is to apply a systemic insecticide in a foliar spray (i.e. Orthene). When applying systemic insecticides by spraying, careful attention should be given to food and herb crops planted in the immediate vicinity to prevent over-spray or drift of the insecticide.
- A further treatment option to consider is a carbaryl insecticide such as Sevin. Applied as a liquid, Sevin can help manage the infestation of many varieties of insects, unfortunately including beneficial ones.
- Finally, the gardener can try applying a fertilizer with Disulfoton, such as Bayer Advanced Garden 2-in-1 Systemic Rose & Flower Care. This serves to both feed and protect for a period of many weeks.
If using any of the chemical options, then it is recommended that you consult the label for dosage rates and safety precautions. Alternating between the treatment options for management of the Leaf Roller caterpillars can help to spare beneficial insects. Additionally, alternating insecticides also prevents insects from building up resistance to any one particular method.