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Canna leaf rollers
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You may have noticed that your beautiful cannas are taking a rather sad turn. The leaves are rolling and the whole stand looks ragged.
Cannas are generally disease free plants that look great on very little care. They are drought tolerant as well, so they are perfect for southern gardens. They do, however, suffer from a few leaf rolling problems, and I have found ample evidence of that this year.
The leaf rollers are two different caterpillars but as the damage and control are the same, the difference is not too important. The larger roller which is Calpodes ethlius, and the smaller roller, Geshna cannalis, both have the same life cycle going from egg to leaf miner to caterpillar to moth.
A brown or tawny butterfly lays eggs on the upper surface of the canna leaf. These hatch into a leaf borer that tunnels between the upper and lower edges of the leaf. Thus far you may not have noticed anything worth treating. The final phase is the problem. The borer develops into a caterpillar that not only munches on the leaf, but spins a silk that drags the upper edge of the leaf over. In this way the caterpillar grows nicely and your canna leaf takes on a very ugly tightly rolled appearance. The leaf is destroyed along with many of the growing flower stalks.
Control of the problem can be at a couple of stages. The eggs can be dealt with, although the usual soaps are said to be ineffective due to the waxy nature of the canna surface. If you can make the soap stick, then the eggs can be dealt with. Wiping the leaf also removes the eggs. The borer is not very accessible, so the next stage is the caterpillar. These are best treated with BT (Bacillus thuringiensis). Although this may not spare the canna, it will stop the caterpillar pupating and forming another moth to lay a second generation of eggs.
For more info: www.katecopsey.com
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