Summer has arrived in the south and the bright colors of the Cannas are everywhere.
Fresh green leaves and elegant stature make this plant a standard for gardens across the south as well as in more northern climates where it is treated as an annual. They seem to thrive in heat and suffer drought without a pause, and the thick leaves are rarely subject to summer bugs which has perhaps made them a much appreciated landscape plants since the Victorians used them.
There is just one major problem with Cannas, and that is that Cannas are prone to a leaf roller, a caterpillar that takes each leaf and binds it into a tight cone. The roller can effect the flowers of the plant as well, making the whole show look like a mottle mess. Both the dark leaf and the more common green leaf varieties suffer from leaf rollers. Evidence is generally noticed when the weather starts to warm up and established Cannas are starting to bloom.
There are two leaf rollers, the greater leaf roller and the lesser leaf roller, but they both have similar life cycles and both destroy the leave in the same way.
The moth, which is either a buff color (lesser leaf roller, Geshna cannalis) or a more chestnut color (larger leaf roller, Calpodes ethlius), lays small white eggs on the upper surface of the Canna leaf. Leaf miners emerge from the eggs and they tunnel into the matter between the upper and lower surface of the leaf. Finally the miner becomes too large and emerges as a caterpillar on the upper surface. The caterpillar spins a line that drags the edge of the leaf over. This action continues as the caterpillar starts to form a cocoon. Finally the moth emerges and the whole thing starts again. Two complete life cycles can occur each summer leaving your stand of Cannas looking brown and unhealthy.
Treatment of the Canna leaf rollers is tough. The eggs are on a leathery surface and oily insecticidal soaps tend to run off rather than coat. The eggs are also small can easy to miss in the mass of green foliage. Likewise the larval mining stage is difficult to treat. The caterpillar though can be treated with the bacteria BT (Bacillus thuringiensis ). This is definitely one of those problems that you need to be watchful for, as treatment is much easier at the first signs rather than when the rolls are tight and the second generation is immanent.
Avoid a problem next year by clearing away all the dead leaves so that the roller cannot survive to infest next year’s Cannas.
Kate is a gardener, a garden writer and a garden educator living in Atlanta, Georgia. She has written for national magazines and local newspapers, plus hosts a weekly radio show. You can visit here website at www.katecopsey.com, her blog at www.katesgardenjournal.com.