Out in the garden there are sometimes sinister pests gobbling up large portions of precious ornamental canna leaves. What’s worse is that you cannot find the culprit at a glance. What could possibly eat so much leaf matter in such a short period of time? Sadly, it is what you cannot easily see that can hurt your canna!
Cannas are popular and successful garden ornamentals grown throughout our area and beyond. Their colorful leaves and almost constant flowering make them a favorite amongst all home gardeners. They seem pretty pest-free, but what is nibbling at the edge of the leaves? And, what is cutting and rolling the leaf edge into a tube-like structure? Not to mention, what is eating one third of the leaf and no pest is seen? If you have cannas, you should suspect the larger canna leafroller! The larger canna leafroller is an insidious caterpillar that “slowly” grows into a two-inch behemoth capable of eating large amounts of leaf matter. The larger canna leafroller is actually the caterpillar of the Brazilian skipper, a butterfly. The brownish, somewhat drab butterfly seems to favor the red-leaved cannas more than the green-leaved types, and varieties with scarlet, red, or orange flowers. The Brazilian skipper lays eggs visible to the naked eye on the lower leaf surface. These eggs hatch in about five days.
As the caterpillar grows, it eats the leaf in such a way that a flap is cut and pulled over the caterpillar with stands of silk. This leaf flap protects it from the sun and predators with a tight, tent-like cover open at the ends. As such, the dark-green caterpillar can safely reach its head out to feed. And feed it does as it finishes that part of its life cycle! One unique and disgusting feature about the larger canna leafroller is its habit of “fecal firing” (say that five times fast!) where it flings its droppings away from the leaf roll to reduce sight and scent traces which may redirect predators or parasites away from the caterpillar.
If you monitor your cannas sufficiently, you should be able to detect and hand-pick the leafrollers before they get too big and destructive. I thought I had done this on my own canna, but missed a few which made it to full size and full leaf-eating capacity. Although there are some natural biological controls taking care of a few of the larger canna leafrollers, there just are not enough. Chemical control is tricky at best because the caterpillar is safely inside the leaf roll. If you try Bacillus thuringiensis (Bt) products as per label directions, target small caterpillars for best results. Otherwise, simply inspect the leaves and hand-pick as needed – it really works quite well!
It is that time of the year again. Monitoring is a chore, but also a relatively simple task that should be part of your Integrated Pest Management (IPM) program in your canna planting – you can defeat the larger canna leafroller! For more information on all types of landscape insect pest management, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Don’t forget to visit our other County Plant Clinics in the area. Please check this link for a complete list of site locations, dates and times – https://blogs.ifas.ufl.edu/charlotteco/files/2018/03/Plant-Clinics-Schedule.pdf. Ralph E. Mitchell is the Director/Horticulture Agent for the Charlotte County Extension Service. He can be reached at 941-764-4344 or ralph.mitchell@charlottecountyfl.gov.
Resource:
McAuslane, H. J. (2017) Larger Canna Leafroller, Calpodes ethlius (Stoll) (Insecta: Lepidoptera: Hesperiidae). The University of Florida Extension Service, IFAS.
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