INSECT PESTS OF CANNA
Insects won't spoil the fun of growing canna.
My mother has always had a large planting of canna. Gardeners have enjoyed this plant for years but it is becoming more popular as new variegated cultivars are being introduced. Another reason for some of its new popularity is the large road side plantings of canna.
Canna (Canna sp.) is a popular perennial with large bold leaves. The foliage dies back each winter. It is called a zone 9 plant but, on the varieties I have seen, the rhizomes overwinters reliably. The ones we have at the farmers market haven't even been mulched. The large flowers are orange, red or yellow. There are nine species. The cultivated cannas Canna X generalis are hybrids of unknown origin, probably Canna flaccida or Canna indica. The reference books refer to two types of flowers but I have only seen one.
Most people use canna in the back of a flower bed or as a focal point. It would be beautiful as a cut flower. I think it would make a bold corsage but I have never seen it used like that. It may be a serious breach of some arbitrary fashion rule.
My mom called canna "cast iron plant". I'm sure it got that name because it was so tough. I don't know how widespread this common name is. Canna is the preferred common name. This will avoid confusion with Aspidistra sp. which is also called cast iron plant.
There are several insects reported on canna. Don't let them scare you because pest control is very simple. The number one strategy is to ignore the small populations. Small populations will be controlled naturally. I was once challenged to name some of the predators that might control these insects. While I can't name a specific predator, something is bound to control them or they would have taken over the world by now. Removing the dead foliage in the winter will prevent overwintering by the lesser canna leafroller. Handpicking is suitable for Japanese beetles. Pesticides can be used to control large insect populations. As always, healthy plants are less subject to insect attack.
Lesser canna leafroller is the most common pest on canna. In some areas of the state it is a regular problem but it is fairly rare in Cabarrus County. This is a yellowish caterpillar feeding inside rolled leaves tied with short silken treads.
The name lesser canna leafroller implies there is also a larger canna leafroller. This is a green caterpillar feeding inside rolled leaves. It eventually gets larger than the other leafroller but both start out small so size doesn't help identify them.
Celery leaftier is another caterpillar that will create webbing. With the celery leaftier, there is no rolling of the leaf. .
There are four other caterpillars occasionally found on canna.
Corn earworm is the one I see the most in Cabarrus County. I think it is the one that eats a hole in the young leaves of canna. Later when the leaves unroll there is a horizontal row of holes. Early corn earworm instars are yellowish white or green with orange or brown longitudinal stripes. When fully grow the stripes are pale, there are black spots with a tan to orange head. The body color may vary..
Saddleback caterpillars are occasionally found in Cabarrus County. I have had several of these submitted for identification because they sting humans. These are brownish with a distinctive green center and brown spot on top. .
There are two of the wooly worms or wooly bear caterpillars that eat canna. One is the saltmarsh caterpillar. It is gray when young and then black with yellow broken lines and cinnamon red hairs. The yellow woollybear is a very hairy caterpillar that is yellow or straw colored with black lines.
Japanese beetle can eat the foliage and the flower of canna but in most landscapes they tend to find something else they like better. Fuller Rose beetles occur in Cabarrus county although I haven't personally seen them on canna flowers. They are a gray weevil with a short broad snout. They are suppose to have a white diagonal stripe across each wing cover but the white often looks mottled to me.
The potato aphid is the same one that gets on our tomatoes. The spotted cucumber beetle can feed on the flowers. It is a small beetle with a yellow body and black spots. Both are common pest in our gardens but rarely get on canna.
Citrus Mealybug has been reported on canna. Like all mealybugs, it has dense white powder and filaments.
Latania scale is the only North Carolina Scale reported on canna. In tropical areas there are several more scales. If you run into scale on canna it would be a good idea to get them identified. They may be a tropical introduction that can't overwinter here in North Carolina.
There are a few diseases listed for canna but, like the insect problems, none have caused serious problems in the past.
The only other problems you might run into are small mammals. Both cotton rats and voles eat the rhizomes. Since this often occurs in the winter, you don't know it is happening until it is too late. It is worth the time and trouble to control voles anytime you realize you have them. Rozol is the product that is labeled for vole control. Snap traps are the only legal option for cotton rats although the rozol might inadvertently kill some of them while you are killing the voles. Cotton rats are not a severe problem in residential settings unless they have lots of ground cover. They prefer weedy fields.
Article was written by David Goforth Agriculture Extension agent North Carolina Cooperative Extension Cabarrus County Center. Visit my homepage http://cabarrus.ces.ncsu.edu/ or http://cabarrus.ces.ncsu.edu/index.php?page=lawngarden or my blog http://gardeninggurugoforth.blogspot.com/
Contact me at David_Goforth@ncsu.edu. Reviewed 2007.