Cannas are big favorites among southeastern U.S. gardeners for their large and showy flowers, as well as their tropical-like foliage.

Bright red is perhaps the most familiar flower color, but cultivars with orange, yellow, pink and in-between colors are also available. Foliage is usually green to dark green, but some cultivars have bronze coloration, and Bengal Tiger has alternating yellow and green stripes.

In sunny locations with good drainage, cannas tend to be reliable and long-lived perennials. However, canna leafrollers can be a challenge, and growers should be familiar with signs of damage and options for control.

As noted last week, there are actually two that are likely to be encountered locally — the larger canna leafroller and the lesser canna leafroller. Both species begin feeding in the larval stage, rolling themselves inside the edges of leaves and spinning silk to hold the “tube” together. Larger, new tubes may be formed as the caterpillars grow. The lesser canna leafrollers skeletonize the leaves they feed on, while the larger canna leafrollers usually chew holes in the foliage.

Management is the same for both. There are a number of insecticides labeled for caterpillars in general, including various pyrethroids, Bt, spinosad and acephate (Orthene). According to a recent canna leafroller article by Onslow County Extension Agent Lisa Rayburn, Bt (Bacillus thuringiensis) and spinosad can be alternated for a long treatment window. Larger caterpillars can be difficult to control with Bt, and Rayburn suggests acephate if the caterpillars are larger than a half inch in length.

Since the infested leaves are rolled up and direct access to the insects is reduced, entomologists recommend applying the sprays downward into the rolled tubes. In addition, a spray adjuvant known as a spreader/sticker should be added to the spray, due to the water repellent nature of the waxy canna leaf surface.

Canna leafrollers can be active from spring through summer, so monitor your plants carefully and be prepared to treat as needed. Once the season is over and we’ve had a couple of hard freezes, be sure to cut and remove dead canna foliage from the site.

Canna leafrollers feed only on cannas, and there’s a strong likelihood they’ll be overwintering on site in any canna plant debris that’s left behind. An annual clean-up of your canna beds can help to keep the numbers low from year to year.

You’ve probably noticed canna plantings that become overcrowded over time, and don’t seem to be flowering as effectively as in prior years. Consider dividing your cannas and opening some space every three to four years, in the springtime. Occasional division along with careful management of the canna leafrollers should pay off with healthier plants and more flowers.

Our next Saturday gardening program will be at 10:30 a.m. Aug. 18 at the Craven County Agricultural Building. Local gardener and garden club member Barbara Odgers will discuss care and propagation of cacti and succulents. Prior to her presentation, there will be a landscape plant selection tour on the grounds at 9 a.m., and a Master Gardener plant sale at 10 a.m. For additional information, call us at 633-1477 or email tom_glasgow@ncsu.edu.

 

Tom Glasgow is the Craven County Cooperative Extension director. He can be reached at tom_glasgow@ncsu.edu.