A canna lily is related to bananas and ginger plants. The shoots grow out of the stem as a long roll, then unfurl. Canna lily flowers are red, yellow, orange or any combination of the three colors. Most cannas have green leaves, but some cultivars have bronze, maroon, brown or variegated leaves. Its small, round, hard seeds are used for the kayamb, a musical instrument from Reunion, an island in the Indian Ocean. Canna indica (arrowroot starch source) roots are eaten raw or cooked. Cannas are low-maintenance and provide color to the landscape throughout the summer, so are popular with landscapers.
Botrytis blight affects the flowers of the canna lily. It is a fuzzy, gray mold. It is caused by one of several species of the fungus botrytis, but the common species is botrytis cinerea. It thrives in cool, rainy whether, especially when there is a spring rain that lasts more than a few days. Symptoms include brown or spotted flowers. Silver gray spores show up on the dead or decaying plant matter. If the plant is heavily infected, the botrytis looks like gray dust when disturbed. Remove and discard any flowers that are infected, so the infection does not spread to healthy flowers on the same plant or on different plants. Keep plant debris picked up, as the disease overwinters in fallen plant matter.
Canna rust mostly affects cannas in the deep South, where there is a lot of humidity and the soil is high in moisture. The rust causes the leaves and stems to have orange spots. The orange spots are the fruiting bodies of the fungus frangipani rust. When you first notice the rust, remove the infected leaves and stems, so that it does not spread to the rest of the plant or to other plants. Discard the infected plant matter in plastic bags in the trash. Do not add it to the compost pile.
Rhizome rot is a product of the fungus Sclerotium rolfsii and fusarium spp. The fungus causes the canna's rhizomes (underground stems) to rot. The rot spreads from the rhizomes to the base of the stems. You might see a cottony-looking fungal growth on the plant. Remove the entire plant, including the rootball if the plant is infected with rhizome rot. To help prevent rhizome rot, thin the plants every couple years, replanting the pulled plants in another part of the garden.