| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Crown rot (Rhizoctonia solani) | Base of stems of callas are infected at or below the soil line, causing a general chlorosis of foliage. | Favored by warm, moist conditions. Fungus is present in most field soils. | Avoid deep planting and overwatering. Treat soil with PCNB before planting. |
| Pythium rot * (Pythium ultimum) | Roots may rot first. Pink and yellow corms develop irregular-shaped, shallow, water-soaked lesions that may coalesce. Infection spreads into interior tissues of root structures, producing irregular-shaped gray lesions that are sharply delimited. | Pathogen enters root structures through wounds. It is present in many field soils and has a wide host range. Disease is favored by warm, moist conditions, heavy soils, and poor drainage. | Avoid injuries to the rhizomes. Clean and dry root structures soon after digging. Store below 50°F. Some of the water mold fungicides would probably be effective in controlling the disease. |
| Phytophthora root rot *
(Phytophthora cryptogea) |
Yellowing of leaf margins of outer leaves followed by general yellowing and wilting. Feeder rootlets are rotted. | Pathogen is present in some field soils. Several other types of plants may be infected. Favored by wet soil conditions. | Grow on raised beds and provide good drainage. Do not overirrigate. Treat with oomycete (water mold) specific fungicide. |
| Soft rot (Pectobacterium (=Erwinia) carotovorum) | A soft rot of the rhizomes. Plants may rot off at the soil line. Bacterium is a common secondary invader of succulent plant parts and generally requires some sort of injury to cause disease. Has odor. | Bacterium is present in some field soils. Favored by warm, moist conditions and plant parts attacked by other organisms. | Avoid injuries to the rhizomes. Do not overwater. Yellow callas are more susceptible than others, but there are new yellow cultivars that are more resistant. |
| Virus or viruslike diseases | Symptoms | Host range and natural spread | Comments on control |
| Dasheen mosaic (Dasheen mosaic virus) |
Mosaic patterns in leaves, which may be severely distorted. Infects plants low in vigor. | Common because callas frequently propagated vegetatively, which spreads the virus. Virus is spread by aphids. Spread in a planting can be rapid. Can be transmitted by sap but not by seed. | Obtain or develop virus-free plants by heat treatment and tissue culture. Control aphids. Remove infected plants. |
| Spotted wilt
(Tomato spotted wilt virus and Impatiens necrotic spot virus) |
Foliage, petioles, and flower stalks are streaked or spotted by whitish or yellowish areas, and sometimes by small, concentric rings. Necrotic areas that develop in leaves may be colonized by secondary fungi. Sometimes the necrotic areas are attributed to fungi, but usually they are secondary invaders. | Common because callas frequently propagated vegetatively, which spreads the disease. Both viruses are also transmitted by several thrips species. Virus is acquired by nymphal stage and transmitted by adult throughout its life. The virus has a very wide host range including many weeds and ornamental plants. | Control weeds and thrips. Destroy infected callas. |
| Callas are also susceptible to leaf spots (Gloeosporium callae, Coniothecium richardiae, and Cercospora richardiae), powdery mildew * (Oidiopsis taurica), Armillaria root rot * (Armillaria mellea), gray mold * (Botrytis cinerea), Phytophthora spp., seedling rot (Rhizoctonia solani), southern blight * (Sclerotium rolfsii), and root knot nematode ** (Meloidogyne spp.) | |||
| * For additional information, see section on Key Diseases. |
| ** For additional information, see section on Nematodes. |