The Calla Lilly: Diseases

Pectobacterium

• An important disease of the calla lily is a soft rot that stems from Pectobacterium carotovorum. The bacteria infect the calla lily through wounds that fungi, insects or even gardeners cause to the foliage or rhizomes. Symptoms include plant parts that become slimy and moist, including rhizomes and leaves that look as if they are drenched. Brown, rotting tissue may form at the soil line or at the base of leaves. The bacteria that cause soft rot thrive in wet or humid conditions. Infected calla lily leaves eventually wilt, turn yellow and fall off.

Erwinia

• Erwinia carotovorum is another bacterium that leads to soft rot in calla lilies. When it attacks a calla lily, a lesion appears on the area of the plant near the soil, and this area becomes doughy. The plant's growth is stunted, it wilts and eventually dies. If rain falls on a diseased plant, the bacteria can become airborne in the rain droplets and spread to other calla lilies. Therefore, immediately dispose of infected plants to avoid infecting others. To prevent soft rot, avoid overwatering and don't supplement the plant food with added nitrogen.

Other Problems

• Thrips, which are small insects with black wings, cause problems for calla lilies on several fronts. They bore into the leaves to eat the sap, disrupting the flow of nutrients to the plant in the process. The wounds they leave invite infection from a variety of pathogens, including calla lily chlorotic spot virus, which causes yellowish green spots on the plant's leaves. Thrips from an infected plant easily spread the disease to healthy plants. Botrytis blight fungal disease also is a problem for calla lilies and includes symptoms such as stem rot and the withering of leaves.

Control

• Fungicides help control soft rot caused by the calla lily pest Pectobacterium carotovorum. Planting calla lilies only in well-drained soil can help ward off soft rot. If you have a calla lily suffering from the effects of Erwinia carotovorum, remove it to prevent the transmission of the disease to nearby plants. Chemical controls are not effective on this type of bacterial disease. Control infestations of thrips with pesticides. Begin spraying all parts of the plant in the spring as soon as the spikes begin to bloom.