Vinca, Annual (Catharanthus)
Plant Health Problems
Diseases caused by Fungi:
Gray mold, Botrytis cinerea.
Flowers turn a papery brown and become covered with gray, fuzzy masses. Senescing flowers are particularly susceptible. Tan to brown spots with a target-like appearance can also develop on the leaves. These patches are often associated with flowers which have dropped onto the leaf surface. Stems can also develop tan cankers and entire plants may collapse. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.
Good sanitation practices including grooming the plants and removing spent or senescing flowers can minimize the potential for infection. These affected tissues should be carefully removed and discarded when they are dry. It is also important to avoid wetting the flowers when watering and crowding plants. Adequate spacing between the plants can promote good air circulation. Control can also be achieved with the use of fungicide sprays applied as soon as symptoms are visible. Among the compounds registered for use in Connecticut are iprodione and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Phytophthora aerial blight, Phytophthora.
Infected plants collapse, wilt, and die, often in a short period of time. Under conditions of high relative humidity, white threads of the fungus may be visible. Large areas of a planting bed are frequently destroyed.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. This disease can be minimized by cleaning up plant refuse and by adequate spacing of the plants to promote good air circulation.
Stem and root rot, Rhizoctonia solani.
The above-ground symptoms are nonspecific and include a general wilting, decline, and collapse of the foliage and the entire plant. This general droopiness or flaccid appearance is often accompanied by browning and rotting of the roots and the crown. Yellowing and death of the outer leaves follows, until finally the entire plant is dead. Blackened lesions can sometimes be visible on infected stems at or near the soil line.
Control can be difficult once plants are infected so prevention is important. It is helpful to avoid overwatering, especially in heavy soils, and to avoid watering directly into the plant. Highly symptomatic plants can be rogued and removed since recovery is unlikely. Attention to spacing is also helpful since it improves air circulation and drying of the foliage.
Leaf spot, Alternaria.
Circular to irregular brown to black spots develop on leaves, stems, and flowers. Heavy infections result in substantial drop of the lower leaves.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when symptoms are first visible. Among the compounds registered for use in Connecticut are mancozeb and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Diseases caused by Phytoplasmas:
Symptoms consist of a yellowing or clearing of the veins in newly infected leaves and shortening of the internodes of the main stem. If plants are infected young, they remain stunted, and if flowers are produced, they are small, abnormal, and often exhibit phyllody, a condition in which flower parts revert to green tissues. Symptoms do not always appear on the entire plant, but may show on only one portion, depending on the time of infection. This phytoplasma is transmitted by leafhoppers. Since the pathogen infects many plants (e.g., daisies, chrysanthemums, plaintain, echinacea, and rudbeckia), vinca may become infected from neighboring plants.
Strategies for control include promptly roguing and removing diseased plants as well as control of the leafhopper vectors.
Diseases caused by Viruses:
Spotted wilt, virus, Impatiens Necrotic Spot Virus (INSV).
Symptoms can appear as a severe distortion or blackened appearance to the newly emerging leaves. This virus is transmitted by the western flower thrips.
Control of this disease is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since this virus has a very broad host range. It is also critical to manage the thrips population.
Insect and mite pests are not known for this plant material.