Periwinkle, Myrtle (Vinca)
Plant Health Problems
Diseases caused by Fungi:
Stem blight and dieback, Phoma sp., Phomopsis sp.
These are the most common diseases of myrtle in Connecticut. Diagnostic symptoms appear as dark brown or black, shiny lesions or spots on older stems. When these lesions girdle the stems, plants collapse and die. Large patches of dead plants are not uncommon. Infections can also develop at the base of new shoots and on stems of runners. These fungi can also infect leaves and appear as dark spots which result in the browning and death of 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. Thinning of the bed can help to increase air circulation and drying of the tissues. It is also very important to rogue and remove symptomatic plants as soon as they develop and when the tissues are dry. Control can also be achieved with the use of fungicide sprays when infection is heavy. Applications usually begin when new growth emerges in the spring. Among the compounds registered for use in Connecticut are copper hydroxide, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Root and stem rot, Rhizoctonia solani.
This disease is often mistaken for stem blight and dieback. Symptoms of infection appear as a blackening or rotting of the roots or the stem near the soil line. Infected plants then wilt and die, often in distinct patches within the planting bed. This fungus inhabits the soil and is fairly common.
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.
Botrytis blight, Botrytis cinerea.
Infections can develop as a stem canker, a leaf spot, and a blight. This disease is particularly troublesome during periods of extended cloudy, humid, wet weather.
Good sanitation practices including removing symptomatic plants 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 overhead irrigation 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 mancozeb and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Insects and mites are not pests of this plant.