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.
Insect Problems:
Insects and mites are not pests of this plant.