Anthracnose (Colletotrichum sp) was recently diagnosed on mandevilla. Anthracnose is common on many ornamental plants. The primary symptoms are leaf spots, leaf blights and dieback. Infected leaves develop tan to brown spots or lesions that are typically associated with leaf veins. In severe cases leaf drop may occur. Because anthracnose symptoms take on different forms and appearances it can be mistaken with other fungal diseases. Submit suspicious plants to a diagnostic laboratory for proper identification.
Moist growing conditions, especially overhead irrigation favors this disease. Anthracnose can be spread from plant to plant by splashing water.
To prevent the disease, avoid overhead irrigation late in the day or during overcast conditions to help reduce the time the leaves remain wet after watering. Remove and discard fallen leaves and infected plants and prune out dead or infected vine branches. Some fungicide options for managing anthracnose include: Pageant (pyraclostrobin plus boscalid, FRAC group 7 and 11), Daconil (chlorathalonil, FRAC group M5), Spectro 90WDG (chlorothalonil + thiophanate methyl, FRAC group M1 and M5), Protect (mancozeb 75%, FRAC group M3).
Geoffrey Njue, UMass Extenson
with input from Angela Madeiras, UMass Extension Plant Diagnostic Lab