How to recognize and combat purple spot or raspberry spur blight

Didymella applanata is a fungus that causes the disease known as purple spot or spur blight on raspberries. This fungus overwinters in the remains of infected plants and in lesions on canes. During spring and summer, when moisture conditions are favorable, the fungus produces fruiting structures known as pycnidia in the lesions. These pycnidia release conidia, which are asexual spores spread by splashing water and wind. Conidia germinate on the surface of the canes and young leaves of raspberries, penetrating through wounds or directly through the epidermis. The fungus grows intercellularly, developing fungal structures that destroy host cells and form new lesions. These lesions expand and develop additional pycnidia, completing the infection cycle and ensuring the spread of the pathogen. In addition, the fungus can survive in soil and crop residues for several years, facilitating the perpetuation of the disease from one season to the next.