Flowering currants are deciduous shrubs that produce bright-coloured flowers and edible fruits, commonly used for jellies and jams. According to the Purdue University Extension website, currants are an easy-to-grow shrub that grows best in cool climates with moist, well-drained soils. Currants come as black, white or red berries, depending on the type of variety. Although most species exhibit hearty growth in their native growing areas, a variety of diseases can affect shrub vigour and fruit production.
Algal Leaf Sport
According to the Purdue University website, bignay or black current tree, is susceptible to algal leaf spot, caused by the algae Cephaleuros tirescens. Algal leaf spot or "green scurf" disease, is caused by a type of green algae, and is common in warm-weather, frequent-rain growing conditions. The University of Hawaii College of Tropical Agriculture and Human Resources states that the disease occurs in any area that favours development, most commonly on the Gulf Cost, where rainfall and temperatures favour a multitude of Cephaleuros species growth. Symptoms of infection consist of orange to brown leaf spots on the upper side of the currant plant's leaves, damage to fruit and visible, velvety fungal growth. Reducing plant stress, sanitation and chemical fungicidal control are common for treating Cephaleuros infections, states the University of Hawaii College of Tropical Agriculture and Human Resources.
Blister rust, caused by the fungal pathogen Cronartium ribicola, is a common disease of many wild and cultivated currant and gooseberry species. According to the Oregon State University Extension website, black currant shrubs are more susceptible to the disease than red currants. Symptoms of infection consist of small yellow to orange spots located on the underside of the currant plant's leaves, visible fungal growth on the leaf spots and defoliation. According to the Oregon State University Extension, white pines are primary hosts of the blister rust, therefore, to prevent infection, remove white pines within 1,000 feet of currant shrubs.
Powdery mildew, caused by numerous fungal pathogens, affects a variety of trees, shrubs and plants, including all species of flowering currants. According to the Cornell University, symptoms of a powdery mildew infection consist of visible, white fungal powder growth, circular powdery spots, leaf death and decline in shrub vigour. Damage to fruit, flower and leaf production varies depending on the extent of the infection. Minor infections rarely cause visible damage and can be treated by physically removing the fungal build-up on the leaves. However, the Cornell University website states that yellowing and leaf drop are common symptoms of a powdery mildew infection. In the case of a severe infection, disease control consists of physically removing fungal growth and the use of a fungicidal spray.