Currants, berries that resemble the grape, are closely related to the gooseberry family. These trees grow easily and are most common in their black and red variations. Currant trees are deciduous and self-fruitful, requiring no pollinator. They produce delicate bluish green foliage, which burns easily in intense sunlight. The flowers bloom in the early spring and produce red, white and pink currants, which can be harvested in the fall. Younger currant trees are particularly susceptible to disease.
Blister rust is a fungal disease that preys on currants. Black currants are highly susceptible to the disease, whereas red currants are mostly resistant. This fungal disease travels through spores that form on tree cankers. Infected currants develop small, slightly raised spots with a yellowish-orange color. Mature fungal spots develop brownish fungal hairs. Severely infected currants will experience defoliation. Though blister rust is not harmful to the currant, it is fatal to the white pine tree; therefore, black currants are restricted in some areas to protect the pines. No effective fungicidal treatments exist for blister rust. The best way to control the disease is keeping currants and white pines at least 200 feet apart.
Botrytis blight is a fungal disease that favors wet, rainy periods, so it thrives in moist, flooded conditions. The spores of this fungal disease mature in defoliating and decomposing debris that rests around the tree. Transported by wind and rain, the fungal spores infect the tree, causing blighted conditions. Infected currants will develop brownish spots and grayish-silver masses. These symptoms survive on throughout the tree, including foliage, stems, blooms, buds and seedlings. A combination of pruning and spray treatments will keep currant botrytis blight under control. Prune away infected areas with sterile shears that are sterilized between each cutting. Fungicidal sprays that include chlorothalonil or neem oil are effective.
Powdery mildew is a serious fungal disease that can kill the tree. During the fall and winter, this fungal disease lies dormant, not only on fallen debris and leaves, but on canes and twigs of the established currant. During the spring and summer, the fungal spores infect the tree, causing reoccurring infections throughout the season. Infected currants will develop powdery white fungal coverings on the surface of the currant’s foliage and fruit. As the disease progresses, the fungus darkens. The currant loses vigor and the infected areas decay. The continued infection and loss of vigor results in the death of the currant. Lime sulfur or fungicidal sprays will control powdery mildew. Severely infected areas must be removed.