Three issues account for most blackcurrant problems: big bud mite, American gooseberry mildew, and currant clearwing moth. All three are manageable if you catch them early, and all three are preventable with good cultural practices — air circulation, clean pruning, and choosing resistant varieties. This guide covers identification, prevention, and treatment for each.
The varieties guide covers resistant cultivars that reduce or eliminate the need for intervention. ‘Ben Hope’ resists big bud mite and mildew. ‘Ben Sarek’ handles mildew well. Starting with a resistant variety is easier than treating problems after they appear.
Big Bud Mite: The Most Common Pest
Big bud mite (Cecidophyopsis ribis) is the most widespread blackcurrant pest. The microscopic mites feed inside developing buds, causing them to become swollen and spherical instead of staying pointed and elongated. Affected buds are visible from late summer onward — they are twice the size of healthy buds and rounder in shape.
The mites also transmit reversion virus, which causes distorted leaves with fewer than the normal five lobes and reduced fruiting. Reversion-affected bushes produce poorly and should be removed entirely — there is no cure.
Prevention: pick off and destroy affected buds from August through March. In severe infestations, remove the entire bush and replace with a resistant variety. Avoid planting new blackcurrants near infested bushes, as the mites spread by wind and on pruning tools.
American Gooseberry Mildew: White Powder on Leaves
American gooseberry mildew (Podosphaera mors-uvae) appears as a white, powdery coating on young leaves, shoot tips, and sometimes fruit in late spring and early summer. Affected shoots are stunted and distorted. The mildew is worse in dry conditions with poor air circulation — paradoxically, plants that are water-stressed but not drought-stressed are most susceptible.
Prevention: prune to open the center of the bush for good airflow. Water at the base, not overhead. Remove and destroy affected shoot tips as soon as you see them. Resistant varieties (‘Ben Sarek’, ‘Ben Tirran’) rarely need treatment.
Currant Clearwing Moth: Wilting Canes
The currant clearwing moth (Synanthedon tipuliformis) lays eggs on blackcurrant stems in early summer. The larvae bore into the center of canes and feed on the pith, causing wilting and dieback of individual canes. Unlike big bud mite, which affects the whole bush, clearwing damage is usually limited to one or two canes.
Identification: look for small holes in the stem with fine sawdust-like frass nearby. Cut into the stem and you will find a white larva inside the hollow pith.
Treatment: cut back affected canes to below the damage and destroy the prunings. The damage is cosmetic in most cases and does not threaten the whole bush. Bird netting applied during egg-laying season (May to June) reduces infestation.
Leaf Spot and Other Minor Problems
Leaf spot (Drepanopeziza ribis) causes brown spots on leaves in wet summers. It is cosmetic and rarely affects yield. Remove fallen leaves in autumn to reduce the spore load for next year.
Gooseberry sawfly can occasionally affect blackcurrants. The caterpillars strip leaves rapidly. Hand-pick small infestations or use an organic insecticide for severe attacks.
The care guide covers the cultural practices — watering, feeding, mulching, and pruning — that keep bushes healthy enough to resist most problems without chemical intervention.
