Blackcurrant bushes are generally health plants. However they blackcurrant bush sometimes attacked by insects and diseases and this article aims to identify the causes and how to treat them. As far as size goes, birds are definitely the largest pest to affect blackcurrants. They are attracted to the developing fruit and destroy them completely.
The aphids also create a sticky liquid which cover the leaves and attracts other insects and diseases. They rarely kill blackcurrant bushes but can seriously reduce the amount of fruit produced. See our detailed article on identifying and dealing with aphids here. One particular aphid can cause red blisters and marks on the surface of the leaves on all the currant bushes. This particular aphid tend to restrict itself only some of the leaves and although the effect looks dramatic it rarely affects the health of the plants. If you want treat it then do as described for aphids above.
Aphids, including the Currant Blister Aphid, are first seen on currant bushes from late April to mid May depending on the climate in your area. If you do intend to spray them, do it at the very first sign of damage for maximum effect. Big bud mite almost exclusively affects blackcurrant bushes. In late winter, January and February time, when the buds would normally begin to form, they do so but are much larger than normal.
Affected buds either fall off or produce distorted growth which fails to produce fruit. Reversion Disease affect blackcurrant bushes almost exclusively. It is a virus which cannot be treated and affected plants should be dug up and burnt. The variety Ben Gairn has been shown to have some resistance to Reversion Disease.
Reversion Disease will cause the yield of your blackcurrant bush to reduce significantly to almost nothing after three years. Mildew often affects blackcurrant bushes and it is normally preventable. The signs are a greyish powder which can appear on the fruit, leaves and in bad cases on the stem. It is unlikely to kill the bush but it will weaken it and make it more prone to other diseases. For a full description of the symptoms and treatments for Powdery mildew, click here. There are chemical sprays available to help kill mildew although prevention is much better than cure. Older varieties of blackcurrants are far more susceptible to mildew so avoid growing those.
Titania also shows significant resistance to mildew. Pruning methods can also significantly reduce the risk of being affected by mildew. See our article of pruning blackcurrants here. If your blackcurrants are susceptible to mildew pay particular attention to keeping the central part of the bush free from congestion. Also take care to remove all crossing and touching branches.
When they rub together they can open up the bark letting in infections. The symptoms are that blackcurrant bushes form green currants normally but around mid May to mid June they fall off before they are ripe. This can be due to several causes and it is known as “run-off”. By far the most common cause is adverse weather conditions especially cold weather. Other causes can be lack of water, pests and diseases, particularly botrytis and mildew. It can occur in one year and then never appear again or can occur in several years depending on the cause.