Pest and Life Cycle (Cryptomyzus ribis) – The foliage damage caused by this insect pest is often more noticeable than the pale yellow aphids that suck the sap on the leaf reverse, starting from late spring to early summer. By midsummer winged aphids are produced which migrate to secondary host plants – these return to the Ribes by autumn, when eggs are laid on the shoots. The eggs hatch in spring and form aphid colonies on the leaf reverse. Currant Blister Aphid affects Red, White and Black Currant, as well as Jostaberry (a Black Currant/Gooseberry hybrid) and Gooseberry (albeit infrequently).
Symptoms – Prominent reddish to purplish blisters are visible on the upper leaf portion of Red and White Currants, while the blisters are usually yellowish-green on Black Currants. Severe leaf distortion may occur with heavy infestations. Black sooty mold from honeydew may also be present. Bushes can still produce a normal crop with foliage symptoms.
Management – If aphids are still present on the leaf reverse, an organic pesticide containing pyrethrins or insecticidal soap (such as ‘Trounce’) can be used at label rate and applied to the leaf reverse to control the pest. Do not spray while bushes are in bloom as this could potentially kill pollinators. Aphids can also be dislodged with a strong spray of water from the hose.
Prevention – 1. Monitor currants and related hosts regularly once in leaf and check for natural predators such as ladybugs – these can also be released should an outbreak occur. 2. Avoid fertilizing with high nitrogen as the resulting lush foliage will attract more aphids to your currant bushes. 3. Spray your dormant Ribes with a winter application of a superior-type horticultural oil to kill overwintering eggs.
Mike's Garden Guide 