Why Are My Blackberry Canes Covered in Aphids?

Aphids colonise the soft growing tips of blackberry canes in spring and early summer, feeding on the sap of young tissue. Rubus aphid (Amphorophora idaei) and black bean aphid (Aphis fabae) are the two species most commonly encountered. Blackberry aphid infestations are rarely as severe as those on related raspberries, but large colonies can cause leaf distortion, produce sticky honeydew, and encourage sooty mould on the canes and leaves below.

Aphids on shoot tips

The softest tissue — the very tip of a growing cane in April and May — is where colonies begin. Colonies at this stage cause leaf curl and distortion at the tip. Left unchecked, colonies move further down the cane as the initially infested tips harden. Squeezing colonies between finger and thumb at the very tip is a highly effective control for small to moderate infestations at this stage. This removes the aphids without any chemical input and without harming beneficial insects.

When intervention is warranted

On an established, healthy blackberry plant, moderate aphid populations on a few shoot tips are not a cause for concern — natural predators will reduce the population significantly by June. Intervention is warranted when: a young plant is heavily infested and significant shoot tip distortion is occurring; the entire cane structure is coated in aphids (unusual but possible in a bad year); or honeydew is causing significant sooty mould on fruit-bearing wood. In these cases, insecticidal soap spray applied directly to colonies is effective, safe and leaves no residues.

Sooty mould

Honeydew secreted by aphids falls onto the leaves and canes below, and sooty mould fungi colonise the sticky coating — leaving a black, powdery deposit. This reduces photosynthesis of affected leaves and can coat developing fruits if colonies are close to fruit clusters. Washing the affected surfaces with water removes sooty mould; controlling the aphids removes the honeydew source.