What happened to that blackberry branch? The leaves are shriveled and curled up, and there’s white wax on the stem and leaves.
This is damage from blackberry psyllid (Trioza tripunctata). Blackberry psyllids are bugs that look like small cicadas. They feed only on blackberry plants. They pierce the stem and suck out the sap.
The adults emerge in October and overwinter in conifer trees. In the spring, they feed and lay their eggs on the blackberry plants. Nymphs hide and feed under the curled leaves. They produce the white waxy substance to protect themselves from predators.