Blackberry psyllid is a fairly common insect in the South (at least I have seen many many blackberries affected — although most are wild blackberries and not commercial), especially in areas near conifer trees. The adults are small insects that resemble cicadas and the nymphs are wingless. Both blackberry psyllid adults and nymphs feed on the cane phloem. Adult blackberry psyllids overwinter in conifers and migrate to blackberries in spring after which they lay eggs. The adults stays on the plant for a few days feeding. Leaf curling will develop after about a week. Adult psyllids lead to curled leaves and shortened internodes. Nymphs feed from the underside of the leaf. Controlling these insects can be done with proper site selection (away from pine trees) or by pruning out affected canes. Spraying with an insecticide should be done only in cases of severe infestation. Below is a photo taken by Robert Hays of blackberry psyllid symptoms.