The strawberry leaf-roller is the most serious insect pest on the strawberry in Iowa. It feeds on the plants thruout the summer, increasing in abundance if not controlled, so that the plants may suffer severe injury after the crop has been removed. In the larva or "worm" stage, the insect feeds between the two halves of a leaf, which is folded along the midrib and fastened together with web. The presence of such leaves in a patch is the best indication of infestation by the leaf-roller. The larvae feed only on one leaf surface, leaving the other intact so that it dries and turns brown.
Fulton, B. B. and Brunson, M. H., "Strawberry Leaf-roller Control" (1928). Circular. Paper 110.