Leaf cupping, twisting and shoestring appearance are common symptoms of injury from 2-4 D and other similar phenoxy herbicides.
Strapping of leaves. Tobacco mosaic virus and Cucumber mosaic virus can also cause symptoms similar to that of phenoxy herbicides.
Vein clearing can be noticed on leaves with injury. Herbicide drift and residue from carry over of prior crop could also be the cause.
A field with the left row with distortion of leaves due to phenoxy herbicide damage. The row to the right have very minimal damage.