Collar of 3rd leaf is visible (once a leaf 's collar forms the leaf no longer expands). This stage occurs ~10 days after emergence, depending on soil tempera- ture, moisture, planting depth, etc. Slow emergence may lead to more injury from pre-emerge herbicides. Insects: Corn earworm (whorlworm) and corn leaf aphids may infest the whorl and greenbugs may infest the leaves although not likely.