Damage threshold vary, but emerging wheat is susceptible to this kind of injury. In many situations, as few as 2 to 3 worms per foot of row can destroy seedlings. If populations get too high, about all you can do is destroy the remaining vegetation, wait 2 weeks for the worms to starve, and then replant. Growers often don't notice infestations until replanting is the only option. Newly hatched worms are pale green and tiny.
Larger ones are darker and have a striped appearance.
Their damage shows up as small round or oval window-panes that the worms create as they feed on the upper wheat leaf surfaces. As the worms grow, they begin to eat entire leaves and may chew plants down to the soil line. They also become increasingly difficult to control, not only due to size, but also they often hide under the soil surface.