Insecticide against the pests in the farm

Some 2 weeks ago, I saw the ruined corn stalks by the pests that seemed to be eating the young leaves. The plants are already 3 feet high and starting to flower. I thought that they will not bear corn anymore. But the farmer said he will buy insecticide to spray on his corn field so the pests will be eradicated.

Today I went back to the nearby cornfield and guess what I saw. In the picture are the corn stalks with the ears coming out. In a week or 2 there will be harvesting and I am expecting to taste the freshly harvested corn again.