Stem borer infestation is higher in later part of the season. Majority of the damage of stem borer is caused by the larvae of the insect which feeds on young leaves and later enter and tunnels inside the stem of the plant. It is particularly difficult to control stem borers using chemicals because the damaging larvae are hidden away deep inside the plant stems. The first signs of stem borer attack in young maize plants are small holes in straight lines across the newest leaves. In older plants, the symptoms include dead heart, plant death, dieback and internal feeding in the stem.