This is a period of very rapid growth. The corn plant requires heavy amounts of moisture and nutrients to develop a structure that can take maximum advantage of sunlight to fill ears. During this period, competition from weeds and damage from insects and disease can seriously affect yields. Weeds use nutrients that are going to build the plant structure that will eventually fill the corn ears. Insects and disease can damage the plant structure and reduce its ability to yield.
Damage can reduce photosynthetic ability by destruction of leaf surfaces.
Damage also can divert nutrients and photosynthetic products to repair damaged tissue rather than to the developing ears. Either way, pest and disease damage rob the plant's ability to yield. The fourth stage is from silking to the hard dent stage in maturity. During this period, most yield reduction comes from damage by pests and disease. By the time of silking, corn plants usually have outgrown most weeds.