During the past week, tassels and silks began appearing in cornfields that were planted during mid-May or earlier. Corn planted in early June may not be not be tasselling and silking until early August. There is usually some variability in pollination within cornfields and the pollen-shed period extends from one to two weeks. This year we can expect even greater variability because saturated soil conditions and loss of nitrogen in poorly drained and compacted areas have inhibited corn growth. Soil moisture deficits due to limited rainfall have also resulted in differential plant growth. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination.

Stress conditions such as drought have the greatest impact on yield potential during the reproductive stage. Past research indicates that four days of stress (i.e. corn wilted for four consecutive days) at the 12-14 leaf stage has the potential of reducing yields by 5-10%. The potential for yield losses to soil moisture deficits increases dramatically when plants begin to flower. During tassel emergence, four days of moisture stress has the potential to reduce yields 10-25%. Silk emergence is the most critical period in terms of moisture use by the plant. During this stage, leaves and tassels are fully emerged and the cobs and silks are growing rapidly. Four days of moisture stress during silk emergence has the potential to reduce yields 40-50%. However, the stress conditions we are alluding to over these four-day periods are severe and involve extensive leaf rolling (characterized by plants with “pineapple” like leaves) throughout much of the day. Also keep in mind that the corn plant is more vulnerable to hail injury during the period from tassel emergence (VT) to silking (R1) than during any other period because the tassel and all the leaves are completely exposed. Complete defoliation of the plant at VT usually results in 100% yield loss.