MAIZE GROWTH AND YIELD FOLLOWING LATE SUMMER HAIL

Leaf damage caused by hail may severely restrict photosynthate product ion, but estimation of yield loss is hindered by lack of an unaffected control for comparison. A field study was modified in 1990 at Ottawa, Canada, to determine the effect of maize growth stage at the time of hail damage on harvest parameters. Hand-harvested above-ground dry mat ter, grain yield, grain moisture, and harvest index were compared amon g nine hybrids with maturities ranging from 2350 to 2800 corn heat uni ts (CHU) and planting dates of 30 April, 16 May, and 29 May. A severe hail storm occurred 28 August when some hybrid maturity x planting dat e treatments were at the milk stage and others were at full dent. A me thod of analysis was developed using above-ground dry matter accumulat ion at tasselling as a pre-hail indicator of yield potential to calcul ate the reduction in harvest dry matter and grain yield resulting from the hail storm. The reduction in harvest dry matter and in grain yiel d was linearly related to the CHU required to reach physiological matu rity at the time of the hail storm (P < 0.10). Late-maturity hybrids w ere most affected by the hail storm and contributed most to these regr essions (P = 0.01 and P = 0.02 for harvest dry matter and grain yield, respectively). Harvest index was not affected by the hail storm (P > 0.10).