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).