How to Estimate Hail Damage to Corn

That's a grower's normal reaction when a hail storm hits a corn field relatively early in the growing season. However, at that stage, more often than not, less damage has actually occurred to the crop than what is initially believed. The growing point resides below the soil surface until approximately five to seven leaves develop, so the corn plant will be affected very little by a hailstorm. After the seven leaf stage (often too late to replant corn) the plant becomes more vulnerable to hail damage, and it stays susceptible up to tasseling stage (most critical stage).

When the corn plant has reached the 10-leaf stage, stem bruising is more likely to occur. The bruised plants may allow a route of entry for stalk rots. Since weather conditions following the damage affect disease severity, it is difficult to determine the degree of damage until maturation. These fields should be considered for early harvest if stalk rot organisms have entered the plants.

After tasseling, hail damage would cause progressively less yield loss as the plant approaches maturity. (See Chart) Harvesting and marketing decisions are driven by late-season storms.

Estimated Percent Corn Yield Loss Due to Defoliation Occuring at Various Stages of Growth

	% Leaf Defoliation
Growth Stage	10	20	30	40	50	60	70	80	90	100
	% Yield Loss
7 Leaf	0	0	0	1	2	4	5	6	8	9
9 Leaf	0	0	1	2	4	6	7	9	11	13
11 Leaf	0	1	2	5	7	9	11	14	18	22
13 Leaf	0	1	3	6	10	13	17	22	28	34
15 Leaf	1	2	5	9	15	20	26	34	42	51
17 Leaf	2	4	7	13	21	28	37	48	59	72
19-21 Leaf	3	6	11	18	27	38	51	64	79	96
Tassel	3	7	13	21	31	42	55	68	83	100
Silked	3	7	12	20	29	39	51	65	80	97
Silks Brown	2	6	11	18	27	36	47	60	74	90
Blister	2	5	10	16	22	30	39	50	60	73
Milk	1	3	7	12	18	24	32	41	49	59
Soft Dough	1	2	4	8	12	17	23	29	35	41
Dent	0	0	2	4	7	10	14	17	20	23
Mature	0	0	0	0	0	0	0	0	0	0

Extracted from National Corp Insurance Service's Corn Loss Instructions

It is often difficult to distinguish live from dead tissue immediately after a hailstorm. Wait seven to ten days to assess damage. Most yield loss occurs in corn as a result of the loss of photosynthetically active leaf area. Yield reduction severity will depend not only the amount of leaf area removed, but also the corn's growth stage, when the hail occurred, pest pressure and growing conditions following the storm.

The chart above only estimates yield loss percentages. Extremely favorable weather conditions following a hailstorm can cause actual yields to be higher than expected. Similarly, unfavorable weather following can result in a reduction in expected yield.