Hail injury V-10 to V-13 corn, Photo by Mark Badertscher, Extension Educator Hardin County

The impact of hail damage is largely dependent on corn’s stage of development.  Hail affects yield primarily by reducing stands and defoliating plants. Most of the hail damage results from defoliation. Generally, the corn plant is little affected by hail prior to the 6 to 7 leaf stage because the growing point is at or below the soil surface and in the leaf whorl. However, once the growing point is elevated above the soil surface due to internode elongation, the plant grows rapidly and becomes increasingly vulnerable to hail damage with the tassel stage/pollen shedding stage (VT) being the most critical period.

Leaf damage by hail often looks much worse than it really is, especially during the early-to-mid stages of vegetative growth. Shredded leaves and plants with broken midribs still have some capacity to contribute to plant growth. Plants not killed outright by hail usually show new growth within 3 to 5 days after injury occurs (i.e. if damage occurs prior to tasseling). For this reason, estimates of hail damage during vegetative development should be delayed several days to allow for this period of re-growth.

The hail insurance adjustor's growth staging system counts leaves beyond the last visible collar to the uppermost leaf that is 40-50% exposed whose tip points downward - usually this results in a leaf stage that is numerically 2 leaves greater than the "leaf collar method" (e.g. a V11 plant according to the leaf collar method would probably correspond to a 13-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Growth stages vary considerably among fields this year due to differences in location, planting date, etc. Moreover, within some corn fields, it’s not unusual to see corn differ by three or more growth stages because of differences in soil color and drainage. Although much of the corn crop in Ohio is at or beyond the tassel (VT) and silking stages (R1), in some areas of the state there was considerable acreage planted in early to mid-June. Some of this late planted corn was damaged by hail last week when plants were at the V10 to V13 stages of development (see pictures). What impact did the hail storms have on corn yield (if we assume stand loss from hail damage was minimal)? Based on estimates of the National Crop Insurance Association (see Table 1 below), at the 13-leaf  stage (or about V11) if 50% of the leaf tissue is destroyed by hail, a corn plant loses 10% of its grain yield potential; if 100% defoliation occurs, a corn plant loses 34% of its yield potential. The pictures suggest significant defoliation injury to plants – probably exceeding 50% but not 100% damage. If the damage had occurred at VT or R1 loss of potential yield would have been much greater (Table 1).

Table 1. Percent yield loss in corn based on growth stage & defoliation

(Adapted from NCIA Corn Loss Instructions, rev. 1984)






Growth Stage*





13-leaf (V11)





15-leaf (V13)





17-leaf (V15)





Tassel (VT)/Silk (R1)





*as determined using the hail adjustor’s leaf staging method; ** approximate V-stage within parentheses

For more detailed information on evaluating hail injury in corn, consult the following:

Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.

Nielsen, RL (Bob). 2008. Recovery from Hail Damage to Young Corn

Corny News Network, Purdue Univ. [On-Line]. Available at http://www.kingcorn.org/news/timeless/HailDamageYoungCorn.html

Vorst, J.J. 1993. Assessing Hail Damage to Corn. Purdue Univ. Cooperative Ext. Service Publication NCH-1. [On-Line]. Available athttp://www.ces.purdue.edu/extmedia/NCH/NCH-1.html

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