Last week we received reports of hail storms that damaged corn fields in northwest Ohio.  The impact of hail damage is largely dependent on the corn crop'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.

Severe hail damage prior to the 6 to 7-leaf stage can also result in “twisted” or “tied” leaf whorls as injured plants recover and new leaves try to unroll; however, most plants usually grow out of this problem and tied whorls seldom cause major yield loss.

Leaf damage by hail usually looks much worse than it really is, especially during the early stages of vegetative growth. Shredded leaves and plants with broken midribs 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, if damage occurs prior to tasseling. For this reason, estimates of hail damage 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 V7 plant according to the leaf collar method would probably correspond to a 9-leaf plant according to the hail adjustor's method).

How do we estimate the potential yield loss from recent hail storms? Corn growth stages will vary considerably depending on location, planting date, etc.. Moreover, there is also variability in growth within fields because of uneven emergence and development. The growth stages of the corn reported damaged by hail storms in NW Ohio last week were at about V5 or earlier when injury occurred (Fig. 1). Based on estimates of the National Crop Insurance Association (Table 1), at the 7-leaf stage (or about V5), if 50% of the leaf tissue is destroyed by hail, a corn plant loses about 2% of its grain yield potential; if 100% defoliation occurs, a corn plant loses about 9% of its yield potential.

For more detailed information on evaluating hail injury in corn, consult "Assessing Hail Damage to Corn" National Corn Handbook Chapter 1 (NCH-1)." Available on-line at

http://www.ces.purdue.edu/extmedia/NCH/NCH-1.html

(verified 6/11/12)

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

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

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