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C.O.R.N Newsletter 2009-17
     June 9, 2009 - June 15, 2009


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Assessing hail damaged corn
by Peter Thomison

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Last week I received reports of hail storms that caused severe injury to corn in southwestern Ohio. The impact of hail damage is largely dependent on the crop's stage of development. Hail affects yield primarily by reducing stands and defoliating plants with most of the damage resulting from defoliation. Corn becomes increasingly vulnerable to hail damage at later vegetative stages of development with the tassel stage/pollen shedding stage (VT) being the most critical period.

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 (i.e. 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. I suspect most corn in Ohio has not progressed much beyond the V7 stage (as of 6-8-09). Based on estimates of the National Crop Insurance Association, at the 9-leaf stage (or about V7), if 50% of the leaf tissue is destroyed by hail, a corn plant loses about 4% of its grain yield potential; if 100% defoliation occurs, a corn plant loses about 13% 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 6/8/09).

Percent yield loss in corn based on growth stage & defoliation (adapted from NCIA Corn Loss Instructions, rev. 1984)
Percent Leaf Defoliation
Growth Stage* 25% 50% 75% 100%
7-leaf (V5)** 0 2 5 9
8-leaf (V6) 0 3 6 11
9-leaf (V7) 1 4 7 13
*as determined using the hail adjustor’s leaf staging method
** approximate leaf collar stage within parentheses


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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.


Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

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