Corn Hail Damage
Chad Lee
Agronomy
June 6, 2007
Assessing hail damage on corn requires a knowing several factors, such as the growth stage, leaf area destroyed and surviving stand. Many times, the hail damage often looks worse than the yield losses will be.
Growth Stage
See the related article in this newsletter for determining growth stages. The growing point usually begins to move above ground as corn approaches the V6 growth stage. Corn is highly tolerant to hail damage at these early stages of growth. As the growing point moves above ground and the corn plant gets closer to tasseling, it becomes more susceptible to hail damage. Corn is most susceptible to hail damage just prior to tasseling through early milk. Once corn passes through the early milk stage, it becomes more tolerant to hail damage.
Percent Leaf Area Destroyed
Estimate the amount of leaf material that is missing or no longer green. Any green leaf material, even that which is shredded, should not be counted as destroyed.
The following table is adapted from the National Crop Insurance Association’s “Corn Loss Instructions” (Rev. 1984). The entire Table can be found in a Nebraska Extension publication (Vorst, 1986). The 8-leaf stage as determined by a hail adjuster is usually equal to a V6 leaf stage (six collars visible). The numbers in Table 1 assume that the corn stand was not reduced by hail.
Table 1. Estimated percent yield loss occurring from defoliation.
Percent Leaf Area Destroyed
Growth Stage*
10
20
30
40
50
60
70
80
90
100
7-leaf
0
0
0
1
2
4
5
6
8
9
8-leaf
0
0
0
1
3
5
6
7
9
11
9-leaf
0
0
1
2
4
6
7
9
11
13
10-leaf
0
0
2
4
6
8
9
11
14
16
11-leaf
0
1
2
5
7
9
11
14
18
22
12-leaf
0
1
3
5
9
11
15
18
23
28
13-leaf
0
1
3
6
10
13
17
22
28
34
*Hail adjusters’ method for staging corn. (8-leaf stage is usually similar to V6 corn, where 6 collars are visible).
Estimating Stand
Reductions in corn stand may reduce yields. For most of Kentucky, stands ranging from 22,000 to 30,000 plants/acre are ideal. Stands below 22,000 plants/acre will cause yield reductions in most cases. The article “Assessing Damage Corn Stands” in this newsletter provides more details regarding stand assessment.
Tied Whorls and Silking
Corn plants damaged by hail early in the season usually recover from tied whorls and bruised stalks. The corn will usually grow through these tied whorls within 3 or 4 weeks (Mangen and Thomison, 2000). Stalk bruising had little impact on lodging. Silking will be delayed on severely damaged corn plants. Corn from V5 through V7 that received 100% leaf damage from hail had a 1 to 1.5 week delay in silking compared with plants that received 80 to 90% leaf damage.
Final Thoughts
Hail damage early in the growing season almost always looks worse than it really is. Wait about five days before making any kind of stand assessment. If replanting does become necessary, then switch to an earlier hybrid.
References
Vorst, J. J. 1986. Assessing Hail Damage to Corn, G86-803-A: http://ianrupus.unl.edu/fieldcrops/g803.htm
Mangen, T. and P. Thomison, 2002. Early season hail damage in corn: effects of stalk bruising and tied whorls. Agronomic Crops Team On-Farm Research Projects 2000. Special Circular 179-01. http://ohioline.osu.edu/sc179/sc179_16.htm
