Recently, severe storms came across parts of Eastern Canada bringing hail that, in localized areas, damaged corn. After the initial shock of viewing a severely damaged corn field has diminished, the process of determining the extent of the damage will begin. Yield loss from hail damage results from leaf area reduction and plant bruising. The severity of each of these factors is important to accurately assess the extent of damage and estimate potential yield loss. To accurately assess potential yield loss from hail, corn plants should be evaluated 7 to 10 days after the storm.2 The plants will have had some time to recover, and a better assessment of the damage can be made.
Leaf Defoliation
Corn in the area generally ranged from V4 to V10 growth stages. Yield loss potential due to defoliation increases significantly as the corn plant approaches tasseling, compared to when the corn is younger (Table 1). Shredded leaves that remain green and attached to the plant will continue to produce photosynthates for the plant (Figure 1).3
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Table 1. Estimated corn grain yield loss from plant defoliation
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Growth Stage (Leaf-over Method)
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Plant Defoliation (%)
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20
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30
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40
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50
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60
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70
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80
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90
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100
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% Yield Loss
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7 Leaf
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0
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0
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1
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2
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4
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5
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6
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8
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9
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9 Leaf
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0
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1
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2
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4
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6
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7
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9
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11
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13
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11 Leaf
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1
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2
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5
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7
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9
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11
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14
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18
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22
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13 Leaf
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1
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3
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6
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10
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13
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17
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22
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28
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34
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15 Leaf
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2
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5
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9
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15
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20
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26
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34
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42
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51
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17 Leaf
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4
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7
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13
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21
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28
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37
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48
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59
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72
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18 Leaf
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5
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7
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15
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24
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33
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44
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56
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69
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84
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19 to 21 Leaf
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6
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11
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18
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27
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38
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51
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64
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79
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96
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Tassel
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7
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13
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21
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31
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42
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55
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68
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83
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100
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Silked
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7
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12
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20
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29
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39
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51
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65
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80
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97
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Silks Brown
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6
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11
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18
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27
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36
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47
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60
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74
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90
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Pre-Blister
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5
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10
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16
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24
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32
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43
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54
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66
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81
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Source: Adapted from National Crop Insurance Survey (Rev. 1994). Found in OMARFA Pub. 811 Agronomy Guide Table 1-30
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Bruising may create a port of entry for pathogens, which can increase the risk for stalk rots and lodging later in the season. Weather conditions during the remainder of the growing season will influence disease development and severity. Fields that contain severely bruised plants may need to be evaluated again at the end of the season.
In some cases, an evaluation of ear damage due to hail will be necessary (Figure 2). To assess the amount of crop loss due to ear damage, perform the following steps: 1) Select ears from ten consecutive plants and count the number of damaged kernels on all the ears.1 2) Determine the total number of kernels on all ten ears. 3) Calculate the percent of total kernels damaged. This figure is the percent loss due to direct ear damage.
Estimate of Yield Loss
Many factors are involved in estimating total yield loss, including effects from defoliation, plant bruising, possible disease infection, stalk lodging, ear damage, and environmental conditions during the remainder of the growing season. Growers should scout for stalk rot and lodging, monitor fields with increased nitrate levels intended for animal feed, and watch for late-season weed flushes due to increased light penetration in defoliated areas. Expected yield loss figures due to damaged or missing plants are only estimates. True yield loss due to the hail storm cannot be fully determined until harvest. Contact your local DEKALB® agronomist for more information regarding the assessment of hail damaged corn.
Hail damanged corn at v3 (above). Notice the stripped leaves on older corn (right). Yield loss potential due to defoliation increases significantly as the corn plant approaches tasseling, compared to when the corn is younger.
Sources:
1 J. Vorst. Reprinted 1993. Assessing hail damage to corn. National Corn Handbook. Purdue University. NCH-1 Electronic Version.
2 J. Lauer. 1994. Hail Damage on Corn. University of Wisconsin Cooperative Extension http://corn.agronomy.wisc.edu (verified 6/9/2014).
3 R. Nielsen. 2001. Hail Damage in Corn: Moving Beyond Grief to Damage Assessment. Purdue University Cooperative Extension. http://www.agry.purdue.edu (verified 6/9/2014).