By Bethany Kroeze, AgVenture Marketing Manager
Approximately one-third of all hailstorms occur between June and September across the United States, which can result in corn yield losses. Hail damage affects yields by reducing stands and defoliating the plant, the latter of which causes the most loss. Proper assessment following a hailstorm can help estimate yield loss and determine optimal solutions for the remainder of the season.
Corn is the most susceptible to hail damage once the growing point is elevated above the soil surface, or approximately three weeks after emergence (V5-V7). The most critical period is from V5 to VT as the plant is growing rapidly. Once corn tassels, hail will cause significantly less yield loss.1
After a hailstorm, assessment should not be attempted the day immediately following the damage. Young corn has the capacity to recover from early season damage, so patience is a key first step. When it’s time to assess the damage, you should look at plant survival, defoliation severity, and whorl and stem bruising.
With 3-to-5 days of favorable weather conditions, plants can show noticeable recovery. R.L. Nielsen recommends evaluating the condition of the main growing point area of the stalk. The growing point region is responsible for creating all the leaves and the tassel of the corn plant.2 By slicing a stalk down the middle and looking for the pyramid-shaped upper stalk tissue, you can identify the vertical position of the growing point. Iowa State University research says that the growing point of a healthy plant will be white to cream color.3 Nielsen says that if hail has damaged the growing point or cut off the stalks below the growing point, those plants should be counted as victims of the hailstorm.4 It is recommended to observe and sample plants from at least three parts of the damaged fields, totaling 1/100th of an acre.5
When observing leaf damage, Nielsen states that the damage tends to look worse than it really is. Damaged leaves that remain green and attached to the plant will continue to photosynthesize. Leaf loss or defoliation prior to V6 stage seldom contribute to yield loss. Plants that are further along in the vegetative or reproductive stages could experience greater yield loss (see Table 1).
Table 1. Estimated percent yield reduction from leaf loss caused by hail damage.6
| Stage* | Percent Leaf Area Destroyed | |||||||||
| 10 | 20 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | |
| V7 | 0 | 0 | 0 | 1 | 2 | 4 | 5 | 6 | 8 | 9 |
| V10 | 0 | 0 | 2 | 4 | 6 | 8 | 9 | 11 | 14 | 16 |
| V13 | 0 | 1 | 3 | 6 | 10 | 13 | 17 | 22 | 28 | 34 |
| V16 | 1 | 3 | 6 | 11 | 18 | 23 | 31 | 40 | 49 | 61 |
| V18 | 2 | 5 | 9 | 15 | 24 | 33 | 44 | 56 | 69 | 84 |
| VT – Tassel | 3 | 7 | 13 | 21 | 31 | 42 | 55 | 68 | 83 | 100 |
| R1 – Silk | 3 | 7 | 12 | 20 | 29 | 39 | 51 | 65 | 80 | 97 |
| R2 – Blister | 2 | 5 | 10 | 16 | 22 | 30 | 39 | 50 | 60 | 73 |
| R3 – Milk | 1 | 3 | 7 | 12 | 18 | 24 | 32 | 41 | 49 | 59 |
| R4 – Dough | 1 | 2 | 4 | 8 | 12 | 17 | 23 | 29 | 35 | 41 |
| R5 – Dent | 0 | 0 | 2 | 4 | 7 | 10 | 14 | 17 | 20 | 23 |
| R6 – Mature | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| * Leaf-collar vegetative staging method. Source: USDA. |
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A final assessment should be made concerning the consequences of whorl and stem bruising. While the eventual yield effects can be difficult to predict, an on-farm study in Ohio suggested that bruising from hail early in the season typically does not result in increased stalk lodging or stalk rot development. Twisted whorl plants – also known as tied or buggy whipped – may be a result from hail injury. An Ohio State University study found that fields with major hail damage exhibited anywhere from 36 to 61 percent twisted whorls. That number was significantly reduced – to a range of 0 to 9 percent – within a month as most plants grow out of the condition.7
Once assessment has been completed, it is time to move on to managing damaged fields. Applications of fungicide and nitrogen should be considered on a case-by-case basis. Consult your AgVenture Yield Specialist to determine the best course of action for your fields. If the hail damage has reduced stand count, weed pressure can increased due to additional sunlight reaching the soil. Paired with additional moisture received with a storm, new weeds may begin to germinate in the days and weeks following the damage assessments. Continue to monitor weed pressure and consider postemergence, layby and harvest aid treatments for any increased pressure.8
1 James V. Vorst, Purdue University.
2 R.L. (Bob) Nielsen, Purdue University.
3 Iowa State University Extension & Outreach, Integrated Crop Management News, Roger W. Elmore and Lori Abendroth, Department of Agronomy.
4 R.L. (Bob) Nielsen, Purdue University.
5 James V. Vorst, Purdue University.
6 Iowa State University Extension & Outreach, Integrated Crop Management News, Roger W. Elmore and Lori Abendroth, Department of Agronomy.
7 Mangen, Todd and Peter Thomison. 2001. Early Season Hail Damage in Corn: Effects of Stalk Bruising and Tied Whorls. Ohio State Univ. Cooperative Ext. Service Special Circular 179-01.
8 Klein, Robert N. and Charles A. Shapiro. 2011. The Board of Regents of the University of Nebraska on behalf of the University of Nebraska-Lincoln Extension.