By Justin McMechan and Roger Elmore
Much of the early planted corn in the Nebraska has reached the V10 stage and some soybean fields are beginning to flower. Over the past couple days, many of us watched severe storms cross the state, reminding us that hail can happen at any time during the growing season. As we move past the V6 stage in corn and into the reproductive stages of soybeans, we have to change our thinking on how we evaluate hail damage.
Estimating yield losses in these crops is helpful for determining future inputs such as water and nutrients. If extensive damage occurs, alternative strategies such as cover crops may need to be considered as a way of reducing nitrogen leaching or soil erosion. The best cover crops or forages for your operation will depend on your needs or the markets available to you. With any hail damage, make sure to contact your Farm Service Agency or Crop Insurance Adjustor before doing anything to the field.
Estimating Yield Losses from Defoliation in Corn
Yield losses in corn from defoliation are estimated after corn reaches the 7th leaf stage using the horizontal leaf method (Table 1). The 7th leaf stage is the development stage when the growing point moves to the soil surface. As with any hail damage to row crops, it is critical to wait at least 7-10 days to allow the crop to respond. For defoliation assessments, this allows for separation between live and dead tissue. Plants may be tattered and broken, but if plant tissue remains green, it’s still photosynthetically active and contributing to the growth and development of the plant.
To determine yield losses due to defoliation, you’ll need to determine the stage of the plant at the time of the hail event. Defoliation should be estimated based on missing leaf area and tissue that is no longer green. Assess defoliation on plants at three places in the field to get an accurate estimate. To estimate yield losses based on these defoliation averages see Table III of the EC126 Evaluating Hail Damage to Corn. It indicates corn at the 13th leaf stage with 50% defoliation could have a production loss of 10%; 100% defoliation would lead to a 34% loss in production. Complete yield losses can occur if all leaf area is destroyed in corn at the VT (tassel stage).
Yield losses from plant stand reductions are still accounted for in corn through the 17th leaf stage. It’s important to note that the Corn Loss Adjustment Standards Handbook has two tables, one for corn prior to 10th leaf (page 80) and another from the 11th to 17th leaf stage (page 81).
For results of Short Season Corn Hybrids planted late, see Table 2.
Methods for Staging Corn Growth Stage
Table 1. Corn vegetative development staging methodsLeaf Collar
(ISU) | Horizontal Leaf
(NCIS) |
|---|
| V1 | N.A. |
| V2 | 3.0 |
| V3 | 4.5 |
| V4 | 5.5 |
| V5 | 6.5 |
| V6 | 8.0 |
| V7 | 9.0 |
| V8 | 10.0 |
| V9 | 11.5 |
| V10 | 12.5 |
| V11 | 13.0 |
| V12 | 13.5 |
| V13 | 14.0 |
| V14 | 15.0 |
| V15 | 15.5 |
N.A. Not applicable
Adapted from: Corn Growth and Development, Abendroth et al. 2011, PMR 1009. Iowa State University Extension |
When talking with your hail insurance agent or adjuster, it's important to understand the method being used to estimate corn growth stage.
The horizontal leaf method of staging is used by the National Crop Insurance Service (NCIS). This method counts all visible leaves where the tip of the leaf points below the horizontal position.
A more common method in Nebraska is the leaf collar method developed by Iowa State University. This method is based on a count of collared leaves?when a leaf partially unclasps from the stem or stalk exposing a collar. The first leaf that emerges is more round tipped than subsequent leaves and is counted as the first leaf. This method is based on Corn Growth and Development (Abendroth et al, 2011., PMR 1009, ISU Extension).
Depending on the stage of development, the NCIS system can be one to two leaves more than the ISU collar system. (See Table 1, where the NCIS method is labeled as the horizontal leaf method.)
Corn growth stages referenced in this article reflect the NCIS method.
Estimating Yield Losses from Defoliation in Soybeans
Like corn, yield loss estimates in soybean should not be taken until 7-10 days after a hail storm. If plants are not in the R1 or flowering stage, yield losses can be estimated based on the percentage of nodes cut off or broken over above the cotyledonary node. Assess damage on at least 20 plants to develop an average. Yield losses can be estimated by using the tables on pages 74 and 75 of the FCIC Soybean Loss Adjustment Standards Handbook. At V5 yield losses are 9.7%, 15.6%, 26.1% and 80.9% for plants with 25%, 50%, 75%, and 100% of nodes cut, respectively. Once plants reach the R1 stage, estimates are made based on a combination of node cut/broken and percent defoliation. A worksheet to estimate total losses is in Evaluating Hail Damage to Soybeans (Nebraska Extension EC128).
Similar to corn, soybeans have different tables for stand loss occurring at different stages of crop development. Stand reductions from 120,000 to 60,000 plants per acre resulted in an estimated yield loss of 14% from VC to R1 stages and 35% from R2 to R3.5 stages. Stand losses from hail are often not uniform. If gaps are less than two feet, plants will be able to branch out to fill in spaces. Gaps greater than two feet can result in additional yield losses.
Other Management Considerations
Hail damage in row crops can alter other management considerations for a crop depending on the timing and extent of damage. With either crop, hail opens up the canopy and can allow weeds to germinate or grow larger with access to sunlight. If large numbers of weeds are present they should be controlled before they are 4 inches tall.
Table 2. Agronomic performance of short season corn hybrids planted mid- to late June and harvested Dec. 10, 1992 at North Platte, Nebraska. (Nordquist) |
| | Yield, Bu/Ac | % Moisture | % Broken | Wt/Bu |
| | Date Planted |
Hybrids | Days* | 6/16 | 6/23 | 6/16 | 6/23 | 6/16 | 6/23 | 6/16 | 6/23 |
1 | 85 | 100 | 71 | 12.9 | 15.7 | 2 | 12 | 54.0 | 50.0 |
2 | 87 | 130 | 104 | 13.6 | 16.5 | 0 | 0 | 55.5 | 53.0 |
3 | 94 | 119 | 91 | 15.4 | 18.0 | 5 | 6 | 54.0 | 52.0 |
4 | 99 | 133 | 92 | 16.1 | 24.3 | 2 | 0 | 48.7 | 44.5 |
5 | 100 | 155 | 120 | 19.7 | 27.5 | 8 | 0 | 46.5 | 46.5 |
6 | 105 | 134 | 101 | 18.1 | 22.4 | 5 | 7 | 50.0 | 46.5 |
*Comparative Relative Maturity Days |
Source : unl.edu