During the week of Sept. 7-11, one or more severe hailstorms went through portions of Kansas, with variable impacts on corn and soybeans. Where a hailstorm occurs this late in the growing season, the main thing producers can do is to understand the potential impact of the hail damage on yields and get an estimate of the expected yield loss.
At this point in the growing season (late reproductive stages), if a large proportion of the leaf area is lost, then the primary yield impact could be related to a reduction in kernel size (seed weight). It is also critical to determine the impact of hail on standability (potential lodging issues), stalk damage, direct damage to the ears, and defoliation of the crop canopy. As the crop gets near physiological maturity and black layer formation, any loss of leaf area will have less effect on yield than if the defoliation had occurred earlier in the season.
The estimated yield loss based on the percent of final defoliation is presented in Figure 1. If a defoliation event took place in your corn close to maturity (from dent to maturity), the yield impact from defoliation could be minimum. At those later stages, even with high levels of defoliation –- 70 to 90% -- the yield impact ranges from just 5 to 20%.
As for management options after a defoliation event, corn with hail damage could mature more quickly but it will not dry down faster than non-damaged corn. Moldy ears could appear much faster if plant tissue was wounded and openings were created due to the hail damage. Scout your fields for lodging and stalk damage, and check for the overall status of the leaf canopy.
Figure 1. Graphic illustrating the relationship between estimated yield loss and percent leaf area loss at different growth stages of corn (based on data from Corn Loss Adjustment Standards Handbook, USDA-FCIC-25080, pages 7-98).
Most of the soybeans have set pods and are entering into the last most critical stages of seed-filling (R5-R6). For indeterminate varieties, defoliation that takes place at beginning of seed formation (R5 stage) will impact yields to a greater extent than an early hail event.
For determinate soybean varieties, loss of leaf area could produce more losses than for indeterminate varieties since the reproductive stages in determinate varieties tend to be more compressed, with less opportunity to compensate if pods are damaged. Determinate varieties have 3% to 17% greater yield losses than indeterminate varieties from hail damage that occurs in the early reproductive stages (R2 to R3), depending on the extent of leaf loss. Yield losses are greatest from damage at R4 to R5.5.
Stand loss: If hail breaks the stems of plants and causes plant death in the R1 to R6 reproductive stages of growth, the remaining plants will normally have only limited ability to branch out and compensate.
Pod fill through maturity (R6.5 and later): Plants cannot compensate through either additional flowering or new branch development after R6.5. Therefore, the way to estimate yields at these stages is to make a direct seed count. Hail damage to leaves at these stages will have little or no effect on seed development or yields.
Scout your acres for late-season hail damage impact on corn and soybeans. The impacts of hail damage on yield can be known with more precision in the 6-8 days after the hail event. If defoliation occurred, the stage of crop development will largely determine the extent of the crop yield loss to be expected.
When the hail damage event takes place close to crop maturity, hail damage could have minimal impact on yields on corn, with any yield loss primarily related to the effects of leaf loss on seed weight. For soybeans, defoliation during seed-filling will have a large impact on seed weight and final yield, with the amount of the yield loss depending on the extent of the defoliation and the timing relative to the stage of the crop. Hail damage that occurs earlier during seed formation will result in a larger expected yield loss than hail damage that occurs close to the end of the seed fill.
Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist
Kraig Roozeboom, Cropping Systems Agronomist