Heavy rain events and strong storms are becoming more frequent in the eastern US corn belt, and have the potential to damage corn crops planted in the region. In addition to heavy rain and wind, hail may also accompany these storms. Damage to corn associated with these storms can manifest as reduced stand due to broken plants, partial to full plant defoliation from leaf loss, or as root lodging (stalks fall without breaking) or stalk breakage (i.e., greensnap).
When assessing damage severity, many crop insurance adjusters employ the “horizontal leaf” method, instead of the more traditional node/leaf collar or V-stage method, to identify the stage of plant development. Rather than counting fully exposed leaf collars (the V-stage method), the horizontal leaf method includes counting leaves that are up to 40–50% exposed. This coincides with the leaf tip becoming more horizontal. The typical result from a horizontal leaf method for staging will be 1–2 growth stages greater than the growth stage calculated using the V-stage method (e.g., 10-leaf plant = V8 growth stage).
This fact sheet presents data collected in Ohio that examines the effect of hail damage, root lodging, and greensnap on corn yield. The data was generated by imposing injury (intentional stand reduction, targeted defoliation levels, and induced root lodging) and from observations after natural events (root lodging and greensnap).
Stand Losses From Hailstorms
Hail damage to corn occurring prior to the 10-leaf (V8) stage can manifest as reductions in plant stands, as hail can damage stalks and growing points in smaller plants in addition to causing leaf damage. Intense hail events may also cause stand loss at later vegetative stages. Research was conducted on Ohio-targeted stand reductions of 17, 33, and 50% at 7-leaf (V5), 10-leaf (V8), and 13-leaf (V11) or 17-leaf (V15) stages. Uniform stand reduction was achieved within each row by removing every other plant, or was done by randomly removing plants to compare if the stand loss pattern influenced yield reductions. Remaining plants were then allowed to grow to maturity and their yield was quantified.
Regardless of the stand loss method (uniform or random), the reduction in yields in comparable stand reduction levels was within 4% of one another in most cases. Stand loss at the 7-leaf stage resulted in 6–16% yield loss with 17–50% stand reduction (Figure 1). Yield losses at the 10-leaf and 13-leaf growth stages were similar to the 7-leaf stage when stands were reduced by 17% and 33%, but yield losses were closer to 20% when a stand was reduced 50%. At the 17-leaf growth stage, 50% stand reduction resulted in an overall grain yield reduction of 30%. This research helps illustrate that yield loss can occur from reduced stands. However, hail damage can also reduce leaf area in plants and this study did not target defoliation in conjunction with stand loss. Using this study’s figures to determine yield losses without considering the effects of defoliation may overestimate the plant’s ability to compensate for yield (particularly at later growth stages) in the event of stand loss.
Defoliation Effects on Grain Yield Production
Defoliation trials conducted from 2013–2015 and 2018–2020 examined single defoliation events or multiple defoliation events (i.e., two hailstorms coming in one season at different growth stages). Defoliation intensity was either 50% leaf area loss or 100% leaf area loss (Figure 2).
While defoliation was not imposed at the same time the stand reduction research was conducted, trials from Ohio suggest defoliation at the 10-leaf stage or earlier may not dramatically affect the final grain yield compared to non-defoliated controls (Table 1). Loss of 50% to 100% of leaf area at the 10-leaf stage resulted in less than a 5% yield loss. However, a separate trial conducted from 2014–2016 revealed that select hybrids may experience severe tassel deformation after 100% defoliation at the 10-leaf stage (rating of 2.7; Figure 3). This could reduce pollen production in the event the entire field was affected. Loss of 50% of leaf area at the 15-leaf growth stage resulted in 12% yield loss, and 100% defoliation caused 35% yield loss. Defoliation during grain fill reduced grain yield by 23, 14, and 7% respectively at blister (R2), milk (R3), and soft dough (R4) stages, though the impact was more severe at R3 and R4 if an early-season defoliation had previously occurred.
|Stage of defoliation and amount (%)||Yield reduction||Years of data||Tassel deformation in select hybrids|
|10-leaf (V8)†||15-leaf (V13)||Tassel (VT)||Blister (R2)||Milk (R3)||Soft dough (R4)||%||Rating (1–3)‡|
|†Developmental stages are identified using the horizontal leaf stage method with the equivalent collar method stage in parentheses.
‡ Only present in a small subset of corn hybrids assessed; plants not included in the yield reduction assessments presented in the following ways: 1 = normal tassel, 2 = tassel with some skeletal properties and reduced number of spikelets, and 3 = mostly skeletal tassels with no spikelets.
Ohio studies indicated that the greatest yield reductions caused by defoliation occurring at or near flowering also impacted grain oil and protein content. Grain oil content was usually less affected by defoliation than grain yield, and it typically required defoliation sufficient to reduce yield by more than 50%, and sometimes as high as 70%, to decrease oil content. Grain oil content was reduced as much as 30–40% with complete defoliation during late vegetative, flowering, and early grain fill, whereas protein content was increased as much as 50%.
Root Lodging and Greensnap Impacts on Corn Yield Reductions
As plants get larger, the likelihood for stand loss decreases though the potential for lodging without experiencing stalk breakage (root lodging) or stalk breakage (greensnap) increases (Figure 4).
When simulating severe root lodging (stalk angles were <20° from soil surface after lodging was imposed) at V10, V13, VT, and R3 in 2018–2020, grain yields were reduced 5–43% (Table 2). Yield losses were greatest when lodging occurred during the pollination window, resulting in increased barren plant numbers and plants with abnormal ears (jumbling of kernels and zippering in ears). Yield reductions when lodging occurred at R3 were only 33%, but kernel size was greatly reduced and many ears close to the ground had kernels germinating on the ears (or showing vivipary). Excessive root lodging can also slow or delay harvest and promote ear rots. This would negatively impact grain quality and can result in price reductions or rejections when marketed to sellers.
|Growth Stage||Percent of Yield Reduction||Percent of Barren Plants||100 Kernel Weight in Grams||Percent of Ears Showing Vivipary|
Research sites in Ohio were subjected to derecho storm events on July 11, 2011 (V13–14 stage) and June 28, 2012 (V12–14 stage). On July 10, 2013, strong windstorms also affected crops at the V14–15 growth stage. Over these three years, seven small-plot, hybrid-by-population response trials were affected and their root lodging damage and greensnap injury was quantified. A relationship between seeding rate and root lodging was observed. Increasing the seeding rate by 1,000 seeds per acre (seeds/A) resulted in a 1.4% increase in plants exhibiting root lodging damage (Figure 5A). Seeding rate changes had minimal impact on greensnap incidence (Figure 5B).
Increasing root lodging had minimal effect on the yield for seeding rates less than 36,000 seeds/A (Figure 6A–C). At 42,000 seeds/A, each 10 percentage-point increase in root-lodged plants reduced the grain yield by 1.5 bu/A. Grain yields reduced by 3.2 bu/A for each 10% increase in root lodged plants at 50,000 seeds/A (Figure 6D–E). The opposite trend was seen for greensnap, where yield losses were greater at more commonly used seeding rates (Figure 7). For each 10% increase in greensnap incidence, the yield was decreased by 5.6 bu/A at 24,000–26,000 seeds/A or 7.9 bu/A at 30,000–36,000 seeds/A (Figure 7B–C). At 50% greensnap, predicted yield losses for the 24,000–26,000 and 30,000–36,000 seeding rates ranged from 13 to 17%.
Obtaining a greater understanding of the potential corn yield losses Ohio farmers may experience from severe storms is important for making in-season management and grain-marketing decisions. This fact sheet describes how plant damage from severe storms at different plant development stages can impact corn and grain yield loss. Most of the data in this fact sheet focused on singular injury types, though it is understood that crops may experience more than one type of injury, as was observed in the root lodging/greensnap trials described earlier.
The authors would like to acknowledge National Crop Insurance Services (NCIS), Pioneer (through the Crop Management Research Award), and DeKalb for their seed donations and funding support for conducting these trials. The authors also acknowledge Rich Minyo, Allen Geyer, and Joe Davlin for their help planting and maintaining these trials, as well as the graduate and undergraduate students and visiting scholars who helped impose each stress treatment. Thanks also to Mark Zarnstorff from NCIS for his review of this fact sheet.
Coulter, Jeffrey A., Emerson D. Nafziger, Peter R. Abendroth, Peter R. Thomison, Roger W. Elmore, and Mark E. Zarnstorff. 2011. “Agronomic Responses of Corn to Stand Reduction at Vegetative Growth Stages.” Agronomy Journal, Volume 103, Issue 3: 577–583.
Lindsey, Alexander J., Paul R. Carter, and Peter R. Thomison. 2021. “Impact of Imposed Root Lodging on Corn Growth and Yield.” Agronomy Journal, Volume 113, Issue 6: 5054–5062.
Lindsey, Alexander J., Allen B. Geyer, Rich Minyo, and Peter R. Thomison. 2021. “Seeding Rate Impact on Root Lodging and Greensnap in Corn.” Crop, Forage and Turfgrass Management, Volume 7, Issue 2: e20112.
National Crop Insurance Services. 2015. Crop-Hail. Corn Loss Instructions. Overland Park, KS: National Crop Insurance Services.
Thomison, Peter R., 2016. “Identifying Vegetative Growth Stages in Corn.” (AGF-127). Ohioline, The Ohio State University.
Thomison, Peter R., Alexander J. Lindsey, Allen B. Geyer, Emerson D. Nafziger, Jeffrey A. Coulter, and Mark E. Zarnstorff. 2017. “Tassel Deformation in Corn Following Early-Season Defoliation.” Crop Forage & Turfgrass Management, Volume 3, Issue 1: 1–3.
Thomison, Peter R., and Emerson D. Nafziger. 2003. “Defoliation Affects Grain Yield, Protein, and Oil of TopCross High-Oil Corn.” Crop Management, Volume 2, Issue 1: 1–9.
Thomison, Peter R., Mark E. Zarnstorff, Jeffrey A. Coulter, Alexander J. Lindsey, Emerson D. Nafziger, and Allen B. Geyer. 2016. Response of Corn to Multiple Defoliation Events. Columbus: The Ohio State University; Urbana: University of Illinois at Urbana-Champaign; St. Paul: University of Minnesota; and Overland Park, KS: National Crop Insurance Services. PDF.