An Overview of Hail Injury and Fungicide Use on Corn

The impact of hail injury on corn depends on several factors including the growth stage at the time of injury, the severity of the hail event, and environment before and after the hail occurs. Fungicide applications are often considered after hail injury due to the plant health statements present on many fungicide labels coupled with the natural desire to take action following a hailstorm (Figure 1). This publication provides farmers and agronomists with research-based information to evaluate the potential benefits of fungicide application, and make the most profitable management decisions following hail injury in corn.

Hail events can leave corn fields looking severely injured, but early impressions rarely tell the whole story. Before making management decisions, it is important to distinguish between crop injury (the immediate, visible alteration of plant tissues, growth, or function) and crop damage (actual economic loss or yield reduction resulting from that injury). Crop injury from hail or any other cause does not automatically translate into crop damage. For example, minor hail injury on corn in the vegetative stages is unlikely to reduce yield as young plants can lose a significant amount of leaf area with relatively minimal long‑term impact (Table 1). Taking time to make a complete assessment of crop injury helps farmers avoid rushing to conclusions and ensures management decisions are based on the crop’s true recovery potential.

See Crop Scouting Basics for Corn and Soybean: Corn Growth Stages for information on corn physiology and how to determine growth stages. 

Table 1. Estimated losses from early season hail. Actual production losses from hail injury during early vegetative stages is estimated to be relatively low. Adapted from the 2025 USDA FCIC Corn Loss Adjustment Standards Handbook (page 86).

¹ FCIC hail-loss tables use a leaf-over growth staging system based on visible leaves where the leaf tip has turned down rather than the modern collar method used for vegetative (V) staging.

Hail can injure corn in multiple ways. Stand losses can occur during early season hail events. Leaves can be shredded or knocked off the plant by hail, which reduces photosynthetic capacity (Figure 2). Stalks can be bruised or broken and may allow for entry of stalk rot pathogens (Figure 3). Hail can injure the plant’s growing point and developing ears (Figure 4). Pollination may be impacted if tassels or silks are destroyed. Field areas where the crop canopy is destroyed can be susceptible to weed infestations. Hail injury often looks worse than it actually is and given time, plants can recover dramatically (Figure 5).

Hail wounds the plant, and after a hail event, people may consider that a fungicide is needed to protect plants from infection by organisms that cause disease. However, fungicides are ineffective at managing diseases caused by bacteria that may enter via wounds. Fungi that infect corn do not need wounds to enter the plant and although some fungi like ear rot and stalk rot-causing fungi may take advantage of wounds that occur, fungicides applied specifically to protect the plant from fungal pathogens after a hail event are not often profitable.

Another reason fungicides are considered after hail injury is to preserve or recover plant health. Some fungicide labels have statements on plant health benefits such as improved plant physiology and abiotic stress reduction. However, research from Land-Grant universities, and other sources, indicates that fungicide use after hail injury on corn is unlikely to provide a consistent return on investment. The ultimate goal of a fungicide application is to protect a crop to maintain yield potential and maximize farm profitability. This most often means more bushels at harvest, but it can also mean improved harvestability (standability). A hail-injured crop can have a reduced yield potential, meaning there is less yield potential that can be preserved by a fungicide. Reduced leaf area from hail may limit the surface available for fungicide deposition, and may result in reduced (poorer) coverage and a shorter effective disease control period. In short, if the fungicide application is not likely to be profitable, it should not occur.

Examples of Research on Fungicide Application After Hail 

• University of Illinois researchers found that fungicide use after simulated hail at V12 resulted in negligible benefits over non-treated controls. 

• Scientists at Iowa State University simulated hail at approximately VT and R2. Fungicide applied several days after the VT hail event resulted in a 32% chance of breaking even on the cost of the application. Delaying the fungicide application to approximately eight days post hail increased the likelihood of breaking even to 65%. With simulated hail at R2, immediate and delayed fungicide applications were 30% and 37% likely to result in break even yield preservation, respectively. 

• Researchers from University of Wisconsin-Madison applied an R1 fungicide to corn several days after it was severely injured by hail. The fungicide application provided no yield benefit over the non-treated control. Fungicide application at V6 (prior to the hail event), also did not result in yield benefits. 

Early Season Hail

Early vegetative stage corn plants are the least susceptible to yield loss from hail injury. The growing point remains belowground until approximately V6 and severe defoliation does not drastically reduce end-of-season yield potential (Tables 1 and 2). 

If replanting is required, follow the guidelines suggested by your state Extension corn agronomist. The best option will change depending on multiple factors. First allow 3-7 days following hail damage to assess plant recovery. Plants that show new leaf growth following a hail event will not have reduced yield potential at early vegetative stages. In addition, consider how later season planting can reduce corn yield potential and the cost of replanting. It may be more cost effective to keep an existing low population than to replant at a higher population due to existing stand termination, seed, fuel, labor, and machinery costs, coupled with a lower yield potential due to late planting. More information on corn replant decisions can be found in the Replant Considerations for Corn Crop Scout School video. 

Mid and Late Season Hail

Corn is most susceptible to yield loss from hail injury at the VT growth stage as pollination can be disrupted. Corn gradually becomes less susceptible to yield loss from hail injury as it progresses towards maturity. However, hail can damage stalks, which may degrade stalk strength and allow entry of pathogens that can cause stalk rot. This may lead to harvest issues if stalks lodge. If hail injures developing ears, there can be an increased risk of ear rots and mycotoxin issues (Figure 6). Severe defoliation during the middle of the season can drastically impact yield, lodging, grain moisture, and leaf area index (Table 2).

Table 2. Corn leaf area index, yield, grain moisture, and lodging in response to defoliation severity and timing from research in Indiana in 2024 and 2025. Data were combined across two years and three corn hybrids. Adapted from Applied Research for Corn Production in Indiana.

* Mean values which contain different letters and are in the same column and within the same defoliation stage are determined significantly different from each other (P<0.1). Leaf area index (LAI) was assessed at R3. Lodging was assessed prior to harvest as a percentage of lodged plants in a plot.

Other considerations for hail-injured corn

• Before any management decisions are made, contact your crop insurance agent to get an assessment. Failure to do so may void your policy.

• Weed seed may germinate if the corn canopy is destroyed by hail, increasing the risk of weed competition and seed bank additions. If herbicides are used, pay attention to pre-harvest intervals, rotation restrictions, plant back situations, and crop injury potential. 

• Grain may dry down more quickly with a defoliated canopy, but if hail injured plants die early, slower drydown could occur. 

• Hail injured corn can be considered for silage if injury occurs from R3 to R5. Consider the potential for higher moisture content silage, nitrate levels, and mycotoxins. If hail injury has occurred, a silage analysis may be beneficial before feeding to determine forage quality, nutrient content, and any changes in feed value caused by crop damage.

How to avoid additional economic loss after hail injury on corn

• Understand your crop insurance coverage policy. Avoid investing additional inputs in a field where the economic impact of the damage cannot be recovered. 

• Do not immediately make decisions about a hail-injured crop, unless it is certain that the field will not recover. Recovery is unlikely when the growing point has been destroyed on most plants throughout a field, stalks are broken below the ear, or the ears have been destroyed. 

• Research indicates that fungicide applications to hail-injured corn are unlikely to improve yield. Fungicides are most profitable when disease risk is high. Hail alone isn’t a reason to apply a fungicide. 

• Do not apply a half rate of fungicide to hail injured crops. Reduced rates can increase the risk of fungicide resistance development. If a fungicide application is made, use the labeled rate to avoid future plant disease issues. A half-rate may save some money but the cost and time required to apply are the same as for a full-rate application. The level of potential disease control may be substantially reduced. 

• If you choose to apply a fungicide to corn after a hail event, do not apply it immediately. Research suggests that waiting 7 to 12 days after hail damage at VT or R2 growth stages increases the likelihood of a positive return on investment. 

• Early-season hail injury can look severe, but corn plants frequently recover if the growing point remains intact. Delay assessments for 3 to 7 days to allow regrowth before determining yield loss or the need for further action.

References

Bradley, C.A. and Ames, K.A. 2010. Effect of foliar fungicides on corn with simulated hail damage. Plant Disease 94:83-86. Article

Conley, S.P., Esker, P., and Gaska, J. 2010. Use of Fungicides in Hail-Damaged Crops. Proceedings of the 2010 Wisconsin Crop Management Conference. Vol. 29. Article

Sisson, A.J., Kandel, Y.R., Robertson, A.E., Hart, C.E., Asmus, A., Wiggs, S.N., and Mueller, D.S. 2016. Effect of foliar fungicides on hail-damaged corn. Plant Health Progress 17:6-12. Article

Acknowledgements

Authors

Martin Chilvers, Michigan State University; Albert Tenuta, Ontario Ministry of Agriculture, Food and Agribusiness; Adam Sisson, Iowa State University; Damon Smith, University of Wisconsin-Madison; and Dan Quinn, Purdue University. 

Reviewers

Daisy Ahumada, North Carolina State University; Tom Allen, Mississippi State University; Mandy Bish, University of Missouri; Travis Faske, University of Arkansas; Andrew Friskop, North Dakota State University; David Hooker, University of Guelph; Heather Kelly, University of Tennessee; Daren Mueller, Iowa State University; Trey Price, LSU AgCenter; and Kiersten Wise, University of Kentucky.

Sponsors

The authors thank the National Corn Growers Association and the United States Department of Agriculture - National Institute of Food and Agriculture for their support.

Citation suggestion: Chilvers, M., Tenuta, A., Sisson, A., Smith, D., Quinn, D. 2026. An Overview of Hail Injury and Fungicide Use on Corn. Crop Protection Network. CPN-4016. https://cropprotectionnetwork.org/publications/an-overview-of-hail-injury-and-fungicide-use-on-corn.