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Hail Resources and Whether Foliar Fungicide after Hail Pays

This article was written by Angie Peltier and Heather DuFault, UMN Extension educators.

Hail event on June 28

Last Friday there was a significant hail event that occurred throughout a large swath of Norman County running west to east and parts of western Mahnomen County. The Grand Forks National Weather Service office received pictures of nickel to quarter-sized hail piled high and some reports of golf ball-sized hail. The effect of all of this hail on the crops that folks struggled so mightily to plant this spring was considerable (Figures 1 & 2). 

Figure 1. A corn field as viewed from the road in Norman County after the June 28th hail event (Photo: Heather DuFault).

Figure 2. Soybeans in Norman County injured by the June 28, 2024 hail storm (Photo: Heather DuFault).


For corn that had reached the V6 of sixth leaf growth stage, the growing point would have been above ground and subject to injury from hail. After giving the crop a couple of days, now would be the time to examine the growing point to see if it is still intact and alive or damaged.


Now is also the time to examine your soybean plants. Soybean plants that have been broken off below the cotyledonary node will not have an axillary bud from which to initiate re-growth. Unfortunately, this hail event also coincides with the inexorable march of waterhemp seedlings emerging. Weed control is going to be a challenge in these fields after the plants that were striving to close rows have been knocked back considerably.


For those with livestock, here is a resource about how hail can impact alfalfa stands, yield and quality and how best to manage hail-damaged stands. 

Crop insurance considerations 

Here are some of the things that a producer should be thinking about when getting their fields assessed for damage.  Immediately after hail storms come through, adrenaline is high and producers want to quickly move on to the next step in the process, but it is important for insurance adjusters to have a bit of time to do their jobs. We will not always like what they will conclude in the near-term. Decisions regarding claims for some fields will be deferred until closer to harvest to see what has made it to the reproductive stages and some fields are going to be a total loss.

Hail insurance is typically a stand alone product, therefore we all pay something different and have different amounts of coverage. So a totaled field to Farmer Jones may mean that he has used all of his coverage (100% of coverage at 100% damage) and a totaled field to Farmer Jay may mean that he had a policy that payed out 100% at 60% damage. Take "coffee shop talk" with a grain of salt.  

The key to all of this is good communication with everyone involved. 

Some crop disease is favored by hail damage

While disease caused by some plant pathogens can be favored in hail-wounded tissue, many of these pathogens cannot be managed with fungicides.  Most of the fungi that cause foliar disease in corn and soybean (think gray leaf spot in corn and Septoria brown spot in soybean) are able to directly penetrate leaf tissue and do not require wounds or natural openings in order to infect leaves. However bacterial diseases such as Goss’s wilt in corn and bacterial blight in soybean are favored by violent weather events such as hail.  Unlike foliar fungicides that can be used in-season to protect plant tissue from fungi, there are not really in-season tools to manage bacterial disease.  This is one reason why careful disease diagnosis is essential.

Foliar Fungicides on Hail Damaged Corn and Soybean

Researchers have taken advantage of naturally occurring hail events to compare yields of hail-damaged corn and soybean in plots that were either treated or not treated with a foliar fungicide. While these experiments are important, as mother nature is unlikely to leave random areas of experimental fields untouched by hail, these experiments are unable to compare the effect of foliar fungicides on disease severity and yield between hail-damaged plots and undamaged plots.

Below is summarized research that took place in Illinois and Iowa on corn and in Iowa on soybean.

Illinois-Corn (Bradley and Ames, 2010.). Former University of Illinois Extension Plant Pathologist Dr. Carl Bradley (currently a faculty member at University of Kentucky) and Research Specialist Keith Ames used a gas-powered weed whipper to simulate hail damage in corn at the twelve-leaf (V12) growth stage in both 2007 and 2008. They then either did not apply a foliar fungicide or applied fungicide active ingredients azoxystrobin or pyraclostrobin to corn at tasseling (VT). Disease severity ratings were collected from each plot 3 weeks after fungicide treatment.

They found the following, that 1) simulated hail damage significantly reduced yield in both years, 2) in one year simulated hail damage increased grey leaf spot severity, 3) in one year foliar fungicides reduced disease severity, 4) when compared with untreated control plots, foliar fungicides did not significantly improve grain yields in either undamaged or simulated hail-damaged plots.

Iowa-Corn (Sisson et al., 2016a.).  Plant pathologists and economists from Iowa State University conducted research trials in 2012, 2013 and 2014 in which they simulated hail damage using either a weed whipper or an ice propelling machine (a modified leaf blower) on corn at the tasseling (VT) or blister growth stages (R2). They then applied the foliar fungicide active ingredients pyraclostrobin and metconazole within 3 or 8 days after injury. Disease severity ratings were collected from plots when plants reached the dent (R5) growth stage.

They found the following, that 1) compared with uninjured plants, simulated hail significantly decreased yield, 2) overall, disease severity was low and hail-injured plants had lower disease severity than uninjured plants, 3) when compared to untreated plots, foliar fungicides did not reduce disease severity in hail-damaged plots, 4) when compared to untreated plots, foliar fungicides did not significantly increase yield in hail-damaged plots, 5) there were positive economic returns when corn injured at tasseling was treated with fungicides 8 days after injury.

Iowa-Soybean (Sisson et al., 2016b). Plant pathologists and economists from Iowa State University conducted research trials in 2012, 2013 and 2014 in which they then simulated hail damage using an modified leaf blower to shoot ice at plants at either beginning flowering (R1) or full pod growth (R4) stages. They then applied either a foliar fungicide (pyraclostrobin) alone or in combination with an insecticide (alpha-cypermethrin) at the beginning pod (R3) growth stage. They then assessed the upper and lower canopy for foliar disease.

They found the following: 1) simulated hail caused significant yield loss compared to uninjured plots, ) there were no consistent differences in disease severity between injured and uninjured soybeans, 3) there were no differences in foliar disease severity between treated and untreated plots, 4) there were significantly higher yields in two of the six site-years when R1-injured soybeans were treated with insecticide or insecticide plus fungicide, 5) when compared with fungicide alone, fungicide plus insecticide was more likely to result in a positive economic return in hail-damaged soybean.

Conclusions and Recommendations

The authors of each of these three articles suggested that factors other than hail-damage (such as disease pressure) should be used to make foliar fungicide decisions.

From Bradley and Ames (2010),

“Results from our research trials indicated that foliar fungicides provided very little benefit to corn injured by simulated hail; thus, growers should consider factors other than hail damage when making fungicide application decisions for corn.”

Sisson et al. (2016a) state:

“Our findings that yield of corn plants receiving hail midseason is not significantly affected by Headline AMP application, and that foliar disease risk is reduced in hail-injured plants, could decrease unjustified pesticide applications and save farmers money during an already difficult growing situation.”

From Sisson et al. (2016b),

“Based on our results, R3 fungicide application to soybean injured by hail at R1 or R4 will likely provide little yield-preserving or disease-limiting benefits when foliar disease severity is low.”

Resources for dealing with Farm & Rural Stress

Click here for resources paid for by your tax dollars that can help in dealing with farm and rural stress.


C.A. Bradley and K.A. Ames. 2010. Effect of Foliar Fungicides on Corn with Simulated Hail Damage. Plant Disease 94:83-86. Online.

A. J. Sisson, Y. R. Kandel, A. E. Robertson, C. E. Hart, A. Asmus, S. N. Wiggs, and D. S. Mueller.  2016a.  Effect of Foliar Fungicides on Hail-damaged Corn. Plant Health Progress. Online. doi:10.1094/PHP-RS-15-0046 Article.

A.J. Sisson, Y. R. Kandel, C. E. Hart, A. Asmus, S. N. Wiggs, and D. S. Mueller. 2016b. Effect of Foliar Fungicide and Insecticide on Hail-Damaged Soybean. Plant Health Progress. Online.  doi:10.1094/PHP-RS-16-0012 Article.

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