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A storm’s aftermath: Evaluate wind, hail damage to crops

Storm injury to corn and soybeans at pollination time takes a toll but may not be as bad as it looks.

Rod Swoboda

July 17, 2020

4 Min Read
Corn plants are broken off from windstorm
GREENSNAP: When corn plants are broken during a windstorm, yield loss is a 1-to-1 relationship. A field with 10% greensnap would have a 10% yield reduction.Rod Swoboda

Strong winds and hail hit areas of Iowa late last week and earlier this week, causing damage to corn and soybean plants in some fields. The storms that moved across the state brought needed rainfall, but the winds and hail were a high price to pay for the hardest-hit fields. 

For farmers dealing with damaged crops, the first step should be to communicate with your crop insurance agent as soon as possible. Additionally, here are some resources that may be useful in evaluating the impact of the damage. This information is provided by Rebecca Vittetoe, Iowa State University Extension field agronomist for east-central and southeast Iowa: 

Hail damage to corn. Many cornfields were tasseling or were just starting to tassel (VT growth stage), which is when hail can do the most injury to corn. When evaluating this hail damage, consider the amount of defoliation as well as stalk bruising and breakage. ISU publication Hail on Corn in Iowa shows how to obtain an estimate of the potential yield loss from hail injury to corn. Another resource is Corn Loss Adjustment Standards Handbook (see Pages 80-84). 

Hail damaged  cornfield in eastern Iowa when a storm went through the area on July 11

HIT BY HAIL: Hail damaged this cornfield in eastern Iowa on July 11.

Hail damage to soybeans. Most soybeans ranged from R1 to R3 growth stage last week when the hail hit. Even when hail damage occurs at this point in the season, it’s still best to wait seven to 10 days to assess injury. The extent of the injury is based on stand loss, broken and cut stems, and defoliation. ISU publication Hail on Soybean in Iowa walks you through how to estimate the potential yield loss from hail injury to soybeans. An additional resource is Soybean Loss Adjustment Standards Handbook (see Pages 62-67 and 71-73). 

Hail-damaged soybean field

SOYBEANS SUFFER: Hail damaged this soybean field in eastern Iowa when a storm went through the area on July 11.

Hail damage to small grains. For oats, wheat, rye, etc., the University of Wisconsin has a good resource for evaluating hail damage

Hail damage to forages. For farmers who have hail damage to forage crops like alfalfa or red clover, the University of Wisconsin agronomists explain how to  evaluate the damage

Fungicides for hail-damaged crops 

A question ISU Extension field agronomists often receive from farmers when hail hits a field is whether to apply a fungicide as was already planned. “A common misconception is that hail-damaged crops will be at a higher risk for disease infection,” Vittetoe says. “Note that fungal diseases like gray leaf spot in corn or frogeye leaf spot in soybeans do not require wounding to infect the plant, whereas bacterial diseases will more commonly infect the plant through open wounds.” 

A University of Illinois article summarizes the research from various universities looking at the impact foliar fungicide application has on hail-damaged crops. See the Illinois Field Crop Disease Hub. Another good resource summarizing the research Iowa State has conducted looking at fungicide use on hail-damaged crops is the ICM Blog post Fungicide Use on Hail Damaged Corn and Soybeans

Wind damage resources 

Wind damage in corn varies from field to field, and it can be related to hybrid, corn growth stage and other environmental conditions. Wind damage may have caused leaning, root lodging, and greensnap or brittlesnap. 

Eastern Iowa cornfield left with wind damage after a July 9, 2020 storm

BLOWN OVER: This eastern Iowa cornfield was left with wind damage after a July 9 storm.

“Like with evaluating hail damage, it’s best to wait a few days to fully evaluate how the plants are recovering,” Vittetoe says. “Corn plants that are leaning or have root lodging issues should stand back up within a few days after the wind event has occurred, if the plants are still in the vegetative stages of growth. However, after tasseling and silking, the ability to stand back up is diminished. Wind damage to corn can also result in poor pollination due to additional plant stress and silks being covered by leaves.” 

For greensnap or brittlesnap, if the plants snapped off above the ear or where the ear would eventually be located on the plant, the plants could potentially still produce an ear from either the primary or secondary ear node.

“However, plants that are snapped off lower than this location clearly represent a direct loss of yield potential,” she notes. “It is typically assumed that for each percent of plants snapped off in a field, it is equal to that same percent in terms of yield loss. This rule of thumb is slightly aggressive since neighboring plants can compensate by producing slightly higher kernel weights.” 

Additional resources to help you evaluate storm damage to cornfields: 




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Hail Damage

About the Author(s)

Rod Swoboda

Rod Swoboda is a former editor of Wallaces Farmer and is now retired.

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