Recent hail storms have brought crop injury in isolated parts of South Dakota. We always hope the old ‘white combine’ adage does not come true, but there is no stopping mother nature. For those effected by serious hail damage, sometimes the next steps are hard to determine.
This first step after any type of crop injury should be assessing the crop damage. This varies by crop, but the only way to get an accurate assessment is to walk out into fields following the weather event. The crop damage as a result of hail and high wind can highly depend on the crop growth stages. Generally, younger plants recover better than the crops that are in the later stages.
When assessing damage, first, you should determine what your crop stand was before injury occurred; this can be done by evaluating an area with minimal injury or a nearby similar field with little injury. Wait approximately 7-10 days following the storm and do the same stand assessment on living plants in the hail-damaged area.
Calculate the percent remaining stand. Young plants may still have growing points underground, so the waiting period can make a significant difference. Corn or soybean plants that are still showing severe crippling or malformation of emerging leaves after 10 days should not be counted, and be considered lost.
Leaves & Stems
If injury is mostly on leaves, estimated losses can be determined based upon the plant growth stage and level of defoliation. Defoliation is simply measured by the amount of destroyed leaf area. Corn plants can experience yield reduction due to loss of leaf area dependent upon growth stage.
However, in soybeans, plant tissue that is still green and attached to the plant should not be considered “destroyed leaf area” as it will continue to grow.
Stem loss should also be considered in soybean plants, and evaluated based upon stems bent and stems broken off. Stem damage and loss are then added to plant defoliation to determine plant damage.
At this stage in the growing season, hail damage to small grain crops simply means harvest decision-making. It is best to wait approximately one week before assessing and calculating hail damage to small grain. The most significant damage usually occurs at milk stage, and can be variable at nearly ripe to ripe grain stages depending upon weather.
To assess hail damage, count one linear foot of damaged stems or heads per row in several areas to get an average number of heads damaged.
Calculating Yield Loss
Once estimated corn yield loss is determined for stand loss, defoliation injury, and ear damage (in late season hail events), they are added to determine total expected yield loss. The National Corn Handbook provides an excellent table and explanation for both corn yield loss due to defoliation as well as many other corn hail damage resources.
In soybean, direct damage is considered the sum of yield losses from stand and pod damage. Plant damage is considered losses due to defoliation and stem damage; plant damage multiplied by the remaining percent stand, results in estimated plant damage loss.
Hail loss is then considered the sum of the resulting direct damage and plant damage loss. Further instructions of this process can be found in the University of Nebraska’s Evaluating Hail Damage to Soybeans publication.
In small grains, plant spacing, kernels per head, and seed weight are taken into consideration. Damaged stems or heads per row-foot is calculated using feet of row per acre multiplied by kernels per head. That figure is divided by seeds per pound for the respective crop, resulting in pounds per acre loss. Further explanation and detailed instructions can be found here.
If replanting is deemed necessary, that should happen as soon as possible following the 7-10 day waiting period and damage assessment. If further information is desired to reach a replanting decision see the Corn Replant Guide or Soybean Replant Guide by the University of Minnesota.
If the damaged crop is kept, there are bacterial plant diseases to be watching for including: bacterial blight and bacterial pustule on soybeans, and Goss’s wilt on corn. If hail occurs earlier in the small grain growing season, bacterial leaf streak and bacterial leaf blight on wheat could become problematic.
However, fungicides do not protect your crop from bacterial diseases; therefore, application of fungicides to control bacterial infection following hail-damaged crops is not warranted.
Due to isolated excess rainfall during some hail events, fungal diseases may begin to develop and become a significant issue. In such cases, fungicides may be efficient at protecting the yield potential of the crop by preventing the disease from spreading further. Be sure to properly scout fields and identify diseases to ensure they are fungal rather than bacterial before making applications.
Haying & Ensiling
In small grain crops, depending upon estimated yield loss due to hail, some producers may choose to hay or ensile their crop rather than harvest for grain. For more information on using you crop as feed see Annual Forages for Feed. If the crop is left to be harvested as grain, keep in mind that herbicide application may be necessary after harvest, as lodging and stem breakage may have given weeds an advantage.
Summer hail storms can significantly impact our anticipated crop yields. Before making any major decisions be sure to:
- Wait 7-10 days to allow crop regrowth to occur.
- Assess crop damages.
- Calculate yield losses due to the weather event.
- Make pre-harvest decisions.