While much of the damage from this month’s derecho is due to strong hurricane-force winds, isolated pockets of hail affected crops also, particularly in parts of Carroll, Greene, Hamilton, Hardin, Boone, and Story counties. When addressing any crop damage, contact your crop insurance provider as soon as damage is identified to determine coverage and avoid loss of coverage. Yield loss for only hail damage is closely related to crop growth stage (maturity) and percentage of leaf tissue lost for soybeans and corn. Several other issues accompany this storm that are more unusual and difficult to quantify in yield loss estimates including underlying drought over most of the area, root lodging, and other stalk or root damage from the winds that accompanied the hail. Below are some reference charts farmers can use to get a rough estimate of potential yield loss from loss of leaf area associated with hail.
Figure 9 shows soybeans in the R4 reproductive stage (full pod) can experience nearly 60% yield loss, while those in the R5 stage could experience up to 75% yield loss. My estimation based on the timing is that most soybeans were in the R4 to R5 (beginning seed) stage of development. Corn was also in a very vulnerable stage during the derecho. We can see severe leaf defoliation at the R4 stage (dough) of corn yield loss can approach 40% (Figure 6).
The other issue to evaluate when looking at hail damaged crops is the amount of stalk bruising in corn and pod damage in soybeans. For more information, consult the publications IPM 0078 Hail on Corn in Iowa and IPM 0079 Hail on Soybean in Iowa.