Assessing Hail Injury to Crops

Several fields across the area experienced hail damage from the past couple of storms. This has led to concerns about the survival of plants and impact on yield.
The growing point on corn is below ground until five leaf collars are visible. Corn will generally re-grow from hail damage before this growth stage.
Later the plant elongates nodes and the growing point moves above the soil surface. For the next weeks, the corn plant becomes more vulnerable to injury from hail with the maximum injury occurring at tassel and then lessens as the plant moves towards maturity.
Data indicates that even with 100 percent defoliation, there will be less than an 11 percent yield loss up through the eight leaf stage. At the 12th leaf stage, 100 percent defoliation will result in 28 percent yield loss. At tassel, 100 percent defoliation will result in 100 percent yield loss.
To evaluate the location and health of the growing point, make a horizontal cut through the corn plant and look for the "small triangle" near the base of the plant or with taller corn, it will be elevated above the soil surface. The tissue should be white in the center.
Sometimes even though the growing point was not cut off, diseases set in after the hail and causes rot to occur. Also, stripped leaves can cause the plant to have a mangled twisted mess of leaves. Often, the plant will push through this. Most of the time, it will take 3-4 days with sunshine to see regrowth and if cloudy, often longer.
Lodged plants with stalks cut will continue to lodge. The depth of the cuts along with bruising makes the impact of this injury difficult to predict its impact on yield.
Soybeans have their growing points above the soil when they emerge. Plants cut off below the cotyledons will not regrow. If plants are broken off above the cotyledons, there is a bud in the axil between the cotyledon and stem and between the unifoliate and trifoliate leaves. Most of the time, the stem will produce new growth. Often it takes about 4-7 days to see regrowth.
If soybeans have been cut off, one should examine the stand for loss and uniformity. Make stand counts to determine the population that will regrow and determine if you have enough existing plants for yield. Be careful as you may want to fill in the stand rather than eliminate an existing stand with the growing season already well into June.
A small amount of leaf area loss, especially at early stages of growth does not usually result in much yield loss. Hail loss estimates on beans are complicated by bruising and the effect of lower stem bruises is hard to evaluate. Deep bruises can result in lodging of the soybeans later in the season.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists with University of Missouri Extension.