Gordon Johnson, Extension Ag Agent, Kent Co.; firstname.lastname@example.org
There was heavy hail damage in the northwest area of Kent County on June 9. Of course, small grains will have large yield losses. Corn that is 10 leaf stage or younger may have limited yield losses.
The following is information from the National Corn Handbook (http://www.extension.iastate.edu/Publications/NCH1.pdf) on assessing losses due to hail in corn.
1) Assess stand losses. Wait about a week and then go out into the field and check for plants that have died or where the growing point is dead. Split suspect plants open and check to see if the growing point is light in color (still alive) or dark in color (is dead or dying).
2) Assess the loss of leaf area.
The following tables from the National Corn Handbook are used to estimate yield losses to stand loss and leaf loss. (Click picture to see larger version.)
The following information is from Iowa State University on hail damage in corn:
In contrast to soybean, corn has an advantage early season when hail damages the aboveground plant, because its growing point remains below ground until approximately the sixth-leaf stage. The sixth-leaf stage of the ISU leaf-collar system correlates to the seventh-leaf stage used by hail adjusters. Several fields that received hail damage are beyond this point, with the growing point at soil level or above.
Two different methods exist for assessing damaged fields based on the developmental stage of the crop when it incurred the damage:
In fields where the corn was at the fifth leaf or smaller, regrowth is expected and yield impacted negligibly. This is true regardless of the amount of defoliation.
In fields where corn was near or beyond the sixth leaf stage, evaluate injured plants to determine whether the growing point is viable. Make assessments of plant survival three to five days after the storm so that surviving plants have a chance to recover. If weather is not conducive for plant growth for a prolonged period after the storm, assessing the remaining stand may require waiting up to a week. It may take that long before it is clear which plants will survive and which will not.
Assessing a damaged field requires that the growing point is located and evaluated. Use a sharp knife and cut lengthwise down the stem in order to cross-section the stem. Assess the viability of the growing point; it should have a white to cream color. Plants with a healthy growing point should survive, especially if the growing point lies below the soil surface.
If most of the corn has not reached the V5-V6 growth stage yet this is good news because the growing point is still below ground and even if the leaves have been destroyed or the plant has been cut off, re-growth from the growing point below ground will occur. The loss of those early leaves will reduce growth rate following the damage but will not affect the overall yield significantly. Corn that had reached the V6 or more advanced growth stages may not be viable due to the growing point having moved above ground. At these growth stages, the plant will continue to grow if only the leaves have been knocked off or shredded and the stem has not snapped. When the stems have snapped at the base of the plant, the plant should not be considered viable. Leaves on the plant may have been shredded, but as long as they are connected to the stem they will continue to be an energy source for the plant and plant growth will therefore continue. Defoliation should not be considered a problem until later growth stages, approximately V7 or greater.
Unlike soybean, corn can do little to change its growth pattern to take advantage of increased space in reduced plant populations. A low plant population of corn will mean fewer ears on an area basis, resulting in a yield reduction. Therefore, stand loss is more of a problem in corn, making estimation of viable plants very important.
See the following for how insurance adjusters evaluate hail damage:
Soybeans were also damaged in the recent storms. The following is information from the Integrated Crop Management Newsletter from Iowa State University
Soybean differs from corn in that as soon as the plant emerges the growing point is above ground and is extremely sensitive to adverse weather events such as hail or frost. In the case of hail, the plant is considered dead if it is in the cotyledon stage and is cut off below the cotyledons, or if it is damaged by hail to such a degree that they have no green leaf tissue or re-growth. The reason is that nutrients and food reserves in the cotyledons supply the needs of the young plant during emergence and for about seven to 10 days after emergence, or until about the V1 stage (one fully-developed trifoliolate leaf). Cotyledons are the first photosynthetic organs of the soybean seedling and are also major contributors for seedling growth. Unlike corn, whose growing point is below ground until it reaches V5-V6, the growing point for soybean is between the cotyledons and moves above the soil surface at emergence. This makes soybean particularly susceptible to damage from hail, frost, insects like bean leaf beetles, or anything that cuts the plant off below the cotyledons early in its life. Stand reductions are likely to follow hailstorms. After V1, photosynthesis by the developing leaves is adequate for the plant to sustain itself. It is important to remember that defoliation during the vegetative stages will seldom have a large impact on yield. However, it is a whole other story during the reproductive stages.