The first step after hail damages corn or soybeans is to determine how much yield potential you have left. Information from the University of Minnesota and the North Dakota State University Extension Services was compiled for the following guide.
The key question to answer about corn is how many plants you have left per acre with healthy growing points that will recover.
To determine whether a corn plant will survive hail early in the season, split stalks and examine the growing point.
A corn plant’s growing point remains below the soil surface until the V5 stage (5 collared leaves). Growing points located near the soil surface can be damaged by freezing from hail accumulation around the base of plants. At the V8 stage, the growing point is located about 1 foot above the soil and has a small tassel at the top of it. Healthy growing points will be firm and white to yellow. If damaged, the growing point will be watery and orange to brown. Plants with damaged growing points will not recover.
Another consideration is stem bruising. Severe stem bruising limits the plant's ability to translocate water and nutrients and also reduces standability. Plants with stem bruising should have their stalks split in order to determine the severity of the stem bruising and whether the growing point has been injured. Plants with stem damage extending beyond the leaf sheaths and into the pith of the plant either will not recover or likely will have large reductions in yield. Fields with severe stem bruising should be harvested early to avoid significant losses from stalk lodging.
When there is whorl damage to corn, new leaves can have difficulty emerging through damaged tissue and can become tightly bound in the whorl. Plants with leaves that are tightly bound in the whorl can sometimes break free after about one week of growth. However, many of these plants are unable to recover. This makes it difficult to assess final plant population within just a few days after hail.
Yield potential for corn is based on plant populations. When gaps of 2 feet or more are present throughout the field, assume an additional 5% reduction in yield.
Another factor is leaf loss. Any green leaf area remaining on a plant will contribute to yield. Only consider leaf area lost if it is removed or brown. See the accompanying corn chart for yield loss estimates based on leaf loss.
Soybean plants with significant amounts of green tissue remaining (more than one green cotyledon and/or remaining leaf tissue) are likely to survive early-season hail damage, as they can regrow from axillary buds located at the juncture of the stem and leaves. Soybean plants cut below the cotyledons or entirely stripped of leaf tissue will not recover. Similarly, larger plants with a small amount of green leaf material remaining are likely to recover, but expect regrowth to occur slowly. Remaining stands will be set back. Soybean plants with significant stem bruising may recover, but will be more susceptible to lodging late in the season.
Soybean can tolerate low plant populations well, with only small reductions in yield potential across wide ranges in stand loss. For instance, populations near 100,000 plants per acre are likely to produce maximum yields, and those around 80,000 will yield about 90% of the maximum. However, expected yields drop more rapidly in stands below 50,000, with 39,000 plants per acre likely to produce about 75% of the normal yield.
For soybean, leaf loss itself through the V4 stage (four fully developed trifoliate leaves) has little effect on yield. See the soybean chart for yield losses based on leaf defoliation.
Caring for your hail-damaged crop
Because a hail-damaged crop has been placed under tremendous stress, it is important to reduce the level of future stresses. The most important and difficult challenge in hail-damaged crops often revolves around weed control.
Good weed control must be maintained season-long; however, maintaining good weed control in an open crop canopy is challenging. If you are considering a postemergence herbicide application to your crop, wait at least four to seven days to assess crop recovery before application. Contact herbicides pose a challenge as their potential stress on recovering leaves needs to be considered. Assess your weed populations to determine if it is worth the risk and consider alternative practices such as inter-row cultivation. Carryover to next year’s corn crop needs to be considered.
While it is crucial to avoid further stress to your crop, foliar fungicides are not likely to improve crop recovery and yield. The most damaging diseases affecting corn and soybean after hail are bacterial in nature. Fungicides have no effect on these bacterial diseases.
Source: University of Minnesota Extension Service