Assessing hail damage to corn and making replant decisions can be difficult. You’ll need to consider many variables when deciding whether to replant or maintain the existing stand.
The yield potential of hail-damaged crops depends largely on the remaining plant population, the type and severity of damage and the growth stage when damaged.
Assessing crop survivability
To determine whether a corn plant will survive and regrow following damage, split stalks and examine the growing point.
The growing point remains below the soil surface until the V5 stage (five collared leaves). When large hailstones land on soft soil and freeze around a plant’s base, it can damage growing points located at or below the soil surface.
In the mid- to late vegetative stages, the growing point is at the base of the tassel.
A healthy growing point will be firm and white to yellow. If damaged, the growing point will be watery and orange to brown. Plants with damaged growing points or stalks broken below the growing point will not recover.
When hail bruises stalks, it limits the plant's ability to translocate water and nutrients. It also reduces standability. If your plants have stalk bruising, split them open to determine the severity of the bruising.
Plants with damage extending beyond the leaf sheaths and into the pith either will not recover or likely will have large reductions in yield. If your fields have severe stalk bruising, harvest early to avoid significant losses from stalk lodging.
In corn with whorl damage, it can be hard for new leaves to emerge through damaged tissue and they can become tightly bound in the whorl.
Plants with leaves tightly bound in the whorl can sometimes break free after about one week of growth. However, many of these plants can’t recover. This makes it hard to assess final plant population just a few days after hail.
When soils are saturated, strong winds can cause corn plants to lean over because it pulls the shallow roots. Within a few days, root-lodged plants typically straighten upright and stalks appear curved.
Wisconsin researchers simulated root lodging in corn by saturating the soil and pushing stalks to a 20 to 30 degree angle from the soil. Most plants straightened upright within three days and yield loss depended on the growth stage when damaged.
Yield reduced by less than 5 percent when damaged at the V10 to V12 stages, by 5 to 15 percent when damaged at the V13 to V15 stages, and by up to 30 percent when damaged at the V17 stage or later. Grain moisture at harvest was unaffected.
Strong winds can also cause stalk breakage, often referred to as green snap. It’s most common between the V10 stage and tassel emergence, when plants are undergoing rapid vegetative growth and stalks are brittle.
Yield loss depends on the percentage of stalks broken and the break’s location. Plants with stalks broken above the ear can produce grain, and unbroken plants next to broken plants can partially offset yield losses because there’s less competition for light.
Concerns about inadequate pollination arise when stalk breakage causes the plant to lose its tassels. However, individual tassels generally produce more than two million pollen grains.
Assuming 800 silks per ear, this corresponds to 2,500 pollen grains per silk, indicating great potential for neighboring plants with lost tassels to adequately pollinate.
How to estimate yield losses
Hail damage is highly variable within fields. To most accurately estimate the surviving corn plant population, count surviving plants in as many locations within a management unit as possible.
Making a replant decision based on a few stand counts near the field entrance will likely lead to a poor decision. Count several areas that are equal to 1/1000th of an acre and average them. Then, multiply by 1,000 to get plants per acre.
Table 1: Length of row equal to 1/1000th of an acre for various row widths
|Row width||Row length|
|30 inches||17 feet, 5 inches|
|22 inches||23 feet, 9 inches|
Table 2: Typical relationship between corn plant population and yield in Minnesota
|Population||Grain yield potential|
|36,000 plants per acre||100%|
|34,000 plants per acre||99%|
|32,000 plants per acre||99%|
|30,000 plants per acre||97%|
|28,000 plants per acre||95%|
|26,000 plants per acre||93%|
|24,000 plants per acre||91%|
|22,000 plants per acre||88%|
|20,000 plants per acre||84%|
|18,000 plants per acre||80%|
|16,000 plants per acre||76%|
Loss of leaf area reduces yield potential. Only consider leaf area lost if it is removed or brown, as any remaining green leaf area contributes to yield.
Typically, losing 50 percent of leaf area reduces corn grain yield by 6 percent if lost at the V10 stage, by 10 percent if lost at V13, by 18 percent if lost at V16 and by 24 percent if lost at V18 Estimates of yield loss at earlier vegetative stages are shown in Table 3.
Table 3: Relationship between corn leaf loss and grain yield
|Corn stage||20% of leaf area destroyed||40% of leaf area destroyed||60% of leaf area destroyed||80% of leaf area destroyed||100% of leaf area destroyed|
|V6||0% yield loss||1% yield loss||5% yield loss||7% yield loss||11% yield loss|
|V7||0% yield loss||2% yield loss||6% yield loss||9% yield loss||13% yield loss|
|V8||0% yield loss||4% yield loss||8% yield loss||11% yield loss||16% yield loss|
Only consider replanting in fields where the crop is a total loss.
Replanting corn for grain after June 5 is not an option as the crop is not expected to reach black layer (maturity) before the first killing freeze.
Replanting corn for silage may work if the corn is quickly replanted with a hybrid that’s 15 or more relative maturity units earlier than a full-season hybrid. However, planting corn silage after about June 25 is not recommended in southern Minnesota.
Managing damaged fields
The most important and difficult challenge with hail-damaged crops often revolves around weed control. Maintain good weed control all season, but avoid contact herbicides that stress the crop.
While it’s crucial to avoid further stress to your damaged crop, foliar fungicides are unlikely to improve crop recovery and yield. The most damaging diseases are bacterial in nature.
Fungicides have no effect on these bacterial diseases. Plus, the defoliated crop is unlikely to effectively take up the fungicide. Instead, focus on pests you can control, like weeds and insects, and avoid applying costly inputs that aren’t likely to increase yield.
Planting a cover crop may be a viable option for areas where the original crop was completely lost. Additional considerations for such fields include weed control and avoiding fallow syndrome.
Carter, P.R. & Hudelson, K.D. (1988). Influence of simulated wind lodging on corn growth and grain yield. Journal of Production Agriculture, 1, 295-299.
Coulter, J.A. (2018). Optimal corn plant populations in Minnesota.
Hicks, D.R., Naeve, S.L., & Bennett, J.M. (2018). The corn grower’s field guide for evaluating crop damage and replant options.
Reviewed in 2018