Managing hail damaged corn and soybean

By Jeff Coulter, Extension corn agronomist, Seth Naeve, Extension soybean agronomist, and Dean Malvick, Extension plant pathologist

Storms during late last week left crops in an area of southern Minnesota affected by severe hail damage. Especially hard hit were Brown, Redwood, Watonwan, and Martin Counties, where much of the corn was around the V6 stage (6 collared leaves) when damaged and soybean was from emergence to around the V2 stage (two fully-developed trifoliate leaves).

Photos: Liz Stahl, U of M Extension

Assessing hail damage and making replant decisions can be difficult, with many variables to consider for making a decision to replant or maintain an existing stand. Information regarding crop yield loss and replanting can be found at:

Corn Hail Damage and Replant Guide
Soybean Hail Damage and Replant Guide

Survivability of corn plants

Yield potential of hail-damaged corn depends on the remaining plant population with healthy growing points that will recover, the amount of leaf area lost on these plants, and the growth stage when the crop was damaged.

Corn growing point assessment

The growing point of corn remains below the soil surface until the V5 stage (5 collared leaves). To determine whether a corn plant will recover, split stalks and examine the growing point. Plants cut off below the growing point or with damaged growing points will not recover. Growing points located near the soil surface can freeze from hail accumulation around the base of stalks. At the V6 stage, the growing point is located about one inch above the soil and appears as a small triangle near the top of the stalk tissue. Healthy growing points will be firm and white to yellow. If damaged, the growing point will be watery and orange or brown.

Corn stalk bruising

Another consideration is stalk bruising. Severe stalk bruising limits the plant's ability to translocate water and nutrients, and reduces standability. Plants with stalk bruising should have their stalks split to determine the severity of stalk bruising and whether the growing point is injured. Plants with stalk damage extending beyond the leaf sheaths and into the stalk are likely to experience significant reductions in yield and standability. Fields with severe stalk bruising should be harvested early to limit yield losses from stalk lodging.

Corn whorl damage

When there is whorl damage to corn, new leaves can have difficulty emerging through damaged tissue and can become tightly bound in the whorl. Leaves that are tightly bound in the whorl can sometimes break free after about one week of growth. However, many of these plants may not recover.

Corn yield loss due to reduced plant population

Yield potential for corn at various plant populations is listed in Table 1. When gaps of two feet or more are present throughout the field, assume an additional 5% reduction in yield.

Table 1. Typical relationship between corn plant population and yield in Minnesota.

Population (plants/A)	Grain yield potential (% of maximum)
36,000	100
34,000	99
32,000	99
30,000	97
28,000	95
26,000	93
24,000	91
22,000	88
20,000	84
18,000	80
16,000	76

Corn yield reduction due to leaf loss

In addition to yield loss from a reduced stand, growers should consider yield reductions due to leaf loss (Table 2). Any green leaf area remaining on corn plants will contribute to yield. Only consider leaf area lost if it is removed or brown.

Table 2. Relationship between corn grain yield and leaf loss.

	Percent leaf area destroyed
Corn stage	20	40	60	80	100
	percent yield loss
V6	0	1	5	7	11
V7	0	2	6	9	13

Survivability of soybean plants

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 and buds 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.

Estimating soybean yield loss

Soybean can tolerate low plant populations well, with only small reductions in yield potential across wide ranges in stand loss. Populations near 100,000 plants per acre are likely to produce maximum yields, and those around 80,000 can yield about 90% of the maximum. Expected yield drops more rapidly when stands fall below 50,000 plants per acre, as 40,000 plants per acre are likely to produce about 75% of the normal yield. Note that the yields of deficient stands can vary widely based on mid- and late-season weather conditions.

For soybean, leaf loss alone through the V4 stage (4 fully developed trifoliate leaves) has little effect on yield.

Replanting considerations

Replanting should be considered only in fields where the crop is a total loss. Replanting corn at this time is not feasible, as the crop is not expected to reach maturity before the first killing freeze.

Soybean may be replanted, but yield will be limited by the shortened season. Soybean planted in late June typically yields about 60% of that planted in early May. Late June or early July soybean plantings should employ soybean varieties with a maturity group that is about 1.0 units shorter than that considered full-season for the location.

Replanting during late June is likely to produce a yield similar to that in an extremely thin soybean stand. Therefore, growers should carefully consider replanting costs, seed availability, and weed control, among other factors. Seed availability may be the primary determinant for replanting or not. Growers should contact their seed suppliers as soon as possible to confirm that early-maturity seed is still available.

Managing a hail-damaged crop

For growers who choose to keep their existing crops, care should be taken to ensure that these fields produce as much as possible. Because the 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 is often weed control. Maintaining good weed control in an open crop canopy is challenging. If replanting soybean, minimizing soil disturbance can reduce weed germination and maximize the effectiveness of soil-residual herbicides already applied to the field. Expected heavy weed pressure should sway replant decisions slightly toward replanting with preplant tillage if stands are very poor.

While it is crucial to minimize further stress to a damaged crop, foliar fungicides are not likely to improve crop recovery and yield (see Do foliar fungicides provide a benefit to corn damaged by hail?). The most damaging diseases affecting corn and soybean after hail are bacterial and other diseases not managed effectively with fungicides. Although there has been much discussion of the value of fungicides to hail-damaged crops, especially corn, we are not aware of replicated studies that demonstrate a clear benefit. If you have solid information showing a benefit from fungicides to hail-damaged corn or soybean, please let us know.

Cover crop options

Planting a cover crop may be a viable option for areas where the original crop was completely lost. See the articles on cover crop options and reducing the risk of fallow syndrome with cover crops.

More Information

More educational resources on crop production are available at Extension's Crop Production website.