Assessing June Hail Damage To Corn And Soybean

By Jeff Coulter, Seth Naeve, and Jeff Gunsolus

Extension Agronomists

Photo 1. Hail damaged corn in Redwood County, MN

Recent storms left a large area of south central Minnesota affected by severe hail damage. Especially hard hit were Brown and Redwood Counties, where much of the corn was at the V8-V10 stage (8-10 collared leaves) when damaged and soybean had three fully developed trifoliolate leaves (V3).

In June, assessing hail damage and making replant decisions can be difficult, with many variables to consider on your way to making a final decision to replant or maintain the existing stand. Information regarding crop yield loss and the replanting can be found in the following online guides:

Corn Damage and Replant Guide: http://z.umn.edu/cornhaildamage (48 KB PDF)

Soybean Damage and Replant Guide: http://z.umn.edu/soybeanhaildamage

Corn

Survivability of corn plants

Yield potential of hail-damaged corn depends primarily on the number of remaining plants per acre with healthy growing points that will recover, the amount of leaf area lost on these plants, and the growth stage at which the crop was damaged. To determine whether a corn plant will survive and regrow, split stalks and examine the growing point. In corn, the 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 one 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.

Estimating 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.

Estimating yield reductions due to leaf loss

In addition to yield loss from a reduced stand, growers should consider added yield reductions due to 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. Information on corn yield and leaf loss is given in Table 2.

Table 2. Relationship between corn grain yield and leaf loss.
Source: Corn Damage and Replant Guide.

Soybean

Survivability of soybean plants

Photo 2. Hail damaged soybean in Redwood County, MN

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.

Estimating yield loss

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 (4 fully developed trifoliolate 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 black layer (maturity) before the first killing freeze.

Soybeans may be replanted, but yields will be limited by the short season remaining. Soybeans planted around the first of July routinely produce a yield of about half of that of normal planting dates. Experience with soybeans after peas has shown that planting a soybean variety that is one maturity group earlier than adapted to the region before July 4 will occasionally produce reasonable yields. Producers are seldom content with yields from crops planted a week or more after July 4. By this time, yield potentials fall to 40% of normal or less.

Seed availability may be the primary determinant for replanting or not. Producers should contact their seed suppliers as soon as possible to confirm that early-maturity seed is still available.

Caring for your hail-damaged crop

For those producers 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 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 replanting soybeans, try to minimize soil disturbance to reduce weed germination and to maximize the effectiveness of soil-residual herbicides already applied to your field. If you are considering a postemergence herbicide application to your crop, wait at least 4 to 7 days to assess crop recovery before application. Contact herbicides, such as Flexstar and Cobra, 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. Also, we are nearing the window for Flexstar applications where carryover to next year’s corn crop needs to be considered (10 months).

While it is crucial to avoid further stress to your 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 in nature. Fungicides have no effect on these bacterial diseases.

Source:umn.edu