Early Season Hail Damage to Corn
- Stand loss and loss of leaf area for photosynthesis are the primary factors contributing to yield reduction in hail-damaged corn.
- Assessment of damage to the growing point and leaves will guide decision making.
- Wait a minimum of five days before making any replant decisions.
What to do After a Hail Event
Questions are being asked by corn farmers of what to do after a hail event. The principal yield losses from hail-damaged corn arise from stand loss and reduction of leaf area for photosynthesis.1 After hail damage occurs to emerged corn, management strategies will depend on the growth stage of the plant and the severity of the above-ground damage. It is important to remember that young corn has the ability to recover from early-season hail damage. Farmers are encouraged to wait a minimum of five days to allow the crop to improve before doing any decision-making assessments to the damaged crop.
Examine the Growing Point
The growing point of the corn plant creates new tissue for above-ground growth. It remains protected below the soil surface until the collar of the sixth leaf is visible (V6). Generally, if the growing point is below the soil surface, the young corn plant can recover from severe hail damage. If hail has damaged the growing point or the stalk below the soil surface, the plant will probably not recover.1 To assess the severity of the damage, examine the growing point of several plants throughout the field by cutting the stalk vertically to expose the pyramid-shaped tissue near the base. Figure 1 shows how to identify the four nodes located beneath the soil. Continue counting nodal lines on the stalk until you reach leaves with visible collars, then continue counting leaf collars to determine the correct corn growth stage. If the growing point is damaged in the majority of the plants examined, a replant may be likely.
The twisted and shredded leaves of hail-damaged plants are usually in better shape to contribute to plant growth than they may appear. Shredded leaves that are attached to the plant may look really rough, but they still have some ability to contribute to plant growth and development.2 If the leaves are twisted, they usually have the ability to grow out and separate within three to five days.
Assessing the Stand
After waiting at least five days for the stand to recover, counts can be taken to estimate the plant population that remains in the field. When evaluating a corn stand, only count plants that have a good chance of survival as described above. Keep in mind that when stands are reduced early in the growing season, yield loss is not directly proportional to the number of plants lost. Surviving plants may compensate for an absent plant by increasing ear size or developing a second ear.1
One way to evaluate corn stands is to count the number of plants in a length of row equal to 1/1,000th of an acre based on row width (Table 1). Multiply the number of plants by 1,000 to get the plants per acre (ppa). Repeat the process in several locations in the field.
After taking stand counts, consider the yield potential of the current stand compared to the yield potential of the target replanting date and population, and the costs associated with replanting. This is the most critical decision of the process, as a later planting date with a full stand may give a reduced yield when compared to an earlier planting date with a thinner stand.3
Managing Moving Forward
The wet weather usually accompanying hail can delay post-emergence herbicide applications. It is crucial to correctly identify the corn growth stage to ensure label specifications are followed and crop injury is avoided. If defoliation and regrowth occur, it is important to not only count visible leaf collars but split open the stalk to ensure all nodes are accounted for (Figure 1).
Some corn diseases, like Anthracnose, infect the corn plant early in its life from inoculum splashing up onto the leaves from heavy rain or wind. Symptoms can show up as early-season leaf blight but cause the most impact later in the season. Torn and damaged leaves are more susceptible to disease and may benefit from early-season fungicide applications to reduce the impact of any infection. If you are assessing hail damage in a corn-on-corn field it may be worth considering an early-season application to preserve your yield potential.
For more information on stand assessment and additional details on replanting, see the publication, Corn Replant Decisions, which is available on agAnytime.com.
1 Nielson, R.L. 2012. Recovery from hail damage to young corn. Purdue University.
2 Thomison, P. Hail damage to corn varies depending on growth stage. The Ohio State University Extension Service.
3 Vorst, J. Assessing hail damage. National Corn Handbook. Purdue University.