When hail damages corn determines outcome

Corn Corner: Plant recovery usually depends upon the timing of the damage.
Apr 30, 2019
Corn was at the V5 growth stage when it was hit by hail. A couple fields were nearly defoliated. Others have ragged leaves. What can I expect from those fields going forward?
The Indiana certified crop advisers answering this question are Jamie Bultemeier, A&L Great Lakes Labs, Fort Wayne; Troy Jenkins, agronomist with Ceres Solutions, Rochester; and Marty Park, Great Lakes Seed Service, Rensselaer.
Bultemeier: The earlier in the season that corn is damaged by hail, the less of an impact it has. Before the V5 growth stage, nearly all leaf tissue can be removed with less than a 10% impact on yield. Once the growing point comes above ground, around V5, damage to the stalk has a greater impact on yield. Regular scouting will be needed through the growing season to avoid any additional yield setbacks.
Jenkins: First, be patient and allow seven to 10 days before assessing plant stand loss. Early-season hail, before the V6 stage, has more impact on stand loss and the decision to replant. Corn plants at V5 or less might look ragged and defoliated, but the growing point is still below ground, and if it’s not broken or severely bruised by the hail, the plant should recover somewhat normally.
Waiting seven days will allow evaluation of the growing points. Sometimes diseases can enter sites of punctured stalks and bruises, and it can take seven days for the disease to kill the plants. Splitting plants with a knife to observe the growing points is advised. Living growing points should be a whitish-yellow color. Sometimes plant leaves trying to unroll at the whorl knot up and become crippled. These plants should be considered dead.   
After plant stand evaluation, the replant decision will be based on yield reduction due to replant date, date itself, availability of suitable hybrids and costs associated with replant.
In young corn, ripped leaves and defoliation aren’t as critical as when corn enters the grand growth stage, which starts at V7. Younger corn hasn’t accumulated a lot of leaf area, which is responsible for photosynthesis. Yield loss on young corn due to defoliation is usually minor, where stand reduction accounts for most of the yield loss.
Park: At the V5 stage, the growing point of the corn is just coming above ground, and the corn has a long opportunity to recover. The impact to final yield should be very limited, if impacted at all. Hail charts do not even start until the seven-leaf stage, and the yield loss is only 1% at 40% defoliation at this stage. 
To monitor the progress of the improvement after damage, flag a couple of plants in different areas of the field and take pictures of them with your phone. Use GPS to mark your location. Periodically, go back out to those plants and assess the recovery compared to the pictures you took right after the hail. I would expect full recovery and normal yields.