They’re violent, loud, dangerous, destructive and often are precursors to tornadoes. Hail storms. The average hail storm lasts less than a couple of minutes but depending on the intensity and size of hail stones, damage can vary from barely noticeable to total crop destruction.
Hail damage to crops basically comes down to these questions – will the plants survive and, if so, will yield be affected? In my experience, more so for corn, the most noticeable effects of hail damage are three-fold: twisting of the leaf canopy, leaf loss, and stem bruising.
Twisting of the leaf canopy is the result of leaves being shredded by hail stones with the shredded remnants being wrapped or twisted by excessively strong winds. (This phenomenon is more prevalent in young corn, usually V6 or smaller.) The reason this can impact plant survival is that the newly emerging leaves in the whorl can’t advance as the plant recovers. Survival rates of plants can improve if the dying, twisted leaves can somehow detach from the plant, making emergence of the new leaves possible. The impact on yield depends on plant death (stand loss) and distribution down the rows (plants that recover quicker can shade out and out-compete adjacent plants.)
Leaf loss is the most obvious effect of hail on plants. The leaves are the photosynthetic factory – capturing sunlight and converting it to energy that supports plant growth. Believe it or not, there are times when complete leaf loss will not impact yield. Such is the case in corn where leaf loss up to about V3 is not detrimental. Reason being, this is before ear development commences and the plant is still dependent on the seminal root system for support.
An excellent chart on the effects of leaf loss on corn yield can found in the University of Nebraska publication: http://extensionpublications.unl.edu/assets/pdf/ec126.pdf. This is my go-to extension publication on this subject and it includes examples of various field situations. For a discussion on hail damage effects on forage/silage quality: http://corn.agronomy.wisc.edu/Management/L039.aspx.
Whorl or stem bruising is often overlooked in assessing hail damage. Hail stones are dense and hard. Young corn plants, however, are tender – very little lignin formation has occurred and so a somewhat rigid stalk rind has yet to develop. As the winds bend over the stalks, the lower sections are exposed and vulnerable to being struck by hail stones. The thing to remember is that the growing point is near or above the soil surface around V5 or V6. If the stone penetrates deep enough, it can bruise and kill the growing point. When this happens, the plant is finished. A sharp knife (and the appropriate protective gear) can help determine the depth of penetration of a hail stone. The growing point should be near white while a damaged or dying growing point will turn brown.
For a discussion of hail damage on young corn, I highly recommend this site, authored by Dr. Robert (Bob) Nielsen at Purdue University: https://www.agry.purdue.edu/ext/corn/news/timeless/HailDamageYoungCorn.html
As with most storm events, its too wet to do anything in the field afterwards so the best advice is to wait and assess plant recovery over a period of about a week. Give the plants time to recover! In the meantime, don’t hesitate to call your seed rep and agronomist and get their opinion. Here are some other resources for various crops:
As always, I want you to do well. ~ph.