Assessing Hail Damage in Corn
June 30, 1994 1(15):111
Joe Lauer, Corn Agronomist
This past weekend many parts of Wisconsin had hail on corn. Those who will be advising
growers faced with the likelihood of hail damage should get ready by consulting
the National Corn Handbook NCH-1 "Assessing Hail Damage to Corn". This
publication does a good job of describing factors to consider, and has charts used
by the National Crop Insurance Association for assessing yield loss due to 1) stand
reduction through tenth-leaf stage only, and 2) defoliation.
Hail affects yields primarily by reducing stands and defoliating the plant. Defoliation
causes most of the loses.Knowing how to recognize hail damage and assess probable
loss is important for decision making.
Because it is difficult to distinguish living from dead tissue immediately after
a storm, the assessment should be delayed 7 to 10 days. By that time regrowth of
living plants will have begun and discolored dead tissue will be apparent.
Some corn in Wisconsin is past the V-10 stage of development. As the season progresses,
hail injury and losses could become more significant. Some comments on concerns
not covered by NCH-1:
- After the tenth leaf stage, yield and stand reductions are on about a one-to-one
ratio (eg. 80% stand = 80% potential) and are in addition to losses shown in the
- Plants with bruised, but not severed stalks or ears will usually produce a near
normal, harvestable ear.
- Growers should monitor stalk rot of severely defoliated plants which have a good-sized
ear. Photosynthate will be mobilized towards the ear rather than the stalk. This
could weaken the stalk and encourage stalk rot development. These fields may need
to be harvested early to avoid standability problems.
- Nitrate levels in corn may become elevated. Animal performance could be reduced.
Growers with complete defoliation and high soil nitrogen levels (due to fertilizer,
manure, or legume plowdown) should test nitrate levels and probably ensile the corn
- Late season leaf loss will allow more light to penetrate to the soil and late-season
weed growth may flourish.
After touring some of the affected areas in Rock, Columbia, Dane, Dodge, Jefferson,
and Walworth counties, I would not expect significant yield losses from this particular
hail storm. Hail was widespread, but not extremely intensive and usually only upper
leaves of the canopy were tattered.