Hail Damage on Corn
Originally written February 1, 2006 | Last updated
February 23, 2014
to storm related damage of crop fields are to: 1) be patient, 2) determine the crop
growth stage, and 3) assess plant health accurately. Go ahead and view the
damage, but do not make any assessments until 7-10 days have passed. It
will take that long for the corn plant to begin growing again if it can.
Hail damage is minimal on plants less than V7 [Table 1 derived from Vorst
(1990)]. Within a few days growth should occur within plant whorls. New leaves will
become visible quickly within a couple of days if air temperature is warm. Now is
a good time to assess the plant growth stage. Crop insurance damage charts are based
upon the stage of crop development, so recording the date of the storm event and
the correct stage of development is key to assessing damage. To assess whether the
plant is healthy the growing point needs to be observed. Look for color other than
a healthy cream or light yellow. The first signs of damage on a growing point are
a change to a light red or brown within about 4-6 days. If the growing point changes
color, then the plant will likely not yield well and may even die.
To assess plant stands that have been damaged and whether a replant or late-planting
may be needed see Corn Replant/Late-Plant Decisions
in Wisconsin (UWEX Bulletin A3353).
Assessing Corn Plant Health
Assessing plant health after a destructive event such as flooding, hail,
frost or insect feeding is important for replant decisions. Often these
events damage the exposed leaves, but will have little or no effect on
the belowground growing point or final seed yield.
To assess plant health after a destructive event and for making a
- Wait a minimum of 3 to 4 days. After a storm event we need to be
patient and let plants respond.
- Observe the growing point. If color is white to light yellow then
plant is alive. If you suspect the plant is not healthy or questionable,
count as Â½ of a plant for population purposes.
- Consult replanting chart. See "Corn Replant/Late-Plant Decisions in
Wisconsin" (Lauer, 1997).
Crop insurance damage charts are based upon the stage of crop
development, so recording the date of the storm event and the correct
stage of development is key to assessing damage. To assess whether the
plant is healthy the growing point needs to be observed. Look for color
other than a healthy cream or light yellow. The first signs of damage on
a growing point are a change to a light red or brown within about 4-6
days. If the growing point changes color, then the plant will likely not
yield well and may even die.
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. The corn plant has the capacity
to compensate for various stresses and it would take this long before
the plant has recovered to its remaining potential. If farmers have hail
insurance, wait until the adjustor has made their measurements and
injury determinations before making any decisions.
Hail adjusters use standard tables to calculate compensation for yield
loss associated with hail. Four assessments are made on corn when hail
occurs after silking (Vorst, 1990) including:
- Determining yield loss due to stand reduction,
- Determining yield loss due to defoliation,
- Determining direct ear damage, and
- Bruising and stalk damage.
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 defoliation chart.
- 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
- 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 before feeding.
- Late season leaf loss will allow more light to penetrate to the soil
and late-season weed growth may flourish.
Determining yield loss due to stand reduction is made by comparing yield
potential of the field at its original population with yield potential
at its now-reduced population. Yield loss after silking is adjusted
directly by determining the percentage of killed plants. Likewise ear
damage losses are adjusted directly by determining the percentage of
damaged kernels on ears.
In corn, most yield reduction due to hail damage is a result of leaf
loss. To determine yield loss due to defoliation, both the growth stage
of the field and the percent leaf area removed from the plant must be
determined (Table 1). Significant yield damage due to defoliation occurs
immediately after silking and decreases as the plant matures.
Damage due to bruising is determined at harvest by counting the number
of lodged plants. Bruising may allow an avenue of infection for stalk
rots and molds that cause mycotoxin problems. Weather conditions during
the remainder of the season affect disease severity.
Table 1. Yield impact of plant leaf defoliation on corn yield at
different stages of development (Vorst, 1990).
Hail during kernel grain-fill is detrimental to grain yield. Depending
on the stage of development and the amount of leaf loss, grain yield can
be reduced from 0 to 41 percent after the soft-dough stage of
development (Table 2). Any losses due to ear dropping would increase
this yield loss estimate.
|Table 2. Grain yield loss after plants killed or defoliated.
|Corn Development Stage Plants
||percent yield loss
|R4 (Soft dough)
|R5.5 (50% kernel milk)
|R6 (Black layer)
|derived from Afuakwa and Crookston (1984)
Management options after Late-Season Hail Events
The types of options available to farmers varies from farm-to-farm and
field-to-field. On a farm basis, the decision hinges on availability of
other corn handling systems involving drying capacity, silage storage
facilities, high moisture corn handling equipment, snaplage equipment,
etc. Using these later systems means that the harvested corn product
will probably have to be fed on-farm to livestock.
On a field basis, things to consider are mold development, moisture
levels for ensiling, and effects on maturation rate, yield and quality.
If ears are damaged, easier entry of mold causing organisms into the ear
can take place. If it is wet for the duration of the season, mold
problems will probably increase. Drier weather may not promote growth of
mold producing organisms. Safer storage of corn predisposed to mold
causing organisms can be achieved by drying grain to 15.5% moisture,
ensiling at the proper moisture for the silo type, or treating high
moisture corn with propionic or acetic acid.
Hailed corn will usually achieve physiological maturity earlier, but
take longer to dry-down than non-hailed corn. Yield and test weight will
likely decrease when stressed by hail.
If ensiling, hail damaged corn should be stored separately from other
silage already put up. Hail damaged corn may have lower quality, and by
storing separately, the farmer will have the option of mixing poor and
good silages to obtain a satisfactory ration, or feeding the damaged
silage to animals that do not have high quality forage requirements. An
estimate of silage yield and quality should be obtained to compare with
the grain yield estimate.
Fields assessed as total losses after silking
Corn that was broken off at the ear will not continue to grow. What
options remain for those planning on silage?
- If the crop was insured, check with insurance adjuster to
ensure that any action does not cause a greater loss in payment than the
value of forage produced.
- Consider the value of the nutrients if the crop is simply
- Harvest the remaining forage for silage as the whole plant
moisture dries down. Make sure the forage to be ensiled is at the proper
moisture. The lower stalk and leaves will ferment if harvested at 60 to
70% (moisture depending on storage type) and produce a low quality
silage adequate for heifers and dry cows.
- A common question is: what can be planted to produce more
tonnage yet this year? Frankly the options are few this late in the
- Do not plant sorghum-sudangrass or sudangrass. This
is a warm season annual that will grow only very little when the average
daily temperature falls below 80o F. Since little growth will occur in
September, the result will be low yield.
- Corn planted August 1 can be expected to yield about 0.7 to
2.8 t/a dry matter in Southern Wisconsin. These yields were achieved in
2006 and 2005 when a killing frost hit on October 12 and October 26.
- Oats planted during the first two weeks of August can be
expected to yield 1 to 2 t/a dry matter in Southern Wisconsin and less
as one moves north.
- Other small grains will yield less because they will not head
- Some acres may be prepared for winter wheat production.
An economic estimate should be made of the options (ie. corn grain,
high-moisture corn, silage, snaplage, etc.) available in the grower's
situation. Estimates of changes in yield and quality due to plant part
loss should be taken into account. For corn grain yield, information
from crop insurance hail adjusters tables would be a good source for
making estimates. Little economic information on hail damage is
available on other harvesting options such as silage, high-moisture
corn, or snaplage. One approach would be to use yield and quality
changes observed under normal development and conditions and adjust
Impact of Defoliation on Corn Forage Quality
Forage yield decreases as leaf removal increased in severity, and as
time of defoliation nears silking (Lauer et al., 2004; Roth and Lauer,
2008). As defoliation increased forage yield decreased at a greater rate
(Figure 1). Averaged across all environments, forage yield decreased 16%
when complete defoliation occurred at V7. Likewise 100% defoliation
decreased forage yield 43%, 70%, and 40% at V10, R1 and R4 growth
stages, respectively. Greater forage yield decreases are measured with
early defoliation (V7 to V10) than predicted grain yield decreases
currently used by hail adjusters. This likely occurs because both
increased leaf removal and decreased grain yield combine to reduce
forage yield. The response to defoliation from simulated hail damage is
different between corn forage and corn grain.
Most quality responses resembled yield responses for each defoliation
treatment across environments (Figure 2). Increasing defoliation either
did not affect quality, especially at V7 and V10 stages, or lowered
quality, especially at the R1 and R4 stages of development. The largest
differences in NDF, ADF, and in vitro true digestibility occurred at R1
and R4 at the complete defoliation level. NDF increased from 44% in the
control to 61 % with complete defoliation at R1 or 51 % at R4. In vitro
true digestibility decreased from 81 % in the control to 73% or 79 %
with complete defoliation at R1 or R4, respectively. Starch content was
most affected with defoliation at R1. Across environments NDF
digestibility was not significantly affected. These forage quality
changes resulted in decreased Milk per Ton and Milk per Acre in most
Wiersma (1993) looked at quality changes in corn silage at five stages
of kernel maturity (Table 3). These values would be for corn silage
under normal conditions. With hail damage, loss of leaves and poor
kernel fill would affect quality by increasing fiber content and
decreasing yield, crude protein, and digestibility. This data may be
helpful in assisting the decision to harvest corn for silage or leave
Fig. 1. Relative corn forage yield after defoliation at V7, V10, R1, and
R4 (Lauer et al., 2004). Relative forage yield was determined by
dividing the forage yield of each plot by the average of the highest
forage yield defoliation treatment for each environment. Dashed lines
and open symbols are corresponding predictive relationships between
relative grain yield and defoliation derived from (National Crop
Insurance Services, 1998) leaf loss charts.
Table 3. Whole plant
dry matter, crude protein, ADF, NDF, and digestibility for
silage at five stages of kernel maturity (Wiersma et al., 1993).
Fig. 2. Changes in corn forage quality changes with defoliation at V7,
V10, R1, and R4 (Lauer et al., 2004). Graph values are treatment means
averaged across environments.
Using Foliar Fungicides
Disease risks associated with hail damage
Fungicide application cannot recover yield potential lost due to hail
damage. Fungicides protect yield potential by reducing disease. There
are some diseases of corn that are favored by wounding, e.g., Goss's
wilt, common smut and stalk rot, but fungicides are not effective
against the pathogens. The foliar diseases managed by fungicides (e.g.,
gray leaf spot, northern corn leaf blight, eye spot, and common rust on
corn, and brown spot and frog eye on soybeans) are caused by pathogens
that do not require wounds for infection.
A simulated hail-fungicide trial was conducted at Urbana in 2007, with
corn plants being damaged with a string trimmer just before tasseling to
simulate hail damage (Bradley, 2008). Some plots were left undamaged as
well. The fungicides Headline, Quadris, and Quilt were applied to the
plots and compared to an untreated check. When the data were
statistically analyzed, fungicides did not significantly improve yield
compared to the untreated check in the "hail-damaged" plots or the
nondamaged plots (Table 4). The simulated hail damage alone did decrease
yield by approximately 30 bu/A compared to the nondamaged plots,
Table 4. Effect of simulated hail damage and foliar fungicides applied
at tassel emergence on gray leaf spot severity and yield of a
susceptible corn hybrid near Champaign, Illinois, in 2007. (Bradley and
Foliar Fungicides in Corn Production: A Look at Local and
Regional Data. Proceedings of the 2008 Illinois Crop Protection
Technology Conference. )
||6 fl oz
||6 fl oz
||14 fl oz
|| 6 fl oz
||6 fl oz
||14 fl oz
|1 Hail was simulated by damaging corn plants with a weed-eater type
2 Gray leaf spot severity (0-100% scale).
3 Fisherâ€™s protected least significant difference (P = 0.05).
Using Gramoxone to dry down corn after a total loss (see Standard label)
In 2009 the Iowa Department of Agriculture and Land Stewardship (IDALS)
secured a crisis exemption label for the use of Gramoxone Inteon
herbicide as a harvest aid on hail damaged corn in northeast Iowa.
Hail-damaged crop standing in the field are typically over 80 percent
moisture and does not dry down much on its own at immature stages, even
though it is heavily damaged by hail. The crop needs to be below 70
percent for proper ensiling. Gramoxone applied to standing hail-damaged
corn will accelerate dry-down so that the crop can be harvested below 70
percent moisture. The Iowa Section 18 label stated 1 to 2 pints per acre
and a 7-day harvest interval. This section 18 label does not allow use
in Wisconsin, so farmers cannot legally apply Gramoxone.
Afuakwa, J.J., R.K. Crookston, and R.J. Jones. 1984. Effect of
temperature and sucrose availability on black layer formation in maize.
Crop Science 24:285-288.
Bradley, C.A. 2008. Making profitable fungicide applications in corn.
[Online]. Available at
(verified July 28, 2009).
Lauer, J.G. 1997. Corn replant/late-plant decisions in Wisconsin.
University of Wisconsin Cooperative Extension Publication, Madison, WI.:A3353,
Lauer, J.G., G.W. Roth, and M.G. Bertram. 2004.
Impact of Defoliation on
Corn Forage Yield. Agron J 96:1459-1463.
Roth, G.W., and J.G. Lauer. 2008.
Impact of Defoliation on Corn Forage
Quality. Agron J 100:651-657.
Vorst, J.V. 1990. Assessing Hail Damage to Corn. National Corn Handbook
Wenkert, W., N.R. Fausey, and H.D. Watters. 1981. Flooding responses in Zea mays
L. Plant Soil 62:351-366.
Wiersma, D.W., P. Carter, K.A. Albrecht, and J.G. Coors. 1993. Kernel
milkline stage and corn forage yield, quality, and dry matter content.
Journal of Production Agriculture 6:23-24, 94-99.