Frost Damage to
Grain Crops Extension Specialist,
University of Kentucky
September 30, 2003
Late corn plantings and cool autumn
temperatures create a recipe for frost damage on corn grown for
silage. The extent of the frost damage on the corn depends on the
temperature, duration of the temperature and corn growth stage at the
time of the frost.
for a Frost
Temperatures below 32 OF for 4
to 5 hours will result in frost damage to the stalk, leaf, and husk.
Temperatures that drop to 28 OF for a few minutes and
return to 32 OF can result in similar injury. Temperatures
between 32 to 40 OF typically result in less frost damage.
Frost at temperatures above 32 OF
usually occur under conditions of clear skies, low humidity, and no
wind. These conditions are ideal for rapid heat loss from the corn
leaves. Under these conditions, temperature of the corn leaves can be
less than the air temperature. Thin stands of corn and corn stands at
the edges of field are more likely to receive frost damage at
temperatures above 32 OF than thicker stands and the
centers of fields. The uppermost leaves of the corn plant are most
susceptible to frost damage at temperatures between 32 and 40 OF.
at Time of Frost
Corn will ensile well at moisture levels
less than 70% for upright silos and less than 75% moisture for
horizontal silos. Corn harvested at 62 to 68% moisture (late-dent
stage) is ideal for ensiling. Frost damage prior to this stage will
reduce yields and may reduce quality. Management of corn damaged by
frost will depend on the stage of growth at the time of frost.
Corn moisture content can be determined
with a microwave or forage moisture tester. A very simple field
technique for determining corn moisture content is to squeeze chopped
corn in your hand for 30 seconds. Release the ball of chopped corn and
examine its shape. You can gain a rough estimate of moisture content
based on the descriptions in Table 1.
Table 1. Field technique for estimating
moisture content of forage
When the ball
holds its shape and there is considerable free juice
When the ball
holds its shape but there is very little free juice
70 to 75%
When the ball
falls apart slowly and there is no free juice
60 to 70%
When the ball
falls apart rapidly
Frost at Milk
If a frost occurs when the corn is at milk
stage or early dough, then the moisture content of the plant is often
too high for proper ensiling. The leaves of the plant will dry very
quickly, which causes the entire plant to appear to be drying more
quickly. However, the entire plant will dry down similarly to corn
that was not injured by frost. If the corn at milk stage is ensiled
immediately after frost, then nutrients will leach away, the silage
will be sour and wet, and livestock consumption will be low.
Waiting to harvest frost-damaged corn at
the milk stage will improve silage quality but will decrease dry
matter yield. Up to 10% dry matter losses will occur the first ten
days after the frost and up to 20% dry matter will be lost 40 days
after the frost. In addition, mold may develop in the ears and cause
further yield reductions. Because of these factors, a compromise
between dry matter yield and ideal ensiling moisture must be made.
In some cases, the corn will need to be
harvested when it is too wet for silage. In these situations, chopped
grain, hay or straw can be added to the silage to decrease overall
moisture. In general, 30 pounds of dry matter per ton of silage are
required to reduce the moisture percentage by one point. For example,
if the corn was at 78% moisture and the target moisture was 68%, then
300 pounds of dry matter would be required for each fresh ton of
Another option for corn with high moisture
contents is to feed it as green-chop. Cattle will consume less
green-chop corn than ensiled corn. However, the quality of the
frost-damaged, green-chopped corn is better than the quality of the
ensiled corn at milk stage.
If a frost occurs when the corn is at the
dough stage, then the corn is often too wet for silage harvest.
Typically, several drying days are necessary before corn will be at
the proper moisture for silage harvest. The corn should be harvested
as soon as it reaches the desired moisture of 70 to 75%.
Frost at the
If a frost occurs when corn is the early
dent stage, then the corn may need to dry a couple days before it is
ready to harvest. If a frost occurs when the corn is at the mid- to
late-dent stage, corn is at or very close to ideal moistures for
ensiling. Corn damaged by frost at the mid- to late-dent stage should
be harvested for silage immediately.
For additional questions regarding frost
damage on corn grown for silage, contact your local county extension
Bitzer, M. J., J.H. Herbek, G.Lacefield,
and J. K. Evans. 1979. Producing Corn for Grain and Silage: AGR-79.
University of Kentucky.
Carter, P.R. and O.B. Hesterman. 1990.
Handling Corn Damaged by Autumn Frost. National Corn Handbook: NCH-57.
Michigan State University.
Nielsen, R. 1996. Potential Yield Losses
in Corn from Fall Frost Damage. Purdue Crop and Livestock Update:
CL-9. Purdue University.
Taylor, R.W. and R. Barczewski. Managing
Frost-Damaged Silage Corn. Agronomy Fact Series: AF-10. Delaware
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