Agronomic Sheet
Grain and Silage Corn Frost Injury
What you need to know
When damaging frosts hit corn fields close to harvest time, it is important to assess the damage
to manage the harvest practices and crop expectations.
Frost damaged silage corn plant must be assessed to produce the
best silage quality. Best silage management practices are critical
to ensure a fermentation process that will ensile the crop into
quality forage.
•T
he appearance of dead leaves on silage corn can be
misguiding to the total moisture content in the plants. Closely
monitor the total silage plant moisture after the frost, depending
on the severity – the plant stock can dry faster than usual.
SYMPTOMS OF FROST DAMAGE
GRAIN CORN
• G
reen or grey water-soaked leaves (husks) that turn brown
shortly after frost damage has occurred.
Grain corn experiencing delayed maturity in combination with a
killing frost will result in corn crops unable to reach physiological
maturity (black layer). Several factors lead to this situation – cool
wet growing season, crop heat units that accumulate at a slower
pace than normal and late planting dates. The level of grain quality
anxiety for most growers is determined by the stage of grain corn
maturity reached before a killing frost.
• F
rost damage becomes evident one or two days after the frost,
and evidence of damage varies with the intensity of the frost.
•W
ait for up to five days, until affected tissues completely
desiccate, to do a complete damage assessment.
When an immature corn plant receives a light frost, damage
first occurs to the leaves, eliminating photosynthesis, reducing
grain filling and often negativelyaffecting stalk strength. If air
temperatures do not fall below -2°C, stalk tissues remain viable
and stalk carbohydrates mobilize to fill the grain as much as
possible. In this situation, the plant is cannibalizing the stalk to fill
the grain, often resulting in stalk lodging. Where temperatures
fall below -2°C as in a killing frost, or stay at -2°C for a prolonged
period with open sky and low wind, both leaves and stalks
are damaged and no further photosynthesis or carbohydrate
mobilization will occur. This terminates grain filling prematurely
and has a negative effect on grain weight and ultimately crop yield.
Higher harvest moistures also exist when grain drydown in the
field is more erratic and influenced by air temperature, relative
humidity and precipitation. Table 1 outlines the potential risks to
yield and grain quality with corn experiencing different levels of
frost damage.
Table 1. Estimated risks to grain corn yield and quality
with late season frost damage.
Estimated
grain
yield loss
(%)
Grain quality
concerns
Crop growth stage
estimated
Frost
damage
Mid-dough
Complete
plant
40
Severe
Mid-dough
Leaves only
25
Severe
Early dent
Complete
plant
25
Moderate
Early dent
Leaves only
15
Moderate
Half milk
Complete
plant
10
Minor
Leaves only
0-5
None
Half milk line
Note:
This table is meant as a guide – differences among hybrids, overall plant
vigour at time of frost, and subsequent temperatures will all affect final
grain yield and quality.
Source: Ontario Ministry of Agriculture, Food and Rural Affairs
The early dent stage is generally the cut-off point where corn
can withstand frost damage to the leaves and still produce a
reasonable grain yield with only moderate grain quality reduction.
This stage is characterized by having kernels showing small
indentations in the crown of the kernel. Grain quality concerns are
based mostly on low test weights. Some regions have grain corn
crop shut down prematurely by a killing frost, causing issues with
below average grain weight, higher than average grain harvest
moisture and standability issues.
SILAGE CORN
Dry down
Although dead, frosted leaves give the appearance of rapid dry
down, most moisture is in the stalk and grain. Frosted corn often
appears to be drier than it really is and does not dry down much
faster than unfrozen corn (about 0.5% per day) and can take
several days of drying to reach the correct moisture content. When
this is happening, frost damaged plants drop leaves and sugars
leach from frosted leaves. Yield losses and moulds increase
with time, and growers need to balance these losses against
fermentation losses and quality issues associated with harvesting
wet silage. With severe frost damage and plants maturing before
frost, the stalk can dry faster than anticipated. Always do a
complete plant moisture test.
Whole plant moisture critical
Harvesting at the proper whole plant moisture is critical for
producing high quality corn silage. Corn silage with a whole
plant moisture content of 62-68% has the best fermentation
and preservation characteristics, and the highest energy value
and intake potential. Seepage is likely at a moisture level greater
than 70%, and results in a loss of nutrients and lowers digestible
dry matter. Wet silage also promotes the production of butyric
acid, causing higher fermentation losses, lower intake and poor
cow performance.
•A
whole plant moisture test should be conducted frequently
on all silage fields including frosted fields to monitor silage
moisture levels. Harvest the crop as soon as moisture levels
drop to within the acceptable harvest range.
•T
o test for whole plant moisture, chop a sample and use a Koster
Tester or microwave test to determine percent dry matter.
Keep in mind that Koster Testers and microwaves tend to
over‑estimate moistures by about 3%.
Microwave test procedure
1. P
ick stalks from different areas of the field to get a
representative sample (at least 10 plants).
Corn silage harvest moisture recommendations
Storage
Moisture
Upright
62-66%
2.Chop plants through harvester.
Bunk
65-68%
3.Weigh 100 grams of well mixed silage material and place
on a paper plate.
Bag
65-67%
4.Spread sample out evenly and place in microwave oven on
high heat for 3-4 minutes.
5.Weigh sample and record weight.
6.Stir sample and place in microwave on high heat for
one minute.
Silage analysis testing
A silage forage analysis is always important to properly formulate
a ration. For corn silage with frost damage, an accurate analysis is
equally important. In the analysis, include a test for toxins to check
for possible pre-harvest mould development in the crop. Allow a
minimum 3 weeks for fermentation before feeding for best results.
7.Re-weigh and record the weight.
8.Repeat this step 6 until weight loss is less than one gram.
This is the dry weight.
9.Calculate the percent moisture using the following formula:
(1-dry weight/wet weight) x100.
Harvest
Harvest the frosted silage as quickly as possible to prevent silage
from getting too dry, reduce further yield losses and reduce the
chance for moulds to develop on the ears while the crop is still in
the field. Frost may kill some of the normal bacteria found on the
plant, so use a good quality bacterial silage inoculants to achieve
optimal fermentation during ensiling.
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