Flooding Effects of Corn
Originally written February 1, 2006 | Last updated October 16, 2012
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Recent rains have caused flooding and ponding in many cornfields. Growers are concerned
about corn growth and development and any yield effects that might occur from short
periods of flooding. Many crop fields were completely destroyed, while
others were left with varying degrees of damage. Before making any
decisions about your fields, you should document and report any crop
damage to your local U.S. Department of Agriculture Farm Service Agency
(USDA FSA) office, your crop insurance agent and the Wisconsin
Department of Agriculture, Trade and Consumer Protection You are
strongly encouraged to take â€˜time-datedâ€™ photos of any damage. Such
information may be critical in federal emergency determinations and your
eligibility for these programs.
The extent to which flooding injures corn is determined by
several factors including: 1) timing of flooding during the life cycle of corn,
2) frequency and duration of flooding, and 3) air-soil temperatures during flooding
(Belford et al., 1985).
Flooding at any time when the growing point is below the water level can
kill the corn plant in a few days, especially if temperatures are high.
Growing point tissues are depleted of oxygen.
After a storm event we need to be patient and let plants respond. Plants can usually
survive short periods of flooding of less than 48 hours (Wenkert et al.,
Respiration is the plant physiological process most sensitive to flooding. Flooding
reduces the exchange of air (oxygen) between soil and atmosphere eventually leading
to decreased total root volume, less transport of water and nutrients through the
roots to the shoot, and formation of sulfides and butyric acid by microorganisms
that are toxic compounds to plants (Wesseling, 1974).
Soils contain pores filled with gas and/or water. The two main gases important for
respiration are oxygen and carbon dioxide. The pathway for oxygen into the plant
is from the atmosphere through soil pores to a thin water film surrounding plant
root hairs. It is relatively easy for oxygen to diffuse into soil when pores are
filled by air, but oxygen does not easily diffuse in water so the main constraint
to oxygen movement is the thin water film surrounding root hairs. This boundary
is magnified in flood/pond conditions. Carbon dioxide rarely accumulates to toxic
levels in soil (Wesseling, 1974).
Roots are injured if the soil remains waterlogged. Continued poor aeration causes
cell death and even death of roots. Measurable short term reductions for root and
leaf growth rates begin immediately within 1-12 hours, but tend to recover quickly
within 2-3 days (Wenkert et al., 1981). Almost immediately leaf elongation ceases
and N, P, and K concentration in leaves decrease, but in roots N, P and K concentrations
increase (Ashraf and Rehman, 1999). Flooding restricts root growth in the upper
18 inches of soil, but root elongation continues in deeper horizons. Soil compaction
and flooding will restrict root growth more severely than either factor separately
All biological processes are influenced by temperature (Wesseling, 1974). Wet soils
have a large heat capacity and considerable amounts of heat are required to raise
their temperature. Thus, usually wet soils are cold and corn growth is slower. Drainage
lowers the moisture content of the upper soil layers so air can penetrate more easily
to roots, and transport carbon dioxide produced by roots, microbes and chemical
reactions to the atmosphere. Lowering soil moisture content also leads to higher
soil temperatures and faster growth.
Evaluating damage from flooding
The growing point of corn is metabolically active and is near or below the soil
surface prior to V6 (6 visible leaf collars). Within about 48 hours the oxygen supply
in a flooded soil is depleted (Purvis and Williamson, 1972; Fausey and McDonald,
1985). Without oxygen, the growing point cannot respire and critical functions are
impaired. If temperatures are warm during flooding (greater than 77 degrees F) plants
may not survive 24-hours. Cooler temperatures prolong survival. If flooding
in corn is less than 48 hours, crop injury should be limited.
To confirm plant survival, check the color of the growing point. It should be white
to cream colored, while a darkening and/or softening usually precedes plant death.
Also look for new leaf growth 3 to 5 days after water drains from the field. Once
the growing point is above the water level, the chances of survival improve greatly.
Things to look for later during the growing season
Even if flooding doesn't kill plants, it may have a long-term negative impact
on crop performance. Excess moisture during the early vegetative stages retards
root development (Wenkert et al., 1981). As a result, plants may be subject to greater
injury later during a dry summer because root systems are not sufficiently developed
to contact available subsoil water.
A considerable amount of oxygen is required in the soil for mineralization of nutrient
elements from organic matter by microbes. Oxygen deficiencies reduce microbe activity,
decreasing the rate at which ammonium and nitrate are supplied to plants resulting
in nitrogen deficiency in waterlogged soils (Wesseling, 1974). Additionally, flooding
can reduce the activity of mycorrhizae essential for symbiotic phosphorus uptake
(Ellis, 1998). Flooding can also result in losses of nitrogen through denitrification
and leaching. Where estimated nitrogen loss is significant in fields not yet tasseling
and yield potential is reasonable, corn may respond to additional applied fertilizer.
Flooding causes greater crop yield losses when it occurs early in the season (Meyer
et al., 1987; Kanwar et al., 1988; Mukhtar et al., 1990; Lizaso and Ritchie, 1997).
When six-inch corn was flooded for 24, 48 and 72 h corn yields were reduced 18,
22, and 32% at a low N fertilizer level. At a high N level, these reductions ranged
from 19 to 14% one year and <5% in another year (Ritter and Beer, 1969). When
corn at a height of 30 inches was flooded for 24 and 96 h, yields were reduced 14
to 30%. With a high level of N in the soil, very little yield reduction occurred
even with 96 h of flooding. When flooded near silking, no reduction in yield occurred
at a high N level, but yield reductions up to 16% occurred with 96 h of flooding
at the low level of N.
Mud and sediment caking leaves and stalks could damage plant tissue and allow development
of fungal and bacterial diseases not typically seen. Due to early season stress
the plant may be predisposed to root and stalk rots later and harvest timing of
fields may need to be adjusted accordingly. A disease problem that may become greater
due to flooding and cool temperatures is crazy top, a fungus that depends upon saturated
soil conditions to infect corn seedlings. With warmer, wet or humid conditions Pythium
can reduce stands despite fungicide seed treatments. There is limited hybrid resistance
to these diseases and predicting damage is difficult until later in the growing
Below are best management guidelines for harvesting, storing, and feeding
flooded field and forage crops including corn, hay crops and pasture.
- Protect yourself from the harmful effects of silt dust on your
health. If you do harvest your flooded crop, use a dust mask (N-95 or
higher) or filtered cab to avoid breathing in dust.
- Flooded crops should be stored separately from the rest of your
feed. In cases of production problems, this allows for feeding or
disposal options without affecting your good feed.
- Flood water from streams and silt can be a source of pathogens.
Farmers are strongly encouraged to work closely with their veterinarian
and animal nutritionist when determining which vaccination and feeding
protocol to use to further protect the herd from possible health issues
associated with feeding flooded crop material.
Harvesting Corn for Silage
- No matter how bad the field looks take the time to properly assess
the damage in each field and determine harvestbility. Because each field
and/or farm is affected differently, no one prescription fits all
- If possible it is best to avoid chopping corn with large amounts of
dirt or silt on it. Soil contamination is the primary source of
Clostridium bacteria which increases the risk of poor fermented
silage. Clostridial fermentation can also increase the risk of
- It is generally recommended to not harvest corn with significant
moldy ears. Mold lowers feed value and increases the risk of mycotoxins.
However, do not assume that all flooded corn will have moldy ears. Ears
with tight husks show no or few signs of mold. It is important to
monitor the corn regularly to assess mold growth and development. You
may consider an early harvest if the mold worsens.
- Silt is abrasive, so it will be very hard on machinery.
Operators will need to take extra care to ensure knives are sharp. Be
prepared for extra repairs.
- Try to cut the corn above the silt line or at least above any heavy
silt line. In areas where plants are heavily silted it may be more
advantageous to harvest the corn as high moisture ear corn or snaplage.
This process requires only the ear to be removed and leaves the
remainder of the plant in the field.
- Good silage fermentation kills or inhibits the growth of many
pathogens; therefore, follow all best management practices to promote
good fermentation by harvesting at the correct moisture content (62 -
68% Moisture content, 32 - 38% DM), proper chop length, high filling
rate, extra packing, and a tight seal to exclude oxygen. In addition,
silage inoculants properly applied can help promote good fermentation by
assuring adequate populations of lactic acid bacteria and silage
preservatives such as buffered acids can help prevent mold and yeast
- If possible the field should be left to reach the proper harvest
moisture for silage. Do not chop immature corn unless necessary.
Chopping immature corn can lead to other fermentation issues. If fungal
growth seems imminent or increasing on the ears or in the stalk and you
still intend to harvest, harvesting slightly earlier that you typically
would can reduce the chances of an unacceptable mycotoxin load.
- Crop dry down rate may be faster than normal, so monitor plant
maturity and whole plant moisture content routinely and be prepared to
harvest when ready.
- Because of the relationship between packing density and oxygen
exclusion, it may be better to err on the side of harvesting at slightly
higher moisture levels than usual. Chopping corn at excessively high dry
matter content will reduce lactic acid bacterial growth and likely
inhibit proper fermentation allowing more spoilage.
- It is advisable to inoculate with lactic acid bacteria from a
reputable company. It may cost a little more for a good inoculant, but
do not skimp on rate or quality. If harvested at the proper moisture
content, it is generally recommended to inoculate with a combination of
homolactic lactic acid bacteria (to lower and stabilize the pH of the
silage) and L. buchneri (to increase acetic acid formation
which extends bunk life and reduces feed out losses). Growth of molds
and fungi are inhibited by acetic acid. Including L. buchneri
in the inoculant can cause excessive production of acetic acid if the
corn is harvested below 32% DM. However, for specific products, talk to
your inoculant dealer about any modifications in inoculant rate and
type. Distribution of inoculants within the forage is also critical so
talk to your dealer about applicators.
- Acetic acid and buffered propionic acid products are also effective
to limit mold and yeast growth, but should not be mixed with bacterial
inoculants in the same applicator tank. Follow specific product
- Remember to store flood damaged corn separately from undamaged corn.
If production problems are detected from this forage then there are
options to either feed it to other
livestock or plan to spread it on your fields as you would manure.
- Avoid feeding for 4 to 6 weeks to allow adequate time for good
fermentation. Some mycotoxin levels can actually decline over time in
- Before feeding, collect a representative sample and have it tested
Flooded Stored Forages
- Before feeding the flooded crop, collect a representative sample and
have it tested for mycotoxins.
- For stored silage that was exposed to flood waters, it is important
to dig into the silage (or open up a few bales) and assess the damage.
Check the smell and color. If it looks and smells good, then it may be
fine. Watch for mold growth.
- Discard forage that is visibly contaminated with silt or mold. In
some cases, silt will even be found inside wrapped bales with the
plastic still intact.
- For round bale silage, re-wrap or patch torn bales to avoid heating
and spoilage and plan to feed these out soon. Flooded wrapped bales are
apt to spoil; even if your bales look fine right after the flood, check
a few in about a month to look for changes.
- Limit the amount of this feed in the ration mixing it with other
good feeds. Monitor your animals closely.
Feeding Flooded Forage
- Flooded forage should be analyzed for nutritional value and
mycotoxins. With added silt, you may find a higher dry matter and ash
content and a lower protein and energy concentration.
- Frequency of testing will be determined by field risk assessment as
well as by evaluation of the feedâ€™s visual appearance and smell.
- Blending or diluting flooded feed with uncontaminated forage may be
one means to reducing impact on herd health. However, check with your
nutritionist and veterinarian to interpret mycotoxin test results before
- Once you start feeding any flooded material, watch your animals
closely. Mycotoxins and other potential pathogens may cause health
problems immediately or over time.
Sampling and Testing for Mycotoxins
The risk of mycotoxin development may increase in crops that have been
flooded and covered in silt. Mycotoxins are poisons that are produced by
fungi. These toxins can be detrimental to both animal and human health.
Mycotoxins can cause problems in production, reproduction and intake
problems, as well as possible irreversible damage to cows' organs, including
the liver and kidneys.
Fungi in the â€˜Fusariumâ€™ family produce many of the common mycotoxins. The
fungi itself is ubiquitous and found in the soil, plant residue and even
blown around through air currents. Mycotoxins associated with â€˜Fusariumâ€™ are
zearalenone, T-2 toxin, fumonisin, and deoxynivalenol, also called DON or
vomitoxin. The following are mycotoxin risk levels for dairy cattle,
expressed on a total ration, dry-matter basis.
- DON (vomitoxin); less than 5 to 6 parts per million
- Fumonisin; less than 25 parts per million
- T-2 toxin; less than 100 to 200 parts per billion
- Zearalenone; less than 300 parts per billion
Aflatoxin produced by the fungi Aspergillus, the most serious carcinogen,
has been found in high levels in peanuts, corn, cotton seed, and grain
and can contaminate milk. This toxin is a serious problem for human and
animal health and can contaminate corn in warmer growing regions.
Aflatoxin requires warm ( 85 oF) and moist conditions. Where fall conditions
are cool, aflatoxin is rarely found.
All flooded forages should be tested for mycotoxin after complete
fermentation but soon enough so you have time to obtain feed if it has
unacceptable levels. Samples should be taken from the storage facility and
the TMR if available. The sampling strategy and frequency will depend on
herd health monitoring. Mycotoxin analysis can be completed at many
Forage Inventory and Farm Decisions
Take an accurate inventory of your volume and quality of stored forage.
Estimate how much feed you will need this winter and whether it is possible
to avoid using the flooded forage. Talk to your feed consultant about
cost-effective options for replacing lost feed. Right now is the time to
make the calculations. If you find you will have to borrow money to buy
feed, talk to a banker early.
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