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 'time-dated' 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., 1981).

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 (Klepper, 1990).

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 season.

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 situations.
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 botulism toxins.
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 growth.
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 recommendations.
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 the silo.
Before feeding, collect a representative sample and have it tested for mycotoxins

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 feed'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 mixing feeds.
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 'Fusarium' 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 'Fusarium' 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 commercial labs.

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.

Literature Cited

Ashraf, M. and H. Rehman. 1999. Mineral nutrient status of corn in relation to nitrate and long-term waterlogging. Journal of Plant Nutrition 22:1253-1268.

Belford, R. K., R. Q. Cannell, and R. J. Thompson. 1985. Effects of single and multiple water loggings on the growth and yield of winter wheat on clay soil. Journal of Science and Food Agriculture 36:142-156.

Ellis, J. R. 1998. Flood Syndrome and Vesicular-Arbuscular Mycorrhizal Fungi. J. Prod. Agric. 11:200-204.

Fausey, N. R. and M. B. McDonald. 1985. Emergence of inbred and hybrid corn following flooding. Agron. J. 77:51-56.

Kanwar, R. S., J. L. Baker, and S. Mukhtar. 1988. Excessive soil water effects at various stages of development on the growth and yield of corn. Trans. Am. Soc. Agric. Engineers 31:133-141.

Klepper, B. 1990. Root growth and water uptake. In Stewart, B. A. and Nielsen, D. R. (editors). Irrigation of agricultural crops. p. 281-322. ASA-CSSA-SSSA, Madison, WI.

Lizaso, J. I. and J. T. Ritchie. 1997. Maize shoot and root response to root zone saturation during vegetative growth. Agron. J. 89:125-134.

Meyer, W. S., H. D. Barrs, A. R. Mosier, and N. L. Schaefer. 1987. Response of maize to three short-term periods of waterlogging at high and low nitrogen levels on undisturbed and repacked soil. Irrigation Science 8:257-272.

Mukhtar, S., J. L. Baker, and R. S. Kanwar. 1990. Corn growth as affected by excess soil water. Trans. Am. Soc. Agric. Engineers 33:437-442.

Purvis, A. C. and R. E. Williamson. 1972. Effects of flooding and gaseous composition of the root environment on growth of corn. Agron. J. 64:674-678.

Ritter, W. F. and C. E. Beer. 1969. Yield reduction by controlled flooding of corn. Trans. Am. Soc. Agric. Engineers 12:46-50.

Wenkert, W., N. R. Fausey, and H. D. Watters. 1981. Flooding responses in Zea mays L. Plant Soil 62:351-366.

Wesseling, Jans. 1974. Crop growth and wet soils. Van Schilfgaarde, Jan (editor). Drainage for agriculture. p. 7-37. American Society of Agronomy, Madison, WI.

Flooding Effects on Corn