Maize for Silage
Technical
Insight 342

LATE SEASON FLOODING OF MAIZE

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EFFECT OF FLOODING ON MAIZE CROPS

Flooding damage to maize is highly dependent on plant stage of development, the length of the flooding period and soil-air temperatures. Maize is affected most by flooding in the early stages of growth. Once it has reached the silking stage, shallow depths of flooding will not usually cause significant immediate damage. In fact, if the growing point of maize is above the water, maize can survive several days to several weeks of flooding (Butzen, 1996).

Flooding causes greater crop yield losses when it occurs early in the season (Lauer, 2001). When six-inch maize was flooded for 24, 48 and 72 hours, maize yields were reduced 18, 22, and 32% respectively at a low nitrogen fertiliser level. At a high nitrogen level, these reductions ranged from 19 to 14% one year and <5% in another year. When maize at a height of 30 inches was flooded for 24 and 96 hours, yields were reduced 14 to 30%. With a high level of nitrogen in the soil, very little yield reduction occurred even with 96 hours of flooding. When flooded near silking, no reduction in yield occurred at a high nitrogen level, but yield reductions up to 16% occurred with 96 hours of flooding at the low level of nitrogen.

In a summary from the Ministry of Agriculture and Food in Canada titled “Maize: Other Problems Affecting Maize Production” it states:

“Flooding stresses the plant by cutting off the supply of oxygen to the root system. Younger maize plants die if submerged in water for more than five days, especially in warmer weather conditions. If air temperatures are high, death may occur in only a few days, as plant processes are sped up and the need for a supply of oxygen to the roots is high. In cooler weather, submerged plants may live for up to a week. After the eight-leaf stage, plants can tolerate being submerged in water for more than eight days but may be more susceptible to disease and may experience limited root development while under water. Yield loss due to flooding is most substantial for plants submerged immediately before and during tasselling and silking. Plants in the vegetative growth stages of 10-16 leaves and/or during the grain filling period display little yield response to flooding.”

Figure 1: Root death from flooding (Nielsen, 2003)

As plants develop beyond V6 (green (v=vegetative) plant with six true leaves), rapid stalk elongation elevates the growing point region above the soil surface and, thus, away from the direct stress of flooded soils. Secondly, an older crop's root system will simply be larger and consequently the crop can tolerate a certain amount of root death without dying or dramatic stunting (Nielsen, 2002).

Although maize plants may not be killed outright by the oxygen deficiency and the carbon dioxide toxicity caused by flooding, root uptake of nutrients may be severely reduced and this may result in deficiencies of nitrogen and other nutrients during the grain fill period.

Professor Bob Nielsen (University of Purdue) inspected maize crops around the dough stage that had been completely submerged for six hours or more and nearly completely caked with mud for up to two weeks. Within two weeks after the floods, substantial levels of kernel abortions were visible. Not only were the tip kernels aborting but also the butt kernels.

Kernels are susceptible to abortion when stressed prior to the late dough or early dent stages of development. The younger the stage of kernel development, the more prone to abortion. The tip kernels on the ear are the most susceptible because they are generally the last to be fertilised and less competitive for nutrients than kernels closer to the butt of the cob. Ears affected by kernel abortion can become “spongy”. Crops that have had the ears covered with water are also particularly prone to cob rots and premature kernel sprouting.

Professor Nielsen has also documented a peculiar form of “leaf firing” that often occurs within a few days of a significant ponding event. The leaf discolouration primarily occurs on the lowest leaf on the plant that was previously green. The entire leaf turns a vibrant orange-yellow while leaves above it remain their normal green. It is thought that this rapid orangeish discolouration is an early response by the plant to initial stages of root death that occurs under saturated soil conditions. The symptom will appear on plants whether they were ponded or simply stressed with "soggy" soils. The symptom does not appear to be caused by true nitrogen deficiency because the remainder of the leaves remain a fairly normal green subsequent to the ponding event. The orange-yellow leaves eventually die completely and wither away (Nielsen, 2003).

Figures 2 and 3: Leaf firing in flooded maize (Nielsen, 2003)

ROOT AND STEM ROT

In flooded fields the potential for increased levels of root rots will be greater due to the soil saturation causing root death. Mud and dirt covering the plant will reduce photosynthesis and may result in the plant cannibalising the nutrients from the stem increasing the risk of stem rot.

Bacterial stalk rot can occur following flooding. The causal bacterium lives as a saprophyte on plant debris in the soil. Infection occurs when the bacteria are blown or splashed onto the plants followed by penetration through natural openings (stomates and hydathodes) or wounds made by injuries.

It is characterised as a tan to dark brown, water-soaked, soft or slimy disintegration of pith tissues at a single internode. Affected stalks suddenly collapse and are usually twisted. The tips of the uppermost leaves often wilt, followed by a slimy soft rot at the base of the whorl. The decay spreads rapidly downward until the affected plants collapse. Lodged plants usually have a foul odour. (Reference: RPD No 200. Corn Stalk Rots, University of Illinois).

Figure 4: Stalk Tissue Death from Flooding (Nielsen, 2003)

COB DISEASE

Bacterial ear rot is caused by one of several species of soft rot bacteria that live as saprophytes on plant debris in soil. During periods of high rainfall, flooding or poor drainage, bacteria are splashed onto plants and infect susceptible tissue. The bacteria normally enter the plant through the leaf stomates or wounds on leaves or stalks (Nielsen, 2003).

Below are a series of pictures from Prof. Bob Nielsen (University of Purdue) found in an article titled: Bacterial Ear Rot in Corn Due to Flooding.

WHAT TO DO AFTER FLOODING

Maize growers should inspect flood damaged crops as soon as the water has receded. 

Check the colour of the growing point. It should be firm and white and cream if healthy. Injury is indicated if the growing point tissue is darkened and soft. (Refer to Figure 4 on page 4).

Because flooding may cause root death as well as increasing the risk of stalk and root rots, standability may be an issue in flooded maize crops. Check the stability of plants and watch for any signs of root or stalk rots.

Monitor the cob thoroughly to ascertain the amount of cob damage.

Crops that show any symptoms of cob, root or stalk rots or badly lodged crops should be earmarked for silage and harvested as soon as possible at the appropriate drymatter percentage.

For maize crops being taken through to grain, again continue to monitor closely for stalk and cob infections, but in any event prepare to harvest as early as ground conditions allow. Early and pro-active communication with your grain company representative and harvest contractor will be particularly important.

MAKING MAIZE SILAGE FROM FLOODED CROPS

Do not be tempted to harvest earlier than 30% drymatter unless the crop is actually dying. Harvesting at low drymatters increases the risk of a Clostridial fermentation and subsequent silage quality and animal intake issues.

Floods contaminate crops with large amounts of organic debris resulting in high levels of yeast, mould and Bacillus spores that will enter the stack with the crop (Seglar, 1999).  Maize silage made from flooded crops is therefore particularly susceptible to poor aerobic stability. (Aerobic stability is a measure of how long silage remains cool and retains its quality after the stack is opened at feed-out time). The prevention of aerobic stability problems requires critical attention to ideal silage management practices such as packing, sealing and maintaining proper feed-out rates.

The use of a Pioneer® brand inoculant that improves aerobic stability (i.e. 11C33) is highly recommended.

References

Butzen, S.,1996. Flooding Damage to Corn. Crop Insights Vol 6 No 12. Pioneer Hi-Bred International.

Integrated Pest Management. 2002. Corn Stalk Rots. University of Illinois Extension.

Lauer, J. 2001. How Does Flooding Affect Corn Yield? Wisconsin Crop Manager. University of Wisconsin.

Ministry of Agriculture and Food in Canada. 2002. Corn: Other Problems Affecting Corn Production.

Nielsen, R. 2000. Flooding & Ponding: How Long Can Corn Tolerate "Wet Feet"?. Purdue University.

Nielsen, R. Bacterial . 2003. Ear Rot in Corn Due to Flooding. Purdue University

Seglar, W. 1999. Coping With Catastrophic Ensiled Forage Losses And Case Studies. Pioneer Nutritional Insight. Pioneer Hi-Bred International.



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Revised: June 2015
Expires: June 2018