By Kevin Putnam, Dan Mongeau, Bill Seglar, Scott Dennis and Bill Mahanna
Floods can contaminate corn with large amounts of silt and organic debris, resulting in high levels of yeast, mold and bacillus spores. The preservation of feed value and prevention of aerobic instability requires critical attention to ideal ensiling management practices such as moisture, inoculation, compaction, sealing and maintaining proper feed out rates.
The goal is to obtain a low pH and prevent oxygen from entering the storage structure. The use of bacterial inoculant such as Pioneer brand® 11C33 helps dominate front-end fermentation while a Lactobacillus buchneri strain hinders yeast and mold growth to improve bunklife and silage bio-security. If the crop is heavily contaminated with silt and/or silage management practices such as adequate compaction and rapid feedout are not attainable, producers may want to consider high levels of multi-acid products for the most severely affected fields.
Flood damaged corn should be closely monitored for proper moisture and stage of maturity for harvest. Incomplete fermentation and increased likelihood of secondary clostridial fermentation can result if flood-damaged corn is harvested before moisture levels drop to recommended levels. High levels of silage acids may be produced by fermenting bacteria; however, they can be diluted in wet forages limiting the ability to drop pH to below 4.5 needed to reduce growth of clostridia and other spoilage organisms.
The likelihood of increased yeast and mold contamination exists anytime down or flooded plants are exposed to bruising and/or increased contamination from silt or flood waters. Mold growth in the field in northern environments will likely be gibberella ear rot that can produce vomitoxin, zearalenone, and T-2 mycotoxins; whereas southern environments will likely be aspergillus ear rot that can generate aflatoxin. Screening for mycotoxins at time of harvest is advisable to make sure the silage is fed to appropriate classes of cattle and to determine if a mycotoxin adsorbant should be incorporated into the ration. The use of Pioneer inoculants or any other forage additive/preservative on the market will not denature preformed mycotoxins that exist on the crop prior to ensiling.
Mold growth may occur during storage if the pH is above 4.5 and oxygen is present. Molds that can grow during silage storage and produce mycotoxins include species of penicillium and aspergillus. Other non-toxic mold may utilize nutrients and produce unpalatable end-products. The mycotoxins produced by storage molds are typically not identified by commercial laboratories; however, another option is to have silage cultured to determine if any potential mycotoxin-producing mold species are present.
Flood damaged corn often dries down faster than normal corn. If the corn plant was devoid of oxygen from being submerged in water for longer than about 48 hours it will start to shut down and will be ready for harvest much sooner than normal. Prolonging the time it takes to harvest flood-damaged corn can contribute to silage aerobic instability due to accelerated dry down. The dry matter of the crop should be closely monitored utilizing a chipper-shredder and a Koster™ moisture tester or microwave.
Corn that went down due to flooding or wind events will dry down faster depending on the maturity of the crop and whether it incurred stalk lodging or root lodging. Root lodging often occurs in areas where there was rain preceding a wind event. In this case, the soil will give way with the wind and uproot the plant. The stalk may not be bent, but exposed roots on the one side will initiate faster dry down. Stalk lodging can occur when soil is crusty, dry, and/or compacted or if stalk disease has weakened the pith at the internode. In this situation, the stalk yields to the wind before the roots. Stalk lodging differs in that it "kinks" the stalk (phloem) similar to a bent "straw" and pinches off moisture to plant parts above the lodged section. Expect this type of lodging to accelerate dry down even greater than that of root lodging. If kernels are still developing when this happens, kernel size will most likely be affected causing lowered starch content and dry matter yields.
Regarding the silage harvest of flooded or down corn, if the corn is laying with the rows, meaning rows planted north and south and corn is laying either north or south, then many consider a row head as the best option. If the corn is lying against the rows, meaning the rows are planted north and south the corn is laying east and west, then a large drum row-independent head harvesting the field diagonal to the rows appears the best option.
Silos that are filled with forages of several qualities may cause good silage to become contaminated with poor silage. Segregation of flood-damaged corn into separate silos is advisable, such as using bagged silos. Dairy managers who detect health and production problems from feeding flood damaged silage then have the option of allocating the feed to other livestock groups or else disposed back into the field.
Target the least affected fields for silage and if possible, harvest above the silt line to help avoid soil (ash) contamination. Analyze silage prior to feeding and pay particular attention to mycotoxins. Soil contamination alone may not be a serious animal health factor, but contamination from manure, sewage treatment plants and other chemicals is unknown and could vary from one situation to another.
Silt build-up on stalks and leaves can be severe immediately after flood waters recede and harvesting the crop too soon after a flood can result in higher contamination levels compared to harvesting later and allowing some of the silt to be washed off by rain water.
Depending upon the maturity of the crop and the severity of the flooding, harvesting as dry or high-moisture grain may be a more viable option than harvesting as silage. Harvesting high moisture corn could result in a more stable and less contaminated crop. Inoculating high-moisture corn grain with Pioneer brand ® 11B91, containing Lactobacillus buchneri can help prevent yeast and mold growth during storage. If harvested as dry corn, the corn should be frequently monitored for foreign material, sprouting and mold growth.