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Aflatoxin Concerns in #Corn

Aspergillus ear rot. Photo courtesy UNL Plant Path Dept. and the following publication: http://www.ianrpubs.unl.edu/epublic/live/ec1901/build/ec1901.pdf

This article originally appeared in http://cropwatch.unl.edu written by Dr. Tamra Jackson-Ziems, UNL Extension Plant Pathologist.

Drought and high temperatures promote development of the disease Aspergillus ear rot (pictured right). The fungi that cause this disease (most commonly, Aspergillus flavus) can produce aflatoxin. Aflatoxin is one of many chemicals in a group known as mycotoxins that are produced by fungi (molds). Mycotoxins, such as aflatoxin, can be toxic to animal and human consumers and, at certain concentrations, can lead to dockage or rejection of grain at elevators.The unusually high temperatures and drought this summer are having severe impacts on Nebraska corn. In addition to reductions in test weight and overall yield, secondary problems are developing in some corn fields as a result of these conditions.

Corn harvested for grain to this point has been predominantly from fields that sustained substantial drought damage leading to early maturation and plant death. Notable aflatoxin contamination appears to be in a small percentage of southeast Nebraska fields, based on samples submitted to several laboratories in the area.

Mycotoxins are common and can be safely consumed at low concentrations. The concentration of aflatoxin that is considered safe for consumption depends on the age and species of the consumer. An abbreviated summary listing the Action Levels identified by the FDA for aflatoxin is listed in Table below.

Testing for Aflatoxin:  Farmers and crop consultants can scout high risk fields for Aspergillus ear rot as an indicator for aflatoxin, but only lab testing of grain samples can accurately identify the concentrations of aflatoxin in the grain. Accurate lab test results for aflatoxin will depend greatly on the quality of the sample that is collected and the laboratory methods used to test it. The test results are only applicable to the sample that is submitted, so it is very important to collect an adequate sample for the best results. Refer to the publication, Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins) for recommendations on how to collect and submit a high quality sample for mycotoxin analysis.

Contact and submit samples to a laboratory that is certified by the federal Grain Inspection Service and Grain Inspection, Packers, and Stockyards Administration (GIPSA) for mycotoxin analysis for the most accurate results. A GIPSA website lists laboratories certified to conduct testing in Nebraska. They include

  • Lincoln Inspection Service, Inc.;
  • Fremont Grain Inspection Department, Inc.;
  • Omaha Grain Inspection Service, Inc; and the
  • Sioux City Inspection and Weighing service Company.

Some grain elevators and individuals may be using a black light (ultraviolet light) to detect for fluorescence as a method for rapid screening of grain samples. This practice is NOT recommended when making decisions about aflatoxin contamination in loads of grain. The component that produces fluorescence under black light is called kojic acid. Although kojic acid is produced by the same fungus that produces aflatoxin, its presence is not necessarily an indicator of aflatoxin and might lead to false positive results and unnecessary rejection of grain.

High Risk Factors for Aflatoxin Contamination in Corn

  • Drought-damaged fields, including rainfed (dryland) fields and non-irrigated pivot corners
  • Fields or areas with higher incidence of corn ear-feeding insects, such as the corn ear worm
  • Grain damaged before or during harvest or after harvest while in storage

Ear rot diseases and aflatoxin are not evenly distributed across fields or in the grain, so scouting and/or sampling should include a substantial portion, at least several acres. The presence of the fungus in kernels does not always correlate well with the presence of aflatoxin, nor does the absence of visible fungal growth necessarily indicate the absence of aflatoxin.Scouting For Aspergillus Ear Rot

  • Open husks to view a large number of ears.
  • Look for the presence of dusty yellow-green to olive-green spores, especially on the surface of damaged kernels or ear tips (Figure above).
  • Pay special attention to higher risk areas.

Harvest and Storage:  If fields have documented Aspergillus ear rot and/or risk of aflatoxin contamination, it is recommended that you harvest and keep grain separate from other grain at less risk, such as irrigated fields. Storage of affected grain is not recommended because ear rot diseases and mycotoxins can continue to accumulate during storage. If storage is necessary, cooling and drying grain to less than 15% moisture within 48 hours of harvest will help to slow fungal growth and aflatoxin production. Grain intended to be stored for longer periods of time should be dried to less than 13% moisture.

Presently, it is too early in the harvest to know the extent of aflatoxin contamination in this year’s corn crop, but at this time only a small percentage appears to be affected.

Resources:  For more information, refer to the list of publications below or view this week’s episode of Market Journal.

Table 1: FDA action levels for aflatoxin contamination in corn intended for livestock.

Commodity Action Level (ppb)
Finishing (feedlot) beef cattle  300
Finishing swine of 100 pounds or greater  200
Breeding beef cattle, breeding swine, or mature poultry  100
Immature animals and dairy cattle  20
For animal species or uses not otherwise specified, or when the intended use is not known  20
Human food  20

Source: FDA Action Levels for Aflatoxin

Drought: Resources & Options for Corn

Well, the heat isn’t letting up.  Sixty-nine Nebraska counties are allowed to hay and graze Conservation Reserve Program (CRP)  lands.  In our area these counties include:  Hamilton, Hall, Webster, Nuckolls, and Thayer.  From Teri Post at the Webster Co. FSA office, this means that:  “If it (CRP) is hayed, it cannot be sold and cost to the livestock person cannot exceed the 10% reduction on contract payment.  Paperwork MUST be completed prior to anything being done.  If you do not have livestock but do have a CRP contract, you can lease your acres to a livestock producer.  They have also released CP25 (wildflower mix) for grazing only.  If you prefer to sell the hay and you qualify for managed haying, you may do that but you will be assessed a 25% payment reduction rather than the 10% with emergency release.  Also keep in mind that use of emergency haying or grazing restarts the time clock for when you can hay or graze next.  If you use the emergency hay or graze release, even if you hayed or grazed in a prior year you are now eligible to hay or graze again.”

Nebraska Farmers who have drought damaged corn which could be swathed and baled, chopped, or grazed can list that on the Nebraska Hay and Forage Hotline.  The hotline is available free of charge for buyers and sellers to list feed resources.  Call the hotline at 1-800-422-6692 to list the forage you have or to list your need for forage.  I’ve been contacted by Extension Dry Panhandle rangelandEducators in the Sandhills asking if we have any producers willing to rent cornstalks for grazing this year to please let me know and we will put you in touch with producers in the Sandhills who need forage.

UNL Extension has developed a Drought Resource Web resource that pertains to crop and livestock producers. Some of you have been asking about options for dryland crops right now.  Research has shown benefits to the following crop if stubble height is left at least 10 inches tall when haying or cutting silage from drought damaged corn fields.  Leaving a higher stubble height will also reduce the nitrate levels in the forage that has been cut. 

When it comes to your options on what to do with weather-damaged corn, Dr. Bruce Anderson, UNL Extension Forage Specialist and Tom Dorn, UNL Extension Educator, recommend to consider the following points before harvesting your crop as forage:

  • If grain prices remain high, grain yield may not need to be very high to justify selecting grain harvest over forage harvest.
  • Sometimes leaving the corn residue can result in increased yield next year and that increase may provide more value than that resulting from forage use. See NebGuide G1846, Harvesting Crop Residues for information on evaluating your situation.
  • Check labels of all chemicals applied to be sure they are cleared for forage use and that the minimum harvest interval has been met.
  • Check with the USDA Farm Service Agency and your crop insurer to maintain compliance with farm programs and crop insurance requirements.
  • Nitrate concentrations can reach toxic levels in weather-damaged corn. The harvest method can affect the nitrate, a particular concern when its being fed to livestock. Leaving a tall stubble (8 or more inches) will reduce nitrate risk but note eliminate it. Choose the harvest method accordingly.

Silage may be the safest method of harvest as fermentation usually (but not always) reduces nitrate levels and risk. Yield is about one ton per acre of silage for each harvested foot of earless corn plant (not counting the tassel). Feeding value is about 70% to 80% of well-eared corn silage. Corn with some grain (less than 50 bushels) tends to produce about one ton of silage for every five bushels of grain with a feed value about 80 to 90% of regular corn silage.

Harvest timing is critical with silage to ensure the correct moisture for proper fermentation. Plants probably are about 80% moisture now and the desired moisture level for silage is about 65%. Plants with any green leaves usually are too wet to chop for silage. For proper moisture, most leaves may need to be dead before chopping. The stalk and ear hold amazingly high water concentrations. For corn with no grain, even if all leaves are dead, the whole plant (and silage) moisture can be 70% if the stalk is still green and alive. Once plants actually die they can rapidly dry down.  There are several ways to reduce moisture content:

  • If corn has pollinated, delay silage harvest until all chances of increased biomass tonnage have passed or plants naturally dry down to appropriate moisture levels.
  • Corn can be windrowed and allowed to partially dry before chopping.
  • Excessively wet material can be blended with drier feeds such as ground hay, cracked grain, or dried distillers grains. However, this can take a lot of material — about 500 lb of grain or hay to reduce each ton of chopped corn with 85% moisture down to 70% moisture.
  • Silage inoculants may improve fermentation and preservation of drought-damaged silage.

Green Chop:  Green chop minimizes waste but may be the most dangerous way to salvage corn. If present, nitrates will start to change into nitrites (about 10 times as deadly) as green chop begins to heat. Chop and immediately feed only an amount that animals will clean up in one feeding. Chop and feed two or three times per day instead of providing excess feed from a single chopping. If any green chop remains two hours after feeding, clean out bunks. Never feed green chop held overnight because nitrites can be exceptionally high. Be sure to allow plenty of bunk space (36 inches per cow is recommended) so boss cows don’t overeat and timid cows can get their share.

Hay:  Hay may be the most difficult method of mechanical harvest, especially if ears have started to form – the stalk and especially the ears will be slow and difficult to dry. If possible, use a crimper when windrowing. Unlike with silage, nitrate levels do not decrease in hay after it is baled. Some of the nitrate risk can be reduced by cutting to leave a tall stubble, about 8 inches. Tall stubble also will elevate the windrow off the ground, allowing air to circulate better through the forage and aid in drying.

Grazing:  Challenges with grazing include acidosis risk for cattle not accustomed to grain if ears have started to fill (smart cows will selectively graze ears), waste from excessive trampling, availability of drinking water, perimeter fencing, and nitrates. Reduce acidosis risk by feeding increasing amounts of grain similar to feedlot step-up rations before turning into standing corn that has much ear development.

Reduce waste by strip-grazing with at least two or three moves per week; daily is best. Back fences are not needed because regrowth is not expected. Water can be hauled in as with winter corn stalks or lanes might be constructed with electric fence to guide animals back to water sites that are nearby. If strip grazing, animals can walk back over previously grazed areas since back fences aren’t needed.

Perimeter fences can be built using the same fencing as for winter stalks. Cows are likely to respect such fencing but inexperienced calves may not remain where desired. To better control calves, use a double strand of electric wire and/or a more visible barrier such as electric polyrope or polytape. Animals not already experienced with electric fences may need some exposure and training before moving them to a corn field.

Nitrates usually are not a problem with grazing since the highest concentration is in the stem base, the plant part least likely to be consumed. Risk increases, though, if animals are forced to “clean-up” a strip before moving to fresh feed and when corn plants are short (probably less than 3 to 4 feet tall) with small, palatable stem bases. Tests for nitrate concentration (whole plant and just the bottom 8 inches of the stem base) can be made prior to grazing to assess risk. If nitrate levels are risky, the hazard can be reduced by offering enough desirable forage to discourage consumption of hazardous plant parts as a major component of diet. Also, delaying grazing until plants more fully mature often lowers nitrate risk.  NebGuide G1865, The Use and Pricing of Drought-Stressed Corn, offers additional information.

Windrow Grazing:  This method includes cutting as you would for hay and then grazing the windrows rather than baling them. It eliminates the cost of baling, transporting bales, feeding bales, and maybe hauling manure. It also eliminates any flexibility in feeding location and may reduce opportunities to sell the corn forage.

Windrowing tends to preserve forage quality better than allowing plants to stand. Usually it is easier to strip graze windrows than standing corn because building fences and estimating strip size are easier. Snow cover rarely causes problems if animals already know the windrows are there. They will use their hooves and face to push snow aside to access the windrow. Thick ice, however, can cause a significant barrier. Follow appropriate management recommendations listed earlier for hay and grazing for best utilization and safety.

Additional Resources: US Drought Monitor Map and High Plains Drought Monitor Map

 

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