AgriGold

Rotten Grain in the Corn Belt

by Mike Kavanaugh, CCA, November 1, 2009

The old adage that a cool wet summer can produce a big crop has certainly shelled out to be true throughout the corn belt in 2009. Although, this year corn growers across the country have found a lot of rotten grain and cobs in the grain tank as well. The cool, wet conditions of grain fill throughout physiological maturity and drydown have triggered the formation of many fungi and corn rotting organisms throughout corn fields. As harvest has progressed the problem seems to be overwhelmingly disastrous in many cases. Usually ear and cob rots are very localized and are in a much smaller scope than what they have been in 2009. The infected area has seemed to become astronomical throughout the corn belt. The main ear rots being found in great numbers this year include Diplodia ear rot, Gibberella ear rot and Nigrospora cob rot. Many questions have arisen about where the rots seem to be regionalized to, how infection takes place, and how infected grain needs to be handled, stored, fed or sold. Another big question that arises is how to prepare for 2010 and beyond when managing against ear and cob rots. The agronomy team from AgriGold has come together to find bits and pieces of knowledge, advice or recommendations in the market place to dealing with ear and cob rots and have compiled some findings in this newsletter.

Where is it?The majority of the corn belt’s ear and cob rots have been found all the way from Ohio to Nebraska and from Mississippi to Minnesota. This map illustrates the most severe hit areas in 2009. Giberella ear rot has been most prevalent in Northern Indiana and Northwest Ohio, reaching into part of Northeastern IL. Diplodia ear rot has been most prevalent throughout Indiana, Illinois, Kentucky, Missouri, Southeast Iowa and small parts of  Nebraska and Kansas. Cob rots, one known as Nigrospora has been prevalent throughout a much larger area. Cob rot has been found throughout most of the central corn belt.

Development & Identification Ear and cob rot development can be explained with a simple triangle. A disease triangle outlines what must be in place for any disease to be present. The three requirements for ear and cob rots to develop is a host crop (Host), pathogen for the rot (Pathogen) and the right environment throughout the season (Environment). When all three requirements are met, a disease has the potential to grow and prosper. If any one of these three are missing, disease establishment is minimized and may not even occur. The following descriptions of common ear rots being seen in 2009 address what requirements are needed for each rot to develop.

Diplodia Ear Rot is caused by the fungus Stenocarpella maydis which is also the cause of Diplodia Stalk Rot. This fungus will overwinter in corn debris, produce spores and splash up onto the corn plant. Infections begin at the base of the corn ear and generally spread until the entire ear is covered in a white mold that almost has the appearance of toothpaste. Diplodia ear rot is favored by cool, wet weather during grain fill and is quite widespread in the 2009 growing season. The good news is that Diplodia will not produce mycotoxins, the bad  news is that test weight and grain quality wind up being extremely poor. Diplodia ear rot is most prevalent in corn following corn rotations and was the case in 2009.

Gibberella Ear Rot is caused by the fungus Gibberella zeae which likes cool, wet weather after silking. This fungus can also cause stalk rot and will overwinter in corn residue. The ear rot starts by spores splashing and blowing up onto silks thus infecting ears and causing a red or pink mold to form starting at the tip of the ear. In some cases the mold may appear white and be hard to tell apart from Fusarium without further tests. Gibberella is a harmful ear rot because it can produce vomitoxin, zearalenone, and other toxins harmful to livestock. Something that has been noticed this year is that Diplodia Ear Rot has covered up the symptoms of Gibberella and hidden the signs of this harmful ear rot.

Nigrospora Cob Rot is caused by the fungus Nigrospora oryzae which is weak in nature and only attacks plants that are stressed or killed prior to maturity. This premature death can be caused when normal plant growth is arrested by leaf blights, stalk and root rots, root feeding, hail, or insects.This fungus occurs late in the season and will deteriorate the cob and kernels, which is easily visible at the butt end. Once again this fungus will overwinter in corn residue, but unlike the others a weakened or dead plant is required for infection to take place.Nigrospora cob rot is not known to produce mycotoxins.

Handling, storing, feeding or selling the grain.
Due to the disease-infected grain, regardless of the specific ear rot, the grain will ultimately have lower test weight and poor grain quality. Test weight is reduced due to the rots infecting the kernels before they have reached physiological maturity. The ear rots interrupt the flow of starch being packed tightly into the kernels prior to the plants natural senescence. Because of this, handling, storing, feeding or selling the grain can be very challenging.

1) Handling and storing rotten corn. Due to the lower test weight, depending on combine settings—the combine may discard infected kernels leaving a grower with less yield. Combine settings can be adjusted to keep the damaged grain, but if the percentage of damaged kernels is too high, elevators may dock and/or reject the sample/load. Special care needs to be taken not to damage healthy, intact kernels as mold will spread and grow on physically damaged kernels.

Moldy corn produces more fines and broken kernels so growers need to monitor their dryers and keep them cleaned out. There have been dryer fires this fall from this. Dry this corn down to 14% and cool it to 50ºF as quickly as possible, this will keep mold from spreading in the bin. Once the grain reaches 30ºF close bin up and try to keep the grain temperature there. Damaged corn will have a shorter storage life even if it has been  successfully dried down. This corn has been stressed and that will cause it to lose condition sooner. Growers  should plan on delivering this grain before their better quality grain.

2) Poor grain quality reduces feed value for livestock. In general, ear rots lower feed value by making the corn unpalatable. In addition, animals such as hogs can actually smell the molds in the grain causing feed refusal. This can cause reduced weight gain in animals. However, the largest concern are the toxins that are produced from these molds, specifically Gibberella. Gibberella ear rot is a serious concern because the fungus produces several different mycotoxins. Deoxynivalenol (DON or vomitoxin) and Zearalenone are the two most common produced in infected kernels. These toxins can impact the health of many monogastric animals, but hogs are particularly sensitive. DON can cause feed refusal and/or regurgitation if grain concentrations are around 1 ppm. The FDA regulates that DON concentrations cannot exceed 5 ppm or 20% of the diet. Zearalenone is an estrogenic factor causing infertility and abortions in hogs and other animals. For hogs, 0.5 ppm concentrations of Zearalenone should not be fed to swine. For other animal guidelines, please refer to the table.

The FDA has established DON advisory levels for animals as follows:

The following tables list specific concentrations, durations, and effects of mycotoxins on swine:

Deoxynivalenol (DON, vomitoxin)

Zearalenone

3) Selling contaminated grain can be difficult. Grain contamination and grain rejection is handled differently by different elevators. Most grain buyers are analyzing samples for overall damage on a percent basis.  A 100 gram sample is inspected for damage and FM. The percent of each is simply the amount in grams divided by 100. This is used to determine the grade of corn. Each grain buyer may handle this differently so corn growers must check with their local buyer on how they will handle damaged corn. Having a good representative sample to show them may speed the process along. Discounts may vary by buyer, however, this discount schedule below seems to be common:

<5% damaged kernels no discount
5-10% damage $.04/point discount
10-20% damage $.05/point discount
>20% damage $.06/point discount
Greater than 30% damaged grain could be rejected depending on the buyer

• Grain buyers may test for mycotoxins if it becomes a problem in the grain they ship to their buyers. The most common way to do this is a strip test similar to the ones used for non-gmo corn. Outbound grain is routinely tested for mycotoxins before it is accepted by the end user.

• Growers wishing to have tests performed on their grain can use a Federal Grain Inspection Service approved lab. There are several in most states. To find one nearby go to the GIPSA website: www.gipsa.usda.gov, then look on the right side for the “I Want To” box, click on “Get Grading or Weighing Services”. Then go to the “I Want To” box on the right side and click on “Find an Official Service Provider”. They will be listed by state. Click on the one nearest you for their contact information and fee schedule. Testing for vomitoxins costs $25-$35 per sample. Testing for aflatoxin costs $20-$30 per sample. Sample size for both is 250 grams (.55#). Check with the inspection service to confirm the price and sample size. If submitting an insurance claim the agent may want to handle the testing.

• Crop Insurance? Growers who have purchased crop insurance should check with their agent to see if they are covered in any way for rotten grain. This should be done now even if grain delivery is not until later. Take a  good representative sample.

• Specialty Contracts? Growers with specialty corn contracts will need to read their contract for the amount of damaged grain the buyer will accept. These contracts are generally more restrictive than selling regular corn. If rejected, growers will probably still be able to sell corn as regular corn. Although premiums may not be capture  and depending on the amount of damage there may be discounts. Growers may also have to deliver the grain to another elevator. Buyers of specialty corns are usually shipping corn that goes into the food markets. These markets are more concerned about the quality of the corn they receive and that is why they pay a premium for it.

• What to do with corn that is rejected by elevator for too much damage? If it is still in the field growers may want to try other areas of the field to determine if the damage is as severe. If corn is still being rejected leave that field and go on to another one. Given the lateness of the harvest it will be advisable to harvest the better quality/higher value corn before heavily damaged corn. If the corn is already in the bin and the remainder of the bin will be as high in damage try to find an outlet for the corn before loading any more trucks. Ask the elevator that rejected the load for any suggestions. Call other elevators in the area; they may be able to handle higher damaged corn. Check with the state’s Grain and Feed Association; they may have a list of elevators willing to handle severely damaged corn. Have a sample to show so the buyer can advise how much the corn will be discounted. This needs to be considered when determining how far the corn can be hauled economically. Some growers may consider mixing this corn with better quality corn in bins. This is an option, however, growers may risk damaging good corn if it can’t get dried down well enough. Keeping it separate is recommended and still leaves the option of blending it later. If grain is insured the most economical disposal method may be spreading it back on a field. That doesn’t sound good, however, it may be the only option.

Bin Safety: Wet and moldy corn can cause crusting to occur in grain bins. This makes it difficult to empty the bin as the corn won’t flow out without some help. This becomes a dangerous situation. In 1992 ten Iowa growers lost their lives in a three month period in grain bin accidents. Normally only one grower dies in a 2-3 year  period. Please follow proper safety procedures when handling this situation. If growers are unsure what to do contact the bin manufacturer or local extension.

Preparation for 2010 and beyond. Since all of these ear and cob rots over winter in the soil or on residue, the next issue that needs addressed is how to prepare for 2010 and the future. Below are few agronomic tips in preparation for 2010 and beyond.

1) Genetic diversity is the number one key when battling ear and cob rots. 2009 showed how vulnerable a grower can be when genetic diversity is not met. It is true that there can be diversity within a hybrid family, although the best way to diversify is through genetics and by planting different families. By planting the exact same genetics year after year after year makes a corn field extremely vulnerable to ear and cob rots and other diseases for that matter. At AgriGold we recommend hybrids from 5 different genetic families in some maturities, each having a totally different genetic makeup. By using genetic families a grower can be assured that he is planting different genetics in each field, each year. This lowers a growers risk and vulnerability to ear and cob rots for next year and for the future. Unfortunately, all hybrids are at risk to ear and cob rot but some much more than others. Contact your local Corn Specialist about mixing genetic families to combat ear and cob rots.

2) Tillage is key when battling ear and cob rots. The fungus from Diplodia, Giberrella and cob rots start on previous years residue and are found in the soil each year. Burying old corn residue can slow the growth process tremendously. Some growers utilize moldboard plows still to bury old residue. This is the ultimate form of tillage because all residue is buried, leaving less infected soil on top of the ground. If corn growers still own a  moldboard plow or have access to one, it would be highly recommended to moldboard some of the most  severely infected fields on the farm first. Disc rippers are still a good tool to use because fresh soil is brought up from down deep and residue is still placed deep into the soil profile. When using a disc ripper in the operation and soil finishing is concluded, very little residue is left on top of the ground. Always make sure conservation guidelines are met when getting aggressive with tillage.

3) Minimum tillage and conservation tillage like no till and strip till are great practices except when dealing with ear and cob rots. Most growers realize the many challenges that are faced when growing corn after corn in no till and strip till environments, so these practices are very minimal throughout the corn belt. If corn growers are utilizing these minimal tillage methods in corn after corn fields and dealing with severe ear and cob rot infestations, it would be highly recommended to move to a crop rotation immediately. Then in years to come try to make good hybrid decisions for those severely infested fields.

4) Crop rotation is certainly a key in combating ear and cob rots. Many growers have been utilizing this practice for years. Crop rotation certainly lowers the level of ear and cob rotting fungi because a different host is utilized. Although just because a field infested with ear and cob rot in 2009, goes to beans or another crop in 2010, a rot free environment can not be assured for 2011. Once severely infected with ear and cob rot fungi, it may take years to get back to minimal levels of the infecting fungi.

5) Stalk shredding and stalk decomposing are practices that may have some merit against ear and cob rot. It makes good sense to chop or pulverize infected stalks and residue to try to lessen the host longevity within the soil. Although more research needs to be done to make sure this is a viable practice in reducing ear and cob rot infections. Decomposing stalks in the fall or early spring with a nitrogen source is a super corn on corn practice and has shown merit to lessening the dreaded nitrogen deficiency that is commonly seen in corn after corn fields. This practice has been utilized for many years and is known as jump starting and front loading with nitrogen in the AgriGold system.

Categories: Plant Health, Corn Harvest

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