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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2010-19

Dates Covered: 
June 29, 2010 - July 6, 2010
Jon Rausch

Why is vomitoxin harmful and how toxic is it?

Vomitoxin research on humans is prohibited for legal and moral reasons, but we do know the effects of vomitoxin on animals with similar body systems to humans (such as pigs and primates).  Low levels of vomitoxin (0.05 to 0.1 mg/kg body weight) can cause vomiting in pigs – this would be similar to exposing a 175lb person to 0.0003 ounces of vomitoxin (a VERY small amount!). In humans, scabby grain has been associated with food poisoning symptoms (nausea, abdominal pain, dizziness and fever) 30 minutes after consumption. Long-term and continuous exposure to even lower levels of vomitoxin may cause dangerous reduction in appetite, weight loss, damage to the gastro-intestinal tract and impair the immune system.   

Does vomitoxin cause cancer?

Vomitoxin has not been reported to cause cancer. However, scabby wheat (and moldy corn) may contain other toxins that are just as harmful as or even more harmful to humans and animals than vomitoxin. Some of these other toxins do cause cancer.

What are the precautions for harvesting grain with scab?

An air-conditioned combine cab with appropriate filters cuts down exposure to dust, and consequently, vomitoxin at harvest. It is important to note that the chaff and other parts of the wheat head contain much higher levels of vomitoxin than the grain itself. The scab fungus infects and spreads through these tissues first as the grain is developing in the field. Dust from chaff containing vomitoxin may be more harmful than dust from ground grain.

Do I still need to use gloves and masks in the seed house?

Yes. It would seem reasonable to think that the problem will decrease once you leave the field, since lots of scabby kernels and most of the contaminated chaff, straw, and dust are left out there. However, if we consider the time spent in the seed house handling scabby grain, the exposure to mold and vomitoxin may be just as high, if not higher.   

How do I know if I am being affected by vomitoxin?

Quite often scabby grain will contain multiple molds and toxins. As such, symptoms of mycotoxicosis (disease caused by mycotoxins in humans and animals) usually result from the combined effects of these toxins, and are often due to the ingestion of contaminated food products. Skin and eye irritations are definitely topical symptoms of over-exposure, but for more serious concerns, laboratory exams and a medical doctor’s opinion will be needed. Some symptoms can be confused with allergic reactions.

What about inhaling vomitoxin?

Vomitoxin is not found “freely floating” in the air.  However, it is present in dust particles from wheat chaff and grain present in elevators, bins, seed houses, grinding facilities, etc.  A dust mask should be worn whenever handling contaminated grain. Read the article by Jepsen and Fleming, Dust Mask Protection from Wheat Dust, (in this issue of C.O.R.N)  for information on the health effects associated with the inhalation of dust particles.

Handling scabby grain with bare hands?

Although mycotoxins are of greatest concern when ingested with contaminated food products, some toxins, including vomitoxin, can be absorbed through the skin. And remember, vomitoxin may not be the only toxin present in moldy grain. Gloves (preferably latex/nitrile) should be worn and handlers should wash hands and other exposed skin thoroughly after handling molds grain.  The biggest danger is bringing hands that have touched scabby grain to your mouth.

What about straw from scabby fields, will it contain mycotoxins?

Yes. Straw from scabby fields does contain vomitoxin and other mycotoxins. Results from studies done at the University of Illinois (with laboratory tests done at North Dakota State University) confirmed that vomitoxin levels may exceed 2 ppm in wheat straw, even in field treated with fungicide. As a result, the same caution exercised when handling and feeding scabby grain should be exercised with dealing with moldy straw. Get the straw tested before using it for silage or bedding. The risk of contamination is much lower when straw is used for bedding; however, you should still avoid straw with very high levels of vomitoxin, since it is impossible to tell how much the animals will munch on the straw.

Over accumulation of grain dust is also hazardous to the performance of the human lungs. As a person continues to accumulate agricultural dusts over multiple seasons, the less effective their lung capacity becomes. Compare the human lungs to a shop vac – a person’s lungs can only tolerate so much dust before it starts to become slow and inefficient.  Agricultural dusts come in multiple sizes, and it’s the fine grain dust that can penetrate deep into the lung cavity and cause the blockage.

Protection from wheat harvest dust is important for everyone. Respiratory protection provides a barrier from the molds and mycotoxins, as well as the other particles that compose grain dust. The good news is that this recommended respiratory protection is not complicated to find or even use.  It’s a dust mask.

There may be several dust masks available at the local farm supply or hardware stores, however not all of them are recommended for agricultural use. The best protection is provided by the two-strap dust masks that are labeled as N95. They should also be identified as NIOSH or MSHA approved (National Institute for Occupational Safety Health and Mine Safety and Health Association). The N95 models mean that 95% of the smallest particles - ones that can get into the lungs where they cause damage - are prevented from going through the mask.

Wearing a mask requires the body to breath differently, and often times can cause trouble for the user. Also, wearing the mask in hot weather can add additional strain on the user. To alleviate some of these problems, manufacturers have added an exhale valve. Look for this feature on the N95 dust mask.

Not all workers can wear a dust mask. Some individuals may already have lung disease and find it impossible to breath through a mask. A person with facial hair cannot obtain an adequate seal around the face, and would need a powered air supply (not self contained). Likewise, persons with glasses need to adjust the straps so they don’t compromise the seal around the nose and cheeks. A physician evaluation will assess the ability to wear a mask, and the trained physician or a nurse can do the fit testing.

Wearing the mask in high exposure areas is recommended. The mask will need replaced after several hours of use in high dust situations, or it may last several days in low dust use. Store the mask in a clean area when not in use – a ziplock plastic bag offers good storage space.

The N95 respirator will protect workers from most of the common agricultural dusts. Like other farm chores, wearing the respirator may take some adjustment. The wearer may need to pace themselves and take more frequent water breaks. However, the initial extra strain it places on the body is a trade off for the protection the mask is offering to the long-term health capacity of the lungs. Protection from molds and dusts is more of an immediate concern than the inconvenience of wearing the mask.

To scout for eggs, inspect a minimum of 20 plants at 5 locations in your field.  Eggs are normally laid on the upper surface of the top most leaves.  Eggs are laid in masses of 20-100, and are first white in color.  After a few days, they turn tan, and then turn a deep purple.  Egg stage lasts about a week, but once eggs turn purple, larvae will emerge within 48 hours.  If 5% or more of corn have egg masses, treatment is necessary once larvae have emerged—western bean cutworms are protected against treatment in the egg stage.  If eggs are located, please contact your local extension educator or one of the field crop insect specialists (, 330-263-3730 or, 330-263-3727).   

Source: OSU Entomology

When flooding occurs for 2 or more days – CO2  (carbon dioxide) builds up in the soil and basically suffocates the roots.  When this occurs the roots are killed and severely damaged.  The roots are still white, they may have brown, black or even purple lesions, but these are not the primary cause of death.  From these roots, the root stele is still intact and the outer layer is easily pulled off – so the roots look like rat tails.  The plants will be stunted and keep most of their leaves, but they will wilt when the weather is hot.  In many cases, these plants will re-root and continue to grow and will yield – how much they will recover really depends on the next 6 weeks.  In some cases, the plants just got can’t recover and they will slowly die over the course of a week or more.

Flooding injury

The root rotters, especially the watermolds, are favored by the saturated soil conditions.  Here once the infections take place and the roots turn brown – they are soft and easily disintegrate between your fingers.  For soybeans at the V3 and later, Phytophthora stem canker can be found – the whole stem, both inside and outside will turn a chocolate brown color.  If you are in doubt, send the samples into the Soybean Pathology Lab, The Ohio State University/OARDC, 1680 Madison Ave., Wooster, Ohio 44691 and we can take a look. 

Symptoms of Phytophthora root root typically appear about 7 to 10 days after a heavy saturating rain. But only on susceptible varieties.  So if a variety has a gene that is effective or has very high levels of partial resistance, then the stem rot phase will not develop.  We never see the stem rot phase after the V3 in North west Ohio where more susceptible varieties are getting clobbered.  The other key is that this will occur on scattered plants.  It may be in a patch, but there will be healthy plants mixed in with the dying plants. If it was flooding injury the whole patch of soybeans will be clobbered.

Phytophthora stem rot

Our heavy soils are making it a bit more challenging this year than in previous years.

In the southern US, soybean rust was identified in Alabama.  That rust supersleuth extraoridnaire, Dr. Ed Sikora was climbing through a kudzu patch.  He reported a total of 9 leaves out of hundreds with a few pustules.  Based on previous years, this will still take a very long time to build up inoculum to impact Ohio.  What this does demonstrate, that our colleagues to the south are fantastic and their monitoring is critical for our management plans.

Breaks in the stalk usually occur at nodes (along nodal plates) below the ear. When soil moisture and temperature conditions are favorable for growth during this stage of plant development, plants elongate rapidly but stalks are unusually brittle. Stalk brittleness is greatest in rapidly growing corn under high temperature, high soil moisture conditions. There is speculation that rapidly growing plants are more susceptible to snapping-off for several days during the few weeks before tasseling because there has been little time for plants to develop lignified tissues at the nodes.

Although we encounter green snap problems periodically in Ohio, it's usually a more serious problem in the western Corn Belt. In Nebraska, where wind storms are more common, green snap has caused major stand losses in the past. Vulnerability to green snap damage does vary among hybrids. However, all hybrids are at risk from such wind injury when they are growing rapidly prior to tasseling. The use of growth regulator herbicides such as 2,4-D or Banvel has also been associated with stalk brittleness, especially if late application or application during hot, humid conditions occur. Once the crop tassels green snap problems generally disappear. Back in the 1990’s, Nebraska researchers observed that it was often the most productive fields with the highest yield potential that experienced the greatest green snap injury. They concluded that factors promoting rapid growth early in the growing season also predisposed corn to greater green snap injury.


Elmore, R. 2005.Mid-to-late season lodging. Iowa State University Integrated Crop Management Newsletter IC-494(21)161-162.
Carter, P.R. and K.D. Hudelson. 1988. Influence of simulated wind lodging on corn growth and grain yield. J. Production Agriculture. 1:295-299.

Strong winds can pull corn roots part way out of the soil. The problem is more pronounced when soil are saturated by heavy rains accompanying winds. If root lodging occurs before grain fill, plants usually recover at least partly by "kneeing up." This response results in the characteristic gooseneck bend in the lower stalk with brace roots providing above ground support. If this stalk bending takes place before pollination, there may be little effect on yield. When lodging occurs later in the season, some yield decrease due to partial loss of root activity and reduced light interception may occur. If root lodging occurs shortly before or during pollen shed and pollination, it may interfere with effective fertilization thereby reducing kernel set. Several university studies have been performed to assess the impact of wind lodging on corn growth and grain yield.

Iowa State University researchers forced V10 corn to “root lodge” at a 45 degree angle in plots with and without rootworms. Grain yield of root lodged corn without rootworms yielded 11 and 40 percent less than the control in the two years of the study while root lodged corn with rootworms yielded 12 and 28 percent of the control. Years were a major factor affecting the yield response. The ISU researchers concluded that “root lodging was more detrimental to biomass accumulation and grain yield than corn rootworm injury caused by larval feeding.” In another ISU study that evaluated natural root lodging, root lodged plants intercepted 28 percent less light than plants that were not root lodged.

In a University of Wisconsin study, root lodging was simulated by saturating soil with water and manually pushing corn plants over at the base, perpendicular to row direction. Wind damage was simulated at various vegetative stages through silking (V10 to R1). Compared to hand harvested grain yields of control plants, grain yield decreased by 2 to 6%, 5 to 15% and 13 to 31% when the lodging occurred at early (V10-V12), mid (V13-V15) and late (V17-R1) stages, respectively.

Elmore, R. 2005.Mid-to-late season lodging. Iowa State University Integrated Crop Management Newsletter IC-494(21)161-162.
Carter, P.R. and K.D. Hudelson. 1988. Influence of simulated wind lodging on corn growth and grain yield. J. Production Agriculture. 1:295-299.

From a pure fertilizer standpoint, wheat straw contains very little in terms of phosphorus (P2O5) but moderate amounts of nitrogen (N) and potassium (K2O).  The actual amounts of N, P2O5, and K2O contained in a ton of wheat straw are 11, 3, and 20 pounds, respectively (or an analysis of 0.55-0.15-1.00 if it were printed on a fertilizer bag).  Actual nutrient content can vary based upon environmental conditions during the growing season and soil nutrient supply, so if one really wants to know the actual value, straw analysis can be conducted by any lab that processes plant samples. 

How much is that straw worth from a nutrient perspective?  Well, it obviously depends upon the current market value of nutrients.  Using today’s prices, a pound of N, P2O5, and K2O costs $0.50, $0.50, and $0.41, respectively.  Thus a ton of straw will contain $15.20 worth of nutrients. Again, this number can be variable, but it gives you a starting point for your own economic analysis.

Tissue testing may yield some insight on the nutrient content of the crop, and the normal range for zinc is 20-70 ppm with values of over 300 ppm considered toxic.  With a foliar application, 0.5 to 1.0 pounds of zinc per acre is the recommended amount if using zinc sulfate.  If a zinc chelate is used, apply the equivalent amount of 0.15 pounds per acre.  With either source or zinc, use 20 gallons per acre of water to treat deficiencies.

If you have not traditionally experienced zinc nutritional deficiencies (and you are not observing deficiency symptoms) then application of zinc is not warranted.  For those fields that are exhibiting zinc deficiency between tile lines yield improvements may occur with foliar applications, but results will likely be variable.  We would really prefer a tissue test that clearly indicates a deficiency before promoting widespread application. 

Other resources

Univ. of Minnesota:


In order for producer’s to protect their rights, it is imperative to report any damage in the required time frame and seek advice from the insurance company before proceeding with harvest or destruction of the damaged crop. Failure to do so may jeopardize the claim. Crop insurance policies require that farmers notify their company within 72 hours of noticing a loss. It is important that farmers be proactive in checking their fields to determine if there is any damage to the crop before harvest. Quality adjustments are available for loss in value for conditions such as low test weight, damaged kernels, and shrunken or broken kernels. Discounts made for crop loss purposes may not be the same as those seen at the elevator. For example, quality discounts begin when the test weight is less than 50 pounds, defects are above 15% or grade is U.S. No. 5 or worse.

Any production of extremely poor quality wheat that has a value not located on the discount factor charts in the Special Provisions of Insurance (“off the discount tables”) is adjusted by taking the actual sale price based upon the Reduction In Value divided by the local market price to equal the discount factor for the production. In the event that the production has a Zero-Market Value Production, RMA loss procedures require insurance providers to make every effort to find a market for the production before declaring a zero value. Therefore, insurance providers will not be making declarations of zero market value until they can firmly establish that there is no market for poor quality grain.

Quality adjustments are based on samples obtained by the adjuster or other disinterested parties authorized by the insurance provider, such as an elevator employee. Harvested and delivered production samples taken from each conveyance and then blended may be accepted under certain conditions. If vomitoxin is suspected, the sample must be collected before the grain is placed in storage to be eligible for quality adjustment. The samples should be placed in a heavy paper bag for delivery to an approved laboratory for a determination of whether vomitoxin is present.  There is a minimum number of samples required based on acreage.  For a field of 10 acres or less 3 samples are required: 40 acres or less 4 samples and the one additional sample for every additional 40 acres or fraction thereof.  Examples: 9 acres = 3 samples; 13 acres = 4 samples; 63 acres = 5 samples; 110 acres = 6 samples.

There are special problems that arise when examining quality adjustments such as vomitoxin in wheat.  The first problem is the elevator’s discounts that are applied to the wheat.  They may not align with the calculations determined by RMA, resulting in a discrepancy between the discounts taken by the elevator and the coverage provided from the indemnity payment.  The second problem is the adjustment that occurs to the proven yield for this year’s crop that becomes part of the farm’s 10 year actual production history (APH).  Since price is fixed at the planting or the harvest price, the quality loss adjustment is attributed to the yield.  In the example below, a producer has purchased 4,500 bushels of coverage (45 bu/a) on his 100 acres of wheat. At harvest 40 bu/a were harvested with an average vomitoxin level of 10 ppm. If no quality adjustment is made, the APH for 2010 is 40 bu/a and the indemnity payment is for 500 bushel.  If quality adjustments are made, the APH becomes 20 bu/a in this example and the payment would be for 2,500 bushels.  This difference in yield might lower the farms APH enough to make the increased indemnity payment less attractive, especially if the discount taken at the elevator was significantly less than the calculated loss.

Example of coverage calculation:

Producer has actual production history (APH) of 60 bu/acre

Producer plants 100 acres; elects 75% coverage level

60 bu/acre X 100 acre X 75% = 4,500 bu coverage

Example with no quality adjustment:

Producer harvested 4,000 bu Production to Count (PTC)

4,500 bu coverage – 4,000 bu PTC = 500 bu shortfall

Indemnity based upon 500 bu X price election

Example with quality adjustment:

Producer harvested 4,000 bu Production to Count (PTC)

Production is quality adjusted to 2,000 bu PTC

4,500 bu coverage – 2,000 bu PTC = 2,500 bu shortfall

Indemnity based upon 2,500 bu X price election

Farmers also need to think about the implication on ACRE and SURE in claiming the quality adjustment for crop insurance purposes.  SURE payments are 60% of the difference between the SURE guarantee and all crop revenue.  All crop revenue includes insurance indemnities, prevented planting payments, other federal aid for same loss, 15% of direct payments, all ACRE, counter cyclical, and market loan program payments, and the estimated actual crop revenue from farm.  Taking the quality adjustments would increase the insurance indemnities while lowering the estimated actual crop revenue for a net sum of zero (or close to zero).  In the event there is a 2010 SURE payment, taking the quality adjustment should have minimal impact on the SURE payment.

If the producer has enrolled in ACRE, the farm’s five year Olympic average is used to set the farm trigger.  There is nothing in the literature that would indicate that the quality adjustment would affect the 2010 crop yield used in this calculation. Producers can still use elevator receipts to verify yield so the actual yield before quality adjustments would be used.  Even if the 20 bushel yield in this example was used in calculating the Olympic average, it would be the low year and excluded from the average. This only becomes problematic if there is another very low year in the past five years or in the future.

As a final comment, producers should contact their crop insurance provider as soon as possible to discuss potential losses and receive the correct procedures to follow. This will help insure that the producer can collect an indemnity payment if the conditions warrant.  Just because a producer contacts their crop insurance provider, does not require them to file a claim, if they choose not to following harvest.

Producers with a Contract                       

 Producers who have a contract with a buyer must look to the contract to determine their rights. All provisions, including any small print on the back of the contract, must be read entirely before assessing legal rights. The language of the contract is what matters; any verbal agreements made outside the contract have very little effect in enforcing legal rights. Even if the producer and buyer agree to certain terms, if the terms do not find their way onto the contract then the parties are probably not bound by the terms.

 In regards to Vomitoxin, the key terms are those describing the quality of the wheat required to be delivered. Contracts usually require No.2 wheat to be delivered. No. 2 wheat is a grade established by the USDA and may have up to 4% damaged kernels. The USDA defines damaged kernels as “Kernels, pieces of wheat kernels, and other grains that are badly ground-damaged, badly weather-damaged, diseased, frost-damaged, germ-damaged, heat-damaged, insect-bored, mold-damaged, sprout-damaged, or otherwise materially damaged.” Therefore, if the only grade standard in the contract is No. 2 Soft Red Wheat, a producer’s wheat should not be rejected or discounted solely for Vomitoxin unless more than 4% of the kernels are diseased or otherwise damaged. The 4% threshold is the accumulation of all damaged kernels and not just a single type of damage.

Some contracts will include more restrictive grade terms such as “must be suitable for human consumption” or “must meet all FDA guidelines.” The FDA has not established a minimum threshold for raw wheat for human consumption. The milling and manufacturing of wheat can reduce vomitoxin levels. Finished wheat products like flour and bran must contain less than 1 ppm if used for human consumption. The FDA has established a 5 part per million (ppm) threshold for hogs and 10 ppm threshold for cattle and poultry. Therefore, a miller that requires wheat to meet FDA standards can reject wheat if the flour or other final product would contain more than 1 ppm vomitoxin. It is important to note that wheat could have less than 4% damaged kernels but have more than 1 ppm vomitoxin. That is, the USDA No.2 wheat grade is a completely different standard that the FDA’s ppm standard. 

Producers that have wheat rejected can have the dual problem of having wheat rejected and still being obligated to fulfill the contract. A worse case scenario would see a producer not being able to sell his wheat due to high vomitoxin levels while still being required to fulfill his contract obligations for untainted wheat with the elevator. Typically a buyer will reject the wheat without requiring the producer to fulfill the contract.

Producers without Contracts

A producer who intends to sell a load of wheat to a buyer without a contract has very little legal protection from the corn being rejected.  The buyer is under no obligation to buy the wheat and can simply opt not to buy the wheat for any reasonable reason.  Without a contract, the buyer is not bound to any predetermined grade standards.  Even the smallest amount of vomitoxin in the wheat could cause it to be rejected.

Disputed Grain Samples

Producers have the right to appeal the grain grading determination performed by the elevator. The Federal Grain Inspection Service (FGIS) oversees grain grading procedures and methods and also provides inspection and appeal services.  A producer who disputes the elevator’s grading can send a sample to FGIS and FGIS’ determination will be binding on both parties. A FGIS office is located in Toledo. For more details and information on grading appeals, contact FGIS at 419- 893-3076‎.

Crop Insurance

Some crop insurance policies cover Vomitoxin damage. The wheat must be checked by an adjuster while still in the field to avoid tainted wheat from being mixed with untainted wheat in bins. Many producers opted to not file a claim on their corn crop due to the significant impact on APH. 

Future Implications

Will we see grain contracts move away from the USDA No.2 Wheat standard and towards the FDA ppm standard for vomitoxin and other mycotoxins?  Buyers relying on the USDA standard could get stuck buying grain that exceeds the FDA’s ppm standards.  Unless blended with non-tainted grain, this grain would seemingly be unmarketable as it could not be used for human consumption, livestock consumption, and/or export. Producers should anticipate possible changes to grading standards in contracts offered by elevators and other buyers.  A careful reading of all new grain contracts should be a must for producers to make sure they fully understand the quality and grade of grain they are expected to deliver to the buyer.

Producers are advised to check with their crop insurance company and Farm Service Agency on harvest restrictions for cover crops.  Harvest of cover crops may not be allowed until after November 1.

If a burndown or residual pre-emergence herbicide was applied earlier this spring, then check the label for restrictions on planting subsequent crops.

A cover crop will help restore the soil tilth and protect the soil from further wind or water erosion. 

Germination of summer seeded cover crops will be improved if drilled versus broadcast.  If hot, dry weather occurs after seeding, a drilled seed has a better chance of establishment.

To prevent cover crops from forming viable seed, mowing or herbicide applications may be needed.  This will ensure that cover crops will not reseed and interfere with next year’s grain crop.  Cost estimates for seeding and managing cover crops should be done so producers are aware of these input expenses.

Will wheat be planted in fall 2010?  If so, there is limited time for cover crop growth and benefit, therefore cover crop expenses should be minimized.  Buckwheat, millet, or sudangrass may be the best options in this timeframe.  Be sure to mow the buckwheat before seed set occurs to prevent unwanted carryover seed. 

Cover crops recommended where wheat will not be planted. 

A mixture of cover crops will ensure that something will fill in over variable soil types and conditions.  Having summer and fall for growth will allow deeper rooting and more time for nitrogen fixation.  Therefore, mixtures which include radish, legume, and a grass species will provide the best overall soil improvement desired, such as compaction correction.  Be aware that planting seeds of different sizes may require using a small seeder attachment on a drill for clover and radish seed.   Radish may bolt when planted mid-summer, so mowing will prevent seed formation.  Radish scavenge nitrogen, form deep taproots to relieve compaction, and compete well with annual weeds.

Cowpea is a summer seeded legume which does better under hot, dry growing conditions. Crimson clover and Berseem clover can also be summer seeded if moisture is not limited.  Winter pea/field pea and Hairy Vetch establish better after August 1.

Oats and cereal rye can also be added as a grass species.   These are best planted after August 1.

Reldan is no longer labeled or allowable as a residue on stored small grains.

Most other products have been discontinued as well and they didn't work all that well anyhow.

Tempo can be used as an empty bin, but it should have been done by now or as soon as possible.

  1. Most populations are now glyphosate-resistant and many of these are also ALS-resistant
  2. It’s usually not possible to use 2,4-D ester and wait 7 days until double-crop soybean planting.
  3. Marestail that were tall enough to be cut off by harvesting equipment will be even more difficult to control. 

Where the marestail are not resistant to glyphosate, application of glyphosate at 1.5 or more lbs ae/A should be an economical and effective approach, or a mixture of glyphosate and Sharpen.  The addition of FirstRate or a chlorimuron-containing product can also improve control if the population is not ALS-resistant, and provide some residual broadleaf weed control.  However, results of a current trial we are conducting suggest that a switch away from a glyphosate-based burndown may be the best strategy where the marestail are resistant to glyphosate.

The population in this trial was resistant to glyphosate and ALS inhibitors, and had survived early-May application of glyphosate.  We applied burndown treatments on June 1 when most of the plants were about 4 to 15 inches tall.  The upper part of the taller marestail plants had branched out in response to the early glyphosate treatment, and were generally more bushy than a marestail left undisturbed through early June. 

We applied a variety of treatments, including combinations of glyphosate with 2,4-D and/or Sharpen, and combinations of Ignite or Gramoxone with 2,4-D and/or Sharpen and/or metribuzin.  None of the treatments provided more than 83% control of the marestail 4 weeks after treatment, although several were in the 80-83% range.  The better treatments included (all treatments included AMS also):

83%    Glyphosate (1.5 lb) + Sharpen (1 oz) + 2,4-D ester (0.5 lb) + MSO
82%    Ignite (32 oz) + metribuzin (4 oz of 75DF)
81%    Ignite (22 oz) + Sharpen (1 oz) + MSO
77%    Glyphosate (1.5 lb) + 2,4-D ester (0.5 lb)
75%    Ignite (22 oz) + metribuzin (4 oz of 75DF)
75%    Ignite (11 oz) + Sharpen (1 oz) + metribuzin (4 oz of 75DF) + MSO
74%    Ignite (22 oz) + Sharpen (1 oz) + MSO


Ignite 32 oz and Metribuzin 4oz Ignite 32 oz and metribuzin 4 oz

We considered this to be a worst-case situation with regard to marestail burndown, and it’s likely that these treatments would be considerably more effective in some populations. 

We applied these same treatments on June 4 in another field where marestail had been growing undisturbed up until that point.  Plants were up to 30 inches tall in this field, but were mostly unbranched.  We did not have prior information about the herbicide resistance characteristics in this population, but our results indicated a relatively low level of glyphosate resistance and apparently no resistance to ALS inhibitors.  At the 14-day evaluation (next evaluation is later this week), almost all of the treatments resulted in 100% control.  The primary exception was glyphosate applied alone, which resulted in about 60% control.

Regardless of the type of soybean planted (RR vs LL vs nonGMO), it’s essential to control marestail and other weeds present at the time of planting.  The treatments shown above should control the other broadleaf weeds present after wheat harvest, although Ignite rates of 22 to 32 oz should be used where grasses are present.  Other considerations include cost of the seed and POST herbicides, potential for POST soybean injury, and need for POST control of marestail that emerges late or regrows following a burndown treatment.  Soybeans planted at this time of the summer should not be subjected to injurious POST treatments that might result in a cessation of growth if possible, since there is limited time for regrowth to reach maximum yield potiential. 

Assuming use of an effective burndown treatment, some of the herbicide/seed type options are:

  • Plant any type of soybean, and include a residual herbicide with the burndown treatment so that POST herbicides are not needed.  A good strategy in Roundup Ready or nonGMO soybeans even where POST treatment is needed, since POST marestail control might be impossible in these systems.  Residual herbicides used at this time of the year should be restricted to those that have little or no carryover risk – such as metribuzin, Valor, or low rates of chlorimuron or cloransulam products.
  • Plant a LibertyLink soybean, and apply Ignite POST as needed.  Probably the best option for control of later-emerging marestail or plants that regrow after the burndown.
  • Plant a Roundup Ready soybean and apply glyphosate POST.  Should work for most weeds, but not a good choice if the POST application needs to control marestail.
  • Plant a nonGMO soybean and apply conventional POST herbicides (Flexstar, Fusion, Select, etc) as needed.  This system has the most potential for soybean injury, but seed may be cheaper than the other systems.  Not a good choice if the POST application needs to control marestail.


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Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.