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Ohio State University Extension


C.O.R.N. Newsletter 2011-05

Dates Covered: 
March 11, 2011 - March 18, 2011
John Yost

“It is well-documented that glyphosate promotes soil pathogens and is already implicated with the increase of more than 40 plant diseases;…...”

Based on the number of acres I’ve walked, the samples we have received, the talks and literature I have attended and read; and our own research here at the OARDC, this statement just isn’t true.  I cannot document that there has been an increase in over 40 diseases in this state, nor in the north central region since 1998 when roundup ready soybeans were first widely planted in Ohio.  Glyphosate inhibits a key enzyme which is involved in the synthesis of key amino acids in the plant, and many fungi and bacteria also have this same pathway.  In plants, aromatic amino acids are the building blocks for many of the defense compounds such as glyceollin in soybean as well as suberin and lignin.  When round-up ready soybeans were first planted this was one concern that was soon alleviated.  Few studies have evaluated the development of specific diseases in response to glyphosate applications, but in those that have, the results did not support this claim.

One of these studies was done by a group at Southern Illinois University, which compared round-up ready soybean cultivars with and without glyphosate for the development of SDS.  There were no significant differences in the level root infection, SDS symptom development, nor colonization of roots between the sprayed and unsprayed plots of the same variety.  Their primary conclusion was that the development of SDS in their region on round-up ready soybeans was due to the lack of resistance to this pathogen and NOT due to glyphosate applications.  We have witnessed this in Ohio as well.  Specifically during 2009, Ohio had widespread occurrence of SDS.  One field in particular still stands out in my mind, where the producer ran out of soybeans of one variety and filled the planter with another variety – and to the row, the SDS was in all of the plants of one variety and none of the other.  Same planting date, same herbicide program, same environment – only the variety was different.

Since 2003, this lab has sampled a great number of fields for soybean and corn seedling blight pathogens, including Pythium spp., Phytophthora sojae, and Fusarium graminearum.  These have been sampled across conventional corn, soybean, as well as fields that receive predominately a round-up ready program.  There are many very reasonable explanations that we have been able to attribute to the development of these pathogens:  changes in resistance levels in varieties, increase in inoculum due to soil conservation practices and changes in seed treatment chemistry.  We have plots on our farms that have not had Round-up as a routine part of the management, we can achieve the same level of disease today (no greater-no less) as previous researchers working on the same pathogen in these very same fields.  One of the strengths of the land grant university system is the ability to maintain these long-term study plots which can monitor effects such as these.

In the scouting we have done, during the last 10 years, the outbreaks of Phytophthora sojae, Frogeye leafspot and Sclerotinia stem rot have directly led to a reduction/or lack of resistance to these pathogens in the varieties.  These were not due to the application of round-up.  A group at the University of Illinois/USDA-ARS screened glyphosate tolerant cultivars for their response to bacterial pustule.  They identified that approximately 30% of the cultivars were susceptible while the rest were resistant in a greenhouse screen.  Again, it was the inherent resistance level in the variety and not glyphosate tolerance that resulted in the development of this disease.  We have seen the same trends when we evaluate varieties for their response to Phytophthora sojae each year for the Performance Trials.  When the glyphosate tolerant lines first entered the trials, there levels of partial resistance were quite low but as time increased, more and more lines had higher levels of resistance.  Much of the resistance that we use in field crops is governed by multiple genes.  It takes a lot of crosses to get that resistance combined with the high yielding genes and many of these resistant traits do not have the best tightly linked markers.

In addition, glyphosate applications have been shown to reduce fungal growth in plates and as a result of applications in the field.  No, we are not going to start recommending glyphosate as a fungicide. Don’t even think about it. But in two cases, studies of soybean rust in Florida and wheat stem rust at Washington State University, researchers were able to show in experimental systems that there was indeed a reduction.  And this makes sense since this enzyme is present in plant and fungi. 

Lastly, every year, soybean pathologists from around the world complete a survey that examines the yield losses in soybean due to plant pathogens.  Alan Wrather at Univ. of Missouri has coordinated this effort for the past 20 years.  These surveys are based on actual field stops, diagnostic samples, and research plots.  These summaries have also not shown an increase in disease.  The following table is a summary of these surveys and the different diseases.  The yield loss recorded for each disease group fluctuates based on the incidence and severity of specific diseases due to the widespread planting of susceptible varieties and/or environmental factors that favor infections.


Yield loss in metric tons (x103) per year

Disease group








































































Leaf diseases = bacterial diseases, brown spot, downy mildew, frogeye leaf spot.

Stem diseases = anthracnose, brown stem rot, pod and stem blight, Sclerotinia stem rot, stem canker.

Root diseases = charcoal rot, Fusarium root rot, Phytophthora root rot, sudden death syndrome.

There is also a statement concerning the occurrence of a “new” pathogen that can be found in soybean and wheat meal that has negative impacts on animal health.  I can’t comment on this new pathogen as there is very little data and a lot of speculation, including that wheat was treated with glyphosate, which at this point wheat is not treated.  For this part, we will have to wait to see what the evidence truly is and what methods were used to identify this “new” pathogen.

One final thought or maybe this is a reality check.  Ohio producers, as well as those worldwide, need to double the world food supply within the next 20 years due to predicted changes in the world population.  Our 2 to 3 bushel per year is not going to cut it.  We will need every single tool, approach and tactic to make this happen and in my opinion includes genetically modified strategies.  We are reaching the limits of doing this via breeding and for some plant diseases, no resistance to the pathogen has been identified; thus novel genetically modified means are going to be the way that we can produce the food for the future.  I would like to say that it is in some plant somewhere but to get the resistance from one plant to another –  a gene transformation procedure can make this happen in 2 years vs 20.  If there are claims on safety – let’s get the data out there so we can adapt, put corrections in place and keep moving forward.  We have a lot of food to produce for a hungry world.  It must be safe and healthy to eat, sustainable to produce and affordable for the consumer.


The letter describes this new life form as being previously unknown, a “micro-fungal-like organism” having the size of a medium-sized virus, and present in “high concentrations” in Roundup Ready® soybean meal and corn, distillers’ meal, pig stomach contents, and pig and cattle placentas.  Furthermore, the letter indicates that this organism has been found in a variety of livestock that have had spontaneous abortions and infertility and that preliminary experiments have shown that it can cause abortions in a clinical setting.  The letter also alludes to a supposed escalation in the frequency of abortions and infertility in US livestock over the past few years, and speculates that this new pathogen may be responsible.

As near as we can determine, this new organism has not yet been described in scientific publications or in oral presentations at scientific meetings.  Results from research demonstrating its ability to cause abortions or other negative health consequences in animals have not been presented in these settings either.  It is very unusual that preliminary experiments that demonstrate an ability of an organism to cause abortion could already be competed without some description of the organism itself being presented to scientists in written or oral communications.  The discovery of a new organism, especially a pathogen, is usually revealed to the scientific community first for review of the findings by one’s peers and to encourage further research on the organism and any potential consequences of the findings on human, animal, or plant health.  If such a new organism, especially one with the potential detrimental effects on livestock health as described in some of these internet postings, has been discovered, the relevant information should be immediately available for review by scientists and veterinary diagnosticians and practitioners.

These postings also refer to the “escalating frequency” of abortions and infertility in livestock in the US.  It is true that abortion and infertility are important causes of decreased animal health and economic loss, and indeed, there are many potential causes of livestock abortion and infertility.  However, we are unaware of any documented “escalation” in their frequency over the last several decades during which time glyphosate or Roundup Ready® varieties of crops have been available and used widely.

Until such time as the claims of a new pathogen and increased levels of animal disease associated with it or glyphosate use, such as described in these recent internet postings, have been subjected to scientific review, farmers and livestock owners should be very cautious about attaching credibility to them.  Good record keeping, preventive health measures, and timely diagnostic procedures and laboratory submissions are the foundation of maintaining animal health.

Dr. Hartzler makes an extremely relevant conclusion in his article, which applies to the core problem with interpretation of some of the claims about glyphosate problems.  In reference to claims about the effect of glyphosate on rhizophere organisms, Dr. Hartzler states, “It is well documented that the presence of glyphosate in the soil can significantly impact microbial populations.  Due to the complexity of the processes that occur within the root zone, it is impossible to completely rule out negative effects of glyphosate on mineral nutrition or disease development in GR crops.  However, results from field research and our widespread experience with glyphosate on GR crops for over a decade do not indicate widespread negative impacts of glyphosate on these factors.”  This last point can be applied to the micronutrient and disease issues as well. 

A major problem we have with the negative glyphosate story being told is the almost complete lack of appropriately designed and repeated field research studies that validate the concerns that are being raised.  The meaning of “appropriately designed” here is that the treatments are designed to accurately assess the effect of one or more factors.  This and the treatment replication within studies, and the repetition of studies, is what allow scientists to draw valid conclusions.  In our opinion, growers trying to evaluate the glyphosate issue should be asking the developers of the negative glyphosate story to show results of this type of field research.  There appears to be instead a lot of discussion of physiological processes and how glyphosate can or does interact with these processes.  Without the appropriate follow up field research there is however no evidence that any of this is occurring in the field or more importantly, that it’s affecting crop yields.  The broader perspective here is that weather still has the most impact on determining crop yields given satisfactory management of the variables that can be controlled by growers, and crop yields continue to increase where weather has been favorable.

In at least one case where the negative glyphosate story contains a reference to field research, the research is inadequate to support the conclusions that are being drawn.   The research does not appear to have an appropriate treatment design, or to be repeated over sites or years (and we assume it’s not from a reviewed and published article).   The following data have been shown for postemergence application of glyphosate and/or various MN sources (means are significantly different when they have different letters).





% weed control*

No herbicide


46 a

0 a


24 oz/A

57 b

100 e

Glyphosate + MnCO3

0.5# Mn/A

75 d

91 de

Glyphosate + MnSO4

0.5# Mn/A

70 cd

93 e

Glyphosate + Mn EDTA

0.25# Mn/A

72 cd

100 e

Glyphosate + Mn AA

0.15# Mn/A

67 c

85 d

We assume that these data are used to support the conclusion that glyphosate reduces MN availability in the plant, because yield increased where MN was added.  However, this cannot be concluded without additional treatments where the MN sources were applied in the absence of glyphosate.  It’s possible that the glyphosate had no effect on MN processes, and the soybeans just responded to the addition of MN because they were deficient.  This is also an example of a confounded study, because the researcher failed to isolate the effect on individual factors on crop yield.  Yield here could be affected by both the absence or presence or MN and weed control, because the study was not conducted under weed free conditions.  In the end it’s impossible to determine the effect of any one factor on crop yield from these data.  The work that Robert Mullen and colleagues have conducted on this is an example of a much more complete approach, due to appropriate treatment design, repetition over sites and years, and determination of tissue MN levels. 

All of us that conduct field research, advise growers, or do the actual growing make daily observations about crop growth and the effect of myriad factors on it.  We can therefore draw rough conclusions that can be reinforced when we make the same observation over time.  Growers also observe trends in yields over time that can help them determine the effect of specific management decisions.  However,  it’s certainly possible to draw the wrong conclusion where general observations are made, but the effects of factors are not separated and tested appropriately.  A good example of this comes from a recent article ( that is largely in support of the negative glyphosate story.  In the article, a situation is described where one section of an Iowa soybean field was suffering from Sudden Death Syndrome (SDS) while the rest of the field was healthy.  The SDS-affected area had been planted to alfalfa the previous year, and the alfalfa was killed with glyphosate at the end of the season.  The part of the field without SDS had been planted to sweet corn the previous year and no glyphosate was used.  The conclusion was that the use of glyphosate in the alfalfa was responsible for the SDS in the soybeans the following year.  This conclusion obviously ignores the vast differences between alfalfa and corn, their effect on soil structure or tilth, and their susceptibility to or ability to host various diseases.  In short, the soybeans had been planted into what were likely two vastly different environments based on the previous crop.  This is not to say that the glyphosate could not have had a role, but without further research, the conclusion that it was responsible for the SDS was erroneous.

A similar example occurs later in the same article where an agronomist in Iowa is quoted as saying that whereas a decade ago corn plants stayed green and healthy well into September, corn has been turning yellow and then brown about 8 to 10 days earlier each season over the past three years.  Yield losses due to this early death were apparent in at least one of these years, and the phenomenon was attributed to increased use of glyphosate.  These observations were apparently not based on field research but instead on general observations.  It’s somewhat difficult to buy that this is a widespread yield-reducing phenomenon based on the high corn yields of the past several years.  As for the previous example, it should be possible to conduct field research to determine whether there is an actual effect of glyphosate on the time of corn death, especially if the phenomenon really is occurring as frequently as the agronomist claims (it’s really just as simple as having replicated strips within multiple fields, where half the strips in each field receive a POST glyphosate application and half don’t).   In both of these situations, we see no evidence of replicated field research, and in the end the reader is left to decide whether he believes a conclusion based on faulty reasoning or observation not supported by research.  This is not to say that the phenomena are not occurring, just that there is a way to concretely prove whether they are or not through well-designed field research, and this has not been done.

In the end, the best thing we can do here is to urge growers to use caution in interpreting the information about glyphosate that is being presented.  Whether this information is applicable to actual crop production situations is debatable and largely unproven.  It’s likely that some valid concerns are being raised, but overall this is just difficult to assess.  Some of the information does appear to be false or based on extreme extrapolation from narrow focus studies, with little to support it in the way of valid field research that investigates specific factors in a complex production system.  We believe it’s important for growers to always accumulate as much valid information about a subject as possible prior to making management changes, and the glyphosate issue is no exception to this.  We probably speak for most of the weed scientists across the corn belt when we state that we would be thrilled if glyphosate was used less frequently in current production systems, but only if this occurs for the right reasons (e.g. herbicide resistance issues).  We agree with the conclusion of the Purdue scientists in their analysis of the issue, which was: “We encourage crop producers, agribusiness personnel, and the general public to speak with University Extension personnel before making changes in crop production practices that are based on sensationalist claims instead of facts”.   

Data has been shared showing exudation of glyphosate from soybean roots may impact microbial communities in a lab setting.  The shift in the microbial community is from an environment dominated by manganese releasing organisms to an environment dominated by manganese fixing organisms.  While this has been demonstrated in a lab setting, does any field data exist to validate that glyphosate application can impact soybean manganese uptake?  The answer is yes.  There are published studies that have shown that application of glyphosate can result in decreased manganese concentration in soybean tissue.  Conversely, data collected from Ohio over 4 site-years has not shown that application of glyphosate (even at rates well in excess of the labeled rate) has influenced soybean manganese tissue concentration even two weeks after application.

The next question is, if application of glyphosate does impact manganese availability (and our data locally does not clearly indicate this), does it require manganese supplementation to alleviate the induced “manganese deficiency”?  Field experiments documenting positive impacts of manganese applications with or following glyphosate application are limited, so Ohio State University initiated its own research into the phenomenon four years ago.  Based upon 8 site-years of experimentation, we found one site-year (Northwest Research Station 2007)  that showed a positive response to foliar manganese application, and that site tends to have lower manganese tissue levels (indicating greater probability of response to foliar manganese).  At the Western Research Station, we have actually documented yield losses due to application of foliar manganese (2007 and 2009).  Tissue concentrations at the Western Research Station tend to be higher than 60 ppm, well above what is considered sufficient. 

Based upon our research into the phenomenon, we are not currently promoting the application of manganese on every acre with or following a glyphosate application (even if you are growing glyphosate tolerant soybeans).  If you are producing soybeans on a soil that tends to be manganese deficient (high soil pH, droughty, high organic matter) then application of manganese is something you should consider.  We recommend that you monitor tissue concentrations to give you some indication as to whether or not you should be making an application.  Tissue concentrations that consistently hover around the lower end of the sufficiency range (<30 ppm) are more likely to show a positive yield benefit, and just as importantly they are less likely to result in a yield decrease due to the application of manganese.  Tissue concentrations well into the sufficiency range (<50 ppm) are unlikely to benefit from manganese supplementation, and there is some risk of yield loss due to the application of manganese (most likely due to toxicity). 

If you do decide to make an application of manganese, our recommendation is to tank-mix the products and use an EDTA chelated form of manganese.  This does not influence manganese uptake associated with the application (from our data here in Ohio), but salt forms of manganese can decrease the efficacy of glyphosate.

If you would like to read a little bit more on the subject check out the following links:

Iowa State University

Purdue University

The debate among farmers and scientists has centered on how much nitrogen the legume actually captures and how much of that is released to a subsequent corn crop.  The economics of the investment of legume seed and extra production management need to be outweighed by the amount of nitrogen generated.

A successful establishment of legumes requires favorable weather conditions which provide enough moisture throughout the growing season.  Hot, dry weather in the summer can greatly reduce legume growth and potential nitrogen contribution.

Once a legume has been established, it is difficult to predict the amount of nitrogen that will be available to the following corn crop.  As the legume decays after tillage or herbicide treatment, the conversion into nitrate nitrogen usable for the corn crop will occur when soil moisture and temperature are favorable. 

There are other benefits of legumes in a three crop rotation like corn-soybeans- wheat including  the ability to reduce compaction, the reduction in soil losses through erosion, and the creation of a more favorable habitat for soil micro/macro-organisms. Even if no additional nitrogen was produced by legumes, these soil benefits alone may improve corn yields.  From our own research at the Northwest Research Station, we have found corn yield increases in a no-till system when red clover was frost-seeded in wheat prior to corn in 2 out of 3 site-years.  Red clover may also be harvested as forage creating another revenue stream for your operation.

Take home message – our data does not suggest dramatically cutting nitrogen rates when a cover crop is established (perhaps 30 pounds of nitrogen), and we have not identified conditions when the nitrogen contribution is more likely to occur. It does appear that in the poorly drained soils of northwest Ohio that a rotational benefit is likely to be observed when a legume cover crop is established after wheat.

1)    Applying chemicals with a sprayer that is not calibrated and operated accurately could cause insufficient weed, insect or disease control which can lead to reduced yields. Check the gallon per acre application rate of the sprayer. This can only be determined by a thorough calibration of the sprayer. Use clean water while calibrating to reduce the risk of contact with chemicals. Read OSU Extension Publication AEX-520 for an easy calibration method (

2)    How the chemical is deposited on the target is as important as the amount applied.  Know what kind of nozzles are on your sprayer and whether or not their patterns need to be overlapped for complete coverage. Make sure the nozzles are not partially clogged.  Clogging will not only change the flow rate, it also changes the spray pattern. Never use a pin, knife or any other metal object to unclog nozzles.

3)    In addition to clogging, other things such as nozzle tips with different fan angles on the boom, and uneven boom height are the most common causes of non-uniform spray patterns.  They can all cause streaks of untreated areas that result in insufficient pest control and economic loss.

4)    Setting the proper boom height for a given nozzle spacing is extremely important in achieving proper overlapping. Conventional flat-fan nozzles require 30 to 50% overlapping of adjacent spray patterns. Check nozzle catalogs for specific recommendations for different nozzles.

5)    Know your actual travel speed, and keep it steady as possible. Increasing the speed by 20% may let you cover the field quicker, but it also cuts the application rate by 20%. Similarly, a reduction of speed by 20% causes an over application of pesticide by 20%; an unnecessary waste of pesticides and money.

6)    Pay attention to spray pressure. Variations in pressure will cause changes in application rate, droplet size and spray pattern. At very low pressures, the spray angle will be noticeably narrowed, causing insufficient overlap between nozzle patterns and streaks of untreated areas. High pressure will increase the number of drift-prone droplets.

7)    Don’t waste your chemical. After all, you have paid for it. Spray drift wastes more chemicals than anything else. Don’t spray when the wind speed is likely to cause drift. Don’t take the risk of getting sued by your neighbors because of the drift damage to their fields. Keep the spray pressure low if it is practical to do so, or replace conventional nozzles with low-drift nozzles. Use other drift reduction strategies: keep the boom close to the target, use drift retardant adjuvants, and spray in early morning and late afternoon when drift potential is less.

8)    Carry extra nozzles, washers, other spare parts, and tools to repair simple problems quickly in the field.

9)    Calibrate your sprayer periodically during spraying season to keep it at peak performance. One calibration per season is never enough. For example, when switching fields, ground conditions (tilled, firm, grassy) will affect travel speed which directly affects gallon per acre application rate.

10)  Be safe. Read the chemical and equipment instructions and follow them.  Wear protective clothing, rubber gloves and respirators when calibrating the sprayer, doing the actual spraying and cleaning the equipment.

Ozkan 1

 Ozkan 2


Be well informed about the specific recommendations for a given pesticide, and follow the laws and regulations on pesticide application. Carefully read the product label to find out the specific recommendations.

For many years the winter temperatures have been used to predict the risk of Stewart's disease because higher populations of the flea beetle survive during mild winters than during cold winters. An index is developed that helps to predict the likelihood of the disease threat. This 'flea beetle index' is calculated as the sum of the average temperatures (Fahrenheit) of December, January and February.  We checked the average temperature for various locations in Ohio to determine the risk level according to the 'flea beetle index' for 2011. The locations and the corresponding indexes developed were: Wooster (OARDC) 75.7, Ashtabula 77.9, Hoytville (Northwest Research Station) 71.4, South Charleston (Western Research Station) 77.6, Jackson 88.6, and Piketon 90.1.

The flea beetle index is uses as such:
- Index values less than 90 indicate negligible disease threat,
- 90-95 indicate low to moderate levels,
- 95-100 indicate moderate to severe and
- values over 100 predict severe disease threat.

Compared with last year, it appears that northern Ohio was slightly cooler while southern Ohio was similar in terms of the index.  Although the overall risk of Stewart's bacterial leaf blight should remain low in much of Ohio, with only southern Ohio (Piketon) again considered to have a low to moderate threat, we would still recommend that growers scout for flea beetles, especially if they have planted a hybrid that is susceptible to Stewart's disease. For growers wishing to take preventive action against flea beetle, commercially applied insecticide seed treatments are labeled for flea beetles. You can see pictures of flea beetle injury and Stewart’s bacterial blight, and get additional information on Stewart's disease of corn, on the Ohio Field Crop Disease web site at Additional information on the flea beetle can be obtained from OSU Extension Fact Sheet CV-1000-94.


Certified Crop Advisor CEU =  0.5 NM, 1.5 CM, 0.5 PM credits.

Commercial Pesticide Recertification CEU = 2.0 hours Category 2A

Registration flyer at

Registration Deadline is March 24.  Call Alan Sundermeier at 419-354-9050 for more details.


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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.