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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2011-04

Dates Covered: 
February 24, 2011 - March 4, 2011
John Yost


Mullen 1


Figure 1.  Von Liebig’s barrel, a visualization of the concept known as the law of the minimum.

While the above statement regarding the law of the minimum is true, the barrel stave concept does have a flaw.  The law of the minimum has also been summed up, by some, with the statement “the availability of the most abundant nutrient in the soil is as available as the availability of the least abundant nutrient in the soil” (Wikipedia).  Is this true?  As it is illustrated, water is the factor limiting achievable yield (this is true quite frequently in dryland agriculture).  Since water is the limiting factor, would application of nitrogen provide any yield benefit?  Based strictly on the visualization and the Wikipedia statement, the answer would be no.  The presence of inadequate water precludes responsiveness to additional nitrogen.  Is this necessarily a true statement?

The short answer is not necessarily.  Using Ohio agriculture as an example, water is typically the nutrient limiting productivity, so does that mean that water deficiency precludes nitrogen response?  The answer is no.  Just to illustrate the concept, let’s consider nitrogen response in three different scenarios (Figure 2). 


 Mullen 2

Figure 2.  Nitrogen fertilizer response when water and phosphorus is a limiting factor (A); when only phosphorus is a limiting factor (B); and when water and phosphorus has been removed as limiting factors (C).

Line A represents nitrogen response when water and phosphorus are limiting, but notice that yield does increase as nitrogen rate increases (to a point).  So the fact that water and phosphorus are clearly at yield limiting levels does not preclude response to nitrogen.  Line B represents a scenario where water has been removed as a yield limiting factor, but phosphorus is still yield limiting; yet we still observe an increase in yield as nitrogen rate increases (again to a point).  So again, despite the fact that phosphorus is a yield limiting factor, supplying water and nitrogen results in a yield increase.  Line C represents a scenario where water and phosphorus have both been removed as yield limiting factors.

These observations are in direct opposition to a strict interpretation of the barrel concept.  Thus, the interpretation should not be that the presence of a yield limiting nutrient factor precludes response of some other limiting factor.  The most limiting nutrient does limit ultimate achievable yield, but removing other yield limiting factors (if they are truly deficient) will likely result in yield increases.

In practice, this means your job as an agronomic producer managing soil fertility/nutrient management should be to identify nutrient-based yield limiting factors to increase productivity.  This also illustrates that historic field research with lower yielding hybrids or varieties, still applies.  Newer hybrids/varieties may be better able to utilize water more efficiently (removing it as such a strong limiting factor), but it does not imply that our newer hybrids/varieties are going to be any more responsive to things like micronutrients.

If you have identified that your soybean crop is manganese deficient, for example, it is not necessarily because of the new variety you are planting (that may have a higher yield potential).  The deficiency was likely there all along. 

 To answer that question, a single broadcast N application was applied on frozen ground in late February or early March as urea, UAN (28%), or ammonium sulfate at the OARDC Northwest Research Station near Custar for three years. For two of the three years, yields from pre-greenup applications were as good as those made at greenup. However, one year, yields were only slightly better than the zero check treatment, indicating significant loss of nitrogen. In that loss year, all three N sources responded in the same manner -- significant reductions in yield. Thus the 28% did not “burn” into the soil, ammonium sulfate did not “stabilize” into the soil, and urea did not stay put until a rain. Basically, all three of the sources moved off the plots with water as the soil thawed out, much like losses from manure on frozen ground.

As a result of this study, Ohio State University does not recommend N applications prior to greenup knowing that in many years, there will not be a yield loss from pre-greenup applications. This recommendation is also based on the time when wheat utilizes nitrogen. Wheat needs very little N until after Feekes 6 or stem elongation (after the end of April). After Feekes 6, N uptake increases rapidly until flowering. Results from the same study above also found that grain yields were not reduced delaying single nitrogen application until Feekes 6. Thus, why take the risk from pre-greenup applications since the crop does not need large amounts of N until Feekes 6 and in some years much of the N may be lost from the pre-greenup application.

 In addition, the producer generally does not get N at a lower fertilizer cost in February or early March, and the producer assumes all risk if the N is lost. As a compromise between when the crop needs it and field conditions suitable for application, the university recommends single application of N to Ohio wheat between greenup and Feekes 6. However, it would not surprise us when producers tell us that they applied it before greenup and had no yield loss, but then there will be those years of regret from that decision.

We are in the middle of a two-year study to determine the most effective approach to burcucumber management in corn.  While we previously had an idea of the relative effectiveness of various PRE and POST herbicides, we lacked information on how to put together the most effective combinations of herbicides and application timings that could provide the most consistently effective late-season control.  There has been little previously published research on management of burcucumber, and none that resulted in the development of an overall effective system for management.

In our research, we were comparing the effectiveness of various residual (PRE) and POST herbicides, and also the timing of their application.   The residual herbicide treatments included Lexar, Corvus+atrazine, and Harness Xtra, which were applied PRE (at planting) vs early POST (V2 corn).  These were followed with various residual and non-residual POST herbicides, including Callisto, Spirit, and bromoxynil.  We also compared the timing of the POST application, and single vs multiple POST applications.  We had one research site in 2010 on nonGMO corn, and are planning for several more sites in 2011, including one or more with glyphosate-resistant corn.  Here’s what we observed in 2010:

- The Lexar and Corvus+atrazine were much more effective than the Harness Xtra for control of burcucumber between planting and the POST application.  Not only was the population of burcucumber much lower with the Lexar and Corvus+atrazine, but the plants were small and had not started to vine at the time of the POST.  Plants in the Harness Xtra treatments were much larger and some had already extended tendrils to the corn plants by the time POST herbicides were applied. 

- There was a trend for more effective control when the residual herbicides were applied early POST compared with application at planting.  But this was much less important than the choice of residual herbicide.  These results do indicate that delaying the residual herbicide application until corn is about V2 could provide more effective control in mid-season, and build a more flexible POST application window. 

- Choice of POST herbicide was more important than choice of PRE herbicide.  Application of Callisto at either 20- or 37-inch corn resulted in half the number of burcucumber plants at the end of the season, compared with bromoxynil.  More importantly, the Callisto resulted in a biomass (total above-ground growth) and burcucumber seed production that was about 97% lower than where bromoxynil was applied.  So the potential for the burcucumber to twine around corn plants and create a mess was much lower with Callisto, as was the seed production.  

- Spirit provided control generally similar to Callisto.  The end of season burcucumber population was higher with Spirit compared with Callisto, but the biomass and seed production were similar, so the Spirit prevented plants from producing substantial above-ground growth.  We were able to obtain similar levels of control where bromoxynil was applied POST twice.  Control with Callisto and Spirit was not improved where they were followed with a late POST (50-inch corn) application of bromoxynil.

- We monitored burcucumber emergence throughout the season in several nontreated areas.  The majority of the plants emerged in mid-June, but emergence started in early May and extended into early July.  We did not observe the substantial emergence that can apparently occur in mid-summer based on grower comments, so our 2010 results may overestimate the end-of-season effectiveness of the herbicide treatments we studied.

 So what does it all mean? 

Effective burcucumber management in corn requires a combination of PRE and POST herbicides.  It’s possible to start with a PRE herbicide that reduces the population, and also the size of plants, at the time of the POST application.  Herbicides capable of doing so include Lexar, Lumax, Corvus+atrazine, and Balance+atrazine.  Any of these should be much more effective for early-season control in comparison to atrazine premix products.  Results of our research so far indicate that the use of a POST herbicide treatment with both foliar and residual activity on burcucumber may be the most important component of a management program.  Callisto or Spirit (both have residual activity on burcucumber) provided more effective end-of-season control than bromoxynil, unless the bromoxynil was applied twice.  We expect that results with glyphosate would be similar to bromoxynil, since both herbicides lack residual activity.  We were able to obtain similar control with Callisto whether it was applied on 20-inch or 37-inch corn, but its possible that the later application could be more effective in a year when the burcucumber emerges in great numbers in late June or July.  We will hopefully know more about this after another year of research.

Quite often, the primary purpose of these new programs is to “preserve” or “protect” yield and not necessarily to manage diseases. Before presenting results from our 2010 trials, let us first recap how the yield is made in wheat in an effort to better understand the rationale behind current management recommendations. Growth and development of the wheat plant can be divided into four distinct phases, tillering, jointing or stem extension, heading, and ripening. The main yield components of the crop are head-bearing tillers per acre, spikelets per head, kernels per head, and kernel size. These components are determined at different stages in the development of the plant, therefore the crop needs to be managed during each of the four stages to achieve the best yield and minimize yield and quality losses.

Seeding rate, planting depth, fertilizer application, planting date, and weed and seedling disease control are all important for determining the number of tillers per acre, and as such, are commonly managed at planting or during the tillering stage of crop development. The head begins to develop and the number of potential spikelets per head and head size are determined during the late tillering and early jointing growth stages (Feekes 5 and 6). Nitrogen application is important at this stage of crop development since it can affect the number of kernels per head. Stresses such as severe drought at Feekes 5/6 may also reduce the potential number of kernels per head. However, the number kernels that ultimately develop per head and size of these kernels depend on pollination and grain fill. The flag leaf (the uppermost leaf of the plant) contributes about 75% of the compounds needed for grain fill. As a result, it is very important to protect the flag leaf from damage caused by foliar diseases and insects, since these may substantially reduce grain yield and quality if the damage occurs before grain fill is complete.          

Before the 2009-2010 growing season, most of the early (before flag leaf emergence) and late (after heading) foliar fungicide application programs had not been tested in Ohio with currently available fungicides. However, results from previous studies showed that the greatest benefits from foliar fungicide applications were obtained when applications were made between Feekes 8 and 10. This is largely because most of our major foliar diseases, with the exception of powdery mildew, usually develop and reach the flag leaf after Feekes 8-9. In 2010, we evaluated the effects of single, split, and double applications of several triazole (Prosaro, Caramba and Folicur), strobilurin (Headline), and combination (Twinline, Quilt, and Stratego) fungicides on powdery mildew, Stagonospora, head scab, and grain yield. Applications were made at green-up, flag leaf emergence, boot, and flowering. Among the single application programs, applications made at flag leaf emergence or boot did better than green-up applications in terms of foliar disease control and yield. A single application of a triazole at flowering provided the best control of head scab. Among the programs with double or split applications, we observed the best results with those treatments that included an application at full rate at Feekes 8-9. A single full-rate application at this growth stage did just as well or better than the grean-up+flag leaf or the flag leaf+flowering applications. Comparing a single application at flag leaf emergence with a single application at flowering, all of the tested fungicides resulted in better control of powdery mildew when applied at flag leaf emergence than when applied at flowering, and comparable levels of Stagonospora control were achieved with the two programs. This is largely because powdery develops early and as such applications made at flowering are generally too late to provide the best control of this disease. Stagonospora, on the other hand, usually develops later in the season, and in a wet growing season like 2010, foliar fungicides may still provide very good control when applied at flowering. In fact, because of the high levels of powdery mildew, Stagonospora, and head scab we had in 2010, the fungicide programs that provided the best overall control of all three diseases and resulted in the highest yield gain were those with a triazole applied at flag leaf emergence followed by a second application at flowering.

However, it is rarely ever beneficial to make two foliar fungicide applications in wheat in Ohio. The yield gain is generally not sufficient to offset the cost of two applications. If foliar diseases are a concern, then one well-timed application between Feekes 8 and 10 should be sufficient to control powdery mildew, Stagonospora, Septoria, and leaf rust. If head scab is of concern, a well-timed application at flowering will provide the best control of scab, while at same time provide protection against the late development of Stagonospora and rust. In general, conditions favorable for scab development are also favorable for Stagonospora.

In summary, here is what we observed in our trials and what we recommend:

1.  For foliar disease control, fungicides provided the best results when applied between Feekes 8 (flag leaf emergence) and Feekes 10 (boot).

2.  Applications made at Feekes 8 or 10 did better than applications made at Green-up or split applications in terms of disease control or yield response.

3.  If the variety is susceptible and weather conditions are highly favorable throughout the growing season, an application at full rate at Feekes 8 or 9 followed by a second at flowering may be beneficial, if the value of the crop is high.

4.  Fungicides are generally not beneficial when resistant varieties are planted.

5.  For adequate head scab control, fungicides should always be applied at flowers or as close as possible to this growth state.

Fungicides with strobilurin chemistry are not recommended for scab control since they have been associated with increased levels of vomitoxin in the grain.

Questions have been raised about the effects of ice on the crop in areas where the snow has melted and the water later becomes frozen. Being a cold season grass, the wheat plant can tolerate fairly harsh weather conditions. It is programmed for this by keeping the growing point (the crown) below the ground until conditions are warm in the spring. However, extremely cold conditions could still cause damage to the plant. Once the leaves are hardened (which occurs in the fall), they can tolerate temperatures between 0 and 10 F. Younger leaves are more tolerant to cold conditions than older leaves. Roots may be killed by temperatures between 23 and 26 F, but these are usually protected from such temperature by being below the soil line. The plant is only killed outright by low temperatures if the crown is damaged. So, essentially, unless the crown is killed, the plant will survive freezing conditions. For varieties adapted to cold conditions, such as those grown in OH, the crown can withstand temperatures as low as -9 to -11 F. The existing snow cover will provide the necessary insulation to prevent temperatures capable of killing the crown. Since most of our wheat was able to harden in the fall before the snow cover, the crown is less vulnerable to damages if the snow melts and extremely cold temperatures occur shortly after.

Over the last few years, interest in nematodes and the use of nematicide seed treatments in corn have increased among producers all across the Midwest. When present and in high numbers, nematodes can indeed cause considerable yield loss in corn, and quite often these losses may go undetected or may be attributed to other causes. In corn, nematode problems are usually very difficult to detect because these pathogens usually cause uneven growth, without any clear above-ground symptoms. Uneven growth could be the result of several factors including other soil borne pathogens, poor drainage, soil compaction, and herbicide carry over; nematodes are rarely ever considered the cause of such a problem. Several different types of nematode can attack corn including spiral, lesion, cyst (this is not the soybean cyst), stubby root, needle, lance, and dagger nematodes, and the level of damage and yield loss depend on the type of nematode present and the population level. Moreover, it is rare to find a single type of nematode causing the damage in any given corn field, these occur as a community which are comprised of a number of different species. Damage is usually caused by a nematode complex made up of several different types of nematodes or a nematode-fungi complex. Initial wounds made by nematodes, especially those that enter and feed inside the roots (endoparasites), may serve as entry points for infection by secondary or opportunistic fungi, adding to the overall level of damage.        

It is unclear whether we do indeed have a nematode problem in corn in Ohio and if a nematicide will be beneficial. As stated above, the impact of nematodes on corn is very difficult to discern. In Ohio, we have a very good database on the distribution and effects of soybean cyst nematode (SCN), but SCN does not affect corn. We do not have any information on the distribution or effect of nematodes on corn in Ohio. A survey of corn fields, focused first on those that are lighter soils and continuous corn is needed to determine which nematode species are present and at what population levels. Such a survey was recently completed in the state of Illinois by Dr. Terry Niblack, extension specialist and nematologist at the University of Illinois. More than 550 fields were surveyed and nematodes were found in every field, at populations ranging from 100 to 4000+ nematodes per 100 cc of soil. Most of these were plant parasitic nematodes, belonging to more than nine different genera, of which the “tylenchides”, nematodes with small styles and pointy tails, were the most frequent. These were found in 99% of the fields. However it is unclear what these organisms are doing in corn fields, since members of this group include plant parasites as well as parasites of fungi and algae. Of the known “tylenchides” observed, the spiral nematode (Helicotylenchus) was the most frequent. These were found in 99% of the soils, in most cases at moderate- to high-risk population levels (above 150 nematodes per 100 cc of soil). The lesion nematodes (Pratylenchus) were the second most prevalent nematode in Illinois cornfields survey by Dr. Niblack and her team. These were found in 84% of the fields. These were also found at population level considered above moderate risk thresholds in more than 50% of the fields in which they were present. Among these was Pratylenchus penetrans, a notoriously damaging species of lesion nematode on other crops such as potato. Greenhouse studies have shown that P. penetrans can also cause severe damage in corn; however, the level of damage caused in corn fields is unclear. The third and fourth most frequently observed nematodes were the stunt and lance nematodes, and these were also found at levels considered above moderate damage thresholds. The pin, ring, dagger, stubby-root, needle, root-knot, and sting were found in localized areas in Illinois, with the needle and sting nematodes found predominantly in sandy soils.         

So, can we assume that the corn nematode population profile in Ohio would the similar or identical to that observed in Illinois? Not really, soil type, crop rotation, and corn hybrids can all influence the distubution and type of nematode communities that may be present in any given area. Surveys are needed to help us determine what we have in Ohio. Even if we find the same set of nematodes, can we assume that they are causing damage to our corn crop? No, studies are needed to determine population levels and damage thresholds on our modern corn hybrids on our soil types in Ohio. However, even without a survey, several of our current crop management practices favor potential nematode problems. According to Dr. Niblack, these include our widely used no-till or conservation tillage and corn-on-corn cropping systems and the abandonment of soil applied insecticides which in the past provided the added benefit of controlling nematodes. So, while we wait for resources to conduct field surveys across the state of Ohio, we can use our understanding of the biology of these pathogens to make a projection as to where nematodes are most likely to be a concern and management practices for minimizing losses caused by these organisms. Nematodes are most likely to cause problems in no-till, corn-on-corn fields, and as such crop rotation and tillage would be the based approach for minimizing these problems (along with other disease problems). However, again, further research is needed in order to provide other management recommendations, such as seed treatments and hybrid resistance or tolerance. The effect of a seed treatment nematicide on the overall nematode population and effect on nematode life cycle are both unknowns.  Trials from other states have shown variable yield responses to nematicides seed treatments among locations and among hybrids.

 By attending one of these cover crops you will be provided with tools and support to enable you to use cover crops next fall.  A registration fee of $20 is required to cover the cost of lunch, snacks and the meeting room. Registration will be $30 dollars if you register at the workshop.

 For more information or to register online visit and scroll down to the cover crops workshops link.  You can also register by contacting the OSU Extension Office at 419-354-9050 or the Wood County Soil & Water District at 419-354-5517 .

The 5 day program is divided into three sessions that can be registered for separately. SESSION I: March 21-22 (1 ½ days) with topics focused on Laser Surveying, Topographic Mapping, & GPS. SESSION 2 is March 22-24 (2 1/3 days) focusing on Agricultural Subsurface Drainage Design, & Installation. SESSION 3 is March 25 (1 day) focusing on Drainage Water Management specifically related to Controlled Drainage System Design and Installation.

Session include both outdoor field use of equipment and lecture sessions.

Dress appropriately to the weather conditions.  Instructors include Land-Grant University Faculty/Staff, NRCS/ODNR/SWCD engineers and technicians, ARS engineers and scientists, and experienced OLICA contractors and associates.

Registration Cost depend upon session length

Full-Program Registration (All Three Sessions), March 21-25, 2011 (5 Days) $600 ($675 per person if register after March 11)

SESSION 1, Laser Surveying, Topographic Mapping, GPS Mapping. March 21-22 (1 ½ Days) $300 ($350 per person if register after March 11)

SESSION 2, Agricultural Subsurface Drainage Design, Drainage Installation.  March 22-24 (2 1/3 Days)  $500 ($600 per person if register after March 11)

SESSION 3, Drainage Water Management, Controlled Subsurface Drainage Design, Installation. March 25 (1 Day) $150 ($200 per person if register after March 11)

The program is sponsored by Overholt Drainage Education and Research Program, Food, Agricultural, and Biological Engineering, OSU Extension, OARDC, The Ohio State University, in cooperation with USDA-NRCS, USDA-ARS, Soil and Water Conservation Districts, Ohio Land Improvement Contractors and Associates.

The Fulton County Fairgrounds is located at 8514 Ohio 108, Wauseon, OH

43567-9663 and is just north of I-80 (Ohio Turnpike Exit 34). Several motel are available in the area.

For detailed program and registration see or contact Dr Larry Brown, or 614.292.3826.


After a welcome and opening comment from Kevin Elder of the Ohio Department of Agriculture, Ohio State University Extension’s Dr. Harold Keener will provide a thirty-minute “Overview of manure Technologies.” Prior to a morning break, Extension’s Dr. Steve Baertsche explores the subject “Anaerobic Digestion and Methane Production.”

Louisiana State University’s Dr. Ron Sheffield should interest farmers and others concerned about phosphorus after the break. “Phosphorus Removal in Dairy Wastewater” could be a great benefit if the task can be accomplished economically. Keith Bowers from Multiform Harvest follows with a similar talk about removing P from swine manure.

After an agribusiness sponsored lunch, Jim Sattler, President and Dr. Megan Smith, Technical Director for NuVention take 45 minutes to detail the process of “Turning Swine Manure into Bioresin.” Northeast farmer Dave Shoup of Shoup Farms and Applied Technology manager Rick Lux from Innovator, Inc. use the next 45 minutes to provide “Bio-oil Demonstration Farm Results.”

Mercer County Extension’s Jim Hoorman wraps up the presentations with “Nutrient (N & P) Removal and Water Quality Benefits.”

OSU Extension’s partners for the event include area SWCD’s, NRCS, Ohio Farm Bureau Federation and the FSA office. Please RSVP on or before March 5 by calling 419-586-2179 if you want to eat lunch!”



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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.