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Ohio State University Extension


C.O.R.N. Newsletter 2012-07

Dates Covered: 
April 3, 2012 - April 9, 2012
Steve Prochaska
Considerations for Early Herbicide Application

Considerations for Early Herbicide Application

The warm and relatively dry weather has many growers chomping at the bit to apply herbicides now, whereas this might have been more likely to occur in several weeks in a more typical spring weather pattern.  It probably makes sense to apply burndown herbicides now in many no-till fields based on the size of the weeds that are present.  Vegetation in no-till fields is larger than usual for this time of the year due to the warm weather, and lack of fall herbicide application in all but a few fields.  Waiting several weeks to apply herbicides will only result in an even more challenging burndown situation.  It can make sense to apply burndown herbicides now even where a field will be tilled later, in fields where there is enough vegetation to interfere with spring seedbed preparation.


This is probably the ideal situation for the use of the higher rates of 2,4-D ester in burndown treatments.  We have been encouraging use of the higher rates to improve control of marestail, which is fairly advanced in rosette size in some fields already.  A reminder that any 2,4-D ester product can be applied 7 days before planting at rates up to 0.5 lb ai/A.  There are several products that can be applied 15 days before planting at rates up to 1 lb ai/A (e.g. Weedone 650, E99, Salvo), but otherwise the higher rates require 30 days.  Treating fields now with the 1 lb rate of 2,4-D ester (with glyphosate or other burndown herbicides), with the intention of planting in two weeks or so, can improve control of larger, older weeds.  As we move closer to planting, or in especially weedy fields, the addition of Sharpen to glyphosate/2,4-D mixtures can improve control.  The addition of products containing chlorimuron (Canopy/Cloak, Valor XLT, Envive, Authority XL) can also improve burndown of some no-till weeds. 


One caution about burndown herbicides, especially in a year when weeds are more numerous and larger than usual.  We have previously mentioned the alternatives to glyphosate/2,4-D for burndown of marestail, which include Liberty/metribuzin and glyphosate/Sharpen.  While the latter two mixtures are effective for burndown of marestail and a number of other weeds, they can struggle some in a situation where the full complement of large no-till weeds is present (they typically work well in fields that have received a fall herbicide application).  Glyphosate/2,4-D still has the lowest cost and most utility across a range of no-till burndown situations, and switching to a mixture that does not include 2,4-D should generally occur only where necessary and where the weed spectrum fits the alternative mixtures.   Optimum activity from mixtures that contain Sharpen, Liberty or Gramoxone will occur with spray volumes of at least 15 gpa and the appropriate nozzles.


A primary concern of many recent callers about our current situation is whether it is too early to apply residual herbicides.  They are undoubtedly aware that applying residual herbicides too early can reduce their effectiveness in late May and early June when the later flushes of marestail and waterhemp are emerging.  Applying residual herbicides this early does introduce an element of variability in their activity later in spring, but this depends somewhat on the progress of soybean planting and crop development.  The ideal scenario would be that soybeans are planted within the next couple of weeks and conditions are favorable for rapid soybean development and formation of a crop canopy.  As a result, the crop is capable of providing control when the residual herbicide activity runs out.  The risk of applying this early is that subsequent wet and/or cold weather will prevent timely soybean planting, which ultimately stretches out the time until crop canopy development.  In this situation, we are likely to see breaks in residual herbicide activity prior to crop canopy, but the control that does occur is certainly much better than not using residual herbicides at all.  It’s a little difficult to predict late-season control of marestail, and we sometimes observe effective residual marestail control regardless of the timing of the residual herbicide application.  Here are a couple of suggestions relative to the early application of residual herbicides:


1.  Increase residual herbicide rates.  We have been suggesting increasing residual herbicide rates above the fairly low “Roundup Ready” rates to improve residual marestail control, and this is especially relevant for early application.  It’s probably feasible to increase rates by 20 to 30% above the low rates for many residual products, or use the higher rates within the rate range for a given soil type (either way, do not exceed the maximum rate for the soil type). 


2.  Split the residual herbicide.  Apply some residual herbicide now with the burndown treatment and the rest when the crop is finally planted.  The advantage of this approach is that it places some of the residual closer to the time of late-spring weed emergence, and also compensates for late soybean planting.  Where soybean planting is delayed, application of the 2nd half of the residual herbicide can also be delayed, and applied when it is most needed. 


There are various ways to split the residual herbicide, but something as basic as half the total amount applied early followed by the rest at planting would work.  Or mix up the residual herbicides, applying one type of residual early and switching to another later.  For products that are relatively short-lived in soil, such as Valor, Authority and metribuzin, the majority of the residual is best applied close to the time of planting.


Getting Your Corn Crop Off to a Good Start in 2012

Mistakes made during crop establishment are usually irreversible, and can put a "ceiling" on a crop's yield potential before the plants have even emerged. The following are some proven practices that will help get a corn crop off to a good start.

Perform Tillage Operations Only When Necessary and Under the Proper Soil Conditions.
Avoid working wet soil and reduce secondary tillage passes. Perform secondary tillage operations only when necessary to prepare an adequate seedbed. Shallow compaction created by excessive secondary tillage can reduce crop yields. Deep tillage should only be used when a compacted zone has been identified and soil is relatively dry. Late summer and fall are the best times of year for deep tillage.

Complete Planting by Early May
The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. However if soil conditions are dry and soil temperatures are rising fast (and the 5 to 7 day forecast calls for favorable conditions), start planting before the optimum date. During the two to three weeks of optimal corn planting time, there is, on average, about one out of three days when field work can occur. This narrow window of opportunity further emphasizes the need to begin planting as soon as field conditions will allow, even though the calendar date may be before the optimal date. However for farmers with Federal crop insurance, planting before the earliest allowable planting date (June 6) will result in loss of replant coverage even if the need for replanting is due to factors other than freeze damage or poor emergence...

Avoid early planting on poorly drained soils or those prone to ponding. Yield reductions resulting from "mudding the seed in" may be much greater than those resulting from a slight planting delay. Also, if dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. Cold water can cause similar injury to seedling structures as they emerge during germination. Such injury in corn seed ruptures cell membranes and results in aborted radicles, proliferation of seminal roots, and delayed seedling growth. When temperatures remain at or below 50 degree F after planting, damage to germinating seed is particularly severe. In 2005, imbibitional chilling injury was a major factor contributing to stand loss and record replanting of corn in Ohio. Keep in mind that should replanting be necessary this year, seed supply could be an issue. In a recent Illinois newsletter article Dr. Emerson Nafziger noted that “We are working with a relatively short seed supply due to low seed yields this past year.” So, farmers might have to opt for less desirable hybrids for replanting.


Adjust Seeding Depth According to Soil Conditions
Plant between 1-1/2 to 2 inches deep to provide for frost protection and adequate root development. In early-mid April, when the soil is usually moist and evaporation rate is low, seed should be planted no deeper than 1-1/2 inches. As the season progresses and evaporation rates increase, deeper planting may be advisable. When soils are warming and drying fast in late May or early June, corn may be seeded more deeply up to 2 to 2-1/2 inches on non-crusting soils. Consider seed-press wheels or seed firmers to ensure good seed-soil contact. One risk associated with shallower planting depths is the possibility of poor development of the permanent (also referred to as secondary or nodal) root system if the crown is at or near the soil surface. Permanent roots may not grow under hot, dry conditions resulting in the "rootless" and "floppy" corn syndromes. Delayed emergence and uneven crop development may also occur. Another potential risk from shallow plantings is shoot uptake of soil-applied herbicides.  2011 OSU research conducted across a range of planting dates from mid May to early June indicated that yields were 14% less for corn planted less than 1 inch deep compared to corn planted at 1-1/2 inch depths. Seeding depth should be monitored periodically during the planting operation and adjusted for varying soil conditions. Irregular planting depths contribute to uneven plant emergence, which can reduce yields.

Adjust Seeding Rates on a Field-by-Field Basis.
Adjust planting rates by using the yield potential of a site as a major criterion for determining the appropriate plant population. Higher seeding rates are recommended for sites with high-yield potential with high soil-fertility levels and water-holding capacity. OSU plant population studies conducted from 2006 to the present suggest that on highly productive soils, with long term average yields of 190 bu/acre or more, final stands of 33,000 plants/acre or more may be required to maximize yields. Lower seeding rates are preferable when droughty soils or late planting (after June 1) limit yield potential. On soils that average 120 bu/acre or less, final stands of 20,000 to 22,000 plants/acre are adequate for optimal yields. On soils that average about 150 bu/acre, a final stand of 30,000 plants per acre may be needed to optimize yields. Seeding rate can be cut to lower seed costs but this approach typically costs more than it saves. Most research suggests that planting a hybrid at suboptimal seeding rates is more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels) and harvest delays occur. When early planting is likely to create stressful conditions for corn during emergence, e.g. no-till in corn residues in early to mid April, consider seeding rates 10 to15% higher than the desired harvest population. Follow seed company recommendations to adjust plant population for specific hybrids.


For other perspectives on planting dates for corn this year check out the following-


Coulter, J. 2012. Planting date considerations for corn. University of Minnesota Extension.


Elmore, R. 2012. Best planting dates for corn in Iowa. Integrated Crop Management. Iowa State Extension and Outreach.


Nafziger, E. 20122. Does It Make Sense to Plant So Early? The Bulletin. University of Illinois Extension.



Successful Alfalfa Establishment

April is a good month to plant and establish a new stand of alfalfa.  The earlier in the month planting is done, the better.  Once an alfalfa plant has germinated, that new plant needs between 6 to 8 weeks to get a good root system established that enables it to handle warmer and drier summer weather.  At about 8 to 10 weeks after emergence the alfalfa plant pulls the growing point below the soil surface.  This process is called contractile growth.   Once contractile growth occurs the alfalfa plant is considered a true perennial.  The protected growing point below the soil surface is the reason why the alfalfa plant can survive winter temperatures, close cutting and grazing.


Some of the most common questions regarding successful alfalfa establishment include soil fertility, planting depth and weed control.  All three factors need to be addressed to successfully establish an alfalfa stand.  The basis for any decisions regarding the application of lime, phosphorus and potassium fertilizer is a soil test.  The recommended soil pH for an alfalfa stand is 6.8.  Remember that it takes 6 to 9 months after lime is incorporated and mixed into the tillage zone before the target pH is reached.  If soil pH is below 6.5, it is probably a wise decision to apply lime this spring and aim for a late summer planting.  A soil test can also help determine if phosphorus and/or potassium needs to be applied before planting.  Phosphorus is a critical element to aid a new plant in establishing a good rooting system.  The point here is that lime and fertilizer can represent a significant dollar investment and guessing as to the need and quantity can be expensive.  So, as the saying goes; “Don’t guess, soil test”.


Weed control in an alfalfa stand really needs to begin before the crop is planted.  Herbicide options in an established alfalfa stand are limited.  Perennial broadleaf weeds and grasses should be managed and controlled in the crops previous to the alfalfa rotation.  The general rule of thumb is that at least 95% of the weed control in a forage crop is provided by developing a dense, healthy stand that will not allow weeds to invade. 


Just like other agronomic crops, weeds that emerge with the new alfalfa seedlings are the most destructive.  The goal should be to maintain the new seeding relatively weed free for the first 60 days.  These factors often make it necessary to use an herbicide with a pure seeding of alfalfa.  There are a few herbicides that are commonly used when establishing a pure stand of alfalfa.  Balan or Eptam can be used as pre-plant incorporated herbicides to provide control of annual grasses and some broadleaf weeds.  Butyrac, and Bromoxynil can be used to provide early post emergent control of some broadleaf weeds when weeds are no more than 2 inches tall. Clethodim and Sethoxydim or Sethoxydim plus Dash can control annual and perennial grasses in alfalfa. Prowl H2O provides residual control of most annual grasses and certain broadleaf weeds, but must be applied  prior to weed emergence and the seedling alfalfa must be in the at least the 2nd trifoliolate stage of growth but not more than 6 inches tall. Imazethapyr and Imazamox control annual broadleaf weeds and suppress or control grass weeds, and must be applied when alfalfa is in the 2nd trifoliolate state or larger and when weeds are 1 to 3 inches tall or when rosettes are no more than 1 to 3 inches wide. More details are also available in the 2012 Ohio and Indiana Weed Control Guide ( Take the time to read and follow label directions. Herbicide use on forage crops such as alfalfa can involve harvest and grazing restrictions, in addition to specific limitations regarding the timing of the herbicide application.


Incorrect planting depth has been responsible for many poorly established stands of alfalfa or seeding failures.  Alfalfa is a small seed and should not be seeded too deep.  The recommended seeding depth for alfalfa is one-quarter to one-half inch deep.  It is better to err on the side of planting shallow rather than too deep. 


Another factor that works hand in hand with planting depth is correct calibration of the planter for seeding rate.  The Ohio Agronomy Guide recommends seeding alfalfa at 15 lbs/acre of pure live seed for a pure stand ( If a coated alfalfa seed is used, be aware that coatings can account for up to one-third of the weight of the seed.  This can affect the number of seeds planted if the planter is set to plant seed on a weight basis. Seed coatings can also dramatically alter the flowability of the seed through the drill, so be sure to calibrate the drill or planter with the seed being planted.


Finally, use fungicide treated seed to provide protection against seedling diseases and make sure the seed is planted with the proper bacterial inoculum that has been maintained under conditions that ensure the inoculant is viable.



Bees and Neonicotinoids

Over the past decade we have discussed the need for growers to be careful when applying foliar insecticides to their crops because of the potential for harming bees that might be foraging for nectar if the crop or nearby plants are in bloom, and to manage their applications carefully to reduce the possibility of drift. 


Recent articles in the popular press and newspapers, including Saturday in the Columbus Dispatch, bring up another possible concern, that being the use of a relatively new class of insecticides, neonicotinoids, which are related to nicotine found in tobacco.  In field crops, their main use is as seed treatments, and includes the insecticides clothianidin (Poncho), thiamethoxam (Cruiser), and imidacloprid.  Recent studies out of Purdue and labs in Europe suggest that the use of clothianidin as a seed treatment might impact bees, either by causing mortality or more likely affecting their behavior and preventing bees from returning to their hives.  There is also the possibility that they might interact with various pathogens that attack bees, making the bees more susceptible to various diseases.  The neonicotinoids, when applied to the seed, apparently can get mixed with the talc that is often used to allow seeds to flow more easily in the planters, and then the insecticides and/or talc enter the environment during planting or when the seed boxes are cleaned. 


At this time, this issue is an on-going story, with much more work to be done.  Currently there are numerous groups calling for a ban on these seed treatments in the U.S, especially clothianidin.   A petition submitted to EPA can be read at     We will continue to follow this story and report information and further developments in the C.O.R.N. newsletter as they arise.   


Nitrification Inhibitors and Spring Planting of Corn

Soil nitrogen (N), whether it is from fertilizer or soil organic matter, is only available to the plant when it is in the nitrate or ammonium form.  In the ammonium form it is considered stable or protected since the negative charged soil particles hold the positive charged ammonium. The negative charged nitrate cannot be held by the soil and is vulnerable to various loss mechanisms. Eventually the ammonium will be converted to nitrate by soil bacteria in a process called nitrification. The first bacterium Nitrosomonas converts ammonium-N to nitrite-N.  The second bacterium Nitrobacter converts nitrite-N to nitrate-N.  And as you know, nitrate-N is the form we are most concerned about being lost (whether by leaching or denitrification).


The purpose of a nitrification inhibitor is to delay the nitrification process by suppressing the bacteria Nitrosomonas in the area where ammonium is to be present. Thus inhibitors extend the time that soil N stays in the ammonium form.  There are three common nitrification inhibitors that are commercially available:  2-chloro-6-(trichloromethyl)-pyridine (nitrapyrin), dicyandiamide (DCD), and ammonium thiosulfate (ATS). Nitrapyrin is the active ingredient found in the DOW® product N-Serve® and Instinct®. The biochemical activity of nitrapyrin and its ability to suppress growth of Nitrosomonas has been known since the 70s and it was initially registered in 1974.   It is quite effective even at relatively low rates.  Dicyandiamide (DCD) is the active ingredient in nitrification inhibitors such as Agrotain Plus®, SuperU® , and Guardian®.  Dicyandiamide is required at a significantly larger concentration to prevent nitrification. Correct concentration level is critical for all nitrification inhibitors to be effective.

Others products claim to be nitrification inhibitors. Some of them have been proven not to even inhibit nitrification. Research is lacking on some products and thus cannot be recommended at this time. North Dakota State University has a good discussion on nitrification inhibitors that may be found at the following URL:

Generally we do not recommend nitrification inhibitors for anhydrous ammonia applied shortly before planting or as a side-dress treatment, since the risk of nitrogen loss is low.  No-till situations are more likely to show positive yield results than conventional till systems for spring applied anhydrous. 

Same would be true for products added to 28% solutions. Also keep in mind that the nitrification inhibitor would only affect the ammonium portion of solution and would not prevent N loss from the nitrate portion.

Nitrification inhibitors are less likely to show an economic benefit when high N rates are used in the field.  Nitrogen losses at high application rates are not likely to affect yield as much if lower rates are applied.


In summary, there are commercial products available that will inhibit nitrification for a short time period when applied at the right concentration. When N is applied near planting or at side-dress, the benefit from a nitrification inhibitor is minimal since the potential for N loss is low at this time.


Considerations for Urease Inhibitors

Urea based N fertilizers are in an organic commercial form that requires a biological enzyme to promote degradation to ammonia.  Ammonia exists as a gas at normal temperature and pressure, thus it may be lost by volatilization if not exposed to water.  Ammonia loss potential by volatilization for incorporated urea products is negligible because soil holds enough water to capture ammonia as ammonium that can be held on the soil’s cation exchange complex.  Surface applications of urea are at risk of loss because there is no opportunity to capture the ammonia as it is produced.

Volatilization risks increase with warmer temperatures, particularly with rapidly drying soil surfaces (ammonia from the urea attaches to the water as it vaporizes from the field). High soil pH also increases the risk of volatilization. We generally recommend not to apply urea-based fertilizers to the surface of fields recently treated with lime.

Urease inhibitors can have different modes of action, and the first question we should ask is do they work?  The active ingredient in the inhibitor can act as a substrate for the urease enzyme, thereby protecting free urea by allowing it to stay in solution longer, or the inhibitor can inactivate the enzyme.  Agrotain® is the most common commercially available urease inhibitor.  The active ingredient in Agrotain® is N-(n-butyl) thiophosphoric triamide.  The mode of action is not clearly defined, but it is thought to act as a substrate for the urease enzyme.  Regardless of the mode of action, laboratory evidence has shown that it does allow urea to be retained in the soil longer.

Other urease inhibitors are marketed, some may have some activity, but it is your job as a producer/consultant to determine whether or not the proposed mode of action makes sense.  We would also encourage you to inquire about lab data indicating that the material being marketed does what it is supposed to do. Some legitimate products have limited data and may not be recommended by universities until more information and testing becomes available. North Dakota State University has a good discussion on recent urease inhibitors that may be found at the following URL:

Even if a urease inhibitor has been demonstrated in a laboratory to have some inhibition properties on the enzyme urease, the agronomic question still remains as to its usefulness in a field setting.  It really depends upon how N is to be applied (and the form) and the rate of nitrogen being applied.  Higher rates of urea nitrogen (under most conditions) likely do not require urease inhibitors.  Surface application of dry urea in high residue situations is a good place for the use of urease inhibitors.  Dribble applications of liquid UAN may benefit from a urease inhibitor in high residue situations, but clean till fields are less likely to benefit.  Injected liquid UAN does not require stabilizers based upon current research. Also keep in mind that the urease inhibitor will only benefit the urea component of the UAN solution.



Weather Outlook

The overall pattern will be more typical of spring in the next 2-3 week. The pattern will go from a warmer pattern to a normal or slightly cooler than normal pattern by next week and the following week as the upper level flow pattern shifts from southwest to northwest bringing in cooler Canadian air. There will be a threat of some freezes especially later next week. Rainfall will be close to normal or slightly below normal the next few weeks in most places.

The outlooks calls for above normal temperatures and normal to below normal rainfall from Apr 2 - Apr. 8. Temperatures will average about 5 degrees above normal. Normal rainfall is 0.75 to 1.00 inches. Most places will see 0.25 to 1.00 inches with the heaviest in the south. A light freeze is possible especially in the north Friday or Saturday of this week.

The outlook calls for near to slightly below normal temperatures next week with near normal rainfall from Apr. 9-Apr. 15. Temperatures will average zero to minus 2 degrees with rainfall of 0.75 to 1.00 inches. A freeze, possibly hard - below 28 degrees for at least 3 hours, is possible late next week.



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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.