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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2013-04

Dates Covered: 
February 26, 2013 - March 12, 2013
Harold Watters

More on metribuzin rates

Following the article in C.O.R.N. about metribuzin several weeks ago, several readers commented that using metribuzin product labels to select an application rate was not as easy as we made it sound.  We would have to agree.  The soybean section of metribuzin labels is outdated, and also overly long and complex.  Rate tables are largely still geared for the long gone days of total PRE programs in soybeans, and there has never been any change in the labels to address the use of metribuzin in a planned PRE followed by POST approach for Roundup Ready soybeans.  

We are currently suggesting that where metribuzin is the primary herbicide for residual marestail control, growers aim for rates of 0.5 to 0.75 lb/A of 75DF.  Use 0.5 lb/A on coarse soils with less than 2% organic matter, and 0.6 to 0.75 lb/A otherwise.  The rate table for metribuzin applied alone specifies PRE rates of 2/3 to 5/6 lb/A 75DF for medium-textured soils with 2 to 4% organic matter, but this same table specifies up to a full pound of 75DF on higher organic matter or fine-textured soils.  It appears to us that the table on the labels showing rates for mixtures of metribuzin with metolachlor may be more appropriate for our purposes.  This table specifies metribuzin rates of ½, 2/3, and 2/3 to 5/6 lb/A for coarse, medium, and fine-textured soils with more then 3% organic matter, respectively, and slightly lower rates for soils with less than 3% organic matter. 

Keep in mind that we often apply a mix of burndown and residual herbicides several weeks before planting.  Metribuzin soil life is relatively short, and rates can be increased to compensate for early application.  Product labels address early application through a “split-shot” approach but do not otherwise specify higher rates for a single application.  When using a premix that contains a lower rate of metribuzin, add additional metribuzin 75DF to reach the equivalent of these rates.   For mixtures of metribuzin with a product that contains Valor or Authority, it may be possible to use rates of 4 to 8 oz/A depending upon soil type and date of application.  We have not conducted enough trials with these mixtures, but will over the next two years in order to develop a more concrete recommendation. 


Soybean burndown options for control of marestail

Most effective management of marestail occurs with either: 1) a program of fall followed by spring herbicides, with most of the residual herbicide applied in spring; or 2) a split-application approach in spring, where burndown and some residual herbicide is applied in late March or early April, and additional burndown and residual applied when soybeans are planted.  Skipping the fall or early spring applications and applying all of burndown and residual herbicide together in spring introduces more variability in marestail control, and delaying application until late April or May can result in inconsistent control of emerged plants with burndown herbicides. 

The burndown treatment for no-till soybeans should obviously include herbicides other than glyphosate that have effective activity on emerged marestail.  Burndown options are outlined below.  Keep in mind that: a) it’s possible to add 2,4-D to any of these as long as the waiting period between application and planting is followed; b) any of these should be combined with residual herbicides to control marestail that emerge after planting.

1.  Glyphosate + 2,4-D ester.  This was the go-to treatment for marestail for years.  While still effective in the fall, and in many fields on small marestail in the spring, it appears to have become more variable on marestail over the past decade, especially when applied from mid-April on in fields not treated the previous fall.  Increasing the glyphosate rate to 1.5 lbs ae/A and the 2,4-D ester rate to 1.0 lb ai/A can improve control.  Allow 7 days between application and planting for 0.5 lb 2,4-D ester/A.  Labels for some products specify a 15-day waiting period between application and planting for rates up to 1.0 lb/A, while the waiting period is 30 days for others.

2.  Sharpen + glyphosate.  Effective on marestail, but can be weak on large giant ragweed and dandelion unless 2,4-D ester is included.  Must be applied with MSO (methylated seed oil) in a spray volume of at least 15 gpa.  Sharpen rate of 1.0 oz/A can be applied anytime prior to soybean emergence.  Higher Sharpen rates are allowed, but must be applied 14 to 44 days before planting, depending upon rate and soil type.  Works well with products that contain metribuzin.  There has been some confusion this winter about whether Sharpen can be tank-mixed with other PPO herbicides.  Currently, Sharpen cannot be mixed with products that contain:  flumioxazin – Valor, Valor XLT, Gangster, Envive; or sulfentrazone - all Authority products, Sonic, and Gangster.  Syngenta claims that the mix of Sharpen and Prefix is approved, but BASF disagrees.  Check with your local reps for the right story which seems to keep changing.  The Sharpen label recommends flat fan nozzles for burndown applications.  The active ingredient in Sharpen, saflufenacil, is also a component of Optill, Optill Pro, and Verdict, and mixtures of any of these with glyphosate should provide similar control (paragraph modified 3Mar2013).

3.  Liberty.  Burndown rates are 29 to 36 oz/A.  Using the higher rates and adding metribuzin generally results in more consistently effective control, especially under cool, cloudy weather conditions.  Apply in a spray volume of at least 15 gpa (20 gpa is preferable in most situations).  Avoid use of nozzles that produce large spray droplets.  Liberty will be most effective when used in spring following a fall herbicide application that removes many of the other “winter weeds” typically found in a no-till field.

4.  Gramoxone + 2,4-D + metribuzin.  Use Gramoxone rates of 3 to 4 pts/A and metribuzin rate of at least 4 oz 75DF/A.  Activity is maximized when applied with COC (crop oil concentrate).  Apply in a spray volume of at least 15 to 20 gpa and avoid nozzles that produce large droplets.  Some dealers have commented that the mix of Gramoxone + 2,4-D has been effective in early spring without metribuzin, but we have observed the three-way mixture to be most effective on plants that are past the rosette stage.

5.  Clarity and some other dicamba products.  We have not previously suggested the use of this in the spring prior to soybeans, but this is an approved use on some dicamba product labels. Labels allow use of 8 oz product/A, but specify that it must be applied at least 14 days before planting and an inch of rain must occur prior to the start of that 14-day period (so the 14 day wait starts after the inch of rain has been received). Dicamba can be more effective on marestail than 2,4-D, and marestail is one of the few weeds that dicamba has much residual activity on.  The combination of the requirements for rain and 14 days means that it can be difficult to determine when exactly soybeans could be planted. However, if the burndown treatment is applied early enough in spring, the addition of a low rate of dicamba to glyphosate/2,4-D mixtures or other burndown treatments can improve burndown of marestail and add at least some residual (paragraph modified 4Mar2013).

6.  Residual herbicides that contain chlorimuron (Classic) or cloransulam (FirstRate) can add some burndown activity, but only where the marestail populations are not resistant to ALS inhibitors.  Products that contain chlorimuron – Canopy/Cloak, Valor XLT, Envive, Authority XL.  Products that contain cloransulam – Sonic, Gangster, Authority First.  In populations that are ALS-resistant, the Valor/Authority component of these products has the potential to cause antagonism and a reduction in the activity of glyphosate/2,4-D.

Soybean cyst nematode – it’s not too late to soil sample

If you didn’t sample for SCN in the fall as recommended, you can still collect soil samples for SCN.  We have been talking about this at Extension meetings and thought it would be good to review how and where to sample.  Here are some of the questions and answers from the winter meetings.

1) Which fields should I target?

If you have never sampled your fields before, here are a few characteristics that we have found to be associated with high numbers of SCN:  low yields – those fields which are off the county average by 5 to 10 bu/A; fields that have been in continuous beans; fields that do not mature evenly, pockets that mature early, presence of sudden death syndrome.  Soybean yield from fields with SCN is highly variable, there will be high and low spots associated with the high and low numbers of SCN.  Target those areas where the yield maps are showing low yields.

2) How to collect the soil sample?

Collecting soil for SCN sampling is similar to collecting for a soil fertility sample.  The top 6 to 8 inches of soil, sample in the row and not between the rows.  Walk in a Z or W pattern, collect cores in a bucket.  Mix them thoroughly and send a good quart bag size (labeled with a permanent marker with your name and location) to the SCN testing lab of your choice.

3) Where do I send them?

There are a number of labs that process SCN soil samples and they are listed here: 

OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic 8995 E. Main St. Bldg. 23

Reynoldsburg, OH 43068


Brookside Laboratory Inc


200 White Mountain Drive,

New Bremen, OH 45869



419-977-2767 fax

Geophyta Inc

2685 CR 254

Vickery, OH 43464


419-547-8538 fax

Spectrum Analytic Inc.

1087 Jamison Rd. NW

Washington Court House, OH 43160



740-335-1104 fax


4) What do the numbers of cysts/eggs mean?

First, this number is an average and an estimate of the number of SCN eggs or cysts within a cup of soil.  SCN populations are highly variable, so we use this number to assess risk and make management recommendations.

Best SCN management strategies for Ohio soybean producers.

Egg Count
per 100 to 200 cc* of soil

Cyst Count

Population Level

Management Strategies

0 – 40


None detected

Continue to monitor field after two crops of soybeans




May begin to measure some yield loss in susceptible varieties at or above 200 eggs/200cc.  Use SCN resistant varieties to limit the increase of SCN numbers.




Plant SCN resistant variety or rotate to a non-host crop. At or above 2000 eggs some yield loss may result on SCN resistant lines




Rotate to a non-host crop next year and return with SCN resistant soybeans the following year

16 to 18 bu/A losses have been recorded in Ohio on Susceptible varieties when grown at these populations.

5000 and over

15-20 and over


Rotate to a non-host crop for two to three years then sample the soil to determine nematode populations before planting SCN resistant varieties

*100 to 200 cc = approximately ½ to 1 cup


5) What if my numbers are high, but I’ve been growing SCN resistant varieties?

This is a good indication that SCN has adapted to SCN resistant varieties.   Most resistant varieties have the same source of resistance (PI 88788), so selection pressure is high for SCN that can break resistance. To get the numbers down, rotate to a nonhost crop for two to three years, then find a variety with a different source of SCN resistance, such as Peking (the source of resistance should be listed in variety descriptions from the seed company or from the seed dealer).  Recheck the SCN numbers before planting soybeans, and don’t include susceptible soybeans in your long-term rotation. Be sure to use a different resistant variety for each soybean rotation.


Don’t Be Confused When Selecting a Lime Source

Many individuals have been asking about lime sources during winter meetings, particularly about whether one source is better than another. When following Ohio State University recommendations, selecting a lime source is one of the easier activities in a nutrient management program.

A producer should always ask for an analysis sheet when evaluating or comparing a lime source. Even though a lime analysis often has information that fills a page, there is only one thing that a producer needs to find to evaluate the material, the Effective Neutralizing Power or ENP. It is required by Ohio lime regulations for liming material sold in Ohio and it value should be given in pounds. It may also be given as a percentage but use the pound value.

Effective Neutralizing Power takes into account all the components that determine the quality of the lime, i.e., neutralizing ability, particle or grind size, and water content. This value will allow a producer to determine the actual price per pound of neutralizing ability for a lime source and also to calculate how much of a source will be needed to equal a ton of recommended lime. For example, if the lime recommendation was for two tons (one ton = 2000 pounds), a lime source with an ENP of 1000 pounds would require an application of four tons to satisfy the two ton lime requirement since for every ton of this lime source it only provides an effective neutralizing ability of 1000 pounds (4000/1000). If the lime source had an ENP of 1500 pounds, it would require an application of 2.7 tons to fulfill the requirement of two ton recommendation of lime (4000/1500).

Now that a producer knows how much lime needs to be applied for a source they can compare price based on ENP. In other words, a producer can determine how much effective neutralizing material they are actually buying in a source.

Shipping, however, is generally the component that adds the most cost to a lime source. In general, the closer a source is to the farm the lower the cost. Thus the closest quarry will most often provide the least expensive lime source.

Notice that we did not mention the calcium or magnesium content. Ohio State research has shown that crop yields and other agronomic features are not affected whether a producer selects “hi cal” lime or lime with magnesium as long as the soil test shows more calcium than magnesium as an exchangeable base, soil test calcium levels are greater than 200 ppm (400 pounds), and the magnesium levels are greater than 50 ppm (100 pounds). Even lime sources with magnesium will generally have more calcium than magnesium in the material. As long as these guidelines are followed there is no such thing as a “too high” of magnesium level on a soil test. I am not aware of a situation in the state where the soils naturally had a calcium level below the magnesium level. Nor am I aware of a soil with the proper pH range that had deficient calcium levels for grain crops or alfalfa. However, there have been documented cases where fields have been deficient in magnesium. If the magnesium level drops below 50 ppm, lime that contains magnesium is the most cost effective way to raise the soil magnesium level.

In summary, when selecting a lime source use the ENP value to compare sources and to determine the application rate. If the soil test levels are adequate for calcium and magnesium, then select the most economical lime source regardless of its calcium or magnesium level, which is generally the one closest to your farm. For additional information, please refer to the Soil Acidity and Liming for Agronomic Production Bulletin AGF 505,


Making Phosphorus and Potassium Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa

Soil testing is the foundation upon which we make nutrient recommendations. Something equally important that is often overlooked is the crop response correlation work that gives those soil test numbers meaning. Together these two pieces are the essential components of making nutrient recommendations to maximize crop production and limit off site movement of nutrients that result in economic loss and potentially affect water quality. The Tri-State Fertilizer Recommendations used by The Ohio State University follows a build, maintenance and drawdown approach to soil fertility management.

The Tri-State Fertilizer Recommendation for both phosphorus and potassium are built around defining a critical level. The authors of the Tri-State define the Critical Level for both immobile nutrients as “…the soil test level above which the soil can supply adequate quantities of a nutrient to support optimum economic growth.”  Below the Critical Level “… the soil is not able to provide P and K requirements of the crop.” Above the Critical Level “… the soil is capable of supplying the nutrient required by the crop and no response to fertilizer would be expected.”

The Maintenance Limit is the upper end of the scale.  The Tri-State authors define the Maintenance Limit as “There is no agronomic reason to apply nutrients when soil test levels are above the maintenance limit level.”

Soil test levels between the Critical Level and Maintenance Limit are define as the Maintenance Plateau Range.  In this range, the recommendations are “Designed to replace nutrients lost each year through crop removal. No response to fertilizer in the year of application is expected. And no response to placement technique such as banding or stripping or the use of P and K starter fertilizer…”

Chart 1 show the Critical Level, Maintenance Limit and Maintenance Plateau for a 160 bushel corn crop and recommends fertilizer recommendation based on soil test level for 160 bushel corn.

 Critical leve chart

Critical levels for phosphorus are defined in the Tristate Fertilizer Recommendations depending on crop. The critical P level for corn and soybean rotation is 15 ppm (30 pounds per acre) or if wheat and alfalfa are included in the rotation 25 ppm (50 pounds per acre). The Maintenance Limit for a corn and soybean rotation is 30 ppm (60 pounds per acre) or if wheat and alfalfa are included in the rotation 40 ppm (80 pounds per acre).

Critical levels and Maintenance Limits for potassium is defined in the Tri-state Fertilizer Recommendations based on CEC (Cation Exchange Capacity) of the soil and are shown in Table 1.

Table 1. Critical and Maintenance Levels for P and K in corn, soybeans and wheat.

CEC (Cation Exchange Capacity)

Critical Soil Test Level for K

ppm (pounds per acre)

Maintenance Limit  Test Level for K

ppm (pounds per acre)


88 (175)

118 (235)


100 (200)

130 (260)


125 (250)

155 (310)


150 (300)

180 (360)

Equation to determine Critical Level at any CEC is Critical Level for ppm K =75+(2.5xCEC)

Three publications that can help farmers looking to develop fertilizer recommendations are:

The Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa can be found at

Developing Phosphorus and Potassium Recommendations for Field Crops (AGF-515-12) walks through developing a nutrient recommendation and how much fertilizer is needed to meet that need found at

An Excel Spreadsheet to calculate P, K and Lime Recommendations (Beta Version-11/2012) for 7 fields or zones and a three crop rotation can be found at  

Other helpful nutrient related publications can be found at


2013 Farm Forum March 2nd in Piqua

You are invited to Congressman Boehner’s Annual Farm Forum this Saturday March 2nd at Edison Community College in Piqua.  Ed Schafer Former Secretary of the United States Department of Agriculture will be the keynote speaker.  Registration begins at 9 with the event to follow at 9:30. 

The program will be Saturday, March 2, 2011, 9:30 am to 12:30 pm at the Edison Community College, 1973 Edison Drive, Piqua, Ohio.

For more information or to make reservations, please call 800-582-1001 or visit


March Agronomic Crops Calendar

March 5

Conservation Tillage Conference (CTC)

Ohio Northern, Ada, OH

2013 dates March 5 & 6, Ada, OH

March 5

Ohio Pesticide Commercial Applicator Recertification Conferences-Columbus

Columbus Convention Center, Columbus, Ohio

Complete requirements for Ohio commercial pesticide recertification in one day. Speakers include Ohio State University Extension state specialists, field specialists, and researchers. Ohio Department of Agriculture personnel and key industry leaders are also on program.

March 11

Overholt Drainage School-Session 1

The Ohio State University Campus, Columbus OH

SESSION I: March 11-12 (1 1/2 days) Topographic Mapping with GPS Monday 9:00 AM to 9:00 PM; Tuesday 8:00 to noon

March 12

Overholt Drainage School-Session 2

The Ohio State University Campus, Columbus OH

SESSION 2: March 12-14, 2 1/2 days Agricultural Subsurface Drainage Design, Layout and Installation Tuesday 2:00 to 9:00 PM; Wednesday 8:00 AM to 9:00 PM; Thursday 8:00 to 9:00 PM 

March 15

Overholt Drainage School-Session 3

The Ohio State University Campus, Columbus OH

SESSION 3: March 15, 1 day Drainage Water Management: Controlled Drainage System Design, Layout and Installation Friday 9:00 AM to 5:00 PM

March 21

Ohio Pesticide Commercial Applicator Recertification Conferences-Sandusky

Kalahari Conference Center, Sandusky, Ohio

Complete requirements for Ohio commercial pesticide recertification in one day. Speakers include Ohio State University Extension state specialists, field specialists, and researchers. Ohio Department of Agriculture personnel and key industry leaders are also on program.



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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.