CORN
Crop Observation and Recommendation Network

October 21 - October 27, 2002
C.O.R.N. 2002-36

In This Issue:

A) Drought, Nutrient Availability and Soil Testing Considerations
B) Fall Applied Nitrogen for Corn Production
C) Fall Herbicide Treatments For Dandelion and Winter Annual Weed Management
D) Baythroid 2 Labeled on Corn & Soybean
E) Intrepid 2F Labeled on Corn
F) Regional Agronomy Meetings Schedule For Ohio's Crop Industry

A) Drought, Nutrient Availability and Soil Testing Considerations - Maurice Watson CORN Questions

The extremely dry 2002 growing season was a very harsh one for producing a profitable crop. Now that the 2002 growing season is over, the question is, "what kind of year will we have next year?" Because of this year's drought, it is possible not as much fertilizer will be needed by next year's crop on the field that was sufficiently fertilized this year. In addition, it is possible that not enough fertilizer was applied this year because of the very wet spring. Unfortunately, long term weather forecasting is not sufficiently precise to allow accurate planning for next year's fertilizer needs. The amount of nutrients removed by a crop is different under wet soil conditions as opposed to drought conditions. It is best to maintain optimum levels of phosphorus (P) and potassium (K) to guard against weather extremes during the growing season. By applying fertilizer that is not needed or not applying enough fertilizer a grower can greatly affect profits.

Nutrient availability and absorption can be affected by extremely dry or excessively wet soil conditions. This is especially true for P and K. Under normal soil moisture conditions, P and K are supplied to the root surfaces by mass movement of water containing these nutrients, diffusion of these nutrients in water surrounding the roots, or by the extension of the roots through the soil as the plant grows. Under severe drought conditions there is very little, if any, mass flow of water to the roots, very little diffusion takes place, and the roots are not extending through the soil because the plant is not growing or growing very slowly. Under extremely water-logged conditions, the oxygen supply to the roots is limited, affecting the uptake of nutrients, even though the nutrients are present in sufficient concentrations. Consequently, since it is not possible to predict what the soil moisture will be during the growing season, it is best to maintain the optimum concentrations of Pand K in the soil. An Optimum concentration of K in the soil is especially important during dry growing seasons.

Knowledge of the amount of P and K removed by a crop during a growing season is useful in realizing the potential for change in soil fertility. Although the amounts of P and K removed by the crop are usually not directly related to specific decreases in soil test levels, it can indicate a trend. The reason for this is that P and K are released from soil constituents, depending on the kind of soil. For example, a sandy soil with low clay and organic matter will have less of a reservoir for these nutrients and will show a greater change in the soil fertility levels than a loam or clay soil. Also, reduction of plant available P and K can occur over time through soil fixation processes. The degree of fixation occurring in the soil depends on the kind of soil and, especially in the case of P, on the pH of the soil. Therefore, even though during a drought year with poor crop growth and lower than normal nutrient removal, it is best to use a soil test to evaluate soil fertility prior to next year's growing season.

In order to understand the P and K terminology used in the fertilizer and the soil testing industries it is important to understand the relationship between P and P2O5 and between K and K2O. P and K are the elemental symbols for Phosphorus and Potassium respectively. The corresponding P2O5 and K2O are the oxide forms of these elements and are known as phosphate and potash respectively. For the most part, the fertilizer industry uses the oxide terminology. Therefore, when a bag of fertilizer containing phosphorus or potassium is purchased, a specific amount of phosphate (P2O5) or potash (K2O) is purchased. When soil testing laboratories test the soil for P or K, they usually express the concentration of these elements in the P and K elemental form. However, when fertilizer recommendations are made on the soil test report the oxide form, P2O5 or K2O is used. Thus, specific lbs/a of P2O5 or K2O are recommended. Conversion between the elemental and oxide forms can easily be made:

The amount of P in P2O5 (phosphate) is 44 %. Therefore, multiplying the amount of P2O5 by 0.44 equals the amount of P present. Example: Assume you have purchased 100 lbs of phosphate, then the amount of elemental P purchased equals 100 lbs P2O5 x 0.44 = 44 lbs of P.

The mathematical equation is: lbs P = lbs P2O5 x 0.44

If you wish to determine the amount of P2O5 that is comparable to a given amount of P, then divide the amount of P2O5 by 0.44. Example: 44 lbs of P divided by 0.44 = 100 lbs P2O5.

The mathematical equation is: lbs of P2O5 = lbs P / 0.44

Similarly for potassium, the amount of K in K2O (potash) is 83%. Therefore, multiplying the amount of K2O by 0.83 equals the amount of K present. Example: Assume you have purchased 100 lb of potash, then the amount of elemental K purchased equals 100 lbs K2O x 0.83 = 83 lbs of K.

The mathematical equation is: lbs K= lbs K2O x 0.83

To convert from K to K2O, then divide the K by 0.83. Example: 83 lbs K divided by 0.83 = 100lbs of K2O.

The mathematical equation is: lbs K2O = lbs K / 0.83

Understanding the differences in the expression of these nutrients and how to convert from the elemental form to the oxide form and vice versa, will allow for a better understanding of a soil test report.

The Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa (Extension Bulletin E-2567 for Indiana, Ohio & Michigan) indicates the following quantities of Phosphate (P2O5) and Potash (K2O) removed per unit of harvested yield.

The crop removal for Phosphorus (expressed as P2O5 ) is:

Grain Corn = 0.37 lbs P2O5/bu
Corn Silage = 3.30 lbs P2O5/t
Soybeans = 0.80 lbs P2O5/bu
Alfalfa = 13.00 lbs P2O5/t

The crop removal for K (expressed as K2O) is:

Grain Corn = 0.27 lbs / K2O bu
Corn Silage = 8.00 lbs K2O /t
Soybeans = 1.40 lbs K2O /bu
Alfalfa = 50.00 lbs K2O /t

Therefore, as an example, calculating the amount of P2O5 and K2O removed by a crop for some estimated average crop yields for the 2002 drought year are as follows:

Amount of phosphorus removed per acre in terms of P2O5:
Corn Grain = 60 bu/a yield multiplied by 0.37 lbs P2O5/bu = 22.2 lbs P2O5/a
Corn Silage = 8 t/a yield multiplied by 3.30 lbs P2O5/t = 26.4 lbs P2O5/a
Soybeans = 25 bu/a yield multiplied by 0.63 lbs P2O5/bu = 15.8 lbs P2O5/a
Alfalfa = 5 t/a yield multiplied by 13.00 lbs P2O5/t = 65 lbs P2O5/a

Amount of potassium removed in terms of K2O:
Corn Grain = 60 bu/a yield multiplied by 0.27 lbs / K2O bu = 16.2 lbs K2O/a
Corn Silage = 8 t/a yield multiplied by 8.00 lbs K2O /t = 64 lbs K2O/a
Soybeans = 25 bu/a yield multiplied by 1.40 lbs K2O /bu = 35 lbs K2O/a
Alfalfa = 5 t/a yield multiplied by 50.00 lbs K2O /t = 250 lbs K2O/a

Even though 2002 was a drought year for most regions of the state, you can see that corn silage and alfalfa remove considerably more potassium from the soil than the other crops. Consequently, even with an understanding of the amount of nutrients removed by the crop, it is very important to conduct a soil test before next year's crop year. Since only a fraction of the total P and K is considered available to the plant, an accurate soil test will measure only the concentrations of plant available P and K in the soil.

The Tri-State Fertilizer Guide, on which the Ohio State University's computerized fertilizer and lime recommendation program is based, lists critical soil test levels for phosphorus (P) and potassium (K) for corn, soybeans, wheat and alfalfa. The levels of these nutrients are expressed as parts per million (ppm) or lbs/acre of the elemental form of P and K. Soil test values below the critical level should be considered as indicating that the soil is nutrient deficient for the growth of that crop. The critical level for K increases as the cation exchange capacity (CEC) of the soil increases. That is, higher levels of K are needed in soils with higher CEC.

In addition to the use of a critical soil test level, the Ohio State University recommendation program incorporates a maintenance range concept. The maintenance range is the optimum range beyond the critical range where it is recommended that the level of P and K be maintained. In order to maintain the soil test concentration of P and K in the maintenance range, the amount of P2O5 and K2O removed by the crop is taken into account in the fertilizer recommendation. The soil test maintenance range for P and K may be different for different crops. Levels of P and K beyond the maintenance range are considered to be in excess of the crop's needs, and the fertilizer recommendation is reduced accordingly.

Test your field soils either this year after harvest or early next spring to determine the adequacy of P and K for next year's crops. Be sure to use a quality soil testing laboratory. Guidelines for choosing a quality soil testing laboratory can be found online at: http://ohioline.osu.edu/hyg-fact/1000/1133.html. More information on fertilizer and lime recommendations for Corn, Soybeans, Wheat and Alfalfa is available in the Tri-State Bulletin E-2567 which can be obtained from your local County Extension Office. If you wish to determine the fertilizer and lime recommendations using the Ohio State soil testing recommendation program, it is available online at: http://ohioline.osu.edu/e2567/

B) Fall Applied Nitrogen for Corn Production - Ed Lentz CORN Questions

Each year after soybean harvest, producers may consider applying nitrogen in the Fall. There are two main advantages to this practice: 1) nitrogen prices may be lower in the fall than the spring, and 2) time and labor may be more available than spring. However, the big disadvantage is the greater potential for nitrogen loss. In some years this nitrogen loss may cause a yield reduction. In an 8-year study, Ohio State University scientists, Stehouwer and Johnson, showed that average corn yields were about 5% higher from spring applied anhydrous compared to fall applied at the 160 pounds of nitrogen per acre. Without a nitrification inhibitor, the difference was almost 10%. Some years this percentage may be less and others more, depending on the weather. Unfortunately, some producers may add more nitrogen to compensate for this potential loss. The Ohio State University strongly discourages this practice since excess nitrogen may leave the field.

Since fall applied nitrogen has to remain in the soil for about six to seven months, the university recommends only anhydrous ammonia plus a nitrification inhibitor as a nitrogen source. As a further deterrent to nitrogen loss, they recommend applications after the soil temperature drops below 50º F and will remain below 50. Generally this occurs after October 20. Warmer conditions will shorten the effectiveness of the nitrification inhibitor.

In summary, fall applied nitrogen is an option for Ohio corn producers. However, this approach has a great potential for nitrogen loss. To minimize these losses consider the following management practices:

1) Only use anhydrous ammonia. Besides being the most economical source of nitrogen, it is the slowest of all nitrogen fertilizers to convert to nitrate-nitrogen.
2) Use a nitrification inhibitor. These products delay the conversion of ammonium to nitrate-nitrogen. The duration of this delay is weather dependent. Warm weather will shorten the effectiveness of the inhibitor.
3) Apply fall nitrogen when soil temperatures stay below 50º F. Cooler temperatures reduce the activity of the bacteria that converts ammonium to nitrate-nitrogen.
4) Apply fall nitrogen only on well-drained soils. Do not fall apply on sandy ground.

Additional information may be found in the publication: Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa at your county extension office, or download from the Internet at http://ohioline.osu.edu/lines/farm.html and select the software option.

C) Fall Herbicide Treatments For Dandelion and Winter Annual Weed Management - Mark Loux, Tony Dobbels, and Jeff Stachler CORN Questions

This article is essentially a condensed version of the dandelion and winter annual articles in the September 3 and 23 issues of C.O.R.N. consult these articles in the C.O.R.N. archive for more information. Herbicide treatments applied between now and about mid-November should effectively control winter annual weeds, dandelion, and biennials such as wild carrot and poison hemlock. Control of these weeds in the fall has the following benefits:

• prevents the dense mat of chickweed and other winter annuals that slow soil drying and warming and interfere with planting and tillage in the spring
  
• reduces the weed cover that can harbor insects
  
• dandelion is effectively controlled in the fall, which prevents it from interfering with early crop growth the following spring. Herbicide treatments in spring are somewhat variable in their effectiveness on dandelion
  
• control of purple deadnettle and several other winter annuals prevents them from serving as hosts for soybean cyst nematode
  
• may reduce the rate of development of herbicide resistance in marestail and other weeds that appear to become readily resistant to glyphosate and ALS inhibitors
  
• prevents winter annuals and dandelions from producing seed, reducing problems in the future

Some general suggestions to maximize the effectiveness of fall herbicide treatments follow:

• Optimum time of application for control of emerged winter annuals is between mid-October and mid-November. We have applied as late as the first week of December under very cold conditions, and still achieved effective control. However, we suggest applying herbicides under relatively warm conditions if possible. Apply by early November, or before a hard freeze, when trying to control dandelion and other perennial weeds.
  
• When using residual herbicides (Canopy, Backdraft, Python, etc) with the goal of controlling weeds as long as possible into the following crop, delay application until mid-November to minimize herbicide degradation.
  
• We recommend including 2,4-D with all treatments, to reduce the risk of herbicide resistance and help control dandelions and a few other weeds. A rate of 1 pint/A should be adequate with most treatments.
  
• Treatments with glyphosate should be applied with ammonium sulfate. Include surfactant if recommended by the glyphosate product label. Most other treatments should be applied with crop oil concentrate.
  
• If possible, wait a minimum of a week or so after crop harvest to apply herbicides, which allows time for crop residue to settle and maximizes contact of spray with weeds.

Some additional points relative to dandelion control:

• Across all of the dandelion studies we have conducted in fields where soybeans will be planted, the most consistently effective dandelion control resulted from application of: glyphosate (26 oz/A of UltraMax or 32 oz/A of other glyphosate products); a mixture of glyphosate (11 to 16 oz/A) plus 2,4-D (1 pt/A); a mixture of Canopy XL plus Express plus 2,4-D; or 2,4-D alone (1 qt/A). While all of these have been effective at low dandelion population densities, glyphosate or glyphosate plus 2,4-D has been the most effective treatment at moderate to high population densities in OSU research.
  
• In OSU studies, mixing glyphosate and/or 2,4-D with Scepter, Pursuit, Valor, or Sencor has occasionally reduced dandelion control, compared to application of glyphosate and/or 2,4-D alone. Backdraft is a premix of Scepter plus glyphosate.
  
• With all treatments, the effectiveness of control and reduction in the dandelion population will be dependent upon the population density. In low to moderate population densities, the treatments mentioned above are capable of controlling all or most of the dandelion present. This level of control may not be possible where dandelion population densities are extremely high.
  
• In our limited comparisons of various 2,4-D products, the 2,4-D rate appeared to be more important that the type of 2,4-D applied. When applied alone, the rate should be the equivalent of at least 1 lb ae per acre (1 qt of 4 lb/gallon products). In combinations with glyphosate or Canopy XL/Express, a 2,4-D rate of 1 pt/A appears to be adequate.
  
• Where corn will be planted the following spring, consider one of the following treatments for dandelion: glyphosate (26 oz of UltraMax or 32 oz of other glyphosate products; glyphosate (13 to 16 oz/A) plus 2,4-D (1 pt); 2,4-D alone (1 qt/A); or Basis plus 2,4-D. Simazine can be added to these treatments to improve control of some winter annuals or extend the period of residual control, but simazine will not have much activity on dandelion. The most economical and broad-spectrum fall treatment for corn may be simazine plus 2,4-D (1 lb ai/A plus 1 qt/A).

We have conducted studies on the effectiveness of fall herbicide treatments over the past several years, which have included most of the treatments that manufacturers are currently promoting. Some brief information on their effectiveness follows. This list does not include every possible combination of herbicides, but should provide an idea of relative effectiveness. Note on glyphosate formulations a rate of 0.75 lb acid equivalent per acre corresponds to the following: Roundup WeatherMax 22 oz; Roundup UltraMax 26 oz; Roundup Original, Glyphomax, Touchdown, and most other glyphosate products 32 oz.

• Glyphosate or glyphosate plus 2,4-D: Very effective treatment for control of dandelion and winter annuals. Possibly the most effective treatment for fields where dandelion is extremely problematic. Can be used prior to corn or soybeans. Primary disadvantage is the lack of residual activity into the following spring, which means that two in-season herbicide applications are likely to be necessary. The minimum rate for glyphosate applied alone in fields with dandelion, wild carrot, and other simple perennials and biennials should be 0.75 lb acid equivalent per acre. When applied with 2,4-D, the glyphosate rate can be reduced unless the population density of these species is extremely high.
  
• 2,4-D (1qt/A): Economical treatment for dandelion and most winter annuals, but will not control chickweed. Can be used prior to corn or soybeans. Primary disadvantage - no residual activity into the spring. Populations of wild carrot can be resistant to 2,4-D, and control of these will be unacceptable. Cressleaf groundsel and curly dock may not be completely controlled, because they have tolerance to 2,4-D.
  
• Backdraft (glyphosate plus Scepter) plus 2,4-D: Similar to glyphosate plus 2,4-D, with the addition of residual activity into the following season. Scepter appears to antagonize the glyphosate/2,4-D occasionally, reducing control of dandelion primarily. Use before soybeans only.
  
• Canopy XL plus Express plus 2,4-D: Effective treatment for dandelion and winter annuals. Provides residual activity into the following season the length of this residual varies with rate of Canopy XL applied. Disadvantage possibility of developing ALS resistance (so use of 2,4-D with this treatment is essentially mandatory) and lack of control of ALS-resistant marestail in the spring. Use before soybeans only. Low rates of Canopy XL may not completely control 2,4-Dresistant wild carrot.
  
• Python plus 2,4-D plus glyphosate: Similar to glyphosate plus 2,4-D, with the addition of residual activity into the following season on certain broadleaf weed pecies. Python will not provide residual control of ALS- resistant marestail into the spring. Can be used before corn or soybeans.
  
• Sencor plus 2,4-D: Effective on many winter annuals, but rarely provides more than 80% chickweed control in OSU studies (usually conducted in very dense chickweed areas). Sencor appears to antagonize the 2,4-D on dandelion occasionally, reducing the control. Sencor does not control wild carrot. Expect shorter period of residual control compared to CanopyXL or Scepter. Can be applied in fall before corn or soybeans.
  
• Valor plus 2,4-D: Variable on most winter annuals in OSU studies, and ineffective for dandelion and chickweed control when applied in the fall. Provides residual control into the spring, but not on giant ragweed. Can be applied before corn or soybeans.
  
• Simazine plus 2,4-D: Effective on winter annuals and dandelion, but a 2,4-D rate of 1 quart/A may be necessary for effective control of dandelion and large purple deadnettle in problem fields. Use in the fall before corn only.
  
• Basis plus 2,4-D: Effective on winter annuals and dandelion. Use in the fall before corn only.

D) Baythroid 2 Labeled on Corn & Soybean - Bruce Eisley & Ron Hammond CORN Questions

Baythroid 2 (cyfluthrin) has received label approval for use on corn (field, pop & seed) and soybeans. The chemical is labeled on corn for all of the common Ohio corn insects including cutworm, armyworm, stalk borer, European corn borer, flea beetles and others. Check label for rates and labeled insects.

Baythroid 2 is labeled on soybean for all of the common Ohio soybean insects including bean leaf beetle, Japanese beetle adults & others. Pre-harvest interval for Baythroid on soybeans is 45 days. Check label for rates and labeled insects.

E) Intrepid 2F Labeled on Corn - Bruce Eisley & Ron Hammond CORN Questions

Intrepid 2F (methoxyfenozide) has received label approval for use on corn (field, sweet & seed). Intrepid is labeled for European corn borer, southwestern corn borer & true armyworm. Check label for rates and restrictions.

F) Regional Agronomy Meetings Schedule For Ohio's Crop Industry - Greg LaBarge CORN Questions

The Annual Regional Agronomy Meetings are an excellent opportunity to receive the last updates on crop production issues across Ohio. These meetings will be presented from 9:00 am until 2:45 pm at 8 locations during the weeks of December 16-19, 2002 and January 14-17, 2003. Presentations vary from site to site depending upon the issues of greatest importance locally. Complete agenda and registration information will be available on October 30 at http://corn.osu.edu/Education/index.html.

All programs will offer Commercial and Private Applicator Credits along with Certified Crop Advisor Continuing Education Credits. Registration includes a copy of the meeting proceedings and other Extension materials, lunch, and other handouts. Pre-registration is $15 until one week prior to the meeting and $20 at the door space available, so register early for cost savings and to guarantee your spot at these meetings.

The Agronomic Crops Team, Ohio State University Extension, Ohio Soybean Council and Ohio Corn Marketing Board sponsor the meetings along with local agricultural businesses. If you would like to become a sponsor of these meetings contact the Host Agent for the site you would like to work with or if you want to be a general sponsor contact Greg La Barge at 419-337-9210.

December 16, 2002
Trumbull County - Warren
Trumbull Career and Technical Center
50 Educational Highway, Warren
Host Agent: Stephen Hudkins
330-675-2595
hudkins.1@osu.edu

December 17, 2002
Wyandot County - Sycamore
Sycamore Community Center
3498 State Hwy 103, Sycamore
Host Agent: Clark Hutson
419-447-9722
hutson.22@osu.edu

December 18, 2002
Henry County - Deshler
Bavarian Haus
St. Rt. 18, 2 miles west of Deshler
Host Agent: Alan Sundermeier
419-354-9050
sundermeier.5@osu.edu

December 19, 2002
Darke County - Versailles
K of C Hall
8440 St. Rt. 47 E, Versailles
Host Agent: Steve Foster
937-548-5215
foster.99@osu.edu

January 14, 2003
Huron County - Norwalk
Community Bldg., Huron Co. Fairgrounds
940 Fair Road, Norwalk
Host Agent: Gary Bauer
419-627-7631
bauer.3@osu.edu

January 15, 2003
Pickaway County - Williamsport
Crownhill Golf Club
9500 US 22 West, Williamsport
Host Agent: Mike Estadt
OSU Extension, Pickaway County
740-474-7534
estadt.3@osu.edu

January 16, 2003
Belmont County - Bethesda
Lone Pine Hall
109 Washington Street, Bethesda
Host Agent: Steve Schumacher
OSU Extension, Belmont County
740-695-1455
schumacher.1@osu.edu

January 17, 2003
Greene County - Xenia
OSU Extension, Greene Co. Office
100 Fairground Road, Xenia
Host Agent: Jerry Mahan
937-372-9971
mahan.2@osu.edu

Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.

Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

Editor: Barry Ward        Web Editor: Tom Rosati

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868

  | C.O.R.N. | Newsletter | Archive | Search | Questions? | Ohioline | Publications |