C.O.R.N. Newsletter 2006-09

Dates Covered: 
April 17, 2006 - April 24, 2006
Editor: 
Steve Prochaska

Nitrogen Credit for Corn following Soybeans and Online User’s Guide

Authors: Robert Mullen, Edwin Lentz

As you are well aware, Ohio State University is moving to a different nitrogen recommendation system for corn this year, and with the new recommendations the nitrogen credit provided for corn following soybeans has changed. Historically, Ohio State has assumed a 30 pound nitrogen credit for corn following soybean compared to corn following corn. Within the new recommendations the credit is closer to 40 plus pounds of nitrogen credit. This adjustment is dictated by the data used to generate the recommendations. Compared to the rest of the Corn Belt this credit is more in line with other Land Grant Universities. While this credit change is noteworthy, remember that the credit is built into the recommendation model and you as a producer or consultant do not need to subtract the credit from the recommendation. You simply need to select the appropriate previous crop.

To provide some direction for the new Excel based economic recommendations, a User’s Guide has been published online to help some of the more frequently asked questions regarding the use of the spreadsheet. The online User’s Guide can be found at https://agcrops.osu.edu/fertility/documents/Users_guide_03_06.pdf .

Foliar Fertilizers; The Agronomic Considerations

Authors: Robert Mullen, Edwin Lentz

Increasing costs of common commercial fertilizers (nitrogen, phosphorus, and potassium) make non-traditional fertilizer forms, specifically foliar fertilizers, more attractive, but can this method of fertilization take care of all the plant’s nutrient needs? The purpose of this article is to discuss the agronomic obstacles of strict foliar fertilization.

We will begin the discussion by stating that land application of any fertilizer (including organic and commercial forms) for higher plant production is relatively inefficient because of soil biological, chemical, and physical properties that can decrease nutrient availability. Remember plants do not have the first shot at any nutrient we apply to the soil, that is reserved for soil microbes. This is especially true of fertilizer nitrogen. Phosphorus and potassium applied to soil are needed for microbial metabolism, but their availability is more dependent upon soil chemistry rather than biology.

Nitrogen

Any nitrogen supplied to a soil system is initially available to the microbial population. This is very evident if a recent high carbon to nitrogen ratio plant residue has been returned to the soil (mature corn and wheat are two good examples). Any inorganic nitrogen supplied to the soil system is taken up by the microbes resulting in nitrogen immobilization. Nitrogen supplied to the soil in an ammonium form (anhydrous ammonia, urea, urea-ammonium nitrate, ammonium sulfate) under warm, moist soil conditions can also be quickly converted to nitrate by soil bacteria which can be lost from the soil system by leaching (coarse textured soils) or denitrification (fine textured soils) under the right environmental conditions. Because of immobilization and nitrification soil biological activity can result in inefficient use of fertilizer nitrogen. This makes foliar fertilization attractive because we remove the soil system from the equation, but can we supply enough to satisfy crop demand throughout the growing season? The answer is yes, but one application of foliar fertilizer is not going be enough to get the crop through the entire year. It will require multiple applications of foliar nitrogen. Agronomically, numerous applications throughout the growing season are probably the most efficient method of nitrogen fertilization, but who can pay for multiple applications? Foliar fertilization is not 100% efficient either. Depending upon what stage of growth the foliar material is applied, a large portion may simply fall to the ground where it is subject to the same fate as any other fertilizer material.

Let’s assume we are going to supply 150 pounds of nitrogen per acre for a corn crop following soybeans. Can all of that nitrogen be applied as a foliar form? In one pass – highly unlikely. Some will have to be applied as a starter (either with the planter or through weed ‘n’ feed). So assume we supply 40 pounds per acre with the planter. That leaves us with a deficit of 110 pounds of nitrogen in our budget. Can that be applied as a foliar application? The answer is still no, especially if we supply it to corn that is 18 inches tall. Corn that short has a lot of exposed soil between rows, and a good amount of the broadcast application of foliar fertilizer will undoubtedly hit the soil rather than the corn plants themselves. So attempting to provide all of the nitrogen as a foliar fertilizer will not work in that situation (because some of it went the soil route). Can foliar fertilization improve nitrogen efficiency to a point that we can decrease application rates? We have not seen any data to lead us to this conclusion.

Phosphorus

Phosphorus use efficiency for higher plant growth is even poorer than nitrogen use efficiency. Unlike nitrogen, phosphorus availability is not dictated by soil biology, instead its availability is controlled by soil chemical reactions. Soil applied phosphorus can readily form insoluble compounds with soil calcium and aluminum decreasing its availability. Because soil applied phosphorus is relatively inefficient foliar fertilization can be attractive, but soil test level must be a consideration. High soil test levels are unlikely to respond to additional fertilizer phosphorus (whether it is soil or foliar applied), so utilizing a foliar material may appear to be working when in reality you do not need phosphorus at all. Continued use of a strict foliar program may result in mining of soil phosphorus to a level that is deficient increasing the risk of yield loss down the road. Foliar phosphorus fertilization can not replace soil applied phosphorus for maximum crop production in the long term!

Bottom line – soil fertilization of macronutrients (nitrogen, phosphorus, and potassium) for crop growth can not be replaced by foliar fertilization completely. When evaluating foliar fertilizers recognize them for what they are – a way to provide a little nutrient to get the crop through a tough time (primarily micronutrients) not as a replacement for a sound soil fertility program. In fact a sound fertility program should limit the need for foliar nutrients. Regarding other non-traditional forms of fertilizer, Dr. George Rehm (University of Minnesota) has recently written two articles that are worth a read.

The Test Plot or The Testimonial at http://www.extension.umn.edu/cropenews/2006/06MNCN17.htm


Enzymes, Microbes, and Other Good Things at http://www.extension.umn.edu/cropenews/2006/06MNCN19.htm

Use Skip- Rows For Soybean Pest Control

Authors: Jim Beuerlein, Anne Dorrance, Ron Hammond, Dennis Mills

There are several late season soybean insect and disease problems that many Ohio growers must deal with. Most fields are planted in narrow (7.5-inch) rows and may be sprayed in late July or in August, well after the soybean canopy has closed which will cause a yield loss due to soybean plants being run down. Fortunately, most commercial sprayers have narrow tires so only two rows may be run down as the sprayer crosses a field, but the actual loss depends in the row spacing and size of the spraying equipment. Running down two rows with each sprayer pass through a 50 bushel crop worth $6.50 per bushel will cause a $6.83 per acre loss. Leaving skip rows will cost only $2.20 per acre because some rows are not planted. It is always less expensive to use a skip-row system than to run down some of the crop with a sprayer.

When forming skip rows it is important that they be the correct distance apart to accommodate the sprayer that will be used. Many sprayers are adjustable and can accommodate a wheel spacing of about eight to twelve feet. The ideal combination of drill and sprayer width is when the sprayer is three times as wide as the drill. With that combination the sprayer will use the 2nd, 5th, 8th, etc. pass of the drill when making applications. If the sprayer is either two or four times as wide as the drill, the first sprayer pass should be positioned to spray from the edge of the field to the center of a drill pass by disabling nozzles on the end of the sprayer. For the remainder of the field use all the spray boom and the appropriate skip rows. Sprayers that are not full multiple widths of the drill will not be able to use skip row systems unless the sprayer size is either increased or decreased to meet that requirement.

For more information about using skip-rows go to: https://agcrops.osu.edu/soybean/skiprow5%20october%202005.pdf

A Marestail Update

Authors: Mark Loux

Observations of marestail populations in various fields indicate that marestail may be sparser or at least no more numerous than in prior years. However, last week’s warm weather spurred the growth of marestail plants, and some plants have started to bolt (produce an upright stem). Marestail is most effectively controlled by herbicides prior to bolting, and applying burndown herbicides soon will help ensure control of existing plants.

Our latest greenhouse research with marestail collected last fall indicates the continued spread of herbicide-resistant marestail. Glyphosate-resistant marestail has now been confirmed in Licking and Mercer Counties as it continues to move to the north and east in Ohio. Multiple-resistant marestail, which is resistant to both glyphosate and ALS inhibitors, has been confirmed in additional fields in Madison and Preble Counties. In two of the newly found multiple-resistant populations, the marestail were initially found to be only glyphosate-resistant after the 2003 growing season. We believe that the subsequent development of multiple resistance was the result of applying a combination of glyphosate plus FirstRate during the 2005 growing season, which selected for resistance to ALS inhibitors as well as glyphosate. This appears to indicate that marestail populations can change their population dynamics quite quickly, sometimes within two growing seasons. Recent Purdue University research has shown that 20% of glyphosate-resistant marestail populations found in southeastern Indiana actually have multiple resistance (to both glyphosate and ALS inhibitors). A similar trend may be occurring in marestail populations in southwestern Ohio. Our latest research also confirmed the presence of an ALS-resistant marestail biotype in Fayette County for the first time.

The most effective control of marestail in burndown herbicide applications in soybeans generally results from a three-way combination of herbicides that includes 2,4-D ester. Based on OSU research, the most effective herbicide combinations for control of marestail plants up to four inches tall are:

- glyphosate (at least 1.1 pounds acid equivalent/A) plus 2,4-D ester (0.5 pounds active ingredient/A) plus one of the following: Canopy, Synchrony, FirstRate, Amplify, or Gangster;
- paraquat (at least 0.64 pounds active ingredient/A) plus 2,4-D ester (0.5 pounds active ingredient/A) plus Sencor (8.0 ounces/A).

Weed Management Publications Available And Free!

Authors: Mark Loux


Weed scientists in Ohio, Indiana, and Illinois recently updated the free publication, “Biology and Management of Horseweed”. While many growers refer to giant ragweed as “horseweed”, this publication provides information to improve management of the true “horseweed”, otherwise known as “marestail”. The publication covers the following aspects of horseweed biology and management:

- identification, including information and photos to help differentiate between horseweed and other species that may be similar in appearance;
- distribution and emergence;
- growth and development;
- herbicide resistance issues;
- strategies for control and suggested herbicide treatments.

We can mail a few copies of this publication to anyone so requesting. Contact us for information on obtaining larger numbers of copies. The publication can also soon be accessed at the OSU weed science website, https://agcrops.osu.edu/weeds .

We have also created a 2-page fact sheet on the benefits of using residual herbicides in Roundup Ready soybeans. This fact sheet includes straightforward information and graphics illustrating the yield penalty from applying glyphosate too late in Roundup Ready soybeans. It also shows how residual herbicides can increase the flexibility in postemergence application windows, improve yield, and improve control of lambsquarters and giant ragweed. This fact sheet is available on the OSU weed science website, https://agcrops.osu.edu/weeds . We have no plans to have a batch of this fact sheet printed, so feel free to download it and distribute as you see fit.

Transgenic Corn And Refuge Planting

Authors: Ron Hammond, Bruce Eisley

With corn planting beginning in Ohio, we want to remind corn growers that when planting transgenic corn resistant to either the European corn borer or western corn rootworm that they must plant a refuge of non-Bt corn within, nearby, or adjacent to fields of Bt corn depending on which type of transgenic corn is being used. This is true for both families of transgenic corn, YieldGard and Herculex. This is a requirement that will serve to preserve Bt technology for the future.
The basic requirement in Ohio is planting a 20% non-Bt corn refuge to 80% Bt corn, regardless of the target insect or brand of corn grown. For transgenic corn for European corn borer control, the refuge must be planted within 1/2 mile of the Bt corn, with 1/4 mile being preferred. For transgenic Bt corn for rootworm control, the refuge must be placed within or adjacent to the field of Bt corn. If using a stacked-trait transgenic corn resistant to both insects, we recommend placing the refuge within or adjacent to the transgenic corn. The design of the field and how the refuge is placed near or within the Bt-corn is very flexible. The refuge can be planted as a block at the end of the field, in rows around the perimeter, or as strips within the field as long as 20% of that field is planted to the refuge. There are numerous other requirements related to the planting of the fields, including what insecticides can be used for control of other insects. Growers should obtain information from their seed dealers on these other requirements.

Cutworm Moths Flying In Ohio

Authors: Ron Hammond, Bruce Eisley

Black cutworm (BCW) moths are being captured in pheromone traps in central Ohio at this time. These moths are migrants and are being blown in from the south by the recent storms moving through Ohio. This is the time of year that moths start moving into Ohio and we use pheromone catches to monitor their movement. There isn't any way to determine whether BCW is going to be a problem in Ohio in corn this year or in what fields it might be a problem. However, we do know that these moths will seek out fields with a lot of weeds, especially winter annuals such as chickweed, to lay their eggs. The eggs are laid in the weeds and the tiny larvae feed on the weeds until the weeds are killed by herbicide or tillage at which time the larvae will move onto the corn planted in the fields. With the wet soil conditions we are experiencing, many of the fields in the state will have more weeds in the next couple of weeks and perhaps will be more attractive to the moths.

Our suggestion to deal with BCW is to scout fields as soon as the corn begins to sprout and emerge from the soil. Rescue treatments can then be applied if necessary. If a field is extremely weedy a preventive insecticide treatment at planting might help to prevent serious cutworm injury. However, there isn't any way to determine which weedy field might have a problem before planting. For additional information about BCW and other early season pests of corn, see OSU Fact Sheet FC-ENT-12 at http://ohioline.osu.edu/ent-fact/0012.html .

There are a number of insecticides that are currently labeled for use on corn against cutworm and they can be found on the web at: http://entomology.osu.edu/ag/545/cicw.pdf .

Weed ‘n’ Feed Nitrogen Application; Should I Put All My Eggs in One Basket?

Authors: Robert Mullen, Alan Sundermeier, Edwin Lentz

With increased diesel costs this year you may be interested in eliminating a field pass, so would it make sense to supply your entire nitrogen budget as a weed ‘n’ feed application? It depends upon how much nitrogen you are willing to risk losing and that depends upon your residue management. The more residue you maintain on the soil surface the greater the risk of nitrogen loss by volatilization if you broadcast apply UAN (28-0-0). Some recent research conducted at the Northwest Research Station over the last four years reveals that applying your entire nitrogen budget as a broadcast application can result in yield loss under the right environmental conditions. In 2002, presence of residue did not make a difference in whether or not nitrogen was lost, all treatments that had the full nitrogen budget as a weed ‘n’ feed had yield losses. In 2003, yields were significantly reduced when nitrogen was supplied solely as a weed ‘n’ feed versus a split (starter and sidedress nitrogen) application. In 2004, yield losses were only observed where there was a significant amount of surface residue, but the tillage treatment that incorporated the majority of the residue did not show the yield loss. In 2005, differences were not observed between the two application methods because 0.3 inches of rain were received after application of the weed ‘n’ feed nitrogen decreasing the loss of nitrogen by volatilization.

Weed ‘n’ feed applications of your entire nitrogen budget are probably not the best option every time and more residue present on the soil surface at the time of the broadcast application the greater the risk of substantial nitrogen loss. Split applications or pre-plant applications that are incorporated perform more consistently from a yield standpoint, but weather conditions obviously play a role.

If you are considering application of your entire nitrogen budget as a weed ‘n’ feed and you maintain a fair amount of residue on the soil surface, you may want to consider the use of a urease inhibitor, especially if rainfall is not in the short-term forecast following the application.

Heat Unit Requirements for Corn Emergence

Authors: Peter Thomison

Corn requires about 100 growing degrees days (GDDs) to emerge (but emergence requirements can vary from 90 to150 GDDs). To determine daily GDD accumulation, calculate the average daily temperature (high + low)/2 and subtract the base temperature which is 50 degrees F for corn. If the daily low temperature is above 50 degrees, and the high is 86 or less, then this calculation is performed using actual temperatures, but if the low temperature is less than 50 degrees, use 50 degrees as the low in the formula. Similarly, if the high is above 86 degrees, use 86 degrees in the formula.

If it takes a corn hybrid 100 GDDs to emerge, and daily high and low temperatures average 70 and 50 degrees following planting, 10 GDDs accumulate per day, and corn should emerge in about 10 days (100 GDDs to emerge/10 GDDs per day = 10 days). However, if daily high and low temperatures are cooler, averaging 60 and 45 degrees after planting, 5 GDDs accumulate per day, and it may take nearly 3 weeks (100 GDDs to emerge/5 GDDs per day = 20 days) for corn to emerge. In 2005, corn planted in mid- April took 3 to 4 weeks to emerge in many fields.

Given the relationship between GDD accumulation and emergence, we should not be too surprised that it takes early planted corn up to 3 or more weeks to emerge. Seedling emergence is dependent on soil temperature and air temperature. Also, keep in mind that estimates of emergence based on GDDs are approximate and can be influenced by various factors including residue cover, tillage, and soil organic matter (soil "color") and moisture content.

Corn emergence can be slowed by inadequate soil moisture. Moreover dry soil conditions can cause uneven emergence in some fields that may impact yield if emergence delays exceed 1.5 - 2 weeks. Crops vary widely with regard to the minimum moisture content required for emergence. For corn, the minimum moisture content at which the radicle emerges is 30% of the seed dry weight. In contrast, for soybean, the reported minimum moisture content required for germination is 50% . However since a soybean seed generally weighs only 2/3 or less the weight of a corn seed, a soybean seed requires less water to germinate.

Ag Answers Is Another Excellent Agronomy Information Source

Authors: Candace Pollock

Producers looking for timely, research-based information, advice and strategies from Ohio State University Extension specialists and Ohio Agricultural Research and Development researchers can look to Ag Answers as an additional news source.

Ag Answers, updated twice weekly, is run jointly by Ohio State University Extension and Purdue University Extension. The electronic news source provides readers with a plethora of news on agricultural production-related topics, issues and events from both Ohio and Indiana researchers and Extension specialists.

Ag Answers is available through http://www.aganswers.net , or through a free e-mail subscription. To sign-up, log on to the Web site and click on the "subscribe" link.

Archive Issue Contributors: 

Ann Dorance, Pierce Paul and Dennis Mills (Plant Pathology), Mark Loux, and Jeff Stachler (Weed Science), Peter Thomison, (Corn Production), Jim Beuerlein, (Soybean Production), Robert Mullen and Maurice Watson (Fertility), Bruce Eisley, Ron Hammond (Entomology), Candace Pollock (Ag Communications). Extension Educators: Howard Siegrist (Licking), Harold Watters (Champaign), Glen Arnold (Putnam), Roger Bender (Shelby), Steve Foster (Darke), Steve Bartels (Butler), Steve Prochaska (Crawford), Bruce Clevenger (Defiance), Gary Wilson (Hancock), Ed Lentz (Seneca), Tammy Dobbels (Montgomery), Todd Mangen (Mercer), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Alan Sundermeier (Wood), Gary Wilson (Hancock) and Keith Diedrick (Wayne).

About the C.O.R.N. Newsletter

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.