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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-09

Dates Covered: 
April 13, 2004 - April 20, 2004
Steve Prochaska

How Deep Should I Plant Corn?

Authors: Peter Thomison

Several factors should be considered when determining a proper planting depth for corn. These include soil moisture and temperature, planting date, soil type, and tillage. Temperatures will be higher at 1 to 2 inches than at 3 inches or deeper. Soils are generally cooler and wetter in mid to late April than in early to mid May. A planting depth of 11/2 to 2 inches is often recommended for corn. In April, when soil is usually moist and evaporation rate is low, the seeding depth should be in the shallower end of this range (not much deeper than 1 1/2 inches). This is particularly important in no-till plantings (especially under heavy corn residue) where soil temperature and moisture will be cooler and wetter than in conventionally tilled soils. However, if you try to plant less than 1 1/2 inches deep, some of the seed may end up much shallower due to variation in the seedbed. These shallow plantings often result in poor nodal root development (that lead to “rootless” and “floppy” corn problems) and expose seed more to surface applied herbicides. As soils warm up and evaporation rates increase, consider deeper planting - up to 2 1/2 inches on non-crusting soils - to reach moist soil. Remember, when conditions vary from the norm, planting depths should be adjusted accordingly to optimize emergence. Don't automatically use the depth setting you finished with last year!

Wheat Condition Update: Southern Areas Showing Rapid Growth

Authors: Patrick Lipps

Relatively warm growing conditions in southern Ohio have favored the rapid development of wheat. Fields in the far south have wheat beginning the stem elongation growth stage (Feekes growth stage 6). Feekes growth stage 6 is also called the 'first joint visible' stage. You can distinguish growth stage 6 by digging up a few plants and examining their tallest tillers. Plants are made up of several tillers or stems. Pull a large tiller from each plant and strip down the several layers of leaves and leaf sheaths to expose the lower stem. A plant is considered to be at growth stage 6 when the first node is detected on the stem above the roots. This node may be from a half inch to an inch and a half above the crown of the plant. Generally plants are from about a foot to 18 inches tall at this growth stage. This is a critical growth stage for wheat because the plant changes from a vegetative growth phase to a reproductive growth phase. This also marks the time when all spring top dress fertilization should be completed so that the plant can take full advantage of the applied nitrogen. Additionally, certain herbicides must be applied before this growth stage to prevent crop injury. Check herbicide labels for growth stage application restrictions.

In northern Ohio most fields are growing slowly due to the cooler night temperatures and corresponding cool soil conditions. Most fields are still in the tillering growth stages and some early planted fields are in Feekes growth stage 5 or 'upright leaf sheath' growth stage. Tillering will continue for about another week or so and fields will appear to 'fill in between the rows' due to tillering and tiller growth. Warmer temperatures later this week and into next week should promote crop development throughout the state. It is likely that most wheat in northern Ohio will reach growth stage 6 by the last week of April. Plan accordingly for top dress nitrogen and herbicide applications.

Wheat Weed Control

Winter wheat is beginning to joint (Feekes Stages 6 and 7) in southern Ohio. This stage of wheat development begins to restrict the usage of some herbicides. Dicamba products should not be applied to wheat once it begins to joint. Some 2,4-D and MCPA labels are also restricted from being used at the jointing stage, however, using lower rates of these products and using the amine formulation will help decrease the injury potential.

Seedcorn Maggot in Field Crops

Authors: Ron Hammond, Bruce Eisley

Seedcorn maggots are larvae of small flies, and are capable of causing significant stand reductions in corn and soybeans under the appropriate conditions. Seedcorn maggot populations are greatly enhanced when a green, living cover crop is plowed or otherwise tilled into the soil, including alfalfa, wheat or rye, and extremely heavy growths of weeds. There is a possibility that heavily manured fields that are tilled might also result in the problem. Although seedcorn maggots are often found feeding on seeds in no-till situations, economic problems are rarely seen. In fields where a green cover is tilled into the soil in the spring, growers should consider an insecticide seed treatment. If the seed is not treated when purchased, growers should check with their dealers for available treatments. If seed treatment is not an option, waiting at least 3-4 weeks after tilling will help to reduce seedcorn maggot injury.

Slug Update

Authors: Bruce Eisley, Ron Hammond

Slug population densities were moderate to heavy in many fields in the fall of 2003, suggesting that spring populations will be high. While sampling for slug eggs last week, we found many fields with numerous eggs. In a few fields, we found eggs in every location of the field we checked, while in other fields, we found very few eggs. Corn and soybean growers who have had problems with slugs in the past should sample their fields. Over the next few weeks, they should check numerous spots in their fields. Slug eggs are usually laid in batches of 3-5 and are found just at or slightly below the soil surface. Growers should move crop residue aside in an area about a foot square, and scrape the soil with a small knife or other instrument. The eggs will be round, slightly smaller than a BB, and usually clear to slightly opaque (see picture at ). Although we do not have thresholds as to what represents an economic problem, finding eggs in the majority of locations suggests a potential problem and a field that needs to be monitored closely. However, not finding any eggs is not a reason to forget that field. All no-till fields should still be monitored this spring for slug injury. However, egg sampling and knowing which fields have a higher damage potential will aid you in managing your slugs this spring. Keep a watch on this CORN newsletter for further updates on this problem.

Update on Soybean Rust

Authors: Anne Dorrance

It’s not here in the continental United States. I’ve been getting a lot of questions over the past few weeks concerning soybean rust and thought I would let everyone know what the status is of this pathogen.

There is a Technical Working Group for Soybean Rust, comprised of scientists from all of the land grant institutions and USDA, representatives from the soybean commodity boards and Dept. of Agriculture officials across the U.S. There is a conference call, approximately every other month, plus various presentations at the meetings I have attended this winter. In fact, I leave for Maryland on Monday (April 12) for another meeting on soybean rust.

As we have mentioned before there are four possible routes of entry of this rust fungal pathogen into the U.S.:

1) via the Central American land bridge;
2) winds of hurricane via the Caribbean;
3) spores on shipments of seed or meal and
4) an act of bioterrorism.

In all likelihood, the last two are very unlikely due to biology and the nature of this pathogen, and a higher likelihood for routes 1 and 2.

When this gets here, we do have a management plan in place. Officials at the Ohio Dept. of Agriculture, USDA, PPQ, Pat Lipps and myself met last month and drafted a response plan. Because soybean rust is a select agent and does not occur here in the US, there are procedures in place for the first find and follow-up notification.

Once soybean rust becomes established we will manage this disease with two disease management strategies: 1: fungicide applications and 2: host resistance.

Host resistance is not going to be like the Rps genes for Phytophthora sojae, but more along the lines of partial resistance used for gray leaf spot on corn and mildew for wheat. This rust adapts very fast, within a year to R-genes that have been deployed. One of the terms researchers have used is called “slow rusting” types. Many of the companies are already screening advanced lines in research stations around the world. USDA is currently screening the soybean germplasm collection. We will hopefully hear about these results soon.

Fungicide applications will be necessary to manage this disease, but this will vary greatly year to year. The primary driving force will be the environment - how early infections begin in the southern US and how soon they begin to travel north. Current data suggest, that this fungal pathogen will not be able to overwinter here in Ohio. The good news, is that the reports from Brazil during 2003 indicate that many fungicides work and there will be many choices. We currently have 3 materials registered in the U.S. and the E.P.A. has approved the first material for section 18. We wrote an application two weeks ago for Ohio to be added to this Section 18. The catch on the Section 18s is that they do not go into effect until soybean rust is found in the continental U.S.
Research at Ohio State University – during 2003, with the help of Mark Loux and his team, we looked at the application of fungicides in combination with glyhosate. Applying fungicides to soybeans is going to be expensive and if we can save application costs then this will be a big help in preserving profits. This maybe too early for most fields, but it is good to get this data in ahead of time. During 2004, we will repeat this experiment, plus we have several trials planned to examine some of these materials alone and in combination with insecticide. We may also have soybean aphids to continue to manage.
Over the summer, we will keep you posted on what may or may not develop during the growing season. Next winter, we will begin a series of articles on fungicides. I hope this answers some of your questions. I have total confidence that we will be able to manage this disease once it gets here, it’s likely to eat at our profits the first few years.

Which Source of Nitrogen is the Best?

Authors: Robert Mullen

This is an often asked question, which unfortunately does not have a simple answer. Like most agronomic questions, there is no all encompassing solution that will work equally across all field conditions and environments. When making a decision on a nitrogen (N) source, economics, soil conditions, and climate must all be considered. Nitrogen applied as anhydrous ammonia, urea, urea-ammonium nitrate (UAN), etc., if applied at equivalent rates of N, all contribute the same amount of N to the soil. Plants do not prefer one formulation over the other.

Anhydrous Ammonia

Because anhydrous ammonia (82% N) has historically been the cheapest source of N, it has been the most popular. Due to the nature of anhydrous, it must be injected into the soil which increases its cost of application. Improper sealing behind injection equipment can result in considerable losses of N. Care should also be taken to inject anhydrous at least 6 to 8 inches into the soil. This is especially important if planting just after application of N. Anhydrous ammonia can cause seed injury.

Dry Formulations

With the cost of anhydrous production within the U.S. rising, the price differential between anhydrous ammonia and alternative formulations has decreased. Urea (46% N) is the most popular dry source of N. Its high N analysis and cheap cost make it an attractive alternative to anhydrous ammonia. Caution should be exercised when surface applying urea in no-till production systems. Considerable losses of N by volatilization can occur, especially if dry weather follows application. Application of urea would ideally be followed by a small rainfall event or incorporation.

Ammonium nitrate (34% N) is another dry formulation consisting of 50% ammonium and 50% nitrate. Its popularity has decreased in recent years. In fact, some retailers no longer sell it in bulk. Ammonium nitrate is an attractive alternative to anhydrous because it does not contain any urea, meaning it is not susceptible to volatilization losses allowing for surface application. However, it is easily dissolved with very little surface moisture making it susceptible to leaching and denitrification.

Liquid Formulations

Liquid formulations of N, primarily as urea-ammonium nitrate (UAN – 28 and 32% N), have gained popularity in recent years. Its ease of application and handling as well as comparative pricing with dry formulations has aided its adoption rate. Due to the nature of UAN, broadcast application in no-till systems can result in considerable interception of the material by residue. Dribble applications of UAN can decrease this affect, or UAN can be injected below the soil surface. UAN is especially attractive as a source of N for sidedressing.

When selecting your source of N, consider all factors. The goal is to select the cheapest source that fits within your farming operation.

Planting Practices for Minimizing GMO Contamination of non-GMO Corn

Authors: Peter Thomison

Managing pollen drift has become an important consideration in the production of non-GMO corn as an Identity-Preserved (IP) grain crop. Corn is a cross-pollinating crop in which most pollination results from pollen dispersed by wind and gravity. Although most of a corn field’s pollen is deposited within a short distance of the field, pollen may travel as far as ½ mile with a 15 mph wind in a couple of minutes. Pollen from corn containing transgenes or genetically modified organisms (GMOs), such as Bt corn, may contaminate (by cross-pollination) nearby non-GMO corn. Producers of IP non-GMO corn need to minimize pollen contamination by GMO corn if they are to obtain premiums. Farmers growing GMO hybrids approved for export also want to avoid contamination of their crops by GMO corns that have not yet received approval in overseas markets. As GMO of other types of Bt and Roundup Ready corn, growers of IP non-GMO corn should become more familiar with planting practices that prevent contamination by pollen from nearby GMO corn fields.

Growers can follow several planting practices to minimize GMO pollen contamination, including use of isolation and border rows, planting dates and/or hybrid maturity.
For more information on these methods, consult Extension Fact Sheet AGF-135, Managing "Pollen Drift" to Minimize Contamination of Non-GMO Corn; it’s available online at

For a good overview of other issues related to producing non-GMO corn grain, check out the following: “Corn Segregation: A Necessary Evil in Today’s Biotech Age” by Dr. Bob Nielsen at Purdue University online at and a recent Powerpoint presentation Bob’s prepped on this topic "Protecting your non-GMO grain from contamination" online at

Soil Temperatures Across Ohio on April 11

Authors: Dennis Mills

Soil temperature (2”) on April 11 was 43ºF at Ashtabula, 48º at Wooster, 51º at Hoytville, 52º at South Charleston and 53º at Jackson, which is equal to or above 2003 but below the 3 year average.

Archive Issue Contributors: 

State Specialists: Robert Mullen (Fertility Specialist), Pat Lipps, Ann Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); Extension Agents: Roger Bender (Shelby), Howard Siegrist (Licking), Ray Wells (Ross), Todd Mangen (Mercer), Mark Koening (Sandusky), Allan Sundermeier (Wood), Glen Arnold (Putnam), Barry Ward (Champaign), Steve Foster (Darke), Gary Wilson (Hancock), Glen Arnold (Putnam), Harold Watters (Miami), Dusty Sonneberg (Henry) and Steve Prochaska (Crawford).

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.