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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2006-08

Dates Covered: 
April 10, 2006 - April 17, 2006
Steve Prochaska

The Soybean Rust Tales Begin

Authors: Anne Dorrance

What happened over the winter? This winter was quite mild compared to last for Ohio, but the southeast as well. Soybean rust did survive at several locations, albeit in very small amounts. The furthest north observation is an abandoned building site in Montgomery, Alabama (We have a very brave colleague, Ed Sikora who will stop at nothing to pursue the elusive kudzu leaf!). Here a few kudzu leaves were protected from the few freezes and these had soybean rust on them. Kudzu, did die back to the coast, but a few leaves survived in protected areas. Jim Marois’ (from University of Florida) talk during the Crop Profit series has some very nice illustrations of this. To see these, go to During January 2005, very, very little kudzu and soybean rust survived last year’s winter, and it took until November 2005 for pustules to be found on one kudzu leaf in Kentucky. So it isn’t rocket science to figure out that Ohio will probably have some soybean rust pustules develop during 2006. The big question still remaining, will rust arrive in time and in sufficient quantities to impact the soybean crop of 2006?

Ohio will soon be planting sentinel plots throughout the state. These will consist of varieties that are 1/2 to a full maturity than the soybeans grown in a given area. These maturities are not economically viable for Ohio. The reason we have moved in this direction is that one of the major findings from the Georgia group this past season, was that soybean rust developed in plots on the earliest maturing variety first, followed by the variety of the next maturity, followed by the variety of the next maturity. The goal here is: if we detect rust in an earlier maturing variety - this will indicate that there is inoculum present and conditions for infection were right. This will give time for fungicide applications to be made on neighboring fields before the varieties reach a truly vulnerable stage. At 10 locations in the state, funded by USDA, we will have four different varieties representing different maturities. In the remaining locations, two maturities will be planted. To reiterate what Greg Shaner from Purdue has said this winter, no one can actually give a hard recommendation on if rust will impact us this coming season. What we can do, is put the best detection methods that we currently have in place, put our best models in place, combine this with our "ground truth"/sentinel system, spore tracking system and give producers, consultants and applicators the best risk assessment.

This is a manageable disease. Our key focus is to keep this economically manageable. This is possible if the spray applications are timed to just prior to major loads of inoculum arriving in fields. The research groups from University of Florida, University of Georgia and Penn State University have all made significant progress this winter on evaluating alternative hosts, following over-wintering populations, evaluating host resistance, and collecting more data for the forecast models. Over the next few weeks, I will focus articles on these findings, and how Ohio will utilize these findings to better manage this disease. In the meantime, continue to do what you already do well – maximize your yields of soybean, don’t change anything.

Soybean Inoculation

Authors: Jim Beuerlein

The soybean is a legume who’s seeds generally contains 37% to 45% protein by weight. Depending on the protein content, a bushel of soybeans will contain between three and four pounds of nitrogen. The production of a 60-bushel per acre crop requires in excess of 300 pounds of nitrogen. Some of the nitrogen comes from the oxidation of soil organic matter with the balance produced by bacteria residing in nodules on the plant’s roots.

Advances in Inoculants

In recent years, inoculant manufacturers have focused their research and development efforts on finding ways to improve inoculants. Combining strains of Bradyrhizobium japonicum that are most productive in different environments results in products that are productive over a wider range of environments. Combining organisms that offer plant growth promotion hormones or disease control in conjunction with regular rhizobials is another new development. Other areas of interest are the biological signals that induce nodulation. The addition of “extenders” to inoculation materials allows the materials to be applied to seed up to thirty days or more before planting without loss of productivity if the seed is stored properly. One new material will allow application up to 60 days before planting even when applied in combination with selected fungicides which allows for seed inoculation at the warehouse instead of the farm.

Caring for Inoculation Products

Rhizobia cells survive best at temperatures of 40 - 80 degrees F. Prior to application, inoculants should be stored in a cool place and out of direct sunlight. Packets exposed to sunlight during the planting season will overheat rapidly due to the greenhouse effect and all the bacteria can be killed in less than an hour of exposure.

Seed inoculated with a product not having an “extender material” should be planted as soon as possible after treatment (12 hours or less) so the bacterial cells will remain moist and survive long enough to infect soybean roots following germination. Seed inoculated with a product having an “extender” can be held up to 30 days before planting depending on the product and which fungicides may be present. For specific product information refer to the product label. Most companies provide compatibility information on their websites. Go to the following for links to soybean inoculant companies

Inoculation Test Results

The average yield increase from 64 Ohio trials is 1.94 bu/ac and has produced a profit of about 300 percent when beans were worth $6.00 per bushel and when the inoculation material costs $3.00 per acre. For most inoculation products, a one half bushel per acre yield increase is profitable. Yield increases of two to seven bushel per acre have been common in productive producer fields where the seed was inoculated properly and planted into moist soil and in a timely manner.

Soybean Fungicides Recommended

Authors: Jim Beuerlein

Soybean diseases in Ohio have increased in number and severity over the past 10 years so that today, the loss of productivity from disease averages over $150,000,000 per year. This loss is greater than from any other factor except weather. The increase in soybean disease is due primarily to short crop rotations or no crop rotation. It is estimated that Ohio soybean producers lose an average of five to eight bushels per acre per year to disease. In most years, several diseases are present but some are not recognized due to low levels of infection. It is noteworthy that by the time symptoms of a particular disease appear, the yield loss has already reached seven to ten percent. In many fields there is significant yield loss to disease even though no symptoms are evident.

In the past, we have relied on varieties’ disease resistance and tolerance to provide some measure of control. Many of the Phytophthora control genes are no longer effective because the pathogens have evolved and can overcome the genes’ defense mechanism. During the past ten years, fungicide seed treatments have been used effectively to improve soybean stands and increase the general health of soybean root systems following planting.

The long term weather forecast for 2006 indicates we will have a wet spring. That means the weather will be ideal for the root rot diseases which are present in all soybean fields. All soybean varieties have some degree of susceptibility to root rot diseases, which means that all the requirement for disease (susceptible varieties, disease present, and proper weather) could come together this spring. The take home message is: use fungicide treated soybean seed this spring. The cost to replant runs between $80 and $100 per acre when you combine the extra cost and the lost yield.

Planting Practices for Managing “Pollen Drift” from Transgenic Corn

Authors: Peter Thomison

Transgenic (GMO) corn acreage is likely to increase sharply in 2006 with wider use of Roundup Ready and Bt corn. Given this development, Ohio growers of identity preserved (IP) non-GMO corn should become more familiar with planting practices that limit pollen drift from nearby GMO corn fields. Pollen from corn containing transgenic traits may contaminate (by cross-pollination) nearby non-GMO corn. Producers of IP corn need to minimize pollen contamination by GMO corn if they are to obtain premiums.

Isolation and Border Rows
One of the most effective methods for preventing pollen contamination is use of a separation or isolation distance to limit exposure of non-GMO corn fields from pollen of GMO fields. The potential for cross-pollination decreases as the distance between GMO and non GMO corn fields increases. Several state seed certification agencies that offer IP grain programs require that non-GMO IP corn be planted at a distance of at least 660 ft from any GMO corn. This isolation distance requirement may be modified by removing varying numbers of non-GMO border rows, the number of which is to be determined by the acreage of the non-GMO IP corn field. The border rows ensure that the non-GMO field is "flooded' with non-GMO pollen which will dilute adventitious pollen from a GMO source. For IP corn fields over 20 acres in size, the isolation distance (of 660 ft) may be modified by post pollination removal of 16 adjacent border rows if the actual isolation distance is less than 165 feet; the distance may be modified by post pollination removal of 8 adjacent border rows if isolation distance is between 165 and 660 feet. These isolation and border row requirements are designed to produce corn grain that is not more than 0.5% contaminated with GMOs.

Planting Dates and Hybrid Maturity
Use of different planting dates and hybrid maturities can also be used to reduce the risk of cross-pollination between fields of GMO and non-GMO corn. For example, planting a short season non-GMO corn hybrid followed by full season hybrid later will reduce the chance for pollen from the GMO field to fertilize the early planted, earlier maturity non-GMO hybrid in an adjacent field. However, there are shortcomings with this approach. Differences in maturity between the early and late hybrid may not be large enough to ensure that the flowering periods of each hybrid will not overlap, especially when unusual climatic conditions accelerate or delay flowering. Moreover this strategy will only work if you control the adjacent fields or can closely coordinate your corn planting operations with those of your neighbors.

Prevailing Wind Direction
The south and west edges of non-GMO fields may be more vulnerable to pollen drift because the prevailing during the summer are from the southwest. I'm not sure how consistent this wind pattern is but if it is an issue, then it may be particularly useful to follow recommendations regarding isolation distances and border row on these sides of non-GMO fields.

Other Cationsonsider
Other factors that can negatively impact non-GMO grain purity are volunteer corn plants resulting from no-till or minimum till continuous corn, purity level of the seed planted, planting errors, and drought or flood conditions which stunt border rows and reduce desirable pollen production and flow.

Planting operations to manage pollen drift are only part of the process of producing an IP corn grain crop. Other major issues include harvesting, drying and storage, along with thorough record keeping. Seed certification offer IP programs for grain. These IP programs, which are similar to seed certification, assist in preserving the genetic identity of a product, and verify specific traits through field inspections, laboratory analysis, and record keeping.Source: Extension Fact Sheet AGF-135, Managing "Pollen Drift" to Minimize Contamination of Non-GMO Corn; it’s available online at .

Scout For Alfalfa Weevil

Authors: Ron Hammond, Bruce Eisley

With warmer temperatures now occurring, alfalfa growers should begin scouting for alfalfa weevil in the coming weeks. The need for scouting is especially true in southern counties where heat unit accumulation has reached the 300 HU needed for egg hatch and beginning feeding. Although central and northern Ohio is behind this accumulation of heat units, growers in those areas should begin their scouting over the next 1-2 weeks. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier.

Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. See the OSU Alfalfa Weevil FactSheet for more on alfalfa weevil scouting and thresholds. For insecticides that are labeled for alfalfa weevil, see . Remember that it is still too early to scout for potato leafhopper since they do not move into Ohio until May.

Predicting Giant Ragweed Seedling Emergence To Better Manage Postemergence Glyphosate Applications

Authors: Brian Schuttte, Kent Harrison, Emilie Regnier

In Ohio agricultural fields, giant ragweed seedling emergence starts in early spring and continues through the growing season into early July. As a result of this extended duration of emergence, three herbicide applications can be required for effective control in Roundup Ready soybeans – a preplant burndown treatment and two postemergence herbicide treatments. Growers often try to reduce the need for a second postemergence application by purposely delaying the first application until the majority of the ragweed plants have emerged. However, the consequence of this is that the early-emerging plants can become large and more difficult to control.

Giant ragweed emerges in a predictable way each year based on temperature and rainfall. In collaboration with Kurt Spokas and Frank Forcella of the USDA ARS North Central Soil Conservation Research Lab at Morris, MN, we have developed a method to predict giant ragweed seedling emergence using meteorological data. Based on this information, we will be updating the progress of giant ragweed emergence this spring and summer on the Agronomic Crops Network website at . Our predictive model was produced with information collected at the OARDC Western Agricultural Research Station in South Charleston, OH, so it should be representative of giant ragweed populations in west-central Ohio agricultural fields. This information is meant to supplement local knowledge and observations of giant ragweed emergence so that growers can target their weed control practices more effectively.

How would information on giant ragweed emergence be helpful in management of postemergence herbicides? During periods of maximum weed emergence, delaying herbicide applications by a couple of days could allow producers to target more giant ragweed seedlings without a great risk of plants growing too large to be readily controlled. However, during a period of slow seedling emergence, plant growth will outpace the rate of seedling emergence, so delaying herbicide application is not advised and producers should make herbicide decisions based more on the size of the ragweed plants that have already emerged. Two examples of how this could work for a grower who has observed a number of giant ragweed plants that are already 6 to 8 inches tall, trying to determine whether he should go ahead and apply postemergence herbicides:

Example 1: If the model predicted that 60% of the total giant ragweed expected for the season had already emerged, and only another 5% emergence was expected in the next week, it would probably make sense to apply postemergence herbicides before ragweed plants get any larger.

Example 2: If the model predicted that 35% of the total giant ragweed expected for the season had already emerged, and another 15% emergence was expected in the next week, it could make sense to delay postemergence herbicide application so that it controls these later emergers (Existing giant ragweed plants will continue to get larger of course, and we would recommend increasing the glyphosate rate to 1.5 lbs ae/A to improve control of large plants).

The majority of giant ragweed emergence occurs in the spring. In typical years, 60% of all giant ragweed that emerges has already done so by early May. After this time, weed emergence continues at a slower rate. However, seedling emergence is dependent on weather conditions and our giant ragweed seedling emergence model accounts for weather effects. Check the Agronomic Crops Network website for the progress of this season’s giant ragweed emergence.

Wild Turnip Control

Wild turnip is becoming more prevalent throughout eastern Ohio in hay and pasture production. Wild turnip has been classified by many as Brassica napus, but not all botanists agree with this classification. It looks similar to birdsrape mustard, canola, and yellow rocket. It will begin flowering very soon and will have large yellow flowers. It can be distinguished from the other species because of its enlarged taproot that looks and tastes like turnip. The life cycle of this species tends to be a winter annual, but emerges a earlier than most in mid-summer.

Because of its quick growth in the spring it is very difficult to control. Research to date has only looked at fall applications which can be very effective. More than likely in the spring, the most effective treatment in pure alfalfa would be Pursuit at 1.44 oz/A plus 2,4-DB at 1.0 qt/A plus crop oil concentrate. In the fall, 2,4-DB at 2.0 qt/A can be effective, but we do not believe that 2,4-DB alone in the spring will be as effective. There is really no date to prove that these two treatments can be effective in the spring, but we believe they should be the best options in the spring. In grass only pastures, apply 2,4-D ester at 1.5 qt/A to provide the most activity. Again, there is no spring application data to prove its effectiveness and a lower rate may be as effective, but we do know it is more difficult to control in the spring. These herbicide applications need to be applied as soon as possible to maximize control and limit its affect upon the forage stand.

If you can not get an herbicide applied, then the next best option is to limit seed production. To stop maximum seed production, cut off the flower stems just above the forage before the seed capsules reach a length of 1 inch. This has been shown to be very effective all though not full proof. Plan to make herbicide applications in the fall to maximize control of the wild turnip.

Corn Planting Tips

Authors: Peter Thomison

Complete Planting by May 10.

If soil conditions are dry, begin planting before the optimum date. (The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10). 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 avoid overworking soils. A major problem in parts of Ohio last year was surface crusting, caused by heavy rains after April 22 and excessively tilled soils (often worked to a powdery consistency during the warmer and drier than normal first half of April). Surface crusting inhibited or slowed emergence. When combined with freezing injury and infection by fungal pathogens, it resulted in major stand loss and the need to replant. In 2005 we often observed that fields not tilled as extensively (i.e. no-till) had a better chance of recovering and showed higher emergence after the freezing rains ended.

If growers have the equipment capability to plant more than half of their corn acres prior to the optimum planting date, then this should allow planting all the corn acres prior to the calendar date when corn yields begin to decline quickly. 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. As a guide, calendar date is more reliable than soil temperature for making the decision on when to begin to plant corn.

Other advantages of early planted corn are earlier maturity in the fall with more time for field drying and higher test weights. Early planting dates result in earlier plant emergence and faster canopy closure in the growing season. Faster canopy closure helps reduce early-season soil losses due to erosion. Early planted corn usually has better stalk quality and may reduce the exposure to various late insect and disease pest problems, such as European corn borer and gray leaf spot.

Plant Full-Season Hybrids First.

Once the full-season hybrids are planted, then alternately plant early-season and mid-season hybrids, to take full advantage of maturity ranges and to give the later-maturing hybrids the benefit of maximum heat-unit accumulation. Full-season hybrids generally show greater yield reduction when planting is delayed compared with short- to mid-season hybrids. In areas with longer growing seasons, consider planting some acreage to early hybrids to have new corn for the early market (which usually commands a premium price and thus partially offsets the income effect of the lower yield associated with early hybrids). Planting early hybrids first, followed by mid-season, and lastly the full-season hybrids spreads the pollination interval for all the corn acres over a longer time period and may be a good strategy for some drought-prone areas.

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 April, when the soil is usually moist and evaporation rate is low, seed should be planted shallower no deeper than 11/2 inches. In 2005, drier and warmer than normal soil conditions prior to April 22 led some farmers to seed corn at depths of 2 inches or deeper. These deeper plantings contributed to emergence problems when we experienced a 10-day period of cold wet weather after than April 22. Corn planted deeper was often slower emerging and was often associated with stand reductions.

When soils are warm and dry, corn may be seeded more deeply up to 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 (or secondary) root system if the crown is at or near the soil surface, some of the permanent roots may not grow under hot, dry conditions (resulting in the "rootless" and "floppy" corn syndromes). Another potential risk from planting less than 1-1/2 inches is shoot uptake of soil-applied herbicides. 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.

When seeding, adjust the seeding 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. On productive soils, with average yields of 160 bu/acre or more, final stands of 30,000 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 may be adequate for optimal yields. Under drought stress conditions, high plant populations do not cause significant yield reduction.

Planting rate or population 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 usually more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels). When planting occurs in cold soils, usually very early planting dates, the seeding rate should be 15% higher than the desired harvest population. Follow seed company recommendations to adjust the population for specific hybrids.

Archive Issue Contributors: 

Ann Dorance, Pierce Paul and Dennis Mills (Plant Pathology), Mark Loux, Brian Schutte, Kent Harrison, Emilie Regnier and Jeff Stachler (Weed Science), Peter Thomison, (Corn Production), Jim Beuerlein, (Soybean Production), Bruce Eisley, Ron Hammond (Entomology). 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), Ed Lentz (Seneca), Todd Mangen (Mercer), Greg LaBarge (Fulton), Mark Koenig (Sandusky), Gary Wilson (Hancock) and Keith Diedrick (Wayne).

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.