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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2005-11

Dates Covered: 
May 3, 2005 - May 10, 2005
Tammy Dobbels

Wheat Development and Disease Update

Authors: Patrick Lipps

Cooler weather during the past two weeks has slowed the development of wheat after the period of rapid growth earlier in April. This puts the wheat crop at about the normal growth stage for this time of year. The wheat in southern Ohio is in various stages of flag leaf emergence and in northern Ohio some of the earliest fields have plants with the flag leaves emerging. Flag leaf emergence is Growth Stage 8 on the Feekes' growth stage scale. You can determine this growth stage by examining 8 to 10 of the largest tillers from the field and assessing the number of leaves on the stem above the first node. Pull or dig a plant from the soil so that roots remain attached, then separate individual tillers so that you can examine them. Peel down the leaf sheaths of the lowest leaves until you expose the lower stem to find the first node. The first node is the lowest node on the stem. Then count the number of leaves above this first node. There are four leaves on the stems of mature plants and the top leaf is the flag leaf. At flag leaf emergence you will count four leaves on the stem with the fourth leaf just visible as a small spike emerging from the top of the plant. With the warmer weather expected during the next week the wheat will develop very rapidly especially in southern Ohio where the crop is expected to be in boot stage by mid next week.

Flag leaf emergence is a good stage to start looking for wheat diseases. Your first step is to determine if the varieties you planted are considered susceptible to certain diseases. The 2004 Ohio Wheat Performance Trial results lists the reactions of wheat varieties to the more important diseases in Ohio. This information is available on the web at The first disease that is usually detected in powdery mildew. Look for the small white pustules on the lower leaves and leaf sheaths in the wheat canopy. If powdery mildew is present in a field planted to a susceptible variety you should watch its development over the next week or so and decide to apply a fungicide if the disease begins to be detected on the leaf below the flag leaf. There are several fungicides with excellent activity on powdery mildew (Tilt, Propimax, Quilt). For additional information visit the Ohio Field Crops Disease web site for information on wheat powdery mildew and fungicide applications at

Soybean Rust Update

Authors: Anne Dorrance

Two new counties were added to the USDA map this past week, Dade County in southern Florida as well as the first sentinel plot in Georgia ( This finding in Georgia is especially interesting and encouraging. In the south they have a problem with volunteer soybeans, not an issue for us in the north with cold temperatures. These soybeans were just beginning to flower – so they were at – what is reported to be a susceptible growth stage. The models that are being used had predicted spores reaching southern Georgia. Then with this find this confirmed the model. Science at work… It took a lot of time and patience for the Georgia crew to find nice sporulating lesions but after spending hours in the field they were successful. The inoculum is still very low and this is still too early for us to base any predictions in Ohio, however, the process on the first trial run, appears to be working. By the time this fungus approaches Ohio, all of the bugs will be worked out of the system. Ohio has FORTY-FIVE sentinel plots planned/planted for this summer plus the Kentucky system.

If rust does approach, fungicide timing is going to be the most critical decision. If you spray too early – you may be spraying more often. If you spray too late, too much damage may have been done. Along with colleagues from both the southern US and the north central region and Ontario, Canada; we have produced a Fungicide Manual entitled “Using Foliar Fungicides to Manage Soybean Rust”. This is currently available on the web at, where you can download the chapters of each pdf file. This book is 60 pages long and should be in your county offices for purchase by the end of next week.

Soybean Seeding Rates and Calibration

Authors: Jim Beuerlein

The ideal timing for putting soybean seed in the ground is mid April to approximately May 20. With this in mind, the importance of calibrating for ideal populations is important, as not to put excessive amounts of seed in the ground. Below are guidelines for target seed populations per acre based on soil type and potential plant height.

Light colored soils, plants reach knee high to 20” – 225,000 seeds per acre
Medium soils expected plant height of approximately 30” – 175,000 seeds per acre
Dark soils with 40” or higher plant height - 150 – 125,000 seeds per acre

You can use this simple formula to calibrate ideal spacing between seeds for a target seed population:

6,272,640 sq. inches per acre / seeds population per acre / row spacing = distance between seeds in row in inches

For more information about adjusting drills for planting visit the web.

Slug Update

Authors: Ron Hammond, Bruce Eisley

Slug eggs have began hatching in Fairfield County, east of Columbus, last week. Although we found mostly eggs, we did see newly hatched juvenile slugs. At least one field had a very high population of eggs. We then sampled a field in Wayne County near the OARDC; although we found numerous eggs, no juvenile slugs were observed. We will continue to sample these fields on a weekly basis, and add additional fields in a few other locations in the state.

From having seen beginning egg hatch, we recommend that growers keep aware of potentially problems beginning within the next 3-4 weeks. As slugs continue to hatch out and grow, the concern with slugs will become greater. Hopefully the early crop planting we are seeing will allow many of our fields to get a good head start over the slugs. However, growers should monitor the slug situation in their fields closely as we head into the coming weeks.

Early Season Insect Pests in Corn & Soybeans

Authors: Bruce Eisley, Ron Hammond

The cool, wet weather we are experiencing does not increase populations of early season pests (ESP) but can make them worse because of slow seed germination. For example, fields that had green material, weeds,alfalfa, etc., which was worked into the soil will favor maggot damage under the current conditions. The adult of the seedcorn maggot (SCM) is a fly that is attracted to decaying organic matter to lay their eggs. Under current conditions, the green material that was worked into the soil is slowly decaying and the fly would be attracted to this decaying material. The corn or soybean seeds that were planted are germinating slowly and susceptible to damage. Seeds treated with one of the new seed applied insecticides or hopper box seed treatments will be protected from SCM injury. If seeds were not treated, then they would
be susceptible to SCM injury. Fields planted no-till are not as susceptible to SCM injury as tilled fields.

Numbers of other early season pests, such as wireworms or grubs, will not be greater under these conditions but they will have a longer time to feed on the seed and developing seedling and thus damage could be worse. The important thing to remember with ESP damage is that there aren’t any rescue treatments available. The only option available to deal with ESP damage is to replant if damage is severe.

Our suggestion is to check areas of fields or fields that have poor stands and inspect the seeds to see if they have been damaged by insects. Several pictures are on the WEB that show damage by some of these ESP. Wireworm damage to corn can be viewed at: SCM damage to corn at: SCM damage to
soybeans at:

Black Cutworm Moth Flights Remain Low

Authors: Bruce Eisley, Ron Hammond

We continue to monitor for black cutworm moths in a couple of locations in Ohio. The numbers of moths remain low up to this point. This does not necessarily mean we won’t have cutworm problems in corn this year but without moths to lay eggs, the number of cutworms should be less. We will continue to trap and trap counts are listed on the web at:

Switching from Preemergence to Early Postemergence in Corn

Authors: Mark Loux

An article in (“What to do when you’re between preemergence and postemergence”) addressed the potential problems with weed control in cornfields that were planted before the wet weather, and specifically those not yet treated with herbicide. We suggest a review of that article prior to making any further herbicide applications in these fields.

Burndown Programs Without 2,4-D Ester

Authors: Mark Loux

The inclusion of 2,4-D ester in burndown programs can help control a number of large or tough weeds, including marestail, dandelion, mustards, and giant ragweed. Treatments that contain 2,4-D ester must be applied at least 7 days prior to soybean planting, which is not a problem early in spring but becomes more of an issue in May. As herbicide applications and soybean planting start again this week, the advantages of 2,4-D must be weighed against the delay in planting as a result of its use.

It is possible to effectively control emerged weeds in a no-till field without the use of 2,4-D. The most effective and economical means of doing so is to increase the rate of glyphosate. In fields where 2,4-D will not be applied, a glyphosate rate of 1.5 lbs acid equivalent per acre can be much more effective than the “standard” rate of 0.75 lbs that many producers seem to like to use in every situation. Glyphosate and 2,4-D ester have become roughly equivalent in price, and as a result, this increase in glyphosate rate is only a few dollars more per acre than the 0.5 lb/A rate of 2,4-D ester. We cannot emphasize enough the importance of a “clean” start in no-till fields. Failure to control winter weeds at this time of the year results in completion their life cycle and production of seed, which perpetuates weed problems for future years. In addition, dandelion is more effectively controlled prior to flower senescence and seed production. Applications later in May can appear to control dandelion topgrowth, but have little impact on the taproot.

Several other soybean herbicides can aid in the control of certain weeds in burndown situations when mixed with glyphosate. Chlorimuron (Synchrony XP, Canopy XL) is probably the most helpful in this regard, especially for control of many winter annuals, dandelion, wild garlic, prickly lettuce, and marestail (except ALS-resistant biotypes). Cloransulam (FirstRate/Amplify/Gangster) can help control ragweeds and marestail, as long as they are not ALS-resistant. Aim can be helpful for control of star-of-bethlehem, but has not improved control of other weeds in OSU research. Valor can improve the speed of burndown of dandelion, but rarely improves final control of this weed, compared to glyphosate alone. Most other soybean herbicides fail to improve the activity of glyphosate, and can occasionally result in antagonism, which tends to be expressed on larger weeds and perennials.

Corn Replanting Considerations - don’t be in rush to replant

Authors: Peter Thomison

The cold wet weather of the past week has slowed corn germination and emergence. According to USDA estimates as of May 1, 2005, 58 percent of the corn crop in Ohio has been planted, but only 3 percent has emerged. Concerns about potential effects of cold stress and saturated soils on corn survival have led to questions about replanting. So far, there is little evidence that corn plantings have been jeopardized by low temperatures and wet soils, except in areas where they have been subjected to ponding or flooding. Don’t make a final assessment on the extent of damage and stand loss too quickly. Replant decisions should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. The following are some guidelines to consider when making a replant decision.

If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:

Original target plant population/Intended plant stand
Plant stand after damage
Uniformity of plant stand after damage
Original planting date
Possible replanting date
Likely replanting pest control and seed costs

To estimate after damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. (Table 1 shows row length needed for various row widths.) Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient.

Table 1. Row length required to equal 1/1000 acre when corn is planted at various row widths.

Row Width(Inches) 1/1000 acre(feet)
20 26.1
28 18.7
30 17.4
36 14.5
38 13.8
40 13.1
A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Tables 2 and 3 show effects of planting date and plant population on final grain yield for the central Corn Belt. Table 2 is a newer chart developed by Dr. Emerson Nafziger at the University of Illinois that includes earlier planting dates and higher optimum plant populations. Table 3 is based on older data from the 1970's, but it still provides a reasonable assessment of potential yield losses, especially for planting dates in June. Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.

Table 2. University of Illinois replant chart developed under high yielding conditions (adapted from Nafziger 1995-96)
Planting Date 10 15 20 25 30 35
      % Optimum yield    
April 10 62 76 86 92 94 93
April 20 67 81 91 97 99 97
April 30 68 82 92 98 100 98
May 9 65 79 89 95 97 96
May 19 59 73 84 89 91 89
May 29 49 63 73 79 81 79

Table 3. Central Corn Belt grain yields for corn planted at various dates and population rates expressed as a percent of optimum planting date and population yield (uniformly spaced within row).
Planting Date     Plants PerAcre atHarvest      
  12000 14000 16000 18000 20000 22500 25000
4/20 72 78 83 87 90 93 95
4/25 75 81 86 90 93 96 98
5/1 77 83 88 92 95 98 100
5/6 78 83 88 92 95 98 100
5/11 77 83 88 92 95 98 99
5/16 75 81 86 90 93 96 98
5/21 73 78 83 87 91 94 95
5/26 69 75 80 84 87 90 92
5/31 64 70 75 79 82 85 87
6/5 59 64 69 73 77 80 81
6/10 52 58 63 67 70 73 75
*Adapted from NCH 30 "Guidelines for Making Corn Replant Decisions"

Here's how these tables might be used to arrive at a replant decision (Table 2 will be used in this example). Let's assume that a farmer planted on May 9 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 2, the expected yield for the existing stand would be 79% of the optimum. If the corn crop was planted the next day on May 29, and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting is 81 minus 79, or 2 percentage points. At a yield level of 150 bushels per acre, this increase would amount to three bushels per acre which would probably not justify replanting costs.

It’s also important to note plant distribution within the row. Remember that the values in Tables 2 and 3 are based on a uniform distribution of plants within the row! Add a 5% yield loss penalty if the field assessment reveals several gaps of 4 6 feet within rows and a 2% penalty for gaps of 1 3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction.

When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio.

You also need to review herbicide and insecticide programs under late planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control. Concerning insect control, if soil insecticides were applied in the row at initial planting, check insecticide label restrictions before re application. Also remember that later planting dates generally increase the possibility of damage from European corn borer (ECB) and may warrant selection of ECB Bt hybrids (if suitable maturities are available). Understand that replanting itself does not guarantee the expected harvest population. Corn replant decisions early in the growing season will be based mainly on plant stand and plant distribution. Later in the season as yields begin to decline rapidly because of delayed planting, calendar date assumes increased importance.

The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is.

The following is an additional on-line source of information on making replant decisions.
Nielsen, Bob. 2002 (rev). Estimating Yield and Dollar Returns From Corn Replanting. Purdue Univ. Cooperative Extension Service publication AY-264-W. Online at [URL verified 5/02/05].


Replanting Roundup Ready Corn – how to kill the first planting?

Authors: Mark Loux

We have to admit, while the potential problem of volunteer Roundup Ready corn in Roundup Ready soybeans was obvious from the start, we had not really considered the following. Where the first planting of Roundup Ready corn results in a poor stand and the producer desires to start over, how can emerged corn plants be effectively controlled? In a field planted with corn that is not Roundup Ready, glyphosate is the obvious choice for this, but another strategy will be necessary to control Roundup Ready corn. Postemergence grass herbicides that are used in soybeans, including Assure II and Select, can effectively control emerged corn. However, all of these herbicides have a short period of residual activity in soil, and labels specify that corn should not be planted for anywhere from 30 (Select) to 60 (Fusion, Fusilade) to 120 (Assure II) days following herbicide application. Paraquat will not consistently control emerged corn, especially when it is small and the growing point is still underground. Another potential option is Liberty, which has no soil residual and could possibly control emerged corn. Liberty is not labeled for this use, however. So – unless we’re missing something it appears that tillage may be the only viable option for control of emerged Roundup Ready corn, where the intent is to immediately replant corn.

Archive Issue Contributors: 

State Specialists: Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Jim Beuerlein (Crop Science - Soybeans), Bruce Eisley and Ron Hammond (Entomology), Mark Loux and Jeff Stachler (Weed Science), Peter Thomison (Crop Science-Corn). Extension Educators: Roger Bender (Shelby), Alan Sundermeier (Wood), Steve Bartels (Butler), Steve Foster (Darke), Gary Wilson (Hancock), Dusty Sonnenberg (Henry), Howard Siegrist (Licking), Harold Watters (Champaign), Tammy Dobbels (Logan), Glenn Arnold (Putnam), Greg LaBarge (Fulton), 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.