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Ohio State University Extension


C.O.R.N. Newsletter 2006-02

Dates Covered: 
January 24, 2006 - February 7, 2006
Harold Watters

Ohio Wheat Growers Annual Meeting - January 25

Authors: Harold Watters

The 2006 Ohio Wheat Growers Annual Meeting and Trade Show will be held Wednesday January 25 from 9AM to 3PM at The Centre, 601 North Main Street in Bluffton.

Membership in OWGA puts you in contact with industry representatives, seed researchers, and wheat producers throughout Ohio. The group has worked with industry partners to bring outstanding enrollment benefits. For more information: The association was founded in 1993 to educate and assist producers, industry representatives and legislators to improve the profitability and marketing strategies for the Ohio wheat industry.

Winter Wheat Condition Concerns

Authors: Jim Beuerlein

What is the weather doing to wheat right now? Will we break dormancy only to get slammed by colder temperatures later?

The soil is cold and that is the growth governor for wheat at this time of year. To break dormancy will take several days and nights of warm temps. The risk is greater to the south than up north. Even if dormancy does break, wheat is still a cool season crop and can tolerate cold temps. History indicates that we rarely have significant damage from warm spells in winter. Western Kentucky has lots of wheat used for double cropping and are further south then us, and they seem to get by fairly well.

Regarding timing of N application. The usual answer is: if there was a fall application, make the spring application anytime in April. If no fall application, make the spring application between mid March and mid April. Generally we don't recommend two applications unless you lose part of the early one.

New Economic Based Nitrogen Recommendations for Corn Are Now Online!

Authors: Robert Mullen

To view the new nitrogen recommendations, visit

This nitrogen recommendation model is for corn only. Nitrogen recommendations for wheat and other crops have not been changed as of yet. The recommendations are contained within a spreadsheet, and you must have Microsoft Excel to view the new recommendations. There are only three cells that you have access to in the Excel spreadsheet 1) previous crop, 2) corn price ($/bu), and 3) nitrogen cost ($/lb N). All other cells are password protected except the calculation of nitrogen cost (left hand side of the spreadsheet). Depending upon the source of nitrogen you are interested in purchasing and the cost of that material ($/ton), you can calculate the price per pound.

Historically, nitrogen recommendations were given as a single rate, but the new strategy actually provides a range of rates. This provides you the user a little more flexibility in your rate decision. Although the range in rates provided by the model is economic, agronomic considerations are also provided for each rate. Below the recommended rates (for the lower bound, maximum return point, and upper bound) is the probability of achieving 95% of maximum yield when applying nitrogen at that particular rate. Higher probabilities (closer to 100) translate into lower risk of being nitrogen deficient at the end of the season.

Nitrogen credits for previous crop are considered in the model, so you do not have to deduct the credit. Manure credits do have to be taken, so if you apply manure in your operation make certain to credit the nitrogen supplied by the manure.

2005 Quadris/Warrior Strip Trials

Authors: Ron Hammond, Anne Dorrance, Dennis Mills

The Quadris/Warrior strip trials consisted of 14 locations across the state coordinated by county extension agents Roger Bender, Mark Koenig, Greg LaBarge, Gene McCluer, Steve Ruhl, Howard Siegrist, Dusty Sonnenberg, Alan Sundermeier, Gary Wilson, and John Yost. Growers applied and harvested treatment strips on their fields using their own sprayers (40-90 ft wide) and combines. Replicated treatments applied in this study were Quadris (6.4 fl oz/A) + crop oil (1% v/v), Warrior (3.2 fl oz/A), Quadris/Warrior + crop oil and a nontreated check. Data was collected from each treatment in all of the fields on the percent of lower canopy defoliation, percent leaf area affected by soybean foliar diseases, the number of aphids per plant and the percent canopy affected due to insect feeding.

Septoria brown spot and downy mildew were found at all locations and frogeye leaf spot was identified at a few locations but at very low frequency. No soybean rust was identified in Ohio during 2005. Aphids were above the 250/plant threshold in 9 of 14 locations. Yield data was collected and ranged from 33 to 70 bu/A. Aphid numbers were significantly reduced in locations that had reached threshold with the Warrior or the Quadris/Warrior combination applied at the R3 growth stage. The yield of the Warrior alone treatment was significantly higher than the nontreated check in 8 of the 14 locations and averaged a 6.9 bu/A increase. The yield of the Quadris/Warrior combination treatment was significantly higher than the nontreated check in 9 of the 14 locations averaging 7.5 bu/A increase. The difference between Warrior and Quadris/Warrior treatments across locations was 0.6 bu/A and was not significant. Quadris alone had fewer aphids than the nontreated, which was significantly better in 4 of the 12 locations for yield. For these four locations, the average yield increase was 3.9 bu/A.

The conclusions derived from the 2005 study are to follow IPM practices, scout and spray only if necessary. Fields where Warrior was sprayed before the threshold of 250 aphids per plant required a second application or did not get as high of a yield response to the insecticide treatment. Therefore for management of aphids, treatments should be applied at threshold and not at plant growth stages. There was no yield advantage to adding fungicide to the insecticide treatments resulting in a negative return on investment.

Yield (bu/A) fields with <5 aphids/plant

County Non-treated Quadris Warrior Q/W Field Mean LSD 0.05
Fayette 36.5 36.3 41.1 38.7 38.4 NS
Hancock 50.0 49.4 50.5 55.5 50.3 5.2
Hardin 64.2 65.4 68.7 70.2 67.1 4.1
Licking 58.6 62.8 61.6 63.7 61.7 2.5
Morrow 50.7 52.9 55.1 55.5 53.6 NS

Yield (bu/A) fields with > 450 aphids/plant
County Non-treated Quadris Warrior Q/W Field Mean LSD 0.05
Fulton 33.0 34.0 46.0 45.5 39.4 4.4
Henry/B 47.9 51.0 54.9 55.2 52.3 1.3
Henry/F 53.9 57.0 67.5 69.2 61.9 2.5
Henry/W 39.8 45.9 51.7 50.1 46.9 4.2
Ottawa 56.1 54.6 64.1 64.2 59.7 2.0
Shelby/J 46.8 46.9 50.6 49.4 48.4 1.6
Shelby/L 57.2 57.4 67.7 73.0 63.8 7.4
Wood/M 40.4 40.0 41.3 44.7 41.7 NS
Wood/S 38.9 44.0 54.1 55.1 48.0 2.1


Northern Ohio Crops Day February 9th

Authors: Mark Koenig

February 9, 2006 is this year’s date for the Northern Ohio Crops Day that will be held at Ole Zim’s Wagonshed, 1375 N. State Route 590 Gibsonburg, Ohio.

Featured on this year’s program will be “Seed Trait Stacking, What is the Story?”, “Fungicide Safety Issues”, “Weed Resistance”, and“Nitrogen Rates for Corn” plus other topics that will be of interest to area producers. Private pesticide credits will be offered to fulfill the re-certification requirements for Core and Categories 1 & 12. (3hours) Commercial pesticide credits for Core, Categories 2A, & 2C will also be offered. (2 1/2hours) At the end of the program we will show tapes to fill other private categories. There will be a charge for Pesticide Re-certification Credits. Private Applicators charge is $15; Commercial Credit will be $15 per credit hour.

The program has been approved for CCA continuing education units for Crop Management, Pest Management, Nutrient Management, and Professional Management

The meeting starts at 9:00 a.m. and continues until 3:00 p.m. A $10.00 donation will be accepted at the door to help with expenses which includes a copy of the “Corn, Soybean, Wheat and Alfalfa Field Guide”. Lunch will be provided courtesy of the Northern Ohio Crops Day Exhibitors. The program is a joint effort of Ottawa, Wood, Seneca and Sandusky County Ohio State University Extension. Please call Sandusky County office (419) 334-6340 with any questions.

Conservation Tillage & Technology Conference February 24 & 25

Authors: Gary Wilson

Plan now to attend the 17th Annual Conservation Tillage and Technology Conference scheduled February 23 & 24, 2006 at Ohio Northern University at Ada, Ohio.

This year's conference will cover a wide range of topics including soil fertility, nitrogen management, planting and seed placement, tillage systems comparisons, cover crops, root development, weed, disease, pest management, and Precision Agriculture Technology. Nearly 70 sessions will be offered over the two day conference with nearly 70 different speakers including University Specialists, Ag Industry Representatives, and producer panels. An added room of seminars was included this your on Manure Science. Featured speakers include George Rehm, Professor, University of Minnesota on managing nitrogen; Dr. Eilleen Kladivko, Purdue University on cover crops; Dr. Mike Plumer, University of Illinois on annual rye grass; and Harold Van Es, Professor, Iowa State University on Soil Quality.

Over 40 credits will be made available for CCA's. Early registration by February 16 is $30.00 a day or $50.00 for both days. For a copy of the conference agenda and registration information contact the Hancock County Extension Office at 419-422-3851 or visit the web site at:

Agricultural Statistics, Least Significant Differences (LSD)

Authors: Robert Mullen

The next item in our discussion of agricultural statistics is the term least significance difference or LSD. This number is often mentioned at Extension meetings where research information is discussed. It also shows up in University publications that provide summaries of field research. The question is “what does this number mean”?

Least significant difference is used to compare means of different treatments that have an equal number of replications. What does that mean? Let’s take our example from the previous CORN Newsletter article (remember back to the beginning of December - We had two different scenarios which can be seen below:

Scenario 1:

Treatment 1
Treatment 2
LSD 0.1
Avg. 53
Avg. 50

Scenario 2:
Treatment 1
Treatment 2
LSD 0.1
Avg. 53
Avg. 50

Each of the different values below each treatment represents replications, and each treatment is replicated 3 times. The value below the replications is the average of each treatment.

Recall back to the previous article that for the first scenario the probability of treatment 1 being different from treatment 2 was 43%. Thus only 43 times out of 100 would treatment 1 be different than treatment 2. For scenario 2, the probability that treatment 1 would be different than treatment 2 was 92%. Thus 92 times out of 100 would treatment 1 be different than treatment 2. This was primarily influenced by the amount of error associated with the experiment.

Now let’s look at this another way using LSD. Again you will have to trust my ability to calculate these LSD values.

For scenario 1, at a significance level of 0.1 the LSD value would be 7.4. For treatment 1 to be different than treatment 2 they must differ by at least 7.4 (which they do not). You may be asking what a significance level is. This is the level of probability that we are using. For this example, if treatment 1 were different than treatment 2 by 7.4, we would be 90% certain that the treatments were indeed different. Stated another way, if treatment 1 was higher than treatment 2 by 7.4 and we conducted this experiment again under the same field conditions, 9 times out of 10 treatment 1 would be different than treatment 2 (boy this is confusing).

For scenario 2, at a significance level of 0.1 the LSD value would be 2.0. Since the differences between the treatments are greater than 2.0, we can say that if we repeated this experiment 100 times (under the same conditions), 90 times treatment 1 would be higher than treatment 2.

Different probability levels can also be used to determine statistical significance. Scientists traditionally use probability levels of 0.05 (95% probability) and some may be slightly less conservative and use 0.1 (90% probability).

Hopefully this will help you understand whether or not two treatments are different the next time you are sitting in an Extension meeting or reading a research summary. Remember, as has been mentioned before, research studies should be conducted over multiple locations and under different environmental conditions to prove their robustness.


Weed Management Considerations for Roundup Ready Corn

Authors: Bill Johnson, Mark Loux

Part I: Weed interference and the role of residual herbicides

Weed control programs in corn utilizing a combination of preemergence (PRE) and postemergence (POST) herbicides often provide more consistently effective control of problem weeds in corn, and the Roundup Ready corn program is no exception. Glyphosate has some advantages over other POST corn herbicides, most notably its ability to control large annual weeds and certain perennial weeds and its better safety on large corn. However, the overall management of glyphosate on Roundup Ready corn should be similar to other programs for which POST herbicides are a component. Proper management of glyphosate and the Roundup Ready system is essential for growers to achieve consistently effective weed control and preserve maximum corn yield. We know the following about weed interference in corn, as it pertains to POST herbicide use:

1) weeds that emerge with the corn can reduce yield if they are not removed by the time they are about 4 inches tall. Research by OSU, Purdue, and other universities shows that, in the absence of PRE herbicides, weeds should be controlled with POST herbicides when they are 2 to 4 inches tall to avoid the risk of yield loss from early-season weed interference. This corresponds to no later than approximately 23 days after corn planting, or before corn exceeds the V4 stage. Purdue research has shown that annual grasses and giant ragweed can be extremely competitive with corn early in the growing season, due to their ability to accumulate nitrogen at the same rate as the crop. When allowed to grow to a size of 6 to 9 inches (grasses) or 16 inches (ragweed), these weeds cause up to 20% corn yield loss, even though they can be effectively controlled by glyphosate at this large size.

2) weeds that emerge within several weeks after an early POST herbicide application can result in unacceptable control later in the growing season, and cause yield loss if present in high enough populations. However, research shows that late-emerging weeds are less competitive with corn, and weeds that emerge later than about 45 days after planting will not reduce yield.

3) Putting the two previous principles together results in the development of the “critical weed-free period”, which is the period during which the crop should be kept weed-free in order to prevent yield loss. While this period will vary with weed population and environmental conditions, it can be considered to start at about 20 days after planting and end at approximately 45 days after planting. Put another way – you can let the weeds grow with the corn for about 3 weeks after planting, but then they need to be controlled and kept out for about another 3 to 4 weeks.

The critical weed-free period is the reason why it is almost impossible to maximize weed control and corn yield when the herbicide program consists of a single POST glyphosate application without the use of residual herbicides. Here’s the problem: 1) Glyphosate can be applied early enough to prevent competition between the weeds and crop, but a single application is unlikely to adequately control later-emerging weeds, and 2) because glyphosate is capable of controlling large weeds, it can be applied later in the growing season in order to control early and late-emerging weeds, but late applications will not adequately prevent the early-season competition between the weeds and crops that reduces yield.

OSU and Purdue weed scientists generally advocate the use of residual herbicides (atrazine, Balance, Harness/Degree Xtra, Bicep II Magnum, Keystone, Guardsman Max, etc) in the Roundup Ready corn system to ensure the most effective weed control and minimize the risk of yield loss due to weed interference. Residual herbicides can be utilized in two ways (assuming that the field is free of weeds at the time of corn planting):

1) PRE herbicides can be applied at the time of corn planting, and followed with a POST glyphosate application. In this approach, the PRE herbicide treatment provides an initial period of weed control following planting, which prevents significant competition between the weeds and crop and allows more flexibility in the timing of the POST glyphosate application. This approach can provide the most effective control of weeds that emerge continuously over the early part of the growing season and late-emerging perennial weeds, because it allows the glyphosate to be applied later, compared to the next approach. This usually reduces the risk of yield loss when weather or a heavy POST workload results in a later than desirable POST application.

2) residual herbicides can be applied in combination with glyphosate in an early POST application. In this approach, herbicides must be applied early, when weeds are no more then 2 to 4 inches tall. The residual herbicides (usually a reduced rate of an atrazine premix) can control weeds for several weeks after application, which prevents yield loss or poor control due to late-emerging weeds. The advantage of this approach over the first one is that it requires only one application (in tilled fields), which can help reduce costs. One major drawback to this approach is the risk of yield loss when herbicides are applied too late, since early-season competition between the crop and weed has not been adequately prevented. This approach may also be less effective than the previous one for control of later-emerging perennial weeds, such as common pokeweed and vines.

We tend to favor the first approach, which involves separate application of PRE herbicides and POST glyphosate, because it has less inherent risk than the early POST application of glyphosate plus residual herbicide. As long as the PRE herbicides have activity on the weeds present, and enough rain occurs soon after planting to promote herbicide activity, some initial weed control occurs and a wider window of application is created for the POST glyphosate application. The net result is that it is almost impossible to incur yield loss due to early-emerging weeds, which is our major concern.

Part II: Which residual herbicide to use?

There are a wide variety of residual herbicides and rates that can be utilized in the Roundup Ready corn system, at a cost of about $6 to $14. Many manufacturers promote a 2/3 rate of their atrazine premix product in this program in order to simplify the decision and maintain sales of these products, but selection should really be based on the weed species diversity and density in each field. There are also programs available from several manufacturers that use incentives to promote use of the full labeled rate of their preemergence products. This can be an economical approach to Roundup Ready corn, when the incentives rebate growers some of the extra seed cost or the cost of the POST glyphosate application.

Where residual herbicides are applied PRE at the time of corn planting, possibilities include but are not limited to:

- atrazine (1 to 2 lbs/A)
- atrazine premix products – 50 to 100% of labeled rate
- Radius
- atrazine plus Balance
- reduced rates of Lumax or Lexar
- Resolve + atrazine
- atrazine + Hornet

Almost any of these will be effective in a field with low to moderate weed pressure when followed by a POST glyphosate application, but dense weed populations and certain weeds will be more effectively controlled with higher rates and broader spectrum products. For example, a field that has a diverse mix of grass and broadleaf weeds could be treated with a 2/3 rate of an atrazine premix product (Guardsman Max, Bicep II Magnum, Keystone, Harness/Degree Xtra) or a mixture of Resolve + atrazine. Fields with significant grass pressure and certain problem broadleaf weeds, such as giant ragweed and lambsquarters, might be treated with a PRE program with more activity on broadleaf weeds, such as a Balance plus atrazine or a 2/3 rate of Lumax or Lexar. Fields with very low grass pressure but high broadleaf weed pressure could be treated with 1.5 to 2 lbs/A of atrazine (although this will not control triazine-resistant weeds). It is important to realize that while annual grass weeds are certainly competitive with corn and PRE herbicide should control grasses for at least a few weeks, problems with glyphosate effectiveness are more likely to occur on broadleaf weeds such as giant ragweed, lambsquarters, annual morningglory, and waterhemp. As a result, it may make sense to choose PRE herbicides that can provide significant help for control of broadleaf weeds, and at the same time control much of the grass weeds for several weeks after planting.

Where glyphosate is combined with residual herbicides in an early POST application, many of the herbicides mentioned above can still be used (Balance cannot be applied to emerged corn). A caution about applying a mixture of atrazine plus glyphosate – the atrazine may not provide enough residual control of later-emerging grasses. Control of later-emerging grasses can be obtained by use of an atrazine premix product at 1/2 to 2/3 the labeled rate, or a mixture of Resolve plus atrazine. Be cautious about relying on atrazine or an atrazine premix product for residual broadleaf weed control in areas where triazine-resistant weeds occur.

Part III: Resistance management

Weed scientists continue to be concerned about the intensive use of glyphosate and the evolution of weed populations that are resistant to glyphosate. While the extensive use of continuous Roundup Ready cropping systems may be inevitable, the choices that producers make in their management of these systems can greatly delay the onset of glyphosate resistance. University weed scientists reasonably assume that more intensive use of glyphosate, and the accompanying increase in selection pressure, may cause the evolution of additional weed populations with an altered response to glyphosate. Several weeds common to midwestern crop production have already developed resistance to glyphosate, most notably marestail (horseweed), but also several populations of waterhemp and common ragweed. Populations of giant ragweed and lambsquarters may also be developing a low level of resistance (research is ongoing in this area, and we’ll have more to report later in the winter).

While resistance to glyphosate will undoubtedly continue to develop, use of certain practices should delay the onset of resistance in at least some weed species. Producers should be aware that continuous planting of Roundup Ready crops and use of herbicide programs consisting of exclusively glyphosate, places them at a higher risk of having resistance problems and likely shortens the time until problems occur. At the other end of the risk management spectrum, producers can choose not to use glyphosate in some years of the rotation and use other herbicides in addition to glyphosate in order to reduce selection pressure. Even in a rotation of Roundup Ready with non-Roundup Ready crops, producers still need to integrate other herbicides with glyphosate to effectively delay the onset of resistance. Some specific suggestions with regard to the use of glyphosate and other herbicides in Roundup Ready systems include:

- Use tillage or burndown herbicides so that corn is planted into a weed-free seedbed.

- For preplant burndown in no-till, do not rely exclusively on glyphosate. Where glyphosate will be used, apply it in combination with 2,4-D or other herbicides that have activity on emerged weeds. Non-glyphosate options for burndown in corn, depending upon the weeds present, include atrazine, Lumax/Lexar, atrazine plus Balance or Radius, or mixtures of any of these with 2,4-D.

- Do not rely on herbicide programs that consist of only postemergence herbicides.

- In Roundup Ready corn, use rates of PRE herbicides that have significant activity on weeds species present in the field, and especially those weeds that are not always effectively controlled with glyphosate. These weeds include giant and common ragweed, waterhemp, Palmer amaranth, annual morningglory, and lambsquarters, among others. The most effective reduction in the risk of glyphosate resistance will occur with higher rates of PRE herbicides, although these rates may not be economical where producers have to pay a tech fee for the Roundup Ready trait.

- Make POST glyphosate applications when annual weeds are less than 4 inches tall (and when giant ragweed is less than 8 inches tall) to minimize their effect on crop yield and ensure more effective control. In situations where the weeds are more than 6 inches tall, apply the highest labeled rate of glyphosate (1.5 lbs of glyphosate acid in soybeans, 0.75 lbs in corn).

- Make a second glyphosate application if weeds appear to be surviving an earlier application. OSU research indicates that, for weed populations that may have developed a slightly reduced response to glyphosate, the second application can control or further suppress plants and greatly reduce seed production.

- Application of glyphosate in combination with other POST herbicides may also slow the onset of herbicide resistance. Should glyphosate resistance develop in a weed that PRE herbicides have limited activity on, such as giant ragweed, it is likely that this strategy will be necessary. However, one of the benefits of the Roundup Ready corn program is the lack of crop response to POST glyphosate applications, and mixtures with other herbicides could increase the risk of crop injury, especially on larger corn.

Part IV: The problem with the multiple glyphosate application approach

Many producers have successfully controlled weeds annually in Roundup Ready soybeans with multiple glyphosate applications, to the exclusion of other herbicides. Use of this approach may result in acceptable weed control in Roundup Ready corn with proper management, but it tends to have more risks associated with it than the previous two approaches. These risks include the following:

1. Risk of yield loss if the first POST application is applied too late, as discussed previously.

2. Failure to use residual herbicides with the first glyphosate application will generally result in many late weed escapes, and a second POST glyphosate application will be required to ensure acceptable control. Late POST applications can require specialized application equipment, and there is some risk of mechanical damage to corn. Where the corn canopy has developed, it may prevent spray particles from reaching low-growing weeds unless drop nozzles are used.

3. Use of only glyphosate in Roundup Ready corn will increase the risk of herbicide resistance, especially in rotation with Roundup Ready soybeans.

Economic Consideration in Agronomic Production Meeting February 22

Authors: Harold Watters

The Ohio Soybean Association and Ohio Corn Growers Association will have a meeting February 22nd in Waldo Ohio at the All Occasions building to help producers make better economic decisions on crop production practices.

Speakers include Dr. Stephen Myers to talk about Identity Preserved Markets, Today and tomorrow as well as a number of our state specialists talking about insects, weeds, disease and crop production. The program will begin at 9AM and adjourn at 3:10 PM. Cost to members is $20 and $40 for non-members. Call to reserve your spot 1-800-686-9211.

Archive Issue Contributors: 

Anne Dorrance and Dennis Mills (Plant Pathology), Jim Beuerlein (Soybean & Small Grain Production), Mark Loux and Jeff Stachler (Weed Science) and Ron Hammond (Entomology). Extension Agents: Dusty Sonnenberg (Henry), Todd Mangen (Mercer), Roger Bender (Shelby), Gary Wilson (Hancock), Howard Siegrist (Licking), Harold Watters (Champaign), Mark Koenig (Sandusky), Alan Sundermeier (Wood), Bruce Clevenger (Defiance), Glen Arnold (Putnam) and Greg LaBarge (Fulton).

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.