C.O.R.N. Newsletter 2009-06

Dates Covered: 
March 16, 2009 - March 31, 2009
Editor: 
Harold Watters

Nitrogen Recommendations for Wheat

Authors: Edwin Lentz

Spring nitrogen should be applied between greenup (now) and beginning stem elongation (Feekes 6). Ohio State University research has shown that yields are not affected by delayed nitrogen until after early stem elongation (generally the end of April). Studies over the last five years have shown that yields were the same or slightly better when a single application occurred at Feekes 6 (first node visible of early stem elongation) compared to initial greenup. Yields dropped 10 – 15% when a single application was delayed to early boot stage. At this time, we would recommend producers to apply N as soon as field conditions allow application equipment. Since we are applying N between initial greenup and early stem elongation, any nitrogen source would be appropriate, so selection should be based on cost and availability.

Ohio State University still recommends the Tri-State Fertility Guide for N rates in wheat. This system relies on yield potential of a field. As a producer, you can greatly increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum nitrogen rate. Once you have selected a value for yield potential, the recommendation may be based on the following equation for mineral soils, which have 1 to 5% organic matter and adequate drainage:

N rate = 40 + [1.75 x (yield potential – 50)]

We do not give any credit for the previous soybean crop, since we do not know if that organic N source will be released soon enough for the wheat crop. Generally, we would recommend that you subtract from the total (spring N) any fall applied N up to 20 lb/A.

Based on the equation above and deducting 20 lb from a fall application, we would recommend a spring application of
- 110 lb N per acre for a yield potential of 100 bu,
- 90 for 90 bu potential;
- 70 for a 80 bu potential and
- 40 lb N per acre for a 60 bu potential.
Since greenup has started across the state, price should be the main factor in selecting a N source. Volatilization losses should still be minimal for urea based fertilizers at this time. Potential loss of N from 28% solution may be furthered reduced by applying in a band (dribble bar). For more information on wheat soil fertility, obtain the Extension Bulletin 938, Improving Wheat Profits in Ohio.

Potential for Nitrogen Loss on Wheat in Saturated Soils of Northern Ohio

Authors: Edwin Lentz

Many producers have been asking about the loss potential of topdressed nitrogen on wheat prior to the heavy rains and flooding in northern Ohio. Unfortunately, a large part of it may have been lost. Ohio State University research completed in 2003 revealed that loss of N from a single N application prior to spring green-up may have yield reductions of 19% compared to applications between initial greenup and early stem elongation. In that year, nitrogen was applied in the first part of March about 10 – 14 days ahead of greenup. The risk is greater when the frost is not completely out of the soil. (Frost was still in the soil before this rain event.) This allows the upper surface to stay wetter and large amounts of water movement to occur as surface runoff (carrying fertilizer). The risk would be greater for an application closer to the rain events; thus recent applications may be more at risk than those in early February. It just depends whether or not the fertilizer got worked into the upper soil surface and attached to the soil before a heavy water event (rain, ground thawing, and so forth). Our research showed that when these loss conditions are present, all forms of fertilizer will be lost (we had ammonia sulfate, 28%, and urea in the study). Even though we do not have data on ESN, our expectation is that if it was laying on the surface where the coated fertilizer could move with the water (float), it too would probably experience a loss under these conditions.

Now the difficult part, how can you tell if any had been lost? There is no quantitative way -- only best guess scenarios. If a producer has a high nitrogen check strip they can compare nitrogen treatments (most likely they do not). You can use a chlorophyll meter but interpretation a little tricky since no check strip (to account for varietal greenness) -- I like scores in the 40's with the meter. The best bet is probably a visual comparison between the suspected nitrogen-loss field and fields with later nitrogen applications. If by Feekes 6 it appears to be significantly less green, then consider an additional 50 - 60 pounds of N, for fields that have a potential for 100 bushels. I do not have the research to back this up and I am using my experience from N rate curves, splits and other N management work. The one thing a producer should remember is that they don't have to get in a hurry to apply more nitrogen. They can easily wait until Feekes 6 without sacrificing yield. In addition, it might be a good time to consider an on-farm experiment to address the question. Check with your County Extension AgNR educator about setting up an on-farm experiment.

Insect Management Issues on Corn and Soybean for the Coming Spring

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Numerous insect issues usually come up around this time of year, just before we get into the planting season. Certain situations sometimes call for taking preventive measures, especially when based on a history of problems in a field, having sampled for the insects, or because of the cropping practices being used. This year, we decided to discuss many of them in a single article.

Taking preventive action against corn rootworm larvae continues to be an appropriate tactic when growing corn following corn. Growers have numerous choices, including transgenic corn hybrids, soil insecticides (which still offer excellent control), and higher rates of seed treatments, although this latter tactic is best used when rootworm pressure is only expected to be relatively low to moderate. Where the first year western corn rootworm variant occurs, mainly in western and northwestern Ohio, growers must decide on the need for preventive tactics. If in these locations, we suggest giving consideration to taking preventive action against the rootworm in first year corn. In areas without the first year variant, rotation is still the most preferred preventive tactic to make. For European corn borer, the decision to take preventive action should be based on having had a history of borer problems. We also have numerous transgenic corn hybrids that give outstanding control of this pest. Where we do see a greater need for these hybrids is for corn that is planted in late May or early June. In those situations, we often see greater problems from European corn borer, and usually recommend that growers consider these transgenics.

If using transgenic corn, we would remind growers about Insect Resistant Management (IRM) requirements which necessitate the use of a refuge. The major requirement is that growers MUST plant a 20% refuge area to non-Bt corn. Growers should be aware that for corn borer, the refuge can be within, adjacent, or near the Bt field, but has to be within 1/2 mile. For corn rootworm, the refuge has to be within the same field as the Bt corn, or adjacent to it. If growers are planting a stacked hybrid, which many are now doing, we recommend using the common refuge approach where the refuge must be within or adjacent to the transgenic field.

The use of commercially-applied seed treatments as a preventive treatment is often recommended against many insects. Although we do not recommend seed treatments for “plant health” purposes, we do realize many growers are using them, and for this reason, need to know where they will be effective. When growers incorporate green organic matter in the soil in the spring, including old alfalfa fields, cover crops, or even heavy weed growth, the chances of enhanced populations of seedcorn maggots and subsequent plant stand reductions is high. Thus, we do recommend seed treatments for both corn and soybeans in these situations; seed treatments are usually effective against this insect.

We do not recommend seed treatments for control of black cutworm because our data and experience from past years suggest that seed treatments are unable to provide acceptable cutworm control. We think the best management for black cutworm is scouting fields beginning at early emergence; we do have a number of insecticides that can be applied as rescue treatments for cutworm. If a field has a history of cutworm damage and/or the field has a high population of winter annuals such as chickweed, then a preventive tactic that works can be used. A grower could apply a soil insecticide at planting or include an insecticide with the pre-emergent herbicide. Alternatively, a grower could use Herculex 1 or Herculex XTRA transgenic corn hybrids because they both have cutworm activity.

On soybean, the use of an insecticide seed treatment is also questionable. Although we are predicting higher soybean aphid populations this summer, we would remind growers that we do not recommend seed treatments for aphid control. Our data from previous years indicate that seed treatments do not offer control of aphids when needed, which is in late July and August. While having a density-reducing impact on early season aphids, the chances of still having a problem in mid to late summer remains high if aphids are in the area. During aphid outbreaks, using an IPM approach based on crop scouting and thresholds to optimally-time foliar sprays results in significantly greater yield compared to prophylactic seed treatments alone. An IPM approach to soybean aphid control also limits insecticide use to when and where it is needed, reduces pesticide exposure and selection for resistance, and helps to conserve natural enemies.

Although seed treatments will control the bean leaf beetle on soybean in late spring, this population of beetles does not cause that much leaf injury unless they are in extremely high numbers, and we seldom see this. As with soybean aphids, seed treatments will not limit later population growth in mid to late summer. Thus, we do not recommend seed treatments as a preventive measure to prevent feeding by this insect.

When producing soybean for seed or food grade soybeans and in other situations where seed quality is a major issue, we slightly change our recommendations for bean leaf beetle management. This change is because of our concern with the beetle’s ability to vector bean pod mottle virus. For growers who choose to control overwintering bean leaf beetles to limit virus transmission, we would recommend an early season foliar spray after plant emergence, followed by a second spray in July for the first generation beetles. Because seed treatments will offer control of the overwinter beetles and reduce feeding injury, growers might want to use seed treatments to replace the early season foliar spray. Currently, we do not have all the answers as to whether controlling the overwintered beetles with seed treatments will reduce virus transmission. Data from other universities suggest that this approach might not give economic control of the virus. However, growers might wish to try these seed treatments on a few fields to see if they work.

Weeds in non-GMO soybeans – the good news, the bad news, and the really bad news

Authors: Mark Loux

The comeback in non-GMO soybeans will undoubtedly result in at least a few messy weed control situations, since weeds are generally more difficult to control with conventional soybean herbicides vs. glyphosate. The presence of ALS-resistant populations in many fields makes weed control in non-GMO soybeans more difficult, along with our tendency to forget that the system is generally less forgiving of poor management compared with Roundup Ready herbicide programs.

The good news: Non-GMO soybean growers should be able to adequately control weeds in most fields by using the appropriate herbicides and following these guidelines:

1) start weed-free at planting with preplant burndown herbicides or tillage;
2) include broad-spectrum residual herbicides in the preplant burndown treatment;
3) apply POST herbicides to small weeds; and
4) if necessary, make a second POST application for late-emerging weeds or to complete control of giant ragweed or other weeds that survive the first POST treatment.

These guidelines, and more detailed information on herbicide selection, are outlined in the OSU/Purdue fact sheet, “Herbicide Programs for Non-GMO Soybeans”, available online at https://agcrops.osu.edu/weeds/. In many fields, the residual herbicide should provide enough control that only a single POST treatment will be needed. Our guidelines emphasize the use of Flexstar and Cobra/Phoenix in the POST applications, due to the prevalence of ALS-resistant populations. It is possible to use Classic or FirstRate as the primary POST treatment, but only where the field is known to be devoid of ALS-resistant weed populations.

The bad news: Weed populations in some fields may have already developed a reduced response to PPO inhibitors (Flexstar, Cobra/Phoenix). We know of at least several fields with a history of non-GMO soybeans where the common ragweed is resistant to both ALS inhibitors and PPO inhibitors. The population in one of these fields has a high level of resistance to both, and we were unable to obtain control with any combinations of ALS and PPO inhibitors, even when we added Basagran. In the other field, we have been working with a common ragweed population with a high level of resistance to ALS inhibitors and glyphosate, and what appears to be a low level of resistance to PPO inhibitors. We have had variable success with Flexstar and Cobra in this field. In 2009 field studies, POST application of Flexstar followed by Cobra resulted in a maximum of 80% control. However, we were able to obtain 95 to 98% control where we applied a residual herbicide at planting, and followed with one POST application of Flexstar. Interestingly, the residual herbicides provided only about 45 to 75% initial control, and the ragweed plants were up to 6 inches tall at the time of Flexstar application, but the combination of PRE and POST was still successful. Variable response is fairly typical for low-level herbicide resistance. Plant size and environment may be major factors in herbicide activity for populations with low-level resistance, whereas these factors have little effect where the level of resistance is high. The bottom line – it may still be possible to control populations that are developing a low level of resistance by: 1) using residual herbicides to reduce the population and slow plant growth; and 2) applying POST herbicides when weeds are small.

The really bad news: The herbicide programs we are recommending, and that most growers are using, will most likely drive more weed populations to become resistant to PPO inhibitors. We suspect this may occur most often for common and giant ragweed. The additional bad news is that there may not be much we can do about it (gulp!). The prevalence of ALS-resistant populations is forcing us to rely on PPO inhibitors for POST control of these two weeds, and frequent planting of non-GMO soybeans will increase their use and also the selection for PPO-resistant weeds. While a number of effective new products are available or in development for weed management in soybeans, these all involve the use of GM traits (Liberty Link, DHT, dicamba-tolerant soybeans) that will not help in non-GMO soybean weed management, except to ensure effective control when planted in rotation with non-GMO soybeans.

The best defense here is a diverse crop rotation and diversity in herbicide use within and among years, at least to the extent that can be economically justified. Non-GMO soybeans should ideally be planted only once in every three to four years in a field. In the other two to three years, the field should be planted to corn, wheat, and/or Roundup Ready or Liberty Link soybeans. Every effort should be made to obtain effective weed control and prevent weed seed production in these crops, so that weed populations are reduced in the year of non-GMO soybeans. In addition, avoid use of ALS inhibitors or PPO inhibitors as primary weed management tools, especially in POST treatments.

Suggestions to avoid over-reliance on any one herbicide mode of action in non-GMO soybeans include the following:

1) In the preplant burndown, use a combination of 2,4-D with either Gramoxone or glyphosate;
2) We expect that ALS inhibitors will be widely used for residual weed control, due to the effectiveness of products such as Scepter, Canopy, Valor XLT, etc. PPO inhibitors (Valor, Spartan/Authority) are often components of these herbicides or mixtures. It is possible to supplement or mix some of these products with additional metribuzin (such as Canopy DF + metribuzin), so that use of PPO inhibitors is deemphasized in the residual treatment. Otherwise, we are using PPO inhibitors in PRE and POST treatments, which increases selection pressure.
3) Where the weed population is not already ALS-resistant, POST combinations of Flexstar with Classic or FirstRate will provide two modes of action. This should in theory reduce the risk of weeds, resistant to one or the other of these modes of action, escaping treatment and producing seed. Both products in the mix should be present at active rates (near or at labeled rates) for this strategy to work. Where the weed population is already ALS-resistant, this strategy will not be effective enough to justify the extra cost.

Supplemental Label for Headline® Fungicide for “Plant Health”: Does this work in Ohio?

Authors: Jim Beuerlein, Peter Thomison, Pierce Paul, Dennis Mills, Anne Dorrance

Recently, a supplemental label for Headline® fungicide was added for the plant health benefits of the fungicide. The team at the University of Kentucky has done a very nice job listing these additional claims and review of this label (http://www.ca.uky.edu/ukrec/newsltrs/News09%20-1.pdf). Briefly the supplemental label claims the following: “The plant health benefits may include improved host plant tolerance to yield-robbing environmental stresses, such as drought, heat, cold temperatures, and ozone damage”. There are numerous additional claims on the label as well.

Across the Midwest and in Ohio specifically, in replicated trials (both on-farm and in research plots) we have not been able to show large increases in yield due to the control of disease ("not" added for correction March 18, hdw). For soybeans brown spot and frogeye leaf spot severity was reduced when Headline® and other strobilurin type compounds were used on HIGHLY susceptible soybean varieties. Only 3 out of 31 on-farm trials from 2004 to 2008 were able to recoup the costs of the fungicide, let alone see any profit. In all three cases, foliar diseases had reached the mid to upper canopy, the key leaves for yield in soybeans.

The results are very similar for corn and wheat. Yield responses tend to be higher and fungicide applications more likely to be profitable when susceptible hybrids or varieties are planted and foliar disease pressure is high. Summaries of more that 200 replicated corn foliar fungicide trials (from more than 13 different states, including more than 25 observations from Ohio) conducted by university-based researchers in 2007 and 2008 showed that the yield differences between fungicide treated plots and untreated checks vary from one trial to another, with an average yield response across all trials of 3.3 bu/A in 2007 and 3.6 bu/A in 2008. In 2007, the yield difference was 6 bu/A when gray leaf spot susceptible hybrids were planted compared to 3 bu/A when resistant hybrids were planted. Similarly, in 2008 the average yield increase over the untreated check was 7.5 bu/A when disease severity was greater than 5% compared to 1.2 bu/A when severity was less than 5%.

As our colleagues in Kentucky have eloquently stated “Thus, at this time, we do not feel that there is a scientifically defensible basis for assertions of improved plant health/stress tolerance in the absence of the diseases the fungicide was originally developed to control”. We concur with our colleagues. Let’s use these tools when they will provide the greatest benefit and keep them useful for the long term – when the timing is such that they impact the fungi that negatively impact our crops.

Pesticides Work Only If They Are Applied Properly

Authors: Erdal Ozkan

Pesticides have played a key role in the abundant and high quality food we enjoy in the United States. However, pesticides must be used with more caution today than in the past, because they are more potent and more expensive than the pesticides used years ago. Efficient use of pesticides must be the primary goal of an applicator to save money, and to protect the environment. Your job as an applicator is to apply the amount recommended. Too little pesticide results in poor pest control and reduced yields, while too much injures the crop, wastes your chemical dollars, and increases the risk of polluting the environment.

Achieving satisfactory results from pesticides depends on five major factors: a) positive identification of the pest, b) choosing the least persistent and lowest toxicity pesticide that will work, c) selecting the right equipment, particularly the right type and size of nozzle for the job, d) applying pesticides accurately at the right time, and e) calibrating and maintaining equipment.

Be well informed about the specific recommendations for a given pesticide, and follow the laws and regulations on pesticide application. Carefully read the product label to find out the specific recommendations.

Here are some general recommendations that will help you achieve maximum efficacy from pesticides.
· Always calibrate the equipment before starting to spray. It is the only way to determine whether a sprayer is actually applying a chemical at the recommended rate. For safety, calibrate with only water as the spray solution. Detailed, stepˆby-step information on calibration can be obtained from Ohio State University Publication AEX-520, available at: http://ohioline.osu.edu/aex-fact/0520.html
· Mix the chemical in a small container first, and then pour into the sprayer tank to achieve a uniform mixing of active ingredients in the tank.
· Find out if the pesticide requires the use of specific adjuvants to provide good product efficacy, influence droplet size or solution evaporation rate, to reduce drift, and to improve deposit and retention on the target.
· Some pesticides are highly volatile and may require incorporation into the soil after application. Follow label recommendations to avoid drift from highly volatile pesticides.
· Carefully examine the components of the sprayer (tank, nozzles, hoses, pressure gauge, pump, etc.) to make sure they are the right type, size, and can function effectively under various operating conditions. Make sure no leakage is occurring anywhere in the spraying system. Check the tank agitation system to make sure the flow to the tank for agitation is sufficient and effective.
· Application equipment generally arrive set up with a particular nozzle spacing that is typical for the type of spraying to be performed (i.e. row crop sprayer, floater, etc.). Choose the equipment setup recommended to achieve the best results (banding, broadcast, directed spraying, etc.).
· Spray pressure affects the performance of a sprayer in several ways. It changes the application rate as well as the size of droplets. Make sure you have an accurate and functioning pressure gauge on the sprayer.
· Boom height affects the spray pattern overlap, deposition uniformity on the target, and the time during which the droplets are exposed to wind and evaporation, both of which directly influence drift. Keep the boom height to a minimum to reduce drift.
· Maintain uniform deposition of spray material on the target across the boom. Uniformity of deposition is as important as the amount deposited. Non-uniform coverage can result from simple reasons such as using misaligned or clogged nozzles, nozzles with different fan angles, or from uneven nozzle height across the boom. These common problems result in streaks, untreated areas, or over-application of chemicals.
· Observe the output pattern of nozzles periodically. Streaks in the pattern indicate that foreign materials are inside the nozzles. Remove and clean nozzles using a soft brush for the tip and screen. Maintain the sprayer in peak condition by periodic inspections and repairs. Carry extra nozzles, washers, other spare parts, and tools for quick repairs in the field.
· Spray drift is one of the most serious problems the pesticide applicators have to deal with. It wastes expensive pesticides, may damage non-target crops nearby, and poses a serious health risk to people living in areas where drift is occurring. Spray drift accounts for about half of all non-compliance cases investigated by the Ohio Department of Agriculture. Various drift reduction strategies are outlined in OSUE Bulletin 816 (http://ohioline.osu.edu/b816/index.html).


2008 On-Farm Research Results Now Available On-line

Authors: Bruce Clevenger

Results from on-farm research studies that were conducted throughout the Buckeye State during the 2008 growing season are now available on-line. They are posted on the Agronomy Team’s Web site at https://agcrops.osu.edu under the Research link or directly at https://agcrops.osu.edu/research/On-FarmResearchReports.php. More results will be posted as they’re finalized, so be sure to check back for more study results.

Archive Issue Contributors: 

State Specialists: Erdal Ozkan (Agricultural Engineering), Peter Thomison (Corn Production), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Mark Loux (Weed Science), Ed Lentz (Agronomy), Jim Beuerlein (Soybean & Small Grain Production), and Jim Noel (NOAA). County Extension educators: Jonah Johnson (Clark), Steve Foster (Darke), Greg LaBarge (Fulton), Roger Bender (Shelby), Harold Watters (Champaign), Todd Mangen (Mercer), Glen Arnold (Putnam), Tim Fine (Miami), Gary Wilson (Hancock), Bruce Clevenger (Defiance), Florian Chirra (Williams), Mike Gastier (Huron), Mark Koenig (Sandusky), Howard Siegrist (Licking), Wesley Haun (Logan) and Marissa Mullett (Coshocton).

About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.