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Ohio State University Extension


C.O.R.N. Newsletter 2004-11

Dates Covered: 
April 27, 2004 - May 4, 2004
Steve Prochaska

Eight Years Later - What we’ve learned about managing weeds in Roundup Ready Soybeans

Authors: Mark Loux

Glyphosate may be the best herbicide ever developed, and the ability to use it in corn and soybeans has certainly changed our expectations of weed control. Especially in soybeans, Roundup Ready systems are among the most consistently effective when properly implemented. We hear much less about a number of weeds than we used to, including Canada thistle, hemp dogbane, common cocklebur, and several annual grasses (e.g. yellow foxtail) that were becoming more problematic in the mid-1990’s. On the flip side, a number of weeds can still be a problem in Roundup Ready systems, especially when producers decide that the flexibility of glyphosate allows them to throw basic weed management principles out the window. The result has been an increase in a number of weeds that can take advantage of poor management or a lack of diversity in herbicide use in Roundup Ready systems. Some examples are dandelion, marestail, lambsquarters, and winter annuals. So – what have we learned about glyphosate and weed management in Roundup Ready soybeans after eight years of use?

1) Weeds can and will develop resistance or reduced sensitivity to glyphosate. Use of glyphosate to the exclusion of other types of herbicides may be a primary cause of resistance, and rotation away from glyphosate for a year does not necessarily prevent resistance from occurring or adequately mitigate existing resistance problems. We have confirmed glyphosate resistance in marestail in Roundup Ready soybean fields following a year of corn. A common theme in these fields seems to be use of only glyphosate in the year the soybeans were grown.

2) When it comes to annual weed control, bigger is not better. Even given the flexibility of glyphosate and its ability to control large weeds at high rates, a number of issues arise when weeds are allowed to become too large before application. Problems with letting the weeds get too large include: A) possibly reduced control, especially if rates are not increased, which leads to a need for resprays and increases the risk of resistance; B) the stalks of several weed species (e.g. ragweeds, marestail, lambsquarters) can be infested with insects, possibly reducing herbicide effectiveness, and the potential for stalk damage increases the longer weeds remain in the field before herbicide application; C) reduced sensitivity of some lambsquarters populations to glyphosate appears to be expressed to a greater degree in larger plants (more than 4 to 6 inches tall); D) large weeds may prevent herbicide particles from reaching smaller weeds lower in the crop canopy; and last but not least, E) weeds that emerge with the crop can reduce yield when they are allowed to reach a size of more than 4 inches (corn) or 6 inches (soybeans).

3) Skipping the early-season burndown application can be a big mistake in no-till soybeans. Delaying the first herbicide application until mid to late May allows a number of weeds, including dandelion, chickweed, purple deadnettle, and annual bluegrass, to flower and produce seed. We have attributed the increase in these weeds across the state to the failure to apply early enough in spring to prevent seed production. This is based partly on our research in producers’ no-till fields in the early 1990’s, when an early-season application of 2,4-D ester plus glyphosate (or 2,4-D plus residual herbicides if applied early enough) was critical for the success of weed management programs. Most of the fields did not have a real problem with winter annuals or dandelions because seed production was prevented. In addition, glyphosate and 2,4-D are much less effective on dandelion after seed production, because movement of herbicide to the root decreases at this time.

4) There are still plenty of good reasons to use other herbicides in combination with glyphosate in Roundup Ready systems. A primary reason to integrate other herbicides is to reduce the overall dependence upon multiple glyphosate applications, thus delaying the development of herbicide resistance. In burndown treatments, the addition of 2,4-D to glyphosate can greatly improve control of dandelion, atriplex, marestail, and lambsquarters, among other weeds, and help mitigate the effects of cold weather or time of day on glyphosate activity. The addition of CanopyXL can improve control of dandelion, marestail, and other weeds, and FirstRate/Amplify can improve control of marestail and ragweeds. In postemergence glyphosate applications, the addition of Classic can improve marestail, morningglory, and dandelion control, and the addition of FirstRate/Amplify can improve marestail, morningglory, and giant ragweed control and provide some residual control of ragweeds.

5) There are still plenty of good reasons to use a residual herbicide, such as CanopyXL, Sencor, Valor, etc, in Roundup Ready soybeans, including the following: 1) seedling dandelion and marestail control; 2) early-season giant ragweed control/suppression to minimize the competitiveness of this extremely competitive weed during the first month of soybean growth and reduce the need for a second postemergence glyphosate application; 3) residual control of lambsquarters, which has developed reduced sensitivity to glyphosate in some fields; 4) minimizing weed/crop interference during the first month on soybean growth, so that unplanned delays in the postemergence glyphosate application do not result in crop yield loss; and 5) control of weeds during the first month or more to compensate for slow soybean development due to poor soil conditions or weather.

The bottom line for Roundup Ready soybeans: glyphosate is not a substitute for basic weed management skills, and there is no substitute for a multiple-pass, diverse herbicide program that creates flexibility in postemergence application windows, protects crop yield, and provides effective control and prevents seed production of winter annual, summer annual, and perennial weeds, reducing future weed populations.

Generics Revisited

Authors: Mark Loux, Bruce Eisley, Ron Hammond

This is a follow up to a recent article on generic herbicides, due to the volume of questions on the their effectiveness. Generic products can broadly be defined as a group of products or trade names that all contain the same active ingredient(s), which are available from companies other then the one holding the original patent. The proliferation of generic products is a natural consequence of the expiration of patents, and we expect this trend to continue. The availability of generic products can be beneficial to producers, since it is often accompanied by a reduction in price. In some cases, generic products are the exact same formulation sold under a different trade name, due to marketing agreements between companies. For example, Dupont sells Cinch ATZ, which is the same formulation as Bicep II Magnum, and Agriliance sells Confidence and Confidence Xtra, which are the same as Harness and Harness Xtra. In other cases, the generic is manufactured by a company other than the one holding the original patent, and the formulation may vary somewhat from the original. This often results in a formulation that is similar to the original with regard to the percentage of active ingredient, however, and the label is often consistent with if not identical to the original. OSU entomologists and weed scientists use both brand name and generic herbicides and insecticides in their research. We have typically not observed any reduction in effectiveness when using generic products, when they are applied at the same rate of active ingredient as the brand name products.

Many recent questions on generics have focused on metolachlor, which is now available in a number of products in addition to those sold by Syngenta (Bicep II Magnum, Dual II Magnum) and DuPont (Cinch, Cinch ATZ). Sipcam sells metolachlor in Stalwart C and Stalwart Xtra, and Drexel sells it in Me-Too Lachlor, Me-Too Lachlor II, and Trizmet.

The generic situation with metolachlor is somewhat different than for most active ingredients, and there are some concerns that the generic metolachlor products will be less effective than those from Syngenta and DuPont. For a good discussion of the differences between metolachlor products and the possible ramifications, we recommend the article “Are All Metolachlor Products Equal? Version 2.0” by Bob Hartzler at Iowa State University. A link to this article can be found at the OSU Weed Management website,

Starane Herbicide

Authors: Mark Loux

Dow AgroSciences recently acquired a label for the use of Starane, or fluroxypyr, in field and sweet corn. Starane is a foliar-applied growth regulator herbicide, affecting broadleaf plants in a manner similar to Stinger (clopyralid). Our research experience with Starane is limited to some trials we conducted a number of years ago on the control of hemp dogbane. Starane is effective on hemp dogbane, but has a relatively narrow spectrum of activity overall. Consequently, it is likely to be used primarily in mixtures with other herbicides in order to broaden the spectrum of activity and control a greater number of weed species. According to the Starane label, it controls catchweed bedstraw, chickweed, cocklebur, common ragweed, hedge bindweed, morningglory, sunflower, velvetleaf, and several other weeds less important to Ohio crop production. We expect to have more information of the utility of Starane in Ohio corn production this fall.

Wheat Advancing Rapidly, Yet Little Disease Evident

Authors: Patrick Lipps

The warm weather over the past week has provided a boost to wheat development throughout the state. In southern Ohio fields are beginning flag leaf emergence (Feekes growth stage 8) and in northwest Ohio fields are in first node visible stage (Feekes growth stage 6). Cooler weather predicted for this week will likely slow down the development of the crop, but growers in northern Ohio can probably expect the wheat to enter the flag leaf emergence growth stage sometime during the first week of May. As the plants advance through the stem elongation growth stages it is time to begin visiting fields to assess the presence of diseases. So far we have seen only a few places with powdery mildew, but in most cases the disease is still on the lowest leaves. Septoria leaf blotch can also be detected on the lower leaves in some fields. If mildew is present, come back at flag leaf emergence to determine if the disease has moved up the plants to the upper leaves. Also check the level of resistance of the variety to see if it is susceptible to mildew or other diseases so that when you come back to scout the field in a week or so you know if the disease may be able to quickly spread in the field. Obviously diseases are more yield limiting on susceptible varieties and fungicides can be used profitably to protect from yield losses on these varieties.

Fungicides Available For Use On Wheat For Managing Wheat Leaf Diseases

Authors: Patrick Lipps, Dennis Mills

Wheat leaf diseases like powdery mildew, Stagonospora leaf blotch and leaf rust have caused significant economic damage to wheat in Ohio when weather conditions favor their development and spread. Now is the time to begin looking at your wheat crop and scouting for diseases that may affect yield. Scouting wheat for disease is an essential step in managing diseases and only after scouting should a fungicide be applied. Fields are most at risk when leaf diseases attack the upper two leaves of the plants between flag leaf emergence and flowering. The month of May is a critical time to look at wheat, especially when wet weather favors disease development. For assistance in assessing diseases in wheat visit the Ohio Field Crop Disease web site at or access 'Wheat Disease Management in Ohio' Bulletin 785 at

Ohio wheat growers have six different fungicides to choose from to control the various diseases: Tilt (propiconazole) , PropiMax (propiconazole), Quadris (azoxystrobin), Stratego(propiconazole + trifloxystrobin), Headline (pyraclostrobin), and Quilt (azoxystrobin + propiconazole). All of these products are excellent materials when used appropriately. Tilt, PropiMax and Quilt have slightly better efficacy against powdery mildew than Quadris, Stratego or Headline. However, Quadris, Stratego and Headline appear to be a bit more effective against leaf rust than Tilt, PropiMax and Quilt, because of their longer residual activity. All have good activity against Stagonospora leaf and glume blotch.

Federal labeling of the various fungicides indicates specific restrictions for timing of application. In general, it has been very difficult to adequately evaluate the level of disease in Ohio wheat fields before flag leaf emergence (Feekes growth stage 8) because disease levels have not yet reached threshold levels. Evaluation of disease levels can usually be accomplished by boot stage (Feekes growth stage 10) and head emergence (Feekes growth stage 10.3). In Ohio, the fungicides that contain propiconazole (Tilt, PropiMax and Stratego) have 24c labels that extend the application timing from flag leaf emergence (Feekes growth stage 8) to just prior to flowering (Feekes growth stage 10.5). This permits better application of the fungicides to achieve optimum disease control. Quadris is labeled for application up to Feekes growth stage 10.5 as well, but Quilt is restricted to applications prior to complete flag leaf emergence (Feekes growth stage 9). Our research confirms that applications from flag leaf emergence up to the end of heading provide the greatest economic advantage when the upper two leaves are in danger of becoming diseased.

The decision to apply a fungicide must be based on sound economic factors that include the cost of the fungicide. As expected the cost of the application depends on the fungicide product, the rate applied and application costs. Based on relative prices for the fungicide the cost will likely range from $10.30 to $23.80/A not including the cost of application. Since each of the products are effective when applied at the proper time, any of the least expensive options should provide adequate disease control.

FungicideRate/AEstimated Cost?APowdery MildewStagonospora blotchLeaf rust
Tilt4.0 oz11.20+++*++++++
PropiMax4.0 oz10.32+++++++++
Quadris6.2 to 10.8 oz13.70 to 23.87
Quilt14.0 oz12.60+++++++++
Stratego10.0 oz12.30+++++++
Headline6.0 to 9.0 oz10.74 to 16.11+++++++++

* the greater the number + signs the relative effectiveness
**(+) indicates greater efficacy at higher application rates

Web Site Predicts the Risk of Head Scab

Authors: Patrick Lipps, Dennis Mills

Growers can now access a web site to help them determine the risk of head scab occurring in their wheat fields. Head scab, caused by a fungus Fusarium graminearum, is a serious disease that can cause significant economic losses for growers when wet, relatively warm conditions occur before and during flowering of the crop. The fungus also causes stalk rot of corn (Gibberella stalk rot) and survives from season to season in crop residues. Over the past four years researchers at North Dakota, South Dakota, Indiana, Ohio and Pennsylvania have been collecting data to develop weather-based forecasting models to predict the occurrence of head scab. This risk forecasting system can be used as an early warning system for Ohio wheat growers. The accuracy of the risk predictions has been about 80% based on validation research. The forecasting system predicts the probability of head scab developing to a level greater than 10% severity based on the weather conditions of the 7 days prior to flowering of the crop. A 10% severity level can be seen as 1 out of 10 heads completely killed by the scab fungus or 10% of the florets on each head diseased. This level is considered an epidemic with economically significant yield losses.

The Wheat Fuasrium Head Bight Prediction Center can be accessed via the web at or through the Ohio Field Crop Disease Web site at

The homepage of this web site provides links to information about the risk prediction model, the biology of the disease and instructions on how to use the 'Risk Map Tool". Enter the page to get a scab risk prediction by clicking on the 'Risk Map Tool'. Within a few seconds you will be asked to provide some basic information to three questions. You need to enter the flowering date of your fields in the calendar to the left of the screen and indicate if you are growing 'spring' or 'winter' wheat (all wheat in Ohio is winter wheat) and if the wheat was planted into corn residue covering 10% or more of the soil surface. After answering these questions click 'OK' and the map of the US will come up. Pointing your mouse to Ohio and clicking will bring up the risk contour map for the state and National Weather Service weather stations represented as blue dots on the map.

At this point you can change the date of flowering by clicking different dates on the upper left calendar, however you can not choose tomorrows date or any future date. The models use only recorded weather data not predicted weather data. The calendar indicates the chosen flowering date in dark blue and the previous seven days utilized by the model in lighter blue. Assuming that you will be looking at this site before your wheat goes into flower, you can watch the potential disease risk by visiting the site each day or viewing the risk predictions for several different days. Please note that the model predictions run on weather data and a prediction will be generated regardless of if there is wheat flowering or not. The colored maps are produced using a source of weather information known as the Rapid Update Cycle (RUC) created by the National Weather Service. The RUC system combines multiple sources of weather information to generate observations on a 12 square mile grid throughout a region. The risk prediction contour maps will be colored red for high risk, yellow for moderate risk and green for low risk. Additionally, you can click on any of the weather station locations to get a risk probability for that location and the web page will provide the risk prediction for the previous seven days in a graph at the bottom of the page.

We recommend that you visit and work in the web site to become familiar with it so you understand it when the time comes to obtain 'real' risk predictions. Please read the sections on "Model Details" and "Reality Check". Also note this is an experimental system and the web site managers will be working with it throughout the season to 'fix' any bugs. If you do not get a prediction for a location, try again in a few hours.

Lastly, it should be noted that the model does have some practical limitations. Specifically this is the weather conditions after flowering are not considered in the predictions. Research has shown that wet conditions during and after flowering and during seed fill have a great impact on the development of head scab and deoxynivalenol contamination in grain. These time periods are not evaluated by the model at this time. Continue reading our articles in future newsletters for updates on the risk of head scab this year.

Alfalfa Weevil in Alfalfa

Authors: Bruce Eisley, Ron Hammond

We mentioned last week that it was time to begin scouting for alfalfa weevil (AW) in central and southern Ohio. With the warm weather last week, alfalfa in northern Ohio should also be checked for AW beginning this weej. It appears that AW activity is very light at this time based on fields sampled in central and north central Ohio. Fields in these areas were checked yesterday for AW larvae and none were found. Adults were present in the fields, probably laying eggs and so larval damage could occur in these fields in the future.

Our recommendation is to scout for AW in all areas of the state beginning this week and continue until harvest. Check for tip feeding by the larvae and if found, use the bucket method found in the fact sheet on the web at to sample the field. The fact sheet also contains information about the number of larvae and damage necessary to require treatment.

Since other weevil larvae may occur in alfalfa, such as the clover leaf weevil, it is important that the larvae found in the field be correctly identified. For example, clover leaf weevil larvae are larger, have a brown head and feed near the bottom of the plant. They normally do not cause economic injury in alfalfa in Ohio.

It is too early to scout for potato leafhopper since they do not move into Ohio until May.

Insect Trap Reports

Authors: Bruce Eisley, Ron Hammond

The black cutworm moth catch increased in all locations sampled this past week. Numbers the week before last were 2 moths/trap/week in the traps at Columbus and Western and increased to 5 and 7 moths/trap last week at these locations. While this catch is not high enough to allow us to predict when cutting should occur, it does indicate that cutworms may be a problem in some fields this year and scouting for cutworm should begin when corn plants begin to emerge.

Common armyworm moths were caught at all locations for the first time last week. We will continue monitoring this important pest and post trap catches on the web at:

Selecting a Liming Material

Authors: Robert Mullen

Liming materials are necessary soil amendments when soil pH becomes too low to support maximum crop production. With so many liming materials now available, selecting a liming material can be a daunting task. Several different kinds of liming materials are available such as limestone (calcitic and dolomitic), slaked lime, burned lime, marl, sludge from sewage treatment plants, and slag from manufacturing facilities. Liming materials are differentiated based on their neutralizing capacity, referred to as Effective Neutralizing Power (ENP). Selection criteria should be based on cost more than any other factor (to compare cost, use the equation below). If soil test reveals a magnesium (Mg) deficiency, dolomitic limestone should be chosen because of its high Mg content.

Pelletized lime is composed exclusively of finely ground lime that is bound together with clay or a synthetic binding agent. Pelletized lime is marketed as a fast-acting lime material that neutralizes soil acidity at significantly lower rates than aglime. Research however suggests that the nature of some binding agents can slow the dissolution of the lime material decreasing the speed of neutralization. One ton of typical aglime, having 50% of material that will pass a 100 mesh screen, contains 500 pounds of material similar in size to pelletized lime. This does not mean that an application of 500 pounds of pelletized lime will be just as effective as an application of 1 ton of aglime. Aglime contains different size particles which neutralize soil acidity over the longer-term (relative - based on your production system and soil texture) because the larger particles take longer to dissolve.

Remember liming materials applied at similar ENP rates affect soil pH and resulting crop yield similarly, so base selection on cost.

Calculating the cost per acre of a liming material:

$/acre = (LR / (ENP/2000)) * $/ton
LR – liming requirement based on soil test (ton/acre)
ENP – effective neutralizing power of liming material (lb/ton)

How To Reduce Spray Drift

Authors: Erdal Ozkan

Spray drift is one of the most serious problems the pesticide applicators have to deal with. In 2003, about 74% of the agriculture related complaints which the Ohio Department of Agriculture investigated involved drift issues. In Iowa, about 66% of the total complaints between 1996 and 2001, were related to drift (ranging from 48% to 81%). Data from a major Insurance Company indicate that in 1996 abut a third of the court cases related to spray misapplication they were involved in were related to drift. This shows the seriousness of the problem. Drift will be even a bigger problem in the future since there is an increase in acreage of genetically modified crops, and use of non-selective herbicides for weed control. Even a small amount of these non-selective herbicides can cause serious damage on the crop nearby that is not genetically modified.

Drift is the movement of a pesticide through air, during or after application, to a site other than the intended site of application. It not only wastes expensive pesticides, may damage non-target crops nearby, it also poses a serious health risk to people living on areas where drift is occurring. Spray drift occurs wherever liquid sprays are applied. Eliminating drift completely is impossible. However, it can be reduced to a minimum if chemicals are applied with good judgment and proper selection and operation of application equipment.

Major factors that influence drift are: spray characteristics, equipment/application techniques, weather conditions, and operator skill and care. Conscientious sprayer operators rarely get in drift problems. They understand the factors which influence drift and do everything possible to avoid them. Spraying under excessive wind conditions is always the most common reason why applicators get sued for creating drift. The best thing to do is not to spray under windy conditions. If you don’t already have one, get yourself a reliable wind speed meter as soon as possible. Only then can you find out how high the wind speed is.

After wind speed, spray droplet size is by far the most important factor affecting drift. Research has shown that there is a rapid decrease in the drift potential of droplets whose diameters are greater than approximately 200 microns (about twice the thickness of human hair). If operators of sprayers pay attention to wind direction and velocity, and have knowledge of droplet sizes produced by different nozzles, drift can be minimized.

The ideal situation is to spray droplets that are all the same size, and larger than 200 micron. Unfortunately with the nozzles we use today, this is not on option. They produce droplets varying from just a few microns to over 1000 microns. Our goal should be to choose and operate nozzles that produce relatively fewer of the drift-prone droplets. Although there is not one magic droplet size that is considered minimum to avoid drift, droplets larger than 150 micron are generally considered as those resistant to drift under most application conditions.

Fortunately, almost all major agricultural nozzle manufacturers have recently introduced their version of so called Low-Drift nozzles. These nozzles are designed mostly for reducing fewer small, drift-prone droplets, than comparable size standard flat-fan tips at the same flow rate and operating pressure. Tests we conducted in Ohio shows that these low-drift nozzles are capable of reducing drift potential by up to 80%. Many applicators carry more than one kind and/or size of nozzles on the boom ready to switch to the nozzle which provides the best protection again drift when the need arises.

Using low-drift nozzles is only one of the many options available to us to reduce drift. Here is a list of other drift reduction strategies which one can adopt to keep drift under control:

1.Use nozzles that produce coarser droplets when applying pesticides on targets that do not require small, uniformly distributed droplets (such as systemic products, pre-plant soil incorporated applications, fertilizer applications).
2.Keep spray volume up, and use nozzles with larger orifices.
3. Follow recent changes in equipment and technology such as shields, air-assisted and electrostatic sprayers that are developed for drift reduction in mind. Adopt some of these technologies when you feel it is time to do so.
4. Keep the boom closer to the spray target. Nozzles with wider spray angle will allow you to do that.
5. Keep spray pressure down, and make sure pressure gauges are accurate.
6. Follow label recommendations to avoid drift with highly volatile pesticides.
7. If you are not using low-drift nozzles, try adding Drift Retardant Adjuvants into your spray mixture.
8. Avoid spraying on extremely hot, dry and windy days, especially if sensitive vegetation is nearby. Try spraying in mornings and late afternoons. Although it may not be practical, from the drift reduction aspect, the best time to spray is at night.
9. Avoid spraying near sensitive crops that are downwind. Leave a buffer strip of 50 to 100 feet, and spray the strip later when the wind shifts.

In summary, allowing spray droplets go outside the application area is basically throwing money away. Alaso, loss of chemical may result in under-application of chemicals and ineffective pest control, which leads to additional applications, reduced yield and higher production costs. More importantly, losses and/or costly litigation may result if sensitive crops in adjacent fields are damaged. Last but not least, drift may contribute to pollution of air and water resources, and may affect the health and safety of susceptible human and livestock populations. Drift will likely to occur if the applicators do not select the right equipment and use sound judgment when applying pesticides. Good judgment can mean the difference between an efficient, economical application, or one that results in drift, damaging non-target crops and creating environmental pollution. If there is any doubt about a spraying job that might result in drift, one should wait until there is no longer that element of doubt. Goal of a conscientious pesticide applicator should be to eliminate off-target movement of pesticides, no matter how small it may be. Drift management strategies mentioned here hopefully can help the applicators achieve this goal.

Archive Issue Contributors: 

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