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Ohio State University Extension


C.O.R.N. Newsletter 2005-03

Dates Covered: 
February 8, 2005 - February 22, 2005
Harold Watters

Selecting Disease Resistant Hybrids for Planting

Authors: Peter Thomison, Patrick Lipps

Several corn diseases have caused appreciable yield losses in corn during recent years. This situation can be blamed on three important factors: the prevailing weather conditions, tillage and rotation systems that favor survival of the fungal pathogens and the use of hybrids that are susceptible to the diseases. There is little we can do about the weather, but we can make adjustments in our farming practices to lessen the impact of these diseases. Using crop rotations that allow one or even two years between corn crops will help. Incorporating corn residues with tillage to hasten their decay will help reduce fungal pathogen populations. However with so much reduced tillage being practiced on farms in Ohio, every grower should be concerned with selecting the best disease resistant hybrids they can find.

How does a corn grower select disease resistant hybrids?

• To start with the grower needs to accurately determine what disease, or diseases, were present in his crop last year and a relative assessment of the amount of yield loss associated with the disease. For example some growers lost over 40 bu/A to northern corn leaf blight last year. That is significant!

• Once the problem disease is identified, then the proper hybrid with an adequate level of resistance can be selected. Specific disease resistance information is needed on each hybrid. Statements like 'a hybrid has a good disease package' mean absolutely nothing. If that is all the information you can get from a seed dealer, then begin to look for a new company to work with.

• A hybrid may have resistance to one or two, and perhaps three different diseases, but do not expect a hybrid to have resistance to all possible diseases. That is unrealistic. Choose resistance based on the most yield limiting diseases in your area. If you have more than one major disease problem, plant several hybrids that include high levels of resistance to at least one of the diseases. It’s also very unlikely all the diseases will occur each year.

• The most valuable information on a hybrid is the relative level of resistance compared to the most commonly planted hybrids that company has in your area. This is particularly important when only partial resistance is available to a particular disease. When race-specific resistance is available then the grower can ask for certain specific resistance genes like the Ht1 resistance gene for northern corn leaf blight. In most cases you should not have to sacrifice yield potential, or other important agronomic characters, for disease resistance. Always match attainable yield potential, standability, grain quality and appropriate relative maturity with disease resistance.

• Corn growers in Ohio should ask their seed corn dealers about the availability of hybrids with high levels of resistance to northern corn leaf blight, Diplodia ear rot, anthracnose stalk rot and gray leaf spot, depending on the intensity of these diseases present on their farms.

Hybrid selection criteria for specific diseases:

Northern corn leaf blight: Ask for the highest level of partial resistance available combined with either Ht1 or Ht2 resistance genes. Most companies have these hybrids available.

Diplodia ear rot: Ask for a high level of partial resistance based on history of disease level in the field. For fields with over 10% of the ears diseased, obtain hybrids with the highest level of resistance even if you must change seed companies to get them. Combine use of resistant hybrids with crop rotation and tillage because the level of disease will be impacted by the amount of fungus surviving in the field.

Anthracnose stalk rot: Ask for the highest level of partial resistance available with hybrids having excellent yield potential and better than average standability. Anthracnose resistance will not compensate for poor standability issues.

Gray leaf spot: Ask for the highest level of partial resistance whenever planting corn into corn residue in areas with a history of the disease. Request yield performance data of these hybrids to make sure you are not paying for the resistance with lower yield potential. However, be realistic with the yield potential of the fields. Most hybrids are capable of producing higher yields in environments that are not subject to gray leaf spot.

High Prices and Fertilizer Application This Year

Authors: Robert Mullen

High fertilizer prices this year may cause some producers to decide not to apply fertilizers at all. Depending upon the fertility of your soil, this may or may not be a wise decision. Fertilizers typically have the greatest impact on crop production, so if your soil is deficient, skipping fertilizers this year may limit production. On the other hand if your soil is high to extremely high in phosphorus (P) and potassium (K), you do not need to apply those nutrients. If you manage different fields and you know your fertility levels through soil testing, make investments in fertilizer for fields that are below the established critical levels (see Tri-State Fertilizer Guide – Remember soil testing is the best way to monitor soil fertility, in years when fertilizers prices are high, knowing how fertile your field is can pay dividends.

So why do I say that if soil test levels are high, you do not need fertilizer? It comes down to the chemistry of P and K in the soil. Like I have said before, soil P and K are like oil in the crankcase of your vehicle. They do not have to be replenished every year if the crankcase is full or over-full. So let’s assume you have a soil that has a soil test level of 100 lb P/acre, how long will it take to deplete the soil to the critical level (30 lb/acre)? Assume we have a corn/bean rotation, which is yielding 150 bu/acre and 60 bu/acre every year, respectively and removing 0.37 lb P2O5/bu in corn and 0.80 lb P2O5/bu in soybean. Remember, in order to change the soil test P level by 1 unit it requires about 15-20 lb P2O5 to be removed. So it would take 20 years to deplete the soil to the critical level (assuming no dramatic changes in soil pH). If the crankcase is over-supplied, it will remain that way for a long while.

Flooded Fields and Fall Applied Phosphorus and Potassium

Authors: Robert Mullen

With all the flooded fields this winter, some may be concerned whether or not the fertilizers (P and K) applied this past fall will be around come spring. It depends upon several things – when and how fertilizers were applied, how much erosion has occurred on the fields, and how much sediment has been deposited.

For the first consideration, fertilizers applied earlier in the fall should have had time to dissolve and move partially into the soil (remember P and K, do not move much) and should be less susceptible to loss. Fertilizers applied later would have been more susceptible to loss, especially if fertilizers were applied to frozen ground (definitely susceptible to loss). If fertilizers were applied and incorporated they would have been much less susceptible to loss and should still be in the soil. If erosion has occurred resulting in exposed subsoil, then P and K (as well as other nutrients) could be deficient, but this will only be isolated to areas that experienced erosion. If erosion has not occurred, then those nutrients should still be in the soil.

Similar to a C.O.R.N. newsletter article written last year, some fields may have experienced deposition of sediment on the soil; those fields may need to be managed this coming spring. To review recommendations on flooded field management go to

Application of Fertilizer Materials to Frozen Ground and Topdressing Wheat

Authors: Robert Mullen, Edwin Lentz

Winter application of fertilizer materials for corn and winter wheat usually occurs during the cold winter months when the ground is frozen and will support the weight of application equipment. While this is convenient and lengthens the application season, some basic concepts need to be considered. Commercial manure application on frozen ground is regulated to mitigate nutrient runoff into surface waters. At present, application of commercial fertilizers is not regulated, but some of the guiding principles that are utilized in manure application can and should be applied to commercial fertilizers. When making winter applications observe setback areas near surface waters. This is to avoid runoff events that could carry applied fertilizers directly to the water source (this also leads to decreased efficiency impacting return on fertilizer investment). Fertilizer applications that contain phosphorus (P) and nitrogen (N) are the ones that present the greatest threat. Avoid applying fertilizers on areas of the field that have a risk of surface runoff (areas that have considerable slope). Frozen ground decreases the contact between soil and applied nutrients increasing the likelihood of nutrient loss via runoff.

Applying N early for the wheat crop may not necessarily be a good idea. Growth encouraged by application of N (if air temperatures allow active growth) too early can actually lead to decreased cold tolerance of the crop and result in frost injury or freeze damage due to cold early spring weather. Nitrogen application can also be susceptible to loss if applied before the crop can utilize it. A study was initiated in 2001 to evaluate the response of wheat to pre-greenup applications of N. The first two years of the study revealed little difference in wheat grain yield due to timing of application, but in 2003 yields were decreased by 19% when N was applied pre-greenup. The difference in yield was attributed to N loss prior to the crop demand.

While no regulations exist for application of commercial fertilizers on frozen ground, using the same principles as applied to manure application should be considered.

S-metolachlor, r-metolachlor – Does it Really Matter?

Authors: Mark Loux

Several articles in university newsletters in the spring of 2004 (the best being one from Iowa State -, discussed differences among metolachlor products. At that time, university data on effectiveness of the newer, generic metolachlor products were extremely limited, since they were included in 2003 field studies at only four universities. In 2004, a number of additional universities tested the generic metolachor products, but the database on which extension weed specialists can base conclusions about relative effectiveness is still small. A recap of the salient points on metolachlor products:

- there are two forms or isomers of metolachlor produced during its manufacture – s-metolachlor and r-metolachlor. S-metolachlor apparently is more active than r-metolachlor. In other words, a given rate of s-metolachlor could provide more effective weed control or greater longevity of control compared to the same rate of r-metolachlor.

- Syngenta sells Dual II Magnum and Bicep II Magnum (sold also by Dupont as Cinch and Cinch ATZ), which are primarily s-metolachlor. They previously sold Dual II and Bicep II, which were a roughly equal mixture of s- and r-metolachlor. As a result of the difference in activity between Dual II and Dual II Magnum, the latter can be applied at lower rates. For example, the recommended rate on a medium soil was 1.95 lbs of active ingredient (ai) for Dual II, but is only 1.27 lbs ai for Dual II Magnum.

- Several generic metolachlor products are available, including: Stalwart C (Sipcam Agro); Parallel and Parallel PCS (Makhteshim-Agan); and Me-Too-Lachlor and Me-Too-Lachlor II (Drexel). These are also available in premix products with atrazine, as Stalwart Xtra (Sipcam Agro) and Trizmet II (Drexel). Here’s the catch - these all contain a roughly equal mixture of s- and r-metolachlor (similar to Dual II), but the recommended rates are about the same as Dual II Magnum. The labels for Dual II Magnum, Stalwart C, Parallel, and Me-Too-Lachlor II recommend 1.33 pints/A on a medium-textured soil, which corresponds to 1.3 lbs ai. This rate of Dual II Magnum contains primarily s-metolachlor while the others contain a roughly equal amount of both the s- and r-metolachlor. So, in theory, the generic products could be less effective or provide reduced longevity of control compared to Dual II Magnum.

- Not all metolachlor products contain a safener to reduce the risk of corn injury, and the safened products don’t necessarily contain the same safener. All except Me-Too-Lachlor and Parallel PCS are formulated with a safener. Dual II Magnum, Bicep II Magnum, and Parallel contain benoxacor as the safener. Stalwart products, Me-Too-Lachlor II, and Trizmet II contain dichlormid, which is also used to safen various acetochlor products. We have not tested Me-Too-Lachlor II or Trizmet II, but we have not observed an increased risk of corn injury with generic metolachlor products to date.

- In addition to the differences in s- and r-metolachlor ratio, the atrazine premix products can vary in the absolute amount of metolachlor for a given soil type. For a medium-textured soil with greater than 3% organic matter, product rates and amounts of active ingredient are as follows:
Bicep II Magnum/Cinch ATZ (2.1 quarts): atrazine – 1.6 lbs ai; metolachlor – 1.3 lbs ai
Stalwart Xtra (2.1 quarts): atrazine – 1.6 lbs ai; metolachlor – 1.3 lbs ai
Trizmet II (2 qts): atrazine – 1.55 lbs ai; metolachlor – 1.2 lbs ai

The big question here is - are there differences in weed control among metolachlor products when applied at recommended rates? In OSU tests in 2004, the generic metolachlor products were similar in effectiveness and longevity in comparison to Dual II Magnum and Bicep II Magnum. So far, other universities appear to have similar findings on this issue. So, while theory would indicate that the generic products could be less effective based on their ratio of s- and r-metolachlor, our database does not support this conclusion. There may be situations where the generic products could be less effective than Dual II Magnum, and Bicep II Magnum, and this should be kept in mind when making herbicide-buying decisions.

The generic metolachlor products may fit best in fields with low to moderate annual grass pressure for two reasons: 1) potential differences in effectiveness among products are less likely to show up in these fields; and 2) the generic products typically do not have the same level of manufacturer support in the event of performance problems, compared to Dual II Magnum and Bicep II Magnum (and Cinch/Cinch ATZ). There are certainly situations where the generic products are equally suitable to their trade-named counterparts, including the following: 1) when applied in advance of a planned broad-spectrum postemergence treatment, since the postmergence treatment can control late-emerging annual grasses; and 2) when applied in combination with Balance, since the Balance can add enough annual grass control to compensate for reduced grass control with a generic product.

2004 Ohio State Organic Corn Performance Test

Authors: Peter Thomison, Allen Geyer, Rich Minyo, Deb Stinner, Alan Sundermeier

Interest in growing corn in organic cropping systems has been on the rise in recent years. In 2004, we conducted an evaluation of corn hybrids marketed for organic producers at the Hirzel Sustainable Systems Site, a certified organic farm located near Bowling Green in Wood County. Five seed companies participated in the 2004 test. Relative maturity ratings of the forty hybrid entries ranged from 81 to 116 days. The test was planted after alfalfa on May 28, 2004, with no fertilizers or pesticides applied to the site. Weed control was provided by mechanical cultivation. Growing conditions were generally favorable for corn production in 2004, however, excessive rainfall in May delayed planting. Grain yields ranged from 74.6 to 123.6 bu/A; stalk lodging from 9 to 56%; and grain moisture at harvest from 18.8 to 28.5%. A complete summary of the results is available online at:

Soybean Rust Update-Fungicide Labeling and Selection

Authors: Anne Dorrance

1. A Section 18 for the product Pristine from BASF will not be supported. ODA received a letter stating such on January 26th. This Section 18 list was assembled over two years ago and at that time BASF was moving forward with this product. It is a combination product of a triazole and boscalid, mainly used in the vegetable market.

2. There has been some discussion on when the Emergency Use Section 18s became effective. A Section 18 label is effective for 3 years. Many of us applied for these last spring (March, 2004) prior to soybean rust arriving in the US, which would mean that we would lose a growing season. EPA has made the decision that the labels for these products will become effective when rust arrived in the US, November 2004. Expect some additional changes to occur on the current labels as this policy makes its way down through the ranks. The reality is also that many of these products should have full Section 3 labeling prior to the end of this 3 year term.

3. It has come as a surprise that statements have been made indicating that Section 18 fungicides cannot be returned to the dealer because of their emergency use status. The Ohio Dept. of Agriculture is looking into this, but from a preliminary examination of the regulations and our Section 18 applications there is nothing to indicate that this is true. More to come on this issue.

4. Curative vs Protective/Preventative. My phone lines have been burning over the last two weeks on this issue. These two terms indicate which part of the disease cycle that a particular chemical may be effective on. Protective/Preventative sprays work on the spore and they must be applied prior to any spores arriving on the plant. They are not effective once those spores have germinated and begun to infect the leaf. Curative fungicides work on the mycelium or body of the fungus. They are not effective on spores. HOWEVER, both of these types of products have the best efficacy when they are applied to plants just prior to spore deposition. At this time, the greatest amount of fungicide is present on the plant– and if you can’t get back to the field for 3 weeks, the field is protected. A curative treatment will not bring back a field once the lesions are all sporulating. They have a very narrow time range for curative activity. My fear is that producers are getting talked into applications that may be far in advance of when rust may arrive in Ohio and that the application will not be effective. Thus one fungicide application is paid for – and by the time this fungus does arrive – there will be no more $ to pay for more treatments, there will be no more fungicide or there will not be enough residual from the first application to do any good. Appropriate timing of these fungicides is critical to managing this thing successfully as well as economically.

5. Differences in the systemic ability among the fungicides. This is an interesting point. Systemic ability indicates how a chemical moves within the plant. As one would expect they are not all equal. In making a decision which fungicide to use, the systemic ability is not one of them. The choice between a triazole and a strobilurin should be based on what the soybean rust infection level is in a field. If it is too high – then only a triazole or a premix product should be used. If there is no disease in a field and it is very early in the growing season, then a strobilurin is going to be the choice here. Section 18 products may be limited to two applications per growing season. If disease arrives early and this policy doesn’t change – we will be limited to cholorothalonils and strobilurins for the first application.

6. If there is one thing I’ve learned over the past month is that this is truly a dynamic situation. More information is coming out of South America, more policies are getting firmed up and many things will continue to change prior to the growing season. We will do our best to keep track of it all. Stay tuned.

A reminder to those who may want to attend an evening event, the February 15th Crop Profit satellite conference will be expanded to provide the latest on the increasing information data base for soybean rust biology and management for 2005. Dr. Anne Dorrance will be returning from several national meetings with the latest on this disease and it’s control measures, so Ohio producers can make sound economic decision going into the next growing season.

Many OSU Extension offices are making the program available. Call your local Extension office or visit for details.

Soybean Rust Workshops Set for Western Ohio March 7-9

Authors: Greg LaBarge

Three soybean rust workshops will be held in Western Ohio during March 7th, 8th and 9th from 8:30 to 1:30. The workshops will include Dr. X.B. Yang, Iowa State University and Dr. Anne Dorrance, Ohio State University, nationally recognized pathology experts talking about soybean rust. The program will cover history, biology, predictive models, fungicides, and decision making for the 2005 production season. A spray equipment panel discussion and presentation from industry representatives will be part of the program.

Monday, March 7 Roberts Convention Center, Wilmington, Ohio
Tuesday, March 8 Der Dutchman, Plain City, Ohio
Wednesday, March 9 The Lighthouse, Findlay, Ohio

The program is sponsored by the Ohio Soybean Association. Cost is $20 for Association members, $40 for non-association members. Call 1-888-769-6446 to make reservations. CCA credits have been applied for.

North Central Branch ASA Meeting March 15 & 16

Authors: Harold Watters

Many of you who read the CORN newsletter are Certified Crop Advisors. The American Society of Agronomy is a professional society for the study of crop production practices – including soils, crops and their interaction. The Society began the CCA program over 10 years ago.

The North Central ASA comprises the states of North Dakota, South Dakota, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wisconsin, Illinois, Michigan, Indiana, and Ohio. The North Central Branch meeting provides a forum for the interaction of persons interested in all aspects of agronomic sciences and management.

The next meeting of the North Central Regional Branch is March 15 & 16, 2005 at the Lied Lodge & Conference Center in Nebraska City, NE. The pre-registration fee received by March 1, 2005 is $110.00; the registration fee received after March 1, 2005 is $140.00.

See the agenda and register on-line: The program is built for practicing agronomists. While the program is quite far west in the North Central Region this year, it will be rotating back to the east over the next couple of years. Attending a distant program helps provide a different perspective and allows discussion with other agronomists.

Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pat Lipps and Dennis Mills (Plant Pathology), Ron Hammond and Deb Stinner (Entomology), Mark Loux (Weed Science), Peter Thomison, Allen Geyer and Rich Minyo (Corn Production), Robert Mullen (Soil Fertility) and Ed Lentz (Agronomy). Extension Agents and Associates: Roger Bender (Shelby), Howard Siegrist (Licking), Dusty Sonnenberg (Henry), Steve Bartels (Butler), John Yost (Fayette), Greg LaBarge (Fulton), Alan Sundermeier (Wood) and Harold Watters (Miami)

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.