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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2009-14

Dates Covered: 
May 18, 2009 - May 26, 2009
Tim Fine

Wet Weather, Should You Be Concerned About Nitrogen Loss?

Authors: Robert Mullen, Keith Diedrick

The wet weather continues and many may be concerned about the risk of nitrogen loss. Some areas of the state have seen sizable rainfall amounts that can increase the risk of leaching or denitrification, but the question is should you be concerned about nitrogen loss? At this point in the season, we would not be overly concerned if you applied anhydrous ammonia as your nitrogen source. As mentioned in a previous CORN article (, anhydrous ammonia is efficient because it is fairly resistant to microbial oxidation due to its fumigant properties; it eliminates the bacteria responsible for nitrification, which is the conversion of ammonium to nitrate, near the band of application. Thus, that material can be in the field for a week or two prior to conversion to nitrate. Additionally, the speed of microbial oxidation is a function of soil temperature. At this point in the growing season, soil temperatures are relatively cool, especially this year. We have computed the growing degree days for soil temperatures between April 1 and May 17 for the last 27 years, and we found that currently we quite a bit behind compared to the long-term average. This is especially true for western and northeastern Ohio.

For fields that may have received dry urea fertilizer, we would be a little more concerned, but only if the field was waterlogged for at least a day. Those few fields that may have received a sizable amount of urea-ammonium nitrate (UAN – liquid 28) would be at a little more risk of loss due to the application of nitrate especially if waterlogged for a day or more. Fortunately, soil temperatures are in our favor as the rainy days were associated with cold fronts. This should minimize the risk of denitrification which is our greatest risk of nitrogen loss early in the season (except on very coarse textured or sandy soils that leach nitrate easily).

Our recommendation is evaluate your crops over the next couple of weeks as soil and air temperatures increase and look for any visual symptoms of nitrogen deficiency (general chlorosis or yellowing). If you are still concerned, you can use the tool we developed a few years ago for evaluating the risk of nitrogen loss (

Have Your Soybeans been Treated and Inoculated Too Long?

Authors: Jim Beuerlein

Many soybean producers took delivery of soybean seed treated with fungicide and inoculated the last half of April expecting to plant that seed relatively soon. Now that planting has been delayed, we are being asked if the fungicides and inoculation materials will perform when the seed does get planted.

The fungicides on the seed will work well whenever the seed is planted unless we have heavy rainfall and saturated soil between planting and emergence of the crop. Excessive rainfall will dilute the fungicide and move some of it out of the seed furrow, thus reducing its’ effectiveness. Typically, fungicide seed treatments are effective for 10 to 20 days after planting which is usually adequate time to get the seed emerged.

Most soybean inoculation materials retain efficacy for 30 to 40 days on the seed if there is no fungicide present, and for varying times depending on the seed treatment fungicides present. So, there is the need to check the inoculation label or call your seed processor, who has the information you need. Seed storage conditions also determine how long inoculation products retain activity once applied to the seed. The bacterial cells are easily killed by either high temperatures or drying of the cells. Most liquid inoculation materials have a component that helps prevent the cells from drying out, thus extending the time they are viable. The ideal storage conditions are temperatures of 50-70 degrees and the humidity above 50 percent. The poorest storage condition is one of low humidity and high temperature.

Properly inoculated soybean seed will have over one million bacterial cells on each seed. Some of them will die soon after application, while others may remain viable for two or more months. The important thing is the number of live cells per seed when the seed is planted. The manufactures know the death rate of cells under various storage conditions and try to provide a product that will perform adequately well past the time period they advertise. Typically, fifteen good, high production nodules per plant are adequate for maximum yield, and that is only 0.0015 percent of what we start with. The number of live cells on the seed at planting is a function of both the length of time between application and planting and the quality of the storage conditions. When stored in good conditions, most soybean inoculation products should perform adequately for up to 45- 60 days or longer.

Should seeding rates be changed for late corn plantings?

Authors: Peter Thomison

Past university research indicates that optimal plant populations for early (mid to late April) and late planted (late May to early June) corn are similar. Based on results of these studies, most extension agronomists recommend that final plant populations should not be changed as planting date is delayed. One of the questions I’ve been asked recently is whether seeding rates should be increased for late planted corn. I’m not aware of studies in the Corn Belt that show consistent yield benefits from increasing plant population in late plantings. If planting is delayed until early June, some Ohio data suggests that certain hybrids are more susceptible to stalk lodging at high populations. In a recent OSU study, effects of early (late April) and late (early to mid June planting dates) plantings on corn response to population (24, 30, 36, and 42000 plants/A) were investigated at three locations. Results suggested that final stands of 30,000 to 36,000/A were required for optimal yield for the late April plantings. However, for the early to mid June planting dates, the results indicated little benefit from increasing seeding rate and a significant yield loss at plant populations above 30,000 plants/A. For corn planted late, grain yields, averaged across the three locations, were 159, 161, 133, and 138 bu/A at 24, 30, 36, and 42, 000 plants/A, respectively. The lack of response to plant population was related to stalk lodging which ranged from 59% at 24,000 plants/A to 97% at 42,000 plants/A.

In delayed planting situations, use the optimal seeding rates for the yield potential of each field. Recommended seeding rates for early planting dates are often 10% higher than the desired harvest population. However, soil temperatures are usually warmer in late planted fields, and as a result germination and emergence should be more rapid and uniform. So, as planting is delayed, seeding rates may be lowered (decreased to 3to 5% higher than the desired harvest population) in anticipation of a higher percentage of seed emerging.

Nafziger, E.D. 1994. Corn planting date and plant population. J. Prod. Agric. 7:59-62.
Nielsen, R.L. and P.R. Thomison. 2002 .Late Planted Corn & Seeding Rates. OSU Crop Observation and Reporting Network Newsletter. May 13 - 20, 2002 C.O.R.N. 2002-13 [URL verified 5/15/08].

Late Plantings and Insects

Authors: Ron Hammond, Andy Michel, Bruce Eisley

With the frequency of rainfall in Ohio this past month, many fields in Ohio have just been planted, or will be over the next week. Because of this, much of the corn and soybean crop will be relatively short in height and growth compared with other years at this time. However, the insect populations are somewhat on schedule. Although there are no indications of abnormally high populations of any of our common pests, growers should be aware that sometimes the presence of smaller plants intensifies the injury that can occur. Many of our thresholds relate to the size of the plants, and thus, our crops will be at a slightly higher risk of economic damage. On corn for example, the black cutworm threshold, 3% or more plants cut or tunneled and larvae still 1 inch or less, is for plants in the second to sixth leaf stage. Much of the corn will not even be reaching the second stage for a few weeks considering it is not yet emerged or even planted. On soybean, bean leaf beetles, as well as slugs, are known to be more damaging to plants that are recently emerged with unifoliate leaves just opening. We would suggest that growers plan on checking their fields closely over the next few weeks to prevent unexpected injury from insect pests that would not be of much concern if crops had been planted on schedule 3-4 weeks ago. See our new Agronomic Crops Insects website,, for information on many of our common pests, including fact sheets, thresholds, and insecticide recommendations.

Planting Delays and Switching to Earlier Maturing Corn Hybrids

Authors: Peter Thomison

Persistent rains have caused major delays in corn planting across Ohio. According to the USDA/NASS ( as of Sunday May 17, Ohio corn acreage planted, at 39 percent, was 13 percent behind last year and 43 percent behind the five year average. Corn emerged was 18 percent, compared to 26 percent last year and 46 percent for the five year average. The weather forecast for the next couple of days looks promising with warmer temperatures and the absence of rain, so hopefully as soggy fields dry, corn planting will be completed soon.

Is there a need to switch from full season to shorter season hybrids due to these weather delays? Probably not - in most situations full season hybrids will perform satisfactorily (i.e. will achieve physiological maturity or "black layer" before a killing frost) even when planted as late as May 20-25, if not later in some regions of the state.

Results of studies evaluating hybrid response to delayed planting dates indicate that hybrids of varying maturity can "adjust" their growth and development in response to a shortened growing season. A hybrid planted in late May will mature at a faster thermal rate (i.e. require fewer heat units) than the same hybrid planted in late April or early May).

In Ohio and Indiana, we've observed decreases in required heat units from planting to kernel black layer which average about 6.8 growing degree days (GDDs) per day of delayed planting. Therefore a hybrid rated at 2800 GDDs with normal planting dates (i.e. late April or early May) may require slightly less than 2600 GDDs when planted in late May or early June, i.e. a 30 day delay in planting may result in a hybrid maturing in
204 fewer GDDs (30 days multiplied by 6.8 GDDs per day).

There are other factors concerning hybrid maturity, however, that need to be considered. Although a full season hybrid may still have a yield advantage over shorter season hybrids planted in late May, it could have significantly higher grain moisture at maturity than earlier maturing hybrids if it dries down slowly. Moreover, there are many short to mid season hybrids with excellent yield potential. Therefore, if you think you may end up planting in late May, consider the dry down characteristics of your various hybrids. In past years, some mid to full season hybrids had grain moisture levels at harvest similar to those of short season hybrids because of rapid dry down rates. Keep this in mind before you trade the hybrids you originally planned to use for shorter season alternatives. Also, late planting dates increase the possibility of damage from European corn borer (ECB) and warrant selection of ECB Bt hybrids (if suitable maturities are available). In recent OSU studies, Bt hybrids planted after the first week of June consistently outyielded non-Bt counterparts even at low to moderate levels of ECB. Since many corn growers will be planting triple stack hybrids this year, which include Bt resistance for ECB, this may be a non-issue unless there’s a need to switch to earlier maturing hybrids.

Corn planting in the northern third of Ohio is most likely to be impacted by more wet weather. If planting delays continue beyond next week, growers in parts of northeast and north central Ohio may want to consider corn hybrids that require 100 to 150 fewer GDD than the adapted full season hybrids usually planted. These areas of the state historically accumulate fewer GDDs during the growing season than other regions of Ohio. For more information on selecting corn hybrids for delayed planting, consult "Delayed Planting & Hybrid Maturity Decisions", a Purdue/Ohio State University Extension publication available online at: .

An incomplete list of products that won’t help glyphosate burn down big weeds in no-till soybeans

Authors: Mark Loux

The delay in soybean planting has resulted in continued questions about substitutes for 2,4-D ester in soybean burndown treatments. We covered this subject in the May 4 edition of C.O.R.N. As a quick reminder, the best bet for burndown in soybeans without 2,4-D ester is to increase glyphosate rates and add a product that contains chlorimuron or cloransulam. Also, use true ammonium sulfate instead of ammonium sulfate replacements, and make sure that adjuvant premix products that contain ammonium sulfate are supplying a high enough rate - 8.5 to 17 lbs/100 gallons of spray mix, depending upon how hard the water is. While glyphosate can be more active when applied in spray volumes of 10 gpa or less, higher volumes can be justified in fields with large and dense weed populations to ensure adequate coverage. Some dealers promote the use of additional nonionic surfactant to improve the activity of glyphosate. This has occasionally improved control in OSU research with certain glyphosate products. Most glyphosate products are formulated with surfactant, however, and increasing the glyphosate product rate also increases the surfactant rate.

Be cautious about adding any number of other products to glyphosate, because many of these contribute very little to the activity of glyphosate. Products in this category include:

Aim, Resource, Cadet, Valor, Spartan, ET, and 2,4-DB (also citric acid, WD-40, blue windshield washer fluid, and antifreeze)

Some of these products can cause the fairly rapid development of symptoms on weeds, usually contact-herbicide type injury, but this contributes little to the eventual control. Products that cause these symptoms can reduce the activity of glyphosate, especially when weeds are large. Exceptions to this would be where the product actually controls a weed well on it’s own, such as the activity of Aim or Resource on velvetleaf. Consider that none of the products listed above have much activity on giant ragweed, and they all have essentially no activity on emerged marestail. Bottom line – make sure you know what the purpose is for adding a product to glyphosate burndown treatments, and consider that increasing glyphosate rates is often much more effective than adding other products that have little activity on tough no-till weeds.

A few more things about 2,4-D ester

Authors: Mark Loux

Just when you thought it was safe to read C.O.R.N. without seeing us preach yet again about the importance of 2,4-D in burndown treatments, we have some final comments to make on this subject. We have had questions about the risk of injury to corn from 2,4-D applied early postemergence. Small, emerged corn is usually extremely tolerant of 2,4-D, and our perspective is that application of 2,4-D to corn that is spiking can be safer than preemergence applications. The primary concern with a preemergence application is that a heavy rain will occur before corn has emerged, moving the 2,4-D down toward the not yet emerged corn shoot. This occasionally results in crop injury, whereas small, emerged corn usually tolerates 2,4-D well.

We are not including this information to discourage preemergence applications of 2,4-D, especially this week when we have a string of dry days in the forecast. Our main point is to provide some reassurance that 2,4-D can be included in herbicide treatments even after corn has emerged. The rate of 2,4-D that can be applied is lower on emerged corn compared with preemergence applications, but most labels still allow up to 0.5 lbs ai/A on emerged corn. Some 2,4-D labels allow broadcast postemergence application anytime after corn has emerged, while others specify that corn should be 4 inches tall. Most labels contain a statement to the effect that 2,4-D should be applied as a directed spray using drop nozzles once corn has reached a size of 8 inches, because the risk of injury increases on larger corn.

Also, a final caution to nonGMO soybean producers about the decision to omit 2,4-D ester from burndown treatments. Doing so can greatly increase the risk of experiencing unsolvable weed control problems in this year’s soybeans (i.e. you may end up with a big mess on your hands). The postemergence herbicides that can be used in nonGMO soybeans are not likely to adequately control the weeds that survive an inadequate burndown. The widespread resistance to glyphosate and/or ALS inhibitors in marestail and ragweeds can make these weeds difficult to control without the use of 2,4-D. Large, aged lambsquarters can also be tough to control with glyphosate alone, or with postemergence herbicides that are not that good on lambsquarters to begin with. Our primary suggestion here, especially in fields with a history of herbicide resistance, is to go ahead and use 2,4-D ester in the burndown, even if it means further delays in soybean planting. The success of your nonGMO soybean crop may depend upon it.

Declare, a New Insecticide

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Cheminova Inc. recently received a federal registration for Declare, a new pyrethroid insecticide labeled on numerous crops, including alfalfa, corn, soybean, and wheat, for a broad range of insects. Declare is gamma-cyhalothrin, the same active ingredient found in Proaxis and Prolex. The preharvest intervals for Declare are 7 days on alfalfa hay, 21 days on field corn, 30 days on wheat, and 45 days on soybean. Please remember to read the label for all insecticides for appropriate application information including preharvest interavals for all crops. We would remind growers with wheat harvest being about a month and a half away and the potential concern from either armyworm or cereal leaf beetle, that many insecticides have a long preharvest interval on wheat of 30 days. Again, READ AND FOLLOW all insecticide label directions.

Alfalfa and Regrowth

Authors: Ron Hammond, Andy Michel, Bruce Eisley

With reports coming in of first alfalfa cutting, our concerns will soon be turning from alfalfa weevil to potato leafhoppers. We will address leafhoppers in a coming newsletter issue. However, we have received many reports of fields being cut with significant alfalfa weevil populations. In those fields, growers should plan on observing the regrowth for signs of continue weevil feeding. Remember that you should have some growth occurring before you spray any insecticide so that there is leaf material to hold the material.

Frost Damage in Wheat

Authors: Pierce Paul, Jim Beuerlein, Dennis Mills

Air temperatures dropped to an average of about 35 degrees on at least two nights over the past week. UnderstandablY, some wheat producers are concerned that these relatively low temperatures may have caused some damage to their crop. Thirty-five degrees is really not a problem, however, we do not know what temperatures the wheat head actually experienced. We will have to see what happens over the next few days. At our current growth stage, between Feekes 9 and 10, in northern counties and between heading and flowering in southern Ohio, the yield effect of frost can range from moderate to very severe if temperatures drop to 24 - 28 F for two or more hours. It all depends on the variety, the growth stage, how cold it was, and the length of time plants were exposed to the cold temperatures. The amount of damage is a function of both time of exposure and the temperature, but no one has any numbers that we know of. We just don't know. For example, 28 degrees for 30 minutes may be as bad as 31 degrees for a long period.

Freezing temperatures between boot and flowering may cause spikes to be trapped in boot, leaf discoloration, floret sterility, and damage to the lower stems. The damage tends to be most severe with the greatest yield impact between heading and flowering. The head has some protection from cold temperatures until it emerges, but is easily damaged after emergence. Sterility and stem damage may lead to yield loss, however, since it is highly unlikely that all the plants in a field were at the same growth stage and were equally exposed to temperatures below 30 F, the overall damage may be minimal and restricted to low areas of the field. At most there may be some leaf tip burn on more sensitive varieties. Wheat is a winter crop and can tolerate cold temperatures.

The visual symptoms of frost injury to the heads appear as bleached glumes (and can be confused with scab or take-all). Additionally, freeze damaged florets appeared to be lighter green in color than unaffected florets on the heads. Remember, you can not detect damaged fields from the roadway; you will need to walk the field and inspect individual heads to see if there is any damage.


Authors: Jim Noel

Everything remains on track. We had about 0.50 to 2.00 inches of rain from northeast to southwest this past week with isolated higher and lower totals as usually occurs.

The outlook is for a dry week which is good news. We will go from below normal to above normal temperatures as highs go from the 60s to 80s this week in much of the state.

Rain returns this weekend in the far south and statewide early next week. More rain is possible the beginning of the following week and temperatures next week and the first week of June will be near average or slightly below.

Overall, much better conditions the next several weeks with more time between rains but still some rain too.

No changes to summer either with near average to slightly below average temperatures and near average rainfall.

Memorial Day Delay

Authors: Tim Fine

Just a reminder that, because of the Memorial Day holiday, next week's newsletter will not be posted on line and will not be emailed until Tuesday evening. Hopefully, between cutting and baling hay, getting crops in the ground, spraying and scouting, you have some time to enjoy your Memorial Day.

Archive Issue Contributors: 

State Specialists: Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel, and Bruce Eisley (Entomology), Peter Thomison (Corn Specialist), Jim Beurlein (Soybean Specialist, Robert Mullen and Keith Diedrick (Soil Fertility), Mark Loux (Weed Specialist), Jim Noel (NOAA). County Professionals: Suzanne Mills-Wasniak (Montgomery), Tim Fine (Miami), Jonah Johnson (Clark), Harold Watters (Champaign), Roger Bender (Shelby), Wesley Haun (Logan), Glen Arnold (Putnam), Bruce Clevenger (Defiance), Alan Sundermeier (Wood), Greg LaBarge (Fulton), Ed Lentz (Seneca), Steve Prochaska (Crawford), Mike Gastier (Huron), Howard Siegrist (Licking), Les Ober (Geauga)

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.