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Ohio State University Extension


C.O.R.N. Newsletter 2013-11

Dates Covered: 
April 30, 2013 - May 6, 2013
Glen Arnold
Weather OutlookWeather Outlook

Weather Outlook

The week of April 29 will feature above normal temperatures across Ohio with generally below normal rainfall except possibly in the far west. High pressure and warm weather will take over this week. The next storm will approach by the weekend.

Normal high temperatures are 65-70 and normal lows are in the mid 40s. Temperatures this week will average 5-10 degrees above normal. This will continue to allow 4 inch soil temperatures warm to around normal.

The best chances for rain will stay west and south of Ohio but western Ohio will see some rainfall. Rainfall totals in the west will be an inch or less. In the east, rainfall totals will be generally 0.25 inches or less.  Normal rainfall is about an inch per week.

The week of May 6th will feature continued above normal temperatures with normal to above normal rainfall returning. Temperatures will average 1-5 degrees above normal. Rainfall is forecast to be 1-2 inches with isolated higher totals. The exception may be in the far east where rainfall could stay at or below 1 inch.

Adjusting No-till Burndown Programs for Later PlantingAdjusting No-till Burndown Programs for Later Planting

Adjusting No-till Burndown Programs for Later Planting

This is a revision of an article we published in C.O.R.N. two years ago, when rain kept us out of fields until early June in some cases.  This year will hopefully not be a repeat of 2011 to that extreme.  Wet weather so far this year and the somewhat delayed planting has already had effects on no-till burndown programs, especially in soybeans.

The weeds obviously continue to get bigger under warm, wet conditions, and what is a relatively tame burndown situation in early to mid-April can become pretty hairy by early May.  It’s obvious from the calls and emails we have received, along with observations of our research plots, that there is a substantial difference in weediness between the fields treated with herbicides last fall versus the lack of a fall treatment.  Among other benefits, the fall treatment does definitely allow a clean start in the spring that persists for a while and ‘buys time’ in a delayed planting situation.  The fields that did not receive fall herbicides are much more of a concern as we try to adapt burndown programs to a delayed start that allows the overwintered weeds to create problems.

For many weeds, increasing the glyphosate rate to 1.5 lbs ae/A or higher in mixtures with 2,4-D or Sharpen, will help compensate for larger weed size.  This will not help with glyphosate-resistant marestail, and the other issue for marestail is that by the time we can finally plant, we will be unable to use 2,4-D rates higher than 0.5 lb (and this rate still requires a 7 day wait to plant).  The mixture of glyphosate plus 2,4-D has become less effective over time in some fields for marestail control.  Recommendations to improve control have included application to smaller plants, and increasing the 2,4-D rate to 1.0 lb/A, and so the current situation will probably introduce more variability in marestail control.  In fields with larger marestail that did not receive a fall herbicide treatment, control could be improved by supplementing the glyphosate/2,4-D with another herbicide that has activity on emerged marestail, or replacing the glyphosate with another herbicide.

A reminder that there are currently some extenuating circumstances that limit the extent to which we can modify burndown programs.  The first of these is the lack of labels that allow the addition of Sharpen to mixtures that contain flumioxazin (Valor), sulfentrazone (Authority), or fomesafen (Reflex).  The second is the depleted supply of Liberty, with an emphasis on the use of current stock for POST treatments instead of for burndown.  A review of the soybean burndown options for larger weed situations follows, with emphasis on marestail control.

1.  Where at all possible, keep 2,4-D ester in the mix, even if it means waiting another 7 days to plant soybeans.  Plant the corn acres first and come back to soybeans to allow time for this.  Have the burndown custom-applied if labor or time is short.

2.  To improve control with glyphosate/2,4-D, add Sharpen or another saflufenacil herbicide, as long as the residual herbicides in the mix do include flumioxazin, sulfentrazone, or fomesafen.  It’s also possible to substitute Sharpen for 2,4-D when it’s not possible to wait 7 days to plant, but this may result in reduced control of dandelion, and large deadnettle and giant ragweed.  Where the residual herbicide in the mix does contain flumioxazin, sulfentrazone, or fomesafen, and it’s not possible to change the residual, adding metribuzin can improve burndown effectiveness somewhat.

3.  Consider substituting Gramoxone or Liberty for glyphosate?  Gramoxone is the less expensive and more available choice here, but generally less effective than Liberty on marestail.  Gramoxone should be applied with metribuzin and 2,4-D in a typical no-till situation.  Use the higher labeled rates of Gramoxone, and a spray volume of 15 to 20 gpa for best results.  A consideration here is that in large no-till weed situations, high rates of glyphosate typically have more value that high rates of Gramoxone or Liberty, with the exception of glyphosate-resistant weeds.

4.  Among all of the residual herbicides, chlorimuron contributes the most activity on emerged annual weeds and dandelion.  This is probably most evident when the chlorimuron is applied as a premix with metribuzin (Canopy/Cloak DF, etc).  This may not be much of a help for marestail control, since many populations are ALS-resistant.  Cloransulam (FirstRate) has activity primarily on emerged ragweeds and marestail, as long as they are not ALS-resistant.  We have on occasion observed the a reduction in systemic herbicide activity when mixed with residual herbicides that contain sulfentrazone or flumioxazin.

5.  It is possible to substitute tillage for burndown herbicides.  Make sure that the tillage is deep and thorough enough to completely uproot weeds.  Weeds that regrow after being “beat up” by tillage are often impossible to control for the rest of the season.  Tillage tools that do not uniformly till the upper few inches (e.g. TurboTill) should not be used for this purpose.

6.  Late burndown in corn is typically a less dire situation compared with soybeans.  Reasons for this include: 1) the activity of some residual corn herbicides (e.g. atrazine, mesotrione) on emerged weeds; 2), the ability to use dicamba around the time of planting; 3) the tolerance of emerged corn to 2,4-D and dicamba, and 4) the overall effectiveness of available POST corn herbicides.  Overall, while not adequately controlling emerged weeds prior to soybean planting can make for a tough season, there is just more application flexibility and herbicide choice for corn.  Having said this, be sure to make adjustments as necessary in rate or herbicide selection in no-till corn fields.

Foliar Fungicide Application for Early Disease ControlFoliar Fungicide Application for Early Disease Control

Foliar Fungicide Application for Early Disease Control

Cool conditions over the last 7-10 days have slowed the wheat down considerably, however, the development of the crop is still close to what is considered normal in Ohio at this time of year. Current growth stages range from Feekes 6, jointing, to Feekes 8, flag leaf emergence. At Feekes 6, the first node is visible at the base of the stem, about an inch or so above the soil line; at Feekes 7, two nodes are visible, one about 2 inches above the soil line and the other about 3-4 inches above the first; and at Feekes 8, in addition to the two nodes seen at Feekes 7, the tip of the flag leaf, the fourth leaf above the first node, is visible. Feekes 8 marks the beginning of the period during which we recommend that field be scouted to determine which disease is present and at what level. Septoria blotch is usually one of the first to show up. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete. Septoria reduces grain fill and the size of the grain, but usually does not affect the number of spikelets per spike, which is defined very early in the development of the plant (before Feekes 6).

Foliar fungicide applications at or before Feekes 6 are less beneficial for Septoria control than applications made at or after flag leaf emergence (Feekes 8). An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual life of the fungicide will not adequately protect the flag leaf. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas and new infections will occur, even after early applications are made. In addition, frequent rainfall may also reduce the residual effects of the early applications, making them even less effective against mid- and late-season foliar disease development.

Over the last few growing seasons, we tested several foliar fungicide programs in wheat to provide answers to question about the benefit of different application times. We evaluated the effects of single, split, and double applications of several fungicides on Septoria, powdery mildew, Stagonospora, and grain yield. Applications were made at green-up, flag leaf emergence, or at both green-up and flag leaf emergence. Applications made at flag leaf emergence did better than green-up applications in terms of foliar disease control and yield. Among the programs with double or split applications, we observed the best results with those treatments that included an application at full rate at Feekes 8-9. A single full-rate application at flag leaf emergence did just as well as or better than the green-up + flag leaf in terms of powdery mildew and Septoria control.

There are several different fungicides available for use on wheat. Refer to the Table below for a more complete list of fungicides, rates, efficacy, and pre-harvest intervals.

Fungicide Efficacy for Control of Wheat Diseases Fungicide Efficacy for Control of Wheat Diseases

Fungicide Efficacy for Control of Wheat Diseases

The North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) has developed information on fungicide efficacy for control of certain foliar diseases of wheat for use by the grain production in industry in the U.S. The one-page summary chart was updated last week and can be found here

Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy is based on proper application timing to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application.

Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table. Table includes most widely marketed products, and is not intended to be a list of all labeled products.

Adjusting Corn Management Practices for a Late Start Adjusting Corn Management Practices for a Late Start

Adjusting Corn Management Practices for a Late Start

As of Sunday April 28, only two percent of Ohio’s corn crop was planted, which compares with 54% for 2012 and 25% for the five-year average ( ). Weather forecasts indicate more rain this week. As prospects for a timely start to spring planting diminish, growers need to reassess their planting strategies and consider adjustments. Since delayed planting often reduces the yield potential of corn, the foremost attention should be given to management practices that will expedite crop establishment. The following are some suggestions and guidelines to consider in dealing with a late planting season.

Although the penalty for late planting is important, care should be taken to avoid tillage and planting operations when soil is wet. Yield reductions resulting from "mudding the seed in" are usually much greater than those resulting from  slight planting delays. Yields may be reduced somewhat this year due to delayed planting, but effects of soil compaction can reduce yield for several years to come. (Keep in mind that we typically don’t see significant major yield reductions due to late planting until mid-May or even later in some years).

If you originally planned to apply nitrogen pre-plant, consider alternatives so that planting is not further delayed when favorable planting conditions occur. Although application of anhydrous N is usually recommended prior to April 15 in order to minimize potential injury to emerging corn, anhydrous N may be applied as close as a week before planting (unless hot, dry weather is predicted). In late planting seasons associated with wet cool soil conditions, growers should consider side-dressing anhydrous N (or UAN liquid solutions) and applying a minimum of 30 lb/N broadcast or banded to stimulate early seedling growth. This latter approach will allow greater time for planting. Similarly, crop requirements for P and K can often be met with starter applications placed in bands two inches to the side and two inches below the seed. Application of P and K is only necessary with the starter if they are deficient in the soil, and the greatest probability of yield response from P and K starter is in a no-till situation.

Remember the longer our planting is delayed the less beneficial a starter with P and K will be (unless the soil test level is below the critical level).  The primary reason they are less beneficial is typically at later planting dates soil temperatures are higher (this is not necessarily true for no-till soils and that is why they are more likely to be responsive).

Keep time expended on tillage passes and other preparatory operations to a minimum.  The above work will provide minimal benefits if it results in further planting delays. No-till offers the best option for planting on time this year. Field seedbed preparation should be limited to leveling ruts that may have been left by the previous year’s harvest - disk or field cultivate very lightly to level. Most newer planters provide relatively good seed placement in "trashy" or crusted seedbeds.

Don't worry about switching hybrid maturities unless planting is delayed to late May. If planting is possible before May 20, plant full season hybrids first to allow them to exploit the growing season more fully. Research in Ohio and other Corn Belt states generally indicates that earlier maturity hybrids lose less yield potential with late plantings than the later maturing, full season hybrids.

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 because of the potential for greater seedling mortality. 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 3 to 5% higher than the desired harvest population) in anticipation of a higher percentage of seedlings emerging.


Risk of Bt Resistant Western Corn Rootworms in OhioRisk of Bt Resistant Western Corn Rootworms in Ohio

Risk of Bt Resistant Western Corn Rootworms in Ohio

For the past few years, the western corn belt has dealt with western corn rootworm resistance to Bt corn containing the Cry3Bb1 gene.  This gene is in Yieldgard varieties, Genuity VT3P, and Smartstax products (but keep in mind Smartstax will also contain a different gene for RW control).  In most cases, the appearance of resistance is strongly associated with continuous corn using this gene for at least 3 consecutive years.

To our knowledge, we have not seen resistance in Ohio.  So, how do we keep resistance out and sustain the use of Cry3Bb1? We agree with the rest of the eastern “Fringe” (see article in Purdue’s Pest and Crop newsletter:, that crop rotation is the best way to remove resistant rootworms and stop their spread.  There are, of course, other options, but these will not be as effective as rotation. To keep resistance from occurring, proactive management is key.

If you are growing continuous corn (regardless of management tactic), we recommend examining roots for the presence of greater than expected damage.  If found, please contact entomologist specialists or OSU Extension Educators.  In addition, if you have continuous corn and would like to be part of our state-wide scouting effort, please contact Andy (  We may be able to do a site visit, help with root digs, and collect adult beetles for further testing. We need to do all we can to keep resistant rootworms out of Ohio.

Western Corn Rootworm Control

For western corn rootworm control in continuous corn, we have been recommending that growers either use a transgenic hybrid containing a Bt protein active against rootworm larvae, or make use of a granule or liquid soil insecticide and a hybrid not containing the protein.  In Ohio, we do not believe that it is necessary to combine both a Bt hybrid plus a soil insecticide to achieve economic control.  Our rootworm populations are seldom severe enough to consider both tactics together, nor do we feel it is appropriate to use a soil insecticide in addition to the Bt protein to prevent resistance from occurring with the Bt tactic; rotation is a much better way to prevent resistance from occurring.

However, we do know that there will be some growers that will apply a soil insecticide to the Bt hybrid, which in addition to those using a soil insecticide as a standalone method of rootworm control, is a tactic that they probably have not used for many years.   This article is a reminder, a strong reminder, that if growers use an organophosphate soil insecticide, that they need to pay attention to possible phytotoxic interactions between the soil insecticide and the various herbicides they might use.

Knowing that different combinations of soil insecticides and herbicides can negatively interact and cause phytotoxicity to corn plants was better known years ago prior to the use of Bt for rootworm control, when soil insecticides were the primary tactic that growers used.  However, most growers have not used them in many years and perhaps need a reminder of the potential danger from applying certain herbicides with the numerous soil insecticides.

Grower are urged to look at Table 8 in the “2013 Weed Control Guide for Ohio and Indiana” ( to see a list of herbicides that if used with certain organophosphate soil insecticides can potentially result in crop injury.   Growers should read herbicide and insecticide labels closely to determine possible interactions, especially for some of the newer herbicides.

Delayed Planting Effects on Corn Yield: A “Historical” Perspective

Rainy weather has delayed corn planting throughout Ohio. According to the USDA/NASS (, for the week ending April 28, corn was 2 percent planted, which was 52 percent behind last year and 23 percent behind the five-year average.

Long term research by universities and seed companies across the Corn Belt gives us a pretty good idea of planting date effects on relative yield potential. The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10. In the central Corn Belt, estimated yield loss per day with delayed planting varies from about 0.3% per day early in May to about 1% per day by the end of May (Nielsen, 2013). These yield losses can be attributed to a number of factors including a shorter growing season, greater disease and insect pressure and higher risk of hot, dry conditions during pollination.

Given these planting date effects, do yield losses associated with late plantings translate into lower statewide yields? Not necessarily. Let’s consider some previous growing seasons that were characterized by a “late start” and what impact this had on crop production. For the purposes of this discussion I’ll consider “late start” years as those in which 40% or more of the corn acreage was not planted by May 20. Since 1980, there have been significant planting delays associated with wet spring weather in nine years – 1981, 1983, 1989, 1995, 1996, 2002, 2008, 2009, and 2011. Table 1 shows the percentage of corn acreage planted by May 20 and May 30, the 50% planting date (the date by which 50% of the corn acreage was planted), yield, the state average yield for the previous five years, and the departure from the yield trend in each of those years. Of these nine years, the greatest delays in crop planting occurred in 2011 when only 19% of the corn acreage was planted by May 30. In five of the nine years (1981, 1983, 1996, 2002, and 2008) average state yields were markedly lower than the state average yield of the previous five years (In six of the  nine years, average yields were five bushels per acre or more below the yield trend line for Ohio). In one of these years, 2002, the average corn yield dropped to 88 bushels per acre (nearly comparable to the record low of 86 bushels per acre in 1988). However in four of the nine years, yields were similar or higher than the than the statewide average yield of the previous five years, and in one of these years, 2009, a record high corn yield, 174 per acre, was achieved.

Table 1.  Performance of Ohio’s “Late” Planted Corn Crop – Yield


% of Crop Planted by



May 20

May 30


Planting Date

Yield (Bu/A)

Avg. Yield of

Previous 5 Years

Departure from Yield Trend (Bu/A)




May 26







May 22







June 4







May 19







June 1







May 28







May 20







May 22







June 5




Data Source: National Agricultural Statistics Service USDA/NASS (


This comparison of statewide average corn yields from past years indicates that lower grain yields are not a certainty with late plantings. While delayed planting may cause yield loss relative to early planting, planting date is just one of many factors that influence corn yield. Figure 1 shows grain yields associated with dates by which 50% of the corn acreage was planted in Ohio from 1980 to 2012 and it does not suggest a strong relationship between planting date and yield. There are other factors that are of greater importance than planting date in determining grain yield. Weather conditions (rainfall and temperature) in July and August are probably the most important yield determining factors. Favorable weather conditions subsequent to planting may result in late planted crops producing above average yields as was case in 2009. However, if late planted crops experience severe moisture stress during pollination and grainfill then crop yields may be significantly lower than average, with 2002 being the most notable example in addition to 1981, 1983 and 1996.


Nielsen, R.L. 2013. The Planting Date Conundrum for Corn.  Corny News Network, Purdue Univ. [online] [URL accessed April 30, 2013].


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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.