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Ohio State University Extension


C.O.R.N. Newsletter 2013-13

Dates Covered: 
May 14, 2013 - May 21, 2013
Debbie Brown

NOAA Mid-May Weather Update

The weather pattern continues to shift toward normal gear. It appears there will be rain chances over the coming two weeks but when all is said and done, rainfall should be average to slightly above average over much of the state of Ohio and the eastern corn/soybean belt. Rainfall averages close to an inch for a week. Temperatures also look to average slightly above normal the next two weeks - 1to 5 degrees.

The 2 week rainfall outlooks by the National Weather Service weather models averaged out can be found on the NWS Ohio River Forecast Center webpage at:

Current forecasts are for 1.5 to 3 inches of rain over the next two weeks.

The last freeze should be over for most of Ohio now but it was advertised on last week's column and with warmer temperatures yet periods of rainfall, conditions should be pretty good to get into most fields over the next 2 weeks.

Will Planting Delays Require Earlier Maturing Corn Hybrids?

This is a revision of an article published in C.O.R.N. in 2011 when persistent rains caused major delays in corn planting across Ohio. According to the USDA/NASS ( for the week ending May 12, corn was 46 percent planted, which was 37 percent behind last year and three percent behind the five-year average. The weather forecast for the upcoming week is mixed with the likelihood of more rain in parts of the state so some fields may not be drying out soon.

 Given this outlook, is there a need to switch from full season to shorter season hybrids? 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 recent years, we’ve seen a wide range of drying conditions. In some years, mid- to- full season hybrids had grain moisture levels at harvest similar to those of short season hybrids because of rapid dry down rates. However in others, cool, wet conditions after maturity slowed dry down and major differences in grain moisture at harvest were evident between early and full season hybrids.

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: .

Impact of Low Temperatures on Corn Survival

Although it’s too early to determine how corn already planted will respond to recent weather, the effects of the low temperatures on corn survival will probably be negligible for the most part. In past years, we have observed that early planted corn that was in the process of germinating or as far along as the V1 stage (one leaf collar visible) survived freezing soil temperatures in April with little impact on crop performance or plant stand. Agronomists generally downplay the impact of low temperature injury in corn because the growing point is at or below the soil surface until V6 (six leaf collars visible), and thereby relatively safe from freezing air temperatures. Moreover, the cell contents of corn plants can sometimes act as an "antifreeze" to allow temperatures to drop below 32 degrees F before tissue freezes, but injury to corn is often fatal when temperatures drop to 28 degrees F or lower for even a few minutes.

 Effects of low temperatures on germination are far more serious when combined with snow and freezing rain. When dry corn seed absorbs cold water as a result of a cold rain or melting snow, “imbibitional chilling injury” may result. Cold water can cause similar injury to seedling structures as they emerge during germination. Such injury in corn seed ruptures cell membranes and results in aborted radicles, proliferation of seminal roots, and delayed seedling growth. When temperatures remain at or below 50 degree F after planting, damage to germinating seed is particularly severe. When this physiological damage is combined with other factors, including saturated soil conditions and seedling blights, you have the potential for widespread emergence problems.

 To assess the impact of freezing temperatures on emerged corn, check plants about 5 days after the freezing injury occurred (and preferably when growing conditions conducive for regrowth have occurred). New leaf tissue should be emerging from the whorl. You can also observe the condition of the growing point (usually located ½ in to 3/4 in below the soil surface) by splitting seedlings lengthwise. If the growing point appears white to light yellow and firm several days after the frost, prognosis for recovery is good.

Assessing Soybean Stands Under Cool Conditions

A significant portion of the state was planted and some (soybean) fields were planted right before this cold period.  With cold temperatures, it is going to take a longer period of time for plants to emerge.  Soil temperatures around the state: 

County                 Research Branch              Temperature (F)

Jackson                 Jackson                                   59.2

Noble                    Eastern                                    59.9

Huron                   Muck Crops                               51.0

Ashtabula             Ashtabula                                  46.9

Sandusky             North Central                             55.1

Wood                   Northwest                                  48.5

Clark                    Western                                     55.5

These soil temperatures are cool enough to delay soybean emergence for as much as 2 weeks.  Warmer temperatures now forecast for the end of the week will help to alleviate this.  When seeds are in the ground under these cool and saturated soil conditions, they are vulnerable to many of the soil borne pathogens.  An effective fungicide seed treatment will help alleviate this and stands will not be affected.  But that is only if that fungicide seed treatment is effective towards the pathogen population in the field.  There have been lots of changes in the seed treatment industry in the past five years and each active ingredient does not control the full spectrum.  If after 2 weeks – you have spotty emergence and or seedlings have brown or pink lesions, send us the dying plants.  We can help sort out which fungicide may be more effective for your field – if we can recover the pathogens.  Send symptomatic seedlings to the Soybean Pathology Lab, OARDC, 1680 Madison Ave., Wooster, OH  44691.

Soybean plant population has been evaluated in many trials conducted by the Ohio State Agronomic Crop Team.  According to Agronomic Crop Team data, 95 to 98% soybean relative yield was achieved when soybean stand at harvest was between 127,000 and 171,000 plants per acre (see Figure 1).   However, soybean plants can achieve optimum yield over a wide range of plant populations if stand is even and uniform.  Some data indicates that 100,000 plants per acre at harvest can achieve maximum yield when planted in narrow rows prior to May 20.  Keep in mind this yield data is based on final plant population at harvest…not seeding rate.  Final population is a function of seeding rate, quality of the planting operation, seed germination percentage and environmental conditions (soil moisture, disease pressure, fungicide treatment, etc).  To quickly estimate stand, count the number of plants in 70 foot of row for 7.5 inch row spacing, 35 foot of row for 15 inch row spacing, or 17.5 foot of row for 30 inch row spacing.  These counts represent 1/1000th of an acre (i.e.,  120 plants in 35 foot of row grown at 15 inch row spacing represents a stand of approximately 120,000 plants per acre). 

Figure 1.

Soybean Plant Date Recommendations

Currently in Ohio, soybean planting is off to a slower start compared to the ten-year average (National Agricultural Statistics Service).  During the week of April 29-May 5, generally 23% of Ohio soybean acres are planted.  However, this year only 1% of the soybean acres have been planted due to cool/wet soil conditions throughout Ohio.

 How does plant date influence yield?  Planting date can greatly influence soybean yield, but only if conditions are suitable for planting.  The yield advantage due to early planting may not be realized if soybeans are planted into cool/wet soil.  In southern Ohio, soybeans should be planted when soil conditions are adequate any time after April 15.  In northern Ohio, planting should begin the last few days of April.  From the Ohio Agronomy Guide, the effect of planting date on soybean yield is shown in Figure 5-4.  Planting after May 10 resulted in a decrease in soybean yield.

Figure 5-4.

  What about seeding rate?  Soybean seeding rate doesn’t need to be adjusted until the last week of May/first half of June.  If planting the first half of June, adjust seeding rate to 200,000 to 225,000 seeds per acre.  If planting during the second half of June, 225,000 to 250,000 seeds per acre is recommended.  Results from a plant date/seeding rate study conducted in Wood Co. last year indicates that soybean yield was similar regardless of seeding rate when planted April 25 and May 11.  By May 31, soybean yield was significantly greater when 225,000 seeds per acre were planted compared to 125,000 seeds per acre (see graph).  If planting late, 7.5-inch row spacing is recommended to facilitate canopy closure.    

 Seed Rate Effect on Yield

 What about relative maturity?  Relative maturity has little effect on yield for plantings made during the first three weeks of May.  During the first half of June, a four-day delay in planting delays physiological maturity about one day.  As planting is delayed, there is concern about whether late maturing varieties will mature before frost.  When planting late, we recommend planting the latest-maturing variety that will reach physiological maturity before the first killing frost.  Soybean flowering is triggered by day length.  As days get shorter (and nights get longer) after June 21, soybeans are triggered to flower which generally occurs around the first week of July.  Later maturing soybeans will put on more vegetative growth before flowering.  Table 5-4 of the Ohio Agronomy Guide gives relative maturity recommendations based on planting date for northern, central, and southern Ohio.

Table 5-4.

Early Spring Field Crop Insect Issues

Black Cutworm – This is probably our main concern over the next month.  Numerous fields being planted have significant weed growth, especially of chickweed.  These fields are especially attractive to female moths for egg laying.  Because of the small size of the corn for the next few weeks, the crop will be very susceptible to injury by cutworms if they are present.  Although a few of the transgenic proteins should offer control, we would remind growers that not all trangenics do, nor do the various seed treatments.  Growers are urged to scout their corn for the next month and take action if cutworm cutting is present at the appropriate levels for the size of your corn.  See the fact sheet for more information, and for insecticide choices.

 Bean Leaf Beetles – With most soybean fields finally being planted across the state, and relatively late at that, our hope is that the overwintered adult population should disperse themselves over a lot of fields, thus resulting in lower populations in most fields to start the growing season with.  However, if there are growers who were able to get in early planted fields a few weeks ago, they should realize that they might be some of the few soybean fields emerged their area.  If so, these fields might receive more adult beetles than usual.  Growers, if they happen to have early planted fields emerging, before other fields in their area, should scout those fields with more diligence. 

 Slugs – As mentioned in a previous newsletter, the small size of both soybean and corn will lead to a greater damage potential from slugs.   Keep a close eye on those fields with a previous history of slug problems.

 Wheat Insects – Although no problems are yet being received, growers should monitor their fields for cereal leaf beetle larvae followed by possible true armyworm infestations.  Timing is good for scouting knowing we will be going into the flag leaf stages. 

 Alfalfa Weevil – Problems are still being reported across the state on alfalfa.  Remember if the alfalfa is reaching 15 to 20 inches in height, early cutting should be considered.  If smaller, insecticide applications should still be considered. 

Mid-May Wheat Development and Disease Update

The wheat crop in Ohio is now at or just past Feekes Growth Stage 8 (flag leaf emergence) and will likely reach the heading and flowering growth stages towards the end of May and early-June. Frequent rainfall and drastic changes in temperatures over the last 7-10 day have led to some concerns about disease development and the need for foliar fungicide application.

Frequent rainfall during most of last week has indeed resulted in fairly rapid development of Septoria tritici leaf spot, especially on susceptible varieties. This disease usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with dark-brown to black spots in the center. Wheat is susceptible to Septoria leaf spot throughout its development; therefore if it indeed continues to rain as is forecasted for the latter half of this week and early next week, this disease will likely continue to develop up the plant, especially if conditions remain cool (50 to 68oC). Cool temperatures will also favor the development of Powdery Mildew, another early-season disease that is already present on the lower leaves in most fields. However, both Septoria and powdery mildew will become less of a concern as temperatures increase, but continue to monitor their development over the next several days. Remember, if the variety is susceptible and conditions are favorable, a fungicide can be applied to prevent there diseases from reaching the flag leaf (the upper-most leaf of the plant) before grain-fill.

Frequent rainfall also puts the crop at risk for head scab development and vomitoxin contamination of the grain, but these will only become a concern if it continues to rain during flowering and temperatures increase. This is because the wheat plant is most susceptible to scab during flowering and the scab fungus infects and causes the most damage when warm, wet or humid weather coincides with flowering. However, although scab is not yet a concern at the current growth stage, the weather forecast for the next week or so suggests that conditions will be ideal for growth and spore production of the scab fungus in crop residue in the days leading up to flowering. This will increase the risk for scab, especially in fields planted with susceptible varieties in or next to fields with corn stubble. Continue to monitor the weather and the development of the crop over the next 7-14 days and, as your crop approach the flowering growth stage, use the web-based risk tool ( to the determine the risk for scab in your area. Remember, fungicides are most effective against scab and vomitoxin when applied at flowering. Earlier applications with provide adequate control of Septoria and Powdery mildew, but will not control scab. Therefore, use the risk tool to help you assess the risk for scab and determine whether a fungicide application at flowering is warranted for scab control.

For more on wheat fungicide, refer to Table 1. (Link to larger table)

Table 1.

New-Look Scab Forecasting and Alert Systems 2013

The Wheat Scab forecasting system ( is up and running and is now available for use in Ohio. This is an excellent tool to help guide fungicide application decisions. Based on the flowering date of your crop and the weather conditions leading up to flowering, you can estimate the risk of scab occurring and make a timely fungicide application to reduce scab and vomitoxin.

This year, the forecasting tool looks a little different, but it still works in the same way. You still need to select your flowering date (day when anthers are first seen sticking out of the heads) and wheat type (winter wheat in Ohio). Color patterns across Ohio and neighboring states will then indicate the level of risk in the region for the flowering date you select: Red = High Risk; Yellow = Moderate Risk; and Green = Low Risk. You can then use the zoom tool to take a closer look at the risk in your area.  (Link to Download Presentation of Scab Risk Tool)

The commentary section, now at the top of the forecasting website, provides up-to-date information to help producers assess the risk of scab and decide if a fungicide should be applied. You can also gain access to these commentaries directly on your cell phone or via email. Commentaries will be updated regularly and sent directly to the emails or cell phones of those who sign up to receive the alerts. Once there is cell phone coverage and email access, you will receive the alerts anywhere in the country. You can then visit the website to see whether your crop is at risk and contact your state specialist for more information. To sign up, click on this link: and complete the form with your name, email address, cell phone number and other requested information. You can choose whether you want to receive the scab alert via email, text message (on your cell phone), or both. You can also choose whether you want to receive alerts from all regions covered by the system or only from the Mid-West / Mid-South Soft Winter Wheat region.

Early Postemergence Application of Preemergence Corn Herbicides

One of the problems with a wet start to the season, when planting gets compressed into short periods, is the lack of time to apply preemergence herbicides and 28% before corn emerges.   Most preemergence corn herbicides can be applied to emerged corn, and some of them have enough foliar activity to control small, emerged weeds without the need to add postemergence herbicides. In addition, the majority of the corn hybrids are resistant to glyphosate and/or glufosinate (Liberty), which can be combined with preemergence herbicides to control weeds emerged at the time of application.  It’s also possible to mix in some other POST herbicides such as Impact, dicamba, 2,4-D, Capreno, etc to control emerged weeds, instead of glyphosate or Liberty.  Some issues to be aware of with regard to postemergence application of preemergence herbicides follow. 

 - Only a few herbicides can be applied using 28% as the spray carrier.  These are Degree, Degree Xtra, and Bullet.  Degree Xtra and Degree can be applied in 28% on corn up to 6 inches tall, when air temperatures are less than 85 F.  Bullet can be applied up to 5-inch corn with the same temperature restriction.  Expect some leaf burn from these mixtures.  All other herbicides must be applied using water as the spray carrier.

- there is usually a maximum corn size specified, which can be based on growth stage or corn height.  This can be as small as the V2 stage for some herbicides, such as Corvus and Balance Flex. 

- Most premixes or tank mixtures that contain atrazine can adequately control small broadleaf weeds, and especially those that contain another broadleaf herbicide (e.g. Lexar, Lumax, Instigate, SureStart).  Grasses more than about an inch tall will require the addition of glyphosate, Liberty, or other herbicide with effective grass activity. 

- Follow adjuvant recommendations closely to minimize the risk of injury and do not assume that it is always possible to use an adjuvant once corn has emerged.

- Based on our research with this type of approach to herbicide management, herbicides should be applied when weeds are less than about two inches tall to ensure that they have been prevented from causing yield loss. 

- Further information can be found on herbicide labels and also in the herbicide descriptions in the “Weed Control Guide for Ohio and Indiana”.  However, we find that labels can lack enough information on adjuvants and tank-mix partners for this situation.    Be sure to check with dealers and manufacturer/distributor agronomists to get specific information when necessary.


This is the time of the year you will get busy with spraying. Just take a moment to review some common sense ideas to get the most out of those expensive pesticides you will be spraying. Achieving satisfactory results from pesticides depends on five major factors: a) positive identification of the pest, b) choosing the least persistent and lowest toxicity pesticide that will work, c) selecting the right equipment, particularly the right type and size of nozzle for the job, d) applying pesticides accurately at the right time, and e) calibrating and maintaining equipment.

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

Tips to Better Spraying

Here are some general recommendations that will help you achieve maximum efficacy from the pesticides.

·         Always calibrate the equipment before starting to spray. It is the only way to determine whether a sprayer is actually applying a chemical at the recommended rate. For safety, calibrate with only water as the spray solution. Detailed, step–by-step information on calibration can be obtained from Ohio State University Publication AEX-520, available at:

·         Some chemicals and/or spray additives are highly dense and may create mixing problems if added to the sprayer tank without further diluting it. In such cases, you should mix the chemical in a small container first, and then pour into the sprayer tank to achieve a uniform mixing of active ingredients in the tank.

·         Find out if the pesticide requires the use of specific adjuvants to provide good product efficacy, influence droplet size or solution evaporation rate, to reduce drift, and to improve deposit and retention on the target.

·         Some pesticides are highly volatile and may require incorporation into the soil after application. Follow label recommendations to avoid drift from highly volatile pesticides.

·         Carefully examine the components of the sprayer (tank, nozzles, hoses, pressure gauge, pump, etc.) to make sure they are the right type, size, and can function effectively under various operating conditions. Make sure no leakage is occurring anywhere in the spraying system. Check the tank agitation system to make sure the flow to the tank for agitation is sufficient and effective.

·         Application equipment generally arrive already set up with a particular nozzle spacing that is typical for the type of spraying to be performed (i.e. row crop sprayer, floater, etc.). Choose the appropriate equipment setup best suited for a given situation (banding, broadcast, directed spraying, etc.).

·         Spray pressure affects the performance of a sprayer in several ways. It changes the application rate as well as the size of droplets. Make sure you have an accurate and functioning pressure gauge on the sprayer, and operate the sprayer within the pressure range recommended by the nozzle manufacturer.

·         Boom height affects the spray pattern overlap, deposition uniformity on the target, and the time during which the droplets are exposed to wind and evaporation, both of which directly influence drift. Keep the boom height to a minimum to reduce drift.

·         Maintain uniform deposition of spray material on the target across the boom. Uniformity of deposition is as important as the amount deposited.  Non-uniform coverage can result from simple reasons such as using misaligned or clogged nozzles, nozzles with different fan angles, or from uneven nozzle height across the boom.  These common problems result in streaks, untreated areas, or over-application of chemicals.

·         Observe the output pattern of nozzles periodically.  Streaks in the pattern indicate that foreign materials are inside the nozzles.  Remove such particles from the nozzle tip using a wooden tooth pick or soft object; clean the nozzle filter using a soft brush. Maintain the sprayer in peak condition by periodic inspections and repairs.  Carry extra nozzles, washers, other spare parts, and tools for quick repairs in the field.

·         Spray drift is one of the most serious problems the pesticide applicators have to deal with. It wastes expensive pesticides, may damage non-target crops nearby, and may pose a health risk to people living in areas where drift is occurring. Spray drift accounts for about half of all non-compliance cases investigated by the Ohio Department of Agriculture. So, take spray drift seriously. Various drift reduction strategies are outlined in OSUE Bulletin 816 (

Chemical manufacturers recommend the proper label. However, how close you can get to their recommendation is your responsibility. You will be hurt economically whether you apply more than the recommended rate or less.  Too little pesticide results in poor pest control and reduced yields, while too much injures the crop, wastes your chemical dollars, and increases the risk of polluting the environment. Hopefully some of the points I raised in this article will help you achieve maximum efficacy from pesticides you apply. 

We Want Your Pigweed

We are trying to get an assessment of herbicide resistance in Ohio pigweed populations, including smooth and redroot pigweed, waterhemp, and Palmer amaranth.  One mechanism for this is to sample small pigweed plants from fields in May and June, bring them back to our greenhouse, and treat them with the herbicides of interest.  We obviously need help finding the pigweed populations.  As you see pigweed emerge over the next month, it would be extremely helpful to us if you would give us a call or email, and we will make arrangements to collect plants.  We need to collect plants that are ideally no more than an inch or two tall, and they can be from field margins where herbicides were not applied as well as within the field.  Fields with a history of pigweed control problems are obviously especially good candidates for this research.  Contact Mark Loux –, 614-292-9081.

Invitation to Midwest Nutrient Applicators Association Meeting

All are invited to attend the Midwest Nutrient Applicators Association Meeting June 11 in Findlay, OH. OSU, ODNR and ODA specialists will discuss current nutrient management topics. 4 hours of Certified Crop Adviser (CCA) Nutrient Management CEU's and 5 hours of Certified Livestock Manager (CLM) credits are available. Indiana Category 14 has been applied for. For details and registration, visit:


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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.