C.O.R.N. Newsletter: 13-2021

  1. CFAES Ag Weather System 2021 Near-Surface Air and Soil Temperatures/Moisture

    A cold, wet pattern put a damper on warming soils this week. In fact, all stations are reporting daily average soil temperatures cooler than one week ago (Fig. 1). Northern sites (e.g., Ashtabula and Northwest) have fallen into the 40s, with 50s being reported elsewhere. Warming will be slow again this week, with overnight lows in the 30s expected for several days. However, as air temperatures reach climatological average (highs in the mid-60s to low 70s) by the weekend, soil temperature should recover.


    The active weather pattern continued this week, with widespread heavy rainfall (even some snow across the northeast). Most of the state picked up 2-3” of precipitation, with a large area of west- and north-central Ohio receiving 3-5” of rain this week (Fig. 2-left). Figure 2 (right) shows the 1-month change in total column soil moisture. Statewide improvements are depicted, with 4-8% more soil moisture over much of the state, and some areas of northwest and northeast Ohio depicting an 8-12% change over the last four weeks. This wetter pattern brought a reduction in last week’s U.S. Drought Monitor, which currently depicts 59% of the state with abnormally dry to moderate drought conditions. This latest round of precipitation will certainly lead to continued improvements on this week’s report.


  2. Growing Degree Days vs. Calendar Days – How Long Will Emergence Take?

    When we examine crop emergence post-planting, two factors can impact speed of emergence – soil moisture content and soil temperatures. If soil temperatures are lower, it can take more calendar days for emergence to occur meaning rowing corn may take a little more time. In the Ohio Agronomy Guide, emergence should begin to occur after approximately 100 air GDDs.

    A difference in 10 degrees in temperature can dramatically affect how quickly crops will emerge. For example, at a temperature of 60 degrees F heat unit accumulation per day would be 60 F – 50 (base temperature for growth) = 10 GDDs. If it takes 100 GDDs to start to see emergence, at this rate it would take 10 calendar days to see the crop start to emerge. If temperatures are 70 degrees F, heat unit accumulation per day would be 70 F – 50 = 20 GDDs. This would shorten the emergence window to 5 calendar days instead, resulting in more rapid emergence from planting.


    Figure 1. Emerged corn on May 6, 2021 planted April 19 near London, OH.

    In recent work from Nemergut et al. (2021), researchers from OSU observed emergence starting at 110 to 120 soil accumulated GDDs (base of 50 degrees F) for corn, which equated to first emergence observed in 4 or 5 days after planting. Some of the difference in calendar date for emergence (though GDD accumulation was similar) was because planting depth was changed, and the 1” planting accumulated GDDs faster than the 2” and 3” planting depths. These studies though were planted in May or early June (2019 wet spring delayed planting), and daily accumulated GDDs was higher than we might expect if planted in late April. Soil accumulated GDDs have been discussed above, and these could vary slightly compared to air accumulated GDDs (calculated using air temperatures). In the work referenced above, accumulated air GDDs in the first four days post-planting were 106-118 GDDs, slightly less than the soil accumulated GDDs.

    If you want to predicate emergence on your farm, the GDD calculator found at https://mrcc.illinois.edu/U2U/gdd/ is a useful tool. It is a two-step process, first find your location on the map, then enter your planting date. The graph will display accumulated GDD’s for your location. Example output in Figure 2 shows GDD accumulation from an April 19, 2021 planting date near London, OH in Madison County. By May 6 the accumulated GDD was 138 and the emerging corn is shown in Figure 1. The GDD calculator can be used to predict growth stage throughout the growing season. This is a handy to time when scouting and management decisions should be made.

    Figure 2. GDD accumulation from April 19 to May 6, 2021 near London, OH.

    As the days turn cooler, don’t be surprised if the crops don’t pop out of the ground quickly due to lower soil temperatures. If emergence is still not observed after two weeks, it may be worth checking the field to see if other issues may be affecting emergence.



    Nemergut, K.T., Thomison, P.R., Carter, P.R., and Lindsey A.J. 2021. Planting depth affects corn emergence, growth and development, and yield. https://doi.org/10.1002/agj2.20701

    Thomison, P., Michel, A., Tilmon, K., Culman, S., and Paul, P. 2017. Chapter 4: Corn production. Bulletin 472 – Ohio Agronomy Guide, 15th Ed. Pages 32-55.

  3. Numbers of Black Cutworm and True Armyworm Moths Increasing but Remain Relatively Low

    Over the past few weeks, we have caught an increasing number of both black cutworm and true armyworm moths in our traps (see https://docs.google.com/spreadsheets/d/1yl_FeI5IJKkBVfdvKJuE6pWkd58OVhCyHeZ6SZM-ePE/edit?usp=sharing ). While our weekly total may be high (119 for true armyworm, and 111 for black cutworm) the numbers are much lower when we look at the number of moths caught per trap and per day.  Most of our traps are reporting far less than 2 moths trapped per day.  Of course, these traps only indicate that flight is occurring.  As we progress through the season, growers should continue to monitor these counts and check both corn and wheat fields for any early appearance of feeding or damage.  On wheat or a rye cover crop, look for evidence of defoliation. Armyworms can often be found on the ground underneath debris and its best to look for them on cloudy days, or during dusk/dawn.  Black cutworms are more difficult to spot, so look for the presence of corn that has been cut, or holes near the based of the plant.  See our fact sheets at our webpage (https://aginsects.osu.edu/home, under Extension Publications).

  4. Adapting Burndown Programs to Late-Planted Situations

    Author(s): Mark Loux

    It’s déjà vu all over again.  We have run this article every few years, and it seems like maybe the frequency is increasing as we deal with wet and cold weather that delays planting.  The questions about this have not changed much, and neither have the suggestions we provide here.  One of the most common questions, predictably, is how to kill glyphosate-resistant marestail and giant ragweed and generally big weeds in soybeans when it’s not possible to delay planting long enough to use 2,4-D ester (Enlist soybeans excluded since there is no wait to plant).  Overwintered marestail plants become tougher to kill in May, so this is an issue primarily in fields not treated last fall.  The good news is that we have more effective herbicide/trait options for help with burndown compared with a few years ago.  The bad news is that nothing we suggest here is going to be infallible on large marestail. 

    A burndown of glyphosate and 2,4-D struggles to control marestail in the spring anyway, especially in the absence of fall herbicide treatments.  Our standard recommendation, regardless of when spring treatments are applied, is to either replace the 2,4-D with something more effective, or to add another herbicide to supplement the 2,4-D.  Sharpen has been the frequent replacement/supplement, and we now have the option to use dicamba in the Xtend soybean system instead of 2,4-D.  While it’s possible to use higher 2,4-D rates in the Enlist soybean without waiting to plant, higher rates do not necessarily solve this issue based on our research, although a follow up POST treatment that includes glufosinate or 2,4-D usually finishes off plants that survive burndown.  There’s a list of suitable soybean burndown treatments in our marestail fact sheet, and also below – these are for fields not treated the prior fall.   

    • Glyphosate + saflufenacil + 2,4-D (+ metribuzin if possible)
    • Gramoxone (3-4 pt) + 2,4-D + metribuzin
    • Glyphosate + dicamba (Xtend soybeans)
    • Glyphosate + dicamba + saflufenacil (Xtend soybeans)
    • Glufosinate + Sharpen (+ metribuzin if possible)

    Salfufenacil herbicides include Sharpen, Zidua PRO, and Verdict.  It is possible to use a mix of glyphosate, saflufenacil, and metribuzin, omitting the 2,4-D, but control can be more variable.  We have observed some weakness also with the glyphosate/saflufenacil combination on dandelion, purple deadnettle, and larger giant ragweed.  There is usually going to be a benefit to keeping 2,4-D in the burndown where possible, as part of a more comprehensive mixture.  We advise against using Gramoxone unless it can be mixed with both 2,4-D and a metribuzin-containing herbicide.  One strategy would be to plant corn first as soon fields are fit, and delay soybean planting so that 2,4-D could still be used.  And a reminder - deciding to include saflufenacil at the last minute can result in a need to alter the residual herbicide program.   Labels allow mixtures of Sharpen/Verdict with herbicides that contain flumioxazin (Valor), sulfentrazone (Authority), or fomesafen (Reflex) only if applied 2 or more weeks before planting. 

    Some other things to consider in a delayed burndown situation:

    1.  Aside from glyphosate-resistant weeds, increasing glyphosate rates may be one of the most effective ways to maintain effective control.  We suggest a rate of at least 1.5 lb ae/A, and higher rates could be warranted.  This will not improve marestail control, but should help with most other weeds, especially under (presumably) warmer May conditions.

    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 not include flumioxazin, sulfentrazone, or fomesafen if it’s within 14 days of soybean planting.  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, 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 or add Sharpen, adding metribuzin or Canopy Blend/Cloak DF to glyphosate/2,4-D can improve burndown effectiveness somewhat.

    3.  Consider substituting Gramoxone or glufosinate for glyphosate?  Gramoxone is less effective than glufosinate on marestail, but glufosinate can struggle some in a dense, large no-till burndown situation.  Either one should be applied with metribuzin and 2,4-D ideally.  Use the higher labeled rates 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 than high rates of Gramoxone or glufosinate, with the exception of glyphosate-resistant weeds.  We know of some growers who have used a mixture of glyphosate and glufosinate for burndown, with the glufosinate in the mix to control marestail primarily.  We do not have enough experience with this mix to make a recommendation in a burndown situation.  The hail mary treatment here is a mix of glufosinate and Sharpen (plus metribuzin ideally), which can be expensive but somewhat of a scorched earth approach on broadleaf weeds at least.

    4.  In the Enlist and Extend systems where it’s possible to use 2,4-D or dicamba without waiting to plant, there can be an advantage to increasing herbicide rates as we move later and weeds become larger.  Another advantage of these systems is the option to use 2,4-D or dicamba again in POST treatments to finish off weeds that survive burndown.  We do have to assume that this strategy would likely select for resistance more rapidly, compared with use just PRE or POST.  Including glufosinate in POST treatments of 2,4-D to Enlist soybeans should mitigate the resistance rate somewhat, although it does not substitute for late season scouting and removal of weeds to prevent seed.  Reminder to consult the appropriate websites to determine the legal options to mix with 2,4-D and dicamba for use in Enlist or Xtend soybeans, especially when developing a more comprehensive mix to deal with tough burndown situations.

    5.  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 that contains metribuzin (Canopy Blend/Cloak DF, etc).  The chloirmuron may not be much of a help for marestail or ragweed 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 a reduction in systemic herbicide activity when mixed with residual herbicides that contain sulfentrazone or flumioxazin.

    6.  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.  One strategy to ensure complete control even in tilled situations is to apply glyphosate several days prior to tillage.

    7.  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 (Enlist corn) 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.

    One of the OSU PrecisionU sessions that past winter dealt with planning for problems caused by wet weather in late spring.  The related video on weed management can be found here


  5. Estimating Fiber Content of Alfalfa in Fields Across Ohio

    Alfalfa stands in Ohio had some early growth due to the warmer temperature in early April. Although it’s been cooler over the past couple of weeks, alfalfa growth has slowly been progressing. While fields start to dry out this week it’s a good idea to start thinking about estimating neutral detergent fiber (NDF) in pure alfalfa stands.

    It is common for many growers to base harvest decisions primarily on alfalfa maturity; however, variable weather conditions affect the rate of bud and flower development in alfalfa and this method can be inaccurate.

    A method developed years ago using alfalfa maturity and height still provides an accurate guide for making harvest timing decisions by estimating neutral detergent fiber (NDF) of the standing crop. This method uses height and maturity stage to estimate NDF in pure alfalfa stands. Visit https://forages.osu.edu/sites/forages/files/imce/Estimate%20Alfalfa%20NDF.pdf for instructions on how to estimate NDF in pure alfalfa fields.

    Below are a few %NDF estimations across Ohio. Alfalfa growers should start harvesting as soon as fields dry off and a weather window opens, especially in Southern Ohio. Over the next few weeks we will be monitoring and reporting alfalfa NDF. This week’s estimated alfalfa NDF at three field locations is as follows:

                Clark County, May 10: 34.8% NDF

                Stark County, May 10:  33% NDF

                Geauga County, May 10: 29% NDF

    In addition to making harvest decisions on alfalfa fields, grass fields in Southern Ohio are already heading out and pushing past 55% NDF. Cereal rye was reported as being headed out last week. Grasses that have already headed out are past the prime for high producing lactating dairy cows.  Grasses in the early heading stage are still good for feeding other classes of livestock with lower requirements than lactating dairy cows.



  6. Additional Application of Late-Season Nitrogen to Winter Wheat

    We’ve had several days of extremely wet weather, and there are some questions regarding the need for additional nitrogen fertilizer. Last week, wheat was between Feekes 8 and 10.2, depending on the area within the state. At this point in the growing season, additional nitrogen fertilizer applied to winter wheat is unlikely to increase grain yield.

    As a reminder, nitrogen should be applied to wheat between green-up and Feekes 6 growth stage. Between Feekes 5-6 growth stage, wheat plants begin to rapidly take-up nitrogen from the soil. Nitrogen fertilizer can be applied as late as Feekes 7 growth stage if wet weather prevented an earlier application, but mechanical damage can occur from applicator equipment.

  7. Fertilizer Training for New Applicators

    Do you apply fertilizer to more than 50 acres of land?  If so, the Ohio Department of Agriculture requires applicators to obtain a Fertilizer Certificate.  The Tuscarawas and Coshocton County offices of Ohio State University Extension will sponsor a training at 7pm on Wednesday, May 19.  The training will be held at the Sugarcreek Stockyards, 102 Buckeye St., Sugarcreek, Ohio.  This three-hour class is for those wishing to obtain a fertilizer certificate and will review laws, water quality, soil sampling & analysis, and nitrogen and phosphorus management.

    There is no cost to attend, but pre-registration is necessary.  Please call 330-339-2337 to register.  All current health guidelines will be followed by Ohio State University.  A facial covering must be worn at all times and the current social distancing practice of six feet per person maintained.  Please stay home if you or someone in your family is not feeling well.


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.


Aaron Wilson (Byrd Polar & Climate Research Center)
Alan Leininger (Educator, Agriculture and Natural Resources)
Allen Gahler (Educator, Agriculture and Natural Resources)
Amanda Bennett (Educator, Agriculture and Natural Resources)
Amanda Douridas (Educator, Agriculture and Natural Resources)
Andy Michel (State Specialist, Entomology)
Ann Chanon (Extension Educator, Agriculture and Natural Resources)
Barry Ward (Program Leader)
Bruce Clevenger, CCA (Educator, Agriculture and Natural Resources)
Chris Zoller (Educator, Agriculture and Natural Resources)
Clint Schroeder (Educator, Agriculture and Natural Resources)
Curtis Young, CCA (Educator, Agriculture and Natural Resources)
David Marrison (Educator, Agriculture and Natural Resources)
Dean Kreager (Educator, Agriculture and Natural Resources)
Dennis Riethman (Educator, Agriculture and Natural Resources)
Ed Lentz, CCA (Educator, Agriculture and Natural Resources)
Elizabeth Hawkins (Field Specialist, Agronomic Systems)
Erdal Ozkan (State Specialist, Sprayer Technology)
Eric Richer, CCA (Educator, Agriculture and Natural Resources)
Gigi Neal (Educator, Agriculture and Natural Resources)
Glen Arnold, CCA (Field Specialist, Manure Nutrient Management )
Greg LaBarge, CPAg/CCA (Field Specialist, Agronomic Systems)
Hallie Williams (Educator, Agriculture and Natural Resources)
Harold Watters, CPAg/CCA (Field Specialist, Agronomic Systems)
James Morris (Educator, Agriculture and Natural Resources)
Jamie Hampton (Extension Educator, ANR)
Jason Hartschuh, CCA (Educator, Agriculture and Natural Resources)
Jordan Beck (Water Quality Extension Associate)
Ken Ford (Educator, Agriculture and Natural Resources)
Laura Lindsey (State Specialist, Soybean and Small Grains)
Lee Beers, CCA (Educator, Agriculture and Natural Resources)
Les Ober, CCA (Educator, Agriculture and Natural Resources)
Mark Badertscher (Educator, Agriculture and Natural Resources)
Mark Loux (State Specialist, Weed Science)
Mark Sulc (State Specialist, Forage Production)
Matthew Schmerge (Educator, Agriculture and Natural Resources)
Mike Estadt (Educator, Agriculture and Natural Resources)
Mike Gastier, CCA (Educator, Agriculture and Natural Resources)
Nick Eckel (Educator, Agriculture and Natural Resources)
Richard Purdin (Educator, Agriculture and Natural Resources)
Stephanie Karhoff (Educator, Agriculture and Natural Resources)
Steve Culman (State Specialist, Soil Fertility)
Taylor Dill (Educator, Agriculture and Natural Resources)
Tony Nye (Educator, Agriculture and Natural Resources)
Trevor Corboy (Educator, Agriculture and Natural Resources)
Wayne Dellinger, CCA (Educator, Agriculture and Natural Resources)


The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

CFAES provides research and related educational programs to clientele on a nondiscriminatory basis. For more information, visit cfaesdiversity.osu.edu. For an accessible format of this publication, visit cfaes.osu.edu/accessibility.