2019 Observations from the Field: Dicamba

Approximately two weeks ago, only a few (11 reported as of July 16) dicamba-related complaints had been filed with the Illinois Department of Agriculture (IDOA), and some held aspirations that the magnitude of off-target issues would be less this year than during the two previous seasons.  Today, it appears those hopeful aspirations are being replaced by the harsh reality that the magnitude of off-target issues in 2019 might be either similar to or possibly exceed those of previous seasons.  By the end of business on July 31, IDOA reported 191 dicamba-related complaints, 132 of which were received between Monday and Thursday of this week.

IDOA also indicated there has been an increase in the number of phone calls during which the caller wanted the Department to know of a damage incident but was unwilling to file an official complaint.  Many callers indicated they wanted to have the incident recorded but didn’t want to “get their neighbor” in trouble with a formal complaint.  Calling IDOA to report an incident of dicamba damage is not the same as filing an official complaint.  IDOA cannot take official action with of a verbal report of damage; a completed pesticide misuse complaint form must be filed to begin the complaint process.  If you choose to file a complaint with IDOA, time is of the essence. The pesticide drift complaint process is started by filling out a complaint form which can be found at: https://www2.illinois.gov/sites/agr/Pesticides/Documents/pesticidemisusecomplaintform.pdf or by calling IDOA’s Bureau of Environmental Programs at 1-800-641-3934 (voice and TDD) or 217-785-2427.  Additional information on pesticide uses and misuses can be found on the agency’s website at: https://www2.illinois.gov/sites/agr/Pesticides/Pages/Pesticides-Uses-Misuses.aspx

Complaint forms must be received by IDOA within 30 days of the incident or within 30 days of when the damage was first noticed. Complaints filed after that will be kept on record, but no administrative action can be taken.

The complaint process:

Once a complaint is filed with the department, a field inspector is assigned the case. In most cases, the inspector will interview the complainant and inspect the site. Various types of samples, such as plants, water, or soil, may be collected for analysis at an approved laboratory.

The inspector may also interview applicators in the area, examine pesticide records and collect weather data in an attempt to determine the nature and cause of the damage. The field investigator will then submit a report to the Department for review.

Both parties will receive written notification if the Department finds a violation and takes an enforcement action. Penalties range from advisory or warning letters to monetary penalties of $750 to $10,000, depending on the type and severity of the violation. Penalties are determined through a point system defined in the Illinois Pesticide Act.

Even if a violation of the Illinois Pesticide Act cannot be substantiated, both the complainant and the alleged violator will be notified in writing of the complaint’s status. Remember, the Department’s role in pesticide misuse incidents is limited to determining whether a violation has occurred. IDOA cannot help complainants recover damages.

Recent observations:

The widespread occurrence of dicamba symptoms on soybean for the third straight year is by itself troubling, but perhaps even more troubling are the feeble theories being promulgated to explain the cause of the soybean leaf cupping.  I addressed these in past articles, but it appears science continues to be sacrificed for sales.  So, we’ll take some time to work through these once again.

Earlier this week several commercial retail applicators shared with me that company representatives were promulgating multiple causes of cupped soybean leaves.  In particular, dry weather stress, Liberty + AMS, and tank contamination are purported to cause soybean leaf cupping.  Furthermore, some postulate multiple causes are involved when entire fields are uniformly cupped.

I would argue dicamba is the only cause of the widespread leaf cupping symptom, but with advancing age and graying hair I hope to be open-minded enough to recognize I might have overlooked other possible causes.  Therefore, I want to address these “multiple causes” with the hope industry representatives can help provide answers or direct me to the published literature where I can find answers to the questions I will pose.

Dry weather stress:

An interesting hypothesis that, if true, likely has been previously researched.  However, I have not been able to locate any peer-reviewed literature that specify or describe the exact (or any, for that matter) environmental conditions that induce the cupping now so prevalent.  If these conditions exist, one would speculate they could be replicated under controlled conditions to confirm their impact on symptom development.  Granted, I have not attempted to complete a thorough review of the agronomy literature, so I hope someone in industry can help answer the following questions:

Please explain how “environmental stress” can induce this widespread leaf cupping?  What occurs to the physiology of the soybean plant that results in leaf cupping under this alleged environmental stress?  Furthermore, please explain how this environmental stress can start and stop at a property line?  And while you’re at it, please explain how the dicamba-resistance trait somehow protects dicamba-resistant varieties from this strange and apparently selective environmental stress?

Ammonium sulfate (AMS):

I had hoped this one was laid to rest last year, but it appears that it is being tossed around again in 2019.  Last year, I posted two comments about AMS and leaf cupping on my Twitter account but since some folks don’t use Twitter I thought I would share my 2018 comments herein:

“I’ve evaluated soybean plots for 25 years at the Univ. of Illinois and never recall observing AMS causing leaf cupping symptoms similar to those caused by dicamba. But now that’s the reason for cupped LL soybean? Wonder why AMS isn’t causing similar symptoms on non-LL soybean?”

The purpose of the second Twitter post was to share the results of a replicated field experiment in which we evaluated soybean leaf cupping following application of different rates of AMS.  I shared the data as photographs since, well you know, a photograph is worth a thousand words:

“Speculation abounds that AMS causes leaf cupping in LL soybean. Here are results of a recent UI trial: 43 ounces of Liberty combined with 3 rates of AMS or a “contamination” rate of dicamba. No leaf cupping from any AMS treatment. No leaf cupping in any other UI LL experiments.”

Again, in my fervent attempt to be open-minded, I hope industry can provide answers to these questions:

Millions of Illinois soybean acres have been sprayed with glyphosate + AMS since 1996 without the widespread leaf cupping common since 2017.  Why, then, did AMS all of the sudden cause widespread leaf cupping beginning in 2017 and continuing in 2018 and 2019?  Can anyone please provide peer-reviewed data generated over multiple environments that speculate, suggest, or even clearly demonstrate leaf cupping is caused by AMS?

Tank contamination:

Yes, tank contamination occurs and I have seen instances of cupping where contaminated application equipment clearly was responsible.  This avenue of exposure was somewhat common in 2017, but less common in 2018 and appears to be even less common in 2019 as applicators gained an enhanced appreciation for sprayer hygiene.  Ag retailers to their credit have invested substantial money and time into segregating mixing systems, tender vehicles, and in many cases installed direct injection systems on their sprayers to keep dicamba isolated from other pesticide mixtures.  They have also extensively contacted growers and mapped the traits of soybean in a concerted effort to manage wind, buffers and “do not spray” label requirements to protect sensitive soybean and other sensitive crops and areas.  If that’s not enough, before applying dicamba in 2019, approximately 3000 licensed Illinois operators completed the process to become licensed applicators thanks to the new label mandate instituted by US EPA for the revised label.  It’s logical to conclude that each of these 3000 applicators operates a spray rig, so is industry suggesting that hundreds of agrichemical facilities and thousands of tender trucks and application equipment in Illinois are contaminated?  Do anyone have physical evidence of this, or is it just more speculation?  If contamination is the cause of even half the instances of soybean leaf cupping, commercial applicators might question the prudence and legal ramifications of applying a product that seemingly cannot be removed from their chemical formulation, transportation and application equipment.

The frequency of entire soybean fields demonstrating uniform cupping symptoms is not suggestive of “multiple causes,” but rather of exposure through volatility of dicamba previously applied.  Multiple university weed science programs have demonstrated volatility of these dicamba formulations can be detected for up to four days after application, yet these results seem to be largely ignored by industry as another possible source of exposure.  Registrants never have referred to these products as non-volatile, but rather with lower volatility than other formulations.  As many have stated previously, low volatility is not synonymous no volatility.  However, industry continues to promulgate theories and speculations that have few (if any) data in their support.  I’m curious if industry will be more transparent with their customers about issues of volatility and recognize this as a potential source of exposure.  Or, perhaps not.

 


Reminder – University of Illinois Weed Science Field Research Tour

The weed science program at the University of Illinois invites all weed management practitioners to our annual weed science field tour on Wednesday, July 10.  Please note the tour will begin at our off-campus field location (“The Lost Forty”) which is located on Cottonwood Road (County road 1700 east) approximately one-quarter mile north of County road 1850 North (see map).

Registration will begin at 8:00 a.m. and refreshments (coffee, juice, and doughnuts) will be available.  Preregistration is not required, but please let us know in advance if you will be bringing a large group of participants so we can plan accordingly for meals.

Participants are welcome to join in a guided (but informal) tour format or review the plots at your own pace.  About mid-morning we will car pool to our research plots at the Crop Sciences Research and Education Center (CSREC).  The tour will provide ample opportunity to look at research plots and interact with weed science faculty, staff, and graduate students. Participants can compare their favorite corn and soybean herbicide programs to other commercial programs and get an early look at a few new products that soon will be on the market. The tour will conclude around noon with a catered lunch at the CSREC Seed House.

Cost for the Urbana weed science field tour is $10, which will help defray the cost of the field tour book, refreshments and lunch. We will apply for 2 hours of CCA credit under the IPM category.  If you have any questions about the weed science field research tour, please feel free to call Charlie Mitsdarfer (217-621-7717) or Aaron Hager (217-621-8963).

 


Late-Season Herbicide Applications

Nearly all herbicide labels (soil-applied or postemergence) have rotational crop intervals that specify the amount of time that must elapse between herbicide application and planting a rotational crop.  This becomes particularly important with late-season herbicide applications.  These intervals are established to reduce the likelihood that herbicide residues will persist in sufficient quantities to adversely affect the rotational crop.  Some herbicide rotational restrictions are based solely on time, while other factors, such as soil pH and the amount of precipitation received after herbicide application, can influence the length of the crop rotational intervals.

Soil moisture is often the most critical factor governing the efficacy and persistence of soil-residual herbicides.  Many herbicides are degraded in soil by the activity of soil microorganisms, and populations of these microorganisms can be greatly depressed when soil moisture is limited.  Additionally, dry soils can enhance herbicide adsorption to soil colloids, thus rendering the herbicide unavailable for plant uptake and degradation by soil microbial populations.  Some herbicide rotational intervals are increased if a specified amount of precipitation is not received by a certain calendar date.

Please keep in mind that the labels of almost all postemergence soybean herbicides indicate a preharvest interval or a soybean developmental stage beyond which applications cannot be made.  Labels of some products may indicate both a developmental stage (before soybean bloom, for example) and a preharvest interval.  Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest.  Failure to observe the preharvest interval may result in herbicide residue levels in the harvested portion of the crop in excess of established limits.  Also, livestock grazing or foraging treated soybean is not allowed on the labels of many postemergence soybean herbicides.  Table 1 contains information regarding preharvest intervals and grazing restrictions for a number of postemergence soybean herbicides.

 

Table 1.  Preharvest intervals and grazing restrictions for postemergence herbicides used in soybean.

Herbicide Preharvest Interval Forage or Grazing
Assure II 80 days No
Basagran None listed on label Yes, after 30 days
Cadet 60 days No
Classic 60 days Yes, after 14 days
Cobra or Phoenix 45 days No
Engenia 45 days after planting or R1 Yes, after 7 days
Enlist One/Enlist Duo 30 days No
FirstRate 70 days Yes, after 25 days
Flexstar/Flexstar GT 45 days No
Fusilade DX 60 days No information on label
Fusion Prebloom No
Liberty/Interline/Cheetah 70 days No
Roundup PowerMax1

Broadcast: through R2

Harvest aid: 14 days

Yes

Yes, after 14 days

Harmony SG 60 days Yes, after 7 days
Marvel 60 days No
Poast or Poast Plus 75 days Hay
Prefix 90 days No
Pursuit 85 days No
Raptor Prebloom No information on label
Resource 60 days No
Select or SelectMax 60 days No
Sequence 90 days No
Storm 50 days No
Synchrony XP 60 days Yes, after 14 days
Tavium 90 days No
Ultra Blazer 50 days No
Warrant Before R2 No
Warrant Ultra 45 days No
XtendiMax/FeXapan 45 days after planting or R1 Yes

1Data, taken from the Roundup PowerMax label, are for broadcast applications in glyphosate-resistant soybean varieties.  Intervals change for applications (spot treatment and preharvest) made to nonglyphosate-resistant soybean varieties.  Forage and grazing allowances can vary among glyphosate-containing products.  Consult the respective glyphosate product label for specific information on forage and grazing restrictions.

 

 


Reminder of Omnidirectional In-Field Buffers

As a reminder, dicamba-resistant soybean fields that exist in counties that might harbor endangered terrestrial dicot plant species and that will be treated with dicamba must have an in-field, 57-foot omnidirectional buffer. The new 57-foot buffer will occur on three sides of the field and be in addition to the required 110-foot downwind buffer.  Non-sensitive areas, as defined in the renewed labels, can be included in the omnidirectional buffer calculation.  This new buffer requirement includes fields in at least 27 Illinois counties (Figure 1).


Layering Soil-Residual Herbicides in Soybean

Applying soil-residual herbicides with non-residual, foliar-applied herbicides can help reduce additional weed emergence following application and, therefore, reduce the need for another application later.  The “lateness” of this year’s soybean crop undoubtedly will decrease the number of acres where layered residuals are applied, but nonetheless keep in mind that labels for most soil-residual herbicides used in foliar applications include soybean growth stages or time intervals beyond which applications cannot be made.  Additionally, these labels include time intervals for rotational crops, such as wheat.  A partial listing of soil-residual herbicides sometimes applied postemergence in soybean is presented in Table 1.  Be sure to consult the label of any product used to determine maximum crop growth stage and rotational crop intervals.

 

Table 1.  Maximum soybean growth stage and wheat rotation interval for several soil-residual herbicides that can be applied postemergence in soybean.

Product                        Maximum soybean growth stage          Wheat rotational interval

Anthem Maxx                Apply through third trifoliolate                1 month at up to 3.25 ounces

Dual Magnum                At least 90 days before harvest             4.5 months

FirstRate                       Prior to R2                                              4 months

Outlook                         Fifth trifoliolate                                       4 months

Prefix                            At least 90 days before harvest             4.5 months

Warrant                        Before soybean reach R2                       4 months

Warrant Ultra                Before soybean reach R2                       4 months

Zidua SC                       Sixth trifoliolate                                      1 month at up to 3.25 fluid ounces

 


IDOA EXTENDS APPLICATION DATE TO APPLY DICAMBA

SPRINGFIELD, IL – The Illinois Department of Agriculture (IDOA) announced today it will extend the application date the herbicide dicamba can be applied on soybeans in Illinois for the 2019 growing season until July 15. In February, the Department approved state-specific labels allowing for dicamba use on soybeans only until June 30.  Dicamba is primarily used on soybeans to control post-emergence broadleaf weeds.

“Due to the extraordinary wet weather seen in this state during the spring planting season and with still over 50% of the soybean crop to be planted, the IDOA will extend the application date to apply dicamba until July 15th,” said John Sullivan, Director, IDOA. “This decision was not taken lightly, however, farmers have been under intense pressure related to the extreme wet weather conditions and hopefully this decision will provide some relief.”

The extension will not be official until the department reviews and approves the registrants’ Special Local Needs (SLN) product registration requests. The additional restrictions on dicamba set in February will remain in effect and are as follows:

  1. Prohibiting application when the wind is blowing toward adjacent residential areas.
  2. Required consultation of the FieldWatch sensitive crop registry before application, as well as compliance with all associated record keeping label requirements.
  3. Maintaining the label-specified downwind buffer between the last treated row and the nearest downfield edge of any Illinois Nature Preserves Commission site.
  4. Recommendation to apply product when the wind is blowing away from sensitive areas, which include but are not limited to bodies of water and non-residential, uncultivated areas that may harbor sensitive plant species.

Anyone who planted before June 1st will remain subject to the original dicamba application cutoff date, which was planting date plus 45 days. Illinois producers who planted soybeans after June 1st will be required to adhere to the newly extended July 15th dicamba application cutoff date.

The intent of all these additional restrictions is to reduce the potential for off-target movement of this product, thereby reducing the potential for possible adverse impacts to dicamba-sensitive crops/areas. The decision to pursue state-specific SLN labels was made in response to the record number of misuse complaints IDOA received during the past two years.


University of Illinois Weed Science Field Research Tour

The weed science program at the University of Illinois invites all weed management practitioners to our annual weed science field tour on Wednesday, July 10.  Please note the tour will begin at our off-campus field location (“The Lost Forty”) which is located on Cottonwood Road (County road 1700 east) approximately one-quarter mile north of County road 1850 North (see map).  Registration will begin at 8:00 a.m. and refreshments (coffee, juice, and doughnuts) will be available.  Preregistration is not required, but please let us know in advance if you will be bringing a large group of participants so we can plan accordingly for meals.

Participants are welcome to join in a guided (but informal) tour format or review the plots at your own pace.  About mid-morning we will car pool to our research plots at the Crop Sciences Research and Education Center (CSREC).  The tour will provide ample opportunity to look at research plots and interact with weed science faculty, staff, and graduate students. Participants can compare their favorite corn and soybean herbicide programs to other commercial programs and get an early look at a few new products that soon will be on the market. The tour will conclude around noon with a catered lunch at the CSREC Seed House.

Cost for the Urbana weed science field tour is $10, which will help defray the cost of the field tour book, refreshments and lunch. We will apply for 2 hours of CCA credit under the IPM category.  If you have any questions about the weed science field research tour, please feel free to call Charlie Mitsdarfer (217-621-7717) or Aaron Hager (217-333-9646).


Weed Management on Prevented Planting Acres

Persistent wet field conditions have increased the likelihood that many farmers will opt to take the prevented planting option through their crop insurance policy.  Even though no crop will be planted, weed control practices still should be implemented to reduce seed production from summer annual weed species.  Any weed seed produced in 2019 will add to future weed control costs.  The old weed science adage “One year’s seedling equals seven years weeding” reinforces the need to adequately manage weeds on prevented planting acres.

Many species of winter annual weeds already have flowered and soon will produce seed.  Additionally, many summer annual weed species have emerged and are growing rapidly.  We suggest the focus of weed management on prevented planting acres should be on summer annual weed species.  Several options exist that could be used singly or in combination to keep weeds under control.

Tillage.  Tillage implements that significantly disturb the soil (tandem disk, field cultivator, etc, but not vertical tillage implements) can effectively eliminate summer annual weeds.  Generally, tillage is more effective when weeds are small and soils are not overly wet.  Large weeds that escape a tillage pass can be very difficult to control later in the growing season.  While usually effective at controlling established weeds, keep in mind that tillage can stimulate germination and emergence of additional weeds.  Multiple tillage operations likely will be needed before a killing frost to prevent summer annual weeds from producing seed.  Fuel consumption/cost and potential for soil erosion are additional factors to consider when using tillage to control weeds on prevented planting acres.

Mowing.  Repeated mowing can help suppress weed growth, but might not prevent seed production of all summer annual species since some seed could be produced from plants that regrow or from tillers present on grasses below the height of cutting.  Adjust the mower to cut as close to the soil surface as possible.  Utilizing mowing followed by tillage likely would be more effective in reducing seed production than mowing alone.  Alternatively, if vegetation is quite large, mowing that precedes tillage by several days might improve the effectiveness of the tillage operation in reducing seed production.

Herbicides.  Non-residual herbicides can control many summer annual species, but will miss any plants/species that are resistant to it.  Combining glyphosate with 2,4-D or dicamba would provide more consistent control of emerged waterhemp, marestail and giant ragweed than glyphosate alone.  Waterhemp’s extended emergence duration will require at least two to three herbicide applications before the first killing frost.  We do not recommend applying soil-residual herbicides as they are unlikely to maintain sufficient weed control in the absence of a planted crop.

Cover crops.  A well-established grass cover crop (such as rye, wheat, sudangrass, etc.) can be quite effective in limiting emergence and growth of summer annual weed species.  It is advisable to control any emerged weeds before seeding the cover crop.  Tillage or non-residual herbicides can be used prior to seeding, but you should allow several days between herbicide application and seeding for the herbicide to control existing vegetation. Drilling cover crop seed likely will result in a good stand that can be very competitive with weeds and also help scavenge soil nitrates.  A growth regulator herbicide (2,4-D, dicamba, etc.) could be applied after the cover crop has emerged to control broadleaf weeds if needed.  Without vernalization, rye or wheat plants are unlikely to produce viable seeds by the end of the growing season but might still provide suppression of fall-emerging winter annual weed species.  Be sure to plant weed-free cover crop seed, which might require cleaning bin-run wheat seed.  Many references on cover crop establishment are available, including one published by the Illinois Nutrient Research and Education Council.


Weed Management Reminders in a Wet Spring

Much of the vegetation visible from the road is comprised of winter annual species, including the now obvious yellow-flowered species cressleaf groundsel (a.k.a. butterweed) and yellow rocket.  Some summer annual weed species, including common lambsquarters, smartweeds giant ragweed and waterhemp, also have begun to emerge.  When field conditions become conducive for planting, several possible scenarios exist for the management of existing weed vegetation.  One possible scenario is that planting will occur before any type of weed management program (tillage or herbicide application) is implemented to control existing vegetation.  In other instances herbicides that were applied earlier this spring often have done well at controlling winter annual species.  The following reminders and suggestions might help overcome some of the weed management problems already visited upon farmers by this season’s challenging planting conditions.

1) The labels of most 2,4-D formulations specify intervals that must elapse between application and planting.  If you plan to make a burndown herbicide application and plant corn or soybean less than 7 days later, leave out the 2,4-D and adjust the rate(s) of the other burndown herbicide(s) or include a different herbicide.

2) Contact herbicides, such as paraquat or glufosinate, may not be as effective as translocated herbicides against larger weeds, but can begin to desiccate existing vegetation much quicker than translocated herbicides.  Adding a triazine herbicide such as atrazine or metribuzin to paraquat or glufosinate often improves overall burndown performance.  When the application of contact herbicides is followed by one or more cloudy days, expect symptoms to take a bit longer to develop.

3) Would applying a burndown herbicide prior to preplant tillage improve control of larger weeds?  This could improve overall control in many situations, but when applying a translocated herbicide such as glyphosate, it would be advisable to wait 24 to 48 hours between application and tillage in order to provide adequate time for the herbicide to translocate within the target vegetation.  Generally, the longer the interval between application and tillage, the more complete the control of existing vegetation ultimately will be.

4) Closing the seed furrow can be difficult if planting in wet soil conditions.  This in itself can lead to crop establishment problems, but if a preemergence herbicide will be applied soon after planting, an open seed furrow provides an avenue for direct contact of the herbicide with the seed.  Labels of many soil-applied herbicides warn that severe crop injury can result if the herbicide comes in direct contact with the seed.

5) Most soil-residual herbicides can be applied either prior to or immediately after planting.  Additionally, some soil-residual products can be applied after crop emergence, whereas others must be applied before crop emergence.  If you plan to use a soil-residual herbicide but are unsure when it will be applied, be sure to check the label to determine if it can be applied after crop planting and/or emergence in case the application is delayed.  Table 1 contains an incomplete list of maximum corn size for postemergence application of soil-residual corn herbicides.  Product labels will indicate whether or not a spray additive or other herbicides should or should not be included when these products are applied to emerged corn.

6) Be especially cautious about making preemergence applications to fields where the corn is within a day or two of emerging, especially with non-selective herbicides or soil-applied herbicides that should NOT be applied after crop emergence.  Even if the crop hasn’t fully emerged or isn’t yet visible from the road, small cracks or other openings in the soil surface may allow the herbicide to come into direct contact with the emerging coleoptile.  Do not use nitrogen fertilizer as the herbicide carrier if corn has begun to emerge.

Fields in which a herbicide was applied several week ago are excellent candidates for scouting prior to planting.  The heavy precipitation in many areas of the state may have moved some soil-applied herbicides deeper into the soil profile than is conducive for good weed control.  If weeds are present, you should consider controlling them prior to planting.  Why not just wait and spray after planting?  That may be a feasible option, but the planting operation will likely injure some of the weeds, and they will need time to recover before being sprayed.  Waiting to control the existing weeds after planting is also “gambling” that the weather will cooperate and allow you to make the application before the existing weeds begin to adversely impact the crop.  The less than ideal growing conditions may also increase the likelihood of corn injury from some soil-applied herbicides.

 

Table 1.  Maximum Corn Size for Postemergence Applications of Soil-Residual Herbicides

Herbicide Maximum Corn Size for Broadcast Application
Prequel, Princep, Sharpen, Verdict Before corn emergence
Balance Flexx, Corvus, Instigate 2 leaf collars
Anthem Maxx 4 leaf collars
Bicep Lite II Magnum, Cinch ATZ, Cinch ATZ Lite, Parallel Plus, Stalwart Xtra 5 inchesa
Breakfree, Breakfree ATZ, Breakfree ATZ Lite, Degree Xtra, FulTime NXT, Harness, Harness Max, Harness Xtra, Keystone NXT, Keystone LA NXT, Resicore, SureStart II/TripleFLEX II, Surpass NXT 11 inches
Acuron, Atrazine, Bicep II Magnum, Lumax EZ, Lexar EZ, Outlookb, Resolve DF 12 inches
Hornet WDG, Python WDG 20 inches (V6)c
Resolve Q 20 inches (through V6)
Armezon Pro, Callisto, Prowl H2O, Zemax 30 inches
Dual II Magnum, Cinch, Me-Too-Lachlor II, Stalwart C, Parallel 40 inches
TriCor Prior to tassel emergence
Zidua SC V4

aAll of these products are labeled for directed applications to corn up to 12 inches tall.

bOutlook is labeled for layby applications to corn up to 36 inches tall.

cHornet is labeled for directed application to corn up to 36 inches tall.

 


Considerations for dicamba application restrictions

On March 1, 2019 the Illinois Department of Agriculture (IDOA) announced it will require Special Local Needs labels (referred to as 24(c) labels) during the 2019 growing season for the four commercial dicamba-containing products labeled for use in dicamba-resistant soybean varieties.  The Special Local Needs labels include five elements, one of which is a June 30 application deadline.  IDOA recognizes the importance of this technology to Illinois soybean growers and is taking this proactive step to reduce the instances of damage to dicot plant species (including sensitive soybean, many specialty crops and native plants such as trees) in order to preserve the technology for future seasons.

In Illinois, there actually are four application timing restrictions for these dicamba-containing products:

  • R1 soybean growth stage (from original registration in Fall 2016)
  • 45 days after soybean planting (from renewed labels in October 2018)
  • V4 soybean growth stage for those using Tavium, a recently labeled dicamba premix
  • June 30, 2019 mandated by the Illinois 24(c) label

Planting delays have some worried whether a dicamba application can be made before soybean or the calendar reaches one of these application restrictions.  What are some steps that still can be taken to increase the likelihood of successful weed control in dicamba-resistant soybean fields?

In fields where broadleaf weeds can be controlled by foliar-applied herbicides other than dicamba, the dicamba application restrictions will have minimal impact.  Similarly, those who have selected a dicamba-resistant variety more for yield potential than as a weed control necessity have alternative postemergence herbicide options.  Soybean growers might also consider checking with your soybean seed dealer about availability of alternative trait platforms in case planting delays force a change from corn to soybean.  Perhaps a similar suggestion can be made for those intending to plant soybean following wheat harvest.

Planting into weed-free conditions is an important first step.  Control any existing vegetation with tillage or herbicides before putting any seed in the ground.  This certainly can be more challenging as time passes and existing vegetation becomes larger and more mature, but eliminating existing vegetation before planting often eliminates unneeded challenges later in the season.  Fields rank with large weeds might require two tillage passes to achieve complete weed control, while herbicides rates might need to be adjusted to achieve successful control.

Select and apply the appropriate rate of a soil-residual herbicide that is effective against the most problematic broadleaf weed species in any given field.  Forgoing or applying a partial rate of an effective soil-residual herbicide increases the potential soybean yield loss if emerged weeds cannot be controlled with a foliar-applied herbicide.  Remember, the most competitive weeds with soybean are those that emerge when the soybean emerge, not those that emerge three or four weeks after soybean.  The longer soil-residual herbicides and/or inter-row cultivation keep weeds from emerging, the less the negative impact on soybean yield from weeds that emerge later.  This principle holds true regardless of the herbicide-resistance trait in the planted soybean variety, but is even more critical if an effective foliar-herbicide cannot be applied.

In dicamba-resistant soybean fields that have not reached an application restriction, consider making a foliar-application of dicamba combined with another soil-residual herbicide to help reduce additional weed emergence, thereby reducing the need for a second foliar application.  The dicamba application restrictions do not impact the application of other foliar-applied herbicides (such as glyphosate) used to control other weed species.