Proper application stewardship of dicamba in dicamba-resistant soybean increases the likelihood of good weed control while concomitantly decreasing the potential for off-target herbicide movement. The labels of two commercially available dicamba formulations approved for application in dicamba-resistant soybean (Engenia from BASF and XtendiMax from Monsanto) include many application guidelines and restrictions that all applicators must follow. The Illinois Fertilizer and Chemical Association (IFCA) recently published a helpful checklist of “do’s and don’ts” for applying dicamba in dicamba-resistant soybean. We strongly encourage all who are considering growing a dicamba-resistant soybean variety to carefully review the entire respective product label well before the beginning of the 2017 growing season to ensure they can meet all application guidelines and restrictions. The IFCA checklist is an excellent resource for review and can easily be printed and posted in your office or mixing area and referenced throughout the growing season.
Newer and longer-term partnerships between personnel in Illinois and personnel in Missouri and Iowa have resulted in several bi-state crops conferences to be held during January 2017 in Western Illinois or Eastern Iowa.
Friday, January 6, 2017: Bi-State Crop Advantage Conference, Burlington, IA, 8:30 AM – 4:00 PM
Location: Comfort Suites, 1708 Stonegate Center Drive, Burlington, IA.
Hosts: Iowa State University and University of Illinois Extension
More Information: Click here to access the flier.
Online Registration: Click here to register
Friday, January 27, 2017: Bi-State Crop Advantage Conference, Davenport, IA, 8:30 AM – 4:00 PM
Location: Rhythm City Casino Resort, 7077 Elmore Ave., Davenport, IA
Hosts: Iowa State University and University of Illinois Extension
More Information: Click here to access the flier.
Online Registration: Click here to register.
Friday, January 27, 2017: Western Illinois-Northeastern Missouri No-till Crop Management Conference, Quincy, IL, 8:45 AM – 2:00 PM
Location: John Wood Community College, 1301 S. 48th St., Quincy, IL
Hosts: University of Illinois and University of Missouri Extension, Illinois and Missouri NRCS
More Information: Click here to access the flier.
Online Registration: Click here to register.
The long-awaited label allowing dicamba use in dicamba-resistant soybean was granted November 9, 2016, by the United States Environmental Protection Agency (EPA), although only one commercial product received that label. Many Illinois farmers anticipate this technology will provide a much-needed solution to challenges caused by weed populations resistant to herbicides from multiple site-of-action groups and other difficult-to-control species. Without question, there are instances and scenarios in which dicamba will improve control of certain weed species, but dicamba will not bring back the “good ol’ days” of POST-only weed control programs in soybean. Current expectations of what this technology can accomplish tend to be a bit more optimistic than what the technology actually will be able to deliver.
Where it fits:
Horseweed control. Many farmers experienced significant challenges attempting to control horseweed (i.e., marestail) before planting no-till soybean in 2016. The “traditional” burndown tankmix of glyphosate and 2,4-D was not as effective on horseweed as many have come to expect. Anecdotally, we suspect resistance to glyphosate is widespread in Illinois horseweed populations, and that this likely contributed to many control failures with burndown herbicides. Horseweed control with spring-applied 2,4-D can be quite variable, and poor control is common when a glyphosate plus 2,4-D tankmix is applied to a glyphosate-resistant horseweed population. Dicamba can provide some remedies because the recently approved dicamba label allows up to 1 lb dicamba acid equivalent to be applied prior to planting dicamba-resistant soybean. This can provide better and more consistent control of glyphosate-resistant horseweed compared with 0.5 lb acid equivalent 2,4-D. Note: Although the new label allows soybean to be planted immediately after dicamba application, it’s still advisable to wait a few days following application before injuring the weeds with the planting operation.
Annual morningglory species are a well-known bane of glyphosate. Control of species such as tall and ivyleaf morningglory with glyphosate is rarely adequate, but dicamba is much more effective on these species. Add to this list common and giant ragweed, two other species that have evolved resistance to glyphosate and ALS-inhibiting herbicides. Dicamba certainly can provide better control of herbicide-resistant ragweeds than can glyphosate or ALS inhibitors.
Where it maybe fits:
Waterhemp. Before the widespread evolution of glyphosate-resistance in waterhemp, glyphosate was considered by many weed scientists to be an excellent herbicide against waterhemp. That same adjective is not ascribed to dicamba. Most university weed control guides list dicamba as good or very good on waterhemp, but not excellent. Dicamba can improve control of pigweed species, but it will never be as effective as glyphosate once was. Illinois farmers have made great strides toward utilizing more diverse herbicide programs for waterhemp control than they were using a decade ago. We suggest that dicamba should be used in a way that does not reduce this diversity. It is imperative to maintain a diverse weed management approach to prolong the effective utility of dicamba. Illinois waterhemp populations have evolved resistance to herbicides from six site-of-action groups, and resistance to dicamba is not a question of “if”, but “when.”
Here are some realities:
What are some limitations of utilizing dicamba for weed control in soybean? The current label contains several mandates related to the actual spray application procedure that are somewhat unique. For instance, there are limitations on boom height, sprayer speed, and nozzle type that applicators must follow. An infield, downwind buffer of 110 or 220 feet (depending on application rate) must be maintained. One of the most significant limitations is the inability to tankmix with other herbicides. There is an avenue by which other herbicides can be approved for application with dicamba, but if the current label remains unchanged during the 2017 growing season, applicators will be required to apply dicamba alone. In other words, farmers will make a separate application of dicamba and another application of other needed herbicides.
Many claims have been made about yield potential of dicamba-resistant soybean varieties and the lower volatility potential of the recently labeled dicamba formulation. We believe that our clientele should be aware that the University of Illinois weed science program has not had the opportunity to evaluate yield or volatility potential. We do not have data that dispute these claims, but neither do we have data to support them. University variety testing programs are now releasing results from yield trials that include dicamba-resistant varieties. Dr. Shawn Conley, soybean and wheat extension specialist at the University of Wisconsin, recently published an article summarizing his research with dicamba-resistant soybean varieties in 2016.
Of particular concern is the apparent confusion about particle drift and volatilization. While the newly labeled formulation is reportedly less likely to volatilize after application, there is absolutely nothing unique about the formulation that will reduce physical drift during application. Off-target movement of dicamba is of particular concern due to the number of sensitive dicot species grown in Illinois. The new formulation of dicamba is no more likely to drift than any other herbicide formulation, but the symptoms that drift did occur can be induced at extremely low concentrations of dicamba. Several years ago, we were able to induce soybean leaves to “cup” with as little as 1/10,000 pint of dicamba. Many media reports suggest that use of older, more volatile dicamba formulations was largely responsible for the widespread off-target injury that occurred in areas of the mid-south during 2016, but volatility is generally a minor component of off-target movement when compared with actual physical drift during application.
One last item to consider is that this new registration for dicamba use in dicamba-resistant soybean will expire on November 9, 2018. EPA documents indicate the registration will automatically expire “…unless the EPA determines before that date that off-site incidents are not occurring at unacceptable frequencies or levels.” In other words, the continued availability to utilize dicamba in dicamba-resistant soybean is very much dependent on those who use it.
Much more undoubtedly will be shared about dicamba use in dicamba-resistant soybean from a variety of sources. We do believe dicamba can provide a solution to unique weed management challenges, but we also believe not all weed management challenges can be met with dicamba. Other herbicide-resistant crop technologies, such as Liberty Link and Enlist (once all import approvals are received), also can provide solutions and remain viable options for soybean producers. Proper stewardship of all technologies only helps prolong their effective utilization.
Herbicides applied in the fall often can provide improved control of many winter annual weed species compared with similar applications made in the spring. Marestail is one example of a weed species that is often better controlled with herbicides applied in the fall compared with the spring. An increasing frequency of marestail populations in Illinois are resistant to glyphosate, and recently we confirmed resistance to ALS-inhibiting herbicides also is present in Illinois populations. Targeting emerged marestail with higher application rates of products such as 2,4-D in the fall almost always results in better control at planting compared with targeting overwintered and often larger plants with lower rates of 2,4-D in the spring.
One question typically posed is whether or not a fall application needs to include one or more herbicides that provide residual control of winter annual weed species. Typically, the earlier the fall application is made (say, early October) the more benefit a soil-residual herbicide can provide since emergence of winter annual weeds is often not complete. However, delaying the herbicide application until later in the fall (say, mid-November) often diminishes the necessity of a soil-residual herbicide since most of the winter annual weeds have emerged and can be controlled with non-residual herbicides. Applying a soil-residual herbicide late in the fall in hopes of having a clean field prior to planting is akin to gambling on the weather. Cold winter conditions can reduce herbicide degradation in the soil and increase herbicide persistence. This might not always be favorable since, depending on the residual herbicide, increased persistence also can cause injury to the following crop. A more moderate winter and early spring warming will increase herbicide degradation, which could result in the need for a burndown herbicide to control existing vegetation before planting.
We recommend fall-applied herbicides target fall-emerging winter annual species, biennials and perennials. We do not recommend fall application of residual herbicides for control of any spring-emerging annual weed species. We are aware some products have 2(ee) recommendations that suggest the product will control certain summer annual weed species following application in the fall. Particularly concerning to us is that “pigweed species” are listed on at least one product label. The extension weed science program at the University of Illinois does not recommend fall-application of residual herbicides to control Amaranthus species the next spring for the following reasons:
- Inconsistent performance: as previously described, the performance consistency of soil-residual herbicides applied in the fall is greatly dependent on weather and soil conditions after application. Our data suggest the greatest and most consistent control of Amaranthus species either at planting or several weeks after planting was achieved when residual herbicides were applied in the spring, not in the fall.
- Increased selection for herbicide-resistant biotypes: soil-applied herbicides are not immune from selection for herbicide-resistant biotypes (please see the April 16, 2013 article titled: “Herbicide Resistance: Are Soil-Applied Herbicides Immune?”). Following a fall application, the concentration of herbicide remaining in the spring when Amaranthus species begin to germinate will be much lower compared with the same product rate applied closer to planting.
Populations of several summer annual broadleaf weed species in Illinois demonstrate resistance to herbicides from more than one site-of-action herbicide class. Their effective management requires an integrated approach that often includes soil-residual herbicides. Applying these herbicides when they will be most effective against these challenging summer annual species is a critical component of an integrated management program.
Palmer amaranth (Amaranthus palmeri) has garnered much attention recently in both academic discussions and popular press releases, and with good reason. Among the weedy species of Amaranthus, Palmer amaranth has the fastest growth rate and is the most competitive with the crops common to Midwest agronomic cropping systems. Soybean yield losses approaching 80% and corn yield losses exceeding 90% have been reported in the peer-reviewed scientific literature.
While most concern focuses on Palmer amaranth in agronomic cropping systems, keep in mind that Palmer amaranth also can become established in noncrop areas. Palmer amaranth populations in noncrop environments obviously do not compete with agronomic crops, but these established plants can produce seeds that ultimately find their way into crop production fields.
We recently verified the identification of a Palmer amaranth population growing in an area enrolled in the Pollinator Habitat Initiative of the Conservation Reserve Program. The origin of this population remains unknown, but some speculate the forb seed mixture purchased to sow the pollinator area might have been contaminated with Palmer amaranth seed. Regardless of how and where a Palmer amaranth population becomes established, it remains critically important to take all appropriate steps to prevent established Palmer amaranth plants from producing seed. We strongly encourage all who have established pollinator habitats with a purchased forb seed mixture to scout these areas as soon as possible. If Palmer amaranth is identified, please take steps to remove these plants before viable seeds are produced on the female plants. Plants should be severed at or below the soil surface and carried out of the field. Severed plants can root at the stem if left on the soil surface, and plants can regenerate from stems severed above the soil surface.
We invite everyone to the University of Illinois Extension Ewing Agronomy Field Day Thursday, July 28, 2016 starting at 9 a.m. at the Ewing Demonstration Center. Every growing season presents challenges to production, and this year is no exception! We are happy to host this summer field day to share with local growers current, ongoing agronomy field research, including cover crop trials on corn and soybeans, nitrogen management in corn, soybean variety trial and row spacing study, ornamental corn and pumpkin variety trials, pumpkin pest management trials, and our continuous no-till area, now in its 48th year of continuous no-till production.
The topics to be discussed at Field Day include:
Managing Nitrogen for Corn
- Emerson Nafziger, Extension Crop Specialist, University of Illinois
The Effects of Cover Crops on Water Quality & Nutrient Cycling in Southern Illinois
- Karl Williard, Professor, Forestry, Southern Illinois University
Weather Trends & Soils
- Duane Friend, Extension Educator, University of Illinois
Definition of Insanity & Weed Management
- Ron Krausz, Manager, Southern Illinois University Belleville Research Center
Exploring New Clover Cover Crops for Corn
- Nathan Johanning, Extension Educator, University of Illinois
The field day is free and open to anyone interested and lunch will be provided. Certified Crop Advisor CEUs will also be offered. The Ewing Demonstration Center is about 20 minutes south of Mt. Vernon located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road. Watch for signs.
To help us provide adequate lunch and materials please RSVP to the University of Illinois Extension Office in Franklin County at 618-439-3178 by Monday, July 25. We hope to see you all there!
Almost all postemergence soybean herbicides have a preharvest interval or a soybean developmental stage beyond which applications cannot be made specified on their respective label. 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 crop in excess of established limits. Table 1 contains information regarding preharvest intervals for a number of postemergence soybean herbicides.
|Herbicide||Preharvest Interval/Maximum Soybean Growth Stage|
|Assure II/Targa||80 days|
|Anthem Maxx/Cadet||60 days|
|Basagran||No interval on label|
|Cobra/Phoenix||45 days/do not apply after R6|
|Dual Magnum1/Dual II Magnum1||90 days/through third trifoliolate|
|Enlist Duo||Do not apply after R2|
|FirstRate||Apply prior to R2|
|Flexstar GT||45 days|
|Fusilade DX||60 days|
|Liberty/Interline/Cheetah/Cheetah Max||70 days|
|Roundup PowerMax2||Broadcast: through R2
Harvest aid: 14 days
|Harmony SG||60 days|
|Poast/Poast Plus||75 days|
|Select or SelectMax||60 days|
|Synchrony XP||60 days|
|Ultra Blazer||50 days|
|Warrant1/Warrant Ultra||Before R2|
1These products will not control emerged weeds but can be applied postemergence for soil-residual weed control.
2Data, 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 non-glyphosate-resistant soybean varieties.
Waterhemp continues to be one of the most widespread and troublesome broadleaf weed species with which Illinois farmers must contend. Factors related to the species’ biology, such as prolonged germination and emergence, obligate outcrossing, and high seed production, contribute to management challenges. The evolution of herbicide resistance in Illinois waterhemp populations adds another very challenging obstacle for effective management. Recently, many have sent questions and concerns regarding the inability to control waterhemp with various postemergence soybean herbicides. A description of herbicide resistance in Illinois waterhemp populations, along with postemergence herbicide options to control waterhemp, follows.
Prior to the evolution of herbicide resistance in waterhemp, ALS-, PPO-, EPSPS- and GS-inhibiting herbicides controlled waterhemp postemergence in soybean. Resistance to ALS-inhibiting herbicides (such as Raptor and Classic), first confirmed in Illinois during the mid-1990s, has become so widespread that this class of herbicides is largely considered functionally ineffective against waterhemp. Resistance to PPO-inhibiting herbicides (such as Flexstar, Cobra, and Ultra Blazer) was first identified in Adams County in 2001, and the first instance of resistance to the EPSPS-inhibiting herbicide glyphosate (Roundup, etc.) was confirmed in Fayette County in 2006. To date, no instance of waterhemp resistance to the GS-inhibiting herbicide glufosinate (Liberty, Interline, Cheetah) has been reported.
Figure 1 shows the range expansion of glyphosate-resistant waterhemp from 2012–2015. These data are based on samples submitted to the University of Illinois for resistance verification with molecular marker assays. Figure 2, using the same data source as Figure 1, shows the current range of PPO-resistant waterhemp in Illinois. It should not be assumed that resistance does not occur in non-shaded counties; a better interpretation is simply that we have yet to test a positive sample from those counties. In other words, it is altogether likely resistance to glyphosate and PPO inhibitors occurs in all Illinois counties.
Waterhemp resistant to PPO-inhibiting herbicide can be controlled with glyphosate, and glyphosate-resistant waterhemp can be controlled by PPO-inhibiting herbicides. However, there are no effective herbicide options to control waterhemp resistant to both glyphosate and PPO inhibitors in conventional or glyphosate-resistant soybean varieties. As mentioned previously, ALS-inhibiting herbicides are ineffective, and 2,4-DB will not improve control. Inter-row cultivation or hand removal represent two options to control multiple-resistant waterhemp.
It remains very unlikely that a herbicide with a novel site of action will be commercialized in the foreseeable future. At the same time, the frequency of multiple resistant waterhemp will only increase. Many eagerly anticipate the ability to apply 2,4-D or dicamba to new herbicide-resistant soybean varieties, but the long-term utility of these herbicides to control multiple-resistant waterhemp will be compromised without thoughtful and implemented stewardship practices.
We would like to take this opportunity to once again extend the invitation to attend the 2016 University of Illinois Weed Science Field Research Tour, to be held Wednesday, June 29th at the University of Illinois Crop Sciences Research and Education Center, located immediately south of the main campus. Coffee and refreshments will be available under the shade trees near the Seed House beginning at 8:00 a.m. 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. The tour will conclude around noon with a catered lunch at the 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 look forward to visiting with you at the Urbana weed science field day on June 29th. Please contact us at 217-333-9646 if you have any questions.
The labels of most postemergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even a state minimum growth stage before which applications should not be made. These growth stages are usually indicated as a particular plant height or leaf stage; sometimes both of these are listed. For product labels that indicate a specific corn height and growth state, be sure to follow the more restrictive of the two. Application restrictions exist for several reasons, but of particular importance is the increased likelihood of crop injury if applications are made outside a specified growth stage or range.
Table 1. Postemergence herbicide application timings based on corn growth stage(s).
|Herbicide||Maximum corn heights and growth stagesa|
|2,4-D||Broadcast before corn exceeds 8” tall; use drop nozzles when corn is taller than 8”.|
|Accent Q||Broadcast up to 20” tall or through the V6 stage. Apply with drop nozzles when corn is 20–36” tall or before the V10 stage.|
|Anthem Maxx||Apply from corn emergence through the V4 (visible fourth leaf collar) stage.|
|Armezon Pro||Apply from corn emergence to the 8-leaf stage or 30” tall.|
|Atrazine||Apply before corn exceeds 12” tall.|
|Basagran||No height specified on label.|
|Basis Blend||Apply to corn from spike through 2 collar stage. Do not apply to corn having 3 fully emerged collars or over 6” tall.|
|Beacon||Broadcast when corn is 4–20” tall. After corn is 20” tall or exhibits more than 6 collars use directed applications up to tassel emergence.|
|Cadet||Apply until corn is 48″ tall or prior to tasseling.|
|Callisto/Callisto GT||May be applied to corn up to 30” tall or up to the 8-leaf stage.|
|Callisto Xtra||Apply before corn exceeds 12” tall|
|Capreno||Broadcast applications must be made to corn from the 1-leaf collar stage through the 5-leaf collar (V5) stage.|
|Clarity or Banvel||Apply between corn emergence and the 5-leaf stage or 8” tall; apply 0.5 pt/A rate when corn is 8 to 36” or if 6th leaf is emerging, or if 15 days prior to tassel emergence. Do not apply when soybean are growing nearby if: 1) corn is more than 24” tall, 2) soybean are more than 10” tall, 3) soybean have begun to bloom.|
|DiFlexx/DiFlexx Duo||Apply broadcast when corn is at the spike through 6-leaf collar (V6) growth stage, or 36” tall, whichever occurs first.|
|Glyphosate (glyphosate-resistant corn)||Apply broadcast through the V8 stage or until corn reaches 30” tall. Use drop nozzles for applications to corn 30–48” tall.|
|Halex GT (glyphosate-resistant corn)||Apply to corn up to 30″ tall or the 8-leaf stage.|
|Harmony SG||Apply to 2–6 leaf corn with 1–5 collars or up to 16” tall.|
|Hornet WDG||Apply broadcast until corn reaches 20” tall or V6 stage. Apply with drop nozzles to corn up to 36” tall.|
|Impact/Armezon||Can be applied up to 45 days before harvest. Do not apply Armezon past the V8 growth stage.|
|Laudis||Apply up to the V8 growth stage.|
|Liberty (glufosinate-resistant corn)||Broadcast until corn is 24” in height or in the V7 growth stage (7 developed leaf collars). Use drop nozzles for corn 24–36” tall.|
|Marksman||Apply between corn emergence and the 5-leaf or 8” height stage.|
|Moxy||Apply prior to tassel emergence.|
|NorthStar||Broadcast applications are made when corn is between 4 –20” tall (V2–V6). Use directed applications when corn is 20–36” tall.|
|Permit||Can be applied from spike through layby.|
|Realm Q||May be broadcast applied to corn up to 20” tall or exhibiting 6 leaf collars.|
|Require Q||Apply to corn 4–20” tall. Do not apply to corn exhibiting 7 or more leaf collars.|
|Resolve Q||Do not apply to corn taller than 20” or exhibiting 7 or more leaf collars.|
|Resource||Apply to corn from the 2-leaf through 10-leaf stage.|
|Shotgun||Broadcast applications to corn up to 4 leaves or 8” tall; directed applications for 5-leaf or 8–11 ¾” tall corn.|
|Solstice||May be applied broadcast up to the V8 growth stage or 30” tall.|
|Spirit||Broadcast applications to corn 4–20” tall. Use drop nozzles when field corn is 20–24” tall or exhibits more than 6 collars (V6).|
|Starane Ultra||Apply broadcast to corn with up to 5 fully exposed leaf collars (V5).|
|Status||Do not apply to corn taller than 36” or past the V10 stage.|
|Steadfast Q||Apply to corn up to 20” tall or exhibiting 6 leaf collars.|
|Stinger||Apply to corn from emergence through 24” tall.|
|Yukon||Apply broadcast or with drop nozzles to corn from spike to 36” tall. Drop nozzles are recommended when corn exceeds 20”.|
|Zemax||May be applied after corn emergence until plants reach 30” tall or up to the V8 stage.|
a When maximum application timings are indicated by two corn growth stages, follow the most restrictive of the two.