Tag: herbicide

Assessing Herbicide Tank Mixes for Postemergence Weed Control in Soybean

Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu
University of Maryland Extension

Research was conducted at the Wye Research and Education Center to evaluate herbicide tank mixes for postemergence weed control in herbicide-tolerant soybean. As herbicide-resistant weeds continue to drive weed management decisions, options are needed to not only provide effective weed control, but also preserve the value of available herbicides.

Figure 1. Example probabilities of developing resistance when using Herbicide A, Herbicide B, and Herbicides A and B. Using two different herbicide groups decreases the probability that a weed will become resistant to both herbicide groups.

Tank mixing multiple, effective herbicide groups is one tactic that can be used to impede herbicide resistance. By including multiple, effective herbicide groups when making an application, there is a lower probability that a weed species will develop resistance to all herbicides used (Fig. 1). Furthermore, tank-mixing different herbicide groups can have a synergistic effect, where the combined effect of two or more groups is greater than the effects of each herbicide alone. For example, previous research has shown Enlist One + Liberty to be more effective in controlling as common ragweed and Palmer amaranth, compared to each individual herbicide.

Furthermore, including a residual herbicide in the tank when making a postemergence application may be necessary for full-season control of certain weeds, such as Palmer amaranth. Including herbicides with both foliar and residual activity, such as fomesafen (Reflex), in tank with other effective herbicides can help to preserve the utility of these herbicides.

This research examined the effectiveness of tank mixing of herbicides with foliar (2,4-D, fomesafen) and residual (fomesafen, ­S-metolachlor) for early and late postemergence weed control in soybean. Plots (10 ft. x 25 ft.) were arranged in a randomized complete block design with 4 replicates. Herbicide treatments consisted of applying Reflex (fomesafen), Reflex + Dual Magnum (S-metolachlor), Reflex + Enlist One (2,4-D) or a three way mix of Reflex + Dual + Enlist One (Table 1). The entire study area received 1 pt/A Dual Magnum within 24 hours of soybean planting Enlist E3 soybeans on June 4, 2024. Early postemergence (EPOST) applications were made 2 weeks after planting and late postemergence (LPOST) applications 4 weeks after planting.

Table 1. Postemergence herbicide treatments for resistant weed mitigation and control in soybean.

Herbicide(s)RateTiminga
Reflex1.5 ptEPOST or LPOST
Reflex + Dual1.5 pt + 1.5 ptEPOST or LPOST
Reflex + Enlist1.5 pt + 2 ptEPOST or LPOST
Reflex + Enlist + Dual1.5 pt + 2 pt + 1.5 ptEPOST or LPOST
a Herbicide treatments were applied early postemergence (EPOST) 2 weeks after planting or late postemergence (LPOST) 4 weeks after planting soybeans on June 4, 2024.

Broadleaf Weed Control

Application timing did not affect common lambsquarters or morningglory control. Reflex + Enlist or Reflex + Enlist + Dual controlled common lambsquarters better compared to Reflex alone, and morningglory species better than Reflex or Reflex + Dual (Fig. 2).

Figure 2. Control of common lambsquarters and morningglory species 7 weeks after soybean planting. Bars of the same color with the same letter are not significantly different according to Tukey’s HSD (α = 0.05).

Giant Foxtail Control

Applications made EPOST provided better control compared to applications made LPOST (Fig. 2), but giant foxtail control varied from 38% to 78%, with no significant differences among herbicide treatments (Fig. 3). It should be noted that Enlist One does not control grasses. Both Dual Magnum and Reflex can provide some grass activity, but only if applied PRE. Better foxtail control with EPOST treatments could be attributed to overlapping residual control with these treatments. Overlapping herbicides is a tactic that involves sequential applications of herbicides with soil-residual activity to lengthen herbicidal activity before the first herbicide dissipates. As Dual Magnum was included in both PRE and POST applications, the EPOST applications likely provided better overlapping residual control due a shorter application window between the PRE and POST applications (2 weeks for EPOST and 4 weeks for LPOST).

Figure 3. Giant foxtail control following early and late postemergence applications 7 weeks after soybean planting. Bars of the same color with the same letter are not significantly different according to Tukey’s HSD (α = 0.05). 

This research highlights the value of adding multiple herbicide groups to the tank at the time of POST applications (Fig. 4). While additional work is needed to confirm the results of this study, the following factors should be considered when deciding which herbicides to include in the tank:

  • The types of weeds are prevalent in the field. Should the spray program focus primarily on broadleaf weeds, grasses, or both?
  • The emergence period for the weeds being controlled. Will a single POST application negate the need for additional treatment, or should an herbicide with residual activity be included?
  • Each herbicide must be effective alone on the target weed. Including multiple herbicides will not be as effective if a weed already has significant resistance to one of the herbicides in the mix.
Figure 4. Weed control with early postemergence applications of a) Reflex + Dual and b) Reflex + Enlist + Dual 7 weeks after planting. Photo credit: Logan Bledsoe.

Acknowledgements

Support for this project was made possible by funding from the Maryland Soybean Board as well as technical support from Jadon Cook, Logan Bledsoe, Sam Denherder, and the University of Maryland Wye Research and Education Center.

Commercial products are mentioned in this article solely for the purpose of providing specific information. Mention of a product does not constitute a guarantee or warranty of products. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by University of Maryland Extension is implied.

New Ecological Mitigation Menus to Reduce Pesticide Runoff

Kurt Vollmer, Weed Management Specialist | kvollmer@umd.edu
University of Maryland Extension

Pesticide runoff can occur when pesticides are carried by water off an application site. This usually occurs when water is applied to the soil faster than it can be absorbed, resulting in excess water flow across the land. Pesticide runoff into streams can pose risks to aquatic life, fish-eating wildlife, drinking water, etc. Therefore, new ecological mitigation requirements are being added to certain pesticide labels to reduce pesticide runoff.

What is the purpose of these new runoff mitigations?

These measures are designed to reduce pesticide movement out of a treated field. These practices are part of a wider strategy to protect endangered and non-target species, and will be part of future pesticide registration decisions.

Will these new runoff mitigation requirements be applicable to all pesticides?

No, only the application of certain pesticides will require these measures be implemented. Check the pesticide label for a section dedicated to runoff/erosion mitigation.

What do I do if I plan to spray a pesticide with one of these new mitigation requirements?

First, determine whether the application area is in a county designated as having high runoff vulnerability. The EPA has classified all counties on the Eastern Shore of Maryland and Delaware, as well as Anne Arundel, Charles, and St. Mary’s counties as having high runoff vulnerability. Initially, only applications to fields in these counties will require additional mitigation.

Are there exemptions for implementing these mitigations?

Yes, additional mitigation will not be required in counties with high runoff vulnerability if any one of the following criteria are met during an application:

  • the soil texture is comprised of over 50% sand, a loamy sand, or sandy loam soil;
  • the application area has a slope of ≤ 3%, or has a perimeter berm system;
  • the application is a partial field treatment, such as a banded or spot spray application;
  • the pesticide is incorporated into the soil mechanically or via irrigation; and
  • the treated field has subsurface or tile drains installed with controlled drainage.

My application area does not meet any of the aforementioned criteria. Now what?

Visit https://www.epa.gov/pesticides/mitigation-menu for a list of options. Even if additional mitigation is required, several EPA accepted practices have already been adopted in the area, such as reduced or no tillage, and the use of cover cropping.

Delmarva Weed Management Twilight at WREC

Join us for the 2023 Weed Management Twilight!

This event will be the third stop on the Delmarva Weed Tour and will include tours of corn and soybean herbicide research trials, integrated weed management projects for watermelon and hemp production, and tours of demonstration plots for organic weed management in corn and soybean.

Date: Wednesday, June 28th, 2023

Time: 4PM – 6PM

Location: Wye Research and Education Center

211 Farm Lane, Queenstown, MD 21658

Pesticide credits will be available for MD and DE.

Dinner will be served at 6:00pm.

For more information and to register: https://go.umd.edu/weedmanagementtwilight

For additional program information, contact Kurt Vollmer at kvollmer@umd.edu or 443-446-4260.

Bt and Herbicide Tolerant Traits in Corn and Current Resistance of Target Insect Pests

Galen Dively, Professor Emeritus | galen@umd.edu
University of Maryland, College Park

Listed below are the corn trait packages to make it easier to understand seed guides, sales material and bag tags. It is an abbreviated version of the Bt trait table plus related extension materials free online at: https://www.texasinsects.org/bt-corn-trait-table.html. Information listed Includes the name of each trait package, bag tag code, Bt toxins expressed (Cry1 types and Vip3A for caterpillars, Cry3 types for rootworms), refuge requirement (RIB=% refuge in the bag or REF=% structured refuge) and herbicide tolerance (GLY= glyphosate /Roundup-Ready, LL=glufosinate/Liberty Link, 2,4D or group 1 ‘fops’ type herbicides). Note that older trait packages, with limited or no commercial availability, are listed, so you can look back and interpret previous year’s planting records, seed guides, and research results.

The widely adopted use of Bt corn has resulted in major benefits to growers and the general public. However, resistance evolution in target insect populations has become a major threat to the sustainability of these crops. In some parts of the US Corn Belt, western corn rootworm rapidly adapted to Bt corn, and currently, some populations show resistance to all commercially available Cry3 traits. The high dose expression of Cry1 and Cry2 traits continues to provide excellent control and areawide suppression of the European corn borer in the US; however, the first case of resistance to the Cry1F toxin was reported in Nova Scotia in 2018 and resistance to other Cry toxins was recently confirmed in several eastern Canadian provinces. For corn earworm, we now have widespread field-evolved resistance to all Cry toxins in Bt corn. However, the Vip3A trait still provides excellent protection against this pest but studies show early stages of resistance developing since 2017, mainly in the southern states. Fall armyworm has been targeted by the Cry1F toxin since 2003, without any evidence of field-evolved resistance until 2010 when widespread control failures in Bt corn were reported in Puerto Rico and recent studies show high levels of resistance in several southeastern U.S. states.

New Web-Based Soybean Herbicide Selection Tool

Alan Leslie, Center Director
Maryland Agriculture Experiment Station

With grant funding from the Maryland Soybean Board, we have developed a new web-based app for selecting herbicides to use in soybean production. The goal for this new tool is to provide guidance in navigating different herbicide options with a simple user interface. The web app allows you to download a summary of your custom herbicide program as a PDF document for your records. Herbicide inputs can then be used to create your custom crop budgets using the web-based crop budget tool.

To use the app, users first select the major weed species from the lists that are the key management concerns on their farm. Choices of herbicides will then appear in three tables: burndown herbicides, pre-emergence herbicides, and post-emergence herbicides. These tables show herbicide options that are effective against at least one of the weed species selected. Users then use these tables to select their burndown, pre-emergence, and post-emergence herbicides, with the option to select between zero and three chemicals for each application. The page is then pre-populated with recommended rates and estimated costs, though actual rates and costs can be inputted by the user. After all of this information is entered, users can click the button to generate a report of everything they entered.

We are interested in gathering feedback and input about this new tool and ways to improve it in the future. After testing the new pesticide selection and crop budget tools, we would appreciate if you could take a few minutes to provide feedback through our online comment form. Feedback will be used to develop better tools in the future.

Figure 1. Screenshot of the web-app tool, showing where to select key weed species, where to view herbicide efficacy information, and where to input herbicide choices.

How’s That Burndown Looking?

Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu
University of Maryland Extension

In last month’s issue of Agronomy News, I discussed considerations for glyphosate-based burndown programs. This month I wanted to share some of my results using similar programs to manage a rye (Fig. 1) and hairy vetch (Fig. 2) cover crop. Treatments were applied on April 11, and consisted of glyphosate, glufosinate, paraquat, glyphosate + 2,4-D, glyphosate + dicamba, glyphosate + glufosinate, and glyphosate + paraquat. Currently, this is what I am seeing:

  • Glyphosate tank mixed with 2,4-D, dicamba, and glufosinate are doing an excellent job controlling hairy vetch, and glufosinate alone is providing similar control (Fig 3.);
  • Vetch control appears to be declining with individual treatments of glyphosate and paraquat, as well as the mixture of the two (Fig. 4);
  • Glyphosate + 2,4-D is doing an excellent job controlling cereal rye (Fig. 3b), but control with glyphosate alone has improved (Figs. 4a, 4b).

Figure 1. Hairy vetch control 2 and 3 weeks after application (WAA).

Figure 2. Cereal rye control 2 and 3 weeks after application (WAA).
*Glyphosate containing treatments consisted of 20.5 fl. oz./A Roundup PowerMax3®; glufosinate containing treatments consisted of 43 fl. oz./a Liberty 280®, paraquat containing treatments consisted of 3 pt/A Gramoxone SL 2.0®, 2,4-D containing treatments consisted of 2 pt./A Enlist One®, and dicamba containing treatments consisted of 12.8 fl. oz./A Engenia®
*Ammonium sulfate (8.5 lb./A) was included in all treatments except the glyphosate + dicamba treatment, nonionic surfactant (0.25% v/v) was included with 2,4-D and dicamba treatments, crop oil (1% v/v) was included with paraquat treatments.
*Treatments were applied using Turbo Teejet 11002 nozzles at spray volume of 15 gal/A.

As previously discussed, the same herbicide program may not have the same desired effect on all species. Here are some things to remember.

  1. There are certain species where control with glyphosate can be difficult, even if those species are not classified as being glyphosate-resistant. Additional trials from the Mid-Atlantic have also indicated lower vetch control with glyphosate alone (Figs. 4a, 4b) compared to glyphosate tank mixtures (Figs. 3b, 3c, 3d).
  2. Group 4 herbicides such as 2,4-D and dicamba, will not control grasses. In addition, including dicamba in a tank mix with glyphosate has been shown to reduce glyphosate’s ability to control grasses (Fig. 3c).
  3. Contact herbicides such as glufosinate and paraquat require good spray coverage for optimal control. If plants are too large, if spray volume is too low, or if nozzles do not provide adequate spray coverage, then plants can regrow (Figs. 4c, 4d).

Figure 3. Efficacy of preplant herbicides for managing a rye/vetch cover crop 2 weeks after application

Figure 4. Differences in herbicide efficacy for managing a rye/vetch cover crop 2 and 3 weeks after application.

Considerations for Burndown Programs in 2023

Kurt Vollmer, Extension Weed Management Specialist | kvollmer@umd.edu
University of Maryland Extension

It’s that time of year when growers are considering which herbicides to include in their burndown programs. Utilizing effective herbicides will help to ensure less weed competition at planting. However, growers should consider not only what herbicides they plan to use in their burndown programs, but also the weed species present in the field.

The most common preplant treatment for both corn and soybean is either a combination of 2,4-D + glyphosate or dicamba + glyphosate. These mixtures can provide good to excellent control of winter annual weeds such as common chickweed and common groundsel, as well as good control of emerging summer annual species such as common lambsquarters and foxtail species. These herbicides can also control henbit, purple deadnettle, and mustard species if sprayed before flowering and seed set. However, control may be reduced with winter annual weeds such as Carolina geranium and field pansy, as well as perennial species such as curly dock. If Carolina geranium and field pansy are present, consider adding atrazine or metribuzin to the tank mix. If curly dock is a problem consider using Harmony + 2,4-D.

The use of these herbicides will also influence planting date if using non-tolerant varieties, such as Enlist® (2,4-D) and XtendFlex® (dicamba). Generic forms of 2,4-D or dicamba should be applied 7 to 14 days before or 3 to 5 days after planting corn. The planting interval for soybean will depend on the amount of product applied. For most generic 2,4-D esters (LVE), wait at least 7 days if using 1 pt/A and at least 30 days if using 2 pt/A. However, some LVE formulations allow a 15 day application interval, be sure to consult the product label for specific instructions. The planting interval for dicamba formulations is at least 14 days if 0.5 pt/A is applied and at least 28 days if 1 pt/A is applied.

Glyphosate resistant weeds such as horseweed (marestail) and common ragweed may also be present at the time of application. Be advised that when using combinations of glyphosate and 2,4-D or dicamba, the 2,4-D or dicamba component is being relied upon to control these weeds. Therefore, these species should be sprayed when they are small (< 6 in.). Local data has shown applications of 2,4-D or dicamba made 30 days before planting to be more effective on horseweed than applications made 14 days before planting. Sharpen® is another option for controlling horseweed that is less than 6 inches tall.

Finally, it is important to note the importance temperature will play in the efficacy of these herbicides. When the temperature is lower than 60˚F, weed growth slows, resulting in reduced uptake and translocation of systemic herbicides like 2,4-D, dicamba, and glyphosate. If the temperature is below 40˚F, it is best to avoid applying these herbicides until conditions are more suitable. Fortunately, it looks like warmer days are ahead!

Will Your Preemergence Herbicides be Effective?

Kurt Vollmer, Wee Management Specialist | kvollmer@umd.edu
University of Maryland Extension

Despite a less than ideal Memorial Day weekend, I’m sure many of us are grateful for the rain. While corn was planted several weeks ago, many places went for weeks without significant rainfall. As a result, many fields lacked adequate moisture to properly activate any preemergence herbicides that were applied. The amount of moisture required to activate a particular herbicide depends on its water solubility (Table 1). The lower the water solubility the more rainfall or irrigation is needed to activate the herbicide and move it into the root zone. Soil-active herbicides such as atrazine, Princep, Balance Flexx, and Prowl need more than 0.75 inches of water to become activated. Under ideal conditions (good activation, no excessive moisture, and sensitive weed species), most preemergence products will provide control for about 3 to 4 weeks after application. Therefore, it’s a good time to start scouting fields to see if an early postemergence application is needed. Remember, preemergence herbicides will not control weeds once they’re up!

Along with products you are considering for postemergence weed control, be sure to include a soil-active herbicide in the tank mix to help extend residual weed control. Group 15 herbicides such as Dual and Outlook can extend control of grasses, pigweeds, and other small-seeded broadleaf weeds. The addition of atrazine can help to improve the efficacy of certain postemergence herbicides as well. Finally, always be sure to consult the label for the proper application rates and tank mix requirements for your crop and soil type.

Table1. The Relative Amount of Water Needed to Activate Common Herbicides and the Duration of Residual Weed Control.

Trade Name Amount of Water Required to Activate (inches) Duration of Residual Weed Control (weeks)
Atrazine > 0.75 4-5
Balance Flexx > 0.75 2-4
Callisto 0.33 2-4
Dual II Magnum 0.33 – 0.5 4-5
Harness 0.5 – 0.75 2-4
metribuzin 0.33 2-4
Outlook 0.33 2-4
Princep > 0.75 4-5
Prowl > 0.75 4-5
Valor > 0.75 4-5
Zidua > 0.75 4-5

*Table adapted from the 2021 Mid-Atlantic Weed Management Guide.

 

Herbicide Last Check Chart: Soybean

Kurt Vollmer, Weed Management Specialist
University of Maryland

This is a quick reference chart to check herbicide efficacy for some of the most problematic weeds in soybean production: marestail, common ragweed, waterhemp, and Palmer amaranth.

Click here to download a PDF copy.

Herbicide Updates

Kurt Vollmer, Extension Weed Management Specialist
University of Maryland

On September 28, Bayer announced that the European Commission has authorized XtendFlex soybean technology for food, feed, import and processing in the European Union. XtendFlex soybeans have tolerance to glyphosate, glufosinate, and dicamba. With this approval, Bayer expects a full launch in the United States and Canada in 2021. However, no dicamba-containing products are currently registered for over-the-top applications in soybean. Previously registered dicamba products including Xtendimax, Engenia, FeXapan, and Tavium are still pending re-registration for use next season.

Over 300 agricultural organizations recently sent a letter (http://wssa.net/wp-content/uploads/Neguse-Udall-FIFRA-letter.pdf) to members of the House and Senate opposing legislation that would drastically amend the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).

For more information on H.R. 7940 and S.4406 (the Protect America’s Children from Toxic Pesticides Act of 2020) visit https://www.congress.gov/bill/116th-congress/house-bill/7940/text?r=7&s=1.

To send a letter to your lawmakers opposing the current legislation visit https://www.votervoice.net/CropLifeAmerica/campaigns/77203/respond.