PRE and POST Herbicide Options for Weed Control in NY Field Corn

Vipan Kumar1, Mike Hunter2, Mike Stanyard3

1School of Integrative Plant Sciences -Soil and Crop Sciences Section, Cornell University, Ithaca, NY 14853, 2Field Crops IPM Coordinator, New York State Integrated Pest Management Program (NYSIPM), Redwood, NY, 3Cornell Cooperative Extension Northwest New York Dairy, Livestock, and Field Crops Program

As the spring weather is warming up in the New York (NY), some producers have started planting their field corn in various parts of the state. Planting is an important time to make decisions regarding herbicide selection for effective weed control throughout the field corn growing season. This article provides an overview and discuss some major herbicide options labelled in the NYS field corn.

Preplant burndown options

If no tillage is practiced, burndown herbicides such as glyphosate (Roundup PowerMax), glufosinate (Liberty), paraquat (Gramoxone), 2,4-D (2,4-D LV4) and saflufenacil (Sharpen) can be helpful to control winter annual weeds prior to corn planting. If glyphosate-resistant horseweed is present in the field, paraquat or combination of Sharpen + 2,4-D can be an effective burndown option. Make sure to use appropriate adjuvants as per each herbicide label to maximize the effectiveness of these burndown treatments. Burndown treatments should be made on actively growing winter annual weeds under optimum weather conditions (sunny conditions with air temperature above 55 F with no forecast of cold weather after applications).

Preemergence (PRE) herbicide options

Preemergence or soil-applied herbicides are generally applied after crop planting but prior to its emergence. However, sometimes these preemergence herbicides can also be tank-mixed with preplant burndown treatments. Several preemergence options are available to use in field corn in the NY. Majority of these preemergence herbicides belong to Group 5, 14, 15, and 27 although there are few options from Group 2, 3, and 4 as well. Major preemergence herbicide options (not a complete list) along with their active ingredients and sites of action (SOA) labelled in NYS field corn are listed in Table 1. Several of these preemergence options are available in premixtures with two or three active ingredients from different groups (multiple SOA) and generally provide longer soil residual activity on summer annual weeds. For example, Harness Extra and FulTime NXT are premixtures of atrazine (Group 5) and acetochlor (Group 15) whereas Lumax EZ and Lexar EZ are premixtures of atrazine (Group 5), s-metolachlor (Group 15), and mesotrione (Group 27). Premixtures containing active ingredients from Group 5, 15 and 27 are most commonly used in field corn for grass and broadleaf weed control. While selecting appropriate preemergence option and its application rate, producers should thoroughly read the herbicide label for target weed species, rotational restrictions on the subsequent crops, cover crops or intercrops as well as consider the soil type, texture, and other soil properties (organic matter, soil pH, etc.).


Table 1.  Preemergence herbicide options labelled in NY field corn.

Herbicides Active Ingredients SOA
Prowl Pendimethalin 3
Aatrex Atrazine 5
Outlook Dimethenamid 15
Surpass NXT Acetochlor 15
Dual Magnum S-metolachlor 15
Harness Xtra, FulTime NXT Atrazine + Acetochlor 5, 15
Bicep Lite II Magnum, Cinch ATZ Lite Atrazine + S-metolachlor 5, 15
Verdict Saflufenacil + Dimethenamid 14, 15
Harness Max Acetochlor + Mesotrione 15, 27
Acuron Flexi S-metolachlor + Bicyclopyrone + Mesotrione 15, 27
Acuron Atrazine + S-metolachlor + Bicyclopyrone + Mesotrione 5, 15, 27
SureStart II Flumetsulam + Clopyralid + Acetochlor 2, 4, 15
Lumax EZ, Lexar EZ Atrazine + S-metolachlor + Mesotrione 5, 15, 27
Resicore, Resicore XL Clopyralid + Acetochlor + Mesotrione 4, 15, 27

*Restricted Use Pesticides      ¥Not for use in Nassau and Suffolk Counties


Postemergence (POST) herbicide options

Postemergence herbicides are applied after emergence of corn and weeds. Redroot pigweed, Powell amaranth, common lambsquarters, common ragweed, horseweed, common waterhemp, velvetleaf, foxtails (yellow, green, and giant), fall panicum, etc. are most common spring/summer annual weeds in NY corn. In addition, Palmer amaranth populations have also been recently found from six counties. In addition, field bindweeds, horsenettle, milkweed, yellow nutsedge, Canada thistle, hemp dogbane, quackgrass, etc. are most common perennial weeds. Johnsongrass populations have also been reported from corn fields in some southern counties of NY. Several postemergence herbicides are available to use in NY field corn to control these annual and perennial weed species. Majority of these labelled postemergence herbicides belong to Group 2, 4, 5, 6, 9, 10, 15, and 27.

Table 2 highlights major postemergence herbicide options (not a complete list) along with their active ingredients and sites of action (SOA) labelled in conventional, Roundup Ready and Liberty Link corn hybrids. Several of these postemergence herbicides are broad-spectrum and can control both grass and broadleaf weed species. For instance, Postemergence applications of Capreno, Realm Q, Impact Core, Roundup PowerMax, Liberty can all help controlling grass and broadleaf weeds. In contrast, postemergence applied Aatrex, Banvel, Clarity, Callisto, Yukon are most effective controlling broadleaf weeds only. Producers should thoroughly read each herbicide label for target weed species, rotational restrictions on the subsequent crops, cover crops or intercrops during selection of appropriate postemergence option and its rate. Make sure to use appropriate adjuvants as per each herbicide label to maximize the effectiveness of these postemergence herbicides. If glyphosate- or triazine-resistant weeds are present, producers should select alternative effective two-pass herbicide program (preemergence followed by postemergence).


Table 2. Postemergence herbicide options labelled in NY field corn.

Herbicides Active Ingredients SOA
For Conventional Corn Hybrids
Accent Q, Steadfast Q Nicosulfuron, Nicosulfuron + Rimsulfuron 2
Permit, Resolve Q Halosulfuron, Rimsulfuron + Thifensulfuron 2
Banvel, Clarity, DiFlexx Dicamba 4
Aatrex*¥ Atrazine 5
Basagran; Moxy 2EC Bentazone; Bromoxynil 6
Callisto; Armezone/Impact; Laudis Mesotrione; Topramezone; Tembotrione 27
Yukon Halosulfuron + Dicamba 2, 4
Capreno Thiencarbazon + Tembotrione 2, 27
Realm Q Rimsulfuron + Mesotrione 2, 27
Impact Core*¥ Acetochlor + Topramezone 15, 27
Kyro*¥ Clopyralid + Acetochlor + Topramezone 4, 15, 27
For Roundup Ready Corn Hybrids
Roundup PowerMax; Durango DM Glyphosate 9
Halex GT Glyphosate + S-metolachlor+ Mesotrione 9, 15, 27
For Liberty Link Corn Hybrids
Liberty Glufosinate 10

*Restricted Use Pesticides      ¥Not for use in Nassau and Suffolk Counties

Note: For further information on currently labelled PRE and POST herbicide options in NY field corn, check the 2024 Cornell Guide for Integrated Field Crop Management (available online).


Field Study in 2023

A field study was conducted in Franklin and Jefferson counties, NY, in 2023 growing season to determine the effectiveness of various preemergence herbicides (Table 3) with and without atrazine (42 fl oz/a) for weed control in field corn. Both field sites had natural infestation of common lambsquarters. Field corn was planted around May 20 at both sites and selected preemergence herbicides were applied immediately after planting. Small plots (10 feet wide by 30 feet long) were used to test each herbicide program. Test plots were laid arranged in Randomized Complete Block Design (RCBD) with 4 replications. All PRE herbicides were applied using CO2-operated backpack sprayer equipped with handheld boom with four nozzles (AIXR 110015). Results indicated no significant differences in common lambsquarters control among all tested preemergence herbicides at 35 days after treatments. Across both sites in Franklin and Jefferson counties, preemergence applied Acuron Flexi, Harness Max, Resicore XL, and Verdict + Outlook alone or with atrazine provided 94 to 100% control of common lambsquarters (Table 3; Figure 1)). In 2024, we plan to evaluate these preemergence applied herbicides (with or without atrazine) across multi-locations again to validate these results.


Table 3. Percent common lambsquarters control at 35 days after applications of various preemergence herbicide premixes alone or in combination with atrazine in field corn during 2023 growing season in Franklin and Jefferson Counties, NY.

 

Herbicide Active Ingredient (s) Site of action (SOA) Rate (oz/a) Franklin Jefferson
% control
Acuron Flexi S-metolachlor/bicyclopyrone/mesotrione 15, 27 72 98 97
Aatrex 4L + Acuron Flexi Atrazine + S-metolachlor/bicyclopyrone/mesotrione 5,15,27 42 + 72 99 94
Harness Max Acetochlor/mesotrione 15,27 64 100 97
Aatrex 4L + Harness Max Atrazine + acetochlor/mesotrione 5,15,27 42 + 64 99 97
Resicore XL Clopyralid/acetochlor/mesotrione 4,15,27 96 99 98
Aatrex 4L + Resicore XL Atrazine + clopyralid/acetochlor/mesotrione 5,4,15,27 42 + 96 100 99
Verdict + Outlook Saflufenacil/dimethenamid-P + dimethenamid-P 14,15,15 16 + 4.6 99 94
Aatrex 4L + Verdict + Outlook Atrazine + saflufenacil/dimethenamid-P + dimethenamid-P 5,14,15,15 16 + 4.6 + 42 99 98

corn rows showing amount of weeds with different treatments
Figure 1. Side-by-side comparison of PRE applied Acuron Flexi and Harness Max with and without atrazine for common lambsquarters control at 35 days after application in Jefferson County, NY during 2023 growing season.

Disclaimer: Brand names appearing in this publication are for product identification purposes only. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.

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2024 Updates on XtendiMax, Engenia and Tavium Registrations and Use in Dicamba-Tolerant Soybeans for NY Producers

Vipan Kumar1, Michael Helms2, Mike Hunter3, Mike Stanyard4

1School of Integrative Plant Sciences -Soil and Crop Sciences Section, Cornell  University, Ithaca, NY 14853, 2Cornell Pesticide Safety Education Program, 3Field Crops IPM Coordinator, New York State Integrated Pest Management Program (NYSIPM), Redwood, NY, 4Cornell Cooperative Extension Northwest New York Dairy, Livestock, and Field Crops Program

soybeanOn February 06, 2024, the U.S. district court in Arizona vacated 2020 registrations of three dicamba containing products (XtendiMax, Engenia and Tavium) for over-the-top (OTT) applications in dicamba-tolerant (Xtend and XtendFlex) soybean. In response to the U.S. district court ruling, the EPA issued an Existing Stock Order on February 14, 2024, that allows limited sale, distribution, and use of these dicamba OTT products that were already in the possession of growers, distributors or in the channels of trade and outside the control of pesticide companies as of February 06, 2024.

According to this Existing Stock Order, the manufacturers/registrants are no longer allowed to distribute these dicamba products in the US other than for disposal or lawful export. However, any dealer with an existing stock may sell these dicamba products until May 31, 2024 (cutoff date in New York (NY)). If soybean producers and applicators in NY are planning to grow Xtend or XtendFlex soybean and thinking to use these dicamba products in 2024 growing season, they should consider the following important points:

  • Only three dicamba containing products (XtendiMax, Engenia and Tavium) are labelled for OTT applications in Xtend or XtendFlex soybean.
  • Only certified applicators (private or commercial) are allowed to use XtendiMax, Engenia and Tavium herbicides for OTT applications in Xtend or XtendFlex soybean.
  • NY growers and applicators must read and understand the EPA’s Existing Stocks Order on the use of XtendiMax, Engenia and Tavium herbicides for OTT applications in Xtend or XtendFlex soybean.
  • Product that dealers had on hand prior to February 06, 2024 can be sold or distributed in NY through May 31, 2024 (the cutoff date for NY).
  • Applicators are allowed to use existing stocks of these dicamba products for OTT applications in Xtend or XtendFlex soybeans until June 30, 2024 (cutoff application date for NY).
  • The NY registrations for XtendiMax, Engenia and Tavium herbicides are set to expire on July 31, 2024. Unfortunately, there are no CleanSweepNY programs currently scheduled for 2024, so alternative disposal options may need to be found.
  • Mandatory dicamba training: Applicators must take mandatory annual dicamba training before applying XtendiMax, Engenia and Tavium herbicides in Xtend or XtendFlex soybean. These online dicamba trainings are offered by following manufacturers/registrants:

Training is reciprocal across brands and applicators only need to take one dicamba-specific training each year (i.e. only one training session either from BASF, Bayer or Syngenta). Contact your local dealer for further information.

  • Note that other dicamba-containing products (e.g. Banvel, Clarity and the many generics) are not labelled for OTT applications in Xtend or XtendFlex soybeans. However, some glyphosate products (Roundup PowerMax, Durango, etc.) can be used in OTT applications in Xtend or XtendFlex soybeans. Some glufosinate (Liberty) products can only be used for OTT applications in XtendFlex soybean, not in Xtend soybean.

Disclaimer: Brand names appearing in this publication are for product identification purposes only. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.

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Cut-Off Date and Other Considerations for Xtendimax, Engenia and Tavium Applications in Dicamba-Tolerant Soybeans

Vipan Kumar1, Lynn Sosnoskie2, Mike Hunter3, Mike Stanyard4

1School of Integrative Plant Sciences -Soil and Crop Sciences Section, Cornell University, Ithaca, NY 14853, 2School of Integrative Plant Sciences – Horticulture Section, Cornell AgriTech, Geneva, NY 14456, 3Cornell Cooperative Extension North County Regional Ag Team, 4Cornell Cooperative Extension Northwest New York Dairy, Livestock, and Field Crops Program

With recent rainfall events and a new flush of summer annual weeds, NY producers are busy applying postemergence herbicide applications in row crops. If you have planted dicamba-tolerant soybeans and are planning for postemergence applications of dicamba-containing products (Xtendimax, Engenia, or Tavium), the following points need to be considered.

    • Xtendimax, Engenia and Tavium are the only dicamba-containing products that are labelled in dicamba-tolerant soybeans (Roundup Ready 2 Xtend or XtendFlex soybeans).
    • Be sure of your trait technology! Do not confuse Xtend traits with Enlist traits. Enlist traits provide crop resistance to 2,4-D but not to dicamba.
    • As per the revised labels in 2021, the legal last day of postemergence applications of Xtendimax, Engenia and Tavium in dicamba-tolerant soybeans is June 30.
    • Only certified applicators with dicamba training are allowed to apply these products.
    • Spray records need to be created within 3 days of applications of these products and should be maintained for 2 years. (Note: In New York State all applications of restricted use pesticides must be maintained for at least three years)
    • An approved drift reduction agent (DRA) and volatility reduction agent (VRA) should be included.
    • Only approved nozzles and tank-mix partners should be used for these products.
    • Wind speed at boom height should range from 3 to 10 miles per hour at the time of application.
    • As per the labels, maximum ground speed of sprayer should not exceed 15 miles per hour and maximum boom height above target pest or crop canopy should not exceed 24 inches.
    • Survey surrounding fields ahead of dicamba applications for sensitive crops (e.g., grapes, fruit trees, snap beans, fruiting vegetables (e.g., tomatoes, peppers), soybeans without dicamba-tolerance trait technology, etc…).
    • DO NOT apply these products if sensitive crops are in a downwind field or a run-off producing rain event is in the forecast in the next 48 hours.
    • After determining no adjacent sensitive crops are downwind, maintain a 240-feet downwind buffer.
    • Stop spraying if winds change direction towards sensitive crops.
    • DO NOT apply dicamba products during temperature inversions. Only spray between one hour after sunrise and two hours before sunset.
    • Ensure the entire sprayer system is properly cleaned before and after dicamba applications are made.
    • Applicator should consult Bulletins Live Two website to make sure no endangered species will be affected by these dicamba applications.

Disclaimer: Brand names appearing in this publication are for product identification purposes only. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.

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Controlling Herbicide Resistant Waterhemp in Soybeans: 2020 Trials

Project Leaders

Bryan Brown, NYS IPM Program
Venancio Fernandez, Bayer Crop Sciences
Mike Hunter, Cornell Cooperative Extension
Jeff Miller, Oneida County Cooperative Extension
Mike Stanyard, Cornell Cooperative Extension

Cooperators

Derek Conway, Conway Farms
Jaime Cummings, formerly NYS IPM Program
Quentin Good, Quentin Good Farms
Antonio DiTommaso, Cornell University
Michael Durant, Lewis County Soil and Water Conservation District
Scott Morris, Cornell University
Ali Nafchi, Cornell Cooperative Extension
Ryan Parker, NYS IPM Program
Jodi Putman, Cornell Cooperative Extension
Joshua Putman, Cornell Cooperative Extension
Matthew Ryan, Cornell University
Lynn Sosnoskie, Cornell University
Ken Wise, NYS IPM Program

Funding Sources

New York Farm Viability Institute

Project Location

Trial locations in Seneca County but results are likely applicable statewide.

Abstract

Herbicide resistant tall waterhemp (Amaranthus tuberculatus) continues to be one of the most problematic weeds in US field crops. Thus far, it has primarily established in western and central New York. Our second year of trial results generally followed our first-year results. Herbicides in WSSA groups 2, 5, and 9 should not be relied on for waterhemp control. However, programs that included at least two non-chemical tactics or herbicides from groups 4, 14, or 15 were very effective. Seedbank modelling showed that control at 95%, 98%, or 100% would cause waterhemp emergence to increase, maintain, or decrease over time, respectively. Our partial budget analysis showed that profitability generally reflected yields. We also found that cereal rye (Secale cereale) residue can provide up to 87% control of waterhemp, which, if used in conjunction with a moderately effective herbicide program, could provide excellent control.

Background and Justification

Herbicide resistant waterhemp has been reported in many western and central NY counties. Soybean farmers have reported yield losses of 50% due to this weed, even after herbicide applications. Our greenhouse spray chamber tests and field trials from 2019 suggest resistance to WSSA herbicide groups 2, 5, and 9 (ALS inhibitors, photosystem II inhibitors, and EPSPS inhibitors, respectively). Our most effective control programs in 2019 relied on herbicides from other groups as well as additional physical or cultural tactics.

Waterhemp in other states has also developed resistance to different herbicide classes, including WSSA groups 4 and 14 (http://www.weedscience.org/Pages/Species.aspx). These groups include dicamba, 2,4-D, Valor, and Cobra. Resistance to these additional herbicides would make successful waterhemp control even more challenging.

Overwintering cover crops such as cereal rye can be sprayed or rolled-down to provide a weed suppressive mulch prior to soybean planting. In NY, Pethybridge et al (2019) showed that rolled rye achieved very effective suppression not only for weeds, but also for white mold. Furthermore, waterhemp and another problematic herbicide resistant weed in NY, called horseweed or marestail (Conyza canadensis), both have very small seeds that lack the stored energy to emerge through deep soil or mulch.

Objectives

Objective 1. Continue to evaluate the effectiveness of several different programs in controlling waterhemp in soybeans.

Objective 2. Assess the potential for rye cover crop mulch to suppress waterhemp emergence.

Procedures

Objective 1.

The trial site was in Seneca County, NY on a field of Odessa silt loam soil where waterhemp had survived various herbicide applications and produced seed in 2018 and was moderately controlled in 2019 in corn. In 2020, the ground was prepared for planting with a field cultivator on May 5 and planted on May 6. Pre-emergence applications were made after planting on May 8. Cultivation occurred on June 16 while the other post-emergence treatments were applied on June 18. All treatments are listed in Table 1. For fertilizer, DAP (10-46-0, 20 lbs N/A, 92 lbs P2O2/A) and muriate of potash (0-0-60, 125 lbs K2O/A) were applied prior to tillage and UAN (32-0-0, 30 lbs N/A) was applied at planting.

Plots were 25’ long and 10’ wide. Each treatment was replicated four times in a randomized complete block design. Spraying was conducted using a backpack CO2 sprayer with a 10’ boom. Spray volume was 20 gal/A applied at 40 psi. Row cultivation was achieved using a Double Wheel Hoe (Hoss Tools) with two staggered 6” sweeps (12” effective width). Two passes were made per row so that 24” of the 30” rows were cultivated.

Weed control was assessed August 15-22 by collecting all aboveground weed biomass within a 2 ft2 quadrat. The quadrat was used four times per plot, placed randomly in the two middle rows of each plot. Weeds were placed in paper bags and dried at 113 degrees F for 7 days, then weighed. Control was calculated by subtracting the biomass of each treated plot from biomass of the untreated plots, dividing by the biomass of the untreated plots, and multiplying by 100. Waterhemp was the dominant species present in this trial. Other species did not provide enough data for comparison. All waterhemp was manually removed immediately after the weed control assessments in order to prevent seed production.

Soybean yield was measured in mid-October by hand harvesting 20-row-feet from the two middle rows of each plot. In our partial budget analysis, gross income was calculated by multiplying the average yield per treatment across all sites for 2019 and 2020 by a soybean price of $10.05 per bushel (Langemeier 2018). Weed treatment costs were estimated based on personal communications with several local custom applicators.

To illustrate the effects of allowing waterhemp to produce seed, we produced a 10-year model of waterhemp emergence based on the number of seeds in the soil. The model was created based on observed waterhemp emergence and biomass production in 2019 and assumed a preceding three-year period of uncontrolled growth. We also assumed that 8% of the seedbank would emerge each year (Davis et al. 2016) and that for a given cohort, viability was reduced by 81% after one year, reduced by an additional 50% after years two and three (Heneghan and Johnson 2017), and reduced by 32% each subsequent year (Davis et al. 2016). We also assumed waterhemp would produce 441 seeds per gram of biomass (Heneghan and Johnson 2017) with a maximum waterhemp biomass of 386 g/m2 based on our results.

Objective 2.

On separate regions of the field near the plots described in Objective 1, we set up two trials investigating the use of cereal rye residue as a waterhemp suppressive mulch. While a cereal rye cover crop was not available for these trials, we transported rye residue from a nearby field and applied it immediately following planting. We used rates of 0, 3570, and 7140 lbs/A. The high- and mid-rates represent attainable rye biomass production in NY with- and without fertilizer, respectively (Mirsky et al 2013; Pethybridge et al 2019). Plots were 5’ by 10’ and each treatment was replicated four times per trial in a randomized compete block design. Waterhemp control was measured in the same manner as Objective 1.

Results and Discussion

Objective 1.

In 2020, waterhemp control was generally similar as 2019 (Table 2). Soil was dry at the time of pre-emergence application but we received 0.9” rain in the first 10 days after application, which was likely sufficient for activation. ValorSX did not perform as well as in the previous year, possibly related to weeds that had germinated prior to activation. WarrantUltra plus metribuzin remained very effective, providing further evidence that at least two effective modes of action ­– WSSA groups 14 and 15 in this treatment – are necessary for successful control.

In the post-emergence-only treatments, this year the Warrant improved the effectiveness of the Roundup and Xtendimax, probably due to our earlier planting and spray dates in 2020 that likely allowed more waterhemp to germinate after the post-emergence application, making use of the residual activity of the Warrant.

Similar to the previous year, the two-pass programs were generally more effective than the pre- or post-emergence-only programs. Having two passes reduces the burden on each pass. So if conditions are not optimal in one of the passes, the other pass can help ensure successful control is still achieved. They are also generally more expensive, but inclusion of more diverse chemistries and/or non-chemical tactics can reduce the risk of worsening the resistance problem.

In our partial budget analysis, the highest grossing (highest yielding) treatments were generally the most profitable (Table 2). The high yields of the row cultivation treatment may reflect the increase in soil aeration and nutrient release associated with soil disturbance. But also, due to small plot size there was some variability in yield results due to random chance.

Our waterhemp production and emergence model demonstrates that programs that control 100% of the waterhemp can result in greatly reduced emergence in subsequent years, whereas programs achieving 98% control or less will perpetuate the problem (Figure 1). Although 95% control would likely allow farmers to avoid a crop yield loss, the resulting waterhemp seed production and increase in emergence in subsequent years would likely make successful control more difficult over time.

Waterhemp congtrol graph
Figure 1. A model of waterhemp emergence for 95%, 98%, and 100% control (dotted, dashed, and solid lines respectively) over time. In this scenario, the newly established waterhemp population grows uncontrolled (shaded region) until year 4. The model shows that greater than 98% control is required to reduce populations over time.

Objective 2.

Across the two trials, cereal rye cover crop residue at high (7140 lbs/A) and medium rates (3570 lbs/A), representing biomass NY farmers could attain with- or without-fertilizer, provided an average of 87% and 73% waterhemp control compared to the untreated check, respectively. Used alone, these levels of control may be sufficient to avoid soybean yield loss. But this tactic could also be used in conjunction with a herbicide program. In such a system, 99% waterhemp control could be achieved with the high level of rye residue plus a herbicide program that only provides 92% control when used alone.

soybean weed comparison
Figure 2. Suppression of waterhemp by cereal rye residue applied at 0 lbs/A (photo A) and 7140 lbs/A (photo B).

References

Davis AS, Fu X, Schutte BJ, Berhow MA, Dalling JW (2016) Interspecific variation in persistence of buried weed seeds follows trade-offs among physiological, chemical, and physical seed defenses. Ecology and Evolution. 6:6836–6845

Heneghan JM, Johnson WG (2017) The Growth and Development of Five Waterhemp (Amaranthus tuberculatus) Populations in a Common Garden. Weed Science. 65:247–255

Langemeier M (2018) Projected Corn and Soybean Breakeven Prices. Department of Agricultural and Consumer Economics, University of Illinois at Urbana-Champaign. Farmdoc Daily 8:66

Mirsky S, Ryan M, Teasdale J, Curran W, Reberg-Horton C, Spargo J, Wells S, Keene C, Moyer J (2013) Overcoming Weed Management Challenges in Cover Crop–Based Organic Rotational No-Till Soybean Production in the Eastern United States. Weed Technology, 27(1), 193-203. doi:10.1614/WT-D-12-00078.1

Pethybridge S, Brown B, Kikkert J, Ryan MR (2019) Rolled-crimped cereal rye mulch suppresses white mold in no-till soybean and dry bean. Renewable Agriculture and Food Systems. doi:10.1017/S174217051900022X

Acknowledgements

Thank you to the New York Farm Viability Institute for supporting this project.

Disclaimer: Read pesticide labels prior to use. The information contained here is not a substitute for a pesticide label. Trade names used herein are for convenience only; no endorsement of products is intended, nor is criticism of unnamed products implied. Laws and labels change. It is your responsibility to use pesticides legally. Always consult with your local Cooperative Extension office for legal and recommended practices and products. cce.cornell.edu/localoffices

For more information on this project, check out: https://nysipm.cornell.edu/agriculture/weed-ipm/

 

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Effective Waterhemp Control Programs and Compatibility with Interseeding in Corn: 2020 Trials

Project Leaders

Bryan Brown, NYS IPM Program
Venancio Fernandez, Bayer Crop Sciences
Mike Hunter, Cornell Cooperative Extension
Jeff Miller, Oneida County Cooperative Extension
Mike Stanyard, Cornell Cooperative Extension

Cooperators

Derek Conway, Conway Farms
Jaime Cummings, formerly NYS IPM Program
Quentin Good, Quentin Good Farms
Antonio DiTommaso, Cornell University
Michael Durant, Lewis County Soil and Water Conservation District
Scott Morris, Cornell University
Ali Nafchi, Cornell Cooperative Extension
Ryan Parker, NYS IPM Program
Jodi Putman, Cornell Cooperative Extension
Joshua Putman, Cornell Cooperative Extension
Matthew Ryan, Cornell University
Lynn Sosnoskie, Cornell University
Ken Wise, NYS IPM Program

Funding Sources

New York Farm Viability Institute

Project Location

Trial locations in Seneca and Oneida Counties but results are likely applicable statewide.

Abstract

Herbicide resistant tall waterhemp (Amaranthus tuberculatus) continues to be one of the most problematic weeds in US field crops. Thus far, it has primarily established in western and central New York. Our second year of trial results generally followed our first-year results. Herbicides in WSSA groups 2, 5, and 9 should not be relied on for waterhemp control. However, programs that included at least two non-chemical tactics or herbicides from groups 4, 14, 15, 19, or 27 were very effective. Seedbank modelling showed that control at 95%, 98%, or 100% would cause waterhemp emergence to increase, maintain, or decrease over time, respectively. Interseeding annual ryegrass in fields where waterhemp has established is not recommended, but Callisto provided acceptable control of waterhemp while not injuring the annual ryegrass.

Background and Justification

Herbicide resistant waterhemp has been reported in many western and central NY counties. Corn farmers have reported yield losses of 20% due to this weed, even after herbicide applications. Our greenhouse spray chamber tests and field trials from 2019 suggest resistance to WSSA herbicide groups 2, 5, and 9 (ALS inhibitors, photosystem II inhibitors, and EPSPS inhibitors, respectively). Our most effective control programs in 2019 relied on herbicides from other groups as well as additional physical or cultural tactics. Generally, two-pass programs with residual activity were best. But residual herbicides can injure interseeded cover crops, which have grown in popularity in NY, reflecting the work of the Western NY Soil Health Alliance and the Genesee River Coalition of Conservation Districts.

Objectives

Objective 1. Continue to evaluate the effectiveness of several different programs in controlling waterhemp in corn.

Objective 2. Continue to assess the compatibility of residual herbicides with an interseeded cover crop.

Procedures

Objective 1.

The trial site was in Seneca County, NY on a field of Odessa silt loam soil where waterhemp had survived various herbicide applications and produced seed in 2018 and was moderately controlled in 2019 in corn. In 2020, the ground was prepared for planting with a field cultivator on May 5 and planted on May 13. Pre-emergence applications were made after planting on May 20. Cultivation and interseeding occurred on June 16, while the other post-emergence treatments were applied on June 18. All treatments are listed in Table 1. For fertilizer, DAP (10-46-0, 20 lbs N/A, 92 lbs P2O2/A) and muriate of potash (0-0-60, 125 lbs K2O/A) were applied prior to tillage, UAN (32-0-0, 30 lbs N/A) was applied at planting, and ESN nitrogen (44-0-0, 150 lbs N/A) was broadcast on June 19.

Plots were 25’ long and 10’ wide. Each treatment was replicated four times in a randomized complete block design. Spraying was conducted using a backpack CO2 sprayer with a 10’ boom. Spray volume was 20 gal/A applied at 40 psi. Row cultivation was achieved using a Double Wheel Hoe (Hoss Tools) with two staggered 6” sweeps (12” effective width). Two passes were made per row so that 24” of the 30” rows were cultivated. For Objective 1, interseeding was established by hand broadcasting annual ryegrass (Mercury Brand, “Ribeye”) at 20 lb/A.

Weed control was assessed on August 16 by collecting all aboveground weed biomass within a 2 ft2 quadrat. The quadrat was used four times per plot, placed randomly in the two middle rows of each plot. Weeds were placed in paper bags and dried at 113 degrees F for 7 days, then weighed. Control was calculated by subtracting the biomass of each treated plot from biomass of the untreated plots, dividing by the biomass of the untreated plots, and multiplying by 100. Waterhemp was the dominant species present in this trial. Other species did not provide enough data for comparison. All waterhemp was manually removed immediately after the weed control assessments in order to prevent seed production.

Treatment costs were estimated based on personal communications with several local custom applicators. Yield was unable to be accurately measured this year due to variability in the field.

To illustrate the effects of allowing waterhemp to produce seed, we produced a model of annual waterhemp emergence based on the number of seeds in the soil. The model was created based on observed waterhemp emergence and biomass production in 2019 and assumed a preceding three-year period of uncontrolled growth. We also assumed that 8% of the seedbank would emerge each year (Davis et al. 2016) and that for a given cohort, viability was reduced by 81% after one year, reduced by an additional 50% after years two and three (Heneghan and Johnson 2017), and reduced by 32% each subsequent year (Davis et al. 2016). We also assumed waterhemp would produce 441 seeds per gram of biomass (Heneghan and Johnson 2017) with a maximum waterhemp biomass of 386 g/m2 based on our results.

Objective 2.

This objective was conducted in Lewis County, NY on a corn field that does not contain any waterhemp. The field (Homer silt loam soil) was tilled June 9 and planted with silage corn (Pioneer, 95 day) on June 1 with 3 gal/A starter fertilizer (7-21-7). Pre-emergence herbicides were applied on June 2, row cultivation June 30, and post-emergence herbicides on July 1. All treatments are listed in Table 2. Interseeding was conducted by the Lewis County Soil and Water Conservation District on July 6 using a 15’ interseeder (Interseeder Technologies) with three drills between each corn row operating at 0.5” depth. Annual ryegrass (Mercury Brand, “Ribeye”) was used at 20 lb/A.

Weed control of the pre-emergence herbicides was evaluated on June 30 by visually estimating the percentage of the ground covered by the most prevalent species or categories – this year only common lambsquarters and “other broadleaf species” were present in sufficient quantity to rate. This was done using the same quadrat system described above and control was calculated in a similar manner.

Performance of the annual ryegrass was assessed on September 17 by collecting the aboveground biomass using the quadrat system and drying samples at 113 degrees F for 7 days before weighing. Although there would have been more cover crop biomass later in the fall, silage harvest would likely have altered the results.

Results and Discussion

Objective 1.

Most of the treatments performed similarly to 2019, but some were clearly affected by insufficient rainfall (Table 3). In the first 10 days after preemergence application, we had 0.5” rain, so some of those residual products were not optimally activated. We continued to see evidence of waterhemp resistance to WSSA groups 2 and 5, as represented by ResolveQ and atrazine, respectively.

We were able to apply only one post-emergence-only application in 2020 and it did not perform well, reflecting the drought conditions. In the 19 days prior to post application, we had 0.1” rain and there was no significant rain until nine days after the post-emergence application. In drought conditions, weeds become stressed and systemic herbicides do not translocate as they should.

The two-pass programs were generally more effective than pre- or post-only programs. They are also generally more expensive, but inclusion of more diverse chemistries and/or non-chemical tactics can reduce the risk of worsening the resistance problem. Furthermore, our waterhemp production and emergence model demonstrates that programs that control 100% of the waterhemp can result in greatly reduced emergence in subsequent years, whereas programs achieving 98% control or less will perpetuate the problem (Figure 1). Although 95% control would likely allow farmers to avoid a crop yield loss, the resulting waterhemp seed production and increase in emergence in subsequent years would likely make successful control more difficult over time.

graph of waterhemp control
Figure 1. A model of waterhemp emergence for 95%, 98%, and 100% control (dotted, dashed, and solid lines respectively) over time. In this scenario, the newly established waterhemp population grows uncontrolled (shaded region) until year 4. The model shows that greater than 98% control is required to reduce populations over time.

Objective 2.

This objective was primarily focused on the effects of residual herbicides on interseeded annual ryegrass, but we also rated weed control prior to post-emergence applications (Table 4). Lambsquarters control was not as effective as in 2019, possibly related to decreased rainfall, but 0.9” rain was recorded in the first ten days following application, so activation should have been achieved. Other broadleaf control was also not as effective for certain treatments, but this may reflect the inclusion of velvetleaf in this category in 2020.

Injury to the interseeded annual ryegrass was similar to the results of the previous year (Table 5). Unfortunately, the 2019 effect of cultivation seemingly reducing the injury caused by Acuron was not observed in 2020. We were surprised in both years that atrazine did not cause more injury, but it may relate to the high organic matter of the field. Overall, Callisto again offered the most effective waterhemp control in Objective 1 trials, while causing minimal injury to the interseeded annual ryegrass. However, overlapping chloroacetamides (like Dual or Harness) is a key aspect of controlling resistant waterhemp and this tactic would not be compatible with interseeding.

Immediately prior to corn silage harvest, we had nearly 90% less annual ryegrass biomass in 2020 compared to 2019. The primary difference was that in 2020 the corn was larger at interseeding and likely outcompeted the annual ryegrass. In 2020, the corn had accumulated 655 growing degree days at interseeding compared to 550 in 2019. To access growing degree day information from a weather station near you visit http://newa.cornell.edu/ .

References

Davis AS, Fu X, Schutte BJ, Berhow MA, Dalling JW (2016) Interspecific variation in persistence of buried weed seeds follows trade-offs among physiological, chemical, and physical seed defenses. Ecology and Evolution. 6:6836–6845

Heneghan JM, Johnson WG (2017) The Growth and Development of Five Waterhemp (Amaranthus tuberculatus) Populations in a Common Garden. Weed Science. 65:247–255

Acknowledgements

Thank you to the New York Farm Viability Institute for supporting this project.

Disclaimer: Read pesticide labels prior to use. The information contained here is not a substitute for a pesticide label. Trade names used herein are for convenience only; no endorsement of products is intended, nor is criticism of unnamed products implied. Laws and labels change. It is your responsibility to use pesticides legally. Always consult with your local Cooperative Extension office for legal and recommended practices and products. cce.cornell.edu/localoffices

For more information on this project, check out: https://nysipm.cornell.edu/agriculture/weed-ipm/

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What’s Cropping Up? Volume 30, No. 3 – May/June 2020

The full version of What’s Cropping Up? Volume 30 No. 3 is available as a downloadable PDF on issuu. This issue includes links to COVID-19 resources on the back page. And as always, individual articles are available below:

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