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.
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 corn production: marestail, common ragweed, waterhemp, and Palmer amaranth.
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.
For states that allow Bayer training, a self-guided computer based training option will be available January 2021. Please check-in at RoundupReadyXtend.com/training for availability.
Also, live Webinars will be led by authorized trainers. Trainees MUST sign-up/pre-register to attend a live webinar.
At the Cromley Farm, U.S. Environmental Protection Agency (EPA) Administrator Andrew Wheeler announced that EPA is approving new five-year registrations for two dicamba products and extending the registration of an additional dicamba product. All three registrations include new control measures to ensure these products can be used effectively while protecting the environment, including non-target plants, animals, and other crops not tolerant to dicamba.
“With today’s decision, farmers now have the certainty they need to make plans for their 2021 growing season,” said EPA Administrator Andrew Wheeler. “After reviewing substantial amounts of new information, conducting scientific assessments based on the best available science, and carefully considering input from stakeholders we have reached a resolution that is good for our farmers and our environment.”
Through today’s action, EPA approved new registrations for two “over-the-top” (OTT) dicamba products—XtendiMax with VaporGrip Technology and Engenia Herbicide—and extended the registration for an additional OTT dicamba product, Tavium Plus VaporGrip Technology. These registrations are only for use on dicamba-tolerant (DT) cotton and soybeans and will expire in 2025, providing certainty to American agriculture for the upcoming growing season and beyond.
To manage off-site movement of dicamba, EPA’s 2020 registration features important control measures, including:
Requiring an approved pH-buffering agent (also called a Volatility Reduction Agent or VRA) be tank mixed with OTT dicamba products prior to all applications to control volatility.
Requiring a downwind buffer of 240 feet and 310 feet in areas where listed species are located.
Prohibiting OTT application of dicamba on soybeans after June 30 and cotton after July 30.
Simplifying the label and use directions so that growers can more easily determine when and how to properly apply dicamba.
The 2020 registration labels also provide new flexibilities for growers and states. For example, there are opportunities for growers to reduce the downwind spray buffer for soybeans through use of certain approved hooded sprayers as an alternative control method. EPA also recognizes and supports the important authority FIFRA section 24 gives the states for issuing locally appropriate regulations for pesticide use. If a state wishes to expand the federal OTT uses of dicamba to better meet special local needs, the agency will work with them to support their goals.
This action was informed by input from state regulators, grower groups, academic researchers, pesticide manufacturers, and others. EPA reviewed substantial amounts of new information and conducted assessments based on the best available science, including making Effect Determinations under the Endangered Species Act (ESA). With this information and input, EPA has concluded that these registration actions meet Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) registration standards. EPA believes that these new analyses address the concerns expressed in regard to EPA’s 2018 dicamba registrations in the June 2020 U.S. Court of Appeals for the Ninth Circuit. Further, EPA concluded that with the control measures now required on labels, these actions either do not affect or are not likely to adversely affect endangered or threatened species.
To view the final registration of the dicamba products, visit docket EPA-HQ-OPP-2020 0492 at www.regulations.gov.
Andrew Kness and Erika Crowl University of Maryland Extension
Drones are becoming increasingly popular in agriculture for not only imagery, but product application. As a result, startup companies offering aerial pesticide application via drone are emerging. Farmers have taken interest in the technology and service for several reasons, but the main benefit to using a drone to apply crop production products in soybean and corn is that it offers a feasible method for in-season foliar product application to fields that are smaller, fragmented, or irregularly shaped, without the potential for damaging the crop with a ground spray rig. Additionally, drones may have an advantage over helicopters or fixed-winged aircraft in small fields because they are more nimble and have the potential to achieve application to field edges that would be missed by aircraft. Finally, drones are much less intrusive to curious neighbors who often raise concerns when they see an aircraft applying products to fields.
Although drones offer a lot of potential, there is very little published data on their efficacy to apply products, which is cause for question and concern as to if drones are a viable and worthwhile means of applying products, such as pesticides, to corn and soybeans. Additionally, drones tend to lack spray tank capacity, so spray volumes with drone applications are low (1-2 gallons per acre). These low-volumes may pose challenges in achieving adequate coverage; however, products are applied at a greater concentration. This research project, funded by the Maryland Soybean Board, aims to collect data regarding drone spray efficacy in corn and soybean.
Methods
Two different drones (Figure 1) were used to apply water to standing corn and soybeans in fields located in Harford County, Maryland on August 27, 2020. Corn was planted on 30-inch rows and at the R4 growth stage during application. Full season soybeans were planted on 15-inch rows and at R6 during application.
The drones were operated by certified pilots who offer custom pesticide application in field crop and nurseries. Weather conditions were sunny and 91°F with variable winds out of the Northeast at 5 mph, gusting to 25 mph.
Prior to spraying, water-sensitive cards (Syngenta AG®, Basel, Switzerland) were placed within the crop canopy at various heights in sets of five replicates. Three heights were used for both corn (top: third leaf from tassel; middle: ear leaf; and bottom: third leaf from bottom) and soybean (top: upper most fully expanded leaf; mid: middle of canopy; and bottom; 1 foot up from soil). When water droplets hit the card, the card arrests the spread of the droplet and stains the card blue. The cards were retrieved then scanned into the computer and analyzed using the software DepositScan (USDA-ARS, Wooster, OH), which calculates percent spray coverage, droplet density, and droplet size.
Each drone applicator flew on water at approximately 4 feet above the canopy at 16 mph onto corn and soybeans at a rate of 1 gallon per acre for Drone 1 and 1.5 gallons per acre for Drone 2 using TeeJet® TXA8002VK nozzles.
Results & Discussion
Due to the extremely high humidity, close canopy, and transpiration rate of the soybean plants, the middle and bottom spray cards in the soybean plots were difficult to read. As a result, data for bottom soybean cards were omitted.
As to be expected, spray coverage was highest in the top of the canopy for both corn and soybean for both drones (Figure 2). Drone 1 achieved 1.61% and 2.40% coverage in the top canopy of corn and soybean respectively. Drone 2 also achieved greater coverage in the top canopy of soybean (1.50%) than corn (1.10%). Both drones delivered nearly identical droplet density (Figure 3) in the top canopy of both corn (18.9 drops/cm2) and soybean (22.0 drops/cm2). Droplet size (Figure 4) in the top canopy of corn for Drone 1 was 146 µm vs. 134 µm for Drone 2 and 171 µm for Drone 1 vs 148 µm for Drone 2 in soybean top canopy.
Figure 2. Average percent spray coverage for water sensitive spray cards placed in the top, middle, and bottom canopy of corn and soybean for two drones.Figure 3. Average droplet density on water sensitive spray cards placed in the top, middle, and bottom canopy of corn and soybean for two drones.
Spray coverage dropped only slightly for Drone 1 (to 1.57%) in corn from top to middle, but much more in soybean (down to 0.68%), likely due to the dense canopy. Coverage dropped to 0.42% for Drone 2 at the ear leaf in corn and down to 0.20% in the mid canopy soybean. Drone 1 achieved 21.65 drops/cm2 for the ear leaf in corn whereas Drone 2 delivered 7.00 drops/cm2. In mid canopy soybean, droplet density was similar for both drones (13.5 drops/cm2 for Drone 1 and 10.17 drops/cm2 for Drone 2). Droplet size for both drones were similar between top, middle, and bottom corn. Droplet size decreased for both drones in middle canopy soybean to 122 µm for Drone 1 and 87 µm for Drone 2.
Figure 4. Average droplet size for Drones 1 and 2 on water sensitive spray cards placed in the top, middle, and bottom canopy of corn and soybean.
Spray coverage and droplet density were similar for both drones in bottom canopy corn. Spray cards for bottom canopy soybeans were not analyzed due to artifacts created by canopy humidity.
It is generally recommended that droplet density should be between 20-30 droplets/cm2 for adequate insecticide application, between 20-40 droplets/cm2 for herbicide application, and at least 50 droplets/cm2 for fungicide applications. Based on these assumptions, both Drones have the capability to deliver densities at or over 20 droplets/cm2 in the upper canopy, which may be adequate for herbicide or insecticide applications. However, a greater density of droplets needs to be achieved for adequate fungicide application. Previous research has shown that flight velocity plays a significant role in droplet density and spray coverage (Hunter III et. al., 2020). Spraying slower would likely improve coverage and efficacy of fungicides applied via drones, which will be an area of future research for this project.
Example Spray Card Images (click to enlarge)
Acknowledgements
We would like to thank the Maryland Soybean Board for funding this research, A1-Aerials, K Drone, and Crowl Brothers, Inc. for collaborating on this research project.
Literature Cited
Hunter JE III, Gannon TW, Richardson RJ, Yelverton FH, Leon RG (2020) Coverage and drift potential associated with nozzle and speed selection for herbicide applications using an unmanned aerial sprayer. Weed Technol. 34: 235–240. doi: 10.1017/ wet.2019.101
Sarah Hirsh, Agriculture Agent University of Maryland Extension, Somerset County
Figure 1. Common ragweed in soybean field when burndown herbicide was applied April 4, April 29, and May 22. Photos taken 2 July 2019.
Figure 1. Common ragweed in soybean field when burndown herbicide was applied April 4, April 29, and May 22. Photos taken 2 July 2019.Herbicide resistant common ragweed (Ambrosia artemisiifolia L.) is prevalent on the Lower Eastern Shore. In 2019, common ragweed populations were found to have two or three-way mode-of-action resistance on the Eastern Shore, and farmers have reported that herbicide-resistant ragweed prevalence is increasing. Some populations of common ragweed on the Eastern shore are resistant to glyphosate (Roundup) (Group 9) herbicide, ALS inhibiting (e.g., FirstRate, Raptor) (Group 2) herbicide, and/or PPO inhibiting (e.g., Valor, Reflex) (Group 14) herbicide.
Common ragweed is one of the first summer annual weeds to emerge in the spring, and early-season management of common ragweed is strongly dependent upon reducing ragweed emergence and controlling ragweed populations prior to soybean planting. A research study was performed on three farms in Somerset and Worcester counties, focused on reducing ragweed emergence and early-spring growth through the combination of delaying cover crop burn-down in order to increase cover crop biomass and competition with weeds, and evaluating preemergence herbicide control. All of the on-farm trials had a wheat cover crop. We evaluated three cover crop termination dates—early April, early May, and at soybean planting. The burndown herbicides used were glyphosate + 2,4-D for the pre-planting applications and glyphosate + Liberty for the soybean planting application. Soybean was planted May 18 to June 3 at the sites.
Our results indicated that there was higher common ragweed prevalence when cover crops were terminated early April than when terminated early May or at planting (Figure 1). Growers will often apply two burndown applications of herbicide prior to planting—a first application to kill cover crops, and a second application at soybean planting. Spraying two herbicide applications prior to ragweed planting did not improve common ragweed control as compared to spraying only one herbicide application at planting time. In fact, at two of the three on-farm trials, spraying just one herbicide application at soybean planting provided even better control of ragweed than spraying two herbicide applications.
Including a residual herbicide (Linex + Dimetric) at soybean planting decreased ragweed prevalence during the growing season, as compared to applying an herbicide at planting that did not include a residual herbicide. The lowest ragweed prevalence occurred when the cover crop was sprayed with a burndown + residual herbicide only once at soybean planting time.
There is concern that allowing a cover crop to grow until soybean planting may decrease yields. We did not find soybean yields to be lower when cover crops were allowed to grow later in the spring.
We also investigated the effectiveness of residual herbicide products—Command (clomazone), Linex 4L (linuron), Dimetric (metribuzin), Command + Linex, Command + Dimetric, and Linex + Dimetric—on herbicide resistant common ragweed emergence and growth. These residual herbicides were applied at soybean planting time. The residual herbicides Command, Linex, and Dimetric and combinations of Command + Dimetric and Linex + Dimetric decreased ragweed prevalence as compared to a burndown that did not include a residual herbicide. There were no differences in soybean yield for any of the residual herbicide treatments as compared to no residual herbicide control.
Acknowledgements
This research was funded by the Maryland Soybean Board.
Kurt Vollmer, Weed Management Specialist University of Maryland Extension
Introduction
In Maryland, populations of common ragweed have developed resistance to three sites-of-action. These include Group 9 herbicides (glyphosate), Group 2 herbicides (ALS-inhibiting; Synchrony, Raptor), and Group 14 herbicides (PPO-inhibiting; Flexstar, Valor). These herbicide-resistant populations limit options for effective postemergence control. Previously glyphosate could be used to control common ragweed at various growth stages. However, herbicides that continue to provide postemergence control, such as glufosinate (Liberty) and 2,4-D (Enlist One) are less effective when common ragweed exceeds heights in excessive of 3 inches tall (Figure 1). If preemergence herbicides are ineffective and/or postemergence applications are delayed, common ragweed can quickly exceed this optimal control height. As a result, multiple post-emergence applications may be required to manage this weed.
Figure 1. Injury following an application of Enlist One applied to common ragweed 3 inches tall or greater.
Objectives
The objective of this study was to evaluate herbicide programs for the management of common ragweed 4 inches tall or greater.
Methods
The study was conducted in a grower field in Snow Hill, MD with a history of herbicide-resistant common ragweed. Enlist E3 soybeans (tolerant to 2,4-D, glyphosate, and glufosinate) were drilled in 15 inch rows on May 19, 2020 at a rate of 52 lb/A. In order to ensure a better stand of common ragweed, additional weed competition was eliminated with a broadcast treatment of glyphosate + Dual II Magnum applied on May 21. Dual II Magnum provides residual control of certain annual grasses and small seeded broadleaf weeds, but does not control common ragweed. Postemergence herbicides were applied on June 9, to 4 to 12 inch tall common ragweed, and a second postemergence application was made 17 days later on June 26. Treatments included Liberty, Enlist One, and Flexstar applied alone or in tank mixes as single or sequential herbicide applications (Table 1).
Table 1. Postemergence herbicide treatments for control of large common ragweed.
Treatment No.
Application Aa
Rate (pt/A)
Application Bb
Rate (pt/A)
1
Liberty
2.7
Liberty
2.7
2
Enlist One
2
—-
—-
3
Enlist One
2
Enlist One
2
4
Enlist One
2
Enlist One + Flexstar
2 + 1.6
5
Enlist One
2
Flexstar
1.6
6
Enlist One + Flexstar
2 + 1.6
Enlist One
2
7
Flexstar
1.6
—-
—-
8
Flexstar
1.6
Enlist One
2
a.Treatments applied June 9, 2020.
b.Treatments applied June 26, 2020.
Results
Sequential applications were needed to provide at least 95% control of common ragweed (Figure 2). On June 17, prior to the second postemergence application, control of common ragweed with Liberty was less than 70%, and control with Enlist One averaged 56%. On July 22, sequential treatments of Liberty, Enlist, and Flexstar controlled common ragweed better than Enlist One applied once.
Figure 2. Common ragweed control with postemergence herbicide treatments in 2020.a a. Ratings for June 17 are the result of application A. Ratings for June 22 are the result of application A + application B. Treatments not followed by (fb) a second treatment were applied once, on June 17.
Summary
These results emphasize the importance of timely postemergence herbicide applications in controlling common ragweed. Delaying applications increases the likelihood that common ragweed will not be controlled with a single application, and sequential applications will be needed to manage this species effectively. However, additional research is needed to confirm these results and help identify consistent treatments.
In addition, herbicide-tolerant soybeans were needed in order to apply Enlist One and Liberty. Historically, Group 2 herbicides, such as Raptor, and Group 14 herbicides, such as Reflex, have been used to control common ragweed in non-herbicide tolerant soybeans. In this study, Flexstar alone provided good control early on, but common ragweed control declined within a month after application (Figures 2 and 3). Furthermore, in Maryland, Flexstar applications can only be made once every other year, and would not be suitable if sequential applications are required. In order to manage these populations, conventional soybean growers will likely have to adopt or continue to use soybeans tolerant to 2,4-D and/or glufosinate. Several soybean varieties are available that contain tolerance multiple herbicide groups. These not only offer more flexibility for postemergence herbicide programs, but also offer the option of tank-mixing different herbicide groups for improved control. Further research is needed on how this approach can improve control of common ragweed and mitigate further herbicide resistance development.
Figure 3. Injury following an application of Flexstar applied to common ragweed 3 inches tall or greater.
Acknowledgements
This research was funded by the Maryland Soybean Board.
Amy Brown, Professor Emerita, Pesticide Education Coordinator University of Maryland, College Park
EPA is taking the next step in its regulatory review of paraquat dichloride (paraquat), a widely-used herbicide. As outlined in the proposed interim decision for paraquat, the agency is proposing new measures to reduce risks associated with paraquat in order to better to protect human health and the environment. These measures include:
Prohibiting aerial application for all uses and use sites except cotton
desiccation;
Prohibiting pressurized handgun and backpack sprayer application methods
on the label;
Limiting the maximum application rate for alfalfa to one pound of active
ingredient per acre;
Requiring enclosed cabs if area treated in 24-hour period is more than 80
acres;
Requiring enclosed cabs or PF10 respirators if area treated in 24-hour
period is 80 acres or less;
Requiring a residential area drift buffer and 7-day restricted entry
interval (REI) for cotton desiccation;
Requiring a 48-hour REI for all crops and uses except cotton desiccation;
and
In addition, EPA is proposing to allow truck drivers who are not certified applicators to transport paraquat when certain conditions are met. Upon publication of the Federal Register notice, public comments will be accepted for 60 days in docket # EPA-HQ-OPP-2011-0855 until December 22, 2020 at www.regulations.gov.
