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Publication #SS-AGR-338

Control of Palmer Amaranth in Agronomic Crops1

J. Ferrell and R. Leon2

Palmer amaranth continues to increase in severity across the crop production regions of the Southeast. Though all populations of this weed are not resistant to commonly used herbicides, some populations are. Since resistant pollen and seed move so easily by wind and farm machinery, it is important to consider all Palmer amaranth populations to be resistant until proven otherwise. Below are some Palmer amaranth control programs for corn, cotton, peanut, and soybeans that can effectively manage this weedy pest. But regardless of which system is adopted for Palmer amaranth management, a "program" approach is essential to success. This means that simply adopting Liberty Link technology, for example, is not sufficient by itself. The technology must be used in combination with a well-planned burndown, preemergence, postemergence, and layby program. Additionally, it is important to time postemergence applications to small (1–3 inch) weeds. Targeting large weeds, regardless of herbicide resistance, can easily lead to lack of control and lost crop productivity.

Corn

Although some atrazine-resistant populations have been found, it is our understanding that atrazine resistance is not as widespread as ALS (acetolactate synthase inhibitor; Cadre, Staple, Pursuit, etc.) or glyphosate resistance. Therefore, atrazine is the key component to a Palmer amaranth control strategy. Atrazine can be applied at a maximum rate of 2.5 lb ai/A/yr if applied at two timings. No single application of atrazine can exceed 2 lb ai/A. See Tables 1 and 2 for more information.

Cotton

A cotton program should start with a good preplant program that includes Valor, Reflex, Direx, or Banvel/Clarity. These herbicides should provide up to 15–30 days of effective control but should still be followed by Prowl, Staple, Cotoran, or Direx at planting. Additionally, Direx + MSMA or Valor + MSMA should be used at layby to effectively control Palmer amaranth with both postemergence and soil residual activity. It must be noted that all preemergence herbicides require activation by either rainfall or irrigation. If these materials are applied and activation does not occur, no control will be realized—particularly if these herbicides were initially applied to dry soil. See Table 3 for more information.

Salvage Treatments. If Palmer amaranth has reached heights of 6" or greater, it is not likely that any postemergence herbicide option (Staple or Liberty 280) will be effective. Depending on cotton size, a directed application may also fail to be effective. If this is the case, a hooded application may be necessary. See Table 4 for more information.

Peanut

The burndown program should contain 2,4-D to ensure that no Palmer amaranth has emerged prior to planting. Additionally, planting in twin rows will shade the soil earlier than wide rows, helping to suppress Palmer amaranth germination. Applying Prowl or Sonalan will have some, but not great, impact on Palmer amaranth control. But incorporating these herbicides with tillage will provide more control than when applications are made to the soil surface. See Table 5 for more information.

If herbicide failure occurs, a wick-bar application of paraquat can be used. This application will be most effective if a 50% herbicide solution is used and if at least 50% of the plant is wiped. Additionally, roller-type applicators are generally more effective than gravity-fed applicators. Increased roller speed generally translates to greater weed control and increased crop injury. A significant amount of time will likely be required to adjust the implement so peak performance can be achieved.

Soybean

If possible, soybeans should be planted in narrow rows (15 to 7.5 inches). Narrow row spacing allows shading of the soil surface to occur faster and helps prevent Palmer amaranth seed germination. Although Valor is labeled for use in soybeans, it is suggested that a metribuzin-containing product be used. This will allow other chemistry to be rotated into your production system (for resistance management) and will preserve Valor for cotton and peanut production. See Table 6 for more information.

There are many ways to manage herbicide-resistant Palmer amaranth and what we have provided in this publication is not an exhaustive list of all possible programs. However, the key to being successful with Palmer amaranth is to develop a diverse program approach. It may be necessary to attempt conventional tillage with herbicide incorporation on one site or rotate into corn on another. But having a plan prior to planting that incorporates many herbicides or other techniques to control Palmer amaranth will give the crop producer the best opportunity to maximize production and minimize Palmer amaranth interference.

Tables

Table 1. 

Palmer amaranth control programs for corn.

Corn Type

Preemergence

Early Postemergence

Late Post (if needed)

Conventional

Atrazine

or

Atrazine + Outlook or Dual II Magnum

Atrazine + Prowl

or

Atrazine + Laudis, Callisto, Aim, Status, or 2,4-D

2,4-D or Banvel/Clarity -directed, or Status over-the-top

Roundup Ready

Atrazine

or

Atrazine + Outlook or Dual II Magnum

Glyphosate + Atrazine, Dual II Magnum, Status, Laudis, Callisto, or Aim

2,4-D or Banvel/Clarity -directed, or Status over-the-top

Liberty Link

Atrazine

or

Atrazine + Outlook or Dual II Magnum

Liberty 280 + Atrazine

2,4-D or Banvel/Clarity -directed, or Status over-the-top

Table 2. 

Plant back restrictions in Palmer amaranth control programs for corn.

 

Sorghum

Millet

Small Grains

Cotton

Peanut

 

Months

Laudis

10

18

4

10

18

Callisto

0

0*

4

10

10

Aim

0

0

0

0

0

Status

1

4

1

1

4

*Pearl millet only.

Table 3. 

Palmer amaranth control programs for cotton.

Cotton Type

Preplant/PPI*

At Planting

Early Postemergence

Layby

Roundup Ready

Valor or Reflex (Preplant)

Prowl + Staple or Direx

Glyphosate + Dual Magnum

(if seedlings have not emerged)

Direx + MSMA

Banvel/Clarity or Direx (Preplant)

Cotoran or Reflex + Prowl

Glyphosate + Staple + Dual Magnum (Dual should not be applied with glyphosate + Staple. Dual should be applied 5 days or more before or after the glyphosate + Staple.)

Valor † + MSMA

Treflan or Prowl PPI

Cotoran or Reflex + Staple

Glyphosate + Dual Magnum (if seedlings have not emerged.)

Valor + MSMA

Liberty Link

Valor or Reflex (Preplant)

Prowl + Staple or Direx

Liberty 280 +

Dual Magnum

(Ignite will control emerged seedlings.)

Direx + MSMA

Banvel/Clarity or Direx (Preplant)

Cotoran + Prowl

Liberty 280 +

Dual Magnum

(Ignite will control emerged seedlings.)

Valor + MSMA

Treflan or Prowl PPI

Cotoran + Staple

Liberty 280 +

Dual Magnum

(Ignite will control emerged seedlings.)

Valor + MSMA

*Preplant incorporated.

†In the interest of resistance management, if Valor or Reflex is applied near planting, it is not recommended to use Valor at layby. Likewise, Direx should not be used on the same acre twice in the same growing season.

Table 4. 

Hooded applications in Palmer amaranth control programs for cotton.

Cotton

Hooded application

Any cultivar

Paraquat

Paraquat + Caparol

Table 5. 

Palmer amaranth control programs for peanut.

Peanut

Incorporated

Preemergence

Early Postemergence

Layby

Any cultivar

Prowl or Sonalan

Valor

Paraquat + Dual Magnum ± Basagran

Cobra + crop oil or Cadre + 2,4-DB

 

Valor + Prowl

Paraquat + Dual Magnum ± Basagran

Cobra + crop oil or Cadre + 2,4-DB

Table 6. 

Palmer amaranth control programs for soybean.

Soybean Type

Preplant/PPI

Preemergence**

Postemergence

Roundup Ready

2,4-D

(Preplant)

Prowl or Dual Magnum + TriCor, Canopy, Authority MTZ, Boundary

Glyphosate + Reflex, Cobra, Ultra Blazer, or Pursuit

2,4-D (Preplant)

+

Prowl or Treflan

(PPI)

TriCor, Canopy, Authority MTZ, Boundary

Glyphosate + Reflex, Cobra, Ultra Blazer, or Pursuit

2,4-D (Preplant)

+

Prowl or Treflan

(PPI)

Valor or Sulfentrazone (Spartan, others)

Dual Magnum +Reflex, Cobra, Ultra Blazer, or Pursuit

Liberty Link

2,4-D

(Preplant)

Prowl or Dual Magnum + TriCor, Canopy, Authority MTZ

Liberty 280

2,4-D (Preplant)

+

Prowl or Treflan

(PPI)

TriCor, Canopy, Authority MTZ, Boundary

Liberty 280 ± Dual Magnum

2,4-D (Preplant)

+

Prowl or Treflan

(PPI)

Valor or Sulfentrazone (Spartan, others)

Liberty 280 ± Dual Magnum

** All metribuzin-containing herbicides (TriCor, Canopy, Authority MTZ, Boundary, etc) have restrictions for use based on soil texture and organic matter content. Before using a metribuzin product, make sure you read the product label and follow the directions. If not, unacceptable soybean injury could result.

Footnotes

1.

This document is SS-AGR-338, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date December 2010. Revised March 2013. Reviewed April 2016. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

J. Ferrell, associate professor, Agronomy Department; and R. Leon, assistant professor, Agronomy Department, UF/IFAS West Florida Research and Education Center, Milton, FL.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label. Use herbicides safely. Read and follow directions on the manufacturer's label.


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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.