Palmer Amaranth (Pigweed) Herbicide Program Suggestions (In Roundup Ready Cotton Only)

The following was sent to us by Scott Brown, Colquitt County, Georgia, Extension Agent

It is not a question of if you will have glyphosate resistant Palmer amaranth in your fields but when. It is going to happen to you sooner or later, so be prepared. Also remember that we have many fields with ALS inhibitor resistant Palmer amaranth in them so precautions should be taken. Use the best yellow and at-plant residual program for your situation.

First Law of Cotton Weed Control: Use a yellow herbicide (Prowl, Treflan or generic equivalent) on every acre.

Second Law of Cotton Weed Control: When in doubt about using a yellow herbicide in cotton refer to First Law of Cotton Weed Control.

RESIDUAL AT-PLANT HERBICIDES: Due to the resistance issue a preemergence at-plant herbicide such as Valor, Reflex, fluometuron (Cotoran), diuron (Direx), or Staple (in some fields) is strongly recommended. Where possible you should irrigate to activate pre-emergence herbicides, if no rain within 5-7 days after planting. Unless you plan to cultivate all residual at-plant herbicides should be broadcast.

Reflex (applied at planting) and Valor (applied preplant) are used interchangeably depending on crop rotation. It is our opinion that only one of these products should be used on the same acreage per crop year. The label does not prohibit the use of both sequentially on the same cropping system but is a UGA recommendation to help prevent PPO resistance development.

Reflex should not be used where sensitive vegetables or other crops will be rotated behind treated cotton (especially brassicas such as: cabbage, collards, turnips, etc). Valor has a short rotational restriction for most crops. Valor can only be used prior to planting: conventionally planted cotton (beds already knocked off) 30 days and a 1 inch rain event; no-till planted cotton 21 days and a 1 inch rain event; strip-till cotton 14 days regardless of rain event). Valent recommends that Valor should always be followed by a preemregence herbicide (Prowl, diuron, cotoran, Staple) at planting. Please check the label. WHEN USING VALOR PLEASE FOLLOW THE VALENT VALOR TANK CLEANOUT PROCEDURE.

Note about STAPLE use: It is our opinion that Staple post plant treatments should not be made if a Staple at plant treatment was applied (Situation 3 below). The label does not prohibit the use of sequential treatments in the same cropping system; this is a UGA suggestion to help prevent ALS inhibitor resistance development.

SITUATION 1.) Fields with major glyphosate resistant Palmer amaranth problems but no ALS inhibitor resistance (if Valor (2 oz/A) is substituted for Reflex then it must be applied at least 14-30 days prior to planting, dependent on cropping system, as outlined above):

Step 1.) Yellow herbicide (use full label rate) PPI or at planting.

Step 2.) Reflex (12-16 oz/A) + diuron (Direx) 4L (16 oz/A) at-plant. Note: Staple at 1.7-2.1 oz/A can be substituted for diuron (Direx) at planting but this eliminates the over-the-top glyphosate + Staple option in Step 3.

Step 3.) Glyphosate (label rate) + Dual Magnum (16-21 oz/A) at 4 leaf stage if no Palmer is emerged. If Palmer is emerged then glyphosate (label rate) + Staple (2.6-3.8 oz/A).

Step 4.) MSMA (32-42 oz/A) + diuron 4L (32 oz/A) + crop oil concentrate. Note: Layby Pro or Suprend may be substituted for diuron. Check label for rates.

NOTE: If Palmer escapes occur earlier than 4 leaf then apply Staple over-the-top beginning at the 2 leaf stage of the crop but before pigweeds are 2 inches tall. This would be between Steps 1 and 2. Do not mix Staple with Dual (or any metolachlor product) or apply within 3+ days either way of a Dual application. Valor is labeled to be used at layby but it is our suggestion to not do so if Reflex was used at planting.

SITUATION 2.) Fields with major glyphosate and ALS inhibitor resistant Palmer amaranth problems:

Same as Situation 1.) but Staple is not an option in Step 2 or Step 3.

SITUATION 3.) Fields with heavy Palmer Amaranth populations but sensitive to glyphosate and ALS inhibitors (if Valor (2 oz/A) is substituted for Reflex then it must be applied at least 14-30 days prior to planting, dependent on cropping system, as outlined above):

Step 1.) Yellow herbicide (use full label rate) PPI or at planting.

Step 2.) Reflex (12-16 oz/A) or diuron (Direx) 4L (16-32 oz/A*) or Cotoran (2-3 pts/A) or Staple at 1.7-2.1 oz/A. If Staple is used at plant then it should not be used in Step 3 or for early escapes.

Step 3.) Glyphosate (label rate) + Dual Magnum (16-21 oz/A) at 4 leaf stage if no Palmer is emerged. If Palmer is emerged then glyphosate (label rate) + Staple (2.6-3.8 oz/A).

Step 4.) MSMA (32-42 oz/A) + diuron 4L (24-32 oz/A*) + crop oil concentrate. Note: Layby Pro or Suprend may be substituted for diuron. Check label for rates.

NOTE: If Palmer escapes occur earlier than 4 leaf then apply Staple over-the-top begining at the 2 leaf stage of the crop but before pigweeds are 2 inches tall. This would be between Steps 1 and 2. Do no mix Staple with Dual (or any metolachlor product) or apply within 3+ days either way of a Dual application.

 *To avoid potential rotational issues do not exceed 3 total pints of diuron (Direx) as a pre and post treatment per year. Further, diuron is potentially more injurious to cotton seedlings at higher rates than Cotoran. On lighter soils lower use rates of diuron should be considered. Diuron should not be used on very sandy soils due to potential injury.

SITUATION 4.) Fields with low-moderate glyphosate and ALS inhibitor sensitive Palmer amaranth problems:

Step 1.) Yellow herbicide (use full label rate) PPI or at planting.

Step 2.) Diuron (Direx) 4L (16-32 oz/A*) or Cotoran (2-3 pts/A) or Staple at 1.7-2.1 oz/A. If Staple is used at plant then it should not be used in Step 3 or for early escapes.

Step 3.) Glyphosate as needed.

Step 4.) MSMA (32-42 oz/A) + diuron 4L (24-32 oz/A*) + crop oil concentrate. Note: Layby Pro or Suprend may be substituted for diuron. Check label for rates. Can layby with Valor, since no Reflex was used.

NOTE: If Palmer escapes occur early then apply Staple over the top beginning at 2 leaf stage of crop but before pigweeds are 2 inches tall. This would be between Steps 1 and 2. Do no mix Staple with Dual (or any metolachlor product) or apply within 3+ days either way of a Dual application.

*To avoid potential rotational issues do not exceed 3 total pints of diuron (Direx) as a pre and post treatment per year. Further, diuron is potentially more injurious to cotton seedlings at higher rates than Cotoran. On lighter soils lower use rates of diuron should be considered. Diuron should not be used on very sandy soils due to potential injury.