Roundup Resistant Weeds: A Battle Plan For 2010

Dr. Ken Smith, extension weed scientist for the University of Arkansas Division of Agriculture, is dead serious about the subject of herbicide resistant weeds, especially the obnoxious pigweed. He wants to see the seed dead before it even has a chance to germinate.

In Pigweed: Kill the Seed, Beat the Weed Smith makes these points:

• Pigweed seed has a fairly short life in the soil.
• Deep tillage is a promising tactic that exploits pigweed’s weakness.
• Burndown does NOT destroy pigweed seed, and it may actually stimulate germination by creating light.
• "Zero tolerance" combines hand hoeing and supplemental herbicide application, a method that may ensure pigweed doesn’t reach maturity and produce seed.

- Debra Ferguson

Purging Valor from herbicide spraying tanks and systems

Valor has emerged as an important herbicide tool where farmers are either trying to prevent Roundup resistant weed development or are coping with this serious problem.

The downside to Valor is that even faint traces of it carried over in later sprays can harm other crops.

Valent, the herbicide's manufacturer, has issued an updated list of recommendations for farmers or applicators who need to purge Valor residue from spray equipment.

Here's the link.

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.

How Fast Can Roundup-Resistant Palmer Pigweed Build? Read This.

Leaving just 5 Roundup-resistant female Palmer pigweed plants per acre - even with 99.9% control the next year - leads to 400 per acre the next year. With similar control, by the third year you’ll have 32,000 female plants producing resistant offspring. See last week's Seminole Co., Ga., E-letter for more info on seed bank concept.

- Owen Taylor

Burndown Herbicide Options For Cotton And Soybeans In 2010

From Donnie Miller, Daniel Stephenson, and Bill Williams, Louisiana State University Weed Scientists

An extremely positive attribute to the herbicides glyphosate and glufosinate, used in a Roundup Ready or Liberty Link weed control system, respectively, is that both can exhibit excellent activity on weed species larger in size than what is recommended for optimum activity on individual labels.

Unfortunately, this can also be an extremely negative attribute to each herbicide.

Delaying herbicide application for the sake of having a greater population present to get more “bang for the buck” with a single application can allow weeds to compete with emerging crops. Early season weed competition in both soybean and cotton can result in reduced yield with little impact often observable prior to harvest. In addition, application to larger weeds can result in reduced control of less-sensitive species with glufosinate (pigweed, goosegrass, and broadleaf signalgrass) and glyphosate (morningglory species, hemp sesbania, and prickly sida).

This in turn can lead to increased weed seed-bank populations in the soil due to continued seed production and negate long term weed management efforts.

Although weed resistance to glyphosate has not been scientifically documented in Louisiana to date, the fact is that various weed populations have proven difficult to control with the herbicide in some cases (amaranths, ragweed, and Johnsongrass).

This “practical” resistance is becoming a larger issue and although attributable to spraying weeds that are too large in some instances, a “red flag” should go up whenever control failures exist. Resistance issues in other states have led to increases in herbicide management costs of 40 to 50$/A with additional herbicides needed or complete field abandonment. The economic impact of weed resistance is also realized in decreased value of the transgenic technology, as weeds previously controlled in the system become less and less susceptible, and potential decreased land rent value.

Use of residual herbicides in today’s transgenic world of soybean and cotton production can result in positive benefits including reduced early-season weed competition through prevention of weed germination in early crop development stages and weed resistance management through introduction of alternative modes of action to glyphosate or glufosinate.

To achieve maximum activity from residual herbicides, proper activation of the material must occur. Activation is placement of the herbicide in the soil region that maximizes opportunity for herbicide uptake by the emerging weed seedling. Herbicide activation is accomplished through rainfall/irrigation or mechanical incorporation. Most labels will call for a rainfall or irrigation amount of 0.5 inches or greater, preferably in one event. Mechanical uniform incorporation of the herbicide in the top 2 to 3 inches will adequately activate most herbicides. The majority of herbicides soil applied at planting will require mechanical uniform incorporation preferably within 7 to 10 days after application if rainfall is not received.

Below is a brief discussion of some of the relatively newer compounds available for preplant use in soybean in 2010, a number of which have been evaluated by LSU AgCenter Weed Scientists.  Please refer to individual herbicide labels for plant-back intervals, precautions/restrictions, soil type and rates, and special requirements/uses (ie reduced rate application in planned PRE/POST programs, incorporation instructions, activation requirements, notes for maximum control of selective species etc.). Herbicide labels can be accessed at the following website: http://www.cdms.net/LabelsMsds/LMDefault.aspx?srchPdt%20=%20&t. A table summarizing replant intervals to field corn, cotton, grain sorghum, soybean, and wheat following application of most pre-plant herbicides also follows.

Newer Herbicides for 2010

Authority First (soybean): Authority First combines the active ingredient sulfentrazone (Spartan herbicide) and cloransulam-methyl (FirstRate herbicide). This product is labeled for control of pigweed (Amaranths), morningglory (suppression on pitted), prickly sida (teaweed), groundcherry, hophornbeam copperleaf, smellmellon, yellow and purple nutsedge, and annual sedge. It provides suppression of most annual grasses. The use rates range from 6.45 oz/A (soils 3% organic matter or less) to 8 oz/A (soils greater than 3% organic matter). Do not apply to soils classified as sands with organic matter less than 1%.

Authority MTZ (soybean): Authority MTZ combines the active ingredient sulfentrazone (Spartan herbicide) and metribuzin (Sencor or Lexone herbicide). This product expressed good activity on pigweed (Amaranths), morningglory, prickly sida (teaweed), groundcherry, hophornbeam copperleaf, smellmellon, yellow and purple nutsedge, and annual sedge. It provides suppression of most annual grasses. The use rates range from 12 to 20 oz/A depending on soil type (see label). On soils with Ph greater than 7.5, use rate should not exceed 12 oz/A. Research has shown excellent activity at the rate of 14 ounces product per acre, which provides an equivalent rate of 5 oz/A metribuzin. The herbicide label should be consulted for listing of metribuzin-sensitive soybean varieties.

Axiom DF (soybean): Axiom DF combines the active ingredient flufenacet and metribuzin (Sencor or Lexone herbicide). The herbicide controls barnyardgrass, crabgrass, foxtail species, goosegrass, and fall panicum. Will provide suppression of seedling johnsongrass, broadleaf signalgrass, pigweed species, prickly sida, Pennsylvania smartweed, and waterhemp. Use rate range is 7 to 13 oz/A. The herbicide label should be consulted for listing of metribuzin-sensitive soybean varieties. 

Envive (soybean): Envive combines the active ingredients of chlorimuron ethyl (Classic herbicide), thifensulfuron methyl (Harmony GT herbicide), and flumioxazin (Valor herbicide) in one pre-mix product. Envive offers the advantage of two independent modes of action, which can aid in weed resistance management.  This product expresses strong efficacy on pigweed, morningglory, sicklepod, prickly sida (teaweed), smartweed, and hophornbeam copperleaf while suppressing annual grasses. Use rates range from 2.5 to 5.3 oz/A. It can be applied up to three days after planting. In non-STS or RR/STS soybean, do not apply within 14 days before or after application of an organophosphate insecticide. Higher rates of Envive may “carry over” when applied to soils with a pH of 7.5 or greater and injure crops planted the following year due to the Classic portion of the herbicide. If a producer wishes to apply Envive on a high pH soil, then Enlite at 2.8 oz/A may be an option. Enlite combines the same active ingredients as Envive except the Classic portion is less. Enlite provides similar performance against the weed spectrum previously listed for Envive.

Gangster (soybean): Gangster is a multi-pack combination of the active ingredients flumioxazin (Valor SX) and cloransulam methyl (FirstRate). Labeled for control of morningglory species, pigweed species, Palmer amaranth, prickly sida, smartweed, copperleaf, and wild poinsettia. Suppression of barnyardgrass, large crabgrass, giant foxtail, goosegrass, panicum, and broadleaf signalgrass can be expected. Use rates range from 3 to 3.6 oz/A. The 3 oz/A rate is equivalent to applying 2.5 oz/A Valor SX and 0.5 oz/A FirstRate.   

Prefix (soybean): Prefix combines the active ingredient s-metolachlor (Dual Magnum) and Reflex (fomesafen). Provides control of barnyardgrass, crabgrass, foxtail species, goosegrass, seedling johnsongrass, pigweed species, wild poinsettia, and smartweed species. It provides partial control of morningglory species, yellow nutsedge, and prickly sida (teaweed). Use rates range from 2 to 3 pt/A depending on soil type.

Sharpen (soybean): Sharpen contains the active ingredient saflufenacil. This product shows good activity on pigweed species, morningglory species, Palmer amaranth, waterhemp, and prickly sida (teaweed). Use rate is 1 oz/A.

Valor XLT (soybean): Valor XLT combines the active ingredients flumioxazin (Valor SX) and chlorimuron ethyl (Classic). Weeds controlled with this herbicide include copperleaf, prickly sida, pigweed species, morninglory species, palmer amaranth, smartweed, and wild poinsettia. Suppression of barnyardgrass, large crabgrass, broadleaf signalgrass, goosegrass, and panicums can be expected. Use rate ranges from 3 to 5 oz/A.


Plantback intervals for at-planting soil applied herbicides in soybean and cotton

Herbicide	Corn	Cotton	Grain Sorghum	Soybean	Wheat
Authority First	10 mo1	18 mo	12 mo	0	4 mo
Authority MTZ DF	10 mo, 4 mo2	12 mo	18 mo, 12 mo2	0	4 mo
Axiom DF	0	8 mo	12 mo	0	4 mo
Boundary 6.5 EC	8 mo	8 mo	12 mo	0	4.5 mo
Canopy3	9/10 mo, 18 mo	10 mo,18 mo	10 mo, 18 mo	0	4 mo
Command 3 ME	9 mo	04, 9 mo	9 mo	0	12 mo
Cotoran 4L/Fluometuron	8 mo	0	9 mo	9 mo	3 mo
Enlite	9 mo	9 mo	9 mo	0	4 mo
Envive5	10 mo, 18 mo	10 mo, 30 mo	10 mo, 18 mo	0	4 mo
FirstRate	9 mo	9 mo	9 mo	0	3 mo
Fomesafen6	See label	0	10 mo	0	4 mo
Gangster	9 mo	9 mo	9 mo	0	3 mo
Lorox DF/Lorox L	0	4 mo	0	0	4 mo
Microtech	0	0	0 (treated seed)	0	See label
metolachlor/s-metolachlor7	0	0	0	0	4.5 mo
Outlook	0	Next spring	0	0	4 mo
Pendimethalin8	0	0	Next year	0	4 mo
Prefix	10 mo	1 mo	10 mo	0	4.5 mo
Pursuit/Pursuit Plus	8.5 mo	18 mo	18 mo	0	4 mo
Scepter	9.5 mo	18 mo	11 mo	0	3 mo
Sharpen	0	See label	See label	See label	See label
Spartan 4F	10 mo	12 mo	10 mo9	0	4 mo
Staple LX/Pyrimax 3.2 L	9 mo, 10 mo10	0	Not next season	10	4 mo
Synchrony XP11	7 mo	8 mo	9 mo	0	3 mo
Trifluralin12	12 mo	0	12 mo	0	4 mo
Valor13	1 mo	1 mo	1 mo	0	1 mo
Valor XLT5	10 mo, 18 mo	10 mo, 30 mo	10 mo, 18 mo	0	4 mo

¹18 month replant interval if 6.45 to 8 oz/A was applied to soils with organic matter 1.5% or less and pH > 7.
² Field corn can be planted 4 months after application at 14 oz/A or less. Grain sorghum can be planted 12 months after application at 20 oz/A or less.
³18 month replant interval for rate greater than 3.5 oz/A and pH > 7. Field corn can be replanted in 9 months given Canopy rate does not exceed 6 oz/A.
⁴Refer to label for Requirements for Planting Time section.
⁵Longer replant intervals must be observed for soil pH 7 or greater.
⁶ Fomesafen is the active ingredient in herbicides such as Dawn, Reflex, and Rhythm.
⁷Metolachlor or s-metolachlor (see specific label for active ingredient contained) is the active ingredient in herbicides such as Dual Magnum, Cinch, Me-too-lachlor, Stalwart, Parrlay, Parallel, and similar commercially available herbicides.
⁸Pendimethalin is the active ingredient in herbicides such as Prowl 3.3 EC, Prowl H₂O, Pendimax 3.3 and similar commercially available herbicides.
⁹18 month replant interval for rates above 8 oz/A.
¹⁰If applied on a band (not exceeding 50% row width) and thorough soil mixing occurs, a 9 month replant interval must be observed. If rate does not exceed 3.8 oz/A total broadcast, a 10 month interval should be observed without additional soil mixing beyond normal in your particular production system.
¹¹See label for additional replant notes.
¹²Trifluralin is the active ingredient in herbicides such as Treflan HFP and Trifluralin 4 EC and similar commercially available herbicides.
¹³One inch rainfall must be received in addition to replant interval. Intervals are for rates of 2 oz/A or less.