Roundup-Resistant Pigweed Management Plan For 2011 From Georgia

R.J. Byrne, Extension Agent in Thomas County, Georgia, has produced a short video (see below) about Georgia's approach for controlling Roundup-resistant Palmer pigweed in cotton. In the video, Byrne interviews Stanley Culpepper, Georgia Extension Weed Scientist.

Here's a supplemental handout that goes into more detail about herbicides, rates and other factors touched on during the video.

Arkansas Resistant Palmer Pigweed Field Day Video From Arkansas

Arkansas Soybean Verification Coordinator, Chris Grimes, discusses this year's experience with trying to control herbicide resistant pigweed in soybean after rain kept researchers from making a much-needed Valor herbicide application.

Louisiana Confirms First Case Of Roundup-Resistant Palmer Pigweed, Water Hemp Issue Also Suspected

Roundup-resistant Palmer pigweed (aka Palmer amaranth) has been confirmed for the first time in Louisiana, according to a memo from Daniel Stephenson, LSU AgCenter Weed Scientist.

The memo was included Sunday morning, September 5, in AMS AG REPORT, the weekly newsletter published by consultant Roger Carter with Agricultural Management Services, Inc., a firm that covers several parishes in east-central Louisiana.

Carter said that Tim White, a consultant in the firm, "has worked on this farm with Dr. Stephenson for several years trying to manage this weed. This particular farm is near Lake St. John."

Stephenson noted in the memo that Roundup-resistant Palmer pigweed already had been confirmed in Alabama, Arkansas, Georgia, Mississippi, Tennessee and several other other states.

Stephenson reported that he had now "confirmed that Palmer amaranth collected from a cotton field in Concordia Parish is resistant to glyphosate."

According to his analysis, 50% of the Concordia Parish population "is approximately 54 times less sensitive to glyphosate compared to the susceptible standard. In other words, if the labeled use rate of glyphosate is 32 fluid ounces/Acre, a producer will have to apply 118 oz/Acre of glyphosate to control 50% of the Palmer population or 723 oz/A to control 90% of the population.”

In a followup memo Sunday afternoon, Stephenson noted that other cases of hard-to-control pigweed were being investigated.

"Unfortunately, LSU AgCenter weed scientists are following up on many other locations throughout Louisiana where Palmer amaranth or waterhemp, another Amaranthus species, have not been effectively controlled by glyphosate," he noted. "Any producer or consultant in Louisiana should be aware of the potentially devastating effect herbicide-resistant weeds can have on their crop. If you suspect that a weed population is resistant to a herbicide (not just glyphosate, ANY herbicide), please contact your local LSU AgCenter county agent.

"AgCenter personnel need to know of these issues so we can help you avoid or mitigate weeds resistance from spreading throughout Louisiana."

- Owen Taylor

Roundup-Resistant Pigweed Getting Away From Tennesse Farmers. Control Options Aren't Promising.

The following is from Larry Steckel, Tennessee Extension Weed Specialist, who this week addressed the fact that wet weather in the upper Delta has caused a huge - read that, expensive - problem with Roundup-resistant Palmer pigweed. He offers options, none of which seem all that promising, considering the way this weed operates in its Roundup-resistant form - Owen Taylor

Roundup-resistant Palmer pigweed is geting away from us fast.

Due to all this wet weather,  the pre applied herbicides are giving out quickly. Moreover, it has often been too wet to spray post emergence as timely as we need to.

This is shaping up into a perfect storm.

I received the first calls of the year on Palmer pigweed issues in soybeans and cotton. One consultant called and said that Prefix applied last week had not controlled 4-inch-tall Palmer.

This is not surprising. A 4-inch-tall gramoxone-resistant (GR) Palmer pigweed (amaranth) is getting too large for any PPO herbicide to control. Ignite at higher rates (32 to 40 oz/A) can control Palmer up to about 6 inches, though this can be inconsistent at times.

The unfortunate truth is that if Roundup/glyphosate is unable to control tall Palmer amaranth due to resistance there is no herbicide that will.

This coupled with the fact that a 2-inch Palmer amaranth can quickly become an 8-inch Palmer amaranth even with 44 ozs/A of Roundup PowerMax on it (as seen in last year’s picture at right) leaves us very few days to get these post herbicides applied.

Other reports have come in on RR Flex Cotton where the management plan was to use overlapping residual herbicides. The problem being that it was too wet to get the second overlapping residual on and now there is a heavy flush of Palmer pigweed in a good cotton stand.

There are not any real good options for fields in this shape with resistant Palmer pigweed. It is still early enough to replant soybeans and if we can get in next week cotton, as well. Depending upon the density of the GR Palmer this would probably be the best option.

The number one question of the week is from folks wanting to spray Ignite on cotyledon WideStrike cotton. The first Palmer pigweed flush is right with cotton emergence in a number of fields. In other cotton fields we are seeing some late regrowth of horseweed.

The main question is how safe is it to spray cotyledon WideStrike cotton with Ignite to control these weeds?

The answer from research we have conducted here as well as some from Georgia is that cotyledon WideStrike cotton tolerates Ignite a little better than 5-leaf cotton. My observations from this work have been that the waxy cotyledons do not seem to show effects from Ignite like a true cotton leaf will. In general we will see about 10% injury on cotyledon WideStrike cotton and typically 15 to 20% injury on more mature cotton.

What about tank-mixing Dual Magnum with my Ignite on WideStrike cotton?

My answer is in areas where GR Palmer amaranth is already established the benefits outweigh the risk. We have conducted several trials with this tankmix (I would like to run several more) and seen anywhere from 0 to 5% more injury compared to Ignite alone. If the Dual Magnum gets activated this may save one or even two over the top Ignite applications to the cotton.

What about tank-mixing Prowl H2O with Ignite on WideStrike cotton?

I have not looked at this tankmix on WideStrike cotton. I have seen it on one trial several years back in Liberty Link cotton. I did not like the results. We saw antagonism on the Palmer amaranth control compared to Ignite alone or Ignite tankmixed with Dual Magnum.

Moreover, the injury to the LL cotton from the Ignite tankmixed with Prowl H2O appeared to be more than I saw with the Dual Magnum tankmix. This is only one trial, but it suggested to me that we need more research on it before we recommend Ignite tank mixtures with Prowl H2O on LL cotton as well as WideStrike cotton.

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.