Roundup-Resistant Pigweed And Johnsongrass Now A Reality In Louisiana

Until just the last year or so, Louisiana has mostly dodged the bullet when it came to Roundup-resistant weeds, especially two severe problems: resistant pigweed and resistant johnsongrass.

But events caught up with the state, and Louisiana State University weed scientists have been confirming more cases of known resistance.

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.

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.

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.

Will Roundup Face A Bleak Future Due To Resistant Weeds?

That's the scenario painted by Steve Powels, an Australian plant biologist, who spoke at the recent Pan-American Weed Resistance Conference in Miami.

“Glyphosate (active ingredient in Roundup) will be driven to redundancy in the cotton, corn and soybean belt,” said Powles in a report by Forest Laws in Delta Farm Press. “Outside of these areas of the U.S., then glyphosate should continue to be effective because it is not massively used.

“Within the cotton, corn and soybean belt the massive reliance on glyphosate means that it will be driven to redundancy because many of the big driver weeds such as Palmer pigweeds, waterhemp, ragweed and Johnsongrass will be resistant. There may be many weed species still controlled by glyphosate, but glyphosate will fail on the driver weeds and that means overall failure.”

Here's a link to the full report. It's worth reading.

Georgia study: why glyphosate stewardship fails to gain ground

Share

Editor's Note: The following is from a press release received today from Weed Science, a publication of the Weed Science Society of America. The journal publishes articles on the biology, ecology, physiology, or management and control of weeds. It also focuses on herbicides, growth regulators, and related topics. To learn more about the society, please visit: http://www.wssa.net/

Farmers who use herbicide-tolerant crops face a growing challenge from herbicide-tolerant and herbicide-resistant weeds, which are evolving and spreading across cropland.

In the southeastern United States , weeds that can tolerate or resist the popular herbicide glyphosate are threatening cotton crops. In the article “Loss of Glyphosate Efficacy: A Changing Weed Spectrum in Georgia Cotton,” (Weed Science Volume 58, Issue 1, 73-79)

Theodore M. Webster and Lynn M. Sosnoskie examine how the use of glyphosate-tolerant cotton (GTC)—created through genetic modification—has affected weed control issues since its introduction in 1997.

The article is featured in the January–February 2010 issue of Weed Science, published by the Weed Science Society of America. As farmers plant more acres of GTC, they are seeing a change in the most prevalent weeds, which now include varieties that tolerate or resist glyphosate.

The two most troublesome weeds in Georgia cotton are:

• Benghal dayflower, which is tolerant to glyphosate and many of the herbicides used in agronomic crops.
• Palmer amaranth, which has developed resistance to many classes of herbicides including glyphosate.

These weeds typically develop in systems without diverse weed control practices. “The management practices necessary for minimizing the development of herbicide resistance have not been widely implemented,” Webster and Sosnoskie write. They see a need for farmers to work toward greater stewardship, which is the sum of the management decisions and practices used to preserve the utility of a crop trait, and try new or varied weed management strategies that often may be more expensive.

“Agricultural practices aimed at delaying or preventing the development of herbicide resistance are not viewed as being economical in the short term and are not readily used by all growers,” they write. “Because herbicide resistance can spread quickly, indiscriminate use of glyphosate may result in a loss of weed susceptibility for all growers, a tragedy of the commons.” Webster and Sosnoskie identify two reasons why growers are not adopting methods that promote glyphosate stewardship:

• The belief that a new technology will be developed to solve the resistance and tolerance problems, although no new herbicides have been introduced commercially since 1998
• The belief that resistance management strategies will be futile because most farmers think herbicide resistance traits are mobile through pollen-mediated transfer and their fields are affected by other nearby farms

The authors outline several possible incentives for cotton farmers, including industry initiatives to promote better glyphosate stewardship and voluntary government farm programs.

However, they say it likely will take a combination of incentives and a move toward new methods to improve weed control.

“Principles of ecological weed management used in conjunction with herbicide-based weed control systems will likely be an important component of future weed management systems,” Webster and Sosnoskie write.

They also identify several areas for future research: how to limit the development of herbicide-resistant and herbicide-tolerant weeds; whether there is a need to limit the use of glyphosate; factors that may improve control and stewardship of herbicide options; how herbicide resistance traits move across the landscape; what factors could be used to determine a species’ risk of developing resistance; and incentives to help improve herbicide stewardship. The full-text article is available at http://www2.allenpress.com/pdf/WEES_58.1_73-79.pdf.

Managing Herbicide Resistant Palmer Amaranth (Pigweed) in Field Corn, Peanut, and Soybean - 2010

Eric P. Prostko, Georgia Extension Weed Specialist, has released a white paper on dealing with glyphosate-, atrazine- and ALS-resistant weeds in that state. He includes a variety of weed control options. including approaches where Roundup/glyphosate and ALS resistance are found in the same field.

Here's a link to the paper.

Roundup Flex: Treat it like regular Roundup Ready cotton now?

The Beltwide Cotton Conference, as you might expect, included plenty of data and comments about Roundup Ready cotton, especially the new Flex varieties that allow Roundup applications past the fifth node, the cutoff point for first-generation Roundup Ready varieties.

More than once, I heard Extension workers and even some crop consultants say that it will be far safer to treat Flex cotton the same as the first-gen varieties. Reasons include the need to hit weeds far earlier than cotton's fifth node to gain better control and reduce potential for more Roundup-resistant weed development. With many of the weed sessions focusing on Palmer pigweed -- and secondarily on marestail (horseweed) and things like Italian ryegrass -- resistance management or prevention was on everyone's mind, whether or not they now have the problem.

One estimate given was that Roundup Ready cotton, in general, had lost $19 per acre of its value for growers due to continued reissntance problems. That number was given by a university weed scientist during the consultants conference, which preceeded the Beltwide.

Roger Carter, a veteran crop consultant from east-central Louisiana, wrote in his Beltwide report on January 10:

"One focus was on the economic value of the cost of transgenics. Surveys of farmers and consultants indicated that the current charges for biotechnology, particularly the Flex charges, are much too high in exchange for the good we are getting. Because of resistance management more residual herbicides are needed than ever before. And more direct contact herbicides are necessary to battle resistant pigweeds and other species. Therefore, the use of glyphosate over the top after the 5th true leaf on cotton is a mute point in areas where we are using resistance management programs. And that should be most of the Cotton Belt. Are you listening, folks?"