Posts Tagged ‘glyphosate’

Glyphosate Resistant Palmer Amaranth on Delmarva

Friday, June 29th, 2012

Barbara Scott, Research Associate; bascott@udel.edu & Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Glyphosate-resistant Palmer amaranth has been confirmed on Delmarva. There has been suspicion of glyphosate-resistance in the region, but this is the first year of confirmed resistance. This discovery is not surprising since Palmer amaranth has a tendency to develop resistance. Fields with Palmer amaranth (or suspected Palmer amaranth) should not be treated with glyphosate alone. In soybeans glyphosate should be tank-mixed with an ALS inhibiting herbicide (group 2) or PPO herbicide (group 9).

Dayflower in Soybeans

Friday, June 15th, 2012

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Last fall there was a sample of spreading dayflower brought into the office (http://www.ppws.vt.edu/scott/weed_id/comco.htm). The field was treated once or twice with glyphosate and the plants were not controlled. The grower was concerned about resistance. As it turns out, dayflower is one of those species that glyphosate will not control. FirstRate is the best option for dayflower control in soybeans.

Will Roundup Ready® Alfalfa Be Back?

Friday, July 9th, 2010

It appears that with a Supreme Court ruling a few weeks ago that Roundup Ready® alfalfa will eventually be available for planting. The questions that remain include not only when will this occur but what restrictions will be imposed on planting the crop and in what sections of the country it will be allowed. If you haven’t had a chance to read some of the articles that expound on the Supreme Court’s ruling, please take the time to look them up and read them over. It seems that both sides are able to claim victory from the ruling so it probably means that there will still be a number of months ahead of us before final rules are set in place so that in some areas and under some conditions, we can return to using this new technology. Monsanto has stated that they believe that plantings will be possible this fall while others doubt that this timeline can be achieved. If you’re interested in the technology and for growers who like to grow pure alfalfa hay or who like the ease of a single herbicide for most weed control, keep in touch with the latest developments in this story to know when it will be permissible to plant Roundup Ready alfalfa again.

Postemergence Control of Glyphosate Resistant Horseweed

Friday, June 11th, 2010

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Options for controlling horseweed resistant to glyphosate after the soybeans have emerged are very limited. Liberty Link soybeans are an exception, because Ignite 280 is fairly effective on horseweed (be sure to keep your rates up).

For non-Liberty Link soybeans the options are very limited. FirstRate or Classic are only effective on small, newly emerged seedlings. However, neither FirstRate nor Classic, will consistently kill large horseweed plants nor plants that were “burned off” and are recovering. These herbicides may provide some suppression, but results have been quite erratic the past few years. Horseweed plants are generally not very tolerant of shade and most soybeans will begin to canopy over the horseweed and out-compete them. In most cases, I have recommended to not spray emerged horseweed plants with another herbicide. Rather, make postemergence applications of glyphosate based on need to control other weed species. Additional glyphosate applications will provide some suppression of horseweed and give the soybeans a chance to outcompete them.

Horseweed is Getting Harder to Control

Thursday, March 25th, 2010

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

We confirmed a population of horseweed (or marestail) in Delaware that is resistant to glyphosate and ALS-inhibiting herbicide. This field had been treated with Finesse and Canopy EX and glyphosate and the horseweed was not controlled. We collected seed from this field and tested it in the greenhouse. This is the first confirmation of multiple resistance for horseweed in the Mid-Atlantic states. Glyphosate will not control this biotype, but neither will chlorimuron or FirstRate. Chlorimuron is the active ingredient in Classic, Canopy SG, Canopy EX, Synchrony, Envive, and Valor XLT. Controlling these populations will require 2,4-D (at 1 qt/A for consistent control), Ignite 280, or Kixor (but Kixor needs to be applied at least 30 days prior to planting in coarse-textured soils). The most cost-effective approach will be use of 2,4-D applied at 1 qt/A at least 30 days prior to planting. Delaying the 2,4-D applications until closer to planting will result in lower rates of 2,4-D being applied, less effective horseweed control, and more situations that are not appropriate for 2,4-D because of emergence of nearby crops and vegetables.

NOTE: There are many circumstances where 2,4-D is not an option due to susceptible plants or greenhouses in the area. Be sure to know the surrounding area before you treat a field with 2,4-D to be sure it is an appropriate treatment for the area.

Glyphosate Formulations

Friday, June 19th, 2009

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Penn State University has a table of various glyphosate formulations, based on amount of active ingredient and amount of adjuvants. With slight modifications, I have posted this on the UD Weed Science Website at: http://www.rec.udel.edu/weedscience/Glyphosates_09.pdf

If you do not find a glyphosate product that you use, let me know and I will update this list.

Postemergence Control of Glyphosate-Resistant Horseweed

Friday, June 12th, 2009

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Options for controlling horseweed resistant to glyphosate after the soybeans have emerged are very limited. FirstRate or Classic are only effective on small, newly emerged seedlings. However, neither FirstRate nor Classic, will consistently kill large horseweed plants nor plants that were “burned off” and are recovering. These herbicides may provide some suppression, but results have been quite erratic the past few years. Horseweed plants are generally not very tolerant of shade and most soybeans will begin to canopy over the horseweed and out-compete them. In most cases, I have recommended to not spray emerged horseweed plants with another herbicide. Rather, make postemergence applications of glyphosate based on need to control other weed species. Additional glyphosate applications will provide some suppression of horseweed and give the soybeans a chance to outcompete them.

Replanting Roundup Ready Corn

Friday, June 6th, 2008

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

There have been a few places where replanting Roundup Ready corn is necessary and existing plants need to be killed. The difficulty is that the corn is Roundup Ready and how best to kill it. A project conducted in this area compared Select Max, Gramoxone alone, and Gramoxone with tankmix partners. Select Max at 6 fl oz/A was effective, but the label requires that the field can not be replanted for at least 6 days after application. The best treatments (95% control) were Gramoxone Inteon (at 1 qt/A) plus 2 oz of Sencor and Gramoxone (1 qt/A) plus Lorox (4 oz/A) applied to 5 inch corn. Applications to 2 to 3 inch corn averaged 80% control or less. Gramoxone Inteon alone was very inconsistent. No treatment consistently controlled all plants. If complete control is necessary, tillage will be required.

Glyphosate Formulations

Friday, April 11th, 2008

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

With increased glyphosate costs and the limited availability of glyphosate this year, you may be looking to buy brands that you are not familiar with. Here are a few things to keep in mind when buying glyphosate.

There are numerous products containing glyphosate in the marketplace, but there is no consistency in how the companies report what is contained “in the jug”. Glyphosate is what kills the plant and it is an acid molecule, but it is formulated as a salt for packaging and handling. Various salt formulations include isopropylamine, diammonium, monoammonium, or potassium. Some brands include more than one salt.

Some companies report their product as acid equivalent (ae) of glyphosate acid, or some report it as active ingredient (ai) of glyphosate plus the salt, and others report both. In order to compare performance of different formulations it is critical to know how the products were formulated. Since the salt does not contribute to weed control and different salts have different weights, the acid equivalent is a more accurate method of expressing, and comparing concentrations.

Adjuvant loading refers to the amount of adjuvant already added to the glyphosate product. Fully loaded products contain all the necessary adjuvants, some contain no adjuvant system; while other products contain only a limited amount of adjuvant (minimal or partial loading) and additional surfactants must be added to the spray tank before application. Refer to product labels for specific recommendations. Most glyphosate brands recommend adding ammonium sulfate (AMS) if using hard water as a carrier or under other challenging conditions. If using AMS, always dissolve it in the spray solution before adding glyphosate.

Finally, some products will support technical service for the performance of the product and others come with no technical support. Usually the lower cost products have limited to no technical support.

So when trying to decide on which formulation of glyphosate to buy, be sure you know:

  • the glyphosate concentration (how much product to add)
  • adjuvant load (whether you need to add any surfactant and how much)
  • whether the product will be “supported” by a technical rep of the dealer or manufacturer