Posts Tagged ‘horseweed’

Double-Cropped Soybean Burndown Considerations

Friday, June 15th, 2012

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

As we move into small grain harvest and considering weed control prior to planting soybeans, we have limited options. And we need to view the options as the best of a difficult situation and be realistic on what we can expect for control. Some things we need to consider are:

Weeds present at time of planting. Horseweed is the one of biggest concern, but horsenettle, ragweed, lambsquarters, grasses, etc are also present. Which of the weeds present can also be controlled after the soybeans have emerged? Are Liberty Link soybeans used, because glyphosate could be used prior to planting and then Liberty (or Ignite) used postemergence. Need to decide what problem is most critical and develop a program to target that species.

What herbicides options are available: product availability, crop rotation constraints, or environmental/soil issues. Liberty/Ignite might be the best product for some of these fields, but it is in very short supply and may not be available. Kixor products may be an option for some fields with medium-texture soils. Always consider what will be planted in the field next season and be sure there is adequate time for the intended crop rotation (it maybe only 9 months until you plant the 2013 crop!)

When glyphosate-resistant horseweed is present and it is the species you are targeting for control, you will need to rely on a herbicide other than glyphosate to control them. No product will consistently control horseweed this late in the season; and we are compounding the problems with cutting the plants off with the combine. If Liberty (or Ignite) is not available and your soil texture prevents use of Kixor, one option to consider is Gramoxone in combination with Canopy, along with crop oil concentrate and nitrogen fertilizer. Canopy is the product I would suggest because it contains metribuzin and chlorimuron. Metribuzin may improve the effectiveness of the Gramoxone. The chlorimuron at the rates used prior to planting, will have some activity on the horseweed as well. The use of crop oil and nitrogen sometimes improve Gramoxone activity, but will also maximize the effectiveness of the chlorimuron. This program is not ideal, but in my experiences it provides the best level of control under many situations. Perennial species (horsenettle or yellow nutsedge) will probably regrow and they will need to be controlled with a later glyphosate application.

If horseweed is not present in the fields then often glyphosate plus a residual herbicide may be the best option for it will control summer annual broadleaves and grasses, as well as start to “work on” the perennials. But since most plants have been damaged during small grain harvest, glyphosate activity may be reduced. But glyphosate will be used again after the soybeans have emerged and should improve overall control.

Postemergence Control of Glyphosate-Resistant Horseweed

Friday, June 15th, 2012

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 Liberty 280 is fairly effective on horseweed (be sure to keep your rates up).

For non-Liberty Link soybeans the options are very limited. Liberty Link soybeans can be treated with Liberty (or Ignite) for fair control of horseweed. For non-Liberty Link soybeans, FirstRate or Classic are effective on small, newly emerged seedlings. However, neither will consistently kill large horseweed plants, nor plants that were “burned off” and are recovering (FirstRate is better option than Classic after the soybeans have emerged). 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. Additional glyphosate applications will provide some suppression of horseweed and sometimes the soybeans have a chance to outcompete them.

Marestail Causing Headaches this Spring

Thursday, May 24th, 2012

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

This spring has been very challenging for marestail control. A number of fields were sprayed early, when horseweed plants well under 6 inches tall, and got excellent control of emerged plants. But this spring we have seen fields with lots of plants that emerged after the initial burndown treatment. In many cases horseweed plants that emerged in April were controlled with a second burndown application that included Liberty or Gramoxone. More frustrating are those plants that were not killed with the initial burndown treatment. Most of these plants were treated when they were over 6 inches tall, or not treated with a full rate of the burndown mixtures. At this time, options are very limited for these fields and often decisions need to be made on a field by field basis.

Touching Up No-Till Soybean Fields

Thursday, May 3rd, 2012

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

I have had a number of calls about burndowns not being effective for no-till soybeans. Poor control can be attributed to a number of reasons, weeds were too large, gallonage was too low, and wrong products or adjuvants were used. But the question is what to do now. First determine what was not controlled. In most cases it is marestail or horseweed, and it needs to be controlled before you plant because there are not effective postemergence herbicides for it (unless you are using Liberty Link soybeans and use Liberty 280). It’s too late to rely on 2,4-D to control marestail because you need the 1 qt rate to provide effective control. The 1 qt rate of most 2,4-D products require 4 weeks before planting and in too many places sensitive plants have emerged. If you are on an appropriate soil type, Sharpen, with all the required adjuvants, is an option (see the label). Sharpen is not an option for coarse-textured soils because it also needs 4 weeks between application and soybean planting. Liberty or Ignite can be used, but it works best on days with full sun shine and requires excellent coverage (at least 20 g/A and medium droplet size). A chlorimuron-based herbicide is another option, but you need to use rates that will provide good suppression/control. Chlorimuron rates equivalent to 1.5 oz of Classic is needed (see table below). In most situations, the chlorimuron-based products should be used with a burndown herbicide (glyphosate or Gramoxone) and refer to their label for adjuvants.

Herbicide Rate oz wt/A Classic Rate Other
Valor XLT 3.6 1.5 Valor
Envive 4.0 1.5 Valor + Harmony
Canopy 3.5 1.5 Metrbuzin
Canopy EX 1.6 1.5 Express

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.

Control of Horseweed Prior to Double-Cropped Soybeans

Thursday, July 2nd, 2009

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

A number of small grain fields had lots of horseweed plants at harvest time and these fields will be going into soybeans over the next week. The best time to control these horseweed plants is before planting. We had a small trial last year comparing control options and only one treatment provided good control (no treatment provided 100% control). The best treatment was Ignite 280 at 36 fl oz/A; we only had one rate of Ignite in this trial. Also included in the trial was glyphosate alone, with Envive, Valor XLT, Canopy, and FirstRate. In all treatments, there was significant injury and growth reduction of the horseweed, but with time they began to regrow. Regrowth was less with the Ignite treatments compared to all other treatments.

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.

Comments on Late Spring Burndowns for Soybeans

Friday, May 23rd, 2008

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

Many soybean fields have not been treated yet and require careful consideration for herbicide application. Weeds are large and thus it is difficult to achieve good weed control because higher herbicide rates are necessary, and it is often difficult to achieve adequate spray coverage due to weed density. Control at this time will have little to no impact on seed production of winter annual species. Use common sense when considering 2,4-D because sensitive crops or plants could be in close proximity (when in doubt, leave it out). Also, remember if 2,4-D is used the labeled rate is well below what is required for consistent horseweed control at this time, and allow for soybean planting in a timely manner. Use a residual herbicide, but choice of product and rate is dependent on what is required. You will need to determine if the residual herbicide is only for control of some summer annual weeds or you need the residual herbicide to assist with control of the emerged weeds. If you need help with horseweed control, use a product that contains chlormuron (Classic) at a rate to provided enough product to get maximum effect (although 100% control may not be achievable with large horseweed plants). The Classic rate should be 1.5 oz/A of product. To get enough chlorimuron (Classic) use the following rates: Synchrony = 1.76 oz; Canopy = 3.5 oz; Canopy EX = 1.68 oz; Envive = 4.06 oz; and Valor XLT – is not currently labeled for this rate. Due to weed size in most situations, glyphosate is the better choice for burndown at this time.

Precaution: reliance on chlorimuron products to control horseweed could accelerate the development of ALS-resistant horseweed. So this is not an approach you want to use every year.