Posts Tagged ‘soybean weed control’

Fall Can Be a Good Opportunity for Getting a Jump on Next Year’s Weed Problems

Friday, September 21st, 2012

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

Fall herbicide treatments have a nice fit for many situations such as small grain weed control, assisting with cover crop management, and reducing the severity of weed infestations for no till corn or soybeans.

Let’s look at each of these situations. Treating small grain fields with a late fall herbicide application has worked well in our trials. As discussed in earlier newsletters there are no herbicides labeled for applications at planting (a preemergence application). As a result we have lots of winter annuals that emerge with or shortly after the crop. Waiting until spring to control these weeds often results in poor control because the weeds are large, and often stressed from the winter weather. On the other hand, an application in the late fall is made while the weeds are relatively small and actively growing. Remember these weeds are winter annual and will continue to grow after a few hard frosts, and the soil temperatures allow for significant growth through the month of November. If there is a lot of spring emergence, then those weeds can be controlled with a herbicide applied in combination with spring nitrogen applications.

Controlling weeds in cover crops that will be used for early-season vegetables can be challenging in some springs (particularly henbit and chickweed). One way around this with a grass cover crop is using a herbicide in the fall to “clean up the cover crop”. Using a broadleaf herbicide such as Harmony Extra or 2,4-D in the fall will control many of the broadleaf weeds and not limit crop rotation in the spring (replant intervals are 1.5 to 3 months). Then when burning down the grass cover crop in the spring, the concern is killing the cover crop, and not worrying about the winter annual broadleaves that can be tough to control that time of year.

Finally, fall treatments for fields that will be planted to no-till corn or soybeans next spring. We have looked at a number of products that could be tankmixed with glyphosate or paraquat with the idea they would provide residual control for spring emerging plants and these fields will not need a burndown herbicide. UD Weed Science Research has not found a consistent herbicide program for this approach. Furthermore, for effective weed control in corn or soybean most fields need a residual herbicide applied prior to or at planting, so a trip across the field for a herbicide application is needed in the spring. Fall herbicide applications of glyphosate or paraquat with 2,4-D are an excellent way to limit the amount of weed biomass in the spring, which in turn allows the soil to warm up faster and possibly conserve moisture. In our experiences, the addition of residual herbicides to the tankmixture of glyphosate, paraquat, and/or 2,4-D has limited utility in most situations.

Cleaning Equipment to Prevent Spreading Weed Problems Around

Thursday, August 2nd, 2012

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

This summer has been very challenging for weed control so I want to remind you to not spread the problems around the farm or from farm to farm. I believe that a lot of our new weed infestations are due to transporting seed on equipment, whether the equipment is mowers, combines, or vegetable harvesters. I have seen a number of fields with heavy weed pressure due to escapes. Some of these are suspected to be resistant biotypes, others just hard to control weeds. If a particular weed is giving you headaches, wouldn’t you rather deal with it in only one field rather than all of your fields? Ask yourself, what you would do if you could no longer use the best herbicide for a problem weed. In vegetables, where we only have one or two broadleaf herbicides, what are your options when they are no longer effective?

Granted weeds that get blown around (like marestail or thistle) or spread (by birds like pokeweed) are difficult to prevent. Nevertheless, many of our problems are due to moving seeds from field to field on equipment; pigweed and lambsquarters are two that come to mind. Take the time to clean the equipment in the field before it gets moved and isolate where those infestations are located. This is true for all fields. A new weed or a resistant biotype does not just take over a field in one year. A few plants get started and they produce seeds which next year leads to more plants and more seeds (see where this is going?). Prevent the problems from developing and spreading. Clean the equipment thoroughly, before it leaves the field, and leave the weed seed where you found it.

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.

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.

Glyphosate Tankmixed with Reflex

Friday, June 15th, 2012

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

There are many situations where both fomesafen (active ingredient in Reflex) and glyphosate will complement each other for weed control. Syngenta has a premix of fomesafen plus glyphosate called Flexstar GT. Also, Reflex and glyphosate can be tankmixed, but there have been some situations of these two products not mixing well. The following is an article from Ken Smith from University of Arkansas entitled “Problem Solving Incompatible Tankmixes of Glyphosate and Reflex®”

“Some growers have experienced cottage cheese spray mixtures when Reflex® and glyphosate were tankmixed in an effort to burn down existing weeds while applying Reflex® prior to cotton or soybean planting.

“It seems that the potassium salts of glyphosate (WeatherMax, Touchdown, PowerMax etc.) are not very compatible with Reflex® . . . . Many of the generic glyphosate formulations are isopropyl or diammonium salts (not potassium salts) and will mix fine. A quick check of the label will give the salt used in the formulation. 

“If a mistake is made and Reflex® and the potassium salt of glyphosate is mixed and found to be incompatible, it can likely be brought back into solution by adding household ammonia. Start with 1% ammonia and begin agitation. More ammonia may be added if needed.”

Control of Volunteer Corn in Soybeans

Friday, June 15th, 2012

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

I have looked at some soybean fields with heavy volunteer corn pressure. The corn is Roundup Ready, so none of the glyphosate formulations will control it. The postemergence grass herbicides (Select Max, clethodim, Assure II/Targa, Fusilade, or Poast) will control emerged corn. In a trial at Purdue University, control was slightly better when these products were applied to 10 to 15 inch tall corn compared to 22 to 25 inch tall corn. If tankmixing these products with glyphosate, many of them recommend including an adjuvant and nitrogen regardless of the glyphosate formulation. Be sure to read the labels.

Nutsedge and Horsenettle Control

Friday, June 1st, 2012

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

This appears to be the year for yellow nutsedge and horsenettle. Only a few products will provide yellow nutsedge control in corn. Glyphosate products are rated as suppressing yellow nutsedge if applied up to 6 inch tall plants. A recently registered product for our region, Permit Plus at 0.75 oz wt/A, is the best product available. Permit Plus contains halosulfuron and thifensulfuron (active ingredients in Sandea and Harmony). Permit Plus can be tankmixed with glyphosate. Basagran will control emerged tissue of yellow nutsedge, but the plants often regrow from the nutlets. Other products list nutsedge suppression but need to be applied to very small nutsedge plants. For soybeans, Basagran and glyphosate are also available, but so is Classic, for nutsedge plants up to 4 inches tall. Classic can be tankmixed with glyphosate.

Nutsedge control in vegetables includes Basagran or Sandea. Later planted vegetables can be treated at planting with Dual and/or Pursuit for control/suppression of yellow nutsedge. Pre-plant incorporated applications of Dual generally provide better yellow nutsedge control than applications to the soil surface.

Horsenettle is a perennial that emerges from creeping rhizomes and is hard to control. Glyphosate is rated as fair for control of horsenettle, but no other soybean herbicide provides control or appears to enhance glyphosate activity. In corn, Callisto provides good horsenettle control. Banvel, or dicamba containing herbicides, provide fair control of horsenettle. Postemergence options in vegetables are very limited; most products will provide some leaf burn but poor control.

Both yellow nutsedge and horsenettle should be treated after harvest with glyphosate. In late summer or fall, these plants are moving sugars to their root systems where the glyphosate can kill the perennial tissue of the plants.

Texas Panicum Control

Thursday, May 24th, 2012

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

In 2011, there were a number of fields with severe infestations of Texas panicum in corn and soybeans. Texas panicum is a grass species that needs to be controlled with postemergence herbicides. UD Weed Research program currently has trials for control in both corn and soybeans, so local data is limited. Based on research in the southern US, options in corn include Accent, Laudis or Impact. These products will provide some residual control, which appears to be adequate for full-season control. Glyphosate or Liberty, which provide no residual control, often require two applications for full-season control. Options for soybeans include glyphosate or Liberty (possibly requiring two applications) or postemergence grass herbicide such as Select, Assure II, Poast, or Fusilade.

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