Posts Tagged ‘soybean weed control’

Updated Weed Control Guides are Available – And They’re Free

Thursday, April 5th, 2012

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

Available from your county Extension office are weed management guides for assistance in weed control in corn, soybeans, or forages. There is a separate guide for each commodity. The first half of the corn and soybean guides deals with soil-applied herbicides and the second half is for postemergence herbicides. These guides include information on pre-mixes and what is in the pre-mix, expanded weed control tables, information on application timing, comments for each of the herbicides, and much more. The forage guides cover alfalfa as well as grass forages. Contact your county extension office for these free guides. Or find them at the UD-REC website: http://www.rec.udel.edu/weedscience/WS_ManagementGuides.html.

A Couple of Yearly Reminders Regarding Herbicides

Thursday, April 5th, 2012

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

Acetochlor
Acetochlor is a preemergence herbicide for corn that controls annual grasses and some broadleaf weeds. It is in the following products: Harness, Harness Extra, Degree, Degree Extra, Topnotch, Fultime, and Keystone. There are use restrictions related to groundwater quality. The restrictions are based on depth of groundwater within one month of planting and the combination of soil type and organic matter. Do not apply acetochlor if the groundwater depth is within 30 feet and you have sands with less than 3% organic matter, loamy sands with less than 2% organic matter, or sandy loam with less than 1% organic matter.

“Activating” Herbicides
Herbicides applied to the soil surface require rainfall or irrigation to move them into the soil where the plants will absorb them; or mechanical incorporation (field cultivator). Some areas have not received much rainfall lately and you need to be aware if your soil-applied herbicides have been activated. If you have irrigation and your herbicides have been applied but you have not received water, you should consider irrigating to activate those herbicides.

Burndown No-Till Fields

Friday, March 30th, 2012

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

Fields that will be planted to no-till corn or soybeans may have excess weed growth due to the warm winter. This will make burndown treatments more challenging, and in some cases it is unrealistic to expect complete control with only one application. In those cases, you may need an application now, followed by an additional application at planting. For weeds that are hard to kill with glyphosate, additional herbicides such as 2,4-D can enhanced the control (for instance, mustards); while other herbicide combinations can reduce glyphosate control (for instance, atrazine in combination with glyphosate for ryegrass control). Be sure to assess each field, and determine the best approach. Do not assume you can spray a week ahead of planting and achieve a clean seedbed to plant into.

Cleaning Equipment to Prevent Spreading Weed Problems Around

Friday, September 9th, 2011

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. 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 and others are due to poor herbicide performance as a result of the summer drought. 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. A new weed species 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 and leave the seeds where you found them.

Fall Control of Perennial Weeds

Friday, September 9th, 2011

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

Fall is the best time to treat most perennial weeds because it is the time that plants are best able to move the herbicide to the roots where it will do the most good. When considering fall weed control the emphasis should be on what the patch of weeds will look like next spring or summer not the amount of dead stems this fall. Also, it is important to consider that a fall application will not eradicate a stand of perennial weeds; the fall application will reduce the stand size or the stand vigor. Fall applications of glyphosate is the most flexible treatment for most perennial weeds such as artichoke, bermudagrass, Canada thistle, common milkweed, common pokeweed, dock, hemp dogbane, horsenettle and johnsongrass. Rates of 1 to 1.25 lb acid per acre are consistently the most economical (or about 1.5X the normal use rate for annual weeds). Allow at least 7 days after treatment before tilling, mowing, or planting through the treated area. Dicamba (Banvel) at 2 to 4 pints is also labeled for artichoke, bindweeds, dock, hemp dogbane, horsenettle, milkweeds, pokeweed or Canada thistle. Allow 10 days after treatment before disturbing the treated plants. Planting small grains must be delayed after dicamba application 20 days per pint of dicamba applied. Fall herbicide applications should be made to actively growing plants. Allow plants to recover after harvest before treating them. Consider keeping the combine header as high as possible so the weeds are quicker to recover; or combining around the weed patches and then spraying those patches immediately after harvesting. Weed species differ in their sensitivity to frost; some are easily killed by frost (i.e. horsenettle) others can withstand relatively heavy frosts. Check the weeds prior to application to be sure they are actively growing.

Weed Control in Double-Cropped Soybeans

Thursday, July 21st, 2011

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

Postemergence applications from 14 to 28 days after planting resulted in similar weed control and yield in studies conducted with the Delaware Soybean Board. Check your fields about 14 days after planting because weeds not killed with the burndown treatment will be starting to re-grow. The heat and high temps can reduce herbicide effectiveness. Treating larger weeds under high temperatures often will further reduce effectiveness as well.

Palmer Amaranth is in the Area

Friday, June 3rd, 2011

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

Last year I saw a few fields in the area (Delaware and Maryland) with infestations of Palmer amaranth. Palmer amaranth is a pigweed, which looks similar to the smooth pigweed that is so common (and often called redroot). However, Palmer amaranth is a very aggressive species that grows very rapidly. It is native to the southwest region of the US, and does better than most plants under dry conditions. Palmer amaranth has been described as pigweeds on steroids because of its ability to grow very rapidly, get very tall, and be very competitive with crops. Palmer amaranth is found throughout the southern US and is moving northward. Palmer amaranth is not as sensitive to Group 2 herbicides as smooth or redroot pigweed (this includes Pursuit, Sandea, Accent, Matrix, etc.). It is sensitive to PPO herbicides (Reflex, Valor, etc); atrazine, and HPPD (Callisto, Impact, and Laudis. Furthermore, glyphosate-resistant Palmer amaranth is present in Georgia, North and South Carolina and other southern states. I am not aware of any herbicide-resistant Palmer amaranth in our area.

It is critical that you control plants early; and that you do not allow the plants to produce flowers. Plants will produce a very high number of seeds that will quickly infest fields. In the southern cotton growing regions where they have herbicide-resistant Palmer amaranth, they have had to resort to hand weeding.

To help identify Palmer amaranth, see the chart, websites, and photos below.

Characteristics Redroot Pigweed Smooth Pigweed Palmer Amaranth
Stem hairs Hairy Hairy No hairs
Stems Often ridges running length of stem Often ridges running length of stem Mostly smooth
Leaf petioles Petioles no longer than length of the leaf Petioles no longer than length of the leaf Long drooping petioles
Seed head Short, stout, prickly Long, slender, slightly prickly Very long, thick, very prickly

A couple of good publications include:

http://mulch.cropsoil.uga.edu/weedsci/HomepageFiles/PalmerBiologyEcology.pdf
http://www.extension.iastate.edu/Publications/PM1786.pdf
http://www.ksre.ksu.edu/library/crpsl2/s80.pdf

 

Smooth pigweed

 

Palmer amaranth

 

Residual Herbicides for Soybean

Friday, April 29th, 2011

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

It is important to include effective broad spectrum residual herbicides at the time of burndown application or at plant (for conventional tillage soybeans). Including a residual herbicide is the first step, using the correct herbicide is the next decision, and the most difficult is the correct rate. The following link includes a table of some of the better soil applied herbicides and the corresponding rates. For no-till soybeans, I prefer to use a pre-package mixture that contains both an ALS-inhibiting herbicide (Group 2) and a PPO-inhibiting herbicide (Group 14). The ALS product will help with burndown control and provides more consistent control in trashy fields. The PPO also may help with burndown, but generally provides a broader spectrum of control than ALS herbicides alone. The two most common Group 2 herbicides for soybeans are chlorimuron (Classic, Canopy, Envive, and others) and cloransulam (FirstRate, Sonic, Authority First, Gangster, and others). In order for the ALS inhibiting herbicide to provide more consistent burndown control and provide adequate length of residual control the chlorimuron and cloransulam rates should be 0.02 to 0.027 lbs active ingredient per acre; which translates to 1.25 to 1.7 oz of Classic or 0.4 to 0.5 oz of FirstRate. A lot of the literature from the companies does not recommend these rates because they are not considering applications at least 14 days prior to planting, or they are not accounting for the residual herbicide to help with burndown. A table to compare various pre-packaged mixtures and comparable rates of chlorimuron and cloransulam can be found at http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2011/04/Soybean-Residual-Comparisons_11.pdf.

 

Water is Needed to “Activate” Soil-Applied Herbicides

Friday, April 29th, 2011

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

Herbicides applied to the soil surface require rainfall or irrigation to move them into the soil where the plants will absorb them; or to be mechanically incorporated (field cultivator). Some areas have not received much rainfall since the herbicides were applied. Some products, like atrazine or mesotrione, may be taken up by the roots and provide some control. But Dual, Harness, and Prowl all need to be absorbed by emerging shoots, so they will not control weeds once they emerge. If you have irrigation and your corn herbicides have been applied but you have not received rain, you should consider irrigating to activate those herbicides.

 

Inconsistent Control With Burndown Herbicides

Friday, April 22nd, 2011

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

There are a lot of fields that have been sprayed with a burndown and the control was not as good as expected. It is not uncommon for early season burndown applications to be erratic, but this season seems worse than others. The most common complaints have been with grass control, henbit, and chickweed. A few observations from my experiences: glyphosate is good on most of these species, but is not great. Glyphosate often provides good to excellent control of grasses if the rate is adequate (at least 0.75 lbs acid equivalent) and the plants are growing. However, annual ryegrass (aka Italian ryegrass) is hard to kill with glyphosate and requires close to a 2X rate if spraying in early spring. The addition of a triazine will significantly reduce the control of annual ryegrass. I often see only fair control of henbit with glyphosate. The addition of a triazine herbicide like atrazine or simazine will help. That is the tough choice, adding a triazine may help with some species, but can reduce the control of other species. You have to determine what weeds you have and which are going to be the most difficult to control and decide.

As far as paraquat, adding a triazine for the burndown before corn almost always improves control. However, grass control of annual ryegrass or grass cover crops will probably not be acceptable due to significant regrowth.