Posts Tagged ‘field corn 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;

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.

Reducing Weed Seed Production in Harvested Fields

Friday, August 24th, 2012

Mark VanGessel, Extension Weed Specialist;

Corn harvest has begun in some areas and the drought has resulted in large areas with stunted plants and very poor leaf development for shading weeds. Both of these situations have created conditions for late season weed growth that could result in significant weed seed production. I believe this is one of the reasons why plants like Texas panicum have become such a big problem in some areas.

The earlier these plants are destroyed, the fewer number of seeds will be produced. The longer weeds are allowed to grow and develop after harvest (or after the decision to not harvest those fields severely impacted by drought) the more likely the weeds are to regrow and eventually produce seed. Disking or non-selective herbicides are options to prevent seed production as well as mowing. Many of these early harvested fields will need at least two mowings to prevent seed production.

Cleaning Equipment to Prevent Spreading Weed Problems Around

Thursday, August 2nd, 2012

Mark VanGessel, Extension Weed Specialist;

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.

Texas Panicum Control

Thursday, May 24th, 2012

Mark VanGessel, Extension Weed Specialist;

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.

Postemergence Corn Products to Provide Residual Weed Control

Friday, May 18th, 2012

Mark VanGessel, Extension Weed Specialist;

Some corn fields need to be sprayed for weeds, but the corn is only 3 to 4 collars. In many ways this is good because the corn leaves will not interfere with herbicide spray pattern and will allow for maximum control. However, that means it may be two to three weeks until the corn canopies over. So relying on glyphosate or Liberty for postemergence weed control, could run into situations of weeds emerging between the postemergence sprays and the time corn canopies over. You should consider a residual herbicide in this scenario. Be sure to read individual labels for information on maximum corn size and recommended adjuvants. The following table of products will help with your selection:

Table of Corn Herbicides

Control of:

Herbicide1 POST activity2 Broadleaf Morningglory Grasses
Atrazine Yes Yes Yes3 No
Callisto Yes Yes No No
Capreno Yes Yes No Limited
Halex Yes Yes No Yes
Impact** Yes Yes No ##
Laudis** Yes Yes No ##
NorthStar Yes Yes No No
Permit Plus Yes Yes No No
Resolve Yes Yes No Yes
Dual No Some No Yes
Prowl H2O No Some No Limited
Warrant No Some No Yes

1Other herbicides maybe be available, but the list includes those UD Weed Extension has evaluated.

2Refers to control of emerged weeds, provided those species are susceptible to the herbicide

3Level of control depends on rate. For residual control of morningglory, rates should be at least 1.25 lbs ai/A

##No local data

Look at Those Early Planted Corn Fields

Thursday, May 3rd, 2012

Mark VanGessel, Extension Weed Specialist;

Some of the earliest planted corn fields were sprayed with preemergence herbicide, but then had 7 to 10 days without rain to activate them. You need to check to those fields for emerging weeds and be prepared to spray earlier than you may have expected. Also, I have seen more yellow nutsedge this year than I have in the past few years. So be sure to identify those “grasses”, and be sure you know what grass species it is or whether it is nutsedge.

Update on Acetochlor Restrictions

Thursday, April 12th, 2012

Mark VanGessel, Extension Weed Specialist;

Last week I wrote about the acetochlor restrictions. I was not aware that these restrictions had been modified and only pertain to applications within 50 feet of a well. The following restrictions do not apply for areas more than 50 feet from a well.

Within 50 feet of a well, do not apply acetochlor if the groundwater depth is within 30 feet of the surface 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.

Sorry about any confusion.

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

Thursday, April 5th, 2012

Mark VanGessel, Extension Weed Specialist;

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:

A Couple of Yearly Reminders Regarding Herbicides

Thursday, April 5th, 2012

Mark VanGessel, Extension Weed Specialist;

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;

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.