Post-emergence herbicides for corn and soybean

At this time of the year, integrated weed management programs focus on scouting and diversifying management practices including non-chemical methods and herbicide sites-of-action. For more information, please visit the United Soybean Board’s TakeAction website for field management guidelines and to learn more about herbicide sites of action. Michigan State University’s Weed Science website has detailed web pages on common weeds in annual crops with biological information and management recommendations. After each field season, the Herbicide Evaluation Program here at the university publishes efficacy data in a research report. Summary ratings for many weed species are located in “Pest Management in Wisconsin Field Crops” available as a free pdf or in print at Cooperative Extension’s Learning Store.

Herbicide Injury Diagnosis for Corn Seedlings at Emergence

Depending upon the herbicide, injury can occur after a pre-emergence application when corn is germinating in cool, wet soils. This year, if corn was planted in mid-April then you may observe some injury. However, it is important to remember that other environmental factors can mimic herbicide injury symptoms such as corn emerging in crusted or compacted soil. For this spring, WCWS has a re-designed online diagnostic tool, available at or from the main page, go to ‘Resources’ and then to ‘Tools’. The diagnostic tool asks three basic questions 1) When do injury symptoms appear? 2) Are both broadleaves and grasses affected or just one group? and 3) What are the symptoms and where do they occur? The original web-based tool was developed by Tim Trower and Chris Boerboom to accompany a handy two-page guide. The following changes were made to the new version:

  1. Each page shows your previous answers.
  2. A ‘Start over’ button is located at the bottom of each page.
  3. For each herbicide mode-of-action, an herbicide chart from the TakeAction Herbicide Classification poster or on the WCWS website under ‘Resources’, ‘Documents’(Fig. 1).
  4. Simplified guides to symptoms that mimic herbicide injury during and after emergence are included on each mode-of-action page (Fig. 2).
  5. Photo galleries for both corn and soybean injury symptoms are located on the same page (Fig. 3).

Figure 1. Herbicide site-of-action groups, chemical  families, active ingredients, and product examples for the seedling shoot growth inhibitor mode-of-action.  Specific sections of the larger TakeAction chart are on each mode-of-action page.

Figure 1. Herbicide site-of-action groups, chemical families, active ingredients, and product examples for the seedling shoot growth inhibitor mode-of-action. Specific sections of the larger TakeAction chart are on each mode-of-action page.

Figure 2. Mimics of herbicide injury to corn during or at emergence.

Figure 2. Mimics of herbicide injury to corn during or at emergence.

Figure 3. Example of a photo gallery for corn and soybean herbicide injury symptoms.

Figure 3. Example of a photo gallery for corn and soybean herbicide injury symptoms.

For pre-emergence applications in corn, the seedling shoot growth inhibitors, particularly the chloroacetamides, may injure seedlings when soils are cool and wet. Injury will not always be apparent aboveground. For example, corn plants with seedling root growth inhibitor damage will display clubbed root tips and grasses will be more affected than broadleaves. To get an idea of injury risk, check out the herbicide tables in “Pest Management in Wisconsin Field Crops” available in pdf and print formats at Cooperative Extension’s Learning Store.

Certified Crop Advisor Training Series


Here is another resource brought to you by University of Wisconsin Extension! Free, online certified crop advisor training videos are available now. In addition to CCA training, they are great for adding to your general knowledge about integrated pest management, soil science, and field and forage crops.

Vince Davis has created a series of weed science videos that can be accessed directly from the videos page.

UWEX Crop Budget Analyzer


Ken Williams, an Extension agent in Waushara county has released an updated Crop Budget Analyzer for corn, soybeans, wheat, seeding alfalfa, and established alfalfa. The Budget Analyzer is a downloadable Excel spreadsheet, which can generate handy one page print-outs.

Other UWEX and USDA resources are available to help with pricing and budgeting.

Diversify your Weed Management Toolbox

The Weed Science Society of America recently held an Herbicide Resistance Summit that brought together leading weed scientists from around the world to discuss the future of herbicide resistance at the National Academy of Sciences in Washington D.C. All of the presentations are on YouTube.

If you have 1 minute or 30 minutes, take the time to hear what the Director of the Australian Herbicide Resistance Initiative, Stephen Powles, says about herbicide resistance in the United States.


Diversify Weed Management

The Transgenic Treadmill

Avoiding the Herbicide Resistance Train Wreck in the United States

Harvest Weed Seed Control

Full Presentation

On the Bookshelf: 2015 Pest Management in Wisconsin Field Crops

Don’t miss this year’s “Pest Management in Wisconsin Field Crops” from University of Wisconsin Extension. This is a comprehensive guide to insect, weed, and plant disease management in corn, soybean, forage, and stored grain crops.

To obtain a print copy of the guide, go here. For a free electronic copy in pdf format, go here for the download. For mobile access, go to University of Wisconsin Extension’s Pest Management Mobile.

More Winter Reading, the 2014 WCWS Research Report


Yep, it is that time of year. Winter is setting in and the 2014 WCWS Research Report is here to chase away the winter blues. Print copies will be distributed at the Pest Management Update meetings and at the Wisconsin Crop Management conference. Check out our Documents page again in December for an updated report with yield data.

App for Pricing Wet Corn


UW-Extension has a smartphone app for pricing high moisture corn. For more information, keep reading the following the press release from UW-Extension’s Greg Blonde.

Contact: Greg Blonde, UW-Extension Waupaca County, 715-258-6230,

Pricing Wet Corn? UW-Extension has an app for that

Waupaca, Wis. – It’s that time of the year when Wisconsin dairy and beef producers and Wisconsin corn growers explore their options of buying or selling high moisture shell corn (HMSC). This is especially true this year in the northern two-thirds of the state with so much wet corn still in the field.

To help farmers better evaluate their options, the University of Wisconsin-Extension released a Smartphone app this fall to provide a simple way to help estimate the market value of HMSC based on three main variables – dry corn moisture, current corn moisture and price per bushel.

The HMSC$ app is free and available for Android smart phones and tablets on the Google Play store by searching for “HMSC”.

Farmers can use this app to help determine an equivalent value for wet shell corn when compared with a dry shell corn price – a link to current local elevator dry corn bid prices is built into the app. The equivalent wet price is then calculated and displayed in both price per ton and price per bushel. Additional costs for drying and/or shelling can be evaluated under the expense tab. The app also features the ability to email the results directly to others.

“Although a desktop Excel spreadsheet for pricing HMSC is available on the Wisconsin Center for Dairy Profitability web site, it doesn’t have the ability to bring up current market information or automatically share the results”, said Greg Blonde, UW-Extension Waupaca County agriculture agent. “When you’re out in the field or on the go, the HMSC$ app is a great resource tool to have on your Smartphone or tablet computer.”

Blonde also noted the app may be useful to grain elevator managers, as well as Ag lenders and farm managers for valuing their grain or feed inventories.

To-Do List: Fall Dandelion Management


It’s time to start planning ahead for fall dandelion management. The Weed Science website at the University of Wisconsin Extension has a thorough description of the dandelion’s life cycle and some suggestions for control. A group of researchers at the University of Wisconsin evaluated fall and spring herbicide applications for control of dandelion in 2011. Their key findings were:

  1. Herbicide applications in the fall were most effective for early-season dandelion control compared to applications at normal corn planting in the spring.
  2. Applications during the spring were ideal for late-season control when soybean planting occurs.

For specific information on herbicides, please see their slide presentation.

The flowering stage of dandelion is easily identified by most. However, identifying the seedling stage is helpful because management is best before dandelions enter the adult stage. The following plant characteristics will help with identifying seedling dandelions:

  • Seed leaves (cotyledons) are oval or spoon-shaped
  • First true leaf is ovular and 0.4 inches (1 cm) long. Leaf margins have a few very small teeth that point back toward the base of the leaf. The midvein is prominent on the underside of the leaf.
  • Later leaves are more elongated and will have the toothed margins and rosette arrangement typical of the mature plant.

Managing dandelions can either be done through the use of herbicide or physical removal in either the spring or fall. However, dandelions are more susceptible to herbicides applied in the fall. If physical removal is the management mode of choice, it must be done in the spring as well as the fall.

Management options for corn and soybean are listed below.


Chemical control options:

  • Fall application of 2,4-D or dicamba at 1 pint per acre applied alone or as a tank mix prior to the first killing frost. Another option is glyphosate but for optimal activity applications need to be made when the air temperature is above 50 degrees F and the plant is still actively growing.
  • Spring applications of 2,4-D ester at 1 pint per acre prior to corn emergence or a tank-mix of 2,4-D with glyphosate will provide some dandelion control. Also, post-emergence applications of growth regulator herbicides typically provide acceptable control.

Mechanical control options:

  • Moldboard or chisel plowing will weaken the plant by disturbing the taproot and may make chemical applications more effective.


Chemical control options:

  • 2,4-D ester may be applied prior to soybean planting if a seven-day interval is observed between application and planting.
  • There are no good post-emergence options for dandelion control in soybeans.
  • If possible, control heavy infestations of dandelions in the fall if the field is to be planted to no-till soybeans.


  1., site accessed July 27, 2014.
  2., site accessed July 27, 2014.
  3., site accessed July 27, 2014.


Madeline Fischer and Liz Bosak

Madeline Fischer is an undergraduate research assistant working for WCWS at the Arlington Agricultural Research Station. In Fall 2014, Madeline will be a sophmore pursuing a degree in Life Science Communcations and Environmental Studies.