Herbicide Resistance Management for Common Lambsquarters and Horseweed

In the June 13th issue of the Wisconsin Crop Manager, I discussed herbicide resistance management for giant and common ragweed. This week’s featured herbicide resistance threats are common lambsquarters, Chenopodium album, and horseweed, Conyza canadensis. Weed scientists across the Midwest and Midsouth have identified eleven species of weeds that are of most concern for herbicide resistance because of their ability to compete with crops and to develop resistance to different herbicide sites of action. In 1979, University of Wisconsin weed scientists identified a population of common lambsquarters resistant to atrazine, a photosystem II inhibitor (www.weedscience.org). Lambsquarters populations in Michigan and Ohio have been found resistant to ALS inhibitors. In 2013, University of Wisconsin researchers identified horseweed plants resistant to glyphosate. Ohio and Delaware have horseweed populations resistant to both ALS inhibitors and glyphosate. Resistance to a single site of action has occurred in over twenty states.

Now is the time to start thinking about fall horseweed management. Emergence typically occurs in the early spring and again in the fall. Long-term no-till systems tend to harbor significant horseweed populations. Scouting in mid to late summer to locate any escapes from spring herbicide applications is important for herbicide resistance management and to decide whether to switch to a horseweed management program that includes both spring and fall control measures. Fall herbicide applications can help to reduce horseweed populations in problem fields. Also, if dandelion is an issue, then there are two reasons to consider fall herbicide applications. University of Wisconsin researchers found that fall dandelion control is best prior to next year’s corn crop. Their results are available as a slide presentation. Kevin Bradley at the University of Missouri has a video, less than five minutes, discussing the importance of application timing for horseweed control.

Ohio State and Purdue University have a great fact sheet on horseweed management. Also, the TakeAction website has a fact sheet with spring and fall herbicide recommendations.

Common lambsquarters can be difficult to manage because of an early and sustained emergence period, long seed persistence, and competitive ability. A 50 percent reduction of seed in the soil seedbank requires about 12 years and 78 years for a 99 percent reduction. Management goals should include: starting with a clean field, using a pre-emergence residual herbicide, scouting, and applying a post-emergence herbicide if necessary. For specific management recommendations, please consult the TakeAction fact sheet.

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.

Start the New Year with Herbicide Resistance Management


Here is another WCWS video discussing strategies to manage herbicide resistance. Get great weed control and save a bag of soybean seed by using a residual herbicide. Check out more WCWS videos at http://wcws.cals.wisc.edu/videos.

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.

To-Do List: Late-Season Scouting

A critical component of herbicide resistance management and integrated pest management is scouting for pests. In this case, it is time to start thinking about scouting for late-season weed escapes. Late-season weed scouting will help to focus your weed management plans for next year- what worked, did not work, and which weed species may be a problem during the next growing season. If you suspect that you have found an herbicide-resistant weed, please contact your local county Extension agent or Vince Davis at vmdavis@wisc.edu

To learn more about late-season weed scouting in soybean, please watch Vince’s videos:


For more videos, please visit our video page, http://wcws.cals.wisc.edu/videos/

Rolling and Crimping Cover Crops

Under Cover Farmers is a video featuring farmers discussing how they use cover crops and specifically rolling-crimping for termination in a conventional system. The video is 28 minutes in length and was produced by the USDA-NRCS.

It’s worth taking a long coffee break and hearing what these farmers have to say.

Just in time for the holidays: Agronomy’s Shawn Conley publishes a children’s book

Shawn Conley, Extension Soybean Agronomist and Associate Professor, along with Judy Mannes and Marsha Rehns, just published a children’s book “Coolbean the Soybean” in cooperation with the American Society of Agronomy and the Wisconsin Soybean Marketing Board. To see a brief excerpt of the book, go here.

Coolbean the Soybean

For the CALS news article, go here. The book is available for purchase from the American Society of Agronomy’s bookstore.

Prof. Shawn Conley’s website for Wisconsin’s soybean producers was recently re-designed. To access the site, go here.

Weed Control Considerations for a Late Spring

News flash, it’s been a late, wet, challenging spring for a number of reasons. Okay, that’s not much of a news flash. The USDA-NASS Wisconsin Crop Progress report released today indicates that as of May 26, 64% corn is planted with 27% emerged, and 29% soybean is planted with 5% emerged. I’m certain that many of those fields were planted right between rain storms. Since that means roughly ¼ of our corn and soybean acres in the state will have seed in the ground without plants emerged, and many of those fields may have been too wet for herbicide and/or fertilizer applications, I suspect there are a lot of critical weed control decisions that could be encountered in the next week, particularly when ‘Plan A’ didn’t work out well.

Considerations for planted corn fields needing herbicide

In corn, some common scenarios for ‘Plan A’ likely included a nitrogen application before the corn was planted. Secondarily, the plan may also have been to apply nitrogen in the form of Urea Ammonium Nitrate (UAN) as a carrier with a preemergence (PRE) herbicide. Those are a couple of traditional practices and there are a lot of PRE herbicides that can be applied before and after corn plants emerge, and a lot of PRE herbicides that can be applied with UAN as a carrier. However, if you chose an herbicide and nitrogen program with the full intention that the applications would be made before plants emerge, and now you find yourself needing to accomplish these applications after plants are emerging, there are some considerations that should be double-checked to avoid problems.

For starters, the maximum growth stage at which an herbicide application can no longer be applied postemergence (POST) is different for every product. Of particular importance, though, is that there are some herbicide products like Fierce, Sharpen, and Verdict (as examples) that cannot be made to emerged plants. Second, there are products that can be applied with UAN after corn plants emerge, but the risk of crop injury is greatly increased with these combinations. Please be cautious and double check the label for recommendations regarding limitations on crop stage, tank-mix combinations including adjuvant interactions, and rates of both herbicides and UAN. If you planned to apply 100% of your nitrogen needs as UAN, you may have to consider side-dressing applications to reduce the up-front nitrogen rate mixed with herbicide if the crop has emerged.

Considerations for planted soybean fields needing herbicide

In soybean, there are also some herbicides that can be applied before and after plants emerge, but there are many more products that CANNOT be applied once the plants start to emerge, and some are further restricted to applications no more than 3 days after planting. These products include (but may not be limited to): Authority Assist, Authority First, Authority MTZ, Authority XL, Enlite, Envive, Gangster, Lorox, Metribuzin, Optill, OpTILL Pro, Sharpen, Sonic, Valor, and Valor XLT.

Moreover, another consideration that may soon be encountered is whether soybean can be planted in fields that were planned for corn. If there have already been herbicide applications made in preparation for corn, the labels of those products will need to checked to make certain it is possible to plant soybean there. There are a few herbicides that can be used at similar rates ahead of both corn and soybean, but in many cases this will be a limiting factor. If corn herbicides have been used that restrict soybean planting, I’m afraid you are ‘locked’ in for corn. Options in this scenario would include proceeding with corn with reduced yield expectation or exercising preventive planting options. For more information about corn agronomic considerations of late planting visit the UW Extension Corn Agronomy web page and for more information about regarding insurance considerations consult a recent article by Ag Economist Dr. Paul Mitchell.

Considerations for fallow fields from prevented planting

If a grower is considering the option of taking a preventative planting payment for not establishing a crop, there are a couple of considerations about weed control that should be taken into consideration. First, an obvious statement, fallow ground will be a haven for weeds to flourish for the rest of the season. An important component in an integrated management system will be to limit any seed production of weeds during the fallow year. Options will include repeated herbicide applications, repeated tillage applications, a cover crop, or some combination of these options. The most immediately important point I want to make is that all of these options will cost money and should be factored into the financial equation during the decision process of whether to take a preventive planting payment without establishing a crop.

Weed control with herbicide:

Why did I say ‘repeated’ herbicide applications? First, there may be several herbicide options to choose from to manage weeds all season, but make certain if you use residual herbicides they are appropriate choices for your rotational crop. Second, don’t expect that a residual herbicide, which provides season-long control in a crop will also provide season-long control on fallow ground. It’s likely that even many expensive residual herbicide programs would need a second application at the end of the season without the help of a competitive crop. Also, realize that striving for fields completely free of vegetation all summer-long may be a tremendous risk to soil erosion. From this perspective, allowing weeds to occupy the field for some vegetative growth may not be a bad thing as long as they are terminated prior to flowering. Unfortunately, if you violate weed size limitations on the labels of non-selective herbicide products, it would not only be accepting tremendous risk of ineffective control, but it would also provide tremendous selection pressure for herbicide resistance. So, to rely on non-selective herbicides that don’t have residual activity will also likely necessitate multiple applications.

Weed control with tillage:

Perhaps the most straight-forward discussion is of repeated tillage applications with tillage equipment, probably a disc, to keep vegetation from going to seed. The only comment here is that this could, depending on soil type, be a tremendous risk to soil erosion or other soil properties.

Weed control with a cover crop:

Establishing a crop to aid the suppression of weeds in this scenario is a great idea. However, keep in mind there are different considerations for establishing a ‘cover’ crop and establishing a ‘forage’ crop. A cover crop will be grown the rest of the year but not harvested. In this case, the major consideration is whether there are possibly any herbicide residues in the soil that would inhibit getting the cover crop species established. However, if you have any intentions of harvesting the crop for any kind of grazing or haying later in the year, that crop is a forage crop. Under this scenario, make certain you understand the implications for crop insurance, and secondarily make sure the following crop planted is allowed as a rotational crop on the pesticide labels that have been used in that cropping system for at least the previous 3 years. There are several herbicides that would prevent a large number of forage crops to be harvested and fed to livestock for as long as 40 months following herbicide application.

Lists of product names mentioned in this article were not meant to be all inclusive or as any product endorsement. As always, read and follow the label directions for all products you are using in a cropping system. Last, good luck and think safety first in this challenging season.

Vince M. Davis, Cropping Systems Weed Scientist

Apps for Ag

Attention Tablet and Smartphone Users!

Universities and private companies have developed an array of applications for agriculture. Here at the University of Wisconsin, the Integrated Pest and Crop Management program has produced three apps: Wisconsin’s Corn Nitrogen Calculator, Nitrogen Price Calculator, and the IPM Toolkit.

Other free apps:

  • ID Weeds by the University of Missouri Extension for Android and iPhone. For the web page, go here.
  • Aphid Speed Scout by the University of Nebraska.
  • Ground Spray by the University of Nebraska for Android and iPhone.
  • PeRK by the University of Nebraska, an app for pesticide record keeping available for Android and iPhone.
  • SoilWeb for Android and iPhone. The California Soil Resource Laboratory designed this app to use data from the USDA-NCRS to identify your soil type based on your phone’s GPS location. If you haven’t bought a smartphone, you can still access the data at the Web Soil Survey.
  • Nitrogen Calculator, University of Illinois, covering Iowa, Illinois, Indiana, Michigan, Minnesota, Ohio, and Wisconsin.
  • Extreme Beans developed by the United Soybean Board.
  • MixTank by Precision Laboratories is free but a fee is charged for integrated weather data.
  • The Northern Plains Integrated Pest Management Guide was developed collaboratively between University of Minnesota Extension, South Dakota State University, Kansas State University, Iowa State University Extension, North Dakota State University Extension, University of Nebraska Lincoln Extension, and the North Central Integrated Pest Management Center.
  • Farm Fuel Budget by North Dakota State University for Android only.
  • FuelLog, by Simon Morgenthaler, will track fuel consumption, miles, maintenance and much more for your vehicles. Free and fee versions available.