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.
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 http://wcws.cals.wisc.edu/herbicide-injury-diagnostic-tool 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:
- Each page shows your previous answers.
- A ‘Start over’ button is located at the bottom of each page.
- 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).
- Simplified guides to symptoms that mimic herbicide injury during and after emergence are included on each mode-of-action page (Fig. 2).
- Photo galleries for both corn and soybean injury symptoms are located on the same page (Fig. 3).
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.
The fields may look cold, wet, and dormant this week but weeds were germinating in some fields in Janesville and Arlington last week. On April 17 at Janesville, common lambsquarters, giant ragweed, and horseweed were emerging (Fig. 1A-D). At Arlington in a plowed area, velvetleaf was emerging (Fig. 2). If you are leasing new land this year or want to get a head start on weed management, then scouting for weeds at the seedling stage before tillage can be a good way to assess density, the number of weeds in a given area, and for which weed species will likely be an issue around planting time. The Weedometer, developed by University of Wisconsin, can predict when weed species will likely be emerging for your location at http://weedecology.wisc.edu/weedometer/ . A guide to identifying the “Common Weed Seedlings of the North Central States” is available in pdf and print formats at Cooperative Extension’s Learning Store, or on the WCWS Weed info page.
Researchers from the Australian Herbicide Resistance Initiative report on the first confirmed case of a weed, Indian goosegrass (Eleusine indica), resistant to three non-selective herbicides, glufosinate, glyphosate, and paraquat along with several ACCase inhibitor herbicides (Jalaludin et al., 2014). The goosegrass population was initially reported in Malaysia by a vegetable farmer and a planter from an oil palm nursery (Jalaludin et al. 2010).
In the United States, E. indica occurs in forty five of the fifty states. In Wisconsin, populations have been identified in the following counties: Columbia, Dane, Grant, Lafayette, Rock, Kenosha, and Milwaukee. The first documented case of herbicide resistant E. indica was from North Carolina in 1973 and the latest confirmation was in 2011 (Heap, 2015).
The amount of glufosinate to kill half of the tested resistant plants was equivalent to applying 40 fl oz per acre (e.g. Liberty 280 SL). The maximum rate for the season in corn is 36 fl oz per acre. The next generation of plants from the resistant population required 657 fl oz per acre of glyphosate (i.e. Roundup Powermax) to kill half of the tested population. These plants also were twice as resistant to paraquat compared to the susceptible plants. Half of the resistant population survived applications of the ACCase inhibitors- haloxyfop-P-methyl (e.g. Verdict) and fluazifop-P-butyl (e.g. Fusilade).
- Heap, I. 2015 The International Survey of Herbicide Resistant Weeds. Online. Available at www.weedscience.org
- Jalaludin, A.; Ngim, J.; Baki, BB.; Zazali, A. 2010 “Preliminary findings of potentially resistant goosegrass (Eleusine indica) to glufosinate-ammonium in Malaysia.” Weed Biology and Management 10: 256-260.
- Jalaludin, A.; Yu, Q.; Powles, S.B. 2014 “Multiple resistance across glufosinate, glyphosate, paraquat, and ACCase-inhibiting herbicides in an Eleusine indica population” Weed Research 55: 82-89.
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.
TakeAction: Herbicide Resistance Management
Update on Herbicide Resistant Weeds in Wisconsin
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