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.

Triple threat herbicide resistant goosegrass

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).

  1. Heap, I. 2015 The International Survey of Herbicide Resistant Weeds. Online. Available at www.weedscience.org
  2. 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.
  3. 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.

For more information about herbicide resistance management, please visit our documents page, video page and/or the TakeAction on Weeds website.

Glyphosate resistance confirmed in two Wisconsin common waterhemp populations

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Recently, Thomas Butts, a graduate research assistant, and Vince Davis confirmed two herbicide-resistant common waterhemp populations in Wisconsin. The full report is now available. For more information, please visit the WCWS documents page.

Palmer amaranth confirmed glyphosate-resistant in Dane County, Wisconsin

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Thomas Butts, a graduate research assistant, and Vince Davis report a new confirmation of a glyphosate-resistant weed in Wisconsin. Their full report is available here. For more information, please visit the WCWS documents page.

Start the New Year with Herbicide Resistance Management

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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.

Event- 2015 Wisconsin Crop Management Conference

The 2015 Wisconsin Crop Management conference will be held at the Alliant Energy Center in Madison, Wisconsin from January 13 until January 15. To save on advance registration, make sure to submit your form and payment by December 19, 2014.

To access the conference programming, go here for a complete list of events and the registration form. Also, online registration is available here.

Vince Davis, Thomas Butts, and Dan Smith will be presenting at this year’s conference. During the Weed Management section on Wednesday January 14, Vince will be talking about “Efficacy of “new” herbicides and program approaches for resistance management.” Tommy will be discussing his latest research results, “Herbicide-resistant pigweeds (Amaranthus spp.) are in Wisconsin, how serious is it?” Dan will be presenting his research on “Cover crop establishment following commonly applied corn and soybean herbicides in Wisconsin.”

More Winter Reading, the 2014 WCWS Research Report

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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.

Hurry! Register for Pest Management Update Meetings

Hopefully, you will have finished or nearing the end of harvest by mid-November and will be ready to attend Extension’s Pest Management Update series. County Extension agents across Wisconsin will be hosting Pest Management Update Meetings during the second and third weeks in November. The purpose of each meeting is to review the past growing season and provide updates on research that can be applied to your farm. The speakers are Extension State Specialists including:

  • Bryan Jensen, Entomologist
  • Damon Smith, Field Crops Pathologist
  • Dan Heider, IPM Specialist
  • Mark Renz, Weed Scientist for Perennial Cropping Systems
  • Vince Davis, Weed Scientist for Annual Cropping Systems

Please register one week prior to the event. For a complete schedule of meetings including county agent contact information, please go here. Registration includes lunch, an information packet, and a copy of the 2015 Pest Management in Wisconsin Field Crops book. Four hours of CEU pest management credits will be available at each location. The registration fee is $40.

Preliminary data suggests glyphosate resistance of two Wisconsin common waterhemp (Amaranthus rudis) populations

Thomas R. Butts and Vince M. Davis

Department of Agronomy, University of Wisconsin-Madison

Common waterhemp (Amaranthus rudis) is a dioecious, small seeded, broadleaf weed species native to North America, specifically common in the Midwest region of the United States. This weed species has become increasingly problematic for corn and soybean growers due to its prolific growth characteristics and highly competitive ability. Among its fellow pigweed (Amaranthaceae) family members, common waterhemp is second only to Palmer amaranth (Amaranthus palmeri) in growth rate and size reaching heights of nearly ten feet 4. Furthermore, common waterhemp can produce over one million seeds per female plant under ideal growing conditions 8. This intensifies the likelihood and speed that herbicide-resistant biotypes can increase in a population and transfer from one location to another through seed dispersal. If common waterhemp is left unmanaged in corn and soybean, growers can see yield reductions of 74 and 56%, respectively2,7.

Control of common waterhemp has become increasingly difficult due to its ability of evolving resistance to numerous herbicide sites-of-action. To date, this weed species has been identified as resistant to six different sites-of-action, including an ALS-resistant biotype located in Wisconsin. Several common waterhemp populations have also evolved resistance to multiple herbicide sites-of-action, further complicating control methods1,5. Glyphosate-resistant common waterhemp biotypes have already been confirmed in fifteen other states including nearby Illinois, Indiana, Iowa, and Minnesota3. Our current research reported here suggests we will add Wisconsin to this list as data from our first greenhouse experiment indicates at least two Wisconsin common waterhemp populations are resistant to glyphosate out of 14 populations examined.

The two weed populations examined were collected from crop production fields in Eau Claire and Pierce counties. They were identified through the Late-Season Weed Escape Survey in Wisconsin Corn and Soybean Fields conducted in 2012 and 2013 by former graduate research assistant, Ross A. Recker. Plants that were collected in the field were likely to have survived a postemergence glyphosate application based on in-field observations of herbicide symptomology, plant locations, personal communication with growers, and other additional data documented during the survey. To confirm glyphosate resistance, seed was collected from 30 mature plants in the field, progeny were grown in the UW-Madison greenhouse, and 10 plants per glyphosate rate were sprayed with Roundup PowerMAX® plus ammonium sulfate at 17 lbs. per 100 gallons of spray solution when they reached three inches tall. Glyphosate rates used were 0, 0.22 (5.5), 0.43 (11), 0.87 (22), 1.74 (44), and 3.48 (88) kg ae ha-1 (fl. oz. ac-1). Plant dry biomass data were collected 28 days after application (DAA). Comparisons between our putative resistant and susceptible biotypes were determined by the effective glyphosate dose needed to reduce plant dry biomass 50% (ED50).

The ten Pierce County plants sprayed at the 0.87 kg ae ha-1 (22 fl. oz. ac-1) rate all survived and grew to an average of three times their spray date height (Figure 1). At the 1.74 kg ae ha-1 (44 fl. oz. ac-1) rate, nine of ten plants survived and grew to an average of two times their spray date height (Figure 2). The ED50 of glyphosate for the Pierce County and susceptible populations was 2.23 and 0.18 kg ae ha-1, respectively (Figure 3). This indicates the Pierce County population has a 12.5-fold level of resistance.

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The ten Eau Claire County plants sprayed at the 0.87 kg ae ha-1 (22 fl. oz. ac-1) rate all survived and grew to an average of five times greater than their spray date height (Figure 4). All ten plants also survived the 1.74 kg ae ha-1 (44 fl. oz. ac-1) rate and quadrupled in size from their spray date height (Figure 5). The Eau Claire County population was not able to be analyzed using the log logistic Dose Response Model in R due to inadequate high rates of glyphosate to reduce dry biomass at 28 DAA. Therefore, linear glyphosate response models were established for the Eau Claire County and susceptible populations and analyzed using ANOVA tables which indicated significant differences at all glyphosate rates (Figure 6) (Table 1).

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There are several key components to an effective control strategy for glyphosate-resistant common waterhemp. The use of alternative herbicide sites-of-action, such as PPO inhibitors, and tank-mixing multiple herbicide sites-of-action will improve glyphosate-resistant weed control. An early planting date will allow crops to gain a head-start and outcompete common waterhemp due to its late emergence timing6. Herbicide applications should be made at the correct timing when weeds are small and actively growing to ensure the greatest efficacy of the herbicide based on label recommendations. Furthermore, special care should be taken to clean tillage and harvest equipment thoroughly as they can quickly spread weed seed among fields. The focus of these best management practices is to diversify weed control measures, reduce weed seed additions to the soil seedbank, and utilize control measures in the most effective method possible.

This research experiment will be repeated to officially confirm glyphosate resistance in these common waterhemp populations. For updates on Wisconsin weeds please visit our Wisconsin Crop Weed Science website at http://wcws.cals.wisc.edu/. Further information on controlling common waterhemp or other glyphosate-resistant weeds can be found at: http://takeactiononweeds.com/. Finally, if you believe you may be facing glyphosate-resistant weeds in your fields, contact your local county extension agent and/or Dr. Vince Davis at vmdavis@wisc.edu or (608) 262-1392.

References:

  1. Bell MS, Hager AG, Tranel PJ (2013) Multiple Resistance to Herbicides from Four Site-of-Action Groups in Waterhemp (Amaranthus tuberculatus). Weed Science 61:460-468
  2. Bensch CN, Horak MJ, Peterson D (2003) Interference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Science 51:37-43
  3. Heap I (2013) The International Survey of Herbicide Resistant Weeds: Web page. http://www.weedscience.com/Summary/home.aspx. Accessed April 01, 2013
  4. Horak MJ, Loughin TM (2000) Growth Analysis of Four Amaranthus Species. Weed Science 48:347-355
  5. McMullan PM, Green JM (2011) Identification of a Tall Waterhemp (Amaranthus tuberculatus) Biotype Resistant to HPPD-Inhibiting Herbicides, Atrazine, and Thifensulfuron in Iowa. Weed Technology 25:514-518
  6. Sellers BA, Smeda RJ, Johnson WG, Kendig JA, Ellersieck MR (2003) Comparative Growth of Six Amaranthus Species in Missouri. Weed Science 51:329-333
  7. Steckel LE, Sprague CL (2004) Common waterhemp (Amaranthus rudis) interference in corn. Weed Science 52:359-364
  8. Steckel LE, Sprague CL, Hager AG, Simmons FW, Bollero GA (2003) Effects of shading on common waterhemp (Amaranthus rudis) growth and development. Weed Science 51:898-903