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
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.
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.
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:
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:
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:
Mechanical control options:
Chemical control options:
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.
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 firstname.lastname@example.org
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/
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.
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).
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 email@example.com or (608) 262-1392.
The 2013 WCWS Research Report is now updated with nine corn and seven soybean herbicide evaluation trials. Some highlights include:
Please check out our new factsheet Herbicide Rotation Restrictions in Forage and Cover Cropping Systems.
Here is a short excerpt:
Designing effective herbicide programs while following pesticide label restrictions can be challenging in any cropping system. With rotations that include forage and cover crops, the challenge can be increased-especially when a planned cover crop might be needed as supplemental or emergency forage. In this case, the best approach is to be aware of crop rotation restrictions ahead of time and plan the most effective solutiuon for all possible scenarios.
For more information on this topic, please see another WCWS article- Is it legal to use a cover crop as a forage crop? Maybe not.
In Wisconsin, it is not easy to get your cover crop seeded after corn silage, corn grain, or soybean harvests. From Penn State, researchers have been working on equipment modifications to seed a cover crop while side-dressing a corn crop with nitrogen and applying a POST herbicide.