Waterhemp is the most problematic weed in Minnesota impacting several thousand acres of soybean in the state. When competing with the row crops, the herbicide-resistant waterhemp populations can reduce the crop yields substantially and the contaminations of waterhemp seeds in soybean can decrease the market value for the produce. Research conducted in 2021 confirmed that the multiple herbicide-resistant waterhemp is present in Minnesota and up to four-way resistance was confirmed.
The multiple herbicide-resistant waterhemp populations are reducing the value of recently developed multiple herbicide-resistant soybeans such as Enlist E3 (2,4-D choline, glyphosate, and glufosinate- resistant), and XtendFlex (dicamba, glyphosate, and glufosinate-resistant). Waterhemp can emerge throughout the growing season and sequential application of soil residual herbicides are recommended for effective control of this weed; however, some of these herbicides may cause carryover issues and injure subsequent sugar beet crops.
This proposed research will continue the effort of screening suspected herbicide-resistant waterhemp populations in Minnesota soybean. In the Fall of 2021, more than 130 waterhemp seed samples from the plants that survived the preemergence and postemergence herbicide treatments were obtained. In 2022, they will be screened for resistance to soybean herbicides (both preemergence and postemergence) in the greenhouse located at the University of Minnesota’s St. Paul campus. If needed, the genetic tests will be performed on selective populations at the Molecular Weed Science Lab at Colorado State University to confirm the results obtained in the greenhouse research. The results will be presented in different Extension meetings and web-posts.
The second objective of this project is to evaluate the effect of integrated weed management on waterhemp control and soybean yield in soybean-sugar beet rotation. In 2021, on-farm research trials were conducted at Clay County and Renville County, MN, and the treatments included herbicide program (low-input and high-input) and soybean row-spacing (15- and 22-inches). In 2022, waterhemp seedbank will be estimated in the experimental plots and waterhemp density will be recorded in sugar beet crop. Moreover, this research will be repeated in soybean in 2022 in a new location in the same field.
This experiment will be conducted in Moorhead, MN (Clay County) and Franklin, MN (Renville County) and that will serve many soybean growers in MN. In 2021, we had an on-farm research demonstration plot tour in Franklin, MN, and the preliminary results were presented in several Extension events in MN and ND. We will continue to do the same in 2022. In several surveys, soybean growers have indicated that weed management is among their top priorities, and in this proposal, we are addressing some of the timely weed management issues that need immediate attention. This research will promote sustainable waterhemp management and enhance soybean yield and profitability in the state.

1. GOAL: Survey of herbicide-resistant waterhemp populations in Minnesota soybean

OBJECTIVE: This research will confirm and document the spatial distribution of multiple herbicide-resistant waterhemp populations in MN.



2. GOAL: Evaluate multi-tactic waterhemp management options in soybean in a soybean-sugar beet rotation

OBJECTIVE: This project will evaluate the multi-tactic management approaches for waterhemp control in soybean-sugar beet rotation. This project will also evaluate the waterhemp seedbank changes in response to integrated weed management.

This team comprises of two faculty with Extension appointments and an Extension educator who is the key personnel to reach out to growers, crop advisers, and other stakeholders. Research plot demonstrations will be organized in summer. The information obtained from this research will also be disseminated using web-based platforms, including, but not limited to, the MN Crop News (over 1,600 subscribers), regional Extension crop newsletters, radio spots, and Minne-Line articles. Social media platforms such as Twitter, and YouTube will be used to share the research updates and short videos. The PIs are active on Twitter and have more than 2,100 followers. Also, the data will be available at the Applied Weed Science Research website (https://appliedweeds.cfans.umn.edu/). The results will be presented at the Crop Pest Management (CPM) Short Course, where the majority of the audience consists of seed company agronomists, farmers, fertilizer/plant protection dealers, and independent crop consultants who influence over three million acres of crop lands in the state. One graduate student will be mentored in this project and this research will be part of his/her thesis work. Peer-reviewed journal articles will also be published from this research.

Objective 1: Survey of herbicide-resistant waterhemp populations in Minnesota soybean
2021 Results: In 2020, putative herbicide-resistant waterhemp samples were submitted by the soybean growers, and Extension Educators. A total of 21 populations
were received and they were screened for resistance using some commonly used soybean and corn herbicides. Results showed that all the populations were resistant to ALS inhibitor (Raptor), and 66% of the populations were resistant to glyphosate (Roundup PowerMax). Moreover, Photosystem II- (Atrazine), PPO- (Flexstar), and HPPD- (Callisto) inhibitor resistance were found in 14, 14, and 5% populations. No population showed resistance to dicamba, 2,4-D, or glufosinate, though a reduced susceptibility against these herbicides was observed in some of the populations tested. Two waterhemp populations showed resistance to four different sites of action reducing the herbicide choices for the soybean and corn growers. In 2021, more than 130 samples were collected from soybean fields in MN (Figure 1) and they will be screened in 2022.
The preliminary results from 2020 waterhemp sample-screening were presented in five Extension events in 2021 and about 180 people attended those events. One MN Crop News article was written to update the stakeholders about the resistance status in waterhemp in MN. One graduate student is mentored and he has presented this initial results in a department seminar at the university and at the North Central Weed Science Society Annual Meeting, and the MN Soybean Research and Promotion Council was recognized as the funding agency in these presentations.
Methodology for 2022 work: Waterhemp escaped following preemergence and postemergence herbicide applications in soybean were surveyed and seedheads were collected in the Fall of 2021. The survey sites were either selected randomly or based on the weed escape information from individual

growers. Depending on their availability, the history (herbicide use, crops, and tillage) of the surveyed fields were obtained from the individual farm owners.
The waterhemp seedheads will be cleaned at UMN’s Plant Growth Facility at St. Paul campus, and the seeds will be kept in a refrigerator for two months in airtight polyethylene bags to overcome the dormancy. The composite seed samples will be planted in plastic trays in the greenhouse at UMN’s St. Paul campus. Seedlings from individual populations (collected from individual soybean fields) will be grown separately and soybean herbicides will be sprayed at 1× and 3× of the labeled doses to check the sensitivity of waterhemp populations to different herbicides. Preemergence herbicides will be sprayed at the same day of planting, and postemergence herbicides will be applied at 4 inches weed height. A nontreated control will be included for comparison. The list of herbicides and their doses are provided in Table 1.
Table 1: List of soybeans preemergence and postemergence herbicides and doses.

Herbicide name Active ingredients Sites of action group* Herbicide dose
Preemergence
Dual II magnum S-metolachlor 15 1.33 pt/A
Metribuzin Metribuzin 5 0.8 lb/A
Prowl H2O Pendimethalin 3 3 pt/A
Postemergence
Raptor Imazamox 2 5 fl oz/A
Enlist One 2,4-D choline 4 2 pt/A
Flexstar Fomesafen 14 16 fl oz/A
Roundup PowerMax Glyphosate 9 32 fl oz/A
Liberty Glufosinate 10 36 fl oz/A
Xtendimax Dicamba 4 22 fl oz/A
*The herbicide site of action group is listed as per the Weed Science Society of America’s classifications.
Waterhemp seedlings emerged after preemergence herbicide application will be counted and the numbers will be compared with the nontreated control. For postemergence treatments, waterhemp injury/control will be estimated visually using a 0 to 100% scale, where 0% meaning no injury and 100% meaning complete death of the plants. Weed biomass (dry) from the treated trays will be measured and compared with the nontreated control.
Selective waterhemp populations that survived the 3× doses of at least three herbicides, will be selected for the whole-plant dose-response bioassays. That population will be sprayed with the eight doses (0, 0.125×, 0.25×, 0.5×, 1×, 2×, 4×, and 16×) of selective herbicides. Injury and aboveground dry biomass data will be collected. Leaf tissue samples from selective waterhemp populations will be collected and sent to the Molecular Weed Science Lab at Colorado State University for testing the molecular mechanisms for herbicide resistance.
Spatial maps to illustrate the distribution of herbicide-resistant waterhemp populations in Minnesota will be developed using R (R Statistical Software, Vienna, Austria). The dose-response data analysis will be performed using a four-parameter log-logistic function in R.
Objective 2: Evaluate multi-tactic waterhemp control options in soybean in a soybean-sugar beet rotation
2021 Project update: On-farm trials were conducted at Franklin, MN, and Moorhead, MN, in 2021 and the research will be repeated in 2022. Also, the waterhemp seedbank and density will be counted in

sugar beet in 2022 and 2023. Data analysis is pending from this research and the preliminary results from this research will be shared in the winter Extension meetings. An on-farm trial demonstration was performed in August 2021 at Sullivan’s Family Farm at Franklin, MN.
Methodology for 2022 work: Field experiments will be conducted in 2022 in Franklin, MN and Moorhead, MN. Locations were selected to represent two different environments. The fields where this experiment will be conducted known to have Acetolactate synthase (ALS)-inhibiting herbicide-resistant waterhemp populations. The Enlist E3 soybeans (2,4-D choline, glyphosate, and glufosinate-tolerant) will be planted. The treatments will be laid out in a split-plot design with soybean row spacing (15- and 22- inches) as the main plot factor and weed control treatment (listed in Table 2) as the subplot, and the treatments will be replicated four times. The subplot size will be 10 × 30 feet, and the herbicide applications will be made using CO2-pressurized backpack sprayers equipped with recommended nozzles.
Preemergence herbicides will be applied at the day of soybean planting, and the early-, and mid- postemergence herbicide applications will be made at V1, and V3 soybean stages, respectively. The weed control treatments are classified into three groups: low-input, high-input, and integrated weed management (listed in Table 2). The integrated weed management treatment will include herbicide treatments along with the waterhemp seed removal (manually) at soybean harvest to simulate the harvest weed seed control (HWSC). The waterhemp control (estimated visually), density, and biomass will be recorded throughout the season. Soybean yield data will be obtained and the gross-profit margins (economics) will be calculated for each treatment. Data will be analyzed using PROC GLIMMIX in SAS.
Table 2: List of treatments for weed control in soybean in a soybean-sugar beet rotation.

Soybean row spacing (main Plot)
1 22 inches
2 15 inches

Weed control treatments (sub-plot)
1 Nontreated control (check)

2 Valor SX (PRE) fb Enlist One (M-POST) Low-input (herbicide)
3 Outlook (PRE) fb Roundup PowerMax (M-POST)

4 Valor SX (PRE) fb Cobra + Warrant (E-POST) fb Enlist Duo (M-POST)
High-input (herbicide)
5 Verdict (PRE) fb Liberty + Warrant (E-POST)

6 Verdict (PRE) fb Liberty + Warrant (E-POST) fb waterhemp seed removal at harvest Integrated weed management (high-input
+ HWSC)
Table footnotes:
- Abbreviations: PRE, preemergence; E-POST, early-postemergence; M-POST, mid- postemergence; HWSC, harvest weed seed control; and fb, followed by

Herbicide doses: Cobra @12.5 fl oz/A, Enlist Duo @4.75 pt/A, Enlist One @2.0 pt/A, Liberty @32.0 fl oz/A, Outlook @14.0 fl oz/A, Roundup PowerMax @32.0 fl oz/A, Valor SX @3.0 oz/A, Verdict @5 fl oz/A, and Warrant @1.5 qt/A

Update:
Research report is attached.

View uploaded report

Update:

View uploaded report

Update:

View uploaded report

The proposed research project will evaluate and document the spatial distribution of herbicide-resistant waterhemp (the most problematic weed) in the state. Also, it will address some of the key management issues for waterhemp control in soybean. It is somewhat difficult to control waterhemp in a soybean- sugar beet rotation and the need for integrated weed management is often realized. The goals outlined in this proposal are timely and need immediate attention. Additionally, this research work will be conducted at multiple locations to represent different environments that will serve a large group of growers and other stakeholders in the state. Our ultimate goal is to obtain information on best management practices (BMPs) that will make weed management sustainable and increase soybean yield and profitability.