Update:
Field Trip Creates Palmer Amaranth Awareness, Improves Identification Skills and Fosters Team Building for Developing Management Solutions

Thomas J. Peters1,2, Alicia E. Harstad3 and Greg R. Kruger4

1Associate Professor, Department of Plant Sciences, North Dakota State University, Fargo, ND, USA and 2University of Minnesota, St Paul, MN, USA; 3Stutsman County North Dakota Extension Agent, Jamestown, ND, USA; and 4Associate Professor, West Central Research and Extension Center, University of Nebraska, North Platte, NE, USA

Executive Summary
Weeds continue to be a production challenge for producers despite chemical, mechanical, and cultural strategies for their control. Practices controlling weeds in fields this year may not provide acceptable weed control in future years because weeds shift. Weed population shifts are the changes in the species that make up the population of a locality, often caused by changes in weed management practices. Pigweed species have become more prevalent in fields in many regions in North Dakota and northwest Minnesota. Moreover, pigweed germinating near the soil surface and following rainfall events from May into early August is well adapted to modern agricultural practices featuring reduced tillage practices and heavier emphasis on use of postemergence herbicides. Finally, pigweed species produce a tremendous amount of seed. Palmer amaranth has spread from its origin in the desert southwest to agricultural fields in most states. Palmer amaranth was discovered in Minnesota in 2016 and in North Dakota in 2018. In both states, Palmer amaranth infestation has been limited to an area within a single field in the county. Experts describe Palmer amaranth as a game changer due to its rapid growth habit, seed production capability and its genetic diversity that has resulted in resistance to at least six families of herbicides. Palmer amaranth can be managed, but control requires an integrated weed management approach and not superficial use of herbicides. North Dakota and Minnesota producers are in a unique position to stay in front of a weed control challenge some midwestern producers have already lost. However, control utilizing an integrated management strategy including cultural, mechanical, and chemical control practices is paramount. Additionally, control will require a cohesive effort from everyone (land managers, farmers, extension, government, county officials, etc.) to win this fight. Agriculturalist from North Dakota and Minnesota visited commercial fields in Nebraska and the University of Nebraska West Central Research and Extension Center, North Platte, NE to learn Palmer amaranth identification and control strategies successfully implemented in Nebraska. The idea is to create awareness and experience that can be utilized in North Dakota and prevent widespread Palmer amaranth outbreaks. Training in December 2019 ensures that all Agents have access to teaching modules including presentations, pictures, and videos. Most importantly, Agents were trained on a best management practices document detailing roles and responsibility and procedures to follow in the event Palmer amaranth is suspected in North Dakota fields.

Introduction:
Palmer amaranth (Amaranthus palmeri) is an invasive weed native to the desert regions of southwest United States and northern Mexico. Palmer amaranth is fast-growing, highly competitive with row crops and has had a devastating effect on soybean production in the mid-south including fields in Arkansas, Tennessee, Kansas, Nebraska, and Missouri. More recently, Palmer amaranth was identified in agricultural fields in Wisconsin, Minnesota, and Iowa.

Palmer amaranth is highly competitive with crops and other weed species. Palmer amaranth can produce up to 130% more biomass at four weeks after planting than other pigweed species (Sellers et al. 2003). Palmer amaranth has wider leaves than other pigweed species including waterhemp (Mallard 2009), which creates a sunlight interception advantage over its counterparts. Rapid growth habit (up to 4 inches per day) and season-long emergence (Jha and Norsworthy 2005; Keeley et al. 1987) means producers have only a narrow window to control Palmer amaranth before weeds are too large and herbicides are no longer effective or the weed begins to reduce crop yield due to competition damage. Palmer amaranth grows vigorously (up to 9 feet tall in a growing season) and competes with other vegetation for light, water, nutrients, and space. Palmer amaranth is a prolific seed producer, capable of making 600,000 seeds per plant (Sellers et al. 2003) thus rapidly replenishing the seed bank.

Palmer amaranth is a C4 plant and is more efficient in water and light utilization than other plants (Downtown 1975). Likewise, Palmer amaranths’ photosynthetic capacity is even greater than other C4 plants. Palmer amaranth outcompetes most other plant species for light because its leaves solar track thereby remaining perpendicular to the direct solar rays (Ehleringer 1983). Palmer amaranth is drought tolerant thereby enabling it to survive and grow under moisture stress conditions in which most plants would hardly thrive in. Palmer amaranth aggressively competes with row crops, causing up to 91% yield loss in corn (Massinga et al. 2012) and up to 78% yield loss in soybean (Bensch et al. 2003) through weed interference in Kansas. Some Palmer amaranth biotypes are resistant to six unique herbicide sites of action; some biotypes are cross-tolerant to multiple sites of action.

North Dakota Extension programing designed to create Palmer amaranth awareness began in 2015. Extension programming focused on teaching weed identification to differentiate Palmer amaranth from other amaranthaceae family species common in North Dakota including waterhemp, redroot pigweed, and Powell amaranth. Extension also emphasized Palmer amaranth’s propensity for weed resistance and its rapid growth habitat which makes controlling Palmer amaranth with herbicides difficult. Extensions’ mantra was to contact and Agent or a Specialist if a weed species in the landscape is observed as being different.

Palmer amaranth was first confirmed in North Dakota in McIntosh County in August 2018. Soon thereafter, Palmer amaranth was confirmed in four other counties including Dickey, Foster, Benson and Richland Counties. Stakeholders managed infestation by hand-pulling and destroying plants. Control of Palmer amaranth will ultimately reside with groups of growers and/or landowners (community) committed to preventing widespread infestations of Palmer amaranth across the state. Widespread infestations of Palmer amaranth threaten the profitability of soybean production in North Dakota by reducing soybean yield from weed competition and increasing the cost of soybean weed control.

Palmer amaranth cannot be allowed to establish in North Dakota before we learn best management practices since the cost of control is too great. Thus, the agricultural community must be proactive. The objectives of this project were to travel to a region of the country where Palmer amaranth is a production challenge and observe and learn firsthand how growers manage Palmer amaranth in soybean. Through experiences, participating Agents will develop training curricula including presentations, images, and video to train non-participating Agents and North Dakota stakeholders.

Materials and Methods
Twenty-five participants including extension agents and specialists, field agronomists, ag-retailers, producers, weed board officers and commodity group members departed from Jamestown, ND to North Platte, NE on August 12, 2019. The four-day bus trip / short-course combined lecture hall presentations, field and greenhouse research tours, ag retailers and growers’ interaction, and numerous commercial field visits. A professional photographer documented the trip with still images and video that were edited and distributed to extension staff after the December in-service training.

Forty-five individuals attended an in-service training meeting for extension staff and weed board officers in Carrington, ND on December 19, 2019. The meeting agenda highlighted topics from the Nebraska trip and considered contrasting attitudes and lessons learned regarding Palmer amaranth in the 2017 vs. 2019 bus trips, pigweed identification and management, herbicide mode of action, impacts of spray quality considerations on Palmer amaranth control and refinement of the Palmer amaranth protocol for first encounter with fields suspected with Palmer amaranth. The protocol highlights step-by-step measures to be followed once Palmer amaranth has been identified and roles and responsibilities for extension staff, weed board officers, the ag-retailer, ND Department of Agriculture and the farmer or landowner. Attendees were surveyed after the bus tour and after the in-service training to collect both qualitative and quantitative data of their learning experiences.

Results and Discussion
Teaching materials developed following the 2017 Nebraska tour were used throughout 2018 and directly and indirectly encountered 7,900 and 60,900 ND producers, landowners, and related stakeholders, respectively. Extension created awareness of the potential economic impact of Palmer amaranth to North Dakota, generating further interest.

The 2019 tour was a working meeting. We viewed University of Nebraska, West Central Research and Extension Center research considering an integrated Palmer amaranth management plan, providing attendees with an understanding of types of programs they may need to implement in North Dakota soybean production. Research combined chemical, mechanical, and cultural control strategies in soybean and in crops grown in the sequence with soybean. Participants also viewed numerous commercial fields on a guided bus tour facilitated by local agricultural retailers (Figure 1). As we traveled, tour guide made observations and indicated what programs their grower customers implemented for Palmer amaranth control. Attendees observed and contrasted various control strategies and results by stopping periodically to allow attendees to walk fields and take pictures. Attendees met several local growers participating in the tour providing their personal perspectives.

Figure 1. Palmer Amaranth about 9-foot-tall pulled from a commercial corn field near Holdrege, Nebraska, August 2020.

Participants observed examples of clean fields when producers used multiple production strategies including soybean-soybean-corn crop sequences, soybean narrow row spacing, layering with PRE, EPOST and POST herbicides, dicamba or Liberty to control escapes, inter-row cultivation or hand-weeding, and cover crops seeded in fields between crops to create competition for Palmer amaranth germination and emergence. But most important, the participants discovered Palmer amaranth can be managed. However, control requires an integrated weed management approach and not superficial use of herbicides. Moreover, North Dakota producers are in a unique position to stay in front of a weed control challenge some midwestern producers have already lost. Finally, control will require a cohesive effort from everyone including land managers, farmers, extension, government, county officials, etc. to win this fight.

An observation of concern was Palmer amaranth growth and seed production in alfalfa. Nebraska alfalfa producers are on a 35-day cut schedule. We observed Palmer amaranth biotypes selected for short-season Palmer amaranth. That is, Palmer amaranth that grows, flowers, and produces a seed head between alfalfa cut cycles. Palmer amaranth seed either reestablishes itself in the field or is bailed in alfalfa hay which potentially could introduce Palmer amaranth to a new location when hay is transported. Palmer amaranth is not on the noxious weed list in Nebraska since it is an indigenous plant in the US / North America.

Quantitative survey results from the 2019 Nebraska bus tour are displayed in Table 1. Most striking was participant development of Palmer amaranth identification skills. Attendees improved their Palmer amaranth identification skills 41% through interaction with ag-retailer staff and field tours (Figure 2). Likewise, attendees improved their knowledge of factors influencing off-target movement and economic losses from Palmer amaranth by 24%.

Table 1. University of Nebraska trip participant survey

Participants learned Palmer amaranth is controlled better in soybean than corn using dicamba with Xtend soybean and other soybean technologies. A participant stated, “This was a real eye opener for me this week. I did not really know what to expect from this tour. I am concerned

Figure 2. Tom Peters explaining Palmer amaranth identification to 2019 bust tour participations, North Platte, NE, August 2020.

when this hits home to what the reaction is going to be. A second attendee stated, “I thought it was a good experience to show everyone how a particular weed can take advantage of poor management strategies.”

Common themes emerging from the quantitative data from the 2019 Nebraska bus tour included:
• Field edges and ditches should be a focus area for Palmer amaranth control strategies.
• Palmer amaranth can adapt to anything including iron. Thus, we must remain vigilant.
• Education will continue to be extensions’ most important deliverable for producers and other extension stakeholders. Extension will address how important it is that producers are prepared to manage Palmer correctly.
• Weed management is complex; we must use all available tools.
• Palmer amaranth control is a team effort between extension, weed boards, consultants, and producers.

Forty-five attendees participated in an in-service training meeting held at the Carrington Research Extension Center, Carrington, ND on December 19, 2019. Topics developed for the training were suggested and led by Nebraska trip participants. Most important was the development and training on the North Dakota Palmer amaranth protocol. Table 2 shows the quantitative data results from the participant survey following the in-service training. Ninety-

Table 2. In-service training participant survey

three percent of in-service training attendees stated they will affectively be able to use the ND Palmer amaranth protocol in the event they need to visit a suspected Palmer amaranth field. Likewise, 27% of participants improved their knowledge of spray droplet technology and how nozzle type, nozzle size, spray pressure, pesticide mixtures and adjuvants affect spray quality.

An in-service training attendee stated, “The commitment to waterhemp/Palmer amaranth management in ND is tremendous. Awareness has prevented minor problems from being major problems.” A second attendee added, “Updated [teaching] resources were great.” PowerPoint presentations, images, video’s, and documents were posted on a server accessible for Extension personnel for further use.

Literature:
1. 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 Sci. 51:37-43
2. Downton WJ (1975) The occurrence of C4 photosynthesis among plants. Photosynthetica 9:96-105.
3. Ehleringer J (1983) Ecophysiology of amaranthus palmeri, a sonoran desert summer annual.
Oeologia 57:107-112.
4. Jha P, Norsworthy JK (2005) Palmer amaranth emergence timing: An aid to develop integrated weed management strategies. Clemson University Research Forum.
5. Keeley PE, Carter CH, Thullen RJ (1987) Influence of planting date on growth of palmer amaranth (Amaranthus palmeri). Weed Sci. 35:199-204.
6. Mallard, DJ (2009) Management of glyphosate resistant palmer amaranth in LibertyLink® soybeans. MS. Thesis. Martin, TN. University of Tennessee. 4-5 p.
7. Massinga, RA, Currie RS, Horak MJ, Boyer J (2001) Interference of Palmer amaranth in corn. Weed Sci. 49:202-208.
8. Sellers BA, Smeda RJ, Johnson, WG, Kendig JA, Ellersieck MR (2003) Comparative growth of six amaranthus species in Missouri. Weed Sci. 51:329-333.

View uploaded report

View uploaded report 2

Weeds continue to be a production challenge for producers despite chemical, mechanical, and cultural strategies for their control. Practices controlling weeds in fields this year may not provide acceptable weed control in future years because weeds shift. Weed population shifts are the changes in the species that make up the population of a locality, often caused by changes in weed management practices. Pigweed species have become more prevalent in fields in many regions in North Dakota and northwest Minnesota. Moreover, pigweed germinating near the soil surface and following rainfall events from May into early August is well adapted to modern agricultural practices featuring reduced tillage practices and heavier emphasis on use of postemergence herbicides. Finally, pigweed species produce a tremendous amount of seed.

Palmer amaranth has spread from its origin in the desert southwest to agricultural fields in most states. Palmer amaranth was discovered in Minnesota in 2016 and in North Dakota in 2018. In both states, Palmer amaranth infestation has been limited to an area within a single field in the county. Experts describe Palmer amaranth as a game changer due to its rapid growth habit, seed production capability and its genetic diversity that has resulted in resistance to at least six families of herbicides. Palmer amaranth can be managed, but control requires an integrated weed management approach and not superficial use of herbicides. North Dakota and Minnesota producers are in a unique position to stay in front of a weed control challenge some midwestern producers have already lost. However, control utilizing an integrated management strategy including cultural, mechanical, and chemical control practices is paramount. Additionally, control will require a cohesive effort from everyone (land managers, farmers, extension, government, county officials, etc.) to win this fight.

Agriculturalist from North Dakota and Minnesota visited commercial fields in Nebraska and the University of Nebraska West Central Research and Extension Center, North Platte, NE to learn Palmer amaranth identification and control strategies successfully implemented in Nebraska. The idea is to create awareness and experience that can be utilized in North Dakota and prevent widespread Palmer amaranth outbreaks. Training in December 2019 ensured all Agents have access to teaching modules including presentations, pictures, and videos. Most importantly, Agents were trained on a best management practices document detailing roles and responsibility and procedures to follow in the event Palmer amaranth is suspected in North Dakota fields.