Climate Matching Map
| Attachment | Size |
|---|---|
| climatematch-amaranthus_palmeri-oregon-20250304.pdf (1.13 MB) | 1.13 MB |
1. Question 1
Yes
1
Very High
Palmer amaranth (Amaranthus palmeri), originally native to the southwestern United States and northwestern Mexico, has become naturalized and invasive in various regions beyond its native range. In the United States, Palmer amaranth has expanded from its native southwestern regions to infest at least 27 states, including areas in the midwest and northeast. Internationally, Palmer amaranth has been reported as naturalized in several countries, including Spain, Sweden, Australia, Cyprus, India (Maharashtra), Portugal (Madeira Islands), and Romania.
“Weed Risk Assessment for Amaranthus Palmeri (Amaranthaceae) - Palmer S Amaranth”. 2020. 1730 Varsity Drive, Suite 300 Raleigh, NC 2760. https://www.aphis.usda.gov/sites/default/files/amaranthus-palmeri.pdf.
2. Question 2
Yes
2
Very High
Palmer amaranth has become naturalized in areas with temperate Mediterranean climates in the US, Europe and eastern Asia. USDA APHIS has predicted that about 81 percent of the United States is suitable for palmer amaranth based on climatic variables.
“Amaranthus Palmeri”. n.d. https://www.gbif.org/species/5384393.
“Weed Risk Assessment for Amaranthus Palmeri (Amaranthaceae) - Palmer S Amaranth”. 2020. 1730 Varsity Drive, Suite 300 Raleigh, NC 2760. https://www.aphis.usda.gov/sites/default/files/amaranthus-palmeri.pdf.
3. Question 3
Yes
2
Very High
Palmer amaranth is recognized as an invasive species both within the United States and globally. It has rapidly expanded its range, becoming one of the most troublesome and economically damaging agronomic weeds in various crops across the country.
“Palmer Amaranth (Amaranthus Palmeri S. Wats.)”. n.d. https://www.invasive.org/browse/subinfo.cfm?sub=5090.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
4. Question 4
Yes
3
Very High
Palmer amaranth has become more widespread in the Pacific Northwest in recent years. In May 2024, the Oregon State Weed Board voted to list Palmer amaranth as an âA-ratedâ weed, targeting it for early detection and containment. It thrives in hot weather, is tolerant of drought, and responds quickly to high levels of available nutrients. It competes aggressively against warm-season crops, and is a prolific seed producer. Palmer amaranth populations have developed resistance to multiple herbicide modes of action, making chemical control increasingly challenging.
“PALMER AMARANTH”. n.d. https://oregonseed.org/resources/palmer-amaranth/.
“Palmer Amaranth (Amaranthus Palmeri S. Wats.)”. n.d. https://www.invasive.org/browse/subinfo.cfm?sub=5090.
5. Question 5
Yes
1
Very High
The Amaranthus genus includes about 70 to 75 species. According to Holm et al. (1991), 36 of these species are classified as weeds, with 14 considered serious or major weeds in at least one country. Among the worst weeds globally are Amaranthus hybridus and Amaranthus spinosus. In the United States, problematic pigweed species include redroot pigweed (A. retroflexus), smooth pigweed (A. hybridus), Powell amaranth (A. powellii), spiny amaranth (A. spinosus), tumble pigweed (A. albus), prostrate pigweed (A. blitoides), and common waterhemp (A. rudis, also known as A. tuberculatus). Pigweeds are fast-growing, aggressive weeds that compete with crops and pose significant challenges for farmers.
“Weed Risk Assessment for Amaranthus Palmeri (Amaranthaceae) - Palmer S Amaranth”. 2020. 1730 Varsity Drive, Suite 300 Raleigh, NC 2760. https://www.aphis.usda.gov/sites/default/files/amaranthus-palmeri.pdf.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
6. Question 6
No
0
Medium
Palmer amaranth is widespread and found in many different climates across the globe. According to CABI and the Climate Matching tool, less than half (
“Amaranthus Palmeri”. n.d. https://www.gbif.org/species/5384393.
7. Question 7
Yes
1
High
The rapid growth and competitive nature of Palmer amaranth allow it to outcompete other species, diminishing native plant diversity and potentially impacting wildlife and pollinators. This information was noted by the University of Arizona Cooperative Extension, which is outside of the climate match region.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
8. Question 8
No
0
Medium
There is a lack of evidence that indicates Palmer amaranth can promote or change fire regimes. However, some sources suggest prescribed fire and propane torching can potentially kill Palmer amaranth seeds (over 1093 degrees Celsius).
“Palmer Amaranth”. n.d. https://cals.cornell.edu/weed-science/weed-profiles/palmer-amaranth.
9. Question 9
Yes
1
Very High
Palmer amaranth (and other Amaranthus spp.) can accumulate high levels of nitrates and oxalates, making it toxic to livestock such as cattle, sheep, goats, and horses. It is a highly aggressive, fast-growing weed that competes with desirable pasture species, reducing forage availability and quality. It can grow more than 2 inches per day under optimal conditions, making it a formidable competitor in grazing systems. It is also reported to cause allergies in humans.
Mohseni-Moghadam, Mohsen, Cheryl Kent, and Jamshid Ashigh. 2013. “Palmer Amaranth Biology and Management”. La Cruces, NM: College of Agricultural, Consumer and Environmental Sciences, New Mexico State University. https://pubs.nmsu.edu/_a/A617/.
“Palmer Amaranth”. n.d. https://cals.cornell.edu/weed-science/weed-profiles/palmer-amaranth.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
10. Question 10
No
0
Medium
There is not enough evidence that suggests that Palmer amaranth creates impenetrable thickets that hinder the movement of animals and humans.
No references cited.
11. Question 11
No
0
High
âPalmer amaranth is a dioecious annual plant that reproduces exclusively through seeds and does not propagate vegetatively. Each female plant can produce a substantial number of seeds, with estimates that surpass 600,000 seeds per plant.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
12. Question 12
No
0
High
Palmer amaranth primarily reproduces through seed production and does not commonly spread via vegetative means. However, there is evidence that detached stem fragments can resprout and produce seeds under certain conditions. Specifically, research has shown that broken-off stems as small as 1 inch can resprout, flower, and produce seed.
Sosnoskie, Lynn M., Theodore M. Webster, Stanley Culpepper, and Jeremy Kichler. 2014. “The Biology and Ecology of Palmer Amaranth: Implications for Control”. https://secure.caes.uga.edu/extension/publications/files/pdf/c\%201000_2.pdf.
13. Question 13
Yes
1
Very High
Palmer amaranth commonly produces viable seeds. These seeds exhibit high initial viability, with studies indicating that over 96% of freshly produced seeds are viable. Some sources report the seeds can be viable after 12 years in the soil, although more than half of the seeds will lose viability after 18 months.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
Vollmer, Kurt. 2021. “Time to Pull Palmer Amaranth”. Agronomy News 12. https://extension.umd.edu/resource/time-pull-palmer-amaranth/.
Sosnoskie, Lynn M., Ted Webster, and Stanley Culpepper. 2013. “Palmer Amaranth Seed Longevity”. Agriculture and Natural Resources, University of California. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10297.
14. Question 14
Yes
1
Very High
Each female plant can produce a substantial number of seeds, with estimates ranging from approximately 600,000 seeds per plant to as many as 1 million seeds under optimal conditions.
Vollmer, Kurt. 2021. “Time to Pull Palmer Amaranth”. Agronomy News 12. https://extension.umd.edu/resource/time-pull-palmer-amaranth/.
15. Question 15
Yes
1
High
Palmer amaranth seeds exhibit significant germination rates in the growing season following their production, without the need for infrequent environmental triggers. Research indicates that approximately 80% of Palmer amaranth seeds lose viability within the first 12 months, suggesting that up to 20% remain viable and capable of germinating in the subsequent growing season. The seeds are known for their rapid germination, often sprouting within 1 to 2 days under favorable conditions, across a broad range of temperatures from 59°F to 105°F.
Schonbeck, Mark. 2012. “Palmer Amaranth (Amaranthus Palmeri)”. eOrganic - Extension Foundation. https://eorganic.org/node/5122.
Loux, Mark. 2019. “Palmer Amaranth and Waterhemp Management: It S All About the Seed”. Ohio State University Extension. https://ohioline.osu.edu/factsheet/anr-76.
16. Question 16
Yes
1
Very High
Palmer amaranth produces viable seeds within its first year after germination. As an annual herbaceous plant, it completes its life cycleâfrom germination to seed productionâwithin a single growing season.
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
17. Question 17
No
0
High
Palmer amaranth plants that emerge in the spring or early summer mostly flower in 5 to 8 weeks, with later emerging plants flowering in 3 to 4 weeks. Plants continue to flower for 40 days after flowers begin, with some viable seeds produced as early as 2 to 3 weeks after the beginning of flowering.
Mohler, Charles L., John R. Teasdale, and Antonio DiTommaso. 2021. “Manage Weeds On Your Farm - Palmer Amaranth”. In . Sustainable Agriculture Research and Education. https://www.sare.org/publications/manage-weeds-on-your-farm/palmer-amar….
18. Question 18
Yes
1
Medium
Seeds consumed by birds can pass through their digestive systems and be excreted at different locations, retaining viability. This suggests that birds may facilitate long-distance dispersal of Palmer amaranth seeds.
Mohler, Charles L., John R. Teasdale, and Antonio DiTommaso. 2021. “Manage Weeds On Your Farm - Palmer Amaranth”. In . Sustainable Agriculture Research and Education. https://www.sare.org/publications/manage-weeds-on-your-farm/palmer-amar….
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
19. Question 19
Yes
1
Medium
While Palmer amaranth seeds are not specifically adapted for wind dispersal, strong winds, including those from extreme weather events, can occasionally transport seeds over long distances. The seeds' minute size (1-1.2 mm in diameter) may help in long-distance dispersal during high-wind events. In contrast, their ability to float enables water to serve as a more consistent and effective means for long-distance seed dispersal.
Mohler, Charles L., John R. Teasdale, and Antonio DiTommaso. 2021. “Manage Weeds On Your Farm - Palmer Amaranth”. In . Sustainable Agriculture Research and Education. https://www.sare.org/publications/manage-weeds-on-your-farm/palmer-amar….
“Amaranthus Palmeri (Palmer Amaranth)”. 2019. CABI Compendium. https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.4649.
20. Question 20
Yes
1
Very High
Seeds can adhere to farm equipment, such as combines and tractors, and be transported to non-infested fields if machinery is not thoroughly cleaned between uses. The species has also been found in seed mixes for restoration plantings and other conservation efforts, resulting in unintended introductions into new areas. â
“Weed Risk Assessment for Amaranthus Palmeri (Amaranthaceae) - Palmer S Amaranth”. 2020. 1730 Varsity Drive, Suite 300 Raleigh, NC 2760. https://www.aphis.usda.gov/sites/default/files/amaranthus-palmeri.pdf.
“Feds Warn of Possible Giant Pigweed Outbreak”. 2017. https://www.salina.com/story/lifestyle/2017/03/24/feds-warn-possible-gi….
Total PRE Score
18
20
85
