The Province of Manitoba has declared the last full week of April as Invasive Species Awareness Week (C.C.S.M. c. I97). The Manitoba Weed Supervisors Association (MWSA) recognizes this week by highlighting two of the invasive plants that are a significant threat to the agricultural landscape of our province; tall Waterhemp and Palmer’s amaranth. Certain invasive plants can often be mistaken for wildflowers. But unlike native wildflowers these species threaten agricultural productivity of both cultivated and non-cultivated land, waterways and natural areas. The Noxious Weeds Act of Manitoba (NWA) (C.C.S.M. c. N110) requires control or destruction measures for different invasive plants. A comprehensive listing of noxious weeds can be found in The Noxious Weeds Regulation. The Act tiers plants according to their threat levels and specifies the areas of the province to which these levels apply. The Act requires that Tier 1 weeds must be eradicated without conditions. Examples of Tier 1 weeds that are negatively impacting Manitoba’s ecosystems are diffuse and spotted knapweed, orange hawkweed, red bartsia, Palmer’s amaranth and tall Waterhemp. Tier 2 weeds are also a significant concern, and include leafy spurge, common tansy, field scabious, and nodding thistle. The MWSA is comprised of; and represents, Weed Supervisors who are individually employed by Weed Control Districts formed by one or more Municipalities. Weed Supervisors are authorized through the NWA to ensure problematic weeds are dealt with appropriately on all lands in the districts they cover. Weed Control Districts, first started in 1964, have developed programs to deal with invasive plants such as leafy spurge and red bartsia. Prevention measures, early detection and rapid response by Weed Supervisors are critical for protecting habitats and agricultural land from these types of invasive species. Tall Waterhemp (Ameranthus tuberculatus) Waterhemp is native to the U.S. but was not considered a major agronomic problem until the 1980's. Herbicide resistance and changing production systems, including more corn and soybean, reduced tillage and more reliance on herbicides for weed control, favored the “weediness” of this plant. This member of the pigweed (Amaranth) family can rapidly take over crop land and significantly decrease yields. The native habitat of waterhemp is wet, low-lying areas, but it also grows well in drier areas. It thrives in reduced tillage and no-till environments. Watch for patches to pop up along field edges or near field entrances, along ditches and waterways. The plant typically grows to 6-8 feet tall, with glossy, hairless and more elongated leaves compared to redroot or smooth pigweed. Waterhemp is well-adapted to warm growing temperatures and intense sunlight and is capable of producing up to a million seeds per plant that can germinate over the whole summer. Waterhemp has very tiny seeds, (similar to red root pigweed seed), so it is easily transported in equipment, with water and wildlife, and can be a contaminant in seed lots. Removing small patches of waterhemp prior to seed set, and destroying the plants, is one of the most effective strategies to eradicate this weed. Tall waterhemp populations can be resistant to multiple herbicide groups, making it very hard to control this weed in field crops. Waterhemp samples in Manitoba have been tested and confirmed resistant to 3 herbicide groups. This has serious implications for local producers. New populations have been discovered since it was first detected in Manitoba in 2019, with confirmed presence in 28 municipalities as of 2023. Palmer’s amaranth (Amaranthus palmeri) Palmer’s amaranth is an aggressive, invasive weed native to the desert regions of the southwest US and northern Mexico. It was accidentally introduced to other areas and has devastated crops in the South and Midwest US as it rapidly became herbicide resistant. With the ability to emerge all season, grow 2-3 inches per day and set seed over the entire season this highly invasive weed can drastically reduce crop yield. Infestations have slowly moved north through contaminated seed, equipment, animal feed and bedding and the digestive tract of wild birds. Palmer’s amaranth was first detected in North Dakota in 2018, and is spreading throughout the state. Considered to be the #1 weed in the US, this plant can grow at least 10-12 feet tall and produce one million seeds and heavy infestations can reduce soybean and corn yields by approximately 80-90%. A member of the Amaranth family like redroot pigweed and tall waterhemp, Palmer’s amaranth can be difficult to distinguish from its cousins. Smooth-stemmed like tall waterhemp, its leaves are a little wider, more like redroot pigweed, but can be distinguished by the long petiole (stem like structure that attaches the leaf to the main stem). Petioles of Palmer amaranth are longer than the leaves, while its cousins have shorter petioles. Long, snaky seed heads that can be up to 2 feet long are a distinctive feature of Palmer’s amaranth. Identification is crucial, and removal of individual plants and small patches is critical to prevent this weed from establishing in our province. Two plants were found in Manitoba in 2021; a single plant was found in 2022 in the same area, with zero plants found in 2023 and another single plant found in 2024 in the same location. Invasive Ornamentals 90% of invasive plants have been introduced intentionally and unintentionally to our environment through agriculture and horticulture. Originally with our pioneering ancestors bringing their crops, herbs, and flowers to the new word, with some of these plants escaping cultivation; to the modern nursery industry providing customers with showy cultivars of Kochia, and (perhaps unknowingly) selling ‘wildflower mixes’ containing Dames Rocket, Baby’s Breath, and Oxeye Daisy. The problem with invasive plants is that they have characteristics that give an unfair advantage over native plants, pasture and grassland ecosystems, and cultivated crops. Invasives are not as affected by local pests and disease, and often have vigorous growth which can allow them out compete native / desired plants. This leads to negative impacts on local economies, environment, and potentially human society and health. Examples of the impact that invasive plants can have on Canadian Agriculture include general crop loss and the devaluation of land, increase in the cost and frequency of required control measures, and losses in soil productivity. Invasive species have negative effects on forestry and landscaping industries along with increasing maintenance and control incurred by towns, cities, municipalities, etc. Invasives harm the environment by affecting soil and water quality and can threaten biodiversity by altering food chains and habitats or the introduction of a new disease. Invasive plants can directly affect humans by impacting the viability of traditional local foods and medicines, they can be poisonous / toxic and cause injury, becoming a fire vector, and reduce the enjoyable quality of outdoor recreational areas. What can be done? Begin with prevention. Do not buy (or move) invasive plants. Each province has lists of regulated Noxious Weeds and Invasive Aquatic Species. Do not buy or move plants unless the seller includes a Latin name you can use to correctly identify it with a guidebook, Plant ID app, or an internet search. Secondly, identify and monitor the plants around you. Find out what plants are growing on your properties and use the tools mentioned or ask a professional (Weed Supervisor, Horticulturalist, Agronomist). Remove or keep track of invasives around you, and report high priority invasives to your local municipal Weed Supervisor or the Aquatic Invasive Species hotline (1-877-867-2470).