Invasive Species Awareness Week in Manitoba April 24-30, 2022
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 just a few of the invasive plants considered to be a significant threat to the landscape of our province. Many of these invasive species are mistaken for wildflowers, but unlike native wildflowers, these species threaten agricultural productivity of both cultivated and non-cultivated land, as well as 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 is found in The Noxious Weeds Regulation, which ranks 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 currently negatively affecting Manitoba’s ecosystems are diffuse and spotted knapweed, orange hawkweed, red bartsia 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
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 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 5-6 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 seed, (similar to red root pigweed seed), so it is easily transported in equipment, with water and by 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 2 new municipalities in 2021.
Palmer’s Amaranth
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 6-8 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.
Hound’s Tongue
A biennial plant, hound’s tongue is a member of the borage family. This plant has origins in Western Asia/Eastern Europe and arrived in North America in contaminated crop seed as early as 1859. Hound’s tongue prefers to grow in dry, well-drained areas, can tolerate alkaline soil, and is able to grow in deciduous and coniferous forests. This is an aggressive, invasive plant that can displace native and desirable vegetation and can take over pastures.
Hound’s tongue forms a rosette the first year, overwinters, and in the second year it will bolt and flower. Branched flower stems are produced in the upper part of the stem. Flowers have five petals, are usually a red/purple colour and hang in small clusters. Each flower will produce four barbed nutlets. Seeds will stay on the plant until disturbed and remain viable for up to three years on the plant. These burr-like seeds can attach to the coat of wild and domestic animals, contributing to the spread of this weed.
The main concern with Hound’s tongue is its toxicity towards cattle, sheep, and horses. Both the fresh and dried plant cause fatal liver damage, due to the presence of toxic alkaloids. Typically, grazing animals don’t consume hound’s tongue in its green state as it is unpalatable, however it could be eaten in hay. Hound’s tongue has been categorized as a Tier 1 noxious weed in Manitoba, meaning this plant poses a significant threat and must be eradicated without any conditions. Contact your local weed supervisor or provincial weed specialist for help with identification and control recommendations.
More information on Invasive plants either threatening or already present in Manitoba can be found in The Noxious Weeds Act (C.C.S.M. c. N110) and the Noxious Weeds Regulation (Man.Reg.42/17), by contacting your local Weed District