Invasive Species Awareness Week

Invasive Species Awareness Week in Manitoba April 21-27, 2019

The Province of Manitoba has declared the last 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.

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 work under the authority of The Noxious Weeds Act of Manitoba (NWA). The NWA sets out requirements regarding various control or destruction measures for different plants. A comprehensive listing of noxious weeds is found in The Noxious Weeds Regulation, which contains schedules that rank 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.

Weed Control Districts, first started in 1964, have developed programs to deal with invasive plants such as leafy spurge and red bartsia, which have managed to establish within Manitoba, causing severe agronomic and economic impacts.

Leafy spurge, an invasive perennial first recorded in Manitoba in 1911 is a serious pest of forage and grazing land. A study conducted in 2010 by the Rural Development Institute (Brandon) estimates that leafy spurge caused a staggering annual economic loss (direct and indirect costs) of approximately $40 million. There’s little doubt that these costs have risen significantly since then.

Red bartsia is another forage and pasture invader. It was first introduced to the Gimli area in the 1950's. The Interlake Weed Control District was formed in 1967, and throughout the ensuing years control measures were undertaken. Unfortunately, a truly effective control program was not initiated until 1999. By that time red bartsia had infested much of the Interlake region. Although the weed is now being controlled on roadsides, the cost is huge. In the 2018 season, a total of $176,849.20 was spent controlling the weed on the district’s rights-of-way. With the district’s total known red bartsia infestation at 1,768.5 miles (one side), extensive seed reserves in the soil, and seed viability in the nine year range, there is no easy, quick fix for this problem. With new infestations of red bartsia already appearing in other parts of Manitoba, it is imperative that all areas incorporate careful monitoring and aggressive control measures to prevent further outbreaks. As with any invader, the best control is to prevent its initial introduction.

Both leafy spurge and red bartsia are on Manitoba’s Noxious Weeds Act as are the follow two weeds which are Tier 1 weeds on the Act. Either of them could pose a greater threat to Manitoba landscapes.

Orange Hawkweed

Orange hawkweed – photo credit: Tammy Jones, Mb Agriculture

Orange hawkweed – photo credit: Tammy Jones, Mb Agriculture

A perennial herb, Orange hawkweed reproduces by seeds as well as by numerous horizontal stolons, and rhizomes underground. It is fibrous rooted, with a milky latex in the stems and leaves Orange hawkweed prefers well drained, coarse textured soils, moderately low in organic matter and typically low pH. The plants tend to exclude desirable plants (including native wildflowers) by forming dense mats that can cover large areas. Orange Hawkweed has been identified in the SE corner of Manitoba within the past few years. Known to have been a problem in neighboring Minnesota, it is suspected to have been transported across the border by construction equipment and recreational vehicles. Other common names include: devil's-paintbrush, king devil, red daisy, flameweed and devil's-weed.

Tall waterhemp – Photo credit: Ingrid Kristjanson, Mb Agriculture

Tall waterhemp – Photo credit: Ingrid Kristjanson, Mb Agriculture

Tall waterhemp

This member of the pigweed family can grow more than 8 feet tall. The leaves of waterhemp plants are often glossy and more elongated (lanceolate) compared to redroot or smooth pigweed. Waterhemp is well-adapted to high temperatures and intense sunlight, and is capable of producing 500,000 seeds per plant that tend to germinate throughout the summer. (Late flushes can keep coming after the control measure window has closed). Waterhemp is native to the U.S. but it was not considered a major agronomic problem until the 1980's when herbicide resistance and changing production systems that included more corn and soybean favored the “weediness” of this plant.

It is a serious threat to soybean production. The native habitat of waterhemp is wet, low-lying areas, but it is quite at home in reduced tillage and no-till environments. Watch for patches to pop up along field edges or near the field entrance. Waterhemp seed is easily transported when equipment moves from field to field. In fact, at least one case of tall waterhemp detection in Manitoba is related to the purchase of equipment from an area where waterhemp is more prevalent.

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 or at the MWSA website,