Ardath Francis

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

A review of biological information is provided for Raphanus raphanistrum L. Native to the Mediterranean region, the species is widely introduced and naturalized in temperate regions around the world. In Canada, it currently occurs in all provinces except Saskatchewan and Manitoba, has only a limited distribution in Alberta, and is also absent from the Yukon, the Northwest Territories and Nunavut. It is most abundant in the Atlantic and Pacific regions and is an important weed of field crops in the Maritime provinces and Quebec. A persistent seed bank, competitive annual growth habit and high fecundity all contribute to its weedy nature and ensure that it will be a continuing problem. It can easily hybridize with cultivated radish, R. sativus L., and commonly does so when they occur together. Limited hybridization with canola, Brassica napus L., has been reported from several experimental field and greenhouse trials. Selective herbicide control is most difficult in canola and other cruciferous crops. It is...

The Biology of Canadian Weeds. 27. Avena fatua L. (updated)

Beckie, H. J., Francis, A. and Hall, L. M. 2012. The Biology of Canadian Weeds. 27. Avena fatua L. (Updated). Can. J. Plant Sci. 92: 1329-1357. An updated review of biological information is provided for Avena fatua. A widespread species originating in Eurasia, A. fatua is one of the 10 worst annual weeds of temperate agricultural regions of the world. Key weediness traits of this highly selfing species include fecundity, seed shatter, and a large and persistent seed bank with variable degrees of primary seed dormancy. The species occurs in all Canadian provinces and most states in the USA. In Canada, it is most troublesome as a weed in the prairies, where it has spread throughout crop areas in all climatic zones. Depending upon plant density and relative time of emergence, A. fatua competition may reduce annual crop yields by as much as 70%. First cohort emergence of A. fatua coincides with planting and emergence of spring-seeded crops, although additional cohorts can emerge throughout the growing season. Avena fatua is more abundant in zero-than intensive-tillage systems; the former regime promotes earlier and greater emergence because of a shallower and less persistent seed bank. Despite the introduction of highly efficacious herbicides in the 1970s and 1980s, abundance of the species has not declined across the Canadian prairies or elsewhere. The continual evolution of herbicide-resistant A. fatua populations, seed spread via farm machinery, and limited herbicide modes of action for its control threaten sustained annual field crop production in many temperate agricultural areas. Further adoption and integration of multiple non-herbicidal weed management practices, such as enhanced crop seeding rate, competitive crops and cultivars, and precision fertilizer placement, should help mitigate A. fatua interference. The species has some beneficial uses as an alternative feed and food constituent or industrial feedstock, as well as potential in cultivated oat (Avena sativa L.) improvement.

The Biology of Invasive Alien Plants in Canada. 8. Lepidium latifolium L.

The cruciferous weed Lepidium latifolium, perennial pepper-grass, is a relatively recent immigrant with a disjunct distribution in North America. Although first reported in the 1930s in Quebec and 1940s in Alberta, L. latifolium only started to attract attention as an invasive weed when it began to spread rapidly in the western parts of its US range in the 1980s, reaching British Columbia in the 1990s. Lepidium latifolium is a perennial weed of coastal wetlands, inland waterways, irrigation ditches, rangeland, hay meadows and waste areas, and tolerates saline/alkaline environments. Prolific seed production, rapid and substantial vegetative growth, creeping rhizomes with high storage capacity, potential for bud production at each node, and deep rhizome penetration have contributed to the widespread establishment of L. latifolium. Canopy height and density, combined with an accumulation of dead stalks in wetlands, has interfered with the regeneration of native plants and the habitats of birds and other anim...

The Biology of Canadian Weeds. 65. Salsola tragus L. (updated)

This account updates that published by Crompton and Bassett in 1985 (classified then as Salsola pestifer A. Nels.). The taxonomy of this species has been controversial and confusing. Salsola tragus is an annual broadleaf weed species native to Eurasia and inadvertently introduced to the Americas in crop seed in 1873. This naturalized species is a common and economically important weed in crop production systems and non-cropped disturbed areas in semiarid to arid regions of western North America; in eastern North America, S. tragus commonly occurs along roadsides, railways, and other dry, stony, and sandy areas. Pollen-mediated gene flow and efficient seed dispersal aids both short- and long-distance spread. As a C4 species, S. tragus is highly competitive in semiarid and arid small-grain cropping systems because of its ability to emerge early, efficiently extract soil available water by its extensive root system, and tolerate heat, drought, and salinity. Moreover, the evolution of acetolactate synthase-in...

The Biology of Canadian weeds. 144. Pastinaca sativa L.

The parsnip, Pastinaca sativa, was introduced to North America shortly after European settlement as an important root-crop. It subsequently escaped cultivation and naturalized as a less palatable “wild” form. Cultivation of parsnip has diminished in Canada to the point where it is now only a minor crop, but the wild form has increased as a troublesome weed, particularly in eastern regions. Wild parsnip is most prevalent in eastern Canada and the northeastern United States, but occurs across the continent except in the far north and extreme southeast. As a monocarpic biennial with a large tap root, it reproduces entirely by seed. A wide variety of habitats and soil types are tolerated. It is considered a noxious weed because of its toxic properties (primarily photo-activated dermatitis) to both humans and livestock. It invades disturbed sites, rights-of-way, pastures, perennial crops, and reduced-tillage fields where it effectively out-competes shorter vegetation. In arable fields, wild parsnip is normally...

The biology of invasive alien plants in Canada. 10. Nymphoides peltata (S. G. Gmel.) Kuntze.

The freshwater aquatic species Nymphoides peltata has been introduced to Canada as an ornamental plant and has been found at sites in Newfoundland, Nova Scotia, Quebec, Ontario and British Columbia. It is currently available through the aquatic nursery trade in Canada and the United States. It may be considered as adventive in Canada since populations readily expand beyond the site of planting, but there is no evidence as yet that it is fully naturalized. In the United States it has naturalized in still or slow-moving waters at widely scattered locations where it replaces native plant communities, changes ecological processes and interferes with human navigation and recreational activities. The short rhizomes over-winter under Canadian conditions, even when complete water drainage results in freezing of the substratum. In its native range, the species has two floral morphs (i.e., is distylous) with a weak incompatibility system, but North American populations usually consist of a single flower morph. A po...

Biology of invasive alien plants in Canada. 13. Stratiotes aloides L.

Abstract The freshwater aquatic plant species Stratiotes aloides (water soldier) is native to Europe and central Asia, where it occurs in seasonally pleustonic or submergent populations. It has been imported into and cultivated in Canada as an ornamental plant. Recently it has been found escaped or persisting at five locations in south-central Ontario. A large population has established in the Trent River where it was likely present for several years prior to its discovery in 2008. The tendency of S. aloides to form dense floating mats can alter aquatic communities through competition and allelopathy, and is likely to inhibit navigation and recreational activities in the Great Lakes-St. Lawrence drainage system should it spread more widely in eastern North America. In Europe it is often abundant in ditches where it impedes flow and increases sedimentation. Moderate success at control has been achieved using herbicides (diquat) in the Trent River population, but manual removal has been inefficient. In spite of these control efforts, the plant is continuing to spread vegetatively downstream. An integrated management plan has been proposed to address its control by: (i) prevention of new introductions (pathway restriction); (ii) early detection and rapid response (newly established or found populations); and, (iii) eradication of known populations.

The Biology of Canadian Weeds. 145. Muhlenbergia frondosa (Poir.) Fernald

Darbyshire, S. J., Francis, A., Crompton, C. W. and Swanton, C. J. 2011. The Biology of Canadian Weeds. 145. Muhlenbergia frondosa (Poir.) Fernald. Can. J. Plant Sci. 91: 205-219. Muhlenbergia frondosa is a perennial grass native to eastern North America, which naturally inhabits moist to wet forest margins and openings, freshwater littoral habitats, and grasslands. In Canada, its spread as a weed appears to have coincided with changes in cultivation practices during the past few decades. Infestations in such crops as maize and soya bean have been reported mainly from southern Ontario and Quebec, and the Midwest and northeastern areas of the United States, where it reduces yields and can be difficult to control. It is shade tolerant and able to compete under the closed canopy of crops. Although this weed can be controlled by herbicides, its ability to spread by regrowth from rhizomes, and its abundant seed production, cause ongoing problems in arable fields, particularly in conservation-tillage systems. As a warm-season C4 grass, growth begins relatively late in the season (early June in Canada), after most intensive weed control measures have already been taken. Timing herbicide application with active growth stages (10-30 cm) is most effective and the use of herbicide-tolerant crops provides additional control opportunities after crop planting.

The Biology of Canadian Weeds. 153. Stachys palustris L.

Darbyshire, S. J., Francis, A., Mulligan, G. A. and Graham, G. 2014. The Biology of Canadian Weeds. 153. Stachys palustris L. Can. J. Plant Sci. 94: 709-722. Marsh hedge-nettle, Stachys palustris, is a perennial Eurasian member of the mint family, which has become naturalized and weedy in some parts of eastern North America. It is a hexaploid member of a holarctic species complex, which differs morphologically from the primarily tetraploid North American forms. The production of fleshy tuberous rhizomes is the most significant distinctive feature. In Canada, it has been a weed of potato and root crops in Nova Scotia, New Brunswick and Prince Edward Island, although other crops and areas, such as soybean in Ontario, are also affected. Usually considered a wetland plant, it readily spreads into drier arable fields from adjacent ditches and wetlands. Several herbicides available for use in Canada have been found to provide limited long-term suppression in agricultural systems, with the best results obtained using combined pre-emergent and post-emergent applications.