Conyza canadensis (L.) Cronq.
Synonyms - Erigeron canadensis, Conyza bilbaoana, Conyza parva (misapplied).
Canadian Fleabane - because it comes from Canada and some plants in this family repel insects or fleas.
Summary:Usually a single stemmed annual with the upper part of the plant forming a pyramid of flowers and fluffy seeds on top of the leafy stem which is up to 1 m tall. It has a short lived rosette at the base and the leaves have hairs on the margins. The leaves tend to be yellow green when compared to other Tall or Flaxleaf Fleabane.
Leaves:Alternate. Forms a rosette that dies as the stems develop.
Petiole - On lower leaves.
Blade - Lower leaves, lance shaped sometimes toothed, wilt before flowering. Fine, short hairs on the edges.
Stem leaves - 10-40 mm long, narrow, lance shaped, smooth edges, bristly hairs restricted to the edges and to the midrib on the underside of the leaf.
Stems:Up to 1000 mm long. Erect. Lower half not branched. Hairy or a few short bristly hairs. Often reddish. Upper part pyramidal or like a pine tree.
Flower head:Many, cylindrical, 2-4 mm diameter in a dense, leafy, compound panicle. Slender flower stalks.
Flowers:Edge florets, female, pink at top. Disc florets bisexual, tubular, 5 toothed, pale yellow.
Bracts - Nearly hairless, oblong, green keels, papery edges. Innermost ones with hair acute or obtuse tips.
Florets - Many outer (ray) ones with a short, narrow, obvious, whitish appendage (ligule) that has 2 teeth and is pink at the tip. Disc florets fewer, pale yellow.
Ovary - receptacle is pitted.
'Petals' - Short, whitish.
Fruit:Achene. 1-1.5 mm. Pale yellow. Furry.
Seeds:1-1.5 mm long. Pappus of 30-40 bristles.
Key Characters:Involucre 3-4 mm wide. Involucre bracts linear. Ray florets shortly ligulate.
Flowering times:Most of the year in SA.
Seed Biology and Germination:Viable in the soil for 1-2 years (Weaver, 2004)
Seed germinates from 15 to 25 degrees C with a base temperature (where germination is expected to be zero) of 14.2 degrees C (Steinmaus et al., 2000).
Can germinate in light and dark conditions.
Hybrids:There are at least 2 varieties in WA, the normal on and variety canadensis.
Allelopathy:Population Dynamics and Dispersal:
Wind spreads seed.
Origin and History:North America.
Distribution:ACT, NSW, QLD, SA, VIC, WA.
Swan coastal plain.
Courtesy Australia's Virtual Herbarium.
Soil:Wide range of soils.
Formerly used as a medicinal herb.
Detrimental:Weed of roadsides, disturbed areas.
Toxicity:Not recorded as toxic.
Management and Control:Grazing should provide reasonable control.
Control seed set.
Seeds readily spread by wind.
Appears to be reduced in systems using group B herbicides. e.g. metsulfuron in late winter or chlorsulfuron, Spinnaker® or Flame® in early winter and where atrazine (group C) has been used.
Crops treated with clopyralid mid-season usually have reduced fleabane infestations due to residual herbicide action.
Reduce row width and increase crop planting rates to reduce the amount and duration of bare area.
Improve agronomy and choose competitive crop and pasture varieties to provide quick cover and consume all the spring moisture. Avoid Chickpea, dryland Cotton and Sunflowers in infested areas.
Cultivate to control mature and/or stressed plants.
Bury seed more than 2 cm deep by inversion ploughing.
Spray at the seedling stage of the weed with glyphosate plus metsulfuron plus 2,4-D or glyphosate plus high rates of 2,4-D or amitrole. Paraquat/diquat plus atrazine, Garlon® plus picloram and dicamba have also given good results. Early treatment with imazapic or Spinnaker can provide residual control in fallows or IT crops. Chlorsulfuron, metsulfuron, dicamba, 2,4-D or 2,4-D/picloram are useful in cereals. Pre harvest sprays with 2,4-D after cereals have reached the firm dough stage can provide good suppression of pre summer germinations.
In wheat, pre plant chlorsulfuron plus a late application of 2,4-D usually provides good economic control. A follow up treatment in summer may be needed for fleabane germinating after the last spray.
In Sorghum use atrazine + paraquat/diquat pre plant then atrazine + fluroxypyr with dropper nozzles in crop.
In Chickpeas use imazapic in the fallow then isoxaflutole + simazine pre planting.
In dryland Cotton, diuron, fluometuron and prometryn are the best bets pre planting followed by bromoxynil pre emergence or inter-row cultivation post emergence.
Paraquat/diquat provides desiccation but plants normally regrow from axillary meristems within a month.
Amitrole has provided good control of seed set on plants that have elongated.
Much higher rates of most herbicides are required after stem elongation.
Growing conditions before and after spraying and the growth stage of the weed have a major influence on the level of control achieved by herbicides.
Increasing the water volume from 100 to 200 L/ha at spraying had no effect on glyphosate performance.
Split spraying has generally provided better control than single applications.
This species appears to have a more Iimited distribution that others yet it is a widely adapted weed. Therefore if found outside it current distribution on the Swan coastal plain then extra effort should be put into containing it.
Spray road shoulders with 2-3 L/ha glyphosate(450g/L) plus wetting agent in early summer to reduce the spread of seed in the slipstream of traffic. On other areas, apply 1 L/ha glyphosate(450g/L) after stem elongation and before flowering in late spring to summer each year when the plants are actively growing. A mixture of 1 L glyphosate(450g/L) plus 2 L water can be used to wipe the stems of plants. Lontrel®750 at 200 g/ha or 4 g plus 25 mL wetting agent in 10 L water can be used for fairly selective control in bushland. Isolated patches can be sprayed with a mixture of 50 mL Tordon®75-D in 10 L water for control of plants and residual control of seedlings.
Hand pulling after stem elongation is effective on loose soils, but on heavier soils a weed fork is required to prevent the plant breaking and regrowing from the base.
Mowing is not effective.
Planting perennial species to increase ground cover and shade will help reduce re-infestation. Continuous grazing usually gives adequate control.
Split spraying has generally provided better control than single applications.
Herbicide resistance:Biological Control:
Chilean Fleabane (Conyza chilensis)
Flaxleaf Fleabane (Conyza bonariensis) is very similar but has long hairs near the tips of the flower bracts.
Rough Conyza (Conyza scabiosifolia)
Tall Fleabane (Conyza albida)
Conyza bilbaoana is very similar and has almost globular flower heads, outer florets are thread like with an inconspicuous appendage and has hairless triangular flower head bracts.
Conyza parva is very similar but has almost hairless stems, hairy leaf margins, cylindrical flower head and involucre bracts are narrow, oblong, hairless and usually have purple apical spots.
Plants of similar appearance:References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P96.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P864.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P361.
Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P160.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #346.3.
Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.