Conyza bonariensis (L.) Cronq.
Synonyms - Conyza ambigua, Conyza floribundus, Erigeron bonariensis, Erigeron crispus, Erigeron floribundus, Erigeron linifolius.
Flaxleaf Fleabane, fleabane refers to the insect (flea) repelling properties of the ground seed.
Summary:A leafy, rather grey and hairy, erect annual or biennial plant, usually less than a metre tall, with fluffy seed heads and stems that are branched from the base, often with the side stems taller than the main stem giving it a candelabra-like shape. It has entire or toothed, greyish, hairy leaves in a basal rosette and up the stem. The small flower heads are cream to white and do not have the radiating petal-like florets seen in many daisies. Instead there are several slender tubular florets. Tiny fruits are topped by a ring of bristles.
It is from North America and flowers from summer to autumn.
Two. Spear shaped. Tip pointed. Base tapered. Edges smooth. Hairless.
First leaves:First and second pair of leaves opposite, spear shaped. Long hairs on the upper surface, few or no hairs on the lower surface. Edges slightly toothed. Tip pointed.
Leaves:Alternate. Form a rosette that withers as the stems grow.
Petiole - none.
Blade - Grey-green, oblong to wedge shaped to oval. 20-100 mm long x 2-10 mm wide, usually about 50 x 5 mm. Twisted near the base. Densely hairy. Edges smooth or toothed and often wavy. Those near the base often wither early.
Stem leaves - Alternate. Smaller and parallel sided to lance shaped with smooth edges or a few teeth near the top.
Stems:Erect. Rough to touch. 200-1200 mm tall. Very leafy. Much branched from the base with few branches near top. Sometimes a single stem at the base and branching above. Side branches as long or longer than the main stem. Some stems striped. Hairy. Hairs curved and fine.
Flower stem - Stalked, short panicle like raceme at the ends of branches.
Flower head:In short racemose panicles, often shorter than the leafy shoots, arising from the upper axils and ends of branches. Flower head, cylindrical to bell shaped, 5-6 mm long, obtuse base. Usually more than 10 mm diameter when dry.
Flowers:White to yellowish.
Whitish often tinged with purple.
Bracts - In 3 rows, different lengths, narrowly oval, pointed tip, dark and pale, narrow, papery edges, white on the inside when bent back, coarsely hairy with longer hairs on the tip, inner ones sometimes have red tips. Intermediate and inner ones awl shaped or tapering to a fine tip.
Florets - Edge ones, numerous, female, many, white, threadlike, slightly expanded at the top with 2-3 pointed teeth often with purple tips, only just sticking out of the flower head. Disc florets, 6-20, tubular, bisexual, 5 toothed. Receptacle of old heads is not or only slightly pitted.
Ovary - Style branches longer than the teeth on the floral tube. Exposed receptacle of old heads not or only slightly pitted.
'Petals' - minute, ligules.
Fruit:Straw coloured achene, 1.5-2 mm long, flattened. Narrowly oval in outline. Thin with thickened edges. Flattened. Sparse, low lying hairs.
Seeds:Small, straw coloured, 1-1.5 mm long x 0.5 mm wide. Pappus of 16-20, cream or pinkish, rough to touch or soft, fine bristles, 1.8-2.5 mm long. On average in Queensland, 110,000 seeds per plant and 400 (190-550) seeds per flower head (capitulum) (Wu and Walker, 2004).
Key Characters:Involucre about 5 mm wide. Bracts linear. Ray flowers tubular.
Annual, biennial or short lived perennial. Seeds germinate from autumn to spring with a flush in late winter to spring. Active growth starts in spring to early summer and it flowers over a long period from September to April. Becomes semi dormant or dies in winter.
Flowering times:September to April in SA.
Spring to autumn in NSW.
October to May in Perth.
September to May in WA.
Seed Biology and Germination:No after-ripening and no dormancy (Wu and Walker, 2004). Fresh seed will germinate in favourable moisture and temperature conditions.
Optimum temperature for germination is 20 degrees C with a base temperature of 4.2 degrees C and a maximum temperature for germination of 35 degrees C (Rolin and Tan, 2004).
Light is required for germination.
Seed only germinates from the top centimetre of soil. Most of the viable seeds germinate from the surface, about half from 0.5 cm, about a tenth from 1 cm and none from 2 cm at 18/25 degrees C over 32 days. Nearly all viable seed (~95%) emerged within the first 10 days with the rest taking up to 20 days (Rolin and Tan, 2004).
50% emergence occurs 4-5 days after moisture is supplied at 20 degrees C (Rolin and Tan, 2004).
1% seed on the soil surface is viable after 3years and 10% seed that is buried 5-10 cm deep is viable after 3 years (S. Walker, GRDC, 2009).
Germinates throughout the year with a strong peak in early spring and early autumn in Queensland. In WA, there is a major germination in spring and early summer with minor emergences up to late autumn.
Population Dynamics and Dispersal:
Seed is spread by wind.
It is a common contaminant of nursery plants.
Rapidly increases in zero tillage cropping systems.
There are often plants of all ages present in the population.
It will flower in a range of photoperiods.
Origin and History:South America. Argentina.
Distribution:ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Flaxleaf Fleabane is the main Conyza species of the northern NSW, Qld and WA cropping areas.
Courtesy Australia's Virtual Herbarium.
Soil:Most soil types.
Plant Associations:Wide range. Open areas especially where the ground is bare.
Ground seed is aromatic and used as an insect repellent.
Detrimental:Weed of cultivation, disturbed areas, roadsides, pastures.
Difficult to control with herbicides and more tolerant to glyphosate than most other annual weeds.
Often increases to high densities in zero tillage systems.
Toxicity:Suspected to be toxic but is rarely eaten if other feed is available. Sap causes a skin irritation.
Management and Control:Flaxleaf Fleabane has generally been more difficult to control than other species of Fleabane.
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.
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:
Canadian Fleabane (Conyza canadensis)
Chilean Fleabane (Conyza chilensis)
Flaxleaf Fleabane (Conyza bonariensis) can be distinguished for Canadian and Tall Fleabane by the presence of hairy involucre bracts and lateral branches which often overtop the main axis.
Rough Conyza (Conyza scabiosifolia)
Tall Fleabane (Conyza albida) is very similar but branches from near the top or is unbranched rather than from the base and does not have long hairs near the tips of the flower bracts.
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. Photos.
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.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P662. Photo.
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). #346.2.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P672.
Moerkerk, M.R. and Barnett A.G. (1998) More Crop Weeds. (R.G and F.J. Richardson, Melbourne). P58. Photos. Diagrams.
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