110 Plant Protection Quarterly VoI.12(3) 1997 Description Detailed descriptions of Oxalis pes-caprae have been given by Clarke (1934), Salter (1944), Meadly (1955), Michael (1958), Par­ Review sons (1973), Peirce (1981, 1983), Lander (1987) and Parsons and Cuthbertson (1992). The fo llowing description is adapted from Clarke (1934): ' ... an almost glabrous The Biology of Australian Weeds perennial, with an annual vertical subter­ ranean stem 2-8 mm thick at ground level 31. Oxalis pes-caprae L. but tapering below into a fine thread-like extension which connects to the parent J.R. Peirce, Agriculture Western Australia, Baron-Hay Court, South Perth, bulb. The whitish, mostly unbranched stem has numerous hair-like adventitious Western Australia 6151, Australia. roots and one to several bulbs in the axils of scale leaves. Often below the bulb is a Name fusiform translucent structure formed by Oxalis, derived from the Greek oxys mean­ now know as members of the family the tuberization of one of the secondary ing sour or sharp tasting, is a Greco-Latin Oxalidaceae. Although it was first de­ roots. word used for certain plants with acidic scribed as O. pes-caprae L., Thunberg At ground level the stem produces sap. Linnaeus (1753) narrowed its use as a (1781), cited by Symon (1961) and Michael leaves which consist of a short, flattened generic name to include only plants we (1964), named the species O. cernua leaf base, a long, cylindrical petiole up to Thunb.; cerullo referring to the night time 13 cm long, and three terminal digitate drooping, or nodding movements associ­ leaflets. Leaflets are obcordate, two-lobed, ated with the foliage and flowers (Clarke 1-4 cm broad, often marked with small 1934). Because centua was so widely ac­ purple spots. Flowers are yellow, droop­ cepted, this name was preferred until ing,3-16 in umbels on long radical pedun­ Sa lter (1939) had the original name re­ cles. Sepals 6 rnm long have two orange establi shed. The name pes-cap rae comes calli at their tips; petals 25 mm long; inner from the Latin pes meaning foot and caprae stamens longer, each with a staminodial of a goat, suggesting that the shape of the appendage towards the base. Capsule ob­ leaf is like a goat's foot (Parsons and long-acuminate, rarely maturing in Aus­ Cuthbertson 1992). Oxalidaceae is a small tralia. Flowering takes place during June­ family of eight genera containing some October'. The plant is illustrated in Fig­ 900 species of mostly herbs with fleshy ure 1. rootstocks and an acid taste (Parsons and Salter (1944) described O. pes-caprae in Cuthbertson 1992). South Africa as a variable species. Michael There are many common names fo r (1964), after studying many of the infesta­ O. pes-caprae L. Soursob or soursobs are tions through the southern states of Aus­ the main common names in Australia tralia, also concluded that considerable (Clarke 1934), while in South Nrica it is variation existed within Australia. He iden­ referred to as geelsuring, oxali s, sorrel and tified major differences in markings on the yellow sorrel (Parsons and Cuthbertson sepals, size and colouring of the petals as 1992). These authors also list buttercup well as differences in shape and markings oxalis as a common name in the UK and on the leaflets. More recently, Peirce USA and cape cowslip for the UK. (1973) expanded the number of variations Sourgrass, Bermuda buttercup and cape of leaflets illustrated by Michael (1964) sorrel are also mentioned by Howes from six to 13. Most of these were made (1974). from collections around the older town sites and the Perth metropolitan region of Western Australia.

b

anthers

stigmas

Figure 1. Mature Oxalis pes-caprae showing bulbs along the thread from parent bulb to contractile organs Figure 2. Variation in leaflets (a) and style-lengths (b) in Oxalis pes-caprae (from Peirce 1973). (from Peirce 1973). Plant Protection Quarterly VoI.12(3) 1997 111 According to Michael (1964) the infesta­ 1979). According to Galil (1968) the spread 1880s, more fruiting material was ob­ tions in South Australia and eastern Aus­ into the Mediterranean was from the earl y tained from eastern Australia (Battye tralia are of one stable 'variety', although introductions into England and western 1913), hence the possibility that more some few years later Alcock (1968) de­ Europe. From there O. pes-caprae gradu­ O. pes-caprae, in particul ar the pentaploid scribed variants from the Eyre Peninsula. ally moved eastwards and was introduced variety, was introduced. The results of In Western Australia, clonal infestations into Israel in the late 19th ce ntury. The these separate introductions are still vis­ are quite common in agricultural aTeas plant is now a weLl established weed in ible today throughout the Swan Valley (Michael 1964, Peirce 1973). lncludingagri­ North Africa (Algiers) (Ducellier 1914), vineyards and a few agricultural infesta­ cultural infesta ti ons, some 33 variants Greece- Crete (Damanakis 1976, Proto­ tions, where distinct vari ants are present have been recognised in Western Aus­ papadakis 1985, Damanakis and Markaki on neighbouring properties. tralia (Peirce 1973). The main leaflet mark­ 1990), and Sardini a (Leoni and Nieddu ings are presented in Figure 2a. 1985). Introducti on into Malta occurred Distribution Within the bulb-forming Oxalis species, about 1810 (Brandes 1991). According to O. pes-cap rae belongs to the group having Magnifico (1984) O. pes-caprae is only a AlIslralia outer bulb scales for protection and inner 'new' weed of importance in Italy. An ac­ Oxa/is pes-caprae is present in all Sta tes and scales for food storage. Of the yellow flow­ count of the spread in the Mediterranean Territories of Australia (Michael 1958, Par­ ered species having flowers borne in false is given by Marshall (1987). sons and Cuthbertson 1992) (Figure 3). In umbels, O. pes-cap rae can be distin guished As in England, Europe and the Mediter­ New South Wales the common pentaploid by: (1) presence of crowded bracts at the ranean, it is probable O. pes-caprae was de­ clone is present in southern coastal towns, base of the umbel of fl owers, (2) stalked liberately introduced into Australia as an south-west slopes and the Riverina area fl owers, (3) a relatively robust habit of ornamental garden plant. The history of (Michael 1964). The distribution for Victo­ growth, (4) rounded (not flattened) leaf the common pentaploid variety and the ria has been given by D.N. McKenzie (per­ stalks, and (5) the presence of a few hairs many tetraploids in Australia is well docu­ sonal communication), Parsons (1973) and on the underside of the leaflets (Clarke mented by Michael (1964). He found con­ Parsons and Cuthbertson (1992). O. pes­ 1934). siderable evidence to suggest that, be­ caprae occurs throughout that State, with Flowers of 0, pes-caprae are tristylic and cause many garden ca talogues contained large infestations present in the Wimmera described as short, mid and long styled illustrations of 0, pes-caprae, or at least a and southern Ma ll ee wheatlands. (Figure 2b), depending on the position of mention of its availability, the introduction The main infestations in So uth Australia the stigmas relative to the two whorls of in most cases would have been intentional. are on the Adelaide Plains, Yorke and Eyre anthers (Michael 1964). The Hackney Nursery in Adelaide, estab­ Peninsulas (Symon 1961, Alcock 1968, According to Michael (1964) the short lished by a former employee of the RJ. Carter personal communication, styled plant with fl ecked lea fl ets, most Loddiges Nursery at Hackney in London, M.J. Catt personal communication). Stride common in Australi a and the Mediterra­ listed 0, pes-caprae under the previous (1960) suggested that dense infestations nean, is a pentaploid (5u = 35). Other vari­ name 0. cem lla in 1845 (Michael 1964). By could cover between 6500 and 10 500 km 2. eties in South Africa (Marks 1956) and Aus­ the 1860s it was recognised as a weed of More recently Rj, Carter (personal com­ tralia (N. Marchant unpublished data) cereals (C larke 1934), O. cern ua was in­ munication) indicated that surveys in 1985 have been identified as tetraploids cluded in a list of plants grown by Si r showed about 8000 km2 of the Eyre Penin­ (411 = 28). William MacArthur at Camden, New sula and west coast of that State to be in­ Baker (1965) also suggested the possibil­ South Wales. Ewart (1907) mentions that fested. ity of existence of a hexaploid (6n = 42) O. pes-caprne was widespread in Victoria, Michael (1964) found many variants of which may have crossed with a tetraploid leading Michael (1964) to conclude that the O. pes-caprae around old town sites in the to fo rm the pentaploid. Although many weed must have been introduced consid­ south-west of Western Austral ia, includ­ tetraploids of different style lengths exist, erably earlier than 1885, when it was first ing paddock inFes tations o f a tetraploid it is thought that the pentaploid as de­ recorded in the National Herbarium of along the Avon Valley near York. A more scribed by Clarke (1934), Meadly (1955) Victoria. Records show that O. pes-caprae recent distribution was g iven by Peirce and Parsons and Cuthbertson (1992), is was recorded in Tasmania in 1865 and (1983), showing infestations of the present only as short-styled plants Queensland in 1875 (Michael 1964). pentaploid va ri ety along the Moore, (Michael 1964). In Western Australia both deliberate Greenough, Avon and Dale rivers. Fur­ There are various keys for identifying and unintentional introductions may have ther infestations are present in cereal and the species of Oxalis in Australia (Black occurred (Michael 1964). While visi ting the sheep areas at Bruce Rock 200 km east of 1948, Symon 1961, Michael 1965c, original farming p roperty of James Perth, and Wagin 240 km south-east of Thompson 1982,Jessop and Toelken 1986, Drummond, who farmed in Western Aus­ Perth. Lander 1987, Conn and Richards 1994). tralia in the ea rly 1840s and was known to Oxalis pes-caprae occurs in Tasmania have had dealings with Loddiges Nursery (Hyde-Wyatt and Morris 1975), Queens­ History in London, Michael (1964) found the land (Everist 1959) and at Alice Springs in Detailed accounts of the origin and spread pentaploid variety of O. pes-caprae grow­ the Northern Territory (Chippendale of 0. pes-caprae have been given by Clarke ing around. old fruit trees and 1964), but is much more restricted than in (1934), Michael (1964) and Parsons and ornamentals. The presence of seeds or other States. Cuthbertson (1992). O. pes-cap rae is of bulbs in soil surrounding rootstocks was South African origin (Salter 1944), and was probably the main method of entry of the Outside Australia deliberately introduced to England in the tetraploid varieties (Michael 1964, Peirce Both the tetraploid and pentaploid mid 18th century as an ornamental plant 1973, 1983). All stylar forms are present in 0, pes-caprne are native to So uth Africa (Clarke 1934). Records suggest that it was South Africa (Sal ter 1944), and since many (Salter 1944). Baker (1965) suggests that cultivated from as early as 1757 and by the of the vine and fruit rootstocks introduced tetraploids have limited establishment in 1790s was listed in ca talogues of garden into Western Australi a came from Medi­ North Africa, India and Australia, while plants in Europe (Clarke 1934). Today the terranean countries (Battye 1913), there is the pentaploid is found in Europe, Medi­ weed is widespread through many coun­ a strong possibility that O. pes-caprae en­ terranean countries, Africa, Australia, tries including India, Morocco, Portugal, tered as a soil contaminant. Due to the de­ Eastern Asia, South America, and western New Zealand, Spain and USA (Holm el al. mand for fruit during the gold rush of the North America. From Ducellier's (1914) 112 Plant Protection Quarterly Vo1.12(3) 1997 In Australia there is a common associa­ tion with orchards (Michael 1958, Parsons and Cuthbertson 1992) but in addition there are significant infestations in cereal crops in South Australia (Michael 1958, Catt 1972, and Blowes 1984), Victoria (McKenzie 1973, Mahoney 1982b, Lane 1984, Parsons and Cuthbertson 1992) and o Western Australia (Meadly 1955, Michael 1958, Peirce 1973). The presence of 0. pes-caprae in cereals has also been men­ tioned in South Africa by Biljon et at. (1988). Where O. pes-cnprae is present in agricul­ tural situations, adjacent domestic gardens are also usually infested (Ducellier 1914, Symon 1961). Cultivation appears to be a common link with most O. pes-caprae in­ festations. However there are infestations in non-cultivated olive groves (Leoni and Nieddu 1985) and pastures (M ichael 1964).

Growth and d evelopment

Morphology The elongated shape and tough nature of the coats surrounding the bulbs and bulbils make them less prone to damage Figure 3. Distribution of DxaUs pes-caprae in Australia (from Parsons and by crushing during cultivation (GaIil1968). Cuthbertson 1992). A contractile root forms soon after sprout­ ing by the enlargement of one of the roots description the pentaploid is common in Substrat1lm arising at the base of a bulb or bulbi!. It has North Africa, Spain, France, Italy, Greece, Henslow (1910) observed O. pes-cap rae the dual purpose of water and nutrient Asia Minor, the Canary Islands and the growing on range of soils varying from storage and assisting in bulbil dispersal Isles of Madeira. Galil (1968) indicates that infertile to 'rich'. According to Parsons and (fhoday 1926). This structure is common the pentaploid is widespread on the coastal Cuthbertson (1992), O. pes-caprae is found to a number of Oxalis species (Rimbach and inland valleys of Israel. The world dis­ mainly on fertile, heavy soils that are well 1895, Rohde 1928, Jackson 1960, tribution is also given by Marshall (1987). drained. GaUl (1968) indicates that in Israel Chawdhry and Sagar 19740). Ducellier the plant is found growing on a wide (1914) gives an account of these structures Habitat range of soils. In South Australia the weed on 0. pes-cap rae, but more thorough treat­ is present on fairly ferti le mallee red sandy ments and illustrati ons of contractile roots Climatic requirements loarns in the lower Murray Basin (Williams and their function in 0 . pes-caprae are The weediness of O. pes-caprae is mainly 1970), and on the lateritic pod sols, given by Clarke (1934) and Galil (1968). associated with Mediterranean-type cli­ solodized solonetz and red-brown ea rths The distance and angle at which the new mates, i.e. dominant winter rainfall and in the lower and eastern Eyre Peninsula bulbs are moved down and away from the dry summers, but the plant grows from (Bickne ll 1970). On the upper Eyre Penin­ parent plant are controlled by the depth of areas of sub-humid and semi-arid warm sula O. pes-caprae is present on light brown the parent bulb, the moisture status of the temperate to sub-tropical regions (Par­ sands that are about 60 em deep and over­ soil and resistance the soil offers to the sons and Cuthbertson 1992). The absence lying clay (Holden 1970). In the upper contractile tubers pulling the bulbs away of severe frosts is also important (Clarke north (Mowatt 1970), lower north from the parent plant (Galil 1968). Parent 1934, Michael 1958, Parsons and (Michel more 1970) and Yorke Peninsula of bulbs close to the surface tend to form con­ Cuthbertson 1992). Ducellier (1914) found South Australia (Webber and Matz 1970), tractile tubers which pull the new bulbs 0. pes-caprae favoured the milder Mediter­ O. pes-cap rae grows on the mallee loams vertically into the soil, while parent bulbs ranean climates associated with the coastal and red-brown earth soils. Catt (1972) con­ at 15-20 cm depth in the soil tend to form areas of Algeria. In Australia it is found cluded that in South Australia there ap­ contractile tubers that are horizontal to the where the average annual rainfall exceeds peared to be no restriction on the type of parent bulb, hence moving the new bulbs 330 mm (Catt 1972). Peirce (1979) showed soil where 0. pes;-caprae would grow. away, up to 47 em, from the parent plant that the rate of bulb sprouting (in the ab­ when contraction is complete (Galill968). sence of moisture) was very sensitive to Plant associations In studies undertaken by Putz (1994) summer temperatures. Soil temperatures In most of the Mediterranean region measurements were taken to quantify the above 30°C and below 10°C reduced O. pes-caprae is mainly associated with ol­ pulling forces exerted by the contractile sprouting to less than 20% for two tetra­ ive, ci trus or vineyards (Ducellier 1914, tubers. ploid and one common pentaploid variety Damanakis 1976, Paspatis 1985, Under situations of high soil moisture, (compared to 60-80% for bulbs stored at Protopapadakis 1985, Brandes 1991). In other contractile roots are formed imme­ 20'C) and dela yed sprouting by 13 and 20 the USA O. pes-ca prae is also associated diately below the crown of the plant at the d ays at 10 and 30· C respectively. The with citrus orchards, but in addition is soil surface (Hyde-Wyatt and Morris 1975, tetraploids were more sensitive to the present in other crops such as artichokes Peirce 1983). These structures may serve lower temperatures. (Hildreth and Agamalian 1985) and narcis­ mainly fo r water and nutrient storage be­ sus (Smith and Treaster 1990). ca use as there are several formed radially Plant Protection Quarterly VoI.l2(3) 1997 113 around the crown on each plant, any con­ 100 traction would be at opposing angles. Sometimes there are bulbs associated w ith "0 these surface contractile organs. If the ~ 0 100 roots were to break away from the stern, E" contraction might aid bulb dispersal Q; C) (Peirce 1983).

100 o Perenl1£ltion Oxalis pes-caprne, although giving the ap­ " pearance of an annual plant because it dies " 0 -" "~ 100 back at the end of each growing season, is "E co nsidered a perennial because it produces c. "E o w bulbs (Clarke 1934). ~ 0 "C" 100 Physi%:51J 0 "Cl ..0-.;:" Oxnlis pes-cnprne is extremely sensitive to .l!! '5 !1l light, the fl owers responding by opening CD E " 0 and fo llowing the sun's path and cl osing as "~ ,,2100 c. the light intensity decreases (C larke 1934). " Movable joints (pulv ini ) located at the ~ 0 4>-.::" 0 bases of stalks of fl owers, leaves and the ~ .c !1l 100 '5 :J junctions of leafl ets effect this and other E f- E movements. :J oE o The plant appears suited to either fu ll 0 100 sun or shade conditions (Galil 1968), al­ though Clarke (1934) suggests these con­ ditions lead to marked differences in the "0 :0'.;: morphological appearance of pla nts. :J !1l 0 100 CD E Other species of Oxnlis have been shown oE to vary in height, leaflet width, chlorophyll content, and seed prod uction depending 0 on light in tensities (Pa ckh am and Will is 1977). Growth differences in height (leaf March April May Ju ne July August September petiole length) and size of leaves ha s been illus trated, but not measured, in O. pes­ Figure 4. Development of Oxalis pes-caprae in Victoria; 0 1976,.1977 (from caprae by Clarke (1934). Mahoney 1982b). Growth rates of va ri ous parts of a pentaploid O. pes-cnprne are given by Michael (1965a). In additi on to the Dangin - Tetraploid pentaploid, growth o f two tetra pla ids from infestations in Western Australi a was described by Pei rce (1983). Compared to • bulbs th e te traploids, th e pentaploid variant o horizonta l roots made much more growth during the first Fa ve rtical roots 60 days afte r sprouting. The tetraploids • flowers th en ma de consid erabl y more lea f growth • leaflets and produced more bulbs. Lane (1984) in­ o petioles dica ted that numbers and dry weights of lea fl ets of the pentaploid were strongly related to size of bulb from w hich th e o 30 60 90 1 20 1 5 0 180 plants developed. Fl owe r product ion is also higher in the pentaploid (Peirce 1983). Northam - Pentaploid Wagin - Tetraploid From limited studies, Clarke (1934) found that the levels of total oxalates in leaves decreased from 29- 25% as the age of the plant increased through June­ August and suggested that this was due to the increasing intensity and duration of li ght. Similar trends have been reported by others but the hi gh values quoted ap­ pear to be questionable. Oxalate levels of about one third of those presented above O ~~~T-~~~~~~~ were given by Hickinbotham and Bennett o 30 60 90 1 20 150 180 o 30 60 90 120 150 1 80 (1931), the former author supervising the Days after planting Days after planting analysis quoted by Clarke (1934). Michael (1965a) also showed a similar trend of de­ Figure 5. Initiation and dry weights of various organs of three variants of creasin g percentage oxalate as age of the Oxalis pes-caprae from Western Australia (from Peirce 1983). plant increased in the sa me pentaploid as 114 Plant Protection Quarterly Vol.I2(3) 1997 studied by Clarke (1934), the levels being differences in the initiation of various or­ in the order of 10% declining to about 6% gans, particularly between the pentaploid in the same period. Peirce (1983) carried and tetraploids (Peirce 1983) (Figure 5). out similar analyses on the common pentaploid and two tetraploids from Mycorrhiza Pent.ploid (5n=35) Western Australia. Similar trends were There is limited documented evidence of found, with declining total oxalate from the existence of an association of 6-8% (39 days), to 3-5% (59 days), rising to O. pes-caprae with mycorrhizae. Infection 8-10% (80 days after planting) and then of O. pes-caprae by vesicular-arbuscular declining rapidly with age. There was also mycorrhizal spores, mainly Acall[ospora a noticeable difference between variants iaevis Gerd. and Trappe, was shown to be of 0. pes-capme, with one of the tetraploids low by Smith (1984). Another Oxalis spe­ having a much higher oxalate content. cies, O. cornicillata L., was shown to have Some attempts had been made in Aus­ 93% of root segments colonized by vesicu­ tralia to analyse for crude protein, fat, car­ lar-arbuscular mycorrhizae mainly from bohydrate, fibre, ash and oxalic acid the Glomus genus (Sail and lffat (1976) (Hickinbotham and Bennett 1931). Similar cited by Lovett Doust e/ al. 1985). Contractile root studies have been carried out in the Medi­ terranean by Maymone e/ al. (1960), cited Reproduction in Michael (1965a) and Biondo and Socini (1960). Floral biology The trimorphic arrangement of flowers is Tetraploid (4n=28) Phenology common within the genus Oxalis (Clarke Growth and development studies of the 1934). According to Ornduff (1964), in penta plaid in Australia reported by tristylous species, plants of three kinds ex­ Michael (1965a) identified three stages ist: plants having fl owers with long styles during the life cycle where changes in and anthers at two levels below the stig­ oxalate metabolism/ transport corre­ mas; plants having mid-styled flowers sponded to distinct growth stages. These with one set of anthers above and another were: below the stigmas; and plants with short­ Figure 6. Variation between two i. at the time of old bulb exhaustion (day styled flowers with two levels of anthers variants in bulb formation on tuber 39-53) when there is a slowing in rate of above the stigmas. Tristyly is associated and thread (from Peirce 1983). oxalate production relative to dry with mechanisms of cross pollination by weight. Leaflet oxalate is at its lowest bees and butterflies (Clarke 1934). Pollen during this time; from anthers on another flower, at the Physiology of seeds and germination ii. at the beginning of development of same level as the stigmas, is required be­ There have been limited observations, bulbs and flowers, when there is a de­ fore seed formation can take place (Symon probably due to the low frequency of crease in oxalate content while tuber de­ 1961). However, Ornduff (1964, 1972) sug­ crossing in Australia, on the seeds of velopment is increasing. By day 76 peti­ gests that while the most productive o. pes-cap rae. Seeds collected in the field or ole oxalate is at its lowest; crosses occur with this arrangement, less from plants housed in glasshouses in iiiat the onset of senescence where there is productive crosses can occur with pollen Western Australia appear to have little a significant decrease in total oxalate. from anthers at different levels to the stig­ dormancy and germinate readily under Chawdhry and Sagar (1973), using autora­ mas. The expression of tristyly in O. cool moist conditions O. Peirce unpub­ diography, identified 10 developmental pes-caprae (Figure 2b) is not well docu­ lished data). Seedlings were often detected stages in relation to the distribution of as­ mented, but for other Oxalis species, on the damp cement floors under tables similates from radioactive carhon dioxide Ornduff (1964, 1972) suggests that tristyly supporting O. pes-caprae plants. Seeds fed to aerial parts of the plant. is controlled by two unlinked loci. stored for more than 12 months at room When plants were grown under uni­ temperature failed to germinate when form growth conditions in a glasshouse, Seed production and dispersal tested O. Peirce unpublished data). Lane (1984) found a development timeta­ Seed production by the pentaploid O. ble similar to that proposed by Michael pes-caprae in Australia is uncommon Vegetative reproduction (1958). Moisture availability influenced (Clarke 1934, Michael 1964), while Although seed formation is important time of emergence (Mahoney 1982b), as tetraploids will seed freely, providing where clones of different style length did bulb size and depth of bulb placement plants having different style lengths are grow in dose proximity, the major (Lane 1984). Mahoney (1982b) studied un­ present (Michael 1964). Dehiscence of seed method of reproduction in O. pes-caprae is disturbed populations of the short styled capsules is through loculicidal slits on the from the production of bulbs (Clarke 1934, pentaploid over two years in the Victorian abaxial sides of the ca rpels, when a turgid Gali11 968, Michael 1965b, Catt 1972, Peirce mallee and concluded that although bulb arH everts and ruptures (Robertson 1975 1983, Lane 1984). Bulbs are produced on germination commenced about the same cited by Lovett Doust et al. 1985). The force tubers and along the rhizomes. Their ini­ time during early March in both years, of ejection can scatter seeds up to 2 m from tiation usually commences between 80 emergence, bulb exhaustion, tuber forma­ the parent plant (Lovett Doust e/ aJ. 1985). and 114 days after the parent bulbs have tion, new bulb formation, flowering and There is no record of other agents dis­ sprouted under artificial conditions senescence varied greatly in time of initia­ persing the seed of 0. pes-caprae in Aus­ (Michael 1965a, Peirce 1983), and between tion and rate of development (Figure 4). tralia. In other species of Oxalis it is com­ mid-June and mid-August (105-150 days) Time and incidence of frosts and rainfall as mon for some rodents to utilize the seeds under field conditions (Mahoney 1982b). well as the amount of the latter were the in their diets, but no testing has been done Mahoney (1982b) recorded bulb pro­ main influences. The phenology for three to assess the viability of seeds after pas­ duction of 20 per plant on small parent clones of O. pes-caprae in Western Aus­ sage through the rodent's digestive tract plants and up to 50 from large healthy tralia indicates that there are marked (Lovett Doust e/ al. 1985). plants. Average values of 10 per plant Plant Protection Quarterly VoI.12(3) 1997 115 were recorded in Israel, with up to 30-40 style lengths on the Eyre Peninsula in Importance per plant under warm winter conditions South Australia and his illustrations of the (GaIil1968). Under glasshouse conditions vari ation of petal, sepal and leaflet mark­ Detrimental bulb production varied from an average ings as well as seed capsul es would indi­ Vigorous infestations of O. pes-cap rae of 19 per plant for the pentaploid, to 28-34 cate that considerable crossing has oc­ cause significant yield losses in cereal crops per plant for two tetraploid vari ants of curred. Some 33 variants were noted in a in Australia (C larke 1934, Michael 1964, O. pes-caprae from Western Australia survey conducted in Western Australia Catt 1972, McKenzie 1973, Peirce 1978, (Peirce 1983). The higher value recorded (Peirce 1973). 1983). In vineyards in Australia (Stride for one of the tetraploids was mainly due 1960) and Greece (Paspatis 1985) its pres­ to the multiple number of bulbs formed at Population dynamics ence interferes with the growing of cover each of the bud scales on the tuber and Despite its competitiveness, particularly in crops used to improve soil ferti lity. In along the rhizome, compared to only sin­ cereal crops (Clarke 1934, Michael 1965, Greece O. pes-cap rae is considered the gle bulbs arising at similar positions for the Catt 1972, Peirce 1973, Mahoney 1982a, country's ninth most important weed as other variants (Figure 6). Lane (1984) re­ Lane 1984), O. pes-caprae is sensiti ve to the its presence under olive trees prevents the corded average bulb numbers of about 11 presence of other plants (Peirce 1983). Bulb common practice of hand gathering of per plant under glasshouse conditions in production and weight in both tetraploid fruits from the ground (Damanikis 1976). Victoria. and pentaploid varieties were reduced by Delfosse (1990) considered O. pes-caprae as Dispersal of the bulbs can be localized a factor of five when plants were grown in a weed of 'sporadic' or 'geographically' due to the action of the contractile roots the presence of wheat and annual ryegrass limited importance to the dried fruit indus­ drawing the bulbs at an angle away from (Loli um rigidum Gaudin). Bulb production try of Australi a. the plant, as illustrated by Clarke (1934) of a tetraploid variety also decreased be­ tn addition to its competitiveness in ce­ and Galil (1968). In addition, bulbs are tween 38 and 67% under field conditions in real crops O. pes-caprae also dominates transported in mud, and beca use they are the presence various cultivars of subterra­ many pastures and because of its high light, Clarke (1934) considers that wind nean clover (Trifolium subterra lleum L.) oxalate content, is linked to stock deaths plays a major role. Bulbs fl oat on water so (Peirce 1976). Measurements taken from by oxalate poisoning, especially sheep this would also be significant. particularly an ungrazed pasture showed that the den­ (Bull 1929, Hickinbotham and Bennett in Western Australia where O. pes-caprae is sity of O. pes-caprae decreased from 890 to 1931, Clark 1934, Gardner and Bennetts associated with some major rivers and 560 plants m·2 in successive years o. Peirce 1956, Dodson 1959, Everist 1959, Stride drainage systems (Peirce 1973). unpublished data). 1960, Gardiner and Royce 1963, Michael Cultivation, particularly using tined im­ The period over which growth occurs 1965a, Healy 1967, Mcintosh 1972). Stock plements, has been responsible for drag­ varies according to the availability of deaths have also been reported as well as ging plant fragments which are capable of moisture (La ne 1984). Bulbs appear to be­ poor meat and milk production in Sardinia regenerating and producing bulbs (Par­ come non-dormant over summer and due to the presence of O. pes-caprae in pas­ sons and Cuthbertson 1992). Intentional sprout as temperatures fall, irrespective of tures (Leoni and Nieddu 1985). propagation in home gardens or in soil the presence of moisture (Peirce 1978). In The fodder value of O. pes-caprne is very nursery stock has aided d ispersal, particu­ field situations this gives O. pes-caprae a low compared to other recognised green larly where orchards and farm house sites competitive advantage over annual spe­ crops or mixed pastures. Hickinbotham were abandoned and came under cultiva­ cies as it is usually the first to appear after and Bennett (1931) found that the plant tion. Birds have also been implicated in the break of the season. However the rate had, in addition to the oxalate problems, moving bulbs (Parsons and Cuthbertson of emergence in anyone season can vary high water content and low crude protein, 1992). between sites (Table 1). Emergence ap­ fat, carbohydrate, fibre, ash and starch peared to be strongly influenced by depth equivalent. Hybrids and friability of soils; sha llow hard setting Oxalis pes-caprae is not known to host The presence of hybrids in field infesta­ soils used for cereal production showed diseases that affect crops. However, tions is uncommon. However, around only about half the emergence in May Lovett Doust et al. (1985) reported that town sites there are often different style compared to deep friable soils used for O. stricta L., O. corniculata L., O. dillen!! lengths present within an infestation and horticulture. Although no measurements Jacq. ssp. dillellii and 0. dillellii Jacq. ssp. free seeding plants produce a range of of bulb sizes were taken it is thought that filipes (Small) Eiten hosted the maize rusts va riation (Michael 1964). This author re­ smaller bulbs were formed in the hard set­ Puccinia sorghi Schw. and P. polysora ported that double-flowered va rieties oc­ ting soils and after sprouting took consid­ Underw., sorghum rust P. purpllrea Che. cur in South Africa and the Mediterranean erably longer to reach the surface. and Andropogon rust P. andropogonis Schw. regions and that variation is more obvious Chawdhry and Sagar (1974b) indicated in South Africa. According to Michael that bulb weight and numbers could be Beneficial (1964), hybrids of crosses between the influenced by defoliation, and that the Oxalis pes-cap rae is not usually regarded as penta plaid and tetraploids have occurred regular removal of top growth would pre­ a weed by orchardists/winegrowers in at Albany in Western Australia. Alcock vent bulb formation. Australia, as its vigorous root system helps (1968) recorded the presence of all three break up heavy soils, allowing aeration and moisture movement (Peirce 1973, Par­ sons and Cuthbertson 1992). The proc­ Table 1. Emergence of Oxalis pes-caprae over time at three sites in Western esses describing how the contractile roots Australia O. Peirce unpublished results). and bulbs form these channels and the forces that are exerted are described by Plants m·2 Piitz (1994) and Piitz et al. (1995). In addi­ Site May July Depth of deepest tion, because the top growth dries off as bulb (em) summer approaches, the area beneath trees and vines is weed free and accessible Northam (cereals) 750 2200 15 during harvest. Paspatis (1985) made the Swan Valley (vineyard) 1310 1490 >25 same observation for southern Greece, Chittering Valley (citrus orchard) 1220 1970 >25 claiming O. pes-caprae inhibited tenacious 116 Plant Protection Quarterly VoI.12(3) 1997 weeds such as Parietarja sp., Amarallthus can recoup the cost of control on roads The introduction in the 1980s of the spp. and Chenopodium spp. Apiarists be­ under Section 60 from adjoining sulfonyl urea group of herbicides, namely lieve the plant is also of some value to their landholders. chlorsulfuron at 12-15 g a.i. ha-t , was so industry (Parsons and Cuthbertson 1992). Oxalis pes-caprae is declared a Secondary effective against O. pes-capme, that it is Noxious Weed under the Plant Protection now virtually eliminated as a problem Legislation Act 1994 for Tasmania (A. Harradine per­ weed in cereals in Australia (Peirce 1983, Victoria, Western Australia, South Aus­ sonal communication) . Under this legisla­ 1985, Parsons and Cuthbertson 1992). tralia, and Tasmania currently have legis­ tion, inspectors can prescribe control More recently another member of this lation in place for O. pes-caprae, In Victoria measures they consider appropriate. group of compounds, metsulfuron methyl l it is a proclaimed noxious weed for the at 3 g a.i. ha- , has also been recommended whole of the State except the Melbourne - Weed management for O. pes-caprae control in cereals (wheat metropolitan area (Parsons and and barley) (Peirce 1990). In South Africa Cuthbertson 1992). More recently D. Lane Herbicides triasulfuron at 10 g a.i. ha-t gave 80% con­ (personal communication) has indicated One of the earliest attempts at control of trol of O. pes-caprae in wheat and barley that under a new act, The Catchment and O. pes-caprae by chemicals was mentioned (Biljon e/ a1. 1988), but in Australia it is reg­ Lands Protection Act, the list of noxious by Clarke (1934), who suggested the use istered as giving suppression only (Par­ weeds will be reviewed and placed under of sodium chlorate. Despite the dangerous sons 1992). In Southern California control four categories: I. Statewide prohibited, properties of the chemical, its use to kill of O. pes-caprae was achieved with pre­ II. regionally prohibited, 1I1. regionally the tops of O. pes-cap rae was supported by and post-emergent applications of controlled and IV. restricted. O. pes-caprae Neal-Smith (1938). Bulb formation was oxyfluorfen in globe artichokes (Cynara is assigned to the regionally controlled cat­ suppressed by the soil fumigant sodium­ scolymlls L.) (Hildreth and Agamalian egory in Horsham, Portland, Co lac, N-methyldithiocarbamate when applied 1985). Paspatis (1985) found that in addi­ Geelong, Central Gippsland and Mel­ at the late post-emergence stage of tion to oxyfluorfen, mixtures with bourne regions. However, D. Lane (per­ growth (Marinos 1958). Some success in simazine, glyphosate, chlorthiamid and sonal communication) suggests that in reducing the competitiveness of O. pes­ dichlobenil also gave good control of light of the availability of chemicals for caprae growing in a cereal crop by using O. pes-caprae in vineyards in Southern control, O. pes-cap rae will have a limited 2,4-diclorophenoxy acetic acid was re­ Greece. This supports earlier work con­ sta tus as a noxious weed. ported by Meadly (1955). Reduced bulb ducted in the same region by Damanakis Western Australia lists O. pes-caprne un­ production and plant size was obtained (1976). The herbicides napropamide, der three categories according to its agri­ using 2.2 kg aj. ha-' of fenoprop (2,4,5- oryzalin, prodiamine and isoxaben + cultural importance: P1 (prevention of in­ trichlorophenoxy propionic acid) (Michael oryzalin have all shown activity on O. pes­ troduction), P3 (requiring populations of 1965c). The substituted urea herbicides caprae (Smith and Treaster 1990). plants to be reduced, using control meas­ linuron and diuron gave more permanent Tables summarizing the various herbi­ ures) for the region of Cunderdin (160 km reductions in bulb numbers and at the cides having activity on O. pes-caprae, prior east of Perth) and P4 (containment pre­ same time worthwhile cereal yield in­ to the introduction of the sulfonyl urea venting movement of the weed outside creases in South Australia (Catt 1972) and compounds, are given by Marshall (1987). existing infestation boundaries) for the re­ Western Australia (Peirce 1978). Non se­ mainder of the State. lective control of O. pes-caprae has been Other treatments According to R. Carter (personal com­ achieved using 3-amino-1,2,4-triazole The use of cultivation foll owed by grazing munication) it took some 25 years to gain (Anon. 1961). Parsons and Cuthbertson from pigs or turkeys to consume the bulbs a recommendation for the declaration of (1992) mention paraquat and diaquat as and tubers was suggested by Clarke O. pes-caprae in South Australia. Itwas first being effective. Good control of O. pes­ (1934) after observing successes in the proposed in 1940, but declaration was re­ caprae became possible under many situa­ Gawler River area in South Australia. jected because it was widely distributed tions with the introduction of glyphosate Clarke (1934) also recognised the va lue of and there were no control measures. After (Mahoney 1982a, Peirce 1983, B10wes 1984, cultivation and sowing a wheat crop, pro­ reports that it was possible to ga in reason­ Parsons and Cuthbertson 1992). Mahoney viding the crop was established early able control and that O. pes-caprae had not (1982a) found that reductions in densities (April) so that it could compete with reached its ecological limits, the Noxious between 52-94% could be obtained in a 0. pes-caprae and prevent it from flower­ Weeds Advisory Committee agreed to the cereal crop when glyphosate was applied ing. The tinling of cultivation was also im­ proclamation in 1965 under the third at 0.54 kg a.i. ha-t as a fallow treatment portant; density of 0. pes-caprae could be schedule of the Weeds Act 1956- 63 for a between June and August in the year prior reduced by delaying seeding while several portion of the State, which included the to cropping. However, she found that this cultivations were undertaken. South East and the Eyre Peninsula. It was level of control was not accompanied by a Michael (1965b) quantified the levels of subsequently proclaimed under the Pest cereal yield increase, and the optimum bulb reduction possible after cultivation Plants Act 1975 and the Animal and Plant timing for the application varied consider­ treatments on the common penta plaid Control (Agriculture and other purposes) ably between experimental sites. 0. pes-caprae in South Australia (Table 2). Act 1986. The latter Act under section 52(2) restricts movement of the plant as a con­ Table 2. N umbers and dry weights of bulbs in uncultivated and cultivated taminant of soil and produce on public areas (from Michael 1965b). roads, sale of the plant, and produce/ goods/soils carrying the plant (section Bulbsm-2 Total bulb dry Mean bulb dry 54(1)(2)) for the whole of the State. For wt (kg ha-') wt (g) part of the State, including the South East Stubble paddocks and the Eyre Peninsula and also any land Uncultivated 5790 7220 0.13 used for extraction or removal of soil, Cultivated 2370 900 0.04 loam, sand, gravel, the landholder is re­ quired under Section 57(2) to destroy the Pasture paddock plant and inhibit its propagation as far as is Uncultivated 4830 2860 0.06 reasonably achievable. Control boards Cultivated 630 150 0.02 Plant Protection Quarterly VoI.12(3) 1997 117 A single cultivation at the time food re­ References Clarke, G.H. (1934). Important weeds of serves in the parent bulb were exhausted Alcock, R. (1968). Soursob forms and dis­ South Australia. No.9 Soursob. Journal was not entirely successful and a further tribution on Eyre Peninsula. The Weed of the Departmen t of Agriwlture cultivation was required later in the sea­ Scene, Department of Agriculture South South Australia 38, 481-505. son to kill plants regenerating from stems Australia 4, 5-12. Conn, B.J. and Richards, P.G. (1994). A new and crowns of plants injured by the first Anon. (1961). Control of nut grass, onion species of Oxalis section Corniculatae cultivation. Mahoney (1982a) in field stud­ weed and oxalis. Agricultural Gazette (Oxalidaceae) from Australasia. Austral­ ies and Lane (1984) in glasshouse studies NsW72, 1972. iall Systemic BotallY 7, 171-81. verified the ability of the plant to recover Baker, H.G. (1965). Characteristics and Damanakis, M. (1976). Control of Oxal is after a single cultivation and thus the ne­ modes of origin of weeds. The genetics pes-caprae L. with pre-emergence and cessity to use multiple cultivations. Other of colonizing species, pp. 142-72. Pro­ post-emergence treatments. Proceed­ problems relating to soil types and condi­ ceedings 1st International Union Bio­ ings 13th British Crop Protection Con­ ti ons have been detailed by Catt (1972). logical Science, Asilomar, California. ference - Weeds, 1, 321-7. Michael et al. (1962) indicated th at O. pes­ Battye, J.5. (1913). 'The encyclopedia of Damanakis, M. and Markaki, M. (1990). caprae was susceptible to competition Western Australia', Volume 2, ed J.S. Studies on th e biology of Oxalis pes­ from dense legume pastures. Peirce (1976) Battye. (Hussey and Gillington, Ad­ caprae L., under field conditions in Crete. measured the reduction of bulb numbers elaide). Zizallology2,171-4. under various cultivars of subterranean Bicknell, K.G. (1970). Agriculture in South Delfosse, E.5. (1990). Biological control of clovers establi shed in dense infestations of Australia. Lower and Eastern Eyre Pe­ weeds and the dried fruits industry. a tetraploid variant of O. pes-caprae. The ninsula. Department of Agriculture Plmlf Protectioll Quarterly 5, 91-7. percentage reduction of bulbs ranged South Australia, Extension Bulletin 34, Dodson, M.E. (1959). Oxalate ingestion from 67% (cv. Geraldton) and 60% (cv. 20pp. studies in sheep. Tlte Alistraliml Veteri­ Dwalganup) to around 38% in the pres­ Bi ljon, J.J. van, Hugo, K.J. and Iwanzik, W. lIary J01lr1la135, 225-33. ence of Clare and Dinninup cultivars. Un­ (1988). Tri aslllfuron: a new broad leaf Ducellier, M.L. (1914). Note sur la vegeta­ der glasshouse conditions, annual herbicide in wheat and barley. Applied tion de l'oxalis cernua, Thunb. en Alge­ ryegrass and wheat (cv. Gamenya) re­ Plant Science 2, 49-52. ria. Revue Generale de Botanique 25, 2. duced bulb production by 77% (Peirce Biondo, G. and Socini, P. (1960). Everist, S.L. (1959). Soursob a declared 1983). Caratteristiche chimiche e nutritive dell noxious weed. Queensland Agricultural Overgrazing of pastures can result in a Oxalis cernua Thunb. raccolta in zone e JOllmaI85 ,610. significant shift of botanical composition, fasi vegetative diverse. Alti Societa Ewart, A.J . (1907) . 'The weeds, poison favouring O. pes-caprae (Carter 1995). A ltaliana delle Scienze Veterinarie 14, plants and naturalized al iens ofYictoria', study conducted at the Waite Institute in 229-32. p. 17. (Gov!. Printer, Melbourne). South Australia indicated that at sheep Black, J.M. (1948). ' Flora of South Aus­ Ga lil,J. (1968). Vegetative dispersal in Oxa­ stocking levels of 7.4-14.8 ha·', O. pes­ tralia'. (Government Printer, Adelaide). lis Cfrlllm. American JOllmal of Botany 55, caprae contributed only 0.8% of the sward, Blowes, W.M. (1984). Commercial devel­ 68-73. but when stocking levels were raised to opment of Roundup for long-term con­ Gardiner, M.R. and Royce, RD. (1963). 22.2 ha·1, the O. pes-caprae content in­ trol of soursob Oxaiis pes-caprae L. Aus­ Oxalate poisoning of ruminants. The creased to 16.6%. tralian Weeds 3,102-4. Journal of Agriculture of Western Aus­ Brandes, D. (1991). Sociology and ecology tralia Bulletin 3098, 10 pp. Na tural enemies of Oxalis pes-caprae in the Mediterranean Gardner, CA. and Bennetts, H.W. (1956). Kluge and C1aassens (1990) identified the region with particular regard to Malta. 'The toxic plants of Western Australia', noctuid moth, Klugeana philoxa!is Phytocoenologia 19, 285-306. pp. 11&-20. (WA Newspapers Ltd ., Perth). Geertsema, as a potential biological con­ Bull, L.B. (1929) . Poisoning of sheep by Geertsema, H. (1990). A new genus and trol agent. The egg, larval and pupal stages Oxalis cernlla: chronic oxalic acid poison­ two new species of Cucullinae (lepidop­ lasted 4-7, 22 days and up to 36 weeks re­ ing. Australian Veterinary Journal 5, 60-9. tera: Noctuidae) from the south-west­ spectively. Although la rval feeding was Carter, T. (1995). Planning and pasture ern Cape Province of South Africa. not limited to O. pes-capme, but extended management pays. Farming ahead with Phytophylactica 22, 273-80. also to other species within the genus Oxa­ the Kondinin group 39, 42-8. Healy, B.P. (1967). Hypocalcaemia and hy­ lis, K. philoxalis was still considered a likely Catt, M.J. (1972). Soursob control. Depart­ pomagnesaemia in breeding ewes. Ag­ ca ndidate for biological control. Another ment of Agriculture South Australia, ricultllral Gazette of NsW 78, 479-81. noctuid moth, K. swartlalldellsis sp. nov., Special Bulletin, No. 5.72, 8 pp. Henslow, G. (1910). Remarkable instances was also identified for potential activity on Chawdhry, M.A. and Sagar, G.R. (1973). of plant dispersion. Journal of the Royal O. pes-cap rae in South Africa (Geertsema An autoradiographic study of the distri­ Horticultllral Society 35, 342-51. 1990). bution of 14C-labelled assimilates at dif­ Hickinbotham, A.R. and Bennett, W.G. Parasitism of O. pes-caprae by Orobanche ferent stages of development of Oxalis (1931). Soursob troubles. Journal of the sp. was noticed in vineyards, citrus or­ latifolia H.B.K. and O. pes-caprae L. Weed Department of Agriculture South Allstralia chards and olive groves in Crete and may Researcl, 13,430-7. 34,1255-9. have potential for integrated control pro­ Chawdhry, M.A. and Sagar, G.R. (1974a). Hildreth, R.C and Agamalian, H. (1985). grams (Paspatis 1985). Dormancy and sprouting of bulbs in Control of buttercup oxalis in artichokes Oxalis latifolia H.B.K. and 0. pes-cap rae L. with oxyfIuorfen. Proceedirlgs oftlie West ­ Acknowledgments Weed Research 14,349-54. em Society of Weed sciellce 38, 187-95. J thank B. Rayner for the technical assist­ Chawdhry, M.A. and Sagar, G.R. (1974b). Holden, K.J. (1970). Agriculture in South ance in conducting much of my research Control of Oxalis latifolia H.B.K. and Australia. Upper Eyre Peninsula. De­ quoted in this paper and J. Dodd, O. pes-caprae L. by defoliation. Weed Re­ partment of Agriculture South Aus­ P.W. Michael and R. Cousens for helpful sea rch 14, 293-9. tralia, Extension Bulletin 11, 28 pp. comments on the manuscript. Chippendale, G.M. (1964). Records of Holm, L. , Pancho, J.V., Herberger, J.P. and Northern Territory Plants. Transactions Plunkett, D.L. (1979). 'A geographica l of tile Royal Society of South Australia 88, atlas of world weeds', pp. 258-60. 175-80. U. Wiley and Sons, New York). 118 Plant Protection Quarterly Vo1.12(3) 1997 Howes, F.N. (1974). 'A dictionary of useful delle vacche da latte regioni meridionali. Parsons, W.T. and Cuthbertson, E.G. and everyday plants and their common Alimentazione Animale4, 467-518. (1992). 'Noxious weeds of Australia', pp. names', p. 187. (Cambridge University McIntosh, G.H. (1972). Chronic oxalate 529-33. (Inkata Press, Melbourne). Press, Cambridge). poisoning in sheep. Australian Veteri­ Paspatis, E.A. (1985). Chemical, cultural Hyde-Wyatt, B.H. and Morris, D.l. (1975). Itary /ournaI48, 535. and biological control of Oxalis pes-caprae 'Tasmanian Weed Handbook', p . 100. McKenzie, D.N. (1973). Soursob - a peren­ in vineyards in Greece. Proceedings of a (Tasmanian Department of Agricul­ nial problem in cereals. Proceedings of meeting of the EC Experts Group, Dub­ ture). the 2nd Victorian Weeds Conference, lin, pp. 27-9. Jackson, D.l. (1960). A growth study of 1 Cereals, pp. 1-4. (Weed Science Society Peirce, J.R. (1973). Soursob (Oxalis pes­ Oxalis latifolia H.B.K. New Zealand joumal of Victoria, Melbourne). caprae L.) in Western Australia its life his­ of Science 3, 600-9. Meadly, G.R.W. (1955). Weeds of Western tory, distribution, morphological varia­ Jessop, J.P. and Toelken, H.R. (1986). Australia - soursob Oxafis pes-caprae L. tion and weed potential. Technical Bulle­ 'Flora of South Australia', Part 2, 4th Edi­ Tile Journal of Agriculture of Western Aus­ tin 20, Department of Agriculture West­ ti on, pp. 709-16. (South Australian Gov­ tralia 4, series 3, 417-9. ern Australia, pp. 9. ernment Printing Division, Adelaide). Michael, P.W. (1958). Some aspects of the Peirce, J.R. (1976). Effect of subterranean Kluge, R.L. and Claassens, M. (1990). ecology and physiology of soursob, clovers on production of bulbs of Klugeana philoxa/is Geertsema Oxalis pes-caprae L., Ph.D. Thesis, Univer­ soursob. Proceedings Australian Weeds (Noctuidae: Cucullunae). The first po­ sity of Adelaide. Conference, Melbourne 1, 7-8. tential biological control agent for the Michael, P.W. (1964). The identify and ori­ Peirce, J.R. (1978). Effect of rates and times weed Oxalis pes-caprae L. jOllma l of the gin of varieties of Oxalis pes-caprae L. of application of diuron, Hnuron and Elltomological Society of Sou them Africa 53, naturalized in Australia. 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