152 Plant Protection Quarterly Vol.21(4) 2006 on which the outer fl owers open fi rst and the inner ones do not develop fully. Fruits are grey-green pods 8–12 cm long. They are rounded at the base, but Review shortly pointed at the tip, similar to a man- go. Each fruit contains hundreds of seeds, which are brown, fl attened and have a tuft of long white hairs 2–3 cm long at one end. Seeds weigh 5.9–7 mg (Amritphale et al. 1984). The biology of Australian weeds The taproot grows up to 4 m long, with spreading lateral roots. Roots form large 45. Calotropis procera (Aiton) W.T.Aiton tubers with a starchy cortex that contains canals full of milky latex, giving roots a Blair S. Grace, Northern Territory Department of Natural Resources, spongy texture. Environment and the Arts, PO Box 30, Palmerston, NT 0831, Australia. Email: [email protected] Taxonomy The genus Calotropis contains three spe- cies, C. procera, C. gigantea (L.) W.T.Aiton and C. acia Buch.-Ham. (Rahman and Wilcock 1991). C. acia is not known to be Name Flowers are more or less tubular, fi ve present in Australia. C. gigantea is distin- The genus name Calotropis is derived from lobed, 2–3 cm across (Figure 1) without guished from C. procera mainly by having Greek calos (beautiful) and tropis (keel of milky sap. They are white with a deep pur- wider corollas and shorter sepals. Strains a boat), referring to scales in the fl owers ple blotch at the base of each lobe and deep of C. gigantea in Australia are sterile, and (Rahman and Wilcock 1991). The specifi c purple scales between the petals and the it is a garden plant that is capable of some name procera is derived from cera, Latin for stamens. Flowers are grouped in umbels limited spread by suckering from roots. wax, referring to the leaves (Parsons and Cuthbertson 2001). Commonly used synonyms for Calotro- pis procera (Aiton) W.T.Aiton (Asclepiad- aceae) include C. procera (L.) Dryand., C. procera (Aiton) R.Br., C. heterophylla Wall., C. busseana K.Schum, C. syriaca Woodson, C infl exa Chiov., Asclepias procera Aiton and incorrectly, C. procera (Willd.) R.Br. ex Ai- ton (Forster 1992). The common names rubber bush, rub- ber tree and Indian milkweed refer to the milky sap or latex produced in the stems and roots. Kapok refers to the fl uffy fi - bre attached to the seeds. Other common names used in Australia include king’s crown kapok, auricula tree, cabbage tree, King Edward’s crown, Prince of Wales’ crown and calotrope.

Description Calotropis procera is a distinctive medium sized shrub or small tree up to 4 m high. Its stems are grey-green, smooth, rather crooked and older stems are covered with a soft, thick corky bark. The plant com- monly branches at the base. Stems exude copious quantities of sticky latex when damaged. Latex is produced by lactifer cells in the stems and roots (Ogundipe 1993). Leaves are large (5–20 cm long, 4–10 cm wide) and elliptic, rounded or ovate, grey-green in colour, with six prominent veins underneath. Leaves are thick in cross section, with a short pointed tip and a heart-shaped base that partly clasps the stem. Petioles are 3–4 mm long and 4–5 mm wide. A brush of hairs occurs at the Figure 1. Floral anatomy of Calotropis procera. Habit of fl owering branch base of the midvein. Each pair of opposite (A), apical view of fl ower (B), side view of fl ower with part of corolla leaves is at right angles to adjacent pairs. removed showing staminal column (C) and side view of staminal corona The plant is not deciduous. and staminal column (D). From Forster (1992) (reproduced with permission). Plant Protection Quarterly Vol.21(4) 2006 153 There are no known hybrids of C. of Queensland and the Northern Territory. procera in Australia. Two subspecies of C. The fact that C. procera is widespread in procera are recognized, but only one, C. tropical areas with over 1000 mm annual procera ssp. procera is naturalized in Aus- rainfall through to arid areas with rain- tralia (Forster 1992). There is considerable fall less that 200 mm suggests that it can polymorphism within C. procera in its na- tolerate a wide range of environmental tive range, but it is morphologically uni- conditions, hence it has a wide potential form in Australia, suggesting that Austral- distribution (Figure 3). ian populations have resulted from one or very few introductions (Forster 1992). Habitat Several authors claim that C. procera History is most common in overgrazed areas Calotropis procera was possibly introduced (Cheam 1984a,b,c, Barkhadle et al. 1994, into Australia through seeds in the pad- Parsons and Cuthbertson 2001, Smith ding in camel saddles, or as an ornamen- 2002), although it can also persist in oth- Figure 2. The distribution of tal plant during a gold rush in North er areas with high levels of disturbance, Calotropis procera in Australia. Queensland (Parsons and Cuthbertson such as coastal sand dunes (Anon. 2001), Data were taken from Forster (1992), 2001). It was fi rst recorded as naturalized watercourses and roadsides (Parsons Parsons and Cuthbertson (2001), around Chillagoe and Georgetown, North and Cuthbertson 2001). It can also form Navie (2004), Australia’s Virtual Queensland in 1935, but was present much dense thickets on alluvial fl ats (Parsons Herbarium (2005), Mark Gardener earlier (Parsons and Cuthbertson 2001). It and Cuthbertson 2001). Although dense (personal communication) and was fi rst observed in the Northern Terri- stands are common in disturbed or heav- Northern Territory Government tory in the Mataranka area, near Katherine ily grazed areas, C. procera is capable of in 1946–7. It spread along the Roper River establishing and persisting in areas with records. from there in the 1950s and the Victoria good pasture cover (Table 1). River, in north-western Northern Territory Most dense infestations occur on well in the 1960s. drained soil such as sandy levee soils along In Western Australia, a small patch near waterways rather than heavier clays (Ta- Kununurra was recorded in 1965, which ble 1). Plants growing in clay have stunted had expanded rapidly to 5000 ha by 1969, growth (Hall 1967). C. procera frequently and the plant now encompasses very large occurs around oases in arid parts of the areas of the Kimberley (Figure 2). Earlier Middle East (Willmer 1988) and is com- records of C. procera may exist in Western mon in boundaries between cultivated Australia, but it was confused with C. fi elds in northern Pakistan (Hussain et al. gigantea. C. procera was fi rst recorded in 2003). Its occurrence on coastal sand dunes northern South Australia in 1989. There is probably related to its ability to toler- is currently concern that it is spreading in ate high soil salinity (Parsons and Cuth- central Australia (Chris Brown personal bertson 2001). Its growth increases with communication). increasing nitrogen, but it is capable of Calotropis procera was introduced to surviving and reproducing in soils with north-eastern Brazil in the early 1900s (El- low nitrogen (Chadwick and Obeid 1963) Figure 3. The potential distribution lison and Barreto 2004). and it is clearly able to persist in very poor of Calotropis procera in Australia. soils in northern Australia. From Thorp and Lynch (2000) Distribution There were no gross morphological (reproduced with permission). Calotropis procera is native to tropical and differences observed between C. procera subtropical Africa and Asia but is more plants growing at low (0–300 m) and high common in the Middle East. It occurs in (1700–2000 m) altitudes (Alwadi and Ab- West Africa as far south as Angola, North ulfatih 1996). This suggests the plant is tol- Seedling growth is strongly affected and East Africa, Madagascar, the Arabian erant of temperatures ranging from frosts by allelochemicals from buffel grass Peninsula, southern and south-eastern to extreme desert heat. Young stems are (Cenchrus ciliaris L.), but seed germina- Asia, to Malaysia (Rahman and Wilcock surrounded by whitish fl uffy indumentum tion and seedling survival is unaffected 1991). The species is now naturalized in (Ogundipe 1993), which would provide (Cheam 1984a,b). Young stems contain Australia, Indonesia, many Pacifi c islands, protection from frost and desiccation. chlorophyll and become porous as they Mexico, Central and South America, the mature (Ogundipe 1993). Caribbean islands (USDA NRCS 2004, Growth and development Rahman and Wilcock 1991) and north- Little is known about the growth, develop- Reproduction eastern Brazil (Radunz 1983, Ellison and ment or phenology of C. procera in Aus- Calotropis procera is capable of producing Barreto 2004). tralian rangelands. In pot trials, seedlings large quantities of seeds. However, suck- In Australia, C. procera is widespread grew quite slowly initially, but growth ering from roots and crowns may be im- in the northern regions and is a problem rates increased after eight weeks (Table portant in the thickening of local patches in native pastures in drier monsoon ar- 2). Much of the early growth went into (Parsons and Cuthbertson 2001, Smith eas of tropical Australia (Martin 1996). It developing a strong root system (Cheam 2001). is found mostly in northern Queensland, 1984a,b). One mature plant from west- northern parts of the Northern Territory ern Northern Territory (2.4 m high, with Flowers and Western Australia (Figure 2). Infesta- stem diameters of 65, 120 and 190 mm) It is unknown at what age C. procera begins tions further south appear to be spreading; had above-ground portions that weighed to fl ower and seed, but Parsons and Cuth- these include patches in northern parts of 6.6 kg and below ground portions that bertson (2001) tentatively suggest that this South Australia and southern Northern weighed 2.2 kg (wet weights) (Stuart Wil- occurs once plants are two years old. Flow- Territory, as well as the Barkly Tablelands son unpublished data). ers appear all year round in the Northern 154 Plant Protection Quarterly Vol.21(4) 2006 Table 1. Results of a survey of 10 experienced landholders and weed specialists in the Northern Territory. Numbers refer to the per cent of respondents that answered each particular question. Question Responses Is rubber bush an important weed? Yes 62% Why? Shades out pasture 36%; Invasive 27%; Hard to control 18%; Hinders mustering 18%; Toxic 19% Should governments invest in control of existing infestations? Yes 72% Should governments invest in research? Yes 78% Should governments invest in limiting spread? Yes 67% Does it invade areas with good pasture cover? Yes 57% What sort of country does it seem to do best on? Well drained soils 100% Do you think it is spreading in your area? Yes 62% Do infestations normally die off or persist? Persist 72% Have you noticed stock or other animals eating it? Yes 100% What animals browse on rubber bush? Cattle 100%, goats 10% What animals never browse on rubber bush? Horses 100% Do you suspect it made animals sick? Yes 14% Do you suspect it killed any animals? No 100% Have you tried to control rubber bush with chemicals? Yes 80% Have you tried to control rubber bush with grazing or pasture management Yes 14% Have you tried to control rubber bush with fi re? Yes 17% What effect does fi re have? Comes back, possibly with fewer seeds. It is not always possible to have suffi cient grass to support a fi re. What would you recommend as the best way to control or manage this Picloram + triclopyr + diesel, basal bark 80% weed? Triclopyr + diesel, basal bark 20% What control techniques have not been successful? Fluroxypyr foliar spray; Tebuthiuron pellets; Hexazinone granules; Glyphosate foliar spray; 2,4-D foliar spray; Mechanical control; Crash grazing How much do you spend controlling rubber bush on your property per mean $7625 year (including labour)?

Territory, although there are fewer fl owers Table 2. Heights of seedlings of Calotropis procera grown in pots over time in the early dry season (April–May) (Hall since germination. Data from Cheam (1984a,b). 1967). 3 weeks 6 weeks 8 weeks 9 weeks Calotropis procera is pollinated by car- penter bees in Israel, where it appears to Seedling height (mm) 45 49.6 50–53 172 be intimately co-evolved with one species (Xylocopa sulcapites Maa) (Willmer 1988). In Australia it is pollinated by a range In northern Australia, seeds germi- was not affected by light. Seed weight and of insects, noticeably bees (Table 3). In nate with the onset of the wet season, effects of scarifi cation have been found to the Northern Territory, fruits mature in and growth is rapid until the dry season. vary between varieties of C. procera (Am- the wet season (November to February) C. procera seeds are commonly observed ritphale et al. 1984). Between 2 and 35% of (Smith 2001). germinating in cattle dung heaps in India seeds collected from India were dormant, (Kumar et al. 1997). and this proportion varied with variety. Seeds Most seeds collected in India germi- More seeds became dormant after being Seeds are produced in November in north- nated at temperatures between 28 and stored at room temperature in the dark western Northern Territory (Stuart Wilson 36°C, and germination decreased at tem- (Amritphale et al. 1984). Very few seeds personal communication). Seeds are dis- peratures above 36°C (Amritphale et al. (0–6%) collected from Brazil were dormant persed short distances by pods bursting 1984). Seeds collected from Brazil germi- and most seeds germinated within one (Smith 2001) and the tufts of hair on the nated best between 23 and 33°C, with little or two days, depending on temperature seeds may assist dispersal over short dis- germination at 34°C or above (Labouriau (Labouriau and Valadares 1976). Mature tances by wind (Hall 1967). Human activ- and Valadares 1976). Seeds may require seeds contain 10–15% water, which they ity, water and possibly animals (Kumar et exposure to red light in order to germinate can retain for up to 45 days in dry condi- al. 1997) would be important in long dis- (Parsons and Cuthbertson 2001), suggest- tions (Labouriau and Valadares 1976). The tance dispersal. The lipid content of the ing that germination is likely to be limited numbers and longevity of C. procera seeds seeds, combined with surface tension from under dense vegetation. However, Amrit- in the soil is unknown. hairs would provide buoyancy. phale et al. (1984) found that germination Plant Protection Quarterly Vol.21(4) 2006 155 Table 3. Insects found on Calotropis procera in northern Australia (Grace unpublished data). Taxonomy follows CSIRO (1991). Order, Family Species (common name) RegionA Comment Hemiptera, Diaspididae Pinnaspis sp. (Scale insect) Bark Linked to defoliated, unhealthy plants Hymenoptera, Apidae Apis mellifera L. (European honey bee) Kath Observed visiting fl owers, probable pollinator Austroplebia sp. (native bee) VRD Observed visiting fl owers, probable pollinator Hymenoptera, Syrphidae unidentifi ed (native bee) VRD Observed visiting fl owers, probable pollinator Hymenoptera, Vespidae Polistes shach Fabricius (paper wasp) VRD Observed visiting fl owers, possible pollinator Hymenoptera, Formicidae Iridomyrmex sanguineus Forel (meat ant) VRD Observed visiting fl owers, unlikely to pollinate. Ants are nectar robbers in Israel (Willmer 1988). Iridomyrmex sp., anceps group VRD Observed visiting fl owers, unlikely to pollinate Diptera, Tachinidae unknown sp. VRD Adults observed visiting fl owers, possible pollinator. Possible parasitoid of Danaus petilia Lepidoptera, Nymphalidae Danaus petilia Stoll = D. chrysippus petilia VRD, Feeds on leaves, common on Asclepiadaceae Miskin (lesser wanderer) Kath, throughout Australia (Common and Waterhouse Kim 1981, Lushai et al. 2005). Capable of sequestering some plant toxins (Rothschild et al. 1975) Lepidoptera, Psychidae unknown sp. (case moth) Kath C. procera leaves had obvious feeding damage A Bark = Barkly regionregion of Northern TTerritory,erritory, Kath = Katherine rregionegion of NoNorthernrthern TTerritory,erritory, VRVRDD = VVictoriaictoria RivRiverer DisDistricttrict of Northern Territory, Kim = Kimberly region of Western Australia.

Population dynamics Table 4. Toxic substances found in Calotropis procera. Very little is known about the population Substance Effect Comment Reference dynamics of this plant (Parsons and Cuth- bertson 2001), a situation that should be re- Latex Heart poisons Little latex in leaves Seiber et al. 1982, Watt and dressed (Meadley 1971, Bebawi et al. 2002) Breyer-Brandwijik 1962 if sound weed management techniques Latex Nausea and Little latex in leaves Parsons and Cuthbertson are to be developed. Dense infestations in vomiting 2001 riparian zones in the Victoria River District Latex Proteolytic activity Watt and Breyer- of the Northern Territory contained seven Brandwijik 1962, Atal and plants per square metre (Hall 1967). Sethi 1962 Investigations into this plant’s longev- ity and competitive ability, in particular, Latex Causes Eye irritation in humans Mahmoud et al. 1979 have been called for (Bastin et al. 2003). keratoconjunctivitis clears up without Anecdotal observations suggest that cer- intervention tain populations of C. procera may persist Latex Killed goats Administered orally, el Badwi et al. 1998 for several years, and then disappear (Hall injected by intravenous 1967, Steve Wingrave personal communi- and intraperitoneal routes cation), but there are few data to back up such claims and some landholders sug- Roots Inhibits oestrus Ethanolic extracts used in Circosta et al. 2001, gest that populations persist (Table 1). A cycle, prevents in-vivo trials with rats Kamath and Rana 2002 large single stemmed plant about 4 m tall pregnancy had a stem diameter of 20 cm, and counts Various Anti-sperm Qureshi and Qureshi 1991 of growth rings were inconclusive (Blair extracts Grace unpublished data). If seeds do have a requirement for red light to germinate, as mentioned by Parsons and Cuthbertson (2001), then re- pasture plants can be shaped by social fac- 1998) and grazing this plant can lead to cruitment is likely to be inhibited under a tors rather than biological or agronomic stock death. Other authors consider it is canopy of vegetation. Bastin et al. (2003), factors (Allan and Whalley 2004). Some only a problem in overgrazed and dis- however, found plant densities were simi- landholders state that C. procera may be turbed areas (Cheam 1984a,b,c) where lar in grazed and ungrazed plots. Most perceived to be a larger problem than it little useful fodder exists, while other au- landholders surveyed considered that C. really is, because it is tall and distinctive thors suggest it can be a useful fodder. procera can invade land with good pasture (Rod McColm personal communication) Some reports suggest that C. procera is cover (Table 1). How pasture, grazing and and sparse populations of tall weeds may a useful source of green forage during the environmental conditions affect seedling prompt the use of control measures for dry season and in droughts, particularly in germination and recruitment needs to be cosmetic reasons rather than because of northern Australia. Important weeds can quantifi ed. effects on pasture productivity (Popay and also have value as pasture (e.g. Gardener Field 1996). et al. 2005). C. procera has been classifi ed as Importance Some authors (e.g. Smith 2001) suggest a problem in pastures and roadsides and There is conflicting information about C. procera is a high priority weed, which unique natural ecosystems (scrubland and the importance of C. procera as a weed successfully competes with desirable pas- savannah) in Brazil (Ellison and Barreto in Australia. Landholder perceptions of ture species (Crothers and Newbound 2004). 156 Plant Protection Quarterly Vol.21(4) 2006 Detrimental boundary of the Sahara Desert (Nolan the plant has been used extensively for Calotropis procera can form dense thick- 1999). In West Africa, sheep and goats eat medicinal purposes in many countries. ets that interfere with stock manage- fl owers and withered leaves, but gener- Traditional uses and pharmacologically ment, particularly mustering (Crothers ally avoid fresh leaves (Watt and Breyer- active compounds in C. procera have been and Newbound 1998, Parsons and Cuth- Brandwijik 1962). In feeding trials in the comprehensively studied (summarized in bertson 2001, Smith 2001, Table 1). Many Northern Territory, sheep initially avoid- Table 5). landholders consider it a problem, mainly ed fresh leaves and fl owers, but ate them Calotropis procera also has a range of tra- because it shades out pasture, is capable readily after six weeks, and cattle read- ditional non-medicinal uses. Arab tribes- of rapid invasion and is hard to manage ily ate hammer milled leaves and fl owers men once burned its wood to obtain a fi ne- (Table 1). There are no data on impacts of (Radunz 1983). Goats readily ate dried C. texture charcoal used in gunpowder. The C. procera on biodiversity. procera leaves as up to 50% of dietary dry fi bres attached to the seeds have been used Calotropis procera contains a range of matter in Sudan (Abbas et al. 1992). in padding and weaving, and intoxicating toxic compounds (Table 4), many of which Calotropis procera is browsed by stock liquor has been produced from this plant are concentrated in the latex. Leaves can in northern tropical parts of Australia, but (Rahman and Wilcock 1991). The latex has take up heavy metals (Pb, Co, Ni, Mn, Cr, it has been suggested that populations in been used to coat arrow heads in India and Cd and Cu) present in the environment arid Australia are not palatable (Crothers Africa. In addition, its anti-nematode prop- (Díaz and Massol-Deya 2003). and Newbound 1998), possibly because erties (Khurma and Chaudhary 1999) have Pastoralists and weed specialists sur- environmental conditions trigger produc- led to it being used as green mulch that veyed found little evidence that stock die tion of defensive compounds (Lev-Yadun can reduce crop losses from nematodes. or become sick as a result of browsing and Ne’eman 2004). It is also possible that Cloth has been produced from fi bres in C. on C. procera in Australia (Table 1), and northern regions have more grass avail- procera stems (Varshney and Bhoi 1988), pathology tests found no evidence of able, so C. procera can be used as a high and the latex has been used to curdle milk toxicity to stock (Radunz et al. 1984). Al- nitrogen supplement to fi bre with low di- and help ferment beer (Watt and Breyer- though ingesting large quantities of latex gestibility, compared to more arid regions, Brandwijik 1962). Proteolytic enzymes in has killed goats and rats, it is important to where less grass is generally available. A the latex have potential commercial uses note that there is little latex in the leaves recent survey of landholders across the in food preparation (Atal and Sethi 1962). (Parsons and Cuthbertson 2001), the part Northern Territory, however, suggests that C. procera has also been well studied as a most likely to be eaten by stock. However, the plant is commonly browsed by cattle potential fuel source. one weed specialist commented that cattle across its range (Table 1). As oil prices increased in the late 1970s, can become sick after eating large quanti- many plants, including C. procera, were ties of leaves, although this rarely happens Benefi cial investigated as potential sources of liq- (Murray Fuller personal communication). Calotropis procera may be more useful as a uid fuel (Cribb 1980). Stems, leaves and Goats that ate larger quantities of la- browse than commonly thought. Much of pods all contained extracts with energy tex, or had it injected died, but ingesting the research on C. procera may have been levels comparable to coal and fossil fuels small doses (0.005 mL per kg body weight biased towards looking at its toxic com- (Erdman and Erdman 1981). Further re- per day) of latex resulted in no deaths, but ponents rather than the potential to use search found that although it is feasible gave rise to symptoms such as nervous it as stock feed (Abbas et al. 1992). Leaves to produce diesel and petrol from resin signs, frequent urination, frothing at the do have useful nutrients; they contain 16– in C. procera stems, this is vastly more ex- mouth, dyspnoea and diarrhoea (el Badwi 20% protein, low tannin (3.1%) (Abbas et pensive than doing so from oilseed crops et al. 1998). Ingesting latex caused rats to al. 1992, Touré et al. 1998) and high levels such as sunfl ower, which are in turn more lose weight, but produced no changes in of minerals, although much of the calcium expensive than crude oil (Bell 1982). More measured blood parameters (Dada et al. is bound up in oxalate crystals (Atal and recently Behera et al. (2000) found that 2002). Feeding high doses (5–10% w/v of Sethi 1962, Ogundipe 1993). Adding up to allowing microbes to break down the C. diet) to rats resulted in severe liver dam- 75% of dietary dry matter from C. procera procera latex could make the process much age and death (Pahwa and Chatterjee leaves improved digestibility of rice straw cheaper. C. procera seeds are 26% oil (Os- 1988). The rate of latex production in India and peanut cake-based diets fed to sheep, man and Ahmad 1981), but they are small, is lowest in the dry season (Atal and Sethi and C. procera was more digestible than and produced in low numbers compared 1962), which is when C. procera is most several other tree forages tested (Touré to many existing crop plants, so C. procera likely to be grazed. et al. 1998). Anecdotal evidence suggests has little potential for use as an oil seed Compounds produced for plant defence that camels suffering from night blind- crop. Much of the oil is saturated, and un- commonly vary with season, stage of plant ness caused by Vitamin A defi ciency can likely to have pharmacological or indus- development, and environmental condi- be cured by forcing them to eat C. procera trial uses (Osman and Ahmad 1981). tions and may even be induced as a result leaves (Abbas et al. 1992). Steers fed C. It has even been suggested that C. of herbivory. Lev-Yadun and Ne’eman procera milled leaves (up to 10 g per kg procera is useful as an obvious indicator (2004) hypothesize that toxic compounds body weight per day) in the Northern Ter- of poor rangeland condition in northern and volatile secondary compounds with ritory actually gained more weight than Australia. Under such conditions, its deep repellent odours in C. procera are likely to the control group that was fed rice and hay root system may also be useful in reducing increase over the dry season. (Radunz et al. 1984). erosion and it could be planted to stabi- Everist (1981) concluded that C. procera It has been suggested that stock may lize sand dunes in its native range (Khan was very unpalatable but sometimes eat- tolerate C. procera as part of the diet under 1997). en by stock. Powdered stems are slightly good conditions, but may die from eating bitter to humans (Ogundipe 1993). The C. procera when stressed (e.g. during mus- Legislation palatability of C. procera to stock may tering) (Anon. 2001, Smith 2001). C. procera Calotropis procera is a Class B weed (growth vary between sites. Cattle and sheep may retains green leaves all year round, even and spread is to be controlled) in the avoid eating the plant in India and parts during poor seasons, so sometimes it may Northern Territory, south of 16°30’ (Miller of Africa, but commonly eat it in Indone- be the only green feed available. 2003). In Western Australia it is a P1 weed sia (Radunz 1983). C. procera contributed Some of the biologically active com- (movement of plants and seeds, including a small (<3%) proportion of the diet of pounds in C. procera have potential for contaminated stock, fodder and machin- sheep, cattle and goats on the southern use in the pharmacological industry and ery is prohibited) north of 26°S, excluding Plant Protection Quarterly Vol.21(4) 2006 157 Table 5. Selected substances found in Calotropis procera with potential or traditional medical or veterinary uses. Substance Effect Comment Reference Flowers, buds, roots Anti-malaria Various fractions tested in vitro Sharma and Sharma 1999 Flowers Steroid with unspecifi ed effects Khan and Malik 1989 Leaves Cures night blindness May help overcome Vitamin A Abbas et al. 1992 defi ciencies in stock Latex Topical fungicide Applied topically to stock. Kills Ahmad et al. 2004 ringworm and promotes hair regrowth Latex Anti-coccidia Latex given orally to treat Eimeria Mahmoud et al. 2001 ovinoidalis Tarım in sheep Latex Treatment of haemorrhoids Administered anally Giday 2001 Latex Topical disinfectant Applied topically latex has bacteriolytic Rahman and Wilcock 1991, activities Shukla and Murti 1961 Latex Anti-diarrhoea Dried Kumar et al. 2001, Burkill 1985 Latex Anti-viral properties Inhibits Tobacco Mosaic Virus infection, Khurana and Singh 1972 when applied to leaves Latex or powdered Treatment of blackleg (Clostridium Administered topically Giday 2001 seeds spp.) in stock Latex Analgesic Various extracts from latex Majumder and Kumar 1998 Root Toothache cure Root used as toothbrush Watt 1889 (in Rahman and Wilcock 1991) Root Anti-infl ammatory, analgesic Extract from roots Basu and Nag Chaudhuri 1991, Rahman and Wilcock 1991 Roots Anti-ulcer Chloroform extract from roots Basu et al. 1998 Root bark Used in treating dysentery, and as Atal and Sethi 1962 expectorant Twigs Anti-diarrhoea Twigs dried and powdered Burkill 1985 Bark Cure for elephantiasis, leprosy, Applied topically Wren 1975 eczema Whole plant Anthelmintic Atal and Sethi 1962

certain municipal districts, and a P2 (tar- Herbicides control’ (Milson 2000). Parsons and Cuth- geted for eradication) weed in certain mu- There are currently no herbicides specifi - bertson (2001) suggest that managing C. nicipal districts (Department of Agricul- cally registered for control of C. procera procera requires drastic changes in grazing ture 2004). It is not currently a declared in Australia, although trials have been management, especially reducing stocking noxious weed in any other Australian completed with the aim of registration rates. Interestingly, only one landholder state or territory. C. procera is specifi cal- (Joe Vitelli personal communication). surveyed had attempted to manage C. ly excluded from the list of plant seeds Herbicides that have previously been procera by crash grazing a small infestation. permitted to be imported into Australia registered for C. procera include picloram, This resulted in a higher density infestation (Schedule 5 of the Federal Quarantine Proc- 2,4-D, imazethapyr and triclopyr (Par- the following wet season. Hard grazing by lamation 1998). However, this list is pres- sons and Cuthbertson 2001, Smith 2001). cattle had some success in controlling the ently under revision. These herbicides were applied using cut- weed in the Victoria River District of the stump and basal bark methods for larger Northern Territory (Hall 1967). Long term Weed management plants, which would be time consuming, weed containment in pastures and range- The vast areas of the Northern Terri- and hence impractical for scattered plants lands requires knowledge of the plant’s tory, western Queensland and northern in rangelands. Smaller plants could be biology (Popay and Field 1996), but such Western Australia infested by C. procera treated with foliar spray. Herbicide treat- information is not available for C. procera make control diffi cult, expensive and of- ments often had to be repeated (Parsons and there are very few data about manag- ten impractical (Parsons and Cuthbertson and Cuthbertson 2001). Basal bark appli- ing weeds using grazing in the tropics. 2001), especially when much of this land cations of picloram plus triclopyr mixed A long-term grazing exclusion trial has little production value. ‘There is no in diesel appears to be the most commonly suggested possible effects of grazing and economical method of controlling exten- used means of controlling C. procera (Table pasture competition on C. procera popula- sive infestations of calotrope [C. procera] 1), giving a kill rate of around 90% (Mur- tions. Five years after cattle were excluded under pastoral situations’ (Cheam 1984c). ray Fuller personal communication). from parts of run-down pastures in the Research into cheaper control options for north west of the Northern Territory, less larger areas, such as biological control and Grazing and pasture management C. procera occurred in grazed plots than in fi re, should be a high priority (Bebawi et ‘Grazing management that promotes a ungrazed plots. After 16 years, the density al. 2002). large body of perennial grass growth is the of C. procera was similar between grazed most positive form of calotrope [C. procera] and ungrazed plots, and there was no 158 Plant Protection Quarterly Vol.21(4) 2006 C. procera recorded after this (Bastin et al. the plant is attacked by few phytophagic Allan, C. and Whalley, R.D.B. (2004). Some 2003). The authors note that grazing pres- insects in its native range (Abbassi et al. factors infl uencing landholder opinion sure outside the exclosures had been low 2003, Lev-Yadun and Ne’eman 2004). Few of the native grass Microlaena stipoides. during this trial, and that it took more insects cause more than minor damage to Rangeland Journal 26, 178-89. than six years for the biomass of peren- C. procera in Australia, and Table 3 lists Alwadi, H.M. and Abulfatih, H.A. (1996). nial grasses to recover both inside and some of these. An unidentifi ed stem borer Uniformity of morphological charac- outside the enclosures. These results sug- destroyed most above-ground growth of teristics of Calotropis procera found at gest that cattle may reduce recruitment of C. procera in several square kilometres in two altitudinal ranges, in Saudi Arabia. C. procera, possibly by feeding on young the Kimberly region of Western Australia, Arab Gulf Journal of Scientifi c Research 14, plants. If seeds do require exposure to red but several months later the insect could 169-76. light to germinate, then a good sward of not be found and the plant had regrown Amritphale, D., Gupta, J.C. and Iyengar, perennial grass is likely to prevent estab- from rootstock (Blair Grace unpublished S. (1984). Germination polymorphism lishment and spread. data). in sympatric populations of Calotropis Growth of C. procera seedlings, but not Ellison and Barreto (2004) suggest that procera. Oikos 42, 220-4. seed germination, was inhibited by allelo- C. procera in Latin America is a suitable Anon. (2001). Calotrope. Facts Pest Series, chemicals from buffel grass (Cenchrus cili- target for classical biological control. In PP41, Queensland Government. aris L.) (Cheam 1984a), concentrated in the a survey of fungi on C. procera in Brazil, Atal, C.K. and Sethi, P.D. (1962). Proteolyt- upper soil surface (Cheam 1984b). Care- Barreto et al. (1999) found three species ic activity of some Indian plants. II. Iso- ful consideration should be made before with potential for use as biological control lation, properties, and kinetic studies of planting buffel grass, as it can be a nui- agents. Phaeoramularia calotropidis Ell. & calotropain. Planta Medica 10, 77-90. sance itself (see Puckey and Albrecht 2004), Everh. forms lesions on leaves. It is wide- Australia’s Virtual Herbarium (2005). and likely to be more of a concern to land spread in tropical America, Egypt, India, Centre for Plant Biodiversity Research, managers of conservation areas than C. Pakistan, Myanmar, Africa and Brazil. Al- Council of Heads of Australian Herbar- procera (John Woinarski personal commu- though damaging in Sudan, it appears to ia (http://www.cpbr.gov.au/cgi-bin/ nication). In addition C. procera commonly have little impact in Brazil. Mycosphaerella avh.cgi). Accessed January 2005. grows alongside buffel grass in northern sp. (possibly a reproductive phase of P. Barkhadle, A.M.I., Ongaro, L. and Pignat- Western Australia (Blair Grace personal calotropidis) covers leaves with black sooty ti, S. (1994). Pastoralism and plant cover observation). As for most weeds of grazing growth and causes leaf distortion. The in the lower Shabelle region, Southern land, grazing management should focus third potential fungus, Uredo calotropidis Somalia. Landscape Ecology 9, 79-88. on promoting perennial grasses. Cummins, requires investigations into its Barreto, R.W., Evans, H.C. and Pomella, taxonomy and host range. A fruit fl y Dacus A.W.V. (1999). Fungal pathogens of Physical longistylus Wiedemann was observed de- Calotropis procera (rubber bush), with Physical removal of C. procera can be effec- stroying fruit in Sudan (Parsons and Cuth- two new records from Brazil. Australa- tive if most of the roots are removed (Hall bertson 2001), but has no potential for use sian Plant Pathology 28, 126-30. 1967), or at least the top 25–30 cm (Parsons in classical biological control because it is Bastin, G.N., Ludwig, J.A., Eager, R.W., and Cuthbertson 2001, Department of Ag- also a pest of crops. Liedloff, A.C., Andison, R.T. and Co- riculture 2004). This can be very hard to biac, M.D. (2003). Vegetation changes achieve (Smith 2001) and would rarely be Acknowledgments in a semiarid tropical savanna, north- economically feasible in rangelands. Single Thanks to the many people who con- ern Australia. Rangeland Journal 25, 3- shallow ploughing is useless as plants rap- tributed to this paper, in particular Mark 19. idly grow back (Hall 1967, Stuart Wilson Gardener and Andrew Mitchell who gave Basu, A. and Nag Chaudhuri, A.K. (1991). personal communication), often as stands valuable comments and suggestions about Preliminary studies on the antiinfl am- of multi stemmed plants that occupy more early drafts. Cameron Yates helped pro- matory and analgesic activities of space than before ploughing (Steve Win- duce maps. Ben Hoffmann, Glenn Bellis Calotropis procera root extract. Journal of grave personal communication). Com- and Graham Brown helped identify in- Ethnopharmacology 31, 319-24. monly used weed control techniques such sects and provided information on their Basu, A., Sen, T., Pal, S., Mascolo, N., Ca- as chaining and stick-raking generally are ecology. The input of everyone who re- passo, F. and Nag Chaudhuri, A.K. therefore unlikely to be effective. plied to the surveys is greatly appreciated, (1998). Studies on the antiulcer activity especially Larry Johns and Murray Fuller. of the chloroform fraction of Calotropis Fire Paul Forster allowed me to use his dia- procera root extract. Phytotherapy Re- The large energy stores in the roots allow grams, and Stuart Wilson kindly dug up search 11, 163-5. plants to regrow after fi re (Anon. 2001). an entire bush and weighed it. Bebawi, F.F., Campbell, S.D. and Stanley, Landholders sometimes burn infesta- T.D. (2002). 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