Status of Biological Control of Parthenium Size

STATUS OF BIOLOGICAL CONTROL OF PARTHENIUM HYSTEROPHORUS L. IN INDIA: A REVIEW

J. SRIKANTH and N. A. PUSHPALATHA Department of Entomology, University of Agricultural Sciences, G. K. V. K. Campus Bangalore 560 065, India

(Received 15 August 1989; revised 7 May 1990)

Abstract—Biological control efforts on Parthenium hysterophorus L. (Asteraceae) in India have gained momentum after the limitations of other methods were realized. Native surveys revealed a large number of insects, but none of them was host specific. Although the introduced beetle Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) has established at the sites of initial releases, its real impact on the weed and performance in different parts of the country need further evaluation. Fungal pathogens of the weed hold promise for classical as well as microherbicidal control. The use of parthenium phyllody MLO as a biocontrol agent requires establishment of host and vector specificity. Mycotoxins are a potential group of herbicides on which serious studies are yet to begin. Studies on control of the weed through interference and allelopathy by Cassia uniflora Mill. (= C. sericea Sw.) (Leguminosae) have produced promising results. Toxic leachates of C. uniflora and autotoxic principles of the weed deserve attention. Integrated biocontrol strategies envisaged for wastelands using introduced insects and pathogens, allelopathic plants, and agroecosystems using native pathogens, mycotoxins and autotoxic principles, will help combat this apparently invincible weed.

Key Words: Parthenium hysterophorus, biological control, Zygogramma bicolorata, mycotoxins, allelopathy, Cassia uniflora

Resume*—Les efforts contrdle biologique sur Parthenium hysterophorus L. (Asteraceae) en Inde se sont accel6res des qu'on s'est rendu compte des limites des autres methodes. Des recherches locales ont revele un grand nombre d'insectes mais aucune d'el les n'etaient un note splcifique. Malgre que le coleoptere Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) recemment introduit se soit etabli sur des sites ou on l'a initialement e~leve~, son impact reel sur I'ivraie et le resultat obtenu dans d'autres regions du pays necessite une plus ample evaluation. Les microbes pathogenes fongaux de I'ivraie donnent une lueur d'espoir tant pour le contrdle classique que pour le contrdle microherbicidal. L'utilisation de la phyllodie du parthenium MLO comme agent biocontrole exige la connaissance de la specificity de l'hdte et du vecteur. Les mycotoxins sont un groupe potentiel d'herbicides sur lesquels on doit commencer des etudes serieuses. Les etudes sur le contrdle des mauvaises herbes au moyen d'interference et d'allelopathie par la plante Cassia uniflora Mill. (= C. sericea Sw.) (Leguminosae) ont donne1 des resultats prometteurs. Les extraits toxiques du C. uniflora et des principes autotoxiques de mauvaises herbes merite une attention particuliere. Les strategies inte'gre'es du biocontrole envisagees pour des terres en friche en utilisant des insectes et des pathogenes introduits, des plantes alleiopathiques, et, peur des agro- ecosystemes, ('utilisation des pathogenes indigenes, des principes mycotoxins et autotoxiques aideront a combattre cette mauvaise herbe apparemment invincible.

347 348 J. SRIKANTH and N. A. PUSHPALATHA

INTRODUCTION employment of polyphagous insects, mycotoxins and MLO diseases, to the more serious efforts Very few weeds in India have generated as much made to import and release exotic natural enemies alarm and concern among the scientific for classical biological control. community and common man as the weed Parthenium hysterophorus L. (Asteraceae). Insects and mites Native to Mexico, the weed, within the last 100 years, has found its way to Africa, Australia and An examination of the list of insects and mites Asia, and currently enjoys worldwide distribution reported on this weed in India (Table 1) reveals (Haseler, 1976; Towers et al., 1977). Although it many of them to be polyphagous pests of was first noticed in India in the year 1956 (Rao, agricultural crops. Although many were noticed 1956), its actual date of entry into the country was as sporadic occurrences causing minor damage, a traced back to 1810 by Bennett et al. (1978) and few occurred in serious proportions often killing confirmed by Maiti (1983). Also popularly called the plant. broom-bush, carrot weed, congress grass, white Amongst the four species of scale insects top, etc., its spread to different parts of the country found attacking the stems and branches, has been very rapid. According to Krishnamurthy Parasaissetia nigra (Nietn.) and Saissetia coffeae et al. (1976), about 2 M ha of land is covered by (Wlk.) caused wilting of parthenium plants in the this weed in the country. However, the weed glasshouse, while P. nigra often killed groups of remained in obscurity for about a decade after its the weed in the field (Kumar et al., 1979). discovery and rose to prominence only after its Similarly, the lantana scale, Orthezia insignis hazardous effects on the lives of people reached Browne, attacked the stem, leaves and flowers of intolerable levels. The interference of this weed in the weed in dense colonies in summer, resulting in agriculture (Vartak, 1968; Kanchan and the wilting and drying of a few plants (Srikanth et Jayachandra, 1976) and animal health al., 1988a). (Narasimhan et al., 1977) has been well Adults and nymphs of the membracid demonstrated. Its distribution, chemistry, hazards Leptocentrus taurus F. attacked the main stem, and control have been extensively reviewed petioles and bases of midribs of about 20% of the (Krishnamurthy et al., 1977; Towers et al., 1977; more than 1000 plants examined (Thangavelu, Basak, 1984; Parihar and Kanodia, 1986; Joshi, 1980). 1990). Several species of mealy bugs were reported Although several methods have been proposed on this weed. Ferrisia virgata (Ckll.) attacked for the suppression of this weed, each has its own especially the roots of young plants which wilted disadvantages (Joshi, 1989). For instance, and dried (Char et al., 1975). Potted plants of the mowing the weed as soon as it flowers, though weed when infested with Planococcus sp. wilted preventing seed production, results in rapid within a week without producing a single seed regeneration of new shoots necessitating repeated (Hegde and Patil, 1979). Similarly, Icerya operations (Gupta and Sharma, 1977). seychellarum (Westw.) killed the weed in the Mechanical uprooting is constrained by the glasshouse, whereas F. virgata when reared and development of dermatitis in workers engaged in released on isolated patches of the weed failed to the operation (Krishnamurthy et al., 1977). kill the latter (Kumar et al., 1979). Chemical control, though effective, is temporary Larvae of the beetle Oberea sp., and grubs and and needs repeated application, besides having adults of the scolytid Hypothenemus eruditus problems of residues, selectivity and cost of (Westw.) were found boring into the stems application. Moreover, it is rather impossible to causing wilting and death of the plants. As many adopt these methods in vast stretches of as 15-20 adults of the latter were seen in a single wasteland. These disadvantages prompt us to plant besides many grubs, and up to 75% of the include biological methods as a component of plants were bored in some areas (Kumar et al., parthenium control programme. In the present 1979). Adults of the flea beetle Luperomorpha paper we review the status of biological control of vittata Duvivier caused characteristic P. hysterophorus in India and discuss its future in skeletonized spots on leaves by scraping the light of several available and potential tools for epidermis. They also fed on stems by scraping the integrated biological control programme. epidermis and scooping the cortex portion The studies made so far in this regard ranged (Srikanth et al., 1991).Larvae of Spilosoma from surveys conducted for natural enemies and obliqua Wlk. voraciously fed on leaves and main Biological control of Parthenium hysterophorus L. 349

Table 1. Insects and mites recorded on P. -hysterophorus in India

Order Family Species Reference

Heteroptera Pentatomidae Chrysocoris stollii (Wolff) Kumar et al. (1979) Dolycoris indicus Stal Kumar et al. (1979)

Homoptera Aphididae Aphis gossypii Glov. Rajendran (1976), Krishnamurthy et al. (1977), Kumar et al. (1979), Raodeo and Tayade (1979), Keshwal (1982) Aphis spiraecola Patch Rajendran (1976)

Cicadellidae Aconurella sp. Mathur (1989) Batracomorphus angustatus (Osborn) Ravi (1983), Mathur (1989) Batracomorphus indicus (Lethierry) Mathur (1989) Empoasca sp. Mathur (1989) Empoasca devastans Distant Padmanabhan (1982) Exitianus indicus (Distant) Mathur (1989) Hecalus arcuatus (Motschulsky) Mathur (1989) Hishimonus phycitis (Distant) Padmanabhan (1982), Mathur (1989) Leofa sp. Mathur (1989) Orosius albicinctus Distant Keshwal (1982), Anantha Murthy (1984), Mathur (1989) Thaia sp. Mathur (1989)

Coccidae Ceroplastes sp. Kumar etal. (1979) Coccus longulus (Dgl.) Kumar etal. (1979) Parasaissetia nigra (Nietn.) Kumar etal. (1979) Saissetia coffeae (Wlk.) Kumar etal. (1979)

Margarodidae Icerya seychellarum (Westw.) Kumar etal. (1979)

Membracidae Coccosterphus minutus (F.) Kumar et al.( 1979) . Leptocentrus taurus F. Thangavelu (1980) Oxyrhachis tarandus (F.) Kumar etal. (1979) Telingana campbelli Dist. Kumar etal. (1979)

Ortheziidae Orthezia insignis Browne Srikanth etal. (1988a)

Pseudococcidae Ferrisia virgata (Ckll.) Char etal. (1975), Kumar et al. (1979) Nipaecoccus corymbatus (Newst.) Kumar etal. (1979) Planococcus sp. Hegde and Patil (1979)

Orthoptera Acrididae Neorthacris simulans (Bol.) Kumar et al. (1979), Raodeo and Tayade (1979)

Coleoptera Cerambycidae Oberea sp. Kumar etal. (1979)

Chrysomelidae Luperomorpha vittata Duvivier Srikanth etal. (1991) Metriona circumdata (Hbst.) Krishnamurthy et al. (1977) Monolepta signata (01.) Kumar etal. (1979) Metriona circumdata (Hbst.) Krishnamurthy et al. (1977) Monolepta signata (01.) Kumar etal. (1979) 350 J. SRIKANTH and N. A. PUSHPALATHA

Table l.Contd.

Curculionidae Ptochus ovulum Faust Kumar et al. (1979)

Scolytidae Hypothenemus eruditus (Westw.) Kumar et al. (1979)

Lepidoptera Arctiidae Spilosoma obliqua Wlk. Krishnamurthy et al. (1977), Vaidya and Vartak (1977)

Noctuidae Trichoplusia orichalcea F. Krishnamurthy et al. (1977) Heliothis armigera (Hub.) Raodeo and Tayade (1979)

Acari Tetranychidae Tetranychus cinnabarinus (Boisd.) Kumar et al. (1979) Tetranychus ludeni Zacher Harish Kumar et al. (1990) Tetranychus macfarlanei Baker & Pritchard Harish Kumar et al. (1990) Tetranychus neocaledonicus Andre- Puttaswamy et al. (1976) (= cucurbitae Rahman & Sapra) •

Tenuipalpidae Brevipalpus phoenicis (Geijskes) Dagar and Singh (1979) stem, completely destroying the plant above the feeding on all the hosts except jasmine and niger ground level (Vaidya and Vartak, 1977). on which slight nibbling by adults was observed Four species of spider mites, namely (Jayanth and Nagarkatti, 1987). After the insect Tetranychus neocaledonicus Andre (= cucurbitae was found safe for field liberation, releases were Rahman & Sapra) (Puttaswamy et al., 1976), made in 500 m2 area of a 10 ha parthenium plot. Tetranychus cinnabarinus (Boisd.) (Kumar et al., The beetles established in about a month and also 1979) and Tetranychus ludeni Zacher and dispersed to about 2 ha. It was active in the field Tetranychus macfarlanei Baker & Pritchard during heavy rainfall, diapaused in soil during (Harish Kumar et al., 1990) were recorded on this summer and emerged with the rains (Jayanth, weed. The false spidermite Brevipalpus phoenicis 1987a). Further studies conducted in the field to (Geijskes) often destroyed the attacked plants of determine the number of insects required to bring the weed and suppressed its growth when about the control of the weed showed that a artificially infested at various growth stages of the population level of 3-5 adults per plant resulted in plant (Dagar and Singh, 1979). complete defoliation of the weed in 6 weeks. Most Sundara Rajulu and Gowri (1976) employed at of the adults dispersed after defoliation leaving random various phytophagous pests found on behind a residual population, which prevented economic plants for the control of the weed. Aphis regeneration of the weed and also suppressed fabae Scopoli, Pseudococcus sp. and Tetranychus newly emerging plants before flowering (Jayanth sp. reduced the growth of potted plants greatly and Geetha Bali, 1990). which often resulted in their wilting when infested A stem borer, Epiblema strenuana (Walker) artificially. When all these pests were introduced (Lepidoptera: Tortricidae) originating from into vast stretches of parthenium fields, they Mexico, that prevents growth by forming stem established in 1 month and in another 2 months galls and also reduces flower production, was plants in about 30-40 acres wilted completely. imported from Australia in 1985. Amongst 49 The first systematic biological control attempt species of plants tested for host specificity, normal to tackle the problem weed by using exotic insects completion of life cycle, egg laying and hatching was initiated at the Indian Institute of observed in niger prompted the IIHR to terminate Horticultural Research (IIHR), Bangalore, with the culture (Jayanth, 1987b). the importation of Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) from Pathogens and mycotoxins Mexico in 1983. The grubs fed on terminal and axillary buds, and peripheral leaves leading to Several fungal, two bacterial and one stunted growth and reduced flower production. mycoplasmal disease have been reported on P. Host-specificity tests with 40 species of plants hysterophorus (Table 2). showed no adult feeding, oviposition or larval Biological control of Parthenium hysterophorus L. 351

Table 2. Fungal, bacterial and mycoplasmal diseases of P. hysterophorus in India

Pathogen Disease Reference

Rhizoctonia solani Kuhn Wilt Kumar et al. (1979) Sclerotium rolfsii Sacc. Collar rot Siddaramaiah et al. (1984) Colletotrichum capsici (Syd.) Butl. & Bisby Leaf spot Rao and Rao (1979) Colletotrichum gloeosporioid.es Penz. Leaf spot Vijayakumar and Rao (1977) Exserohilum rostratum (Drechsl.) Leaf spot Rao and Rao (1987) Leonard & Suggs Fusarium semitectum Berk, and Rav. Leaf spot Rao and Rao (1987) Alternaria tenuis Auct. Blight Rao (1965), Datar (1981) Alternaria zinniae Pape Blight Rao(1965) Oidium sp. Powdery mildew Mhaskar (1972), Datar (1981) Oidium parthenii Satyaprasad and Usharani Powdery mildew Satyaprasad and Usharani (1981) Pseudomonas solanacearum Smith Wilt Ram Kishun and Ramesh Chand(1987) Xanthomonas parthenicola Blight Ghosh and Singh (1979) MLO Phyllody Anupam Varma et al. (1974), Phatak et al. (1975), Hegde and Patil (1976), Kumar et al. (1979), Mali and Vyanjane (1979), Deshpande et al. (1982), Padmanabhan (1982), Mathur (1989)

The root rot fungus, Rhizoctonia solani Kuhn coloured spots on the lower leaves which enlarged caused wilting in a few plants of the weed (Kumar and coalesced turning the leaves dark brown. The et al., 1979). Similarly, infection by Sclerotium prevalence of the disease was up to 23% (Datar, rolfsii Sacc. resulted in wilting and death of 1981). seedlings. The pathogen caused pre-emergence A powdery mildew caused by Oidium sp. rot and post-emergence death of seedlings in produced white floury patches on leaves which pathogenicity tests (Siddaramaiah et al., 1984). withered and dropped in later stages. The disease The leaf spot disease produced by incidence was found to be up to 10% (Datar, Colletotrichum gloeosporioides Penz. was 1981). Satyaprasad and Usharani (1981) also characterized by necrotic lesions which gradually noticed widespread incidence of a similar increased in size and covered the entire lamina. powdery mildew caused by Oidium parthenii Pathogenicity tests with spore suspensions Satyaprasad and Usharani. produced symptoms in 5-6 days and reisolations The bacterial blight caused by Xanthomonas yielded the fungus (Vijayakumar and Rao, 1977). parthenicola produced dark brown water soaked A similar leaf spot caused by Colletotrichum lesions on usually lower leaves which coalesced capsici (Syd.) Butl. & Bisby showed no disease to form larger patches resulting in complete symptoms in some local varieties of chillies when blighting of leaves. Purplish to light brown streaks cross inoculated (Rao and Rao, 1979). appeared on the stem close to the ground level, Alternaria tenuis Auct. and Alternaria zinniae turning darker in due course of time (Ghosh and Pape were found causing a very serious blight in Singh, 1979). The wilt caused by Pseudomonas this weed (Rao, 1965). A. tenuis, which was solanacearum Smith led to drooping of leaves pathogenic when inoculated, produced grey followed by wilting and death of plants. Browning 352 J. SRIKANTH and N. A. PUSHPALATHA

of stem at soil level became prominent with the moniliforme Sheldon produced typical wilt advancement of disease (Ram Kishun and Ramesh symptoms in 5-6 hr whereas those of other Chand, 1987). pathogens needed 36 hr to produce symptoms in The first observations on the occurrence of treated plants. phyllody in parthenium seem to be those of Anupam Varma et al. (1974) and Phatak et al. Parasitic plants (1975). Typical witches' broom symptoms, reduction in leaf blades, floral abnormalities, Orobanche aegyptiaca Pers. was recorded sterility and failure to produce seeds were parasitizing the roots of parthenium in addition to observed in infected plants (Anupam Varma et al., many other hosts (Dagar, 1981). Similarly, the 1974; Phatak et al., 1975; Hegde and Patil, 1976; parasitic plant Cuscuta reflexa Roxb. was found Deshpande et al., 1982; Padmanabhan, 1982; growing extensively on this weed often Mathur, 1989). The incidence of phyllody was weakening smaller herbs (Deshpande et al., found to be about 10% (Hegde and Patil, 1976; 1982). Ravi, 1983), while it varied from 15.5-100% in plots near agricultural fields and 8-73% in vacant Competitive replacement and allelopathy areas (Mathur, 1989). The incidence was maximum from September-December, while it The work of Desai and Bhoi (1981) appears to was low from January-April. The infected plants be the first attempt made to control the weed by showed a 25.9% reduction in number of flowers competitive replacement. Broadcasting seeds of per plant and 96.3-100% sterile flowers per plant stylo, Stylosanthes hamata (L.) Taub. (Keshwal, 1982). (Leguminosae), after uprooting parthenium, The causal organism was identified as a followed by light and complete cultivation of the mycoplasma like organism (MLO) on the basis of plots resulted in significant control of the weed in electron microscope studies (Anupam Varma et the second year. Similarly, replacement of the al., 1974), and transmission studies and antibiotic weed in its natural habitat by Cassia uniflora Mill. therapy (Mali and Vyanjane, 1979). Although (= C. sericea Sw.) (Leguminosae) was observed Phatak et al. (1975) suggested that parthenium by Singh (1983), Syamasundar and Mahadevappa phyllody may be the same as sesamum phyllody (1986) and Mamatha and Mahadevappa (1988). since association of strikingly similar organisms The allelopathic properties of C. uniflora and with sesamum phyllody was recorded earlier, the the weed were demonstrated in the laboratory by pathogen was not found infecting sesamum or any Jayakumar (1985). Seed germination and other test host (Mali and Vyanjane, 1979). seedling growth of the weed were inhibited by Mechanical sap inoculation failed to transmit aqueous extracts of various parts as well as higher the disease, but it was successfully transmitted by seed density of C. uniflora, the latter being grafting (Keshwal, 1982; Padmanabhan, 1982). attributed to phenolic compounds leaching from An unidentified species of aphid that was found the seed (Syamasundar and Mahadevappa, 1987; infesting the diseased plants was inferred to have Joshi, 1991a). The inhibitory effects of C. uniflora transmitted the disease (Hegde and Patil, 1976), on parthenium were also observed in field plot whereas the disease was not transmitted by the experiments (Singla et al., 1990). On the contrary, aphid, Aphis gossypii Glover (Keshwal, 1982). undiluted extracts and higher seed density of the The leafhopper, Orosius albicinctus Distant weed significantly promoted the growth of C. transmitted the disease to parthenium and uniflora. In addition to the allelopathic effects on Thchodesma sp. (Keshwal, 1982), and to the weed, undiluted extracts of C. uniflora parthenium and 10 other host plants (Mathur, inhibited seed germination, and root and shoot 1989). The leafhopper Hishimonus phycitis growth of certain cultivated crops in petri plates (Distant) was found transmitting the disease to and pot culture (Vasudevan, 1986). parthenium (Padmanabhan, 1982), Sesamum Studies conducted in wastelands for 3 years orientalis L. and Gomphrena globosa L. indicated that C. uniflora was capable of replacing (Keshwal, 1982), whereas the leafhopper parthenium gradually and the replacement would Empoasca devastans Dist. failed to transmit the be faster if parthenium plants are pulled out in the disease to parthenium (Padmanabhan, 1982). initial stages of competition (Mahadevappa and Deshpande (1981) tested the efficacy of toxic Ramaiah, 1988). Long-term field trials currently metabolites of seven species of fungi as weed in progress indicate that C. uniflora can reduce the killing agents. Metabolites of Fusarium weed by over 90% in 4-5 years with substantial Biological control of Parthenium hysterophorus L. 353

monetary returns (Joshi, 1989; Joshi, 1991b). A weed only during the absence of their primary package of practices for growing C. uniflora to hosts. For instance, the scale O. insignis heavily control the weed and its seed multiplication has colonized the weed in summer when its primary been recommended (Mahadevappa and Joshi, host Lantana camara L. collapsed under the 1985; Joshi, 1990). pressure of a heavy population buildup of the Besides C. uniflora, several other plants have insect (Srikanth et al., 1988a, b). All the above also been shown to possess allelopathic characteristics render these insects and mites principles. Aqueous extracts of fresh leaves, leaf unsuitable candidates for biological control litter and bark of Alstonia scholaris R.Br. notwithstanding the apparently impossible (Apocynaceae) inhibited the germination suggestion to produce host specific strains by percentage, early seedling growth and emergence recurrent selection (Vaidya and Vartak, 1977). of first leaf of parthenium (Ghildiyal, 1987). Yet Sundara Rajulu and Gowri (1976) claiming Similarly, aqueous extracts of aerial parts of complete control of the weed with a highly ill Hyptis suaveolens Poit. (Lamiaceae) inhibited conceived and futile exercise of using the seed germination of the weed completely whereas polyphagous pests A.fabae, Planococcus sp. and the seeds of five crop plants were unaffected (Rao Tetranychus sp., disregarded all principles and et al., 1987). Aqueous and organic leachates, and procedures of biological weed control. In a later methanol, water and chloroform fractions of survey in the same area, Thangavelu (1980), Eucalyptus sp. (Myrtaceae) reduced cell survival, however, not only failed to record A.fabae, but chlorophyll content, soluble proteins, RNA and also pointed out the need for confirmation of its carbohydrates of leaves of the weed to various occurrence in tropical India. levels when sprayed on 2 months old seedlings Concerted efforts for classical biological (Kohli et al., 1988). Amongst 20 species of plants control of parthenium commenced in the country examined, Cassia tor a L. (Leguminosae) and with the introduction and subsequent studies on Stylosanthes fruticosa Alston. (Leguminosae) host specificity, field releases and recovery of Z. brought about 40-50% suppression of parthenium bicolorata (Jayanth, 1987a; Jayanth and (Joshi, 1990). Nagarkatti, 1987). Although the beetle Parthenium is vulnerable not only to the established at the sites of release and showed allelopathic activity of other species of plants but slight dispersal, its activity appears to be limited also to its own leachates. Such autotoxicity to by the distribution of rainfall as it was observed to leachates from leaves and inflorescence undergo diapause in the dry months of the year manifested in the form of reduction in percentage (Jayanth, 1987a). This perhaps necessitates cell survival and chlorophyll content, prevention detailed studies on the extent of survival and of rooting and sprouting, and reduction in carryover of the beetle to the next season to regeneration potential in treated plants (Kumari ascertain the need for supplementary releases at and Kohli, 1987). the beginning of the rainy season coinciding with the emergence of diapausing individuals. It will DISCUSSION also be worthwhile to ascertain the possible impact of other flea beetles, such as L. vittata that The search for natural enemies, particularly attack parthenium, on the populations of Z. insects of P. hysterophorus in India appears to bicolorata in the event of delayed or inadequate or have begun many years after its discovery in erratic rainfall for a couple of years (Srikanth et 1956. Lack of information on the occurrence of al., 1991). As the beetle is likely to perform better pests or diseases on the weed (Jayachandra, 1971), in well distributed heavy rainfall areas (Jayanth, except for a blight (Rao, 1965), could be due to the 1987a), its introduction and evaluation in fact that no serious surveys were conducted prior different parts of the country need attention. At to 1971. Asystematic survey (Kumaretal., 1979), the same time, the possibilities of importing other in addition to several casual observations revealed potential natural enemies from Mexico, its place an array of insects and mites attacking the weed. of origin, as well as from other countries where However, majority of them were sporadic though they have been found to be promising, should be some appeared to be endemic like the membracid explored. For instance, the host specific delphacid L. taurus (Thangavelu, 1980) and some others Stobaera concinna (Stal) (Homoptera: were found in high intensity, such as the scolytid Delphacidae) (McClay, 1983), the narrowly H. eruditus (Kumar et al., 1979). Most of the oligophagous defoliator Bucculatrix parthenica insects lacked host specificity and attacked the Bradley (Lepidoptera: Buccutatricidae) (McClay 354 J. SRIKANTH and N. A. PUSHPALATHA

et al., 1990) and other insects (McClay, 1981) the country will pave the way for their use as found in Mexico are likely candidates. As the microbial herbicides. For example, the powdery phenomenon of diapause and a possible lag phase mildew fungus O. parthenii (Satyaprasad and in the buildup of populations of Z. bicolorata are Usharani, 1981) and the bacterium X. likely to result in rapid growth of parthenium parthenicola (Ghosh and Singh, 1979), recorded populations with the onset of monsoon, there is a as new species, may be specific to the weed. need for other insects which can attack the weed Similarly, the failure of C. capsici to produce early in its growth stages. Stem borers that destroy symptoms in some varieties of chillies when cross plants before flowering, such as the weevil inoculated (Rao and Rao, 1979) suggested the Listronotus setosipennis (Hustache) (Coleoptera: possible presence of host specific strains. Even if Curculionidae) (McFadyen, 1985) and flower host specific strains are absent in natural feeders, such as the weevil Smicronyx lutulentus populations, such strains can be created by genetic Dietz (Coleoptera: Curculionidae) (McClay, improvement using conventional mutation and 1981) should be accorded priority. The stem borer strain selection process or by the new recombinant E. strenuana showed considerable impact on the genetic techniques (see Charudattan, 1985). weed in Australia (McFadyen, 1985) after it was Besides host specificity, genetic alterations can approved for field release due to its restricted host also induce adaptability to adverse environmental range (McClay, 1987). The same insect, however, conditions. was not approved for field release in India as it fed In addition to pathogenic fungi, parthenium is and reproduced on niger in host specificity tests known to harbour a great variety of floral (Jayanth, 1987b). Such failures should not hinder (Padmabai Luke, 1974), rhizosphere and further natural enemy exploration. rhizoplane (Padmabai Luke, 1976), phyllosphere The fact that fungal pathogens have received (Ghosh and Singh, 1979) and seed (Bharathi and less attention than insects as biocontrol agents of Renuka Rao, 1983) mycoflora. Despite the fact parthenium in India is evident from the that some of these rhizosphere and rhizoplane considerably fewer diseases reported on this weed mycoflora, such as A. tenuis and Fusarium sp. are (Table 2). None of these diseases caused any potentially pathogenic, they did not seem to appreciable damage even though some incidence produce any symptoms in the plants. Changes in of powdery mildew (Satyaprasad and Usharani, the composition or amount of root exudates were 1981) and blight (Datar, 1981) was reported. Thus suggested to be responsible for the differential the status of these diseases appears to be growth of fungal populations in the rhizosphere analogous to that of insects. Fungal pathogens, by soil of pre- and post-flowering stages of the weed virtue of their abundance, destructive nature, (Padmabai Luke, 1976). Although this amenability to mass culture and formulation, and phenomenon may impose a limitation on the use ability to actively penetrate the host (Charudattan, of fungal pathogens, it can be easily surmounted 1985), constitute a very promising group of weed by synchronizing their application time with the killing agents. Of the three approaches, viz. most susceptible stage of the weed. Similarly, a classical, augmentative and microbial herbicide water soluble spore germination inhibitor was strategies, classical strategy is best suited for located in the leaf surface wax of the weed, but controlling weeds in undisturbed areas and addition of glucose to sprays allowed germination rangelands (Charudattan, 1985). The rust caused of certain fungal spores. Thus, altered nutritional by Puccinia abrupta var. partheniicola (Jacks.) status of the foliage rendered it a more suitable Parmelee (McClay, 1985) and other pathogens habitat for the pathogen and it was suggested that (Evans, 1987) found in Mexico are worthy of selective activation of leaf or root microflora may consideration for the control of parthenium in trigger the mechanism for initiation of successful wastelands. The microbial herbicide method infection (Deshpande, 1981). which relies on native, endemic diseases that are Yet another method that can be conveniently adapted to local conditions (Charudattan, 1985), incorporated into the microbial herbicidal is best suited for the control of the weed in approach for parthenium control is the agricultural ecosystems. Such diseases have been employment of mycotoxins. Although toxic successfully utilized commercially for the control metabolites of F. moniliforme which produced of milkweed vine and northern jointvetch rapid wilt symptoms in the weed in preliminary (TeBeest and Templeton, 1985). Intensive trials are promising, partially purified toxin of the surveys for the identification of host specific fungus Helminthosporium tritici-repentis Died species or strains of pathogens of parthenium in was inactive due to its binding by leaf surface Biological control of Parthenium hysterophorus L. 355 wax, but produced symptoms in dewaxed leaves to the use of this strategy is the removal of the (Deshpande, 1981). While further studies on the weed prior to sowing the competitor plants. This host selectivity in laboratory trials, and operation becomes impracticable in large tracts of effectiveness and stability under field conditions wasteland in addition to the problem of allergy. of F. moniliforme should be continued, a careful Ongoing field trials with C. uniflora indicate that study of leaf components of the weed prior to the broadcasting or sowing the seeds in 1-2 cm deep utilization of mycotoxins of H. tritici-repentis furrows in standing parthenium, also results in and other similar fungi, will facilitate the good germination and establishment (Joshi, formulation of foliar sprays with dewaxing 1990). Another constraint in the use of this method agents. In addition, large scale screening of is the differential rates of natural propagation of metabolites of other fungi may yield several the weed and competitor plant owing to the potential mycotoxins. differences in their seed size and growth rate. MLOs have not yet been seriously considered Extensive human efforts are required to manage weed killers in any part of the world. Although the and manipulate seed dispersal as in the case of C. MLO that causes phyllody in parthenium cannot uniflora (Joshi, 1990) to overcome this be projected as a promising weed killer at the disadvantage. Although undiluted extracts of the present, its present status and future potential as a weed inhibited seed germination and seedling biocontrol agent merit consideration. The growth of C. uniflora (Jayakumar, 1985) and pathogen is capable of causing 100% incidence extracts of C. uniflora affected seed germination (Mathur, 1989) resulting in significant reduction of a few cultivated crops (Vasudevan, 1986) in the in flowering and complete sterility of flowers laboratory, these leachates are unlikely to occur in (Keshwal, 1982). Despite the fact that the disease such high amounts in the field and hence, may not intensity is dependent on variations in local constrain the use of this method. However, studies climatic conditions, activity of leafhoppers and in the field are necessary to establish the safety of presence or absence of agricultural crops (Mathur, C. uniflora to various cultivated crops. In 1989), the MLO is widely distributed in many addition, its safety to human beings in terms of the parts of the country unlike fungal and bacterial allergenic properties of pollen should be diseases, which occurred in isolated patches ascertained before it is recommended for large suggesting that it is well adapted to a wide range scale use in the field. The nutritional value of the of climatic conditions. The absence of the disease seed (Ramachandra and Monteiro, 1990) and in sesamum or any other test host (Mali and other uses suggested by Joshi (1990) should be Vyanjane, 1979) stresses the need for studied in greater detail as a large quantity of confirmatory studies with vectors, such as H. biomass is produced in the field. Studies on phycitis which transmitted the disease to sesamum identification of plants with allelopathic (Keshwal, 1982), to establish the host specificity principles, such as A. scholaris (Ghildiyal, 1987), of the pathogen. Any attempts to use MLO for H. suaveolens (Rao et al., 1987), Eucalyptus biological control of parthenium primarily depend (Kohli et al., 1988) and other plants (Joshi, 1990) on its host specificity. This assumes greater should give due consideration to the aspects significance in the light of the polyphagous nature discussed above. While employment of C. of established vectors, the rapidity with which uniflora which requires a fairly long time to they can transmit the disease, and the establish and replace parthenium is best suited for susceptibility of various cultivated and wild wastelands, the extracted leachates of C. uniflora plants, the latter possessing the potential to form and autotoxic principles found in the weed reservoirs of the disease. (Kumari and Kohli, 1987) seem to hold promise for its control in agricultural lands as pre- A new approach that is being projected as an emergence bioherbicides. The exploitation of effective alternative to conventional biological these toxic principles depends on several factors control methods is the employment of dominant including selectivity and residues. plant species to replace parthenium by their vigorous growth or allelopathic activity. A beginning has been made in this direction by CONCLUSION Desai and Bhoi (1981) and Mahadevappa and Joshi (1985) whose attempts with S. hamata and Although biological control is the most viable C. uniflora, respectively have produced and practical solution to the problem of encouraging results. However, a major limitation parthenium, serious efforts to use this method 356 J. SRIKANTH and N. A. PUSHPALATHA

have been far from satisfactory. A surprisingly subcontinent with special reference to large array of; tools, namely insects, pathogens, Karnataka. M.Sc. (Agric.) Thesis University mycotoxins, allelopathic plants and autotoxic of Agricultural Sciences, Bangalore, India. principles await exploration by biological weed Anupam Varma, Asha Sang, Ghosh S. K., control specialists. Barring the trials on the Raychaudhuri S. P., Chenulu V. V. and Nam introduced chrysomelid Z. bicolorata and the Prakash (1974) Probable mycoplasmal allelopathic plant C, uniflora, no serious attempts etiology of broom-bush witches' broom. Curr. are underway to use the other components. Sci. 43, 349-350. Integrated use of these tools improves the overall Basak S. L. (1984) Parthenium—a big threat to efficiency of biological control attempts. The agriculture and health in 1980s. Indian Agric. combined action of Z. bicolorata and an 28, 137-143. introduced or native pathogen may have a Bennet S. S. R., Naithani H. B. and Raizada M. B. devastating effect on the weed since several leaf (1978) Parthenium L. in India — A review feeding beetles are known to serve as mechanical and history. Indian J. For. 1, 128-131. vectors or create points of entry for bacterial, Bharathi P. and Renuka Rao B. (1983) Seed fungal and viral pathogens. For example, field mycoflora of some Asteraceae weed seeds. populations of water hyacinth infested by the Indian J. Weed Sci. 15, 115-118. weevil Neochetina eichhorniae Warner and the mite Orthogalumna terebrantis Wallwork Char M. B. S., Nagendran C. R. and Ganesh D. showed higher incidence of the fungus (1975) Mealy bugs on the roots of Parthenium Acremonium zonatum (Saw.) Gams and other weed. Curr. Sci. 44, 207. necrotic leaf spot diseases while in laboratory Charudattan R., Perkins B. D. and Littell R. C. tests, water hyacinth could be killed by the (1978) Effect of fungi and bacteria on the combined effects of the weevil and A. zonatum decline of arthropod-damaged water hyacinth (Charudattan et al. , 1978). The almost complete (Eichornia crassipes) in Florida. Weed Sci. control of water hyacinth within one growing 26, 101-107. season when arthropod attacks were combined Charudattan R. (1985) The use of natural and with diseases, such as Cercospora rodmanii genetically altered strains of pathogens for Conway (Charudattan, 1985) also gives credence weed control. In Biological Control in to this approach. The reduction in parthenin and Agricultural IPM Systems (Edited by Hoy M. phenol content of parthenium plants attacked by A. and Herzog D. C), pp. 347-372. Academic MLO is likely to increase the susceptibility of the Press, London. weed to insects and diseases as evidenced by the Dagar J. C. (1981) A note on some new hosts of rapid germination of spores of Helminthosporium Orobanche aegyptiaca Pers. /. Bombay nat. sp. in the root zone of diseased plants (Deshpande Hist. Soc. 78, 626. et al., 1982). While introduced insects and Dagar J. C. and Singh V. P. (1979) Parthenium pathogens, and allelopathic plants are best suited hysterophorus — a new host for Brevipalpus for undisturbed ecosystems like wastelands, phoenicis. Curr. Sci. 48, 71-72. others, namely native pathogens, mycotoxins and Datar V. V. (1981) A note on occurrence of some autotoxic principles can be used as bioherbicides diseases of Parthenium hysterophorus L. Res. in unstable agroecosystems. An integrated Bull. Marathwada Agric. Univ. 5, 49-50. biological control approach will be the forerunner Desai S. N. and Bhoi P. G. (1981) Comparative for a lasting solution to the poisonous weed competitive response of parthenium and parthenium. stylosanthes in the control of the parthenium. /. Maharashtra agric. Univ. 6, 266-267. Acknowledgements—We wish to thank Mr. S. Deshpande K. (1981) Phytopathogens as weed Ramani, Department of Entomology, University control agents. In Proc. 8th Asian Pacific of Agricultural Sciences, Bangalore, for his WeedSci. Soc.Conf., pp. 157-159. Bangalore, critical review of an earlier draft and useful India. suggestions. Deshpande K. S., Deshpande U. K. and Rathore O. S. (1982) Biocontrol of Parthenium REFERENCES hysterophorus L. Indian bot. Reptr. 1, 40-42. Evans H. (1987) Fungal pathogens of some Anantha Murthy H. V. (1984) Taxonomic studies subtropical and tropical weeds and the on Opsiina and Scaphytopiini (Homoptera: possibilities for biological control. Biocontrol Cicadellidae: Deltocephalinae) of the Indian News Infor. 8, 7-30. Biological control of Parthenium hysterophorus L. 357

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