Asteraceous Weeds Research Articles

Response of the invasive fireweed (Senecio madagascariensis) to variable levels of larval stem-boring by Gasteroclisus tricostalis (Coleoptera: Curculionidae), a potential biological control agent

The stem-boring weevil Gasteroclisus tricostalis (Thunberg) (Curculionidae) is under investigation as a biological control agent for Senecio madagascariensis Poiret (Asteraceae) in Australia and Hawaii. Besides mandatory host-specificity testing, pre-release studies on the weevil’s impact can be a useful predictor of its efficacy when released in the invaded range. In this study, we investigated the response (i.e., growth, floral production, and biomass accumulation) of mature flowering S. madagascariensis plants to varying densities of G. tricostalis larvae in their stems. Although there were weak negative relationships between plant response variables and larval densities, these were only significant in the production of side branches (shoots) and floral components (capitula). Regression analyses estimated that six and 12 larvae per mature plant could prevent the production of new capitula and new shoots, respectively. A significant negative relationship between the percentage of eggs that resulted in larval recoveries and the number of eggs deposited per plant may suggest aggressive interactions between the larvae. Given precedents from other biocontrol programmes against asteraceous weeds, G. tricostalis may exhibit higher impacts on young pre-flowering plants than on mature plants, a possibility that requires confirmation. Because G. tricostalis is present is the field throughout most of the year, additional testing involving multiple generations of the weevil can assess the ultimate impact of sustained damage on plants. Since high floral production is a major driver of invasions by S. madagascariensis, substantial reductions in flowering by G. tricostalis would likely make a significant contribution to the weed’s management.

Biological Control of Tithonia spp. (Asteraceae) in South Africa: Challenges and Possibilities

Biological control programmes against the asteraceous weeds Tithonia rotundifolia (Mill.) S.F. Blake and Tithonia diversifolia (Hemsl.) A. Gray were initiated in South Africa in 2007, and that against Tithonia tubaeformis (Jacq.) Cass in 2017, following its discovery in Mpumalanga Province (MP). Permission to release two leaf-feeding beetles, Zygogramma signatipennis Stål and Zygogramma piceicollis Stål (Chrysomelidae) against T. rotundifolia was granted in 2014, while permission to release a defoliating tortoise beetle, Physonota maculiventris Stål, against T. diversifolia was granted in 2018. The two Zygogramma spp. were released in Gauteng (GP), KwaZulu-Natal (KZN), Limpopo (LP), and MP provinces from 2014 to 2019. Zygogramma signatipennis established at only a few sites in MP, where it persisted for up to four years and later collapsed. Zygogramma piceicollis initially established in GP and perished a year later. Physonota maculiventris was released in KZN, LP and MP, and has overwintered at 50% of the release sites. Investigations to explain the demise of both Zygogramma spp. and determine ways to improve their release and establishment are underway. Host-specificity testing of a stem-boring weevil, Lixus fimbriolatus Boheman (Curculionidae), a candidate agent for T. rotundifolia, was successfully completed. An application for permission to release the weevil will be submitted to the regulatory authorities in due course. Additional host-specificity testing of agents for T. diversifolia has prioritised a leaf-mining moth, Melanocinclis sp. (Cosmopterigidae) for further assessment, while a leaf-feeding plume moth, Hellinsia sp. (Pterophoridae), and a stem-boring moth, Suleima skinnerana (Heinrich) (Tortricidae), were rejected. Investigations to determine the full identity, origin and host range of a leaf-sucking lace bug (Hemiptera: Tingidae), discovered on T. diversifolia in KZN, LP and MP, are underway. Surveys in climate-matched regions of the Central American native range of the target Tithonia spp. are imperative to identify natural enemies that may be more adaptable to persist across the plants' distribution in South Africa.

HERBICIDAL ACTIVITY OF Ageratum conyzoides AGAINST PARTHENIUM

This study was carried out to explore herbicidal potential of an asteraceous weed Ageratum conyzoides against an exotic noxious weed parthenium (Parthenium hysterophorus L.). Different concentrations (0, 2, 4, 6, 8 and 10%) of aqueous extracts of various parts of the tested weed were used in laboratory bioassays. ANOVA revealed the significant effect of plant part bioassay and extract concentration on germination as well as various root and shoot growth parameters. Leaf extract was found the most herbicidal where a 10% extract completely inhibited the germination and growth of parthenium. Root and inflorescence extracts were also highly inhibitory in suppressing the germination up to 89% and 95%, shoot length up to 80% and 89%, root length up to 86% and 91%, and plant biomass up to 89% and 98%, respectively. Stem extract showed the least herbicidal activity causing up to 46%, 59%, 73% and 37% reduction in germination, shoot length, root length and plant biomass, respectively. This study concludes that leaf, root and inflorescence extracts of A. conyzoides possess strong herbicidal potential against germination and growth of parthenium.

Complete chloroplast genome of glyphosate resistant Sonchus oleraceus L. from Australia, with notes on the small single copy (SSC) region orientation

Sonchus oleraceus, common sowthistle, is an asteraceous weed in Australian agricultural systems and has recently developed resistance to glyphosate. We present the complete chloroplast sequence of S. oleracueus reconstructed from Illumina whole genome shotgun sequencing. This is the first complete chloroplast genome available for the genus Sonchus. The complete chloroplast sequence is 151,808 bp long. A Bayesian phylogeny of the chloroplast coding regions of the tribe Cichorieae (Asteraceae) is presented. The S. oleraceus chloroplast genome is deposited at GenBank under accession number MG878405.

Establishment and impact of insect agents deployed for the biological control of invasive Asteraceae: prospects for the control of Senecio madagascariensis

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.

ANTIFUNGAL ACTIVITY OF Cirsium arvense EXTRACTS AGAINST PHYTOPATHOGENIC FUNGUS Macrophomina phaseolina

ABSTRACT Leaves, stems, roots and inflorescence of the asteraceous weed Circium arvense were extracted in methanol for two weeks. Methanol was evaporated in a rotary evaporator. Different concentrations (1, 2, 3, 4 and 5%) of methanolic extracts were prepared, and their antifungal activities were studied against Macrophomina phaseolina, using malt extract broth as growth medium. In general, extracts of all plant parts showed antifungal activities to variable extents. The highest antifungal activity occurred due to methanolic extract of leaves, followed by stem and root extracts, resulting in 10-74%, 6-57% and 11-39% reduction in fungal biomass over control, respectively. Inflorescence extract showed the least antifungal activity, resulting in 2-30% reduction in fungal biomass over control. There was a linear and inverse relationship between extract concentrations and fungal biomass for extracts of all the four parts. GC-MS analysis showed that there were 10 compounds in most effective methanolic leaf extract. Among these, 10-octadecanoic acid, methyl ester (26.442%), 2H-1-benzopyran, 6,7-dimethoxy-2-2-dimethyl (20.195%), hexadecanoic acid, methyl ester (15.752%) and 9,12-octadecadienoic acid (Z,Z)-, methyl ester (12.628%) were predominant compounds in the extract that may be responsible for antifungal activity. This study concludes that methanolic leaf extracts of C. arvense can be used for the management of M. phaseolina.

Pathogenic mycobiota of the weeds Bidens pilosa and Bidens subalternans

Bidens pilosa and B. subalternans are highly noxious herbaceous neotropical asteraceous weeds. A survey of fungal pathogens associated with these two species was undertaken in Brazil, aimed at finding natural enemies in order to establish the potential for introducing novel specific pathogens from other regions of the world, as classical biological control agents. Ten fungal species were found associated with both B. pilosa and B. subalternans, namely: Cercospora bidentis, C. maculicola, Entyloma bidentis, E. compositarum, E. guaraniticum, Neoerysiphe cumminsiana, Plasmopara halstedii, Podosphaera xanthii, Uromyces bidentis, and U. bidenticola. Three other species were found solely associated only with B. subalternans: Colletotrichum bidentis, Pseudocercosporella bidentis and Sphaceloma bidentis. Pseudocercosporella bidentis is described herein as new to science.

Seedling morphology in taxonomic study of two common weeds – Ageratum conyzoides L. and A. houstonianum Mill. (Asteraceae)

In the present communication the details of seedling morphology in taxonomic study of two common Asteraceous weeds viz. Ageratum conyzoides L. and A. houstonianum Mill. from Varanasi District, Uttar Pradesh have been provided. Some juvenile characters of seedlings are found to be very useful in distinguishing the taxa studied and have been utilized for formulation of key at species level. RS values at different leaf stages, date of appearance of different leaves and total observation period were also recorded.

Reaction of Certain Solanaceous and Asteraceous Plant Species to Inoculation with Phytophthora infestans in Cameroon

AbstractExperiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (S. lycopersicon) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agroecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry and potato infected the same host plants as well as gboma eggplant (S. macrocarpon) and two asteraceous weeds; Billy goatweed (Ageratum conyzoides) and Dichrocephala (Dichrocephala integrifolia). Inoculum from potato caused late blight symptoms on haemorrhage plant (Aspilia africana); while inoculum from tomato resulted in late blight on worowo (Solanecio biafrae). This is the first report of late blight infection on S. macrocarpon, A. conyzoides, Sol. biafrae and Asp. africana in Cameroon. The research results indicate that some asteraceous and solanaceous weeds may be alternative hosts of P. infestans in the potato agroecosystem.

Survey of current crop management practices in a mixed-ricefield landscape, Mekong Delta, Vietnam — potential of habitat manipulation for improved control of citrus leafminer and citrus red mite

In the Mekong Delta, Vietnam, the citrus leafminer Phyllocnistis citrella (CLM) and the citrus red mite Panonychus citri are major pests in both sweet orange ( Citrus sinensis) and Tieu mandarin ( C. reticulata). Survey data indicate that these pest problems might be aggravated after farmers have completely destroyed the weed flora in their orchard. As citrus farmers only perceive the larger predators such as the weaver ant Oecophylla smaragdina and spiders, and have no idea about the existence of predatory mites or parasitoids, they do not know about potential positive attributes of weeds in pest management which sustain populations of natural enemies and their alternative food. IPM training programmes could use the weaver ant as an introduction to educating farmers about predatory mites and parasitoids, and should likewise emphasise the importance of beneficial asteraceous weeds such as Ageratum conyzoides. Non-crop trees such as Spondias dulcis, Mangifera indica, Eucalyptus tereticornis and Ceiba pentandra are commonly known to offer good refuge for the weaver ant. These trees should be further studied for their temporal contribution as food resource for other natural enemies of CLM and mites. Small adjustments of current weed management techniques are suggested to improve availability of pollen and nectar for beneficials at crucial moments in the cropping season, with due respect to implications at the landscape level.

Biological control ofParthenium hysterophorusL. (Asteraceae) byCassia unifloraMill (Leguminosae), in Bangalore, India

Abstract Parthenium hysterophorus L. (parthenium), an obnoxious Asteraceous weed, has spread over millions of hectares of land in India after its inadvertent introduction in the 1950s. This weed has reduced the yield of grasses and crops. It is a health hazard to sensitized humans and cattle and the routine weed control methods have failed to check its spread. Cassia uniflora a leguminous undershrub of some economic value, is found to suppress the growth of parthenium. It has successfully replaced parthenium by over 90% in an area of 4800 m2 over a period of 5 years. While the leachates from the germinating seeds of C. uniflora inhibited the germination of parthenium seeds and hampered the establishment of summer generation of parthenium due to allelopathy, the robust colonies of C. uniflora prevented the establishment of winter generation of parthenium below them. Cassia uniflora is dispersed slowly to neighbouring places through rainwater. Sustained efforts to introduce C. uniflora hold out great promis...

An Economic Evaluation of Control Methods forParthenium hysterophorusL.

ABSTRACT An Asteraceous weed, Parthenium hysterophorus L. (parthenium) was inadvertently introduced into India in the 1950's. It has spread with menacing speed and covered millions of hectares of uncultivated land resulting in the reduction of forage production by over 90% in the infested areas. Controlling this weed in arable land is expensive to farmers. Parthenium is also a health hazard to sensitised humans and livestock. The economics of various methods of its control are discussed. The introduction of Cassia sericea, a legume that controls parthenium through interference, is the most cost effective solution. Substantial monetary returns, are expected by adopting this method. However an integrated approach may be more effective for hastening the success of this method.

Crude extracts of asteraceous weeds

Petrol and ethanolic extracts of six asteraceous weeds were added to artificial diets to screen for growth inhibition and mortality of the variegated cutworm,Peridroma saucia (Hbn). Petrol and ethanolic extracts ofArtemisia tridentata andChamomilla suaveolens and ethanolic extracts ofChrysothamnus nauseosus andCentaurea diffusa severely inhibited larval growth at five times the natural concentrations. The twoC. suaveolens extracts and the ethanol extract ofA. tridentata were active at the natural concentration (100%) and were further examined at 20, 40, 60, and 80% of this level. Inhibition of larval growth was directly related to concentration for each of the three extracts tested. EC50s (effective concentration to inhibit growth by 50% relative to controls) for the three extracts were 36-42% of the naturally occurring level in the plants. Nutritional indices were calculated for secondinstarP. saucia feeding on the activeA. tridentata EtOH extract and the petrol extract fromC. suaveolens. Addition of the activeA. tridentata EtOH or theC. suaveolens petrol extract to the diet resulted in significant reduction in the relative growth rate of larvae, although theA. tridentata extract was much more inhibitory. Dietary utilization was significantly lower for larvae fed theA. tridentata EtOH extract.