Search

Globally, huge amounts of synthetic herbicides are used to manage weeds in arable lands. However, their widespread use has resulted in various toxicological effects on the environment and human health, besides resulting in the emergence of herbicide-resistant weed biotypes. To overcome these problems, there is an urgent need to search for novel compounds, particularly natural plant products, with potential herbicidal activity. In this area, we studied the phytotoxic effect of volatile oil from lemon-scented eucalypt on littleseed canary grass, a noxious weed of wheat fields. Our findings show that under laboratory conditions the emergence and earlier growth of the weed decreased and completely ceased using a very low concentration of eucalypt oil (0.0714%, v/v). Treatment with eucalypt oil of the 4-week-old pot-raised weeds caused visible damage such as chlorosis and necrosis, wilting and even plant death. The effect was concentration-dependent. At low concentrations, 2.5 and 5%, v/v of eucalypt oil, plants were damaged but recovered later, whereas at concentrations higher than 5%, v/v, of eucalypt oil plants showed severe injury with little or no sign of recovery, and death. There was a severe effect on the photosynthetic and respiratory ability of treated plants 7 and 21 days after treatment. Eucalypt oil treatment caused a rapid electrolyte leakage in the P. minor leaf tissues, indicating a loss of membrane integrity. The study concludes that lemon-scented eucalypt oil offers a good option for control of littleseed canary grass and could be included as a viable component of integrated weed management under sustainable agricultural practices. [ABSTRACT FROM AUTHOR]

The influence of different combinations of illumination and shaking on the growth dynamics, pathogenicity and toxin production of the fungus Fusarium oxysporum f. sp. orthoceras, a biocontrol agent of Orobanche cumana, was studied. The fastest biomass accumulation was obtained under shaking, with or without illumination, with the highest biomass obtained after 3–4 weeks of growth. The biological activity of chloroform extracts of the culture filtrate was characterised: it contained at least two main toxic metabolites that caused necrosis and wilting of various plants and led to mortality of germinating seeds of O. cernua, O. aegyptiaca, O. ramosa and O. cumana. The highest toxic activity of the chloroform extract was obtained under illumination without shaking after 3–4 weeks of growth. The two toxic metabolites were purified and identified as fusaric acid (FA) and 9,10-dehydrofusaric acid (DFA). Both FA and DFA production began in the first week of growth, increasing gradually to their maxima after 4 weeks. The highest level of pathogenic activity of the fungus was obtained after three or more weeks of fungal growth. It can be concluded that in order to produce high levels of toxin and pathogenic activity, the fungus should be grown under illumination without shaking for 4 weeks. [ABSTRACT FROM AUTHOR]

Kudzu, Pueraria montana var. lobata, is an exotic invasive weed that is difficult to control with available products and management practices. The fungal pathogen, Myrothecium verrucaria, is being developed as a bioherbicide for kudzu and other invasive vines. This biological control agent might be applied with conventional herbicides to improve the efficacy or spectrum of weed control. The survival of M. verrucaria was measured over time in simulated tank-mixes of commercial formulations of the herbicides: amniopyralid (Milestone✠), metsulfuron (Escort XP), and fluroxypyr (Vista). The fungus was also grown in vitro in the presence of these herbicides to evaluate any growth inhibition. M. verrucaria was highly tolerant to all concentrations of amniopyralid and metsulfuron for up to two days in simulated tank-mixes, while mixtures with fluroxypyr resulted in a gradual loss of spore viability. The fungus grew on media supplemented with amniopyralid and metsulfuron with only small effects on the growth rate, but fluroxypyr caused growth inhibition. These studies provide insight for developing effective, integrated control strategies for kudzu. [ABSTRACT FROM AUTHOR]

Olive mill wastewater (OMW) produced from small units scattered in rural areas of Southern Europe is a major source of pollution of surface and subsurface water. In the present work, a treatment scheme based on physical separation methods is presented. The investigation was carried out using a pilot-plant unit equipped with ultrafiltration, nanofiltration, and reverse osmosis membranes. Approximately 80% of the total volume of wastewater treated by the membrane units was sufficiently cleaned to meet the standards for irrigation water. The concentrated fractions collected in the treatment concentrates were characterized by high organic load and high content of phenolic compounds. The concentrates were tested in hydroponic systems to examine their toxicity towards undesired herbs. The calculations of the cost of the overall process showed that fixed and operational costs could be recovered from the exploitation of OMW byproducts as water for irrigation and/or as bioherbicides. [ABSTRACT FROM AUTHOR]

In greenhouse and field experiments, an oil-in-water emulsion of unrefined corn oil and Silwet L-77 increased the biological weed control efficacy of Colletotrichum truncatum (Schw.) Andrus et Moore for control of the weed, hemp sesbania ( Sesbania exaltata[Raf.] Rydb. ex A.W. Hill). The surfactant – corn oil emulsion stimulated germination and appressoria formation in vivo and in vitro and delayed the need for dew. We hypothesize that the corn oil protected the conidia from desiccation during the dew-free period and the surfactant stimulated spore germination and appressoria formation. In field experiments conducted over 3 years, a single application of a 50% (v/v) unrefined corn oil tank mixture containing 0.2% (v/v) Silwet L-77 surfactant controlled hemp sesbania in soybeans an average of 95%. Aqueous fungal suspensions or adjuvants alone did not visually affect or control hemp sesbania. The soybean yields were significantly higher in the plots where weeds were effectively controlled. These results suggest that formulating C. truncatum in unrefined corn oil and surfactant greatly increases its infectivity and the biocontrol potential of this pathogen. [ABSTRACT FROM AUTHOR]

An isolate of the fungus Myrothecium verrucaria was evaluated for its biocontrol potential against common purslane, horse purslane, spotted spurge, and prostrate spurge, all serious weed pests in commercial tomato fields in the southeastern US. In greenhouse and field tests, M. verrucaria was highly virulent against these weeds when applied as conidial sprays formulated in 0.2% Silwet L-77 surfactant, even in the absence of dew. In field test plots naturally infested with these weeds, seedlings in the two-to-three leaf growth stage treated with M. verrucaria at 2×107 conidia mL-1 in 0.2% Silwet, exhibited leaf and stem necrosis within 24 h following inoculation, with mortality occurring within 96 h. After 7 days, M. verrucaria had killed 90–95% of both purslane species and 85–95% of both spurge species. Tomatoes that were transplanted into plots treated with M. verrucaria remained healthy and vigorous throughout the growing season. Since M. verrucaria effectively controlled several common weeds under field conditions, this fungus appears to have potential as an effective bioherbicide for pre-plant weed control in production systems with transplanted tomato. [ABSTRACT FROM AUTHOR]

Control of Taraxacum officinale (common dandelion) and other broad-leaved weeds in temperate turfgrass has been readily achieved with phenoxy herbicides. The herbicide option has been revoked through municipal and provincial legislation in many regions of Canada, necessitating alternative approaches. We examined the effects of dandelion accessions, age and grass competition on the performance of Sclerotinia minor (IMI 344141) as a biological control for dandelion in turfgrass. Disease symptoms were identical on all 14 different accessions of dandelion and the above- and below-ground biomass were reduced by 94% and 96%, respectively, with no difference among accessions. Foliar damage and dandelion mortality caused by S. minor was affected by plant age and the presence of grass competition. Dandelions of all ages were more severely affected by S. minor in the presence of grass competition. Grass competition had greater impact on foliar biomass, whereas the fungus had a greater impact on root biomass of newly established dandelions. In addition to competition for resources, we were hypothesised that the grass sward provides a microenvironment favouring the success of S. minor as a biological control agent of dandelion. Thus, proper management of the turfgrass environment may be complementary to the efficacy of S. minor as a biocontrol for dandelion. [ABSTRACT FROM AUTHOR]

Abstract: Valdensinia heterodoxa (Sclerotiniacae) is a potential fungal bioherbicide for control of salal (Gaultheria shallon). The effect of culture media, substrates and relative humidity (RH) on growth, sporulation and conidial discharge of V. heterodoxa was determined for two isolates PFC2761 and PFC3027 in vitro. Culture media significantly affected the growth, sporulation, and conidial discharge of V. heterodoxa. Of eight agar media used, colony radial growth was optimal on salal oatmeal agar and salal potato dextrose agar for isolates PFC2761 and PFC3027, respectively; whereas sporulation was at an optimum on salal oatmeal agar for both isolates. Of the eight liquid media tested, mycelial production was highest on wheat bran–salal–potato dextrose broth. Growth on solid substrates greatly stimulated sporulation and conidial discharge of V. heterodoxa. Of the 12 solid substrates used, the greatest numbers of discharged conidia were observed from wheat bran and wheat bran–salal within 14d of sporulation. Sporulation on solid substrates continued for 42d. RH significantly affected the sporulation and conidial discharge for both isolates across all solid substrates tested. No conidia were produced or discharged below 93 % RH on wheat bran–salal and millet. With an increase of the RH from 93 to 97 %, sporulation and the number of discharged conidia increased significantly for both isolates on wheat bran–salal, but not on millet. [Copyright &y& Elsevier]

In controlled environment experiments, the bioherbicidal fungus Myrothecium verrucaria (Alb. & Schwein.) Ditmar:Fr. was tested alone, in combination with, prior to, and following treatment with glyphosate [N-(phosphonomethyl)glycine] for control of kudzu [Pueraria lobata (Willd.) Ohwi], redvine [Brunnichia ovata (Walt.) Shinners], and trumpetcreeper [Campsis radicans (L.) Seem. ex Bureau] at temperatures of 20, 30, and 40°C. At all temperatures, kudzu was most adversely affected by the fungus, followed by trumpetcreeper and redvine, as indicated by greater mortality and dry weight reductions. Trumpetcreeper and redvine mortalities and dry weight reductions significantly increased when the fungus was applied 2 days after the glyphosate treatment. Application of the fungus combined with or prior to glyphosate treatment resulted in reduced weed control. Although pathogenesis and mortality also occurred at 20°C, disease development was favored by higher temperatures (30 and 40°C). Infected weeds of each species exhibited similar disease symptomatology within 12 h following treatment at incubation temperatures of 30 and 40°C. Disease symptomatology was characterized by necrotic flecking on leaves that coalesced into large lesions. Symptoms progressed, initially infecting cotyledons and leaves, and later (within 48 h) producing stem lesions. The fungus sporulated profusely on infected tissue and was easily reisolated. These results suggest that timing of glyphosate application in relation to combined treatment with the bioherbicide M. verrucaria can improve the control of kudzu, redvine, and trumpetcreeper. [ABSTRACT FROM AUTHOR]

In greenhouse experiments, unrefined corn oil, Silwet L-77, and an invert emulsion were tested as adjuvants with the mycoherbicidal fungus Colletotrichum gloeosporioides, a weakly virulent pathogen of sicklepod (Senna obtusifolia). A 1:1 (v/v) fungus/corn oil tank mixture containing 0.2% (v/v) Silwet L-77 surfactant reduced the dew period requirements for maximum weed infection and mortality from 16 to 8 h, and delayed the need for free moisture for greater than 48 h. This formulation also resulted in the ability of the pathogen to infect and kill weeds in larger (>5 leaf) growth stages. The invert emulsion resulted in similar effects upon these parameters. These results suggest that invert emulsions, unrefined corn oil and Silwet L-77 surfactant greatly improve the bioherbicidal potential of this pathogen for control of sicklepod, a serious weed pest in the southeastern US. [ABSTRACT FROM AUTHOR]

Plectosporium alismatis is a fungal pathogen that is being investigated as a biocontrol agent for suppressing starfruit (Damasonium minus), a significant weed of Australian rice fields. The aim of this research was to study the effect of the fungus on weed competition and its interactions with chemical herbicides. Conidial germination was significantly reduced by Londax® (bensulfuron-methyl), while MCPA had no effects. Glasshouse trials showed evidence of synergism between the fungus and 1.56% of the recommended dose of Londax®, in reducing the weed growth. The application of inoculum (conidia suspended in water) in the glasshouse eliminated weed competition with rice. In the field, the reduction in weed growth caused by the fungus did not significantly eliminate starfruit competition with rice. This is thought to be due to the presence of other weeds. [ABSTRACT FROM AUTHOR]

Abstract: Microsphaeropsis amaranthi and Phomopsis amaranthicola are potential biological control agents for several Amaranthus species. In an effort to understand the initial infection processes with these pathogens, a study was conducted of the conidial germination and germ tube length (μm) on the weed leaf surfaces at 21°C and 28°C. Weeds included Amaranthus rudis, A. palmeri, A. powellii, A. retroflexus, A. spinosus, A. hybridus, and A. albus. For P. amaranthicola, conidial germination and germ tube length varied among the seven weed species at both temperatures, while for M. amaranthi the differences in germ tube lengths were significant among weed species only at 21°C. While the conidia of M. amaranthi and P. amaranthicola germinated on the leaf surfaces of all seven weed species, temperature appeared to impact the number and length of germ tubes on the leaf surfaces. The percentage of germinated conidia and the length of germ tubes at both temperatures were often greater for M. amaranthi than for P. amaranthicola. In order for the fungal pathogen to successfully infect and kill a weedy host, conidia must germinate and form a germ tube, two processes that vary with host species and temperature for M. amaranthi and P. amaranthicola. The extent to which successive infection processes, e.g., penetration, invasion and colonization, contribute to host specificity warrants study. [Copyright &y& Elsevier]

Abstract: Mycoleptodiscus terrestris has potential as an inundative biological control agent for the management of hydrilla, one of the world’s worst aquatic weeds. Essential to producing a marketable bioherbicidal product was the development of liquid culture procedures that would yield propagules that maintained biocontrol efficacy. Since M. terrestris did not produce conidia in liquid culture, various nutritional conditions were evaluated as a means to produce high concentrations of stable fungal propagules such as microsclerotia. Evaluations of propagule formation and biomass yield were carried out in liquid culture media containing a basal salts solution amended with corn steep liquor powder or cottonseed meal combined with 4% or 6% glucose. Hyphal aggregation was observed by day 2, and by day 8 abundant melanized microsclerotia were present in the broth cultures. When applied as a liquid inoculum to hydrilla at rates of 0.1 and 0.2ml/l, the microsclerotial matrix was capable of significantly reducing hydrilla shoot biomass by as much as 99%. Air-dried microsclerotia were capable of hyphal germination in 24h and sporogenic germination in 72h. These capabilities have significance for the use of microsclerotia of M. terrestris as the preferred inoculum for biocontrol purposes. Hyphae germinating from microsclerotia on hydrilla plant surfaces can establish initial infection sites followed several days later by secondary infections resulting from the development and release of spores from the surface of the microsclerotia. The capability of microsclerotia of M. terrestris to remain stable as a dry preparation and to germinate both hyphally and sporogenically upon rehydration enhances the potential of this fungus for use as a nonchemical, biological control agent for hydrilla. [Copyright &y& Elsevier]

Microbial products offer a non-chemical alternative to manage noxious weeds with the goal of reducing input into the environment of harmful chemicals that are otherwise used for the same purpose. During the present investigations cell-free culture filtrate (CFCF) of Phoma herbarum FGCC no. 75 was evaluated for its phytotoxic property against Parthenium hysterophorus L. The results of shoot cut, detached leaf and seedling bioassays revealed the presence of a toxic metabolite in the CFCF that was responsible for the toxicity against the target weed. Further, the toxic metabolite was characterized after the CFCF extraction with butanol, hexane, chloroform, acetone and ethyl acetate. The residues left after solvent evaporation were evaluated separately for their toxicity against the weed. Residue obtained from ethyl acetate fraction showed very distinct toxicity when compared with others. On the basis of analysis by gas chromatography- mass spectrometry, the tentative structure of the phytotoxic compound was deduced to be 3-nitro-1,2-benzenedicarboxylic acid (3-nitrophthalic acid). This is the first report confirming the potential of this particular toxin from Ph. herbarum as a biorational, which can be applied as a phytotoxin against Par. hysterophorus. [ABSTRACT FROM AUTHOR]

The fungus, Alternaria alternata (Fr.) Keissler Strain 501, has been evaluated as a bioherbicide for control of Eupatorium adenophorum Spreng., but the biology of the pathogen–host interaction and the optimal environmental conditions for disease development and effective weed control are unknown. Disease development of A. alternata Strain 501 mycelia on E. adenophorum was assessed under several factors including pathogen inoculum concentration, plant age, dew period duration, post-dew temperature, storage temperature and duration. The minimum inoculum concentration required to kill E. adenophorum seedlings was 3.2×10 6 mycelial fragment mL -1 . E. adenophorum seedlings at the four-leaf-pair stage were more susceptible than the older plants, especially those at the older than seven-leaf-pair stage. With a dew period of at least 14 h, 100% mortality occurred. The optimal post-dew temperature for disease development was 18–25°C. Storage at [ABSTRACT FROM AUTHOR]

Acacia cyclops A. Cunn. ex G. Don (Fabaceae, Mimosoideae), originating from Western Australia, is a serious environmental weed in South Africa. A dieback disease of A. cyclops occurring in South Africa is described, and a fungus herein named Psuedolagarobasidium acaciicola Ginns sp.nov. (Basidiomycetes, Polyporales, Hyphodermataceae) was consistently isolated from diseased roots of A. cyclops trees showing early dieback symptoms. Isolates of P. acaciicola caused 100% mortality in pathogenicity screening tests using seedlings of A. cyclops. Saplings of A. cyclops were inoculated with one isolate of P. acaciicola, and all plants were killed within 2–3 months. No control plants died. Psuedolagarobasidium acaciicola was reisolated from all inoculated plants that died. Trees growing in the field were inoculated at two sites on two occasions. Most inoculated trees died within 2 years, whereas no control plants died. Eventually P. acaciicola fruited in vitro and in vivo allowing the basidiomes and cultures to be described. This fungus has potential to be developed as a bioherbicide to aid in the control of this serious environmental weed. [ABSTRACT FROM AUTHOR]

The fungus, Sclerotinia minor Jagger is under development as a bioherbicide for control of dandelion and many broadleaf weeds in turfgrass environments. The effect of S. minor on dandelion survival was evaluated under different mowing heights and compared with a commonly used herbicide Killex™. In the greenhouse, the onset of symptoms was more rapid, foliar damage was more severe, and the reduction of aboveground biomass and root biomass was greater for the bioherbicide than the herbicide. The bioherbicide reduced root biomass ≥10-fold compared with untreated plants. Under high weed infestation levels in the field, S. minor caused a greater initial reduction of dandelion density than did the herbicide during the 2-week post-application period, although reductions were greater in herbicide treated plots by 6 weeks after application. Over the growing season, S. minor and the herbicide had similar suppressive effects on dandelion density except under the closest mowing height (3-5 cm). After treatment, close mowing favored dandelion seedling recruitment and the biocontrol had no residual activity. Survival of dandelion roots was significantly less after spring than fall treatment of S. minor and season long mowing at the close height significantly reduce root survival. Close mowing may be detrimental for S. minor applications on heavily infested domestic lawns and amenity grassland areas. [ABSTRACT FROM AUTHOR]

Abstract: Recent initiatives by the pesticide regulatory departments of European and North American governments have significantly renewed interest in biopesticide technologies as alternatives for pest management following plans to deregister many chemical pesticides within the next 10 years. The literature is abundant with studies on screening for microorganisms with attributes of biopesticidal activity, however, very few of the authors have considered formulating the microorganisms with commercial applications in mind. A concerted plan in formulation development for biopesticides and bioinoculants by multi-disciplinary teams is required to optimize biopesticide yield, efficacy, storage stability and delivery for this technology to evolve and meet today''s agricultural demands. [Copyright &y& Elsevier]

Scentless chamomile, a noxious weed in western Canada, has a high natural tolerance to many herbicides. Colletotrichum truncatum , a host specific fungal pathogen, is suppressive to scentless chamomile when applied inundatively. A broadcast application was used at 200 L ha -1 to evaluate biocontrol potential of this pathogen under a range of dew temperatures (DT), post-inoculation conditions (PIC), and pathogen doses (PD). A DT between 20 and 25°C was more conducive to infection, resulting in higher levels of disease and weed suppression as compared to 15 and 30°C. Under similar post-inoculation temperature regimes, disease was only slightly more severe in growth chambers than in the greenhouse. There was a positive linear relationship between the PD and weed suppression. An inoculum concentration >1×10 8 spores mL -1 reduced plant fresh weight by approximately 50% when compared to untreated controls. These results indicate that biocontrol of scentless chamomile using C. truncatum in the semi-arid Canadian prairies will likely encounter frequent non-favourable field conditions. [ABSTRACT FROM AUTHOR]

Phomopsis amaranthicola, a newly described species discovered in Florida, is under development as a biological control agent for weeds belonging to the genus Amaranthus . Host-range testing was performed on the fungus, using the centrifugal phylogenetic scheme, with Amaranthus hybridus as the focal plant. Forty-five accessions of 21 species in the genus Amaranthus were tested for susceptibility to infection by this fungus. Fifty-six plant species outside the genus Amaranthus were also tested. The latter included crops in which the fungus might be used as a bioherbicide, members of genera that are closely related to Amaranthus , and selections of species that have been reported as hosts of other species of the genera Phomopsis or Diaporthe . Phomopsis amaranthicola did not infect any of the plants from outside the genus Amaranthus but was highly pathogenic to several species in the genus Amaranthus . All Amaranthus species tested were infected to varying degrees by P . amaranthicola ; the resulting mortality levels were also variable. Thus, P . amaranthicola appears to be host-specific to the members of the genus Amaranthus . The generic level of specificity of this pathogen renders it not only a safe bioherbicide agent but also one that could be used against several weedy Amaranthus species. [ABSTRACT FROM AUTHOR]

Abstract: Several plants in the genus Amaranthus are weeds in cropping systems throughout the world, and some biotypes have developed resistance to a number of herbicide families. In an effort to develop alternative, biologically based weed management tactics, studies were initiated to quantify the selective ability of two fungal organisms to several Amaranthus species. Response of weed seedlings to Microsphaeropsis amaranthi (3×106 conidia.ml−1), Phomopsis amaranthicola (1×107 conidia.ml−1), and a mixture of the two organisms (1.5×106+4×106 conidia.ml−1, M. amaranthi and P. amaranthicola, respectively) were tested under controlled and field conditions at Urbana, IL in 2004. Weeds included Amaranthus rudis; A. palmeri; A. powellii; A. retroflexus; A. spinosus; A. hybridus; A. albus; and A. blitoides. Seeds of each species were sown in the greenhouse, and conidial suspensions were applied at the 2- to 4-leaf stage, and then pots were placed either in a dew chamber (24h) and back in the greenhouse, or in the inter-row of a soybean field. Treatment with fungal organisms infected most weeds, reducing growth and survival, although responses in the greenhouse were less than those observed in the field. Percent seedling mortality for A. albus and A. blitoides were between 80 and 100%, 14 to 15 DAT for the mixture or M. amaranthi alone, in greenhouse and field trials. In the greenhouse, the mixture of two organisms and M. amaranthi alone significantly reduced A. albus and A. blitoides height. Fungal treatments reduced biomass of A. powellii, A. albus and A. blitoides. In field experiments, all eight weed species treated with M. amaranthi or the mixture of both organisms had severe disease ratings 15 DAT, and mortality ranged from 74% to 100%. In addition, these treatments reduced biomass of A. rudis, A. retroflexus, A. spinosus, A. hybridus, and A. albus. Height of A. rudis, A. hybridus, and A. albus was reduced by all fungal treatments. This research indicates seedlings of several Amaranthus species are susceptible to conidial suspensions of P. amaranthicola and M. amaranthi in both controlled and field environments. [Copyright &y& Elsevier]

Sclerotinia minor Jagger is a promising biocontrol agent for dandelion in turfgrass. When a flowering dandelion population was treated with S. minor , flowering accelerated to the fruiting stage within 4 days. This developmental response was 4–5 days earlier than in the control, untreated plants and was not observed in herbicide-treated plants. Seeds obtained from the fungal-treated plants were smaller, lighter and their germination rate was reduced by 48.4 and 47.3% for spring and fall applications, respectively. S. minor was not detected in dandelion seeds from the fungal-treated plants. In addition to effective control of mature (flowering) dandelions, seeds dispersed by dying plants have reduced germination and are not transferring S. minor off target. [ABSTRACT FROM AUTHOR]

Paraffinic-vegetable and vegetable oil emulsions were investigated for their ability to increase efficacy of the fungal pathogen Phoma herbarum as a bioherbicide to control dandelion ( Taraxacum officinale ) under sub-optimal leaf wetness durations (LWDs) in controlled environments. Mycelia of P. herbarum (20%, v/v) were formulated in 10 oil emulsions; two based on paraffinic-vegetable (soybean) oil mixtures, and eight based on vegetable (canola, coconut and soybean) oil emulsions alone. Emulsions were applied to dandelions using an automatic track sprayer and plants were exposed to sub-optimal LWDs simulating dew periods in field conditions. An aqueous formulation of P. herbarum was included as a standard treatment and formulations without P. herbarum were included as controls. Eight of 10 oil emulsions (two paraffinic-vegetable and six vegetable) significantly increased damage ratings caused by P. herbarum compared to the standard treatment under certain sub-optimal LWDs ( P =0.05). However, all oil emulsions caused at least some phytotoxicity when applied alone under most LWDs. Also, the high viscosity of nine oil emulsions caused mixing and application problems. These results indicate that oil emulsions increase damage ratings caused by P. herbarum on dandelion under sub-optimal LWDs, but may not be suitable formulations due to their phytotoxicity and high viscosity. [ABSTRACT FROM AUTHOR]

The fungus Alternaria eichhorniae isolate 5 (Ae5) is being developed as an effective mycoherbicide against water hyacinth in Egypt. To improve its pathogenicity, integration with 3,4-methylenedioxy trans -cinnamic acid (MDCA), a phenylpropanoid pathway inhibitor that weakens the plant's defense system, was explored. The severity of the disease induced by Ae5 increased when applied to water hyacinth plants pretreated with MDCA. Infection with Ae5 amplified the total phenol concentration in diseased water hyacinth leaves, whereas MDCA reduced it. Plants treated with both Ae5 and MDCA contained a comparable level of total phenols to that in the untreated control plants. Phenol-storing cells were located at three sites in the leaf, within the adaxial palisade tissue, above the abaxial epidermis and in the vicinity of the vascular bundles. Dimensions of these three cell types were increased by infection with Ae5, decreased by MDCA treatment and, in the combined treatment, were similar to those in control leaves. Increased numbers of phenol-storing cells were found only in the region near vascular bundles of plants treated with either Ae5 or MDCA. [ABSTRACT FROM AUTHOR]

Biological weed control is a selective, environment-friendly process, utilizing host-specific control agents towards targeted weeds that prevent damage to non-target crops or native plants. The objective of biological control for weeds is not to eradicate but, rather, to regulate weed populations below levels that cause economic injury. There has been criticism that biological weed control research efforts aim to substitute one purchased input (a bioherbicide) for another (a chemical herbicide). It is essential to remember that ‘bioherbicides’ and ‘biological weed control’ are not synonymous. Biological control of weeds involves using any organism to reduce or eliminate the detrimental effects of weed populations, whereas bioherbicides utilize plant pathogens repeatedly. The integration of herbicides, both chemical and biological, into ecologically based weed management is an essential process for the sustainability of agriculture. Throughout this review, the constraints affecting the implementation of biological weed control are described. Greater understanding of the morphology, phenology and genetic diversity of targeted weeds is emphasized and the need to examine all aspects related to biocontrol agents is stressed. Improved technologies, better public support and financial aid, and more scientific interest, will all contribute to the progress of the ‘science of biological weed control’. [ABSTRACT FROM AUTHOR]

Trichoderma virens (Gliocladium virens) (Miller et al.) von Arx is a soilborne fungus with a high degree of rhizosphere competence that produces a potent herbicidal compound, viridiol, and therefore has potential for development as a bioherbicide. We investigated the possibility of using composted chicken manure (CCM) as a medium for the production and deployment of T. virens. We chose CCM since the safe disposal of chicken manure presents significant logistic problems, and composted manures, as well as serving as an organic source of nitrogen, have been shown to support the activity of other biological control agents. Composted chicken manure supported the growth of T. virens and the rapid production of high concentrations of viridiol, but only when it was supplemented with large quantities of nutrients, including sucrose (16% w/w). Viridiol was not stable when stored in CCM, with a rapid decline in viridiol concentrations observed in T. virens-inoculated CCM cultures. Clearly, a cheaper alternative to sucrose is required as a carbon source for T. virens in CCM or similar media, and effective storage methods would need to be found for a T. virens-based bioherbicide product. Importantly, CCM did not need to be sterilized to support the growth of T. virens and its concomitant production of viridiol, suggesting that on-farm production systems may be feasible. Trichoderma virens-colonized CCM reduced the emergence and seedling growth of redroot pigweed (Amaranthus retroflexus L.) in a greenhouse experiment and dramatically reduced the emergence of a mixed community of broadleaf weeds in the field. [ABSTRACT FROM AUTHOR]

Based on an assessment of 706 fungal isolates obtained from Canada and Europe, a group of Colletotrichum sp. isolates, tentatively identified as C. truncatum , was moderately efficacious for biocontrol of scentless chamomile (Matricaria perforata). In this study, 19 C. truncatum isolates , 11 from Canada and eight from Europe, were compared for virulence, crop safety, and minimum dew requirement for infection to narrow the selection of candidates. Applied at 1×10 6 spores mL -1 , these isolates expressed variable virulence under controlled environments, with slightly higher variations observed on the Canadian isolates. There was also a slight difference in host specificity among the isolates tested; most isolates caused disease only on chamomile species ( M. perforata and M. recutita ) but two Canadian isolates also infected lentil, flax, or both. At 20°C, most isolates required more than 20 h dew for maximum infection. This requirement can be an impediment for using this fungus as a biocontrol agent in western Canada where the climate is semi-arid. Treatment of scentless chamomile at the 10-leaf stage with the herbicide metribuzin 48 h prior to fungal inoculation increased weed control to 72%, compared to 40 and 47% by the herbicide and fungus applied alone. However, a similar treatment using the herbicide bentazon did not enhance the weed control significantly as compared to the herbicide alone. [ABSTRACT FROM AUTHOR]

Abstract: A number of techniques exist that have potential to be integrated into low-external-input weed management systems but it is not the norm for these different techniques to be investigated in combination. Here, we evaluate the weed management potential of two cultural weed management techniques, cover cropping and fertility management, with two allelochemical-releasing organisms compared to herbicides. Trichoderma virens (=Gliocladium virens), which releases the herbicidal molecule viridiol, is applied incorporated in composted chicken manure (CCM), and rye, which is known to release the herbicidal molecules (3H)-benzoxazolinone (BOA) and 2,4-dihydroxy-1,4-(2H)benzoxazine-3-one (DIBOA), is used as the cover crop. Both T. virens-inoculated CCM and rye cover crops provided significant weed control in some experiments without a significant loss of crop vigor and yield. Yield was comparable to those obtained with chemical herbicides, although the results were not consistent. Clear weed suppressive activity exists with these nonherbicidal treatments, and effective weed management in transplanted vegetables seems feasible with these approaches. However, further refinements in these treatments is needed to ensure reliable performance prior to grower acceptance. [Copyright &y& Elsevier]

Abstract: The economic value of biological control of introduced, invasive weeds in Hawaii with fungi is estimated to surpass $100 million. The history of biological control of invasive introduced weed species with fugal pathogens in Hawaii began in 1967 motivated by the request of a Kauai rancher whose pastures were infested with ‘Kolomona,” Senna surattensis. A disease of unknown origin present in his ranch was studied. This led to the first successful control of an invasive species in the Islands by wound-inoculating the isolated pathogen, an Acremonium sp., on the weed in 1968, which killed ‘Kolomona’ in more than 10ha of land. Hamakua ‘Pa-makani,’ Ageratina riparia, was the most serious invasive weed of range and forests of Hawaii in 1973. The release of the white smut Entyloma compositarum from Jamaica in 1975 induced spectacular disease epidemics in the late 1970s, “wiping out the weed.” This specific pathogen cleared ‘Pa-makani’ from more than 200,000ha of infested rangeland, and kikuyu grass (Pennisetum clandestinum) pastures were rehabilitated in less than 6 years, saving the ranchers millions of dollars. These results convinced the Hawaii Department of Agriculture that fungi were a valuable tool in the management of invasive weeds. Koster’s curse, Clidemia hirta, was considered by environmentalists the most serious introduced species in 1984. The specific fungal pathogen, Colletotrichum gloeosporioides f. sp. clidemiae, was introduced in 1985 from Panama, and approved for field inoculations by the Hawaii Board of Agriculture in 1986. Repeated inoculations with this fungus have caused striking decline of the weed in Aiea State Park and Palolo Valley, Oahu. This fungus becomes airborne only during extended windy and rainy periods, which limits its natural distribution. Therefore, repeated applications are required to enhance it as a bioherbicide. Banana poka (Passiflora tarminiana), from the Andean region between Colombia and Ecuador, was the most serious invasive species of high-elevation (800–2200m) forests of Hawaii in 1983. This climbing vine threatened the pristine koa forests of Hawaii, Maui, and Kauai and the numerous endangered species of Hawaii’s flora in the undergrowth. In 1991, Septoria passiflorae was found on infected banana poka seedlings at Ipiales, Colombia. The pathogen was introduced to Hawaii in 1993 for host-range study in a containment laboratory. Host-range studies showed the fungus to be specific only to banana poka. Inoculations by spraying spore suspensions on adaxial leaf surfaces during 1996–1997 in the Hilo Forest Reserve resulted in major epidemics that severely defoliated the vines. One year after inoculations, the weed biomass was reduced from 40 to 60% and by more than 95% five years later. By 2003, banana poka had been eliminated from most forests, except from north Kona, Hawaii where acid rain killed the fungus. Bush lantana (Lantana camara) has been in Hawaii since 1858, and the only pathogen that affects the Hawaiian accessions is a Septoria sp., which was introduced from Ecuador in 1984. The US Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) granted permission to use this pathogen for field inoculations at Kokee State Park in 1996. Sites inoculated in 1989–1999 are showing significant decline in the lantana population, and it is expected that effective control of the weed will occur in time. [Copyright &y& Elsevier]

The herbicidal effect of volatile oils from leaves of Eucalyptus citriodora against the noxious weed Parthenium hysterophorus was tested. In a laboratory bioassay, seed germination and seedling length, chlorophyll content and respiratory activity of Parthenium decreased with increased concentration of eucalypt oils from 0.2 to 5.0 nL mL-1. Germination was completely inhibited at 5.0 nL mL-1 eucalyptus oils. Further, for 4-week-old plants of Parthenium sprayed with different concentrations of volatile oils, visible damage increased and chlorophyll content and respiratory activity decreased with increased concentration from 0 to 100 µL mL-1, the week after spraying. At concentrations up to 50 µL mL-1, plants showed some recovery over time but plants sprayed with 75 and 100 µL mL-1 died 2 weeks after treatment. Plants sprayed with 50 µL mL-1 and higher concentrations of eucalypt oils were desiccated and wilted in appearance. At concentrations of 5-75 µL mL-1, eucalypt oils caused a rapid electrolyte leakage from the Parthenium plants thereby indicating an effect on membrane integrity. It is concluded that volatile oils from E. citriodora possess weed-suppressing ability and could be used as a potential bioherbicide for future weed management programmes. [ABSTRACT FROM AUTHOR]

Phomopsis amaranthicola, a bioherbicide agent for Amaran thus spp., was tested in vitro for its compatibility with commercial formulations of 16 adjuvants, 24 herbicides, nine fungicides and four insecticides at 2X, 1X (highest labelled product dose rate), 0.75X, 0.5X and 0.25X concentrations. These chemicals were tested for their effects on spore germination. Selected herbicides and fungicides at IX were also tested for their influence on colony growth and sporulation. All tested cornpounds were finally categorized in compatibility classes regarding germination, mycelial growth and sporulation such as low, medium and high compatibility. High compatibility in terms of germination and fungal colony growth was only observed with the herbicide bentazone. Many of the adjuvants tested were highly compatible in the germination studies. Most fungicides and insecticides had medium and low compatibility with P. amaranthicola. Effects of pesticides on spore germination did not fully correspond with their effects on colony growth. Thus, it is possible to integrate the use of P. amaranthicola with some herbicides, fungicides, insecticides and adjuvants but not others. A case-by-case selection of application methods, such as tank-mix or sequential application, along with proper timing of applications of the fungus and the chemical agents will be necessary. [ABSTRACT FROM AUTHOR]

A pathogen isolated from lesions on blighted leaves of crabgrass in three different locations of China was identified as Curvularia eragrostidis . Isolate QZ-2000 was the most virulent of six isolates tested. Experiments on morphology, pathogenicity, effect of environmental factors, and host-range of isolate QZ-2000 were conducted in the laboratory, greenhouse and field to assess the potential of this isolate as a biocontrol agent for grassy weeds. Pathogenicity was quantitatively determined based on mortality and dry-weight reduction of infected large crabgrass. Inoculum concentration, rapeseed oil concentration in formulaton, post-inoculation dew temperature and duration, and plant growth age all significantly influenced the efficacy of the isolate. A total of 85-100% control of large crabgrass was obtained when inoculum concentrations were ≥1×10 6 conidia mL -1 , oil concentrations ≥0.9% (v/v), dew period ≥24 h and air temperatures 20-30°C in the greenhouse. A total of 51 plant species in 20 families were screened against isolate QZ-2000 in host-range studies. Six other species of grassy weeds were susceptible to isolate QZ-2000, but no mortality or significant dry-weight reduction was observed for maize (Zea mays), rice (Oryza sativa), soya bean (Glycine max), cotton (Gossypium hirsutum), or any other economically important crops and plants. In field trials, with 5×10 6 conidia mL -1 inoculum density, 60-7% reduction in dry weight was achieved for large crabgrass seedlings under natural dew-free conditions. These results indicate that isolate QZ-2000 is a potential microbial bioherbicide for control of large crabgrass in crops such as corn, soybean, cotton, water-melon, and peanut. [ABSTRACT FROM AUTHOR]

Selected cultural and environmental variables were investigated for their influence on the efficacy of Phoma herbarum and Phoma exigua to cause disease on dandelion ( Taraxacum officinale ) under growth room conditions. In both species, mycelial fragments caused significantly greater disease severity on dandelion than spore suspensions. Mycelial age was not an important factor in disease severity caused by P. herbarum , with all cultures causing high disease ratings. However, younger cultures of P. exigua caused the greatest disease severity on dandelion, but significantly less than that caused by P. herbarum . The initial pH of the growth medium (potato dextrose broth) did not affect disease severity caused by either Phoma species. Increasing concentrations of mycelia of P. herbarum were applied to dandelions that were then exposed to various leaf wetness durations. Disease severity increased with increasing leaf wetness duration. For dandelions exposed to no leaf wetness duration, the greater the mycelial concentration, the greater the disease rating. However, for dandelions exposed to all leaf wetness durations, all concentrations of mycelia caused similar disease ratings. As P. herbarum caused high disease ratings on dandelion, it therefore warrants further investigation as a potential bioherbicide for the control of this weed. [ABSTRACT FROM AUTHOR]

Eichhornia crassipes (water hyacinth), a major aquatic weed in India, is one of the targets in a biological weed control research programme in India. A fungal pathogen, Alternaria alternata, is being evaluated as a biological control agent for this weed. The feasibility of solid substrate for the mass production of A. alternata has been examined. Conidia production and virulence of A. alternata were affected by temperature, light and incubation period. The highest number of conidia were produced on rice seed followed by wheat, sorghum, maize seeds and cornmeal at 20°C when exposed to near-ultraviolet than on the other substrates, while the least conidia were observed on these substrates under light conditions. At 20°C, large numbers of virulent conidia were produced on rice seeds after 4 weeks of incubation under constant dark conditions. Henceforth, the use of rice seeds as a solid substrate for production of A. alternata could be a feasible method to produce conidia in a village co-operative scenario in India. [ABSTRACT FROM AUTHOR]

Studies the potential of plant pathogens as bioherbicides using Alternaria cirsinoxia for control of Canada thistle, Cirsium arvense, as a case study. Biological and ecological characteristics of potential biocontrol organisms; Genetic variability in host and pathogen; Mechanism of pathogen attack.

Fusarium nygamai has been isolated and identified from diseased Striga hermonthica plants collected from sorghum fields in the Sudan. Fumonisin B 1 , produced by this fungus, was isolated and purified. In in vitro experiments, the bioherbicidal potential of this mycotoxin was evaluated against S. hermonthica and S. asiatica . Different concentrations (250, 500 and 1000 μg L -1 of water) of fumonisin B 1 , applied during the conditioning phase of the Striga seeds significantly reduced the germination of both species in a range of 19.8-32.2 and 34.5-47.6%, respectively. In addition, the length of the germ tubes was reduced and the germ tubes became brownish. Fumonisin B 1 slightly delayed the emergence of Striga when 250 mg fumonisin B 1 dissolved in 1 L of water were applied into the soil per pot before sowing sorghum. By the way of contrast, fumonisin B 1 was very phytotoxic when Striga seedlings (leaves and stems) of different heights and ages were sprayed with a concentration series of 250, 500 and 1000 μg fumonisin B 1 mL -1 until run-off, or when plants were injured with a scalpel before fumonisin B 1 was applied into the injury at concentrations of 250 and 500 μg mL -1 . One day after application, the plants showed symptoms of wilting, first at the top and then moving downwards. Leaves turned black and stems desiccated at the point of injuries. Within 4 days after the application, 55% of the plants tested were completely destroyed. In total, at the end of the experiment, 40 days after the treatment, 85% of the treated plants were killed by fumonisin B 1, regardless of the concentration applied and the application technique used. [ABSTRACT FROM AUTHOR]

Diagnostic molecular markers, generated from random amplified polymorphic DNA (RAPD) and used in polymerase chain reaction (PCR), were developed to selectively recognize and detect the presence of a single strain of the biocontrol fungus Colletotrichum coccodes (183088) on the target weed species Abutilon theophrasti and from soil samples. Several isolates of C. coccodes, 15 species of Colletotrichum, a variety of heterogeneous organisms and various plant species were first screened by RAPD-PCR, and a strain specific marker was identified for C. coccodes (183088). No significant sequence similarity was found between this marker and any other sequences in the databases. The marker was converted into a sequence-characterised amplified region (SCAR), and specific primer sets (N5F/N5R, N5Fi/N5Ri) were designed for use in PCR detection assays. The primer sets N5F/N5R and N5Fi/N5Ri each amplified a single product of 617 and 380 bp, respectively, with DNA isolated from strain 183088. The specificity of the primers was confirmed by the absence of amplified products with DNA from other C. coccodes isolates, other species representing 15 phylogenetic groups of the genus Colletotrichum and 11 other organisms. The SCAR primers (N5F/N5R) were successfully used to detect strain 183088 from infected velvetleaf plants but not from seeded greenhouse soil substrate or from soil samples originating from deliberate-released field experiments. The sensitivity of the assay was substantially increased 1000-fold when nested primers (N5Fi/N5Ri) were used in a second PCR run. N5Fi/N5Ri selectively detected strain 183088 from seeded greenhouse soils as well as from deliberate-released field soil samples without any cross-amplification with other soil microorganisms. This rapid PCR assay allows an accurate detection of C. coccodes strain 183088 among a background of soil microorganisms and will be useful for monitoring the biocontrol when released into natural field soils. [Copyright &y& Elsevier]

Senna obtusifolia (Syn. Cassia obtusifolia; Fabaceae), commonly known as sicklepod, is a problematic weed in the USA and tropical regions of Africa, Asia, and South America. It is very common in Brazilian agricultural lands and causes major problems in west-central soybean production areas. The fungus Alternaria cassiae was discovered in 1992 in a disease survey of various regions of Brazil. The objective of this research was to study the effects of different dew durations and temperatures on infection of S. obtusifolia by a Brazilian isolate of A. cassiae. Sicklepod plants were inoculated with conidia of A. cassiae and incubated at 25 °C and different dew durations (4, 6, 8, 12, 24, or 48 h). The disease incidence (number of dead leaves) was greater on plants submitted to 24- and 48-h dew periods. Plants that were not submitted to a dew period did not show any disease symptoms. Dry-matter accumulation in fungus-treated sicklepod plants decreased as the dew duration increased. The combined effects of dew duration and temperature were evaluated by submitting A. cassiae-inoculated sicklepod plants to five different temperatures (17, 20, 23, 26, or 30 °C) and three dew durations (8, 12, or 16 h). Under the lower temperatures (17, 20, and 23 °C), disease incidence was greater at 8 and 12 h of dew compared to the higher temperatures (26 and 30 °C). When plants were incubated at 16 h of dew, the different incubation temperatures did not influence disease incidence, with the exception of 30 °C. Inoculated sicklepod plants accumulated greater dry matter under higher temperatures. A. cassiae requires lower temperatures and dew durations greater than 12 h for maximum expression of its biological control effects on sicklepod. [Copyright &y& Elsevier]