Biocontrol options for Cirsium arvense with indigenous fungal pathogens

As a first step in the development of a mycoherbicide for biological control of Cirsium arvense indigenous fungal pathogens that had been isolated from diseased hosts were tested both singly and in combination on potted plants under environmental conditions. Disease symptoms (necroses, chloroses and macerations) and parameters of growth and development were evaluated to determine the potential for weed control. During 1998, Phoma destructiva, Phoma hedericola, a Mycelia sterilia and Puccinia punctiformis were inoculated singly. With the exception of the obligate biotroph P. punctiformis (local infections), the single inoculations reduced the measured parameters. A combined inoculum of P. punctiformis and Ph. hedericola was less effective than Ph. hedericola alone. In 1999, Ph. hedericola, Ph. destructiva, Ph. nebulosa and the Mycelia sterila were applied both singly and as a combined inoculum. Of all the tested inocula, the mixture of four pathogens had the greatest potential for biocontrol, significantly reducing reproductive capacity of the plants. These results demonstrate the importance of taking advantage of synergisms in developing a mycoherbicide.     

Phomopsis cirsii: a potential biocontrol agent of Cirsium arvense

Cirsium arvense is a noxious perennial weed which has become an increasing problem in north European countries. Biological control by natural antagonists is of increasing interest to supplement mechanical and chemical control. Several attempts to use fungi such as Alternaria cirsinoxia, Puccinia punctiformis and Sclerotinia sclerotiorum as biocontrol agents have been initiated. No mycoherbicides against C. arvense have been developed and the search for aggressive pathogens continues. In a Danish survey, several fungi were isolated from C. arvense. Four are new records in Denmark: the white rust fungus Pustula andropogonis, the leaf spot fungi Ramularia cirsii, Septoria cirsii and Phomopsis cirsii. Our study shows that P. cirsii is pathogenic to C. arvense, causing stem canker and die back, and that it may have potential as a mycoherbicide against its host. Growth characteristics of P. cirsii on artificial media are described, as well as a scale measuring severity of visible symptoms of P. cirsii on C. arvense. The taxonomic characteristics of Phomopsis spp. are compared and discussed in relation to other records of Phomopsis spp. found on Cirsium spp. and C. arvense.     

Bean rust as a model system to evaluate efficieucy of teliospore induction, especially in the potential mycoherbicide Pucdni a punctiformis

The use of teliospores of the rust fungus Pucdnia punctiformis (Str.) Röhl., a potential mycoher-bicide against the dicotyledonous weed Cirsium arvense (L.) Scop, has shown promise. Methods to increase teliospore production for systemic infections were investigated using two dicotyle-donous host-pathogen systems, the thistle rust and the bean rust (Phaseolus vulgaris-Uromyces appendiculatus). Three different approaches (culture filtrate extracts of different Aphano-fadium album strains, application of Ajoen and dark periods) were tested for their capacity to induce teliospore production in the above-mentioned host-pathogen systems. The methods significantly increased the teliospore production in the model system (bean-rust), although differing in the order dark period > A. album extract ajoen. The effect of the A. album extract depends on the strain used. A two-day dark period increased the teliospore production of bean rust in addition to precipitating its onset. The same effect was noted for thistle rust using A. album extract. The advantage of bean rust as a model organism together with combined applications and host pathogen reaction mechanisms are discussed. La rouille du pois comme système modèle permettant d'évaluer l'efficacité de l'induction de téliosopores, en particulier chez le mycoherbicide potentiel Puccinia punctiformis L'utilisation de téliospores de la rouille Puccinia punctiformis (Str.) Röhl, un mycoherbicide potentiel, s'est montrée prometteuse pour la lutte contre la mauvaise herbe dicotylédone Cirsium arvense (L.) Scop. Des méthodes permettant d'augmenter la production de téliospores pour des infections systémiques ont étéétudiées sur deux systèmes hôte-pathogène de dicotylédones, la rouille du chardon et la rouille du haricot (Phaseolus vulgaris-Uromyces appendiculatus). Trois approches différentes (extraits de filtrats de culture provenant de différentes souches d'Aphanocladium album, application d'Ajoen et périodes obscures) ont été testées pour leur capacitéà induire les téliospores dans les systèmes hôte/pathogène précédents. Les méthodes accroissaient significativement la production de téliospores dans le système modèle (haricot-rouille) bien que différant en efficacité dans l'ordre: période obscure extraits d'A album Ajoen. L'effet de l'extrait d'A album dépendait de la souche utilisée. Une période obscure de deux jours accroissait la production de téliospores de la rouille du haricot et avanßait son démarrage. Le même effet était observé chez la rouille du chardon avec des extraits d'A album. L'avantage de la rouille du haricot comme organisme modèle, ainsi que d'applications combinées est discuté, de même que les mécanismes de la relation hôte/pathogène. Der Bohnenrost als Modellsystem zur Abschätzung der Effizienz unterschiedlicher Verfahren der Teleutosporeninduktion unter Berücksichtigung des potentiellen Mykoherbizids Puccinia punctiformis Die Verwendung der Teleutosporen des Rostes Puccinia punctiformis (Str.) Röhl. zeigt erfolgversprechende Ansätze als Mykoherbizid gegen das Unkraut Cirsium arvense (L.) Scop. Methoden, die für systemische Infektionen der Kratzdistel erforderliche Teleutosporenbildung zu steigern, wurden an 2 dikotylen Wirt-Pathosystemen, der Kratzdistel und der Bohne (Phaseolus vulgaris/Uromyces appendiculata), geprüft. Es wurden 3 unterschiedliche Methoden angewandt, um die Teleutosporenbildung in den erwähnten Systemen zu induzieren (Kulturfiltratextrakte unterschiedlicher Aphanocladium-album-Stämme, Ajoen und Dunkelperioden). Alle Anwendungen steigerten die Teleutosporenbildung im Modellsystem Bohnenrost signifikant, jedoch graduell unterschiedlich: Dunkelphase > A.-album-Extrakt > Ajoen. Dabei war der Effekt des A-album-Extraktes eindeutig von dem verwendeten Stamm abhängig. Die 2-tägige Dunkelphase steigerte die Teleutosporenproduktion des Bohnenrostes und bewirkte ein früheres Einsetzen der Teleutosporenbildung. Der gleiche Effekt konnte für den Kratzdistelrost auch unter Verwendung des A.-album-Extraktes festgestellt werden. Die Vorteile des Bohnenrostes als Modellorganismus sowie kombinierte Appli-kationen und mögliche Wirt-Pathogen-Reaktions-mechanismen werden diskutiert.     

Impacts of applied Sclerotinia sclerotiorum on the dynamics of a Cirsium arvense population

A field experiment was conducted from October 1992 to March 1997 in a sheep‐grazed pasture in Canterbury, New Zealand, to determine the effects of the fungus Sclerotinia sclerotiorum on the long‐term dynamics of a population of Cirsium arvense. The pathogen was applied in mid‐spring either once or in three consecutive years when the C. arvense shoots were vegetative rosettes, using a granular, mycelium‐on‐wheat preparation that lodged on the C. arvense leaves, stems and in the leaf axils. The single application caused disease in the C. arvense that was confined to the application year. The disease resulted in a temporary (17 months) reduction in population size through initial mortalities among treated shoots and resultant reductions in root growth, adventitious root bud, subterranean shoot and, subsequently, aerial shoot population sizes. The soil seedbank was 80% lower in the treated plots than in the control plots in the first year. Seedlings were never found. The annually repeated application of S. sclerotiorum did not result in the expected continuing decline in the C. arvense population relative to the control population.     

Effect of the rust fungus Puccinia chondrillina TU 788 on plant size and plant size variability in Chondrilla juncea

Chondrilla juncea is one of the most serious introduced weed species in Australia. Successful biological control has been achieved by the release of the rust fungus Puccinia chondrillina. Although P. chondrillina is thought to reduce the competitive ability of C. juncea by reducing plant size, the precise mechanism by which the pathogen controls its host is poorly understood. In this experiment, we examined the effect of P. chondrillina TU 788 infection on individual plant size, and size variability, in two genotypes (one resistant, one susceptible) of C. juncea. Exposure to P. chondrillina significantly reduced the average size of susceptible C. juncea plants, a reduction apparent in both roots and shoots. Plant size variability of the susceptible C. juncea genotype was also reduced by P. chondrillina. Plant size, and plant size variability of the resistant genotype were unaffected by exposure to rust, or association with rust‐affected plants. The effect of P. chondrillina on plant size in rust‐susceptible C. juncea plants shows how effective bio‐control of this weed may occur in field populations.     

Mycoherbicides and other biocontrol agents for Senecio spp

Classical biocontrol of Senecio jacobaea (ragwort) has generally utilised herbivorous insects, although the nisi Puccinia expansa has also been considered. Although this rust is specific and damaging in the glasshouse. It has not been used in the field. Research into the ecophysiology of Senecio vulgaris (groundsel) infected by the rust Puccinia lagenophorae has revealed the extent to which the effects of infection are dependent on environmental factors. The damage caused by rust is enhanced under mild drought conditions, during periods of frost in winter and by competition between groundsel and neighbouring plants, bui is reduced by nutrient deficiency. Rust injury is also greatly increased by secondary infection of pustules by necrotrophic fungi. Such secondary infection can be achieved artificially with a range of opportunistic necrolrophs and can selectively kill groundsel: the effective inoculum dose of both fungi is significantly reduced. Attempts to apply our understanding of rust-necrotroph injury to ragwort have been partially successful but we have not succeeded in causing significant mortality of this host. This paper discusses these, and other weed—pathogen—environment interactions, and their possible application to biocontrol.     

Teleutospores as origin of systemic infection of Cirsium arvense by Puccinia punctiformis

Teleutospores ofPuccinia punctiformis were used for germination and inoculation experiments. The percentage of germination increased with increasing root extract concentration separately from the spore-suspension present in the same Petri dish.Volatile substances in root extracts of the thistle plant markedly promoted the germination of the teleutospores.Inoculation experiments showed that underground parts of plants ofC. arvense can be infected. The percentage of diseased shoots emerging from inoculated root segments was higher than of those emerging from seeds. Three types of systemically infected shoots could be distinguished.The development of spermogonia on the diseased shoots indicates that at first the hyphae are haploid, but later on become dikaryotic as shown by the formation of uredosori. Teleutospores are thus responsible for the systemic infection of the plants.Samenvatting Teleutosporen vanPuccinia punctiformis zijn gebruikt voor kiemings- en incubatieproeven.Vluchtige substanties, aanwezig in wortelextracten van de akkerdistel, hebben een grote invloed op de kieming van teleutosporen. Het percentage kiemende teleutosporen nam toe bij toenemende concentraties van het wortelextract, aanwezig in dezelfde petrischaal als de sporensuspensie.Inoculatieproeven toonden aan dat ondergrondse plantedelen vanC. arvense kunnen worden geïnfecteerd. Het percentage aangetaste scheuten opkomend uit wortelsegmenten was groter dan dat van scheuten verkregen uit zaden. Behalve systemisch geïnfecteerde scheuten werden ook enkele lokaal geïnfecteerde scheuten aangetroffen. De systemisch geïnfecteerde planten konden worden onderscheiden in drie verschillende types.De ontwikkeling van spermogonia op de systemisch aangetaste scheuten wijst er op dat het aanwezige mycelium haploid is, zoals ook te verwachten is bij infecties met basidiosporen. Pas later worden de hyphen dikaryotisch, zoals blijkt uit de vorming van uredosori.     

Genetic variation in tolerance to defoliation in Cirsium arvense

The perennial weed, Cirsium arvense (creeping, Canada or Californian thistle), is notorious for its ability to tolerate defoliation by mowing, herbivores or herbicides. The tolerance of 36 genotypes of C. arvense was examined by establishing pairs of clonal replicates that were assigned to a clipped or unclipped treatment. Three clippings were applied from spring to early summer to simulate repeated mowing. The average final percentage reduction caused by the repeated clipping was 18%, 72%, 32% and 50% for shoot biomass, root biomass, number of shoots and shoot height respectively. While nearly all genotypes were negatively affected by clipping, some overcompensated, and achieved greater shoot biomass, number of shoots, or increased height than their unclipped counterparts. No genotype was able to overcompensate, or fully tolerate, the lost root biomass due to repeated clipping. Genetic variation for tolerance to defoliation was detected for the number of shoots, maximum shoot height and for relative height growth rate. For relative growth rate, significant genetic variation was not detected until after the third clipping event, indicating that genotypes were equally tolerant to a moderate degree of defoliation, but upon more severe defoliation, genetic differences were evident. Since repeated defoliation is a recommended control technique, selection for more tolerant genotypes is possible and should be considered for the management of this weed.     

Quantitative reproductive potential of Heterodera schachtii on weeds typical for late summer fallow in sugar beet rotations

In Europe, sugar beet is often produced in a 3‐year rotation with cereals, leaving stubble fields fallow from cereal harvest until primary tillage in autumn in the year prior to sugar beet production. The weed flora on such fields could include host plants of Heterodera schachtii that is one of the most important pests of sugar beet. Crop sequences with non‐hosts and cover cropping with resistant cruciferous hosts during this period have been crucial for its management. Availability of resistant and tolerant sugar beet cultivars could entice growers to forego cover cropping, exacerbating weed problems during the fallow period. The objective of this study was to determine the reproductive potential of H. schachtii on weeds that develop during this period. Under glasshouse conditions, reproduction on 39 plant species was compared with that on oilseed radish and sugar beet of differing nematode host status. In 2 years in field microplots, 18 previously tested species were grown in H. schachtii‐infested soil during the typical fallow period at 60 plants m^?2, and nine of these species were also grown at 180 plants m^?2. There were variable results between years after 8 weeks of growth, but most weeds allowed lower reproduction (<10%) than the susceptible sugar beet; only Stellaria media at 180 plants m^?2 and Thlaspi arvense at both plant densities increased nematodes. Such weed densities may seldom occur under commercial conditions; thus, weed management for nematological considerations during the stubble period may have limited importance.     

Three-way fungal interactions affect the potential biological control of Himalayan balsam,Impatiens glandulifera

Himalayan balsam (Impatiens glandulifera) is one of the most invasive weeds across Europe. The rust fungus, Puccinia komarovii var. glanduliferae has been introduced as a biological control agent, but success has been patchy. Here, we investigated whether mycorrhizal and endophytic fungi can affect rust efficacy and plant growth. Over three experiments, we found that AM fungi and the rust alone or together consistently reduced plant growth, but this depended on the identity of species in the AM inoculum. Meanwhile, AM fungi increased infection frequency of the endophyte Colletotrichum acutatum. Rust inoculation had no detrimental effects on mycorrhizal colonisation or C. acutatum infection, but the latter two fungi reduced rust sporulation. However, plant size was reduced when all three fungal types were present, suggesting that a combined fungal inoculum offers a promising approach for the control of this weed.     

Seasonal dynamics of ground cover in Cirsium arvense – a basis for estimating grazing losses and economic impacts

Analysis of the economics of managing Cirsium arvense in grazed pastures worldwide has been hampered by a lack of data on the within‐year seasonal dynamics of the weed and its impact on the yield of palatable herbage. To redress this, the seasonal pattern in within‐patch percentage ground cover of the weed was determined from measurements on 39 dairy and 66 sheep and/or beef cattle farms in New Zealand during 2009–2010 and 2010–2011. This pattern was then scaled using farmer estimates of peak whole‐farm cover to derive mean monthly covers for dairy, beef, sheep/beef, sheep and deer farms. These monthly covers corresponded, respectively, to mean annual percentage covers of 2.7, 1.7, 3.0, 5.9 and 2.9% and to mean annual percentage losses in pasture growth (palatable herbage yield) of 3.6, 2.3, 4.0, 7.8 and 3.9%. The latter, in combination with 2011–2012 farm statistics, revealed that C. arvense caused a national loss in pastoral farm gross revenue in New Zealand in 2011–2012 of $685 million ($446 m dairy, $233 m sheep/beef, $6 m deer). Beyond the scope of this paper, the monthly covers and their corresponding monthly losses in pasture growth provide a basis for modelling the economic impacts of C. arvense and its management at a farm scale. More generally, the analytical method that we have developed is appropriate for evaluating the economic impact of any weed in a grazed pasture, particularly those exhibiting pronounced seasonal patterns in occupancy, such as annuals and deciduous perennials.     

Composition of the stubble weed flora and its role for Heterodera schachtii in the year preceding sugar beet production

In Germany, sugar beet is often rotated with 2 years of cereal. Extensive fallow periods between cereal harvest and autumn primary tillage allow for a weed flora to develop. Broad‐leaved weeds could potentially be alternate hosts for the common nematode Heterodera schachtii, one of the most important pests of sugar beet. Between 2009 and 2012, annual weeds developing in cereal stubble fields during July to mid‐October in the season prior to sugar beet were surveyed, including known hosts of H. schachtii. Yearly weather patterns and agronomic practices possibly impacted weed species composition and weed population densities. During September, Chenopodium album, Cirsium arvense, Convolvulus arvensis, Mercurialis annua, Polygonum spp., Solanum nigrum and Sonchus spp. occurred at the highest frequencies. Weed hosts of H. schachtii were present, but densities, frequencies and uniformity were limited. In 2010 and 2011, staining for nematodes in roots revealed juvenile penetration of some weeds but few adult stages. No indication of nematode reproduction of H. schachtii was found on these weed hosts. A fairly stable weed flora was detected on stubble fields that could provide some carry over for weed species. An elevated risk for nematode population density build‐up on these weeds was not found and management of these weeds at the observed densities during the stubble period for nematological reasons appeared unnecessary.     

Cirsium arvense (L.) Scop. competition with winter wheat (Triticum aestivum L.)

A series of field experiments was conducted to evaluate the competitive effect of Cirsium arvense (L.) Scop. on winter wheat (Triticum aestivum L. ‘Norstar’) yield. Grain yield at the centre of dense C. arvense patches ranged from 28–71% of the yield in adjacent weed-free plots, based on measurements made at 11 experimental sites over a 2-year period. The mean reduction in yield was 49%. Two models were used to describe grain yield reduction in terms of C. arvense shoot density: (a) linear regression of percentage yield reduction on the square root of shoot density, and (b) non-linear regression, based on a rectangular hyperbola. Both models give similar yield loss estimates at commonly occurring shoot densities of C. arvense, but the non-linear model accounted for more of the observed variation in grain yield. The major yield component affected by C. arvense competition was spikes per unit area, with kernel weight affected to a lesser extent.     

An emerging system management approach for biological weed control in crops: Senecio vulgaris as a research model

A ‘system management’ approach of biological weed control in crops is proposed and compared with other method's of biological weed control. It is based on the management of a weed pathosystem in order to maximize the natural spread and disease severity of a native or naturalized pathogen. This approach may be well-suited to situations where it is necessary to control single weed species in crops, and where no immediate and complete control is required, the production of large amounts of the agent is rather limiting (e.g. when using biotrophic fungi), and/or the importation of an exotic agent is not possible. This strategy provides fundamental knowledge of underlying mechanisms of crop production systems and is aligned with the view of modern agro-ecology, in which complete eradication of weeds is not desirable. The fundamental research required for a successful application of the ‘system management’ approach will be illustrated with the biological control project of Senecio vulgaris L. using the naturalized rust fungus Puccinia lagenophorae Cooke. A five-step procedure, together with selected results, will be presented. Main emphasis is given to the infection window, the study of the genetic structure of the plant and pathogen population, and the management of the infection conditions (a) to maximize the spread of the disease and the impact on the plants, and (b) to minimize the development of resistant plant populations. Joint application of herbicides at low doses, additional necrotrophic pathogens, and of biochemicals interfering with the weed's defence also will be envisaged, as well as their integration into general pest control practices. In this regard, biological weed control agents have to be seen as stress factors, not as weedkillers, and biological weed control as an integral part of a well-designed pest management strategy, not as a sole cure.     

Mechanical and cultural strategies to control Cirsium arvense in organic arable cropping systems

Infestation with Cirsium arvense in organic cropping is an increasing problem in many parts of Europe. Non‐chemical management strategies against C. arvense, based on cultivation tactics and/or different cutting regimes, have received very little attention for many years. This study presents results from four experiments, undertaken under organic growing conditions, on the effects of repeated mowing or hoeing during the first part of the growing season, used in combination with competition from a suppressive crop (grass/white clover mixture or red clover). The strategies were mainly aimed at diminishing the regenerative capacity of C. arvense and the effects were thus measured in the subsequent year in spring barley crops, in the absence of any weed control. In general, number of passes of mowing and hoeing linearly reduced the amount of aboveground C. arvense biomass in the subsequent year. Increased competition induced by the competitive crops further reduced C. arvense biomass. Differences in barley yield were explained by the amount of C. arvense biomass only in one experiment, where this weed was most abundant. Our results suggest that an acceptable level of C. arvense control can be achieved through an intensive hoeing or mowing campaign, within one growing season only. This may lead to increased crop yield in the subsequent year.     

Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens

Brandsæter LO, Fogelfors H, Fykse H, Graglia E, Jensen RK, Melander B, Salonen J & Vanhala P (2010). Seasonal restrictions of bud growth on roots of Cirsium arvense and Sonchus arvensis and rhizomes of Elymus repens. Weed Research 50 , 102–109.

Summary

The success of weed management aimed at depleting the regenerative structures of perennial weeds depends largely on the sprouting activity of rhizome and root buds. Seasonal variation in sprouting of these buds on Cirsium arvense, Sonchus arvensis and Elymus repens was studied for plants collected from Denmark, Finland, Norway and Sweden. At 2‐week intervals from July to October, 5‐cm fragments of roots or rhizomes were cut from plants grown in buckets and planted into soil in pots, half of which were placed immediately into growth chambers at 18°C for 4 weeks. The other half of the pots were initially placed in a dark room at 2°C for 4 weeks before being transferred to the same growth chamber, also for 4 weeks. During the growth chamber period, the numbers of emerged shoots in each pot were counted weekly. The sprouting activity of C. arvense and E. repens was relatively uniform during this period and bud dormancy was not apparent. In all ecotypes of S. arvensis, innate bud dormancy developed during the latter part of the growing season. For all three species, differences in sprouting readiness were found among ecotypes. The results imply that C. arvense and E. repens are more likely to be controlled by mechanical measures in autumn than S. arvensis.     

Impacts of cropping system and management practices on the assembly of weed communities

Understanding how weed communities assemble as a function of biotic and abiotic filters and transform through time has important implications for the sustainable management of agronomic systems. In a three‐year study, we evaluated weed community responses to lucerne (Medicago sativa, perennial) vs. continuous spring wheat (Triticum aestivum, annual, CSW) and weed management practices where weeds in the CSW system were managed with three contrasting approaches (herbicide, tillage or sheep grazing). Our results indicated no differences in weed diversity between the perennial and annual crops or across the different management practices in CSW. However, there were differences in weed community composition. Lucerne, with the exception of the establishing year, impeded the growth and reproduction of several annual weeds, including Amaranthus retroflexus, Thlaspi arvense, Lamium amplexicaule and Chenopodium album, but favoured perennial broad‐leaved weeds such as Taraxacum officinale and Cirsium arvense. The replacement of herbicide treatments in pre‐plant and post‐harvest in CSW with soil tillage or sheep grazing selected for different weed communities beyond the second year of establishment. The weed species driving the differences in CSW systems were Androsace occidentalis, more common in CSW managed chemically; Asperugo procumbens, more common in CSW managed with tillage; and T. officinale and Lactuca serriola, more common in CSW managed with sheep grazing. Understanding how cropping systems modify weed communities is a necessary step to shift from reactive weed control programmes to predictive management strategies.     

Recent Advances in the Use of Plant Pathogens as Biocontrol Agents of Weeds

Abstract

Among various organisms attacking skeleton weed, Chondrilla juncea, in Europe, a rust fungus, Puccinia chondrillina, and two powdery mildews, Erysiphe cichoracearum and Leveillula taurica f. sp. chondrillae were found to be the most damaging. P. chondrillina was shown to be specific to Chondrilla and has recently been introduced into Australia where skeleton weed is important in wheat cultivation. It has already spread throughout the weed infestations and is beginning to reduce plant populations. Encouraged by the result of the Chondrilla rust, the possible use of Puccinia xanthii for the control of Xanthium strumarium and X. spinosum has also been studied. Current research on the possible use of phytopathogens in the biological control of some other weeds is reviewed.     

Herbicidal control of Cirsium arvense (L.) Scop,roots and shoots in no-till spring wheat (Triticum aestivum L.)*

Three herbicide treatments were applied each year over a period of 4 years to Cirsium arvense (L.) Scop, infestations in no-till spring wheat (Triticum aestivum L.) in North Dakota, USA. Both chlorsulfuron at 30 g ai ha^?1+a non-ionic surfactant and a mixture of clopyralid+2,4-D at 70+280 g ai ha^?1 gradually reduced Cirsium arvense shoot density, root biomass, and adventitious root buds over the 4-year treatment period in two trials. These two treatments did not merely induce adventitious root buds to become dormant. They virtually eliminated roots to a depth of 50 cm by year 4. Tribenuron methyl at 10 g ai ha^?1+ a non-ionic surfactant was less effective in reducing shoot density and root biomass. Lutte herbicide contre les racines et les tiges de Cirsium arvense (L.) Scop, dans du bli de printemps non laboure (Triticum aestivum L.) Trois traitements herbicides ont été appliqués chaque année pendant 4 ans, contre des infestations de Cirsium arvense (L.) Scop, dans du blé de printemps (Triticum aestivum L.) non labouré dans le Dakota Nord, USA. Tant le chlorsulfuron à 30 g m.a. ha^?+un surfactant nonionique qu'un mélange de clopyralide+2,4-D à 70+280 g m.a. h^? ont reduit progres-sivement la densité des pieds de Cirsium arvense, la biomasse racinaire, et les bourgeons racinaires adventices pendant les 4 années de traitements dans les 2 essais. Ces traitements ont à peu près éliminé les racines sur une profondeur de 50 cm en 4 ans. Ces deux traitements n'ont pas induit de dormance des bourgeons racinaires adventices. Le tribenuron methyl à 10 g m.a. ha^?+un surfactant non ionique a été moins efficace dans la réduction de la densité de plante et de la biomasse racinaire. Chemische Bekämpfung von Cirsium arvense (L.) Scop, in direktgesätem Sommerweizen (Triticum aestivum L.) In direktgesäter Sommerweizen (Triticum aestivum L.) wurdel in North Dakota. USA, Bestände von Cirsium arvense (L.) Scop, über 4 Jahre jährlich 3 Herbizidbehandlungen unterzogen. Sowohl Chlorsulfuron mit 30 g AS ha^?1 nichtionischem Netzmittel als auch eine Mischung von Clopyralid+2,4D mit 70+280 g AS ha^?1 verringerten die Sproßdichte der Acker-Kratzdistel, die Wurzelbiomasse und die Adventivknospen an den Wurzeln in 2 Ver-suchen graduell. Durch diese beiden Behand-lungen wurden nicht nur die Adventivknospen dormant, sondem auch die Wurzeln bis zu einer Tiefe von 50 cm bis zum 4. Jahr fast ganz elimi-niert. Tribenuron-methyl mit 10 g AS ha^?1 nichtionischem Netzmittel war hinsichtlich der Reduktion von Sproßdichte und Wurzelbiomasse weniger wirksam.     

First report of rust disease on ohia and the causal fungus, <Emphasis Type="Italic">Puccinia psidii</Emphasis>, in Japan

In 2007, a rust disease of ohia (Metrosideros polymorpha) was found in Japan. We identified this pathogen as Puccinia psidii based on its morphological characters and the internal transcribed spacer (ITS) sequence of the ribosomal DNA. This pathogen was pathogenic on Eucalyptus amplifolia and E. rudis in addition to previously reported host species. This is the first report in Japan of a rust disease on ohia and the occurrence of its causal fungus, P. psidii.