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.     

Tracing the origins of White Tip disease of Cirsium arvense and its causal agent,Phoma macrostoma

Cirsium arvense (Asteraceae) is known as creeping thistle in its native range in the UK and Canada thistle in its invasive North American range. Recently, the fungus Phoma macrostoma was registered in Canada as a bioherbicide in turfgrass, where it causes severe chlorosis (White Tip disease) and death of C. arvense and other broadleaved weeds. It was hypothesised that the disease originated in the UK on its thistle host and, therefore, that fungal isolates from both countries should be biologically and genetically similar. Twenty‐six strains in the genus Phoma– isolated during surveys in the UK – were compared morphologically with the type culture of P. macrostoma, tested for bioherbicidal activity using the inoculum mat bioassay and genetically screened with bioherbicide‐specific primers. White tip disease was found to be restricted to the eastern and southern counties of England. Phoma macrostoma was isolated consistently from diseased bleached tissues. Bioherbicidal isolates of P. macrostoma occupy a unique clade, which is phylogenetically distinct but morphologically indistinguishable from the type culture. Most isolates from the UK had the same bioherbicidal activity and similar genetic make‐up as strain SRC 94‐44B, the active ingredient in the registered Canadian product. The origin of all bioherbicidal strains found to date has a clear presence in both Canada and the UK, with strong genetic similarities, supporting the view of a common ancestry. Thus, on the evidence presented, the ‘white tip’ clade of P. macrostoma evolved in southern England. Therefore, the bioherbicide based on strain SRC 94‐44B should also be eligible for registration in the UK, based on the pest risk assessment data already available.     

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.     

Biology of milk thistle (Silybum marianum) and the management options for growers in north-western Pakistan

Milk thistle ( Silybum marianum ) is cultivated as a medicinal plant but it also can be a troublesome weed. It is an annual or biennial herb that prefers high rainfall and fertile soils. Milk thistle has become a widespread weed in north-western Pakistan, where it causes yield reductions ≤37% in wheat and poses harvesting problems due to its thorny nature. Shortcomings in cultural practises, such as a low crop seed rate, wide row spacing, broadcast fertilizer, and limited crop rotation have contributed to milk thistle becoming a severe weed problem for farmers in this region. This paper reviews the biology of milk thistle and discusses the possible management options for its control, considering the socioeconomic conditions of farmers in Pakistan.     

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.     

Assessment of the compensation point of Cirsium arvense and effects of competition,root weight and burial depth on below‐ground dry weight – leaf stage trajectories

Farmers are recommended to employ mechanical control when Cirsium arvense is most sensitive to disturbance. Earlier studies suggest that this occurs at a stage of minimum below‐ground dry weight, coinciding with three to seven or seven to ten leaves per shoot, depending on the definition of below‐ground dry weight. However, some farmers notice better effects when mechanical control is performed at earlier leaf stages. To estimate the compensation point (CP), defined as the minimum weight of the entire below‐ground structure of C. arvense and to further understand links between initial root weight, planting depth and crop competition, three outdoor pot experiments were performed in Sweden in 2013‐2014. We hypothesised that (i) CP likely occurs before C. arvense has developed three leaves, (ii) relative depletion of the below‐ground system at CP is less at lower initial root weight compared with higher weight, and (iii) methodological variations in CP estimations have minor impact on the results. We found that the CP for C. arvense in all treatments occurred before shoots had developed three leaves and that treatment effects were minor (<0.5 leaf stages). Leaf and leaf stage definitions, choice of leaf range and model also had minor effects on CP estimates. Depletion of planted root fragments ceased around leaf stages 3‐4, and their partial replenishment also constitutes evidence for a CP at early leaf stages. For agronomy, our results imply that mechanical control of C. arvense should be performed earlier than previously recommended, probably before reaching an average of three to four leaves per shoot.     

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.     

Sprouting capacity from intact root systems of Cirsium arvense and Sonchus arvensis decrease in autumn

Perennial weeds are often controlled by mechanical means, which aim at stimulating axillary and adventitious buds to sprout. This happens when the apical dominance of the main shoot is removed by defoliation or when the underground system is fragmented. By repeating the measures, the result is a depletion of storage compounds, which weakens the plants and reduces their capacity to grow and reproduce. However, timing is critical. Earlier research has indicated that emergence from fragments of Sonchus arvensis cease during a period in autumn, while the seasonal pattern of sprouting in Cirsium arvense appears to be inconsistent. We studied the emergence pattern of defoliated plants with undisturbed root systems, from late summer to early spring. Potted plants grown outdoors were exhumed at regular intervals, put under forcing conditions for 4 weeks, after which shoots above and below soil level were counted and weighed together with the remaining root systems. In both species, the number and weight of emerged shoots decreased during a period in the autumn. In C. arvense, underground shoots were constantly produced during the same period, while fewer underground shoots were present in S. arvensis. For the latter species, apical dominance does not fully explain the effect; thus, endodormancy might be involved. Root weight increased until withering and did not explain the lack of emergence. Our results suggest an impaired sprouting capacity of undisturbed root systems of C. arvense and S. arvensis during September–October, which has implications for the timing and method of control of these species.     

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.     

Effects of two pathogens on the performance of Cirsium arvense in a successional fallow

Biological control of weeds by natural antagonists is of increasing interest. To reduce densities of the weed Cirsium arvense (creeping thistle) in a successional fallow, we applied spores of two pathogens, the biotrophic rust Puccinia punctiformis and the perthotrophic Phoma destructiva, for three consecutive years individually at different dates and combined. The proportion of systemically Puccinia punctiformis-infected C. arvense was not influenced by the treatments, but local rust infection was a good predictor of systemic infection in the following season. Artificial inoculations with P. destructiva increased the incidence of this pathogen in the third year as a result of synergistic effects, when co-inoculated with P. punctiformis. Inoculations with either pathogen had little effect on C. arvense shoot density, although there were transient reductions after combined inoculations with both fungi compared with the fungicide treatment. Cirsium arvense decreased from 60% to 5% cover within 3 years, while the cover of the co-occurring fallow vegetation increased. Under field conditions, with an already high degree of natural P. punctiformis infection, the effects of inoculations of the single pathogens were minor, but reductions in shoot density after combined inoculations indicate that this inoculation may have the potential to cause a decline of this weed.     

Floral attractants for the female soybean looper, Thysanoplusia orichalcea (Lepidoptera: Noctuidae)

BACKGROUND: The soybean looper, Thysanoplusia orichalcea (F.), is a polyphagous insect pest of vegetable crops. Indonesian in origin, it has spread to Europe, India, Africa, Australia and New Zealand. The identification of an attractant for female T. orichalcea could enable the development of alternative pest management strategies to those provided by insecticides or sex pheromones, which are often only attractive to males. RESULTS: Traps baited with synthetic lures derived from Canada thistle, Cirsium arvense (L.) Scop., floral volatiles attracted female T. orichalcea. Phenylacetaldehyde, a floral compound attractive to many Lepidoptera and present in C. arvense, was tested alone as an attractant for the soybean looper and caught significantly more female than male T. orichalcea. Trap catch was greatest when phenylacetaldehyde was combined with five prevalent volatiles present in C. arvense headspace collections: 2‐phenylethyl alcohol, methyl salicylate, dimethyl salicylate, benzaldehyde and benzyl alcohol. Twice as many female moths as males were collected. CONCLUSION: Successful trapping of female T. orichalcea in either a lure‐and‐kill or a mass trapping system may offer an effective way to manage its population size. Copyright © 2008 Society of Chemical Industry     

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.     

Weight loss in overwintering below‐ground parts of Sonchus arvensis under current and temperature‐elevated climate scenarios in Sweden

Weight loss in overwintering below‐ground parts of perennial weeds has been attributed to respiration, but neither its temperature dependence nor its relevance for biomass dynamics under changing climate conditions have been investigated. In two experiments, we quantified weight loss of the perennial weed Sonchus arvensis, by measuring weight changes over time of sprouting roots in dark rooms at temperatures of 4, 8 and 18°C. Dry weight loss rates were 0.47, 0.64 and 1.47% day^?1 at 4, 8 and 18°C, respectively, giving a half‐life time of 149, 110 and 47 days, respectively. A factor by which weight loss rates increase for every 10° rise in temperature (Q₁₀) was equal to about 2.3. Cumulative weight loss may comprise >40% of the below‐ground biomass during overwintering periods. Applying weight loss rates and Q₁₀ to elevated soil temperature projections showed that losses during winter seasons in central Sweden will remain basically constant, the effect of increased weight loss at higher temperatures being balanced by shorter winters. This implies that need for control of S. arvensis in a changing climate will persist, but that shorter winter seasons will provide a longer time window for control of S. arvensis prior to sowing crops.     

Modelling the sprouting capacity from underground buds of the perennial weed Sonchus arvensis

Sonchus arvensis is a problematic perennial weed species causing problems in many crops. Control measures often rely on soil tillage or mowing; both methods are used to exhaust the root system. This approach fails during periods of restrictions in sprouting capacity or shoot regrowth. The aim of this study was to develop a simulation model for prediction of shoot sprouting capacity in underground buds of S. arvensis. We hypothesised restricted regrowth to be induced as a function of photoperiod and temperature sum and released as a function of cold temperature sum. The model was parameterised and calibrated against observations of shoot regrowth from an experiment on intact roots of S. arvensis. Subsequently, it was validated against observations of regrowth from another experiment on intact roots and sprouting from fragmented roots from a third experiment. Restriction in regrowth was attributed to reduction in the photoperiod, observed when the day length decreased below a threshold of 16.5 h, but also to a daily mean temperature below 16.8°C. Resumed regrowth occurred in late autumn at a daily mean temperature threshold of 4.7°C. The pattern of changes over time in shoot regrowth from an intact root system was well predicted by the model. The temporal change in sprouting capacity from buds on fragmented roots followed the same pattern, but with a quantitative difference between the model prediction and the observed sprouting capacity. We conclude that the model can be used to predict the pattern over time of sprouting capacity in intact roots of S. arvensis.     

Demography of Salsola australis populations in the agricultural region of south-west Australia

Salsola australis is a widespread annual weed of broad-scale cropping and pasture systems throughout Australia, and is of concern in the wheat belt of Western Australia. The population dynamics of S. australis was monitored at four sites in the Lake Grace district of Western Australia. At all sites, two to three cohorts emerged in summer and autumn or winter. While initial seedling density varied, density-dependent mortality ensured that the total number of senesced plants at each site was not significantly different. Estimated seed production ranged from 95 to 19 596 seeds per plant, although seed viability was low (approximately 9% for seeds that were shed and 15% for seeds that were retained on the mature plants). Total annual seed production per unit area was highly variable within sites but was not significantly different between sites. These data will facilitate the development of improved control strategies for S. australis .