Pasture Weeds Research Articles

Economic Impact of Tropical Soda Apple (Solanum viarum) on Florida Cattle Production

A written survey administered to 3,500 Florida cattle producers in 2006 documented tropical soda apple as the most common pasture weed across the state of Florida. Over 80% of the survey respondents reported tropical soda apple on their ranches, and over 65% declared the plant to be a major problem for their cattle operation. On ranches that reported tropical soda apple infestations, the level of pastures infested with this weed ranged from a low of 4% in north Florida to a high of 12% in central Florida. The cattle producers' most common strategies to tropical soda apple were herbicide application and mowing. These strategies were used by 32% of respondents in north Florida, 75% in central Florida, and 76% in south Florida. On a statewide basis, 20% of cattle producers used herbicides alone, 7% used mowing alone, and 20% used both methods. Some cattle producers reduced the cattle stocking rate as a consequence of tropical soda apple infestations. This negative impact was reported by only 2% of cattle producers in north Florida, 6% in central Florida, and 7% in south Florida. With the use of the economic input/output model IMPLAN, tropical soda apple control costs resulted in economic losses throughout Florida of $15 million annually in 2006 to cattle producers and their supporting business sectors.

History of the series on the Biology of Canadian Weeds

In the mid-1960s the founding of the Canadian Botanical Association provided a forum for the discussion of new botanical initiatives in Canada. At that time there was, coincidentally, a much increased interest in several areas of botany that had previously been little studied or ignored (e.g., plant autecology, plant population biology). As a result, many research projects became focused on individual species or small groups of closely related species. Botanists studying the native flora as well as those working with weed species became aware of the need for the compilation of all available information on important species, essentially in the format pioneered in Great Britain in the ‘‘Biological Flora of the British Isles’’. Botanists from the Central Experimental Farm in Ottawa (the Plant Research Institute) and the Botany Department at the University of Western Ontario in London decided to prepare a manuscript format for a Canadian version of the Biological Flora. Gerald Mulligan and Paul Cavers agreed to undertake this work. The initial plan was to ask the Editorial Board of the Canadian Journal of Botany to initiate a series with a tentative title ‘‘The Biological Flora of Canada’’. However, the Editor of the Canadian Journal of Botany did not accept this proposal. When we re-examined all the letters and other material received while the original proposal was being prepared, it was evident that by far the greatest support had come from scientists studying weeds and invasive plant species. In particular, many members of the Canada Weed Committee (later known as the Expert Committee on Weeds and currently as the Canadian Weed Science Society) enthusiastically recommended that this series be established. The Agricultural Institute of Canada, publishers of the Canadian Journal of Plant Science, agreed to publish the series under the title ‘‘The Biology of Canadian Weeds’’. We quickly revised the manuscript format to include aspects of weed biology not featured in the original proposal and published it in July 1972 (Cavers, P. B. and Mulligan, G. A. 1972. A new series The Biology of Canadian Weeds. Canadian Journal of Plant Science 52: 651 654). Gerry Mulligan was the first Editor of the series and Paul Cavers took the lead in finding authors and maintaining a list of Accounts in Preparation. The first account, published in October 1973, dealt with sheep-laurel (Kalmia angustifolia L.), a native species that is a weed of lowbush blueberry fields and pastures in eastern Canada. Since then, more than 150 accounts have been published, many on two or more species. In recent years, updates of several of the early accounts have been published. These updated accounts incorporate information on well-studied species published after the original account appeared. The series was popular from the outset, in fact there was such a great demand for many articles that the authors’ stocks of reprints soon were exhausted. In 1979, a book containing the first 32 accounts in the series was published by Agriculture Canada. Gerald Mulligan was the Editor and Compiler. In 1984, a second volume containing the next 29 accounts, with the same Editor/ Compiler and publisher, was printed. Volumes 3, 4 and 5 were published with Paul Cavers as the Editor/ Compiler by the Agricultural Institute of Canada in 1995, 2000 and 2005. In total, 129 original accounts plus three updated accounts were published in these five volumes (Table 1). In 2003, a new complimentary series was started, ‘‘The Biology of Invasive Alien Plants in Canada’’, in response to an expanding need for information on plants newly established or showing increased expansion in Canada, but for which there may be relatively little information available in a Canadian context. This series was intended to be similar in style and scope, but to concentrate on non-native plant species that have been more recently introduced into Canada than many of our common agricultural weeds, and for which there is substantial evidence that they may generate adverse economic impacts and management difficulties in agricultural systems or a broader landscape. The format for the Biology of Canadian Weeds has changed little over the years. Each contribution consists of 13 sections. The first section lists the currently accepted scientific name and the English and French vernacular names plus any synonyms that appear in the weed literature. The second section begins with a brief

Polyphagy in the Australian population of South African citrus thrips (Scirtothrips aurantii Faure)

The South African citrus thrips, Scirtothrips aurantii Faure, 1929, is highly polyphagous in its country of origin. Introduced to Australia in about 2002, populations of this thrips have been found only on the pasture weed Mother of Millions, Bryophyllum delagoense (Eckl. & Zeyh.) 1900. To evaluate the potential risk by these populations to plants of economic significance, under laboratory conditions, whether S. aurantii collected from Mother of Millions in Queensland can survive, reproduce and maintain populations over multiple generations on non-target hosts was tested. That this thrips can form self-sustaining populations on mango, grape, chilli, pea, green bean and blueberry was showed. Extended adult lifespan and some juvenile production were found on lemon and orange, but populations did not persist on these hosts. Furthermore, female thrips accept mango and grape for oviposition as readily as Mother of Millions. This degree of polyphagy under laboratory conditions suggests that caution is needed before promoting this thrips as a biocontrol agent against the pasture weed.

First Report of Downy Mildew Caused by Peronospora sordida on Butterflybush (Buddleja stachyoides) in Brazil

Butterflybush (common name in Brazil, verbasco), Buddleja stachyoides Cham. & Schltdl. (Buddlejaceae), is an erect herb or small shrub, native to Brazil, that is listed both as a folk medicinal plant and as a pasture weed (4). In March 2012, a group of B. stachyoides plants growing in a pasture in Viçosa (state of Minas Gerais, Brazil), were found bearing typical downy mildew symptoms. The only pathogen reported associated with this plant species is Podosphaera xanthii (1) and because there is no record of downy mildew on members of Buddleja in Brazil, an investigation was carried out to clarify the pathogen identity. Diseased plants had lesions on living leaves that were vein-delimited, chlorotic, coalescing, and becoming necrotic adaxially and bearing downy mildew-like colonies over diseased tissues abaxially. The samples were dried in a plant press and a representative specimen was deposited in the local herbarium at the Universidade Federal de Viçosa (Accession No. VIC 31836). Reproductive structures were scraped from leaves with a scalpel and mounted in lactophenol. Preliminary observations indicated the pathogen as belonging to Peronospora (Peronosporaceae). The pathogen had the following morphology: Sporangiophores are 288 to 641 μm long, dichotomously branching up to seven times, hyaline, smooth, 5 to 16 μm wide at the trunk, branches 63 to 202 μm long; tips subacute, in pairs or rarely single, 5 to 19 μm long; sporangia subglobose to ellipsoidal, 12 to 22 × 11 to 17 μm, pale yellowish brown, non-papillate. Only one species of Peronospora is known to infect members of Buddleja, namely Peronospora hariotii Gäum. (1). Nevertheless, the pathogen on B. stachyoides has smaller sporangia as compared to those of P. hariotii (20 to 26 × 16 to 21 μm) (2) and it was closer to P. sordida (3). DNA of the pathogen from B. stachyoides was extracted and the cytochrome c oxidase subunit II (COX2) and internal transcribed spacer (ITS) regions were sequenced. Sequences were deposited in GenBank (COX2 as JX982637; ITS as JX982638). A BLAST search yielded 99% and 100% of maximum identity with P. sordida for COX2 and ITS, respectively. A more detailed phylogenetic study is necessary to clarify the relationship between P. sordida, P. hariotii, and related species causing downy mildew on closely related hosts. To our knowledge, this is the first report of P. sordida occurring on a member of the genus Buddleja. This is also the first time that P. sordida is reported from South America.

Effects of waterlogging on the solubility and redox state of Sb in a shooting range soil and its uptake by grasses: a tank experiment

AimsThe effects of waterlogging on redox state and solubility of antimony (Sb) in a calcareous shooting range soil and its uptake by forage grass Lolium perenne L. and pasture weed Holcus lanatus L. were investigated.MethodsGrasses were grown on semi-waterlogged or waterlogged shooting range soil in a laboratory tank. The soil solution was sampled at various depths over time and analyzed for the concentrations of Sb(III), Sb(V) and total Sb, as well as other trace elements.ResultsAlthough the reduction of Sb(V) to Sb(III) under increased waterlogging time decreased Sb solubility, it increased Sb uptake by L. perenne from 1.1 to 1.7 mg kg−1 (and to a lesser extent H. lanatus), implying preferential uptake of Sb(III) by this grass. The tank showed considerable variation in redox conditions with depth and plant treatment. The soil root zone (30 cm for L. perenne and 15 cm for H. lanatus) instead of the water saturated bottom, showed the highest manganese (Mn) and iron (Fe) concentrations in solution, accompanied by a higher proportion of Sb(III) in solution than the bottom zone of the tank.ConclusionsWaterlogging can increase the risk of Sb entering the food chain from shooting range soil.

Disturbance intensity, timing and history interact to affect pasture weed invasion

Past disturbance events shape future community trajectories if their ecological legacies interact with contemporary disturbance regimes to affect recruitment and reproduction. In pastures, large-scale disturbance events can become undetectable in aboveground community components but persist as augmented weed seedbanks, suggesting disturbance history may be a predictor of weed invasion magnitude following subsequent disturbance. Using a randomized block factorial design, we investigated how soil disturbance intensity, timing and history interact to affect weed recruitment, diversity and reproduction by implementing a range of disturbance intensities in April and June 2004 in pastures of differing disturbance history. Response variables were followed for two years. Disturbance timing interacted with disturbance intensity and history to affect recruitment, with some June treatment combinations having ≥48% higher weed abundance than those in April. Relative to undisturbed controls, low to intermediate disturbance intensity facilitated recruitment by ≥117% but high intensity disturbance had highest recruitment, particularly in previously disturbed pastures (≥543% increase). In both years, weed species richness was highest in intense disturbances in previously disturbed pastures. Importantly, weed reproduction was nearly one order of magnitude higher in intense disturbance patches, especially in previously disturbed pastures, and increased through time by ≥243%. These findings indicate weed recruitment, diversity and reproductive output are seed- and microsite-limited, and that intense soil disturbance may result in high long-term weed abundance. Although moderate disturbance facilitated recruitment, reproduction here was low, suggesting modest disturbance will not appreciably increase weed abundance. The most common species were Taraxacum officinale and Poa pratensis, both of which can benefit forage-livestock production, but most establishing species were of low palatability. We recommend grassland managers explicitly integrate disturbance history into dynamic management planning, consider augmenting seedbanks with ‘desirable’ weed species to help communities recover following inevitable disturbance events and do not rely exclusively on aboveground characters to evaluate their system's vulnerability to undesirable plant establishment and persistence.

Growth, Development, and Morphological Differences among Native and Nonnative Prickly Nightshades (Solanumspp.) of the Southeastern United States

Prickly nightshades are troublesome weeds of natural habitats, pastures, feedlots, right-of-ways, and croplands. Native and nonnative invasive weedy species of prickly nightshades were compared to determine growth, development, and morphological differences. Six (Solanum bahamense, Solanum capsicoides, Solanum carolinense, Solanum dimidiatum, Solanum donianum, andSolanum pumilum) of the 18 species of prickly nightshades studied are native to the US. Two species,Solanum citrullifoliumandSolanum rostratum, are annuals; the others are perennials or are short lived perennials or annuals in northern extremes of their range in North America. Tables were developed from new and existing data to differentiate vegetative and reproductive characteristics among 18 species of prickly nightshade found in the southeastern US. In greenhouse experiments, average plant height ranged from 24 and 26 cm (9.45 and 10.24 inch) forS. carolinenseandSolanum jamaicense, respectively, to 100 and 105 cm forSolanum tampicenseandSolanum sisymbriifolium, respectively at 10 wk after emergence (WAE). By 10 WAE, the average number of leaves per plant ranged from < 10 forS. carolinenseandSolanum torvumto > 40 leaves/plant forS. rostratumandS. dimidiatum. Average number of nodes/plant main stem ranged from 11, 12, and 14 nodes inS. jamaicense, S. torvum, andS. carolinense, respectively, to 54 nodes inS. rostratum. Average plant dry weights were collected at 10 WAE and were greatest forSolanum mammosumand (> 17 g/plant) (0.6001 oz/plant) and least forS. carolinense(1 g/plant). Based on these data, nightshade growth rate and dry weight were variable among some species and variability may be a result of phenology and life cycles, annual or perennial. Plants ofS. rostratum, an annual, were relatively tall and produced high number of nodes and leaves and had the shortest period from emergence to flower among the prickly nightshades evaluated.

Allelopathic potential of extracts the from marine macroalga Plocamium brasiliense and their effects on pasture weed

Four extracts from the marine red alga Plocamium brasiliense (Greville) M.A.Howe & W.R.Taylor were prepared to identify and characterize their potential allelopathic effects on seed germination, radicle elongation and hypocotyl development of the weeds Mimosa pudica L. and Senna obtusifolia (L.) Irwin & Barneby. The four extracts were prepared in a sequence of solvents of increasing polarity: n-hexane, dichloromethane, ethyl acetate and ethanol/water (7:3). The germination bioassay was carried out at 25 °C with a 12 h photoperiod and the radicle elongation and hypocotyl development at 25 °C with a 24 h photoperiod. The dichloromethane extract showed inhibitory effects on seed germination of both plants (35 and 14%, respectively, in M. pudica and S. obtusifolia), radical germination (52 and 41.7%, respectively) and hypocotyl development (17.1 and 25.5%, respectively). Given the high sensitivity of this parameter to the potential allelopathic effects and the insufficient number of references found in the literature, these results are expected to stimulate new tests with other species of marine algae. Given the high sensitivity of the method for the detection of allelopathic potential, the species P. brasiliense emerges as a possible source of allelopathic substances against weed species. The results are attributed to the chemical composition, especially in relation to the presence of halogenated monoterpenes.

Biological utilities of Parthenium hysterophorus

Parthenium hysterophorus L. (Asteraceae) is a serious weed of pastures, wasteland and agricultural fields in world. Various problems are posed by the weed to human health, agriculture, live stock production and biodiversity. It is used as folk remedy against various afflictions. The review discusses several prominent biological utilities of P. hysterophorus as it contains several important chemical constituents mainly histamine, saponin, glucosides and triterpene (sesquiterpene) and can be of use for the purpose of biocontrol of various pathogens , for its medicinal utility and even for the purpose of food.

The Effects of Increasing Grazing Height on Establishment of Pasture Weeds in Management-Intensive Rotationally Grazed Pastures

Weeds can infest management-intensive grazed pastures and impact forage quantity, forage quality, and animal health. Common burdock, plumeless thistle, and Canada thistle are three common pasture weeds in the midwestern United States that are managed to avoid these impacts. Experiments were established at two sites to determine if increasing grazing heights from fall through summer would reduce emergence and survival of burdock, plumeless thistle, and Canada thistle seedlings. Five simulated grazing heights (5, 10, 15, and 20 cm and a not-clipped treatment) were implemented in October 2008 and repeated in May through August. Density of all species was reduced from May to September, with reductions ranging from 65 to 78%, regardless of treatment. Treatments that left at least 15 cm of residual grass had reduced densities of burdock and Canada thistle compared to the 10-cm treatment. Regression analysis demonstrated that reduction in burdock and summed planted weed density was related to increased intercepted photosynthetically active radiation from forage in April. However, total biomass yield was reduced up to 60% when grazing heights were increased from 5 to 20 cm, although differences were only observed at the fall and early spring grazing events. Relative forage quality (RFQ) was similar across treatments, except at the third grazing event for which the 15 and 20-cm treatments had reduced RFQ compared with other treatments. Results suggest that increasing grazing heights can reduce emergence and survival of burdock and Canada thistle but can also result in a reduction in forage quantity in the fall and early spring.

Optimising control of an agricultural weed in sheep-production pastures

Optimal integrated control strategies for the weed blackberry (Rubus anglocandicans) infesting sheep pastures in Australia are analysed for a range of different circumstances. A wide range of control strategies with moderate to high costs and efficacies are analysed, including chemicals, mowing, grazing goats and biological control. The study employs a stochastic dynamic simulation model and a stochastic dynamic programming model to find the optimal control strategies under different levels of infestation. Results show that the application of a biological control agent (Phragmidium violaceum) increases expected net present value (ENPV) by so little that it is not worth introducing. Results indicate that for higher initial infestation areas, the optimal control strategies include fewer control options, resulting in lower cost but also less effective control. This is because the control costs are proportional to the infestation area, so applying expensive control strategies in high infestation area has lower net benefits. When the labour cost of spraying chemicals increases and infestation area is high, it is optimal to replace chemicals with mowing. If the efficacy of chemicals increases it is optimal to use less effective and cheaper chemicals.

Cogongrass Control with Aminocyclopyrachlor in Pastures

Aminocyclopyrachlor is a new pyrimidine carboxylic acid herbicide that controls a wide range of pasture weeds. Recent research has shown that it may also have some activity on cogongrass which is an increasing problem in pastures and hayfields. Since current herbicide options for cogongrass control in pastures are non-selective, any new selective tools would be useful. We evaluated aminocyclopyrachlor applied at fall or spring timings against glyphosate and imazapyr for cogongrass rhizome, shoot, and seedhead control. At 12 months after treatment (MAT), aminocyclopyrachlor reduced rhizome biomass by 28% while glyphosate and imazapyr reduced rhizome biomass by 77 and 80%, respectively. Both fall and spring treatment timings resulted in a similar pattern of good spring control of shoot growth and flowering but new shoot growth occurred during the summer and fall. Additional aminocyclopyrachlor dose response studies indicated that repeated fall treatments inhibited cogongrass spring flowering at low rates but did not effectively control shoots even at high rates. These results indicate that aminocyclopyrachlor does provide short-term vegetative control of cogongrass and can strongly inhibit flowering the year after treatment. This ability to prevent cogongrass flowering while suppressing vegetative cover may allow aminocyclopyrachlor to be useful in certain pasture situations.

Dogfennel (Eupatorium capillifolium): Biology and Control

Dogfennel is currently the number one most commonly occurring pasture weed in Florida. Many people think it is only unsightly, but it causes significant bahiagrass yield loss and can cause dehydration when ingested by cattle. This revised 3-page fact sheet was written by B. A. Sellers and J. A. Ferrell and published by the UF Department of Agronomy, September 2011. SS-AGR-224/AG233: Dogfennel (Eupatorium capillifolium): Biology and Control (ufl.edu)

Are environmental factors important facilitators of pompom weed (Campuloclinium macrocephalum) invasion in South African rangelands?

The absence of natural enemies being keystone to the success of invasive alien plants (IAPs) can only be accepted once all the factors governing the invader and the ecosystems it invades have been established. Few studies have attempted this approach. This study reports on the relations between the invasive alien forb Campuloclinium macrocephalum (Less.) DC. (pompom weed), herbivory and the ecology of the rangelands invaded in South Africa. Eighty invaded rangelands in Gauteng Province were studied. Pompom weed herbivory was insignificant with the greatest damage being caused by native grasshoppers. Rainfall, topography and soil texture were the primary drivers of vegetation pattern. Pompom weed exhibited disturbance-mediated invasion strategies, favouring rangelands affected by non-sustainable commercial grazing practices, abandoned agricultural fields and drained wetlands. It invaded vegetation in poor condition with sward basal cover <19%. Weed density was exacerbated by high fire frequency. Vegetation susceptible to pompom weed was also invaded by other alien and native pasture weeds. The absence of natural enemies could give pompom weed a competitive advantage over native pioneer cohorts in disturbed rangelands, but is unlikely to increase fitness enabling its establishment in vegetation in good condition. Grazing strategies that promote the dominance of grass species adapted to frequent non-selective defoliation appear to restrict pompom weed better than degraded rangelands that are not utilised. Biotic resistance of rangelands to pompom weed invasion will be greatest in vegetation in good condition and under good management. The low abundance of pompom weed in rangelands in communal areas and fence-line contrasts in invaded and un-invaded road reserves warrants further investigation.

Differential effects of historical migration, glaciations and human impact on the genetic structure and diversity of the mountain pasture weed Veratrum album L.

Aim Today’s genetic population structure and diversity of species can be understood as the result of range expansion from the area of origin, past climatic oscillations and contemporary processes. We examined the relative importance of these factors in Veratrum album L., a toxic weed of mountain grasslands. Location Continental Europe. Methods Forty populations from the Asian border (Urals and Caucasus) to Portugal were studied using amplified fragment length polymorphisms (AFLPs) combined with selected plant and population measures. The data were analysed with phylogenetic, population genetic and regression methods inferring both genetic structure and diversity from geographic and ecological factors. Results Fragment frequency clines together with genetic distance clustering and principal coordinates analysis indicated an east–west direction in the genetic structure of V. album, suggesting ancient migration into Europe from a proposed Asian origin. However, the strong geographic pattern in the genetic structure, pronounced isolation by distance (R2 = 0.74) and moderate overall population differentiation (FST = 0.13) suggests high historical gene flow, possibly during glacials, and vicariance into mountainous regions during interglacials. Occurrence of V. album during the last glaciation in several areas along the periphery of the Alps and recolonization of this mountain range from both eastern and central–western areas was indicated. Genetic diversity was highest in central Europe, a pattern that did not agree with the expectations from east–west migration into Europe. Furthermore, managed habitats showed higher levels of genetic diversity compared to unmanaged habitats. Stepwise linear regression determined shoot density and soil phosphorus as the main predictors of within-population genetic diversity (R2 = 0.40). Main conclusions Our results showed that V. album retained genetic imprints of historical range expansion into Europe, although this was alleviated by the influence of climatic oscillations and contemporary processes. For example, genetic population structure was strongly affected by post-glacial vicariance while patterns of genetic diversity seemed mainly to be influenced by human land use. Our findings highlight the importance of applying a synthetic approach, testing the influence of both historical and contemporary processes on genetic structure and diversity in order to understand complex phylogeographic patterns. This may especially apply to widespread species, such as weeds. Implications of our findings for biological control are briefly discussed.

New habitats, new menaces: &lt;i&gt;Centaurea x kleinii (C. moncktonii x C. solstitialis)&lt;/i&gt;, a new hybrid species between two alien weeds

Anthropic alteration of habitat opens the door to the cohabitation of imported species that in their native range would never coexist. Centaurea solstitialis and Centaurea moncktonii are two invasive species whose natural distributions in Eurasia do not overlap. After introduction in North America, invasive spread led to overlapping distributions. Although the environmental requirements differ between the two species, the close proximity of diverse habitats (within pollinator range) has resulted in several cases of natural hybridization between the two. The result of the cross between these two distantly related species is a sterile perennial. Many of its characteristics are intermediate between its parents, but morphologically it is closer to Centaurea moncktonii (probably the maternal parent, and itself of hybrid origin). The plant could possibly become an invasive weed through clonal reproduction. The apparent maternal parent, which the hybrid may more closely resemble physiologically as well as morphologically, is a wellknown creeping weed in alpine pastures throughout Europe.

Control Techniques and Management Strategies for the Problematic Navua sedge (Cyperus aromaticus)

AbstractNavua sedge, a member of the Cyperaceae family, is an aggressive weed of pastures in Fiji, Sri Lanka, the Malay Peninsula, Vanuatu, Samoa, the Solomon Islands, and Tahiti and is now a weed of pastures and roadsides in north Queensland, Australia. Primarily restricted to areas with an annual rainfall exceeding 2,500 mm (98.4 in), Navua sedge is capable of forming dense stands, smothering many tropical pasture species. Seventeen herbicides were field tested at three sites in north Queensland, with glyphosate, halosulfuron, hexazinone, imazapic, imazapyr, or MSMA as the most effective for Navua sedge control. Environmental problems, such as persistence in soil, lack of selectivity, and movement off-site, may occur using some herbicides at the predicted 90% lethal concentration (LC90) control level rates. A seasonality trial using halosulfuron (97.5 g ai ha−1[1.4 oz ac−1]) gave better Navua sedge control (84%) by spraying in March to September than by spraying at other times (50%). In a frequency trial, sequential glyphosate applications (2,160 g ae ha−1) every 2 mo was more effective for continued Navua sedge control (67%) than a single application of glyphosate (36%), although loss of ground cover would occur. In a management trial, single applications of glyphosate (2,160 to 3,570 g ae ha−1) using either a rope wick, ground foliar spraying, or a rotary rope wick gave 59 to 73% control, whereas other treatments (rotary hoe, 3%; slashing, −13%; crushing, −30%) were less effective. In a second management trial, four monthly rotary wick applications were much more effective (98%) than four monthly crushing applications (42%). An effective management plan must include the application of regular herbicide treatments to eliminate Navua sedge seed being added to the soil seed bank. Treatments that result in seed burial, for example, discing, are likely to prolong seed persistence and should be avoided. The sprouting activity of vegetative propagules and root fragmentation also needs to be considered when selecting control options.

Biological Flora of the British Isles: Cirsium arvense (L.) Scop.

Summary 1. This account presents information on all aspects of the biology of Cirsium arvense that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, conservation and management. 2. Cirsium arvense, creeping thistle (Californian thistle, Canada thistle), one of the world’s most troublesome and persistent weeds, is native to Europe and the east northern hemisphere but introduced to North America and the southern hemisphere. Latitudinal distribution north or south is limited by low winter and summer maximum temperatures and by a long day requirement for flowering. 3. Cirsium arvense is believed to have originated in the temperate Middle East and its spread has closely followed human migration and agricultural activity. Colonization of new sites is by seed which establishes best in bare or disturbed ground, mirroring its prehistoric ecology as an opportunist pioneer of bare ground and organic residues. It is now a widespread and scheduled agricultural weed in both arable crops and pastures and also a constituent in over 70 British (National Vegetation Classification) plant communities, occurring mainly on waste neglected land, roadsides, hedgerows and disturbed areas. 4. Its presence in crops leads to yield losses and in pastures seriously interferes with utilization due to the deterrent effect of the leaf spines on grazing animals. This has led to a long history of investigation into control measures: mechanical, chemical, biological and integrated, which are summarized. Combination treatments and integrated control have achieved some success but effective control requires follow‐up procedures over a number of seasons. Climate change studies suggest C. arvense could grow better and be more difficult to control in future. 5. Success and persistence derives from an extensive, far‐creeping and deep rooting system which ensures survival and rapid vegetative spread under a wide range of soil and management conditions, and a means of escape from sub‐aerial control treatments. New adventitious buds capable of shoot development can arise at any point along the horizontal roots, even when these are cut into pieces or damaged. Root buds remain dormant until released from dormancy through damage or decay of the aerial shoots. Carbohydrate root reserves, stored in swollen cortical tissue, fall to a minimum just before flowering and are then replenished for perennation during the subsequent winter. Strategies for control aim to treat the plant when root carbohydrate reserves are at a minimum, to exhaust these reserves and to prevent replenishment for further perennation. 6. Balanced against its difficulty as a weed, C. arvense has significant conservation value as a host to numerous insects, many attracted by copious and accessible nectar and strong flower fragrance. It is however a strong competitor to low‐growing plants in natural communities. 7. Cirsium arvense is dioecious and for flowering has a 14–16 h day length requirement. Seed set is successful if male and female plants are no more than 50–90 m apart to allow insect pollination. In spite of the conspicuous wind‐borne pappus, this rarely carries a seed which normally falls near the parent plant. The flower heads and other plant parts are regularly attacked by numerous insects and less frequently by diseases. 8. Germination of seed is mainly during the high temperatures of early summer in the year following dispersal and establishment is most successful in open areas. Development of the branching root system and vegetative spread follow rapidly. 9. A combination of dioecy and vegetative reproduction has resulted in the maintenance of genotypic and genetic diversities within populations allowing efficient colonization and persistence, contributing greatly to success in the species.

Seedling emergence and early survival of Carduus spp. in three habitats with press and pulse disturbances1

Abstract Species may reach novel habitats through dispersal but nevertheless be restricted in their establishment at different life history stages by local conditions. However, disturbances may alter local conditions within a habitat and hence change establishment outcomes. We investigated the establishment of two non-native weeds of pastures and roadsides, Carduus nutans and Carduus acanthoides, in three contiguous habitats (abandoned pasture, forest edge, and forest) under three disturbance treatments: no disturbance, initial disturbance only (pulse disturbance; i.e., temporary), and initial disturbance with weeding (press disturbance; i.e., sustained). For both species, establishment was not limited by seedling emergence in any habitat, although emergence in the pasture and forest edge relied heavily on disturbance. Combined emergence and survival in the pasture and forest edge were also significantly increased by disturbance, but disturbance had no effect in the forest, where seedlings were unable to ...

Prospecção química de compostos produzidos por Senna alata com atividade alelopática

Senna alata é uma espécie daninha frequente em pastagens da região amazônica. Suas folhas apresentam propriedades medicinais capazes de influenciar a germinação e o desenvolvimento de outras plantas. Objetivou-se neste estudo a prospecção química e a avaliação da atividade alelopática dos compostos presentes nas folhas de S. alata. O material vegetal foi seco, triturado e submetido à extração exaustiva, com solução água:metanol (3:7). O extrato obtido foi então fracionado por coluna cromatográfica por via úmida. As frações mais puras foram submetidas à espectroscopia de Ressonância Magnética Nuclear, para determinação das fórmulas estruturais das moléculas. Na avaliação dos efeitos das substâncias químicas isoladas, utilizaram-se as concentrações de 50, 100, 150 e 200 ppm, tendo como eluente solução hidrometanólica (3:7 v/v). As frações foram adicionadas em placas de Petri e seus efeitos avaliados sobre a germinação de sementes e o alongamento da radícula e hipocótilo de três espécies daninhas de áreas de pastagens: Mimosa pudica, Senna obtusifolia e a própria S. alata. Os compostos com atividade alelopática encontrados em folhas de S. alata pertencem à classe dos flavonoides glicosilados, cujo núcleo aromático é um kaempferol, e causaram maior inibição sobre o crescimento da radícula e sobre a germinação de S. obtusifolia e M. pudica. Já os efeitos autotóxicos desse composto são pouco significativos para o desenvolvimento da plântula e nulos sobre a germinação.