Establishment of Senecio jacobaea L. from seed in grassland and in boxed swards

The effects of a high or a low level of nitrogen fertilizer and the presence or absence of a grass-suppressing herbicide (propyzamide) upon the establishment of Senecio jacobaea L. (common ragwort) in three sizes of bare soil patch in a perennial ryegrass sward (Lolium perenne L.) were investigated both in boxed swards and in the field.     

Selectivity factors relative to asulam for Senecio jacobaea L. control in Medicago sativa L. II. Metabolism*

Metabolism of ¹⁴C asulam applied with surfactant was studied in Senecio Jacobaea L. and Medicago saliva L. Plants were harvested 48, 96 and 144 h after treatment and extracted with acetone. The aqueous residue of the acetone extract was partitioned with ethyl acetate and the ¹⁴C activity in the ethyl-acetate phase, the aqueous phase and the plant residue was determined. A significant amount of ¹⁴C activity was not extracted by acetone from either species. This amount increased with time in M. sativa but remained relatively constant in S. jacobaea. More ¹⁴C activity was found in the aqueous phase than in the ethyl-acetate phase in M. sativa while the reverse was true in S. jacobaea. Significantly lower amounts of free asulam were identified in M. sativa than in S. jacnbaea. Still, results of these and previous studies on retention, uptake and translocation do not completely account for differences in sensitivity found in greenhouse and field applications. Other possible explanations for selectivity are discussed.     

Population flux and mortality in a ragwort (Senecio jacobaea L.) infestation

Actuarial data on the progress through the life-cycle and the death of individual plants of Senecio jacobaea in permanent pasture were obtained over a period of one year by repeated mapping of all the plants in twenty permanent quadrats. The data were used to construct a model of population flux and mortality in a hypothetical population in which germination, maturation and death were constant from year to year and equal to those in the real population in the year of study. In the hypothetical population 57% of all plants died as seedlings. 35% as vegetative rosettes and 8% immediately after flowering. Of plants which flowered in the first 2 years or survived into a third year 8% were annuals or winter annuals, 39% were biennials and 53% were perennials.     

Control of Senecio jacobaea L. (ragwort) by autumn or spring herbicide application

A range of herbicides was sprayed in October 1976 or May 1977 on grassland infested with S. jacobaea. Control, measured by reduction in the number of flowering stems in July 1977, was extremely good with all herbicides, October spraying gave 99% control of 5. jacohaea and is provisionally recommended for grassland which is to be cut for silage. Lutte contre Senecio jacobaea L. (séneçonjacobée) parun traitement herbicide d'automne ou de printemps Une série d'herbicides ont été appliqués en octobre 1976 ou en mai 1977 sur des herbages infestés de séneçon jacobée. L'éfficacité, mesurée par la réduction du nombre de tiges fleuries en juillet 1977, a été extrêmement bonne avec tous les herbicides. Le traitement d'octobre a détruit 99% de S. jacobaea; il est provisoirement recommande pour les prairies de fauche dont la recolte doit etre ensilee. Bekümpfung von Senecio jacobaea L. (Jakohs-Kreuzkraut) durch Herbizidanwendung im Herbst oder Frühjahr Auf Grünland, das mit Jakobs-Kreuzkraut verseucht war, wurde eine Reihe von Herbiziden im Oktober 1976 oder im Mai 1977 eingesetzt. Die Bekämpfung, gemessen am Rückgang blühender Pflanzen im Juli 1977, war mit alien Herbiziden äusserst zufriedenstellend. Die Spritzung im Oktober ergab für S. jaco baea einen Bekämpfungsgrad von 99% und wird für Grünland, das für Silagegewinnung genutzt wird, vorläufig empfohlen.     

Changes in the incidence of ragwort (Senecio jacobaea L.) infestation of grassland over a 4-year period in NE Scotland

A roadside survey of 4749 fields in eight areas of NE Scotland was conducted annually from 1979 to 1982. The proportion of grass fields infested with ragwort remained steady at 18–19% from 1979 to 1981 but fell to 13·5% in 1982. This fall resulted from fewer fields becoming newly infested and from more fields that had remained in grass ceasing to be infested. The proportion of infested fields remaining in grass that showed a reduction of two or more points on a 0–5 logarithmic scale of ragwort density (a possible indication of the frequency of control measures) was 24·0% in 1979–1980, 21·7% in 1980–1981 and 36·3% in 1981–1982. The incidence of ragwort infestation was consistently higher in some areas than in others and was not related to the proportion of arable crops. The change in incidence of infestation varied greatly between different areas, as did the proportion of infested fields whose score on the 0–5 scale fell by two or more points. In 1979–1980 and 1980–1981 this proportion had to exceed 22% to effect a net decrease in the incidence of infestation in an area, but in 1981–1982 no relationship was evident between these two measures of change. The incidence of infestation in all areas increased with increasing sward age but one area (Moray and Nairn) had a much higher proportion of young grass infested than any of the others. Over 99% of ragwort infestations consisted of Senecio jacobaea, infestations of S. aquatints Huds. being rare.     

Selectivity factors relative to asulam for Senecio jacobaea L. control in Medicago sativa L. I. Retention,uptake and translocation*

Senecio jacobaea L. and Medicago sativa L. plants grown in a glasshouse were treated with foliar applications of aqueous solutions of asulam. Retention on foliage, uptake and translocation were measured in both species. Retention was greater in S. jacobaea than in M. sativa when no surfactant was added and similar when surfactant was added. Addition of surfactant modified spray distribution and increased asulam uptake in M. saliva but did not in S. jacobaea. S. jacobaea translocated over twice as much asulam from the treated area as M. sativa. These data suggest that surfactant should not be added for maximum selectivity. Differences in species response to asulam treatments are partially, but not entirely, explained by differences in retention, uptake and translocation.     

Effect of 2,4-D on the water-soluble carbohydrate content of ragwort (Senecio jacobaea L.) leaves

Leaves of Senecio jacobaea plants sprayed with 2,4-D had a higher water-soluble carbohydrate (WSC) content than unsprayed leaves 9–14 days after spraying. Insofar as WSC is a measure of palatability, this implies an increased risk of Senecio poisoning in grazing cattle for more than 14 days after spraying with growth regulator herbicides. Total unsaturated pyrrolizidine alkaloid content may also be increased by 2,4-D, making the plant more toxic.     

Can the occurrence of Senecio jacobaea be influenced by management practice?

Senecio jacobaea is a poisonous weed in grasslands of various countries (e.g. Great Britain, New Zealand, Central European states) and the further spread of the species into farmland must be prevented. To assess the influence of management practice and site conditions on the occurrence of S. jacobaea, we conducted a survey in the northern and central part of Switzerland. Botanical assessments were carried out on grassland plots with S. jacobaea occurrence and on neighbour plots without S. jacobaea. For these plots, we analysed the soil nutrients and the details of management practice, such as type and intensity of management and fertiliser application. The most important factors influencing the occurrence of S. jacobaea were related to management: There was a high risk for the occurrence of the species on parcels with low nitrogen fertilisation, continuous‐extensive grazing (set stocking) and a very open sward. Senecio jacobaea was not present in intensively managed meadows cut more than twice per year. As an exception, with a high propagule pressure from the vicinity, S. jacobaea was also found in intensively grazed pastures and in meadows of moderate management intensity (two cuts). We conclude that long‐term control of S. jacobaea can best be achieved by avoiding sward damage and by preventing the species’ seed formation in the pasture and local vicinity.     

Differential growth between and within triazine-resistant and triazine-susceptible biotypes of Senecio vulgaris L.

A comparative study of differential growth, time to flowering and resource allocation was made on three triazine-resistant and five susceptible populations of Senecio vulgaris grown in the absence of herbicides under spaced non-competitive conditions. The results show that: (1) the vegetative and total biomass production of all susceptible populations was greater than that of the resistant populations and (2) that many, but not all, of the susceptible populations showed greater seedling dry weight, earlier flowering, greater reproductive dry weight and greater reproductive effort as compared with the resistant populations. Estimates of between-population differences within a given biotype indicated that the resistant populations from all three widely separated locations were homogeneous in their growth response. The five susceptible populations were more dissimilar, exhibiting a broader range of response in growth parameters. Differences de croissance entre les biotypes de Senecio vulgaris L. sensibles ou résistants aux triazines Une étude comparative des differences en ce qui concerne la croissance, l'époque de floraison et le potentiel de ressources a été réalisée sur trois populations de Senecio vulgaris résistantes aux triazines et cinq populations sensibles, cultivées en l'absence d'herbicides, dans des conditions d'espacement non compétitives. Les résultats montrent que: (1) la production végétative et la biomasse totale de toutes les populations sensibles ont été plus élevées que celles des populations résistantes; (2) beaucoup des populations sensibles, mais non la totalité, avaient un poids sec de plantules plus élevé, une floraison plus précoce, un poids sec reproductif plus grand et manifestaient une meilleure aptitude à la reproduction que les populations résistantes. Les estimations des differences entre populations à l'intérieur d'un même biotype ont montré que les trois populations résistantes, qui provenaient de trois stations fort éloignées les unes des autres, étaient homogénes quant a leur croissance. Les cinq populations sensibles étaient plus disparates: elles ont donné un éventail de réponses plus large entre les paramétres de croissance. Unterschiedliches Wachstum zwischen und innerhalb Triazin-resistenten und Triazin-empfindiichen Biotypen von Senecio vulgaris L. Vergleichende Untersuchungen über unterschiedliches Wachstum, über den Blühzeitpunkt und die Herkunft wurden mit drei Triazin-resistenten und fünf empfindlichen Populationen von Senecio vulgaris, die in Abwesenheit von Herbiziden und ohne Konkurrenz gewachsen waren, durchgeführt. Die Resultate zeigen. dass I. die oberirdische und die Gesamt-Biomassepro-duktion bei alten empfindlichen Populationen grösser war als diejenige der resistenten Populationen und 2., dass viele, aber nicht alle der empfindlichen Populationen, ein höheres Keimlingstrockengewicht, früheren Blühzeitpunkt, grösseres Trockengewicht der Vermehrungsorgane und höhere Repro-duktionsraten aufwiesen als die resistenten Populationen. Schätzungen von Unterschieden zwischen den Populationen innerhalb eines gegebenen Biotyps deuten darauf hin, dass die resistenten Populationen, alle drei von weit auseinander-liegenden Orten stammend, bezüglich ihres Wachstums homogener reagierten. Die fünf empfindlichen Populationen wiesen eine grössere Variabilität in ihren Wachstumsparametern auf.     

Survival and growth of seedlings of Rumex obtusifolius L. and Rumex crispus L. in newly sown grassland

The survival and growth of seedlings of Rumex obtusifolius L. and Rumex crispus L. were investigated from 1982 to 1984. A sward was established by the sowing of seeds of Dactylis glomerata and Trifolium repens and managed under two cutting frequencies. Five hundred seeds of each Rumex species were sown m^?2. The total number of emergent seedlings of each Rumex species over two seasons was 230–360 m^?2. About 85% of them emerged within 3 months of sowing. Both Rumex species showed the same pattern of survivorship. Survival was clearly enhanced by frequent cutting during the second season. About 20% of the emerged plants survived through to the third season. Plants that emerged during the first season only flowered during the second season. The flowering percentage of total surviving plants was significantly higher in R. obtusifolius than in R. crispus. Rumex obtusifolius was higher in dry matter of aerial parts defoliated during the second season and more individual plants survived through to the third season than for R. crispus. Moreover, dry matter production of grass and clover was depressed by 25–30% in mixtures with R. obtusifolius. compared with production in mixtures with R. crispus.     

Evolution of resistance to simazine in Senecio vulgaris L.

Fruits were collected from populations of S. vulgaris growing on commercial fruit farms and progenies were tested for susceptibility to simazine. The five least susceptible populations, which originated from sites where simazine had been applied annually for periods ranging from six to ten years, were subjected to two generations of artificial selection for simazine resistance. Two control populations which originated from unsprayed sites were treated similarly. One population originating from Malpas, Cheshire showed a significant response to selection. The simazine resistance of the other six populations was not improved by artificial selection. Selected progenies of the Malpas population were completely unaffected by simazine at 2.8 kg ha^?1. The potential for evolution of resistance to simazine in S. vulgaris is discussed and the effects of ecological and genetic factors on the rate of evolution are assessed.     

Growth, development and nutrient accumulation in Senecio vulgaris L. and Chenopodium album L.

Growth, development and nutrient accumula tion in Chenopodium album and Senecio vulgaris grown in pure and mixed stands were investi gated through several experiments conducted under glasshouse conditions. Results showed that the two weeds were different in their growth, development and tissue concentration and accu mulation of mineral elements. The mean concen trations of nitrogen, phosphorus, potassium, calcium and magnesium in shoots of C. album were higher than those of S. vulgaris, while root concentrations of nitrogen, potassium and mag nesium were lower for C. album. Marked dif ferences between the two weed species in their responses to different potassium levels were found. C. album had a high specific requirement for potassium while the reverse was true for S. vulgaris. The competitive ability and accumula tion of nutrients by C. album appeared to be greatly dependent on the availability of high potassium levels in the media.     

Chemical control of marsh ragwort (Senecio aquaticus Huds.) in established grassland

Infestations of marsh ragwort, Senecio aquaticus Huds., in established ley grassland were sprayed at the rosette stage in April or May with MCPA, 2,4-D, asulam or a 2,4-D asulam mixture. All treatments gave better control in the year after spraying than in the year of spraying. The most effective herbicide was 2,4-D ester at 1–68 or 1–12 kg/ha with or without the incorporation of asulam at 1–12 kg/ha. MCPA at 1–68 kg/ha was less effective, especially in the year of spraying and asulam alone at 1-12 kg/ha gave consistently the poorest control of all treatments. Spraying in May gave better control in the year of spraying than April application, but in the year after spraying date of application made no difference to the degree of control. S. aquaticus at the various sites differed in general susceptibility to herbicides in the year of spraying, but in the year after spraying these differences disappeared.     

Possible rôle of allelopathy in the competition between tomato, Senecio vulgaris L. and Chenopodium album L.

Summary. The allelopathic effect of Chenopodium album L. (fat-hen) and Senecio vulgaris L. (groundsel) on tomato ( Lycopersicon esculentum Mill cv. Ailsa Craig) plants was investigated under glasshouse conditions. A new technology was used to separate competitive from allelopathic effects. These experiments suggested that C. album had an effect on tomato through allelopathy. C. album leach-ates significantly reduced shoot fresh and dry weights and the accumulation of N, P, K, Ca and Mg of tomato shoots. No effect was found on the quantities of these elements in tomato roots. Leachate of five plants of C. album per pot was sufficient to reduce tomato growth. Addition of 10 or 20 g kg⁻¹ of C. album dried shoots to the soil mixture significantly decreased the fresh and dry weights of tomato plants. S. vulgaris leachates did not show significant effects on the growth or nutrient accumulation of tomato plants.     

Competitive growth of Echium plantagineum L. and Trifolium subterraneum L.

Echium plantagmeum is a widespread, persistent, and often dominant votunteer species in southern Australia. In pastures. it commonly grows with Trifolium subterraneion. This paper describes glasshouse studies investigating the effects of soil fertility. plant density. sward composition, defoliation frequency. and delayed estabilishment of t. subserraneum on the growth of E. pluntagineum and T. subterraneum when grown in pure swards and in mixtures. Generally. herbage production of swards was increased by the presence of E. plantagineum. the addition of nutrogen and phosphorus fertilizers, and increasing density, It was decreased by defoliation. E. pluntagineum plants generally produced more shoots and roots than did T. subterraneum. Both species responded. E. plantiagineum generally more than T. subterraneum. to added phosphorus and nitrogen fertilizers. Both species showed a non-linear reduction in plant size as plant density of the sward was increased. especially during early growth. E. plantagineum was, however. more plastic in its response to density than T. subterraneum. Defoliation reduced the plant weight of both species. more for E. plantagineum than for T. subterraneum. In mixtures. there was little competition between the two species during early growth. when swards were defoliated and when both species established at the same time. T. subserraneum was, howerver. sometimes suppressed during later growth if swards were undefoliated. if soil fertility was high. and if E. plantaginteum established before t. subserraneum. Such competition appeared to be between shoots rather than between roots. In the field. E. plantagineum is likely to be fovoured in undergrazed situations, where soil fertility is high and when false or early seasonal breaks allow it to establish earlier than t. subterruneum. Its high productivity under a wide range of pasture situations - especially in autumn and winter when pasture availability is ofter critically low and the fact that it is relatively nutritious and readily eated by stock suggest that it is a useful pasture species.     

Inter- and intraspecific competition of fat-hen (Chenopodium album L.) and groundsel (Senecio vulgaris L.)

The responses of Chenopodium album L. and Senecio vulgaris L. to inter- and intra-specific competition were investigated in both additive and replacement series experiments under glasshouse conditions. When grown with tomato the two weed species had similar effects on shoot dry weight at low densities but 5. vulgaris showed more competitive effect at higher densities. Weed density did not affect the concentrations of N, P, K, Ca or Mg in tomato shoots but dry matter and total amounts of nutrients were reduced increasingly with the increase in density of both weeds. The concentration of nutrients in the shoots of the weeds was not affected by density but dry matter yield and total nutrient accumulation per plant fell as the density increased. The concentrations of N, P, K and Mg in the shoots were higher in C. album than S. vulgaris but that of Ca was lower. In a replacement series experiment the two weed species behaved differently. With C. album, both dry matter yield and total nutrient per plant were reduced as its proportion in the mixture increased but, with S. vulgaris, dry matter per plant increased with its proportion in the mixture. One plant of C. album grown with five S. vulgaris gave a higher shoot dry weight than when present in higher proportions or in a pure stand. In a pure stand of six plants the shoot dry weight per plant of C. album was 26% of that of one plant grown with five S. vulgaris. In comparison, the shoot dry weight of one S. vulgaris in pure stand was 120% of that of one plant grown with five C. album. The reduction in growth of C. album was associated with a greater reduction in its ability to accumulate K than other elements. The competition index (CI) of C. album in terms of dry weight decreased with its proportion in the mixture but the reverse was true for S. vulgaris. The relative competitive ability index (RCAI) of C. album was almost 3–5 times that of S. vulgaris. The results showed that differences between the weeds in inter- and intraspecific competition were closely related to the growth of their root systems. Compétition inter- et intraspécifique du chénopode (Chenopodium album L.) et du senecon (Senecio vulgaris L.) Les réponses du chénopode (Chenopodium album L.) et du sénecon (Senecio vulgaris L.) à la compétition inter- et intra-spécifique ont étéétudiées en serre lors d'expériences à séries additives ainsi qu'à séries de remplacement. Quand elles étaient cultivées avec des tomates, les deux mauvaises herbes avaient des effets similaires sur la matière sèche des parties aériennes à faibles densités, mais S. vulgaris se montrait plus compétitif à fortes densités. La densité des mauvaises herbes n'affectait pas les concentrations en N, P, K, Ca et Mg dans les parties aériennes de la to-mate. Par contre, la matière séche et les quantités totales de nutriments étaient d'autant plus réduites que la densité des deux mauvaises herbes était élevée. La concentration en nutriments dans les parties aeriennes des mauvaises herbes n'était pas affectée par leur densité mais le rendement en matière sèche et l'accumulation totale de nutriments par plante décroissaient lorsque la densité augmentait. Les concentrations en N, P, K et Mg dans les parties aériennes étaient plus élevées chez C. album que chez S. vulgaris mais celle de Ca était plus basse. Dans une expérience à séries de remplacement, les deux espèces de mauvaises herbes se comportaient différemment. Chez C. album, le rendement en matière sèche ainsi que la quantité totale de nutriments par plante diminuaient lorsque sa proportion dans le mélange augmentait mais, chez S. vulgaris, la matière sèche par plante augmentait avec sa proportion dans le mélange. Un pied de C. album cultivé avec 5 pieds de S. vulgaris produisait davantage de matière sèche aérienne que lorsqu'il était présent en proportions plus importantes ou en culture pure. Dans une culture pure de 6 plantes, la matière sèche aérienne par pied de C. album représentait 26% de celle d'une plante cultivée avec 5 pieds de S. vulgaris. En comparaison, la matière sèche aérienne par pied de S. vulgaris en culture pure représentait 120% de celle d'une plante cultivée avec 5 pieds de C. album. La réduction de croissance de C. albumétait associée à une réduction de sa capacitéà accumuler K, qui était plus marquée que pour les autres éléments. L'Indice de Compétition de C. album en terme de matière sèche diminuait avec sa proportion dans le mélange, mais l'inverse était vrai pour S. vulgaris. L'Indice Relatif d'Aptitude à la Compétion de C albumétait presque 3,5 fois plus élevé que celui de S. vulgaris. Les résultats montraient que les différences entre les mauvaises herbes en ce qui concerne la compétition inter- et intra-spécifique étaient étroitement liées à la croissance de leur système racinaire. Inter- und intraspezifische Konkurrenz des Weißen Gänsefußes (Chenopodium album L.) und des Gemeinen Greiskrauls (Senecio vulgaris L.) Die inter- und intraspezifische Konkurrenz von Chenopodium album und Senecio vulgaris wurde sowohl in additivem als auch substitutivem Versuchsansatz im Gewächshaus untersucht. In Mischbeständen mit Tomate hatten beide Unkrautarten bei geringer Pflanzendichte eine ähnliche Wirkung auf die Sproß-Trockenmasse, doch Senecio vulgaris war bei hohen Dichten konkurrenzstärker. Die Unkrautdichte hatte keinen Einfluß auf den N-, P-, K-, Ca- oder Mg-Gehalt der Tomatensprosse, aber die Trockenmasse und der gesamte Nährstoffgehalt nahm mit zunehmender Dichte der beiden Unkräuter ab. Der Nährstoffgehalt in den Sprossen der Unkräuter wurde durch die Pflanzendichte nicht beeinflußt, aber die Trockenmasse und der gesamte Nährstoffgehalt nahm mit zunehmender Dichte der beiden Unkräuter ab. Der N-, P-, K-und Mg-Gehalt war bei Chenopodium album höher als bei Senecio vulgaris, doch der Ca-Gehalt war niedriger. In einem substitutiven Versuchsansatz verhielten sich die beiden Unkrautarten verschieden. Bei Chenopodium album wurden sowohl die Trockenmasse als auch der gesamte Nährstoffgehalt pro Pflanze im selben Maße reduziert, wie sein Verhältnis im Mischbestand zunahm; bei Senecio vulgaris stieg die Trockenmasse pro Pflanze mit seinem Anteil im Mischbestand an. Chenopodium album entwickelte bei einem Mischungsverhältnis von l Pflanze zu 5 Senecio-vulgaris-Pflanzen eine höhere Sproß-Trockenmasse als bei höheren Verhältnissen oder im Reinbestand. In einem Reinbestand von 6 Pflanzen war bei Chenopodium album die Sproß-Trockenmasse pro Pflanze 26 % der Masse einer Pflanze, die mit 5 Senecio-vulgaris-Pflanzen wuchs. Bei Senecio vulgaris dagegen war die Sproß-Trockenmasse pro Pflanze im Reinbestand 120 % der Masse einer Pflanze, die mit 5 Chenopodium-album-Pflanzen wuchs. Mit der Wuchshemmung ging bei Chenopodium album eine Abnahme seiner Fähigkeit, K und andere Nährstoffe aufzunehmen, einher. Der Konkurrenzindex von Chenopodium album, bezogen auf die Trocken-masse, nahm mit seinem Anteil in den Mischbeständen ab, während bei Senecio vulgaris das Gegenteil der Fall war. Die relative Konkurrenzfähigkeit von Chenopodium album war fast 3.5mal so groß wie die von Senecio vulgaris. Die Unterschiede der inter- und intraspezifischen Konkurrenz der beiden Unkrautarten stand in enger Beziehung zur Entwicklung ihres Wurzelsystems.     

psbA mutation (Asn266 to Thr) in Senecio vulgaris L. confers resistance to several PS II-inhibiting herbicides

DNA sequence analysis of the psbA gene encoding the D1 protein of photosystem II (PS II), the target site of PS II-inhibiting herbicides, identified a point mutation (Asn266 to Thr) in a bromoxynil-resistant Senecio vulgaris L. population collected from peppermint fields in Oregon. Although this mutation has been previously reported in Synechocystis, this is the first report of this particular point mutation in a higher plant exhibiting resistance to PS II-inhibiting herbicides. The resistant population displayed high-level resistance to bromoxynil and terbacil (R/S ratio 10.1 and 9.3, respectively) and low-level resistance to metribuzin and hexazinone (R/S ratio 4.2 and 2.6, respectively) when compared with the susceptible population. However, the population was not resistant to the triazine herbicides atrazine and simazine or to the urea herbicide diuron. A chlorophyll fluorescence assay confirmed the resistance levels and patterns of cross-resistance of the whole-plant studies. The resistant S. vulgaris plants produced fewer seeds. Differences in cross-resistance patterns to PS II-inhibiting herbicides and the difference in fitness cost could be exploited in a weed management program.     

Clonal growth and fragment regeneration of Rumex obtusifolius L.

Clonal growth and fragment regeneration of Rumex obtusifolius L. were analysed in two dif ferent studies. Clonal growth system was des cribed by a morphological study of underground structure of different-aged individuals, using maximal branching order in the stem system as an age estimator. Glasshouse experiments were conducted, testing the regenerative capacity of different below-ground parts and the estab lishment of above root-collar fragments planted at different depths under contrasting water regimes. Results showed the presence of a ‘phalanx’ type clonal growth system in grassland populations of Rumex. The main structure in volved in clonal growth proved to be the stem system; the region above the root collar was also the only part able to regrow after damage. Stem fragment regeneration occurred to depths of 15 cm, but was prevented in soils maintained at waterlogging and field capacity. The significance of these results in relation to nonchemical con trol of Rumex populations in grasslands is discussed.