bluuebunny/crossref_metadata_2025 huggingface dataset:
Studying the population dynamics of weeds
Authors: FERNANDEZ‐QUINTANILLA C.
Published: July 2006

Studies of weed population dynamics may be conducted at various levels of complexity. The simplest level involves monitoring a single component of the population throughout several seasons, determining population trends and rates of change. This approach is highly descriptive and, therefore, has a low predictive value. However, it may be useful to evaluate the long‐term effects of various control techniques. In demographic studies, the life‐cycle of the species is divided into various functional stages and the number of individuals present in each stage is monitored throughout the season. From these data, various demographic parameters can be calculated. Population changes through time can be predicted by simulation techniques. This approach offers a practical compromise between the simplicity of long‐term studies and the high analytical and predictive power of more complex analyses. In mechanistic analysis, the population is broken down into a large number of components connected by various physiological und ecological processes. Detailed studies are conducted on each of these individual processes, determining their relationships with environmental factors. The data obtained are integrated into computer models in order to predict the dynamics of the population under various situations. Often the inquirer is confronted by the problem of choice of level of complexity at which it is necessary to study the populations concerned. This choice may depend on the goal of the study, the resources and experience of the people etc. Making the right choice is not always easy, but is essential for the success of any research programme.
Herbicide bioassay
Authors: STREIBIG J. C.
Published: July 2006

One of the most commonly used techniques to assess the efficacy of herbicides is to apply to the principle of bioassays. A bioassay is defined as an experiment for estimating the potency of a herbicide by analysis of the reaction that follows its application to living organisms. The analysis of variance is central to most applications of statistical methods in the analysis of experiments. This is true for bioassay, but perhaps the fundamental importance of regression and related concepts is here particularly apparent. The purpose of this presentation is to quantify herbicidal effects of applying non‐linear regression models to herbicide bioassays, and to demonstrate how some general hypotheses about the mode of action of the assayed herbicides can be incorporated into the regression models. The validity of herbicide bioassay data is discussed in view of the general principles used in bioassay in other biological sciences.
Broomrape (Orobanche spp.) control with ethylene dibromide and chloropicrin
Authors: JACOBSOHN R. , KELMAN Y. , SHARED RACHEL , KLEIN L.
Published: July 2006

Summary: Résumé: Zusammenfassung

Ethylene dibromide effectively controlled Orobanche crenata Forsk. and O. cernua Loefl. but was not effective against O. aegyptiaca Pers. and O. mutelii F. Schultz. Chloropicrin was considerably less effective than ethylene dibromide. Mixtures of both compounds did not result in improved broomrape control but nonetheless had a positive effect on crop yield.

Destruction des Orobanches avec du dibromure d'ethylène et de la chloropicrine

Le dibromure d'éthylène a été efficace contre Orobanche crenata Forsk et O. Cernua Loefl, mais non efficace contre O. aegyptiaca Pers, et O. mutelii F. Schultz. La chloropicrine est beaucoup moins efficace que le dibromure d'ethylène. Les mélanges des deux matières actives n'ont pas amélioré l'efficacité sur orobanches mais néanmoins ont eu un effet positif sur le rendement de la culture.

Bekämpfung von Orobanche‐Arten mit Ethylendi‐bromid und Chlorpikrin

Mit Ethylendibromid konnten Orobanche crenata Forsk. und O. cernua Loefl., aber nicht O. aegyptica Pers. und O. mutelii F. Schultz bekämpft werden. Chlorpikrin war beträchtlich weniger wirksam. Mischungen der beiden Wirkstoffe ergaben keine bessere Wirkung, beeinflussten aber den Ertrag der Kulturpflanzen positiv.
Transplant survival of Rumex obtusifolius L. and Rumex crispus L. in three old reseeded grasslands
Authors: HONGO A.
Published: July 2006

A transplant experiment was performed to compare the survivorship of Rumex obtusifolius L. and Rumex crispus L., and also to determine the environmental characteristics of grasslands seriously colonized with R. obtusifolius. One‐month‐old seedlings of each Rumex species were transplanted into three old reseeded swards with different infestation levels of R. obtusifolius plants. Rumex crispus was absent from all swards. Their survival was monitored at monthly intervals for 4 years (May 1982 to May 1986). The mortality of R. obtusifolius was greater in the third and fourth years in all swards, less than 2% of the phytometers being alive in the fifth spring. The number of R. crispus transplants declined more gradually in the course of the experiment and 4–24% of the phytometers still survived by the end of the experiment. This suggests that R. obtusifolius plants colonized in sown grasslands in the cool‐climate region have a comparatively short life expectation of 3–4 years. Mortality rate, growth in size and flowering percentage tended to vary significantly between sites: higher in more productive swards. In years 2 and 3 there were seven‐fold differences in mean dry matter weights of plants that produced an inflorescence and those that remained in a vegetative phase. The mortality of transplants was not size dependent in either Rumex species. Phytometers died at random irrespective of the individual sizes.
Dicotyledonous weeds of spring cereal crops in north‐east Scotland
Authors: SIMPSON M. J. A. , CARNEGIE HAZEL M.
Published: July 2006

A survey of dicotyledonous weeds of spring cereals was conducted prior to herbicide application in 1985 in six districts of north‐east Scotland, which involved a total of 113 fields. Results were similar to those from an earlier survey in 1973. The main species remained the same but in four of the six districts, total weed densities were lower. Stellaria media was the most common species except in Upper Banffshire and Morayshire where Galeopsis spp. and Polygonum aviculare, respectively, were predominant. The main changes apparent were a decline of Spergula arvensis and Polygonum persicaria, and an increase in Matricaria perforata and Viola arvensis in several districts.
Quantitative bioassays for determining residues and availability to plants of sulphonylurea herbicides
Authors: GÜNTHER P. , RAHMAN A. , PESTEMER W.
Published: July 2006

A bioassay procedure for quantitative determination of sulphonylurea herbicides is described. Turnips (Brassica rapa) were found very suitable as test plants and gave results within 10 days. Six sulphonylurea compounds were investigated for their activity in three widely differing soils. The potential availability to plants was calculated from the dose‐response curves of vermiculite (non‐sorptive substrate) and the corresponding ED50‐values of the soils. The dose‐response relationship (logistic curve) was described by a computer model by a position parameter, the slope of the curve and the minimum and maximum fresh weights of plants. The limit of quantitative detection in the range of ED30 in vermiculite was 0·06 μg 1−1 for sulfometuron and 1·03 μg 1−1 for DPX‐L5300, methy12‐([4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl (methyl)carbamoyl]‐sulphamoyl) benzoate. Results with turnips showed that sulfometuron was the most active compound in all substrates (ED50 in vermiculite 0·12 μg 1−1) followed by chlorsulfuron, metsulfuron‐methyl, triasulfuron, DPX‐M6316, methyl 3‐([(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)aminocarbamoyl]‐aminosulphaphamoyl)‐2‐thiophenecarboxylate, and DPX‐L5300 which had ED50 or 1·98 μg 1−1, The Horotiu sandy loam soil showed the highest ED50‐values and the lowest plant availability for all compounds compared to the other soils. Probit and logistic evaluation methods for deriving dose‐response relationships are compared and their applicability is discussed.
Weed flora in the Middle Valley of the Guadalquivir, Spain
Authors: SAAVEDRA M. , GARCIA‐TORRES L. , HERNANDEZ‐BERMEJO E. , HIDALGO B.
Published: July 2006

A floristic study of the weeds in irrigated crops in the Guadalquivir River Valley (southern Spain) revealed a total of 284 species in the 267 fields surveyed, of which about 100 can be considered highly harmful. The families with the highest numbers of species were Compositae, Gramineae, Leguminosae, Cruciferae and Umbelliferae. Although 77·8% of the species were therophytes, geophytes were important in spring‐sown crops. Most species were of Mediterranean origin, especially in autumn‐sown crops; Cosmopolitan and Neotropical species were more important in the spring‐sown crops. At the early and late crop growth stages 7% and 10%, respectively, of the fields had severe or very severe infestations.

The relationships between the main weed species and crops were studied by cluster analysis, using the corrected frequency of each species in each crop as the reference parameter. This allowed classification of the species into subgroups and hierarchical groups according to their agro‐ecological preferences. A close relationship was found between a given crop, its cycle and the usual soil management practices and the phenology of certain species, reflecting the influence of these factors in restricting the germination period. The analysis differentiated the typically winter, summer and intermediate weed floras.
The effect of nitrogen fertilizers on the germination and seedling emergence of wild oat (A. fatua L.) seed in different soil types
Authors: AGENBAG G. A. , de VILLIERS O. T.
Published: July 2006

Ammonium‐containing fertilizers such as granular limestone ammonium nitrate (LAN) and liquid ammonium nitrate (AN) proved to be most effective in stimulating germination and emergence of wild oat in sandy and loamy soil. In pot experiments, rates as low as 25 kg N ha−1, significantly increased seedling emergence of wild oat. In sandy soil percentage emergence increased with increasing levels of LAN‐fertilizer up to 125 kg N ha−1 which gave 76·1 % emergence after 60 days. In control pots where no nitrogen was applied, only 21·6% of seeds planted emerged after 60 days, In loamy soil, as for AN in both soil types, high levels of LAN initially delayed seedling emergence. This negative effect disappeared approximately 15 days after seeding, resulting in no significant difference in emergence of wild oat where 25 to 125 kg N ha−1 was applied as LAN or AN. All these rates, however, increased seedling emergence between 25 and 35% compared to the no‐nitrogen treatments. Since the same rate of ammonia gas is not equally effective in breaking dormancy of semi‐ and deeply dormant wild oat seed, results of these experiments are not necessarily applicable to wild oat seeds differing in dormancy status.
On difficulties with allelopathy methodology
Authors: QASEM J. R. , HILL T. A.
Published: July 2006

Summary. The main techniques and the common experimental methods used in studying allelopathy are reviewed. Problems associated with both methodology and conclusions drawn based on certain techniques are discussed. The accuracy obtained using these techniques is evaluated and show that some of the techniques could be a misleading tool. Some changes are suggested.
Short soaking in water inhibits germination of Datura ferox L. and D. stramonium L. seeds
Authors: REISMAN‐BERMAN ORNA , KIGEL J. , RUBIN B.
Published: July 2006

Summary. Seed coat structures may play a major role in determining the germination of seeds. The involvement of seed coat characteristics in the inhibition of germination observed when dry seeds of Datura ferox L. and D. stramonium L., were rinsed or soaked in water for 1–5 min (‘soaking effect’) was investigated. Germination was inhibited by soaking D. ferox seeds even at late stages of the germination process up to one day before root protrusion. Simulation of the ‘soaking effect’ was achieved by blocking the hilum with lanolin, enamel lacquer or agar during imbibition. Blocking the hilum did not prevent water uptake by the seeds. Seed coat integrity was necessary for the ‘soaking effect’ since germination inhibition was eliminated by removing or cracking the seed coat. Drying the seeds up to 12 h after soaking reversed the inhibitory effect. SEM observations of both species revealed a loose outer parenchymatous tissue covering the hilum, an inner spongy tissue between the nucellus and the hilum and a space between the seed coat and the nucellus. We concluded that during soaking, water is trapped in the space between the seed coat and the nucellus, and in the intracellular spaces of the spongy tissue within the hilum. This water ‘plug’ may limit the diffusion of gas(es) to and from the embryo through the hilum, thus inhibiting germination.
The relative movement and persistence in soil of chlorsulfuron, metsulfuron‐methyl and triasulfuron
Authors: WALKER A. , WELCH SARAH J.
Published: July 2006

Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half‐life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron‐methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha−1, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar‐beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year.
Diclofop‐methyl antagonism by broadleaf weed herbicides: the importance of leaf expansion rate
Authors: ANDREWS M.
Published: July 2006

Avena saliva cv. Amuri and A. fatua were sprayed with diclofop methyl (1.0 kg a.i. ha−1) alone and in combination with 2,4‐D (1.1 kg a.i. ha−1), bentazone (1.0 kg a.i. ha−1), chlorsulfuron (15 g a.i. ha−1) or dicamba (0.3 kg a.i. ha−1). Effects of the herbicides on leaf extension rate during the first 8 to 10 days after spraying and subsequent growth (dry weight) after 57–75 days were determined by comparison with unsprayed plants. Diclofop‐methyl applied alone did not cause a decrease in leaf extension rate of A. saliva or A. fatua until at least 4 days after spraying. All broadleaf weed herbicides in combination with diclofop‐methyl caused a decrease in leaf extension rate of both species within 2 days of spraying. Ten days after spraying, leaf extension rates for plants sprayed with a broadleaf weed herbicide plus diclofopmethyl (all combinations) were lower than for unsprayed plants but greater than for plants sprayed with diclofop‐methyl alone. With the exception of A. fatua sprayed with bentazone, long‐term growth of plants sprayed with a broadleaf weed herbicide plus diclofop‐methyl (all combinations) was lower than for unsprayed plants but greater than for plants sprayed with diclofop‐methyl alone. Bentazone applied with diclofop‐methyl caused a substantial decrease in leaf extension rate of A. fatua within 24 h of spraying but at harvest, dry weight of plants from this treatment was similar to or less than that for plants sprayed with diclofop‐methyl alone. Application of diclofop‐methyl with bentazone at a rate of 0.3 kg a.i. ha−1 also caused a reduction in leaf extension rate of A. fatua within one day of spraying. At this rate of bentazone, dry weight of plants at harvest was intermediate to that of unsprayed plants and those sprayed with diclofop‐methyl alone. It is proposed that decreased leaf expansion rate during the first few days afte spraying is the cause of broadleaf weed herbicide antagonism of diclofop‐methyl.
Saure Hydrolyse von Metsulfuron‐methyl
Authors: SABADIE J.
Published: July 2006

Deux voies de dégradation sont observées au cours de l'hydrolyse du métsulfuron méthyle en solution aqueuse acide: hydrolyse de la fonction urée et hydrolyse du substituant méthoxy. L'abaissement du pH (6 à 1) accélère fortement le processus sans en modifier la sélectivité. L'augmentation de la température (25 à 55°C) favorise la vitese (EA= 84 kj mol−1) et l'hydrolyse de la fonction urée, Les effets d'autres facteurs (cations de métaux de transition, acides humiques, argiles) généralement limités ne concement que la vitesse de la transformation.
Weed size hierarchies in Denmark
Authors: JENSEN P. K.
Published: July 2006

In 962 field trials in different crops, the size of a number of weed species was investigated. The weeds were ranked according to their size on a single occasion. The ranks of the species were examined relative to two weed species, Viola arvensis and Matricaria inodora. The ranking was, however, independent of which of the two species were used as standard. The correlation between the rankings with Viola arvensis as standard, and the rankings with Matricaria inodora as standard were r= 0‐93 for spring sown crops, and r= 0.84 for autumn sown crops. Sinapis arvensis was the largest weed species in spring sown crops, with a weight of 14.5 times that of Viola arvensis, followed by Brassica napus, Galeopsis spp., Thlaspi arvense and Amsinckia spp. Viola arvensis. Veronica spp. and Lamium spp. were the smallest weed species in spring sown crops. Galium aparine was the largest species in autumn sown crops, whereas spring germinating species such as Polygonum spp. were among the smallest. The ranks of Viola arvensis, Myosotis arvensis, Lapsana communis, Matricaria inodora and Lamium spp. were almost identical in spring sown crops and in autumn sown crops.
Räumliche Verteilung der Samenbank–ein Vergleich statistischer Methoden
Authors: DESSAINT F.
Published: July 2006

La répartition spatiale du potentiel semencier a été analysée à partir de données simulées et de données réelles provenant d'une parcelle expérimental. Trois types d'approches statistiques ont été comparés quant à leur capacitéà déterminer la structure spatiale de populations: (1) l'ajustement de la distribution des fréquences observées à une distribution théorique (Poisson et Binomiale négative); (2) le calcul d'indices basé sur la moyenne (m) et la variance (V) d'échantillonnage (rapport V/m, la ‘mean crowding’ et l'indice d'agrégation de Lloyd); (3) le calcul d'un coefficient d'autocorrélation (le I de Moran) permettant de prendre en compte la position géographique des prélèvements. Au vue des résultats obtenus à partir des données simulées, il apparait que seul le coefficient d'autocorrélation est adaptéà la description des structures spatiales. Appliqué aux données réelles, il a permis de définir la répartition spatiale des principales espèces.
Seed dormancy and seedling emergence studies in Avena fatua L
Authors: PETERS N. C. B.
Published: July 2006

Studies were made of seedling emergence of three phenotypes of Avena fatua L. with dif ferent coloured lemmas (fA, fB, fC) originally collected from one site. Each phenotype was grown under the same conditions in 1975 and the resulting seed buried 25 mm deep in soil im mediately after collection. The soil was either left uncultivated (all phenotypes) or cultivated monthly (phenotype fA only). Seedling emergence was assessed weekly and the number of remaining viable seeds was determined at the end of three years. Seeds of different lines of A. fatua (fA phenotypes) obtained from separate locations were grown under the same conditions in 1983, buried and seedling emergence moni tored for 85 months.

Without cultivation, overall emergence (mean of three phenotypes) in successive autumns and springs was 9%, 18%, 9%, 33%, < 1%, 14% and <1%. A further 3% of viable seeds were recovered at the end of the experiment. Periodicity of emergence was the same for all phenotypes. Actual numbers of seedlings emerging in each of the periods varied between phenotypes. Total emergence of seed from the inner zone of panicles was significantly less than that from the outer zone, although there was little difference between the two zones in each of the natural emergence periods. Cultivation increased emergence, particularly from secondary seed in the first spring after burial, but did not changes its periodicity. By the second spring seed numbers had declined, and seedling counts were similar from cultivated and non‐cultivated soil. No viable seed remained in the cultivated soil after three years. Emergence from the two lines of fA was very different. Seedling emergence occurred after hot dry con ditions, or in warm periods immediately after periods of chilling, particularly those below 4°C.
Fate of fluroxypyr in soil
Authors: LEHMANN R. G. , LICKLY L. S. , LARDIE T. S. , MILLER J. H. , BALDWIN W. S.
Published: July 2006

Fluroxypyr‐MHE (methylheptyl ester) was applied to small field plots containing Londo sandy loam soil. After 30 days, fluroxypyr had degraded to about 60% of the initial concentration, but was still the main component, while after 120 and 366 days the methoxypyridine metabolite was the main component in the soil. At 30, 120, and 366 days, lettuce, turnips, green beans, soybeans, and wheat were planted and grown with no observed injury. Residues of 14C in the edible crop fractions were indistinguishable from 14C in control plants exposed to 14CO2, while residues in plant greens and chaff were low (0.1–0.2 mg kg−1), with little evidence of fluroxypyr and no evidence of metabolite uptake. These results indicate that the methoxypyridine metabolite, if present in the soil, does not harm and is not taken up into the plants.
Dégradation chimique ou microbiologique des sulfonylurées dans le sol. I. Cas du sulfbméturon méthyle
Authors: CAMBON J. P. , ZHENG S. Q. , GERAP J. BASTIDE
Published: July 2006

Résumé: Summary: Zusammenfassung

La Vitesse de transformation du sulfométuron méthyle dans un sol, et en solution au même pH, a été mesurée à différentes temperatures. Aussi bien en solution que dans le sol, la relation d'Arrhénius est bien vérifiée dans la gamme de température étudiée 20°C‐75°C. L'énergie d'activation calculée est respectivement de 94 kJ mol−1 et de 117 kJ mol−1 dans le sol et en solution. Du fait que la loi d'Arrhénius est vérifiée dans le sol jusqu'à 70°C, un mécanisme de dégradation est proposé: la dégradation chimique. L'analyse des produits formés dans un sol stérile et non stérile a été réalisée a partir du sulfométuron méthyle marqué au 14C sur le cycle pyrimidine. Dans les deux sols le métabolite principal retrouvé est la 2‐amino‐4,6‐diméthyl‐pyrimidine. Aucune différence significative n'est mise en évidence entre le sol sterile et non stérile.

Chemical or microbial degradation of sulfonylurea herbicides in soil. I. Sulfometuron methyl

The rates of degradation of sulfometuron methyl in a soil and in aqueous solution at the same pH were measured at different temperatures. The Arrhenius relationship was verified between 20°C and 75°C. The calculated activation energy in soil and in solution was 94 kJ mol−1 and 117 kJ mol−1, respectively. From the fact that the Arrhenius relationship is followed up to 70°C, it is proposed that the mechanism of degradation in the soil is chemical. Analysis of the metabolites formed in sterile and non‐sterile soil was performed using sulfometuron methyl labelled with 14C in the pyrimidine ring. In both soils the main metabolite isolated was 2‐amino‐4,6‐dimethylpyrimidine. No significant difference has been observed between sterile and non‐sterile soils.

Chemischer oder mikrobiologischer Abbau von Sulfonylharnstoffen im Boden. I. Sulfometuronmethyl

Die Abbaurate von Sulfometuron‐methyl wurde in einem Boden und in wäßriger Lösung mit gleichem pH‐Wert bei verschiedenen Temperaturen untersucht. Die Gültigkeit der Arrhenius‐Gleichung wurde zwischen 20 und 75°C überprüft, mit Aktiviemngsenergien von 94 oder 117 kJ mol−1 für den Boden bzw. die Lösung. Aus dem linearen Abbau im Boden bis zu 70°C wurde auf chemischen Abbau geschlossen. Bei der Analyse der Abbauprodukte von 14C‐Sulfometuron‐methyl (markiert am Pyrimidin‐Ring) in sterilisiertem und nicht sterilisiertem Boden wurden keine signifikanten Unterschiede festgestellt und hauptsächlich das 2‐Amino‐4,6‐dimethylpyrimidin gefunden.
Interrelated effects of temperature, light and oxygen on Amaranthus caudatus L. seed germination
Authors: GUTTERMAN Y. , CORBINEAU F. , CÔME D.
Published: July 2006

Summary: Résumé: Zusammenfassung

The aim of this study was to investigate the effects of temperature, light and oxygen on the germination of Amaranthus caudatus (var. viridis) seeds. At the highest temperature studied (35°C), seed germination was found to be most rapid and highest in both the dark and the light. Germination was inhibited by continuous white light. The lower the temperature, the greater the inhibitory effect of light. The far‐red and blue spectral regions were the most effective in light inhibition. The light effect was also dependent on the percentage of oxygen in the atmosphere around the seeds; it was less marked in O2‐enriched atmospheres. Light/ oxygen dependency resulted from the action of the seed coat and endosperm. Scarified seeds were much less sensitive to light and hypoxia than non‐scarified seeds.

Effets combinés de la température, de la lumière et de I'oxygène sur la germination des graines d'Amaranthus caudatus L.

Le but de ce travail était d'étudier les effets de la température, de la lumiere et de I'oxygène sur la germination des graines d'Amaranthus caudatus (var. viridis). A la temperature la plus élevée utilisée (35°C), la germination était la plus rapide et la plus complète tant à la lumière qu'à 1'obscuritè. La germination était inhibée par la lumière blanche continue. Plus la temperature était basse, plus 1'effet inhibiteur de la lumière était important. Les radiations rouge sombre et bleues du spectre étaient les plus in‐hibitrices. L'effet de la lumière dépendait aussi de la teneur de 1'atmosphère en oxygène; il était moins marqué dans des atmosphères enrichies en oxygène. L'interaction lumière/oxygène provenait du tégument et de 1'albumen. Les graines scarifiées étaient beaucoup moins sensibles à la lumière et a 1'hypoxie que les graines non scarifiées.

Wechselwirkungen von Temperatur, Licht und Sauerstoff auf die Keimung der Samen von Amaranthus caudatus L.

Sowohl im Dunkeln als auch im Licht keimten die Samen von Amaranthus caudatus (var. viridis) bei 35°C, der höchsten Temperatur der Versuche, am schnellsten und meisten. Durch weiβes Dauerlicht wurde die Keimung gehemmt. Je niedriger die Temperatur, desto hölier die Hemmung durch Licht. Im entfernt roten und blauen Spektralbereich war die Lichthemmung am stärksten. Die Wirkung des Lichts hing auch vom Sauerstoffgehalt der die Samen umgebenden Luft ab: Bei O25‐Anreiche‐rung war sie weniger deutlich. Die Licht/ Sauerstoff‐Wechselwirkung wurde von der Samenschale und dem Endosperm beeinfluβt: Geritzte Samen waren gegenüber Licht und O2‐Mangel viel weniger empfindlich als ganze.
Réactivité de l'herbicide chlorsulfuron; synthèse et structure de ses produits de dégradation
Authors: SABADIE J.
Published: July 2006

Résumé: Summary: Zusammenfassung

Des conditions opératoires appropriées permet‐tent de transformer sélectivement le chlorsulfuron en différents produits précédemment observés au cours de sa dégradation chimique. Leurs structures ont été précisées.

Reactivity of the herbicide chlorsulfuron: synthesis and structure of its degradation products

By selecting appropriate experimental conditions it was possible to convert chlorsulfuron into the various breakdown products observed as a result of chemical degradation. Proposed structures for these compounds are presented.

Reaktionen des Herbizids Chlorsulfuron: Synthese und Struktur seiner Abbauprodukte

Durch angepaβte Versuchsbedingungen konnte Chlorsulfuron in verschiedene Abbauprodukte überführt werden, wie sie bei seinem chemischen Abbau beobachtet werden. Ihre Struk‐turen wurden genau bestimmt.
Photosynthetic and accessory pigments inCuscuta campestrisYuncker and some host species
Authors: DINELLI G. , BONETTI A. , TIBILETTI E.
Published: July 2006

Summary: Résumé: Zusammenfassung

Photosynthetic and accessory pigments (chlorophyll a and b, a and ß carotenes and xanthophylls) were evaluated inCuscuta campestrisYuncker during the course of its biological cycle, taking into account both autotrophic and heterotrophic phases, and different parts of the parasite. Chloroplast activity inC. campestriswas measured and comparisons were made with the chloroplast activity inBeta vulgarisL. andConvolvulus arvensisL. The effects of parasitization ofC. campestrison the main and accessory photosynthetic pigments ofB. vulgariswere also evaluated.

Finally, a hypothesis was formulated to explain the different distribution of pigments in different parts and at different stages of the growth cycle inC. campestrisand its chloroplast activity.

Pigments photosynthétiques principaux et accessoires chez Cuscuta campestris Yuncker et des espèces hôtes

Les pigments photosynthétiques principaux et accessoires (chlorophylles a et b, α et β carotènes, xanthophylles) ont été déterminés chezCuscuta campestrisYuncker durant son cycle biologique. Les phases auttorophes et hétérotrophes ont été prises en compte et les mesures ont porté sur différentes parties des plantes. L'activité chloroplastique a été déterminée chezC. campestriset a été comparéà celles deBeta vulgarisL. et deConvolvulus arvensisL. Les conséquences du parasitisme deC. campestrissur les pigments principaux et accessoires deB. vulgarisont aussi étéétudiées.

Enfin, une hypothèse a été avancée pour expliquer les différences de distribution des pigments dans les différentes parties deC. campestrisà divers stades de son cycle biologique, ainsi que son activité chloroplastique.

Photosynthese‐ und akzessorische Pigmentre inCuscuta campestrisYuncker und einigen Wirstspflanzenarten

BeiCuscuta campestrisYuncker wurden im Verlaufe ihres Lebenszyklus die Photosynthese‐ und akzessorischen Pigmenten (Chlorophyll a und b, a‐ und ß‐Karotin, Xanthophylle) sowohl in autotrophen als auch heterotrophen Phasen und in verschiedenen Pflanzenteilen untersucht. Die Chloroplastenaktivität wurde gemessen und mit der vonBeta vulgarisL. undConvolvulus arvensisL. vergleichen. Die Wirkung der Parasitierung vonCuscuta campestrisauf die Photosynthese‐Pigmente vonBeta vulgariswurd erfaßt. Eine Hypothese über die Chloroplastenaktivität und zur verschiedenen Verteilung der Pigmente in den verschiedenen Pflanzenteilen und in verschiedenen Entwicklungsstadien vonCuscuta campestriswurde formuliert.
Dégradation du chlorsulfuron et du metsulfuron méthyle en présence d'acides humiques
Authors: SABADIE J.
Published: July 2006

Résumé: Zusammenfassung: Summary

Après dépôt sur de l'acide humique solide, le chlorsulfuron et le metsulfuron méthyle se dégradent à 25°C selon le schéma d'hydrolyse précédemment observé en solution aqueuse: hydrolyse simultanée de la fonction urée et du substituant méthoxy. La présence d'eau accélère notablement la conversion et favorise l'hydroxylation de la molécule. L'addition de méthanol provoque la méthanolyse de la fonction urée.

La forte affinité des composés hydroxylés intermédiaires pour la matière humique sèche a été mise en évidence.

Abbau von Chlorsulfuron und Metsulfuron‐methyl in Gegenwart von Huminsäuren

Nach Anlagerung an feste Huminsäure wurden Chlorsulfuron und Metsulfuron‐methyl bei 25°C in derselben Weise hydrolysiert, wie vorher in wäßriger Lösung beobachtet, nämlich mit simultaner Hydrolyse der Harnstoff‐ und der Methoxygruppe. Durch Feuchtigkeit wurde die Reaktionsrate beachtlich erhöht und die Hydrolyse gefördert. Zugabe von Methanol leitete die Méthanolyse der Harnstoffgruppe ein. Es wurde eine hohe Affinität der intermediären Hydrolyseprodukte zu trockener Huminsubstanz beobachtet.

Degradation of chlorsulfuron and metsulfuron methyl in the presence ofhumic adds

The chemical degradation of chlorsulfuron and metsulfuron methyl on solid humic acid was investigated at 25°C. Hydrolysis followed the same pathway as that observed previously in aqueous solution: simultaneous hydrolysis of the urea function and of the methoxy radical. Moisture enhanced the rate of reaction and favoured hydroxylation of the molecule. Methanolysis of the urea function was induced by methanol.

A high affinity between dry humic material and hydroxylated intermediate compounds was observed.
Mauvaises herbes des céréales de la Chaouia (Maroc). II. Aspect écologique.
Authors: TALEB A. , MAILLET J.
Published: July 2006

Résumé: Summary: Zusammenfassung

La répartition régionale des espèces adventices des céréales de la Chaouia est conditionnée par deux facteurs prépondérants: la nature du sol et le climat régional qui permettent d'établir cinq grands groupes écologiques. II existe une bonne correspondance avec les groupes phytosociolo‐giques déjàétablis par ailleurs, mais cette appro‐che permet de mieux mettre en évidence les transitions qui existent sur le terrain. Les risques liés à une évolution des techniques culturales sont appréciés en fonction des groupes d'espèces actuels.

Weeds of cereals in Chaonia (Morocco) II. Ecological aspects.

The regional distribution of weeds of cereals in Chaonia is controlled by two major factors, soil type and climate, which allows five large ecological groups to be defined. There is a good correlation between these and groupings established in other ways but this approach shows more clearly the transitions which occur on the ground. The risks associated with agricultural development can be evaluated with reference to the species currently present.

Unkräuter des Getreides im Gebiet von Chaouia (marokko) II. Ökologische Aspekte

Die regionale Verteilung der Ackerwildpflanzen den Getreides im Gebiet von Chaouia ist durch 2 entscheidene Faktoren bestimmt: die Boden‐arten und die regionalen Klimabedingungen, die 5 große ökologische Gruppen sich entwickeln lassen. Es besteht eine gute übereinstimmung mil den bereits andernorts beschriebenen pflan‐zensoziologischen Gruppen, mit deren Hilfe die naturräumlichen übergange deutlich heraus‐gearbeitet werden können. Die Wahrschein‐lichkeit agrotechnisch bedingter Entwicklungen der aktuellen Artengruppen wird abgeschätzt.
Variation in the annual dormancy cycle in buried seeds of the weedy winter annual Viola arvensis
Authors: BASKIN J. M. , BASKIN C. C.
Published: July 2006

Seeds of Viola arvensis collected in different years and in different months within those years were buried in soil under natural seasonal temperature cycles, and changes in their germination requirements monitored. Seeds were dormant at maturity in May or June, but nondormant by autumn. During winter, some seeds entered dormancy, while others entered conditional dormancy, i.e. retained the ability to germinate at 15/6 and 20/10oC but not at other thermoperiods. Dormant and conditionally dormant seeds became nondormant the following summer. Seeds collected in 1981 exhibited an annual dormancy:nondormancy cycle, while those collected in 1982 exhibited an annual conditional dormancy:nondormancy cycle. The type of dormancy cycle found in these seed lots during their first year of burial persisted in subsequent years. Thirty–five and 36% of seeds collected in May 1983 and 1986, respectively, were conditionally dormant the following May, while only 5 and 9% of those collected in the same field in June 1983 and 1986, respectively, were conditionally dormant. Dormant seeds collected in 1981,1982 and 1984 and buried at 5oC during summer germinated to 0, 33 and 0% respectively, at 15/6oC in autumn. After the 1982 seeds became nondormant during summer, only 25% entered conditional dormancy when buried at 5oC, but after the 1981 and 1984 seeds became nondormant, 100% entered conditional dormancy at 5oC. Thus, the persistent seed bank of V. arvensis at a population site may consist of seeds with an annual dormancy:mondormancy cycle and others with an annual conditional dormancy:nondormancy cycle. This is the first report of the two types of annual seed dormancy cycles in the same species.
A method to obtain fast and uniform emergence of weeds for field experiments
Authors: KEMPENAAR C. , SCHNIEDERS B.J.
Published: July 2006

In studies on competition between crops and weeds it may be desirable to manipulate time of emergence, density and spatial arrangement of weeds. This requires a method to obtain a fast and uniform emergence of weeds. Two planting methods were compared that differed in the medium (agar or blotting paper) on which seeds were germinated, and in the method of transplanting the seeds (with or without the medium). In wet soil, emergence started earlier when seeds were germinated on agar and subsequently planted with agar. Root tips of seeds germinated on blotting paper may have been damaged to a greater extent during transplanting, because root tips tended to grow into the blotting paper. The duration, heterogeneity and final level of emergence were not affected by the planting method. In dry soil in a greenhouse experiment, the final level of emergence was much less when seeds were planted using the blotting paper method than when they were planted using the agar method. The agar may have provided a small source of water which reduced dehydration of emerging plants. The results were similar for the three species studies, namely, Chenopodium album L., Senecio vulgaris L. and Solanum nigrum L.
Germination behaviour in seeds of Diplotaxis erucoides and D. virgata
Authors: PEREZ‐GARCIA F. , IRIONDO J.M. , MARTINEZ‐LABORDE J.B.
Published: July 2006

The seed germination behaviour of four populations each of Diplotaxis erucoides (L.) DC. and D. virgata (Cav.) DC, two weedy Brassicaceae species widely distributed in the Mediterranean region, was studied under controlled light, temperature and moisture conditions. Germination rates in D. virgata were generally higher at alternating (25/15^C) and low (15^C) temperatures, whereas in D. erucoides optimal germination rates were achieved at higher temperatures (25^C). No correlation between seed weight and germination was found in either species. In D. virgata, the geographic origin of the seed had an important effect on germination percentage. Great germination variability was found among the populations and even among seeds belonging to the same population. In this species, the application of gibberellic acid stimulated germination, especially in the populations with higher dormancy levels. Dormancy was found in mature D. virgata seeds but not in those of D. erucoides. In both species, germination percentages decreased after a certain period of storage at low temperatures. This period varied depending on the species and the population considered.
A comparison of the dynamics of root growth and biomass partitioning in wild oat (Avena fatua L.) and spring wheat
Authors: BINGHAM I. J.
Published: July 2006

The dynamics of early root growth and dry matter partitioning were compared in spring wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) grown in solution culture. Total root length was greater in wheat than wild oat throughout the experiment; a result of a greater number of seminal axes and greater production of lateral root length per axis. The final number of adventitious roots was greater in wheat than in wild oat, but their length was similar. Relative growth rates were also similar as was shoot:root dry weight ratio and rate of root respiration. However, wheat used the dry matter partitioned to its roots more efficiently, producing a greater specific root length (SRL, length per unit weight). Caution must be exercised when relating these results to plants growing and compet‐ing in the field, but three general points are raised. First, the initial number of seminal axes can have a profound effect on the rate of early root development; second, the adventitious root system of wild oat is not inherently more vigorous than that of wheat; and third, future studies should compare SRL of wheat and wild oat in the field. If differences similar to those in the present study are found they may contribute to the greater competitive ability of wheat.
Etendue de distribution et degré d'infestation des adventices dans la rotation cotonnière au Nord‐Cameroun
Authors: Le BOURGEOIS T. , GUILLERM J. L.
Published: July 2006

Résumé: Summary

L'étude des adventices dans la rotation cotonnière au Nord‐Cameroun a porté sur l'observation de 180 parcelles à trois époques du cycle cultural. L'analyse floristique qualitative met en évidence une flore de 280 espèces, réparties en 141 genres appartenant à 42 families botaniques, dont les mieux représentées sont les Poaceae, Fabaceae, Cyperaceae et Asteraceae. L'analyse floristique quantitative réalisée en fonction des saisons et des trois régions phytogéographiques de la zone d'étude montre que les espéces les plus fréquentes sont Ipomoea eriocarpa R. Br., Digitaria horizontalis Willd. et Commelina benghalensis L. et que les mauvaises herbes qui posent des problèmes majeurs d'infestation dans les cultures annuelles sont C. benghalensis, D. horizontalis et Striga hermonthica (Del.) Benth.

Weed distribution and abundance in cotton rotation in northern Cameroon

This weed study in cotton rotation in northern Cameroon concerns observations of approximately 180 fields on three occasions during the crop season. Qualitative floristical analysis shows a flora of about 280 species, in 141 genus among 42 botanical families in which the commonest representatives are Poaceae, Fabaceae, Cyperaceae and Asteraceae. Quantitative floristical analysis was carried out in relation to the three seasons and the three phyto‐geographical areas of the region. It shows that the more frequent species are Ipomoea eriocarpa R. Br., Digitaria horizontalis Willd. and Commelina benghalensis L., and the weeds that cause most damage in annual crops are C. benghalensis, D. horizontalis and Striga hermonthica (Del.) Benth.
Effect of non‐ionic nonylphenol surfactants on surface physicochemical properties, uptake and distribution of asulam and diflufenican
Authors: SHARMA S. D. , KIRKWOOD R. C. , WHATELEY T. L.
Published: July 2006

The effect of non‐ionic nonylphenol (NP) surfactants containing 4–14 ethylene oxide (EO) molecules on the distribution of asulam and diflufenican was investigated in Pteridium aquilinum L. Kuhn and Avena fatua L. The distribution of the herbicides was dependent on the EO content and concentration of surfactant and differed between plant species and herbicide. The surface properties of contact angle, droplet diameter and surface tension were examined. For solutions of asulam, the greatest reductions in contact angle, surface tension and greatest droplet diameter were obtained with surfactants of EO 6.5–10 (at 0.001–0.1%). For solutions of diflufenican, these responses were greatest when applied with surfactant of EO 4. Surfactants of EO 6.5–10 increased the uptake and translocation of [14C]asulam in P. aquilinum, particularly at surfactant concentrations of 0.01 % and 0.1 %. All surfactants increased uptake of [14C]asulam in A. fatua with no significant effects of surfactant EO number or concentration. For both species, there was a positive correlation between the optimum surface characteristics of the herbicide droplets and the uptake of asulam. With diflufenican, greatest uptake and translocation by mature frond tissue of P. aquilinum occurred at the highest concentration of surfactant EO 4; in A. fatua, however, uptake and translocation were not significantly affected by any of the surfactants.
Influence of nitrogen on competition between cereals and their natural weed populations
Authors: JØRNSGÅRD B. , RASMUSSEN K. , HILL J. , CHRISTIANSEN J. L.
Published: July 2006

The effects of nitrogen fertilizer on the growth and density of natural weed populations in spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) were investigated in the absence of herbicide. An increased level of applied nitrogen did not enhance: weed germination, tended to decrease the total weed biomass and had a differential effect upon the biomass of individual weed species in both wheat and barky. In competition with barley, Chenopodium album L. and Lamium spp. had lower nitrogen optima than the crop, while Urtica urens L. had a higher nitrogen optimum. In competition with wheat, Stellaria media (L.) Vill., Lamium spp. and Veronica spp. had lower nitrogen optima than the crop. The systematic changes in nitrogen effect with time were analysed by fitting orthogonal polynomials to the growth and density curves. The methodology could be recommended for other studies in which time or other systematic factors are included, as it supplies information which a traditional analysis of variance cannot provide. Since seed production is positively correlated with biomass, so nitrogen level affects seed production and, hence, the seed pool and future weed population, suggesting that fertilizer usage can be exploited in an integrated programme of crop: weed management. A trend towards lower N fertilizer application owing to concerns about the environment willfavour most of the weed species investigated in these experiments and change the composition of weed populations.
Weed populations in olive groves under non‐tillage and conditions of rapid degradation of simazine
Authors: SAAVEDRA M. , PASTOR M.
Published: July 2006

In 49 olive tree groves in southern Spain under non‐tillage and treated in the autumn with simazine, a total of 315 weed species was identified. However, only eight annual specics reached a moderate mean infestation of infested ficlds. In each field the number of observed species ranged from 4 to 78. The most important annual species that survived simazine treatment were Lolium rigidum, Galium tricornutum and Sherardia arvensis and, locally in a few fields, others such as Amaranthus spp., Conyza spp., Pulicaria paludosa, Sinapis alba. Torilis arvensis and Rumex bucephalophorus. Sedum album, R. bucephalophorus, P. paludosa, Briza maxima and Hypericum perforatum were mainly found in slope soils with high altitude and low carbon content. Cyperus rotundus, Conyza banariensi, Amaranthus blitoides, Galium spurium and Diplotaxis virgata were found at high densities in irrigated fields. Simazine residues recorded 6 months after herbicide application were very low, amounting on average to levels less than 3% of the applied rate. In soil treated with simazine for 7 years. simazine degradation was much faster than in previously untreated soil, particularly at temperatures of 15‐25°C.
Estimation of the seedbank of Striga spp. (Scrophulariaceae) in Malian fields and the implications for a model of biocontrol of Striga hermonthica
Authors: SMITH M. C. , WEBB M.
Published: July 2006

Striga seeds were extracted from soils collecled in Mali and the viahility of these seeds was estimated. Striga seeds were found in 45 of 46 samples taken from 23 fields. Siriga hermonthica (Del.) Benth. growmg on the host crop millet, was present at all 46 sites sampled. The a size uf the Striga seedbaiik measured lo a depth of 15 cm was estimated to be 38 800 m ‐2 of surface area (geometnc mean 11 500). The average number of S. hermonthica plants observed per millei hill was 8.83 (geometric mean 3.89) or 13.98 m‐2 (gcometrie mean 5.69 m‐2). Higher crop hill densities tended to result in higher densities of emerged S. hermonthica per hill. The relationship between seeds m‐2 and S. her‐monhica plants m‐2 was fitied to a reetungular hyperbola and used to reassess an existing model of S. herniouhica control.