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.     

Uptake and translocation of [14C]asulam and [14C]bromacil by roots of maize and bean plants

The uptake and translocation of ¹⁴C-ring-labeled asulam (methylsulfanilcarbamate) and bromacil (5-bromo-3-sec-butyl-6-methyluracil), were compared after root application to maize (Zea mays L.) and bean (Phaseolus vulgaris L.). Autoradiographs showed the distribution of bromacil throughout these and other plant species, and the retention of asulam in the roots. The recovery of both compounds in quantitative radioassays was between 90 and 100%. The absorption of bromacil and asulam was rather similar. Absorption of bromacil increased up to 20% of the applied dose in bean plants after 2 days of exposure, and up to 11% in maize plants after 4 days. Absorption of asulam in bean plants was 22% of the applied dose after 2 days, and 8% in maize plants after 4 days. The pattern of distribution of bromacil and asulam was completely different. After 4 h of exposure of the roots about half of the absorbed bromacil had accumulated in the shoots, while two-thirds or more was translocated to the shoots after exposure periods of 1 to 4 days. Not more than one-eighth of the absorbed asulam was found in the shoots. In consequence, the bromacil content in the transpiration stream relative to that in the ambient solution was much higher than that of asulam. The leakage of asulam from bean and maize roots into herbicide-free nutrient solution was lower than that of bromacil. The reasons for these differences are not yet clear. There was only some metabolism of asulam in maize, but not in bean plants. No metabolites of bromacil were detected in the two plant species.     

The effect of nitrogen, plant density and competition between Bromus sterilis and three perennial grasses: the implications for boundary strip management

The competitive ability of Festuca rubra L., Hoicus lanatus L. and Poa trivialis L. when grown from seed, in monoculture and in 1:1 additive mixtures with Bromus sterilis L. was studied. B. sterilis was more aggressive when grown in additive mixtures with F. rubra than P. trivialis or H. lanatus. H. lanatus was less dominated by B. sterilis at the second harvest; visual observations suggested that this dichotomy was due to its slower initial growth rate, and its subsequent dense vegetative growth habit. There was no statistically significant difference between the Relative Yield Total (RYT) of B. sterilis in additive mixtures with F. rubra, H. lanatus or P. trivialis, indicating that they were competing for the same resources. B. sterilis produced significantly more reproductive tillers and seeds as a result of nitrogen application, and such production was accentuated in the absence of interspecific competition. The implications of sown grass strips for field margin management are discussed.     

The effectiveness of old and new strategies for the long‐term control of Pteridium aquilinum,an 8‐year test

There is a need for management strategies to control dominant perennial weeds and restore seminatural communities. We compared the effects of five weed control treatments on dense Pteridium aquilinum relative to an untreated experimental control over an 8‐year period with the aim of restoring acid grassland. The weed control treatments tested were as follows: cutting and bruising, both twice and thrice annually, and herbicide treatment (asulam in year 1 followed by annual spot retreatment of all emergent fronds). Pteridium aquilinum performance and plant species composition were monitored. Data were analysed using Bayesian mixed‐effect models and multivariate techniques. Cutting twice and thrice yearly and the asulam treatment all reduced frond density to zero; both bruising treatments were ineffective. The plant communities in the cut and asulam‐treated plots showed differences from the untreated and bruised plots; the asulam‐treated plots contained more ruderal species and the cut plots were more typical of acid grassland. Acid grassland recovery was fastest in the asulam‐treated plots, but the cut plots caught up after approximately 5 years. There were two important conclusions. First, an intractable weed like P. aquilinum can be eradicated and a vegetation more suited for grazing can be achieved by the continuous application of some treatments over many years. Here, success was achieved by cutting twice/thrice annually, or by a single asulam application followed by annual spot spraying of all emergent fronds for 8 years. Second, bruising, a treatment favoured by some conservation organisations, did not work and cannot be recommended. The use of long‐term, continuously applied treatments might be considered for all perennial weeds with large underground root/rhizome systems.     

Seasonal emergence of weeds in cultivated soil in New Zealand

Patterns of seedling emergence of ten weed species from soil cultivated at intervals of approximately one month are described. All species examined showed clearly defined emergence patterns. Polygonum persicaria L. seedlings emerged in spring and early summer. Seedlings of Chenopodium album agg., Portulaca oleracea L. and Solanum nigrum L. emerged in late spring, summer and early autumn.Plantago major L., Rumex spp. (mostly R. obtusifolius L.) and Trifolium spp. (mostly T. repens L.) emerged mostly in spring and early summer. Coronopus didymus (L.) Sm. and Juncus bufonius L. tended to emerge in both autumn and spring.Veronica persica Poir. emerged in spring, summer and autumn. Close similarity between emergence patterns in New Zealand and northern Europe, despite differences in rainfall and temperature, suggests that annual dormancy:nondormancy cycles of seeds buried in the soil are largely responsible for seedling emergence patterns. In New Zealand, seedling emergence tended to be more spread out than in Europe, although seasonal patterns were still distinct. Further work on dormancy cycles in these species would be useful, as would a comparison of the factors inducing and breaking dormancy of comparable seed populations in northern and southern Europe and New Zealand. When seeds were left buried for several years before being encouraged to germinate, seedling emergence patterns tended to be of smaller amplitude, although the overall patterns were still very similar.     

The effect of different frequencies of harrowing in the autumn or spring on winter wheat, and on the control of Stellaria media (L.) vill., Galium aparine L. and Brassica napus L.

Cultivating with a flexible tine harrow in the autumn reduced densities of Stellaria media (L) Vill., Galium aparine L. and Brassica napus L. plants and thinned the wheat crop. Effects were more severe with two passes at right angles (plant stands were approximately halved) than with a single cultivation. Despite crop thinning, wheat yields were not reduced by autumn harrowing owing to compensatory increases in 1000-grain weights. Summer biomass of S. media and G. aparine was reduced more by spring than by autumn harrowing, while biomass of B. napus was only reduced by autumn harrowing. It was concluded that weakly rooted climbing or scrambling species are more easily controlled by cultivating in the spring, while species that develop a tap-root are more readily controlled by cultivating at an early growth stage in the autumn. L'effet de différentes fréquences d'hersage en automne on au printempssur le blé d'hiver, etsur les controles suivants Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. Les façons culturales effectuées à 1'automne avec une herse à trilles flexibles réduisaient le nombre de Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. et éclaircissaient la culture de blé. Les effets étaient plus importantes après deux passages perpendiculaires (densité des plantes divisée par environ 2) que par un seul passage. En dépit de l'éclaircissement, les rende-ments du blé n'ont pas été réduits par le hersage d'automne grâce à une compensation par le poids de 1000 grains. La biomasse d'été de S. media et G. aparineétait plus réduite par un hersage de printemps que d'automne, alors que la biomasse de B. napus n'était réduite que par un hersage d'automne. Les espéces grimpantes et faible-ment enracinées sont done plus facilement com-battues par des travaux de printemps, alors que celles qui présentent un racine pivotante sont plus facilement combattues par un hersage d'automne, à un stade précoce. Die Wirkung verschieden häufigen Eggens im Herbst oder im Frühjahr auf Wintenveizen und auf die Bekämpfung von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. Eggen im Herbst mit einer beweglichen Zinkenegge verringerte die Dichte von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. und reduzierte den Weizenbestand. Die Wirkungen waren durch 2 Arbeitsgänge im rechten Winkel zu einander, wobei der Pflanzenbestand ungefähr halbiert wurde, gegenüber einer einzelnen Bearbeitung ver-stärkt. Aufgrund eines ausgleichenden Anstiegs des Tausendkorngewichts wurden die Weizenerträge trotz Ausdünnung der Bestände nicht durch Eggen im Herbst reduziert. Die Sommerbiomasse von S. media und G. aparine wurde mehr durch Eggen im Frühjahr als durch Eggen im Herbst verringert, während die Biomasse von B. napus nur durch Eggen im Herbst reduziert wurde. Daraus folgt, daß schwach wurzelnde und kletternde Arten einfacher durch Eggen im Frühjahr bekämpfbar sind, Arten mit einer Pfahlwurzel besser im Herbst zu einem früheren Entwicklungsstadium.     

The ecological life cycle of Thlaspi perfoliatum and a comparison with published studies on Thlaspi arvense

Thlaspi perfoliatum L. is an introduced winter annual that grows in waste places, but it is not a troublesome agricultural weed. Seeds are dormant at maturity in spring, afterripen during summer and germinate in autumn. Non-dormant seeds that fail to germinate in autumn are induced into secondary dormancy by low winter temperatures and cannot germinate the following spring. These seeds afterripen during summer and germinate in autumn if conditions are suitable. Vernalization is not an absolute requirement for flowering. However, it shortens the time to flowering, and vernalized plants produce many more flowers and seeds than non-vernalized plants. Results from studies on seed germination and flowering of T. perfoliatum are compared to published studies on the life cycle of Thlaspi arvense L., an introduced species that is a serious agricultural weed which behaves both as a winter and a summer annual.     

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.     

Shrub presence and shrub species effects on ground beetle assemblages (Carabidae,Curculionidae and Tenebrionidae) in a sandy desert,northwestern China

Shrub presence has an important effect on the structuring of ground beetles in desert ecosystems. In this study, in order to determine how shrubs and different species influence ground beetle assemblages in a sandy desert scrubland dominated by two different shrub species, namely Calligonum mongolicum and Nitraria sphaerocarpa, we sampled the ground beetles using pitfall traps during spring, summer and autumn in 2012. At the community level, the activity density of the ground beetles was shown to be significantly higher under shrubs than in intershrub bare habitats in spring; but an opposite pattern occurred in autumn, suggesting the presence of season-specific shrub effects on the activity density of the ground beetles. Meanwhile, at the trophic group level, the activity density and species richness of predators were significantly greater under shrubs than in intershrub bare habitats in spring, whereas an opposite trend occurred on the activity density in autumn. N. sphaerocarpa shrubs had a positive effect on the activity density of herbivores in the three seasons, and C. mongolicum shrubs had a positive effect on the activity density of detritivores in spring and autumn. At the species level, more Microdera sp. was captured under shrubs than in intershrub bare habitats in spring. During the same time, we also found that C. mongolicum shrubs had a positive effect on Blaps gobiensis in spring, Carabus sp. in autumn, and Tentyria sp. in spring and autumn, and N. sphaerocarpa shrubs had a positive effect on Cyphogenia chinensis, Sternoplax setosa in spring and summer, and Curculionidae sp. 1 in summer and autumn. The study results suggest that shrub presence, shrub species and season variation are important factors for ground beetle assemblages in this desert ecosystem, but the responses of beetles differed among trophic and taxonomic levels.     

Improvement of carpet grass (Axonopus affinis Chase) pasture by fertilization and oversowing with the aid of selective herbicides

An experiment was done to determine the effect of spring and autumn application of asulam and dalapon, nitrogen fertilizer and oversown white clover (Trifolium repens L.) on the productivity of subtropical pasture dominated by carpet grass (Axonopus affinis Chase). Assessments were made of pasture yield, botanical composition, weed invasion and recolonization by pasture species during the 12-month period following herbicide application. Both herbicides decreased the yield of carpet grass and increased that of the more productive paspalum (Paspalum dilatatum Poir.) except after autumn application when the yield of paspalum was greatly reduced by dalapon. White clover became established only on plots treated with herbicide and only after autumn application. Clover yields were greatest on plots treated with dalapon. Asulam was considered to be the most suitable herbicide for altering the balance between carpet grass and paspalum because dalapon initially reduced paspalum yield after autumn application and delayed recovery of total pasture. In addition, dalapon permitted greater invasion by broadleaf weeds. This work showed that herbicides have a potential role for speeding up botanical changes in unproductive carpet grass pasture and further refinement of the technique might provide a useful tool for increasing pasture productivity.     

First records of two mealybugs,Maconellicoccus hirsutus (Green) and Phenacoccus peruvianus Granara de Willink,in Tunisia and the North of Africa

During the summer and autumn of 2014 the mealybugs Maconellicoccus hirsutus (Green, 1908) (Hemiptera: Pseudococcidae) and Phenacoccus peruvianus Granara de Willink, 2007 (Hemiptera: Pseudococcidae) were observed in different localities of Sousse (Tunisia). This is the first record for both of these species in Tunisia and in North Africa. For M. hirsutus, this was also the first record of the species in a Western Mediterranean country. It was observed on Hibiscus rosa‐sinensis (Malvacae). P. peruvianus was collected from Bougainvillea glabra (Nyctaginaceae) and Citharexylum quadrangularis (Verbenacae).     

Asulam mixtures for weed control in flax

Five field experiments were conducted from 1972 to 1975 to evaluate weed control in flax (Linum usitatissimum L.) using post-emergence treatments of asulam [methyl (4-aminobenzenesulphonyl) carbamatel alone and in combination with other herbicides. The ¹⁴C-asulam absorption by leaf segments and roots of glasshouse grown wild oats (Avena fatua L.) was also investigated. Asulam at 1.12 kg/ha gave good wild oat control and acceptable control of green foxtail (Setaria viridis (L.) Beauv.). However, wild oat control was poorer when asulam was combined with other herbicides: on a 3-year average, as compared with asulam alone at equal rates, the asulam+MCPA mixture resulted in a greater antagonism and a significant 6% reduction in flax seed yield, whereas the asulam+bromoxynil/MCPA mixture gave the least antagonistic effect, improved broadleaf weed control and increased yield by 13%. In mixtures, the potassium salt of MCPA was more compatible with asulam for weed control than the amine form. Both leaf segments and roots of wild oats absorbed and distributed less ¹⁴C-asulam from solutions containing MCPA than from those containing bromoxynil or bromoxynil/MCPA.     

Effect of non-ionic nonylphenol surfactants on surface physicochemical properties, uptake and distribution of asulam and diflufenican

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.     

Uptake, translocation and phytotoxicity of root-absorbed haloxyfop in soybean, Festuca rubra L. and Festuca arundinacea Schreb

The concentrations of haloxyfop in nutrient solution required to reduce the total plant dry weight of soybean (Glycine max L. Merr. ‘Evans’), red fescue (Festuca rubra L. ‘Pennlawn’), and tall fescue (Festuca arundinacea Schreb. ‘Houndog’) by 50% (GR₅₀) were determined. The GR₅₀) values for soybean, red fescue and tall fescue were 76 μM, 3μM and 0.4 μM, respectively. The reduction in growth in roots and shoots of soybean was similar. In contrast, the relative reduction in root tissue weight was greater than that for foliar tissue in both grass species. The amount of ¹⁴C-haloxyfop in soybean roots or shoots was higher than in red fescue or tall fescue. Red fescue accumulated less haloxyfop in the foliage than in the roots. On the other hand, similar amounts of ¹⁴C-haloxyfop accumulated in both organs in both soybean and tall fescue. ¹⁴C-haloxyfop appeared to be actively absorbed by the roots of all species. Soybean absorbed more nutrient solution, but utilized it less on a per gram dry matter produced basis than the grass species. Differences in the uptake and translocation of haloxyfop by roots do not account for differences in tolerance between species. However, a higher level of retention of haloxyfop in the roots of red fescue than in tall fescue may provide the former with an additional selectivity advantage under conditions where there is significant root exposure to the herbicide.     

Quantitative resistance to symptomless growth of Leptosphaeria maculans (phoma stem canker) in Brassica napus (oilseed rape)

Quantitative resistance to Leptosphaeria maculans in Brassica napus was investigated in field and controlled environments using cultivars Darmor (with quantitative resistance) and Eurol (without quantitative resistance). In field experiments, numbers of phoma leaf spot lesions in autumn/winter and severity of stem canker the following summer were assessed in three growing seasons. There were no differences between Darmor and Eurol in number of leaf lesions in autumn/winter. However, stem cankers were less severe on Darmor than Eurol at harvest the following summer. In controlled-environment experiments, development of leaf lesions at different temperatures (5–25°C) and wetness durations (12–72 h) was investigated using ascospore inoculum; symptomless growth of L. maculans along leaf petioles towards the stem was quantified using quantitative PCR and visualized using GFP-expressing L. maculans ; growth of L. maculans within stem tissues was investigated using GFP-expressing L. maculans . There were more leaf lesions on Darmor than Eurol, although there was no difference between Darmor and Eurol in L. maculans incubation period. There were no differences between Darmor and Eurol in either distance grown by L. maculans along leaf petioles towards the stem or quantity of L. maculans DNA in leaf petioles, but L. maculans colonized stem tissues less extensively on Darmor than Eurol. It was concluded that quantitative resistance to L. maculans operates during colonization of B. napus stems by the pathogen.     

Effects of shrub presence and shrub species on ground beetle assemblages (Carabidae,Curculionidae and Tenebrionidae) in a sandy desert,northwestern China

Shrub presence has an important effect on the structuring of ground beetles in desert ecosystems. In this study, in order to determine how shrubs and different species influence ground beetle assemblages in a sandy desert scrubland dominated by two different shrub species, namely Calligonum mongolicum and Nitraria sphaerocarpa, we sampled the ground beetles using pitfall traps during spring, summer and autumn in 2012. At the community level, the activity density of the ground beetles was shown to be significantly higher under shrubs than in intershrub bare habitats in spring; but an opposite pattern occurred in autumn, suggesting the presence of season-specific shrub effects on the activity density of the ground beetles. Meanwhile, at the trophic group level, the activity density and species richness of predators were significantly greater under shrubs than in intershrub bare habitats in spring, whereas an opposite trend occurred on the activity density in autumn. N. sphaerocarpa shrubs had a positive effect on the activity density of herbivores in the three seasons, and C. mongolicum shrubs had a positive effect on the activity density of detritivores in spring and autumn. At the species level, more Microdera sp. was captured under shrubs than in intershrub bare habitats in spring. During the same time, we also found that C. mongolicum shrubs had a positive effect on Blaps gobiensis in spring, Carabus sp. in autumn, and Tentyria sp. in spring and autumn, and N. sphaerocarpa shrubs had a positive effect on Cyphogenia chinensis, Sternoplax setosa in spring and summer, and Curculionidae sp. 1 in summer and autumn. The study results suggest that shrub presence, shrub species and season variation are important factors for ground beetle assemblages in this desert ecosystem, but the responses of beetles differed among trophic and taxonomic levels.     

THE CONTROL OF BROAD-LEAVED DOCK (RUMEX OBTUSIFOLIUS L.) IN NEWLY-SOWN RED CLOVER (TRIFOLIUM PRATENSE L.) WITH TRIFLURALIN, CARBETAMIDE AND ASULAM

Summary. Trifluralin (2,6-dinitro- NN -dipropyl-4-trifluoromethylaniline) pre-sowing, and carbetamide ( d - N -ethyl-2-(phenylcarbamoyloxy)propionamide) and asulam ( N -(4-aminobenzenesulphonyl)methylcarbamate) pre-sowing or post-emergence were evaluated for the control of Rumex obtusifolius L. in autumn-sown red clover ( Trifolium pratense L.). All herbicides gave good control of if. obtusifolius from seed. Asulam at 2 or 4 kg/ha gave the best control of R. obtusifolius from rootstocks, followed by trifluralin at 1 kg/ha and carbetamide at 2 kg/ha. Poa annua L. was controlled by trifluralin and carbetamide but not by asulam. The results are interpreted in terms of the mode of action and method of application of the herbicides.
La lutte contre la Patience sauvage (Rumex obtusifolius L.) dans un semis récent de trèfle rouge (Trifolium pratense L.) avec la trifluraline, le carbétamide et l'asulame     

Studies of the mechanism of action of asulam in plants. Part I: Antagonistic interaction of asulam and 4-aminobenzoic acid

Studies have been carried out on the herbicidal action of asulam [methyl (4-aminophenylsulphonyl)carbamate] and sulphanilamide, alone or in association either with 4-aminobenzoic acid (4ABA) or 4, 6-diamino-1-(3, 4-dichlorophenyl)-1, 2-dihydro-2, 2-dimethyl-1,3,5-triazine (DCDT). The soaking of wheat seeds (Triticum estivum L.) for 12 h at 30°C in asulam and DCDT in a 10:1 ratio doubled the inhibition of root growth produced by soaking in asulam alone; the addition of 4ABA partially reversed the activity of asulam. Foliar applications of a mixture of asulam + DCDT (1.1 + 0.55 kg ha^?1) markedly increased the activity of asulam in susceptible wheat, wild oat (Avena fatua L.), tolerant flax (Linum usitatissimum L.), and in Stellaria media L. The activity of asulam at 1.1 kg ha^?1 was reversed by 4ABA at 2.2 kg ha^?1 by about 50% in wheat and wild oat, 82% in flax and 100% in S. media. The results indicate that asulam and sulphanilamide act by similar mechanisms in apparently inhibiting the biosynthesis of folic acid.     

Seasonal variation in the emergence of annual weeds — an introductory investigation in Sweden

Seeds of thirteen annual weed species were collected in early autumn. Within a few weeks they were incorporated in soil. They were stored either in the field or in climate chambers where seasonal variations in field soil temperature were simulated. Seedling emergence under various conditions was determined at different times, within a period of 1 or 2 years after the incorporation of seeds in soil. Some material was transferred from the storage places at different times of year and placed in cabinets with standardized temperature regimes for 3-week emergence tests. These showed increased emergence during late autumn and winter and a maximum at some time in winter in both summer and winter annuals. Some winter annuals showed a second maximum in late summer. Counts of seedlings in the storage places, in unstirred soil, showed maximum emergence in spring for both winter and summer annuals — or in summer for Spergula arvensis and, possibly, Capsella bursa-pastoris. In certain treatments in the field, the soil was stirred once, on different dates, simulating tillage at different limes of year. The emergence following stirring of the soil was greatest in spring for the summer annuals, except for Spergula arvensis, which showed more emergence from early to mid summer. Several winter annuals showed an emergence peak after stirring in late summer or early autumn. Variations saisonnières dans la levèe des mauvaises herbes annuelles-étude préliminaire en Suède     

A profile of the potential flora in maize fields of the Po valley

Qualitative and quantitative surveys (biological and ecophysiological spectrum, structural organization, seed bank size) of the potential flora (PF) in maize (Zea mays L.) fields of the Po Valley are reported. Data were collected from 45 sites and two sampling depths (0–20 cm and 21–40 cm). Soil seed content was highly variable, ranging from 1660 to 53371 seeds m^?2, with an average value of 10391 seeds m^?2 and a median of 5500 seeds m^?2. Seed stock was lower than 2000 seeds m^?2 in 6.6% of the sites and over 10000 in 26.6%. Six species were found in more than 50% of the sites, representing 27.7% of the total stock: Anagallis arvensis L., Chenopodium album L., Stellaria media (L.) Vill., Echinochloa crus-galli (L.) P. Beauv., Amaranthus spp., Polygonum persicaria L. + P. lapathifolium > L. Overall, 63 species were recorded, the species number per site ranging from 4 to 25, with a median value of 11. Therophytes accounted for 90.6% of the species and 94.3% of individuals. Of the species, 39.8% were assignable to the summer, 21.9% to the spring, 8.1% to the winter and 5.3% to the autumn germinating group, and 24.9% were non-seasonal. Simpson's dominance index for PF ranged from 0.11 to 0.525, with an average value of 0.21 and a median of 0.195. The Shannon diversity index had a range of 1.15–2.43, with an average value of 1.93 and a median of 1.91. In some cases (13.3%) compensation phenomena are evident, sustained by different species from site to site. These results form the basis of a discussion on the effectiveness and the limits of management strategies designed to reduce soil seed stock. Un profil de la flore potentielle des champs de mais de la Vallee du Pô Des enquêtes quali-quantitatives (spectre biologique et ecophysiologique, organisation structurale, taille du stock grainier) de la flore potentielle (FP) dans les champs de maïs (Zea mays L.) de la vallée du Pô, sont rapportées. Les données ont été collectées dans 45 sites à 2 profondeurs d'échantillonage (0–20 cm et 21–40 cm). La teneur en graines du sol était fortement variable, allant de 1660 à 53371 graines m^?2 pour une moyenne de 10391 et une médiane de 5500. Le stock grainier était inférieur à 2000 graines m^?2 dans 6,6% des sites et supérieur à 10000 dans 26,6%. 6 espèces ont été trouvées dans plus de la moitié des sites, représentant 27,7% du stock total: Anagallis arvensis L., Chenopodium album L., Stellaria media (L.) Vill., Echinochloa crus-galli (L.) P. Beauv., Amaranthus spp., Polygonum persicaria L., +P. lapathifolium L. Globalement, 63 espèces ont été inventoriées, avec le nombre d'espèces par site allant de 4 à 25 avec une médiane de 11. Le groupe biologique des therophytes concernait 90,6% des espèces et 94,3% des individus. Au sein des espèces, 39,8%étaient estivales, 24,9% indifférentes, 21,9% des printanières, 8,1% hivernales et 5,3% automnales. L'index de dominance de Simpson pour PF allait de 0,11 à 0,525 avec une moyenne de 0,21 et une médiane de 0,195. L'index de diversité de Shannon allait de 1,15 à 2,43 avec une moyenne de 1,93 et une mediane de 1,91. Dans quelques cas (13,3%) les phenomenes de compensation sont évidents, alimentés par différentes espèces d'un site à l'autre. Ces résultats forment la base d'une discussion sur l'efficacité et les limites des stratégies en vue de réduire le stock grainier du sol. Potentielle Flora in Maisfeldern der Po-Ebene Bei einer sowohl qualitativen als auch quantitativen Aufnahme der potentiellen Verunkrau-tung von Mais-(Zea-mays-)Feldern der Po-Ebene wurden Daten über das biologische und ökophysiologische Spektrum, die Struktur und den Umfang des Samenvorrats im Boden in 0–20 und 21–40 cm Tiefe an 45 Orten erhoben. Der Samenvorrat variierte erheblich und reichte von 1660 bis 53371 Samen m² bei einem Mittelwert von 10391 und einem Median von 5500. An 6,6% der Orte war er <2000, an 26,6% > 10000. 6 Arten wurden an > 50% der Orte gefunden und machten 27,7% des gesamten Samenvorrats aus: Anagallis arvensis L., Chenopodium album L., Stellaria media (L.) Vill., Echinochloa crusgalli (L.) P. Beauv., Amaranthus spp., Polygonum persicaria L. +Polygonum lapathifolium L. Insgesamt wurden 63 Arten gefunden, an den einzelnen Orten zwischen 4 und 25, im Mittel 11. Zur Lebensform der Therophyten zählten 90,6% der Arten und 94,3% der Samen. 24,9% waren indifferente, 21,9% Frühjahrs-, 39,8% Sommer-, 5,3% Herbst-und 8,1% Winterkeimer. Der Simpson-Dominanzindex der potentiellen Flora reichte von 0,11 bis 0,525 mit einem Mittelwert von 0,21 und einem Median von 0,195. Der Shannon-Diversitätsindex lag zwischen 1,15 und 2,43 mit einem Mittelwert von 1,93 und einem Median von 1,91. In einigen Fällen (13,3%) war eine deutliche Kompensation der Arten erkennbar. Anhand der Befunde werden die Wirksamkeit und die Grenzen einer Strategie zur Verringerung des Samenvorrats im Boden diskutiert.