ALBERT

Notes: Awned seeds of four grasses were submitted to humidity changes on dry and damp soil to see how far the awns assisted in distribution and seed burial. The results indicate that awns on their own are probably of limited importance. In another study, seeds of seven species were soaked in water with high or low oxygen levels to determine whether dormancy could be induced. Waterlogging delayed germination briefly but did not induce dormancy except in Avena fatua. Oxygen level proved unimportant. The effect of temperature on germination and dormancy was examined in seeds of Agrostis capillars. Seeds of this species germinated best at fluctuating temperatures with a minimum difference of 10°C between day and night temperatures. Constant or slightly fluctuating temperatures over 20°C or under 10°C induced dormancy in a small percentage of seeds.

Notes: Seven field experiments in spring wheat and barley with natural infestations ot A. fatua were set up to investigate the effects on grain yield of removing the weeds by hand at intervals during early growth stages. Only three sites showed any significant yield reductions and these all had populations of wild oats of 150 stems or more per m2 at harvest. No significant yield reductions occurred at lesser densities (20–100/m2). At the three higher-density sites, competitive effects did not start until the crop had four leaves, about 4–5 weeks after it had emerged. A further experiment in a glasshouse designed to test if competition occurred prior to the emergence of crop and weed indicated no effect at all during this period. Lépoque du déclenchement de la compétition entre la folle avoine (Avena fatua L.) et les céréales de printempsSept essais ensemencés en blé de printemps et en orge on t été implantés dans des champs présentant des infestations naturelles d'Avena fatua, en vue dévaluer les effets, sur le rendement en grain, de l'extirpation des mauvaises herbes à la main, à des intervalles réguliers durant les premiers stades de la croissance.Trois essais seulement on t accusé des réductions significa-tives des rendements et ceux-ci avaient tous des populations de folle avoine de 150 pieds ou plus au m2 à la récolte. II n'y a pas eu de réductions significatives de rendement pour des densités inférieures (de 20 à 100/m2). Dans les trois essais à densitéélevée, les effets compétitifs ne commencérent pas avant que la plante cultivée ait atteint le stade 4 feuilles, 4 à 5 semaines environ aprés sa Ievée. Une expérience ulté-rieure en serre réalisée pour rechercher si la compétition se produit avant la levée de la plante cultivée et de la mauvaise herbe n'a montré aucun effet durant cette pédode. Der Zeitpunkt des Beginns einer Konkurrenz zwischen Flughafer (Avena fatua L.) und SommergetreideEs wurden sieben Feldversuche mit Sommerweizen und-gerste mit einer natürlichen Verseuchung von A. fatua angelegt, um den Einfluss einer Beseitigung der Unkräuter von Hand zu verschiedenen Entwicklungsstadien auf den Kornertrag zu messen. Nur bei drei Versuchen waren ge-sicherte Ertragsrückgänge festzustellen; die Flughaferdichte betrug in diesen Fällen zum Erntezeitpunkt 150 oder mehr Halme je m2. Bei geringeren Dichten (20–100/m2) waren keine gesichterten Ertragsminderungen feststellbar. In den drei Versuchen mit den höheren Dichten setzte die Konkurrenz nicht ein bevor das Getreide im 4-Blattstadium war; das waren etwa 4–5 Wochen nach dem Aufiaufen. Es wurde ein weiterer Versuch im Gewächshaus angelegt, um festzustellen, ob die Konkurrenz vor dem Auflaufen des Ge-treides und des Unkrauts eintrat. Während dieser Periode war kein Einfluss festzustellen.

Notes: Weeds in a total of 450 fields of winter oilseed rape in nine areas of central southern England were surveyed, just prior to harvest during summer 1985, to identify those that had survived herbicide treatment or had not been sprayed and, thus, were capable of re-infestation or contamination of the harvested crop. Sixty-two species were identified; their levels of infestation were scored and distribution within the field noted. The most frequent species was Galium aparine, which occurred in 57% of fields. Mayweeds (Tripleurospermum inodorum, Matricaria recutita and Anthemis cotula) occurred in 23% of fields and Papaver rhoeas in 21%. All other species occurred in less than 20% of fields, the most prevalent being Sonchus asper(18%). Grassweeds were relatively infrequent, reflecting the widespread use of effective graminicides; the most prevalent was Arena spp., found in 9% of fields. Although most species were distributed throughout the field, Geranium dissection (13%) and Sisymbrium officinale (7%) were virtually confined to field margins (extending 1 m into the crop) and headlands (10m into the crop), respectively. Several species exhibited a well-defined regional distribution; Silene alba was virtually restricted to the most southern counties surveyed, whilst Papaver rhoeas and Viola arvensis were conspicuously absent from the eastern area.

Notes: Numbers of viable seeds in the 0–15 cm soil layer were determined for 64 arable fields, mainly heavy soils cropped with cereals and leys, in north Oxfordshire and south Warwickshire. When first sampled in 1972 or 1973, there was a range from 1500 to 67 000 seeds m−2 with a median of 4360 m−2. Seeds of Poa annua L. occurred in all fields, often in large numbers (up to 35 550 m−2), while Polygonum aviculare L., Stellaria media (L.) Vill., Bilderdykia convolvulus (L.) Dumort., Aethusa cynapium L., Alopecurus myosuroides Huds., Veronica persica Poir., Chenopodium album L., Veronica arvensis L. and Capsella bursa-pastoris (L.) Med. also occurred frequently. When the fields were sampled again 2 and 4 years later many showed little change either in total seed bank or in species representation. The most pronounced fluctuations involved the annual grasses A. myosuroides, which tended to increase where winter cereals were grown, and P. annua which increased where leys were established. The results are discussed in relation to crop management and compared with those from other surveys.Les stocks de graines dans quelques sols arables des Midlands d'AngleterreLe nombre des graines viables présentes entré 0 et 15 cm de profondeur a été déterminé pour 64 sols arables, principalement des sols lourds occupés par des céréales et des prairies temporaires, dans le nord de l'Oxfordshire et le sud du Warwickshire. Lors de la première estimation, en 1972 ou 1973, les comptages ont donné de 1500 à 67 000 graines m−2 avec une médiane de 4360. Des graines de Poa annua L. ont été trouvées dans tous les champs, souvent en grand nombre (jusqu'à 35 550 m−2); on a aussi trouvé fréquemment des graines de Polygonum aviculare L., Stellaria media (L.) Vill., Bilderdykia convolvulus (L.) Dumort., Aethusa cynapium L., Alopecurus myosuroides Huds., Veronica persica Poir., Chenopodium album L., Veronica arvensis L. et Capsella bursa-pastoris (L.) Med. Beaucoup de dénombrements opérés 2 et 4 ans plus tard n'ont montré que peu de changements du nombre total de graines ou de la représentation des diverses espèces. Les fluctuations les plus notables ont été observées à propos des graminées annuelles A. myosuroides, qui tendaient à s'accroitre dans les cultures de céréales, et P. annua, qui augmentait dans les prairies temporaires. Les résultats sont discutés en relation avec la conduite des cultures et comparés avec ceux d'autres dénombrements.Samenvorrat in einigen Ackerböden in MittelenglandIn den obersten 15 cm von 64, meist schweren, mit Getreide oder Grasgemischen bepflanzten Ackerböden im nördlichen Oxfordshire und südlichen Warwickshire wurde die Anzahl keimfähiger Samen bestimmt. Bei der ersten, 1972 oder 1973 erfolgten, Bestandesaufnahme wurden zwischen 1500 und 67 000, im Mittel 4360 Samen m−2 gezählt. In allen Böden wurden Samen von Poa annua L., oft in sehr grosser Zahl (bis zu 35 550 m−2), gefunden. Häufig waren auch Polygonum aviculare L., Stellaria media (L.) Vill., Bilderdykia convolvulus (L.) Dumort., Aethusa cynapium L., Alopecurus myosuroides Huds., Veronica persica Poir., Chenopodium album L., Veronica arvensis L. und Capsella bursa-pastoris (L.) Med. 2 und 4 Jahre später durchgeführte Zählungen zeigten in vielen Fällen nur geringe Veränderungen, sowohl in Bezug auf Samenzahl als auch auf vorhandene Arten. Die markantesten Aenderungen wurden bei anuellen Gräsern festgestellt; so zeigte A. myosuroides eine zunehmende Tendenz auf mit Wintergetreide bepflanzten Flächen, während P. annua in höherer Anzahl auf Flächen gefunden wurde, wo Grasland angelegt worden war. Die Ergebnisse werden in Bezug auf Kulturmethoden und Fruchtwechsel diskutiert und mit den Resultaten anderer Untersuchungen verglichen.

Notes: The effects of reduced-cultivation Systems on weeds in cereals are reviewed. Increasing dependence of these Systems upon Chemical weed control together with changes in the soil physical environment are expected to modify existing weed floras. Annual-grass weeds are likely to remain a problem with the use of minimal cultivations, particularly when early drilling is practised, while hitherto unimportant species may become more prevalent, e.g. Bromus spp. Furthermore, reduced cultivations may encourage the establishment of wind-disseminated species. However, annual dicotyledonous species characteristic of arable land are expected to continue to decline.

Notes: Summary. Monthly samples of field-grown rhizomes and aerial stems of Polygonum amphibium were tested for innate dormancy during parts of 2 years in England and during 5 months of a third year in southern Germany. All stems and rhizomes were cut into two-node fragments, planted in soil in a warm glasshouse, and the new shoots counted after 3 weeks. Dormancy per month for different categories of stems varied from 0 to 23%, averaging 4–3% for all fragments tested but only 1–3% for mature buds. No evidence of a dormant period was found in either country.Incidence de la darmance dans une tige à deux noeuds et des fragments de rhizome de Polygonum amphibium L.

Notes: Details and results are given of the first of two surveys, which are designed to measure the changes taking place in the incidence of forty species of arable weeds in Britain.