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1.
The invasive plant, Eupatorium adenophorum, produces large numbers of small seeds with a high germination rate. However, this investigation showed that E. adenophorum populations in an evergreen broad‐leaved forest had a high proportion of seedlings when compared with clonal plants. Whereas an opposite pattern was found in a deciduous broad‐leaved forest and in a roadside site. A seed addition experiment where E. adenophorum seeds were added to each of the three habitats did not increase the number of E. adenophorum seedlings at any of the three field sites. Field and greenhouse experiments demonstrated that a soil litter layer significantly reduced the number of E. adenophorum seedlings during the early seedling emergence period. However, at later periods, the litter cover did not affect survival and growth of individuals. The emergence of E. adenophorum seedlings was significantly increased in field experiments when there was no litter, and parental plants were removed. Finally, the growth of seedlings was significantly reduced when planted with their parental plants in a root box experiment. In the low‐resource environment of the evergreen broad‐leaved forest, E. adenophorum reproduced primarily by its abundant seed production. In the more open deciduous broad‐leaved forest and roadside site, the populations reproduce primarily by vegetative clones that can grow quickly, are better competitors and could take advantage of the high‐resource environment. 相似文献
2.
The long-term effect of different depths of soil cultivation on weed seedling emergence from naturally occurring populations of weed seeds in the soil was examined in four experiments on land previously in pasture, raspberry canes or intensive vegetable production. At approximately monthly intervals, weed seedlings were counted and then killed with contact herbicides, after which plots were cultivated to 250 or 10mm, or were left undisturbed. The treatments were continued for 7 years. One experiment was then discontinued whilst the previously uncultivated plots on the other three were cultivated to 150 mm at approximately monthly intervals for a further 4 years in one experiment, and for 8 years in the other two. After the first year, very few seedlings emerged in the uncultivated and shallow cultivated plots, and seedling numbers declined slowly in the deep-cultivated plots. Under repeated deep cultivation, seedling emergence of almost all species declined exponentially. Different species declined at different rates, with Rubus idaeus L., Plantago lanceolata L., Veronica arvensis L. and Ranunculus spp. being the most rapidly declining group. Rates of decline for individual species were similar to those observed in Europe.Juncus bufonius L. behaved differently from the other species, and showed no decline in seedling numbers. In the initial 7-year period, 28 000 weed seedlings per m?2 emerged from the deep-cultivated plots on soil previously cropped with vegetables. Over the same period, less than 11 000 seedlings emerged in shallow-cultivated plots, and just over 4000 in uncultivated plots. In the second phase of the experiments, fewer seedlings of most species emerged than in the first phase, and the decline in numbers of Coronpous didymus (L.) Sm. seedlings was slower. Résumé Les effets à long terme de différentes profondeurs de travail du sol sur la levée des mauvaises herbes ont étéétudiés sur des populations naturelles dans des parcelles dont les précédents étaient: paturage, framboisier ou maraichage intensif. À des intervalles d'environ un mois, les jeunes plantes de mauvaises herbes étaient dénombrées puis détruites à l'aide d'herbicides de contact, aprés quoi les parcelles étaient travaillées sur 250 ou 10 mm, ou laissées sans intervention. Cette premiére phase a duré 7 ans. Une expérience a alors été arretée et les parcelles précédemment non cultivées des trois autres ont été travaillées à une profondeur 150 mm, à des intervalles d'environ un mois pendant 4 ans dans un expérience, et pendant 8 ans dans les deux autres. Aprés un an, trés peu de mauvaises herbes levaient dans les parcelles non cultivés et dans celles travaillées superficiellement, et le nombre de levées diminuait lentement dans les parcelles travaillées profondément. Lá oú le travail profond était répété, les levées de presque toutes les especes declinaient exponentiellement. Les différentes espéces déclinaient à des vitesses différentes,Rubus idaeus L., Plantago lanceolata L., Veronica arvensis L. et Ranunculus spp. déclinant le plus rapidement. Les vitesses de diminution pour les differentes espéces étaient similaires à celles observées en Europe. Juncus bufonius L. se comportait différemment des autres espéces et ne montrait aucune décroissance du nombre de levées. Au cours de la période initiale de 7 ans, 28 000 mauvaises herbes par m?2 levaient dans les parcelles maraicherés travaillées profondément. Au cours de la meme periode, moins de 11000 mauvaises herbes lavaient dans les parcelles travaillées superficiellement et un peu plus de 4000 dans les parcelles non travaillées. Dans la seconde phase de I'expérience, on observait moins de levées de la plupart des especes que au cours de la premiére et la decroissance du nombre de levés de Coronpous didymus (L.) Sm. était moins rapide. Einfluβ der Bodenbearbeitung auf Keimung und Populationsdynamik von Unkrautern Der langfristige Einfluβ verschieden tiefer Bodenbearbeitung auf die Keimung von Unkrautern aus der naturlich gegebenen Samenbank im Boden wurde in 4 Versuchen auf Flachen untersucht, die vorher als Weide oder mit Himbeer oder intensiven Gemusekulturen genutzt worden waren. Die Keimpflanzen wurden 7 Jahre lang etwa monatlich ausgezahlt und mit Kontaktherbiziden abgetotet, danach wurden die Parzellen 25 tief 15 cm, tief oder gar nicht bearbeitet. Ein Versuch wurde beendet, wahrend eine der 3 ubrigen unbearbeiteten Parzellen fur weitere 4 Jahre und die anderen beiden fur weitere 8 Jahre in etwa monatlichen Abstanden 15 cm tief bearbeitet wurden. Am Ende des ersten Jahres liefen auf den unbearbeiteten und den flach bearbeiteten Flachen sehr wenige Keimpflanzen auf; auf den tief bearbeiteten Flachen nahm die Zahl der Keimpflanzen langsam ab. Bei wiederholt tiefer Bodenbearbeitung verringerte sich die Zahl der Keimpflanzen fast aller Arten exponentiell. Am schnellsten sank die Keimrate bei Rubus idaeus L., Plantago lanceolata L., Veronica arvensis L. und Ranunculus spp. Die Abnahme der Keimrate war bei den einzelnen Arten ahnlich wie in Europa beobachtet. Juncus bufonius L. verhielt sich von den anderen Arten abweichend und lieβ keine Abnahme der Keimrate erkennen. In der anfanglichen 7-Jahres-Periode keimten auf den vorher gemusebaulich genutzten, tief bearbeiteten Flachen 28000, den flach bearbeiteten weniger als 11 000 und den unbearbeiten gut 4000 Samen m?2. In der 2. Versuchsphase wurden bei denmeisten Arten weniger Keimpflanzen als in der 1. beobachtet, und die Abnahme der Keimrate von Coronopus didymus (L). Sm. war langsamer. 相似文献
3.
Roger J. Haggar 《Pest management science》1976,7(4):417-421
Under normal systems of grassland management, most sown swards become invaded by weed grasses. This ingress is usually associated with a depletion in the size and number of the sown species. Selective herbicides can be used to combat this grass invasion and the results of two experiments are presented to show how low-dose dalapon in mid-July can be used for this purpose. When the sown grasses are too severely depleted, some method of introducing seed is required. A new one-pass technique is now being developed for establishing grass and clover seed into existing swards. After sowing, ways of increasing the clover content are being studied, based on the use of grass-suppressing herbicides in late winter. In one experiment several-fold increases in clover growth were recorded 5 months after applying carbetamide (2.8 kg/ha) and propyzamide (0.8 kg/ha). 相似文献
4.
H. A. ROBERTS 《Weed Research》1964,4(4):296-307
Summary. Four replicated experiments were begun in successive years to study the behaviour of viable seeds of eleven species of annual weeds when mixed with a 3 in. layer of cultivated soil. The soil was confined in pots sunk in the ground outdoors, seedling emergence was recorded, and the numbers of viable seeds remaining at the end of the experiments were assessed. One experiment was continued for 3 years, the others for 5 lull calendar years after the freshly collected seeds had been sown.
Initial emergence was greatest with Stellaria media, Senecio vulgaris and Poa annua , and least with Chenopodium album and Thlaspi arvense . Subsequently, the numbers of seedlings which emerged each year declined at a rate which was constant for each species. In the fifth year after sowing, the number of seedlings of Senecio vulgaris was only 0.3% of the initial number of viable seeds, while for Thlaspi arvense and Veronica hederifolia the figure was 3.2%.
The proportions of viable seeds which produced seedlings ranged from 37 to 86%, while from 0 to 11% were still present in the dormant state after 5 years. Most species showed marked patterns in the seasonal distribution of emergence which were modified by variations in weather from year to year, but in any one year, the distribution of emergence was not influenced by the length of time the seeds had been in the soil.
Germination et longévité dans des sots cultivés de semences de quelques mauvaises herbes annuelles 相似文献
Initial emergence was greatest with Stellaria media, Senecio vulgaris and Poa annua , and least with Chenopodium album and Thlaspi arvense . Subsequently, the numbers of seedlings which emerged each year declined at a rate which was constant for each species. In the fifth year after sowing, the number of seedlings of Senecio vulgaris was only 0.3% of the initial number of viable seeds, while for Thlaspi arvense and Veronica hederifolia the figure was 3.2%.
The proportions of viable seeds which produced seedlings ranged from 37 to 86%, while from 0 to 11% were still present in the dormant state after 5 years. Most species showed marked patterns in the seasonal distribution of emergence which were modified by variations in weather from year to year, but in any one year, the distribution of emergence was not influenced by the length of time the seeds had been in the soil.
Germination et longévité dans des sots cultivés de semences de quelques mauvaises herbes annuelles 相似文献
5.
Management of newly established field margins on nutrient-rich soil to reduce weed spread and seed rain into adjacent crops 总被引：1，自引：1，他引：0
We studied the effect of different ways to establish and to maintain unfertilised field margins on the development of potential weeds and seed dispersal into adjacent crops. Plant communities in field margins either developed spontaneously or were sown with different seed mixtures of grasses and forbs. Margins were mown twice a year and the cuttings were either removed or left in situ. Three years after establishment, the importance of the unsown rhizomatous species Elytrigia repens and Urtica dioica was significantly higher in the unsown community or when cuttings were not removed after mowing. Seed dispersal from the margin into adjacent crops was important in the unsown community during the first year after establishment. Between 82% and 99% of the seeds were disseminated within 4 m from the margin strip. Overall risk of contaminating the adjacent crop with weeds originating from the field margin strip was concentrated within a few metres of the crop edge. In order to minimise the dissemination of weed species and invasion by noxious vegetatively propagated weeds on nutrient‐rich land, it is recommended that field margins are established by sowing and cuttings removed after each cut. 相似文献
6.
实生苗是植物种群更新的主要资源。通过对实生苗种类组成和数量的分析 ,研究了典型草原冷蒿 -小禾草群落的种群更新特点 ,结果表明 :不同年度实生苗的数量和主要植物的实生苗的优势地位均有差异 ,这是降雨分布与实生苗出现时间共同作用的结果 ;不同放牧率的实生苗数量以无牧区最低 ,轻牧区最高 ,随放牧率的增加有先升高而后降低的趋势 ;浇水后实生苗的数量大大增加 ,主要是增加了一年生藜属植物的数量 ,对种类的影响不大。 相似文献
7.
J. L. HAMMERTON 《Weed Research》1967,7(1):1-21
Summary. Seeds ni Polygonum lapathifolium from several sources or after certain treatments were subjected to various periods of moist chilling and then incubated for 3 weeks, during which time the numbers that germinated were recorded.
Populations from different localities differed in both seed weight and in the response of the seeds to chilling, but no relationships between the response and the environment of the locality of origin were found. Seeds from individual plants and from single inflorescences within populations also varied in both seed weight and germination with and without chilling. Application of dichlorprop to the parent plants was found to affect seed weight and % germination, the effect varying with both population and dose.
Etudes sur des espèces de mauvaises herbes du genre Polygonum L.
IV. Variations du poids et des modalités de germination des semences chez P. lapathifolium L. 相似文献
Populations from different localities differed in both seed weight and in the response of the seeds to chilling, but no relationships between the response and the environment of the locality of origin were found. Seeds from individual plants and from single inflorescences within populations also varied in both seed weight and germination with and without chilling. Application of dichlorprop to the parent plants was found to affect seed weight and % germination, the effect varying with both population and dose.
Etudes sur des espèces de mauvaises herbes du genre Polygonum L.
IV. Variations du poids et des modalités de germination des semences chez P. lapathifolium L. 相似文献
8.
Summary. The effects of several herbicides on the rates of CO2 uptake and transpiration of intact plants were measured. A simple technique is described which reveals whether photosynthesis-inhibiting herbicides are inactivated by plants. By this method, the inactivation of simazine by maize could be confirmed. Evidence is presented for physiological inactivation of monuron by Plantago lanceolata , of cycluron (OMU) and pyrazon by sugar beet, of N'-(4-butoxyphenyl)-NN-dimethylurea by of 5-bromo-6-methyl-3-phenyluracil by flax. Certain plant species showed different reactions to some other new herbicides. The effect of herbicides in the culture solution on CO2 uptake by the leaves is probably largely determined by the rate of transpiration of the plants. Assuming that uptake in proportional to transpiration rate, estimates of the concentration of the herbicides inside the plant were made.
L'inactivation physiologique de quelques herbicides produisant une inhibition de la photosynthèse 相似文献
L'inactivation physiologique de quelques herbicides produisant une inhibition de la photosynthèse 相似文献
9.
Annual weed populations establish every year from persistent seed banks in the soil. This 3 year study investigated the relationship between the number of weed seeds in the soil seed bank and the resultant populations of major broadleaf and grass weeds in 30 maize fields. After planting the crop, 1 m2 areas were protected from the pre-emergence herbicide application. Soil samples were collected soon after spraying to a depth of 100 mm and the weed seeds therein were enumerated. The emerged weed seedlings in the field sampling areas were counted over the following 8 weeks. Up to 67 broadleaf species and five grass weeds were identified, although not all were found at every site and some were specific to a region or soil type. For the most abundant weeds in the field plots, on average 2.1–8.2% of the seeds of the broadleaf species and 6.2–11.9% of the seeds of the grass weeds in the soil seed bank emerged in any one year, depending on the species. Overall, the results showed a strong linear relationship between the seed numbers in the soil and the seedling numbers in the field for all the grasses and for most broadleaf weeds. For some species, like Trifolium repens , only a weak relationship was observed. In the case of Chenopodium album , which had the largest seed bank, there was evidence of asymptotic behavior, with seedling emergence leveling off at high seed numbers. An estimate of the soil seed bank combined with knowledge of the germination and behavior of specific weed species would thus have good potential for predicting future weed infestations in maize fields. 相似文献
10.
The population response of the two sympatric annual weeds, Galinsoga ciliata (Raf.) Blake and G. parviflora Cav., which occur abundantly in croplands and early secondary successional communities in the north-eastern hill region of India was studied in relation to sowing pattern (clump or scattered sowing), population density and soil moisture and texture. In a given sowing pattern, seed germination of both species declined with increase in sowing density and moisture stress. However, sowing of seeds in clumps and an increased proportion of sand in soil enhanced the germination, Fewer weeds died in the population raised from scattered sowing than from clumped distribution. Plants grown at high moisture level matured earlier, and fertility of the survivors was negatively correlated with both density and moisture stress in both species although G. ciliata was less affected. Seed output and dry matter yield per pot of both species increased with population density but the increase was not linearly related to the increase in plant numbers, and density-induced reduction in seed output was observed at high densities. Galinsoga ciliata appears to tolerate greater density-stress than G. parviflora. Asubstantial decrease in production of capitula, seeds and dry matter at low moisture level indicates the role played by soil moisture in regulating the population growth of the two weeds. An increased proportion of sand in soil resulted in significantly greater seed production in G. parviflora. Galinsoga ciliata also showed a similar trend although the differences were not statistically significant. 相似文献
11.
E. D. WILLIAMS 《Weed Research》1973,13(4):422-429
Summary. Seedlings and plants derived from single-node rhizome fragments of Agropyron repens and Agrostis gigantea were grown in au unheated glasshouse, separately or together with wheat ( cv. Kolibri), in sandy loam soil in well-spaced pots, adequately watered and moderately fertilized. Samples of crop and weeds were taken for growth analysis in mid- May, late June and early August (when the wheat was ripe).
On average, wheat decreased the weight of weed shoots by 84% and of rhizomes by 77%, but the weeds decreased the weight of wheat shoots by only 7% and of grain by 13%. Without wheat, seedlings of both weed species had, by late June, grown as much as plants from rhizomes, but with wheat, the weed seedlings were throughout most of the experiment more susceptible to competition than were plants from rhizomes. There was no simple relationship between the final dry weights of the weeds and the amount they decreased wheat yield: although Agropyron seedlings in competition with wheat were much lighter than Agrostis from rhizomes, they decreased grain yield of wheat as much, suggesting that they competed more intensely for a limiting factor, possibly nitrogen.
It is concluded that the faster initial growth rate of wheat seedlings relative to the weeds from rhizomes and a larger initial seed reserve relative to the weed seedlings enabled the wheat to dominate the weeds.
Comparaison de la croissance et comportement compétitif de plantules et de plantes issues de rhizomes d'Agropyron repens ( L.) Beauv. et d' Agrostis gigantea Roth 相似文献
On average, wheat decreased the weight of weed shoots by 84% and of rhizomes by 77%, but the weeds decreased the weight of wheat shoots by only 7% and of grain by 13%. Without wheat, seedlings of both weed species had, by late June, grown as much as plants from rhizomes, but with wheat, the weed seedlings were throughout most of the experiment more susceptible to competition than were plants from rhizomes. There was no simple relationship between the final dry weights of the weeds and the amount they decreased wheat yield: although Agropyron seedlings in competition with wheat were much lighter than Agrostis from rhizomes, they decreased grain yield of wheat as much, suggesting that they competed more intensely for a limiting factor, possibly nitrogen.
It is concluded that the faster initial growth rate of wheat seedlings relative to the weeds from rhizomes and a larger initial seed reserve relative to the weed seedlings enabled the wheat to dominate the weeds.
Comparaison de la croissance et comportement compétitif de plantules et de plantes issues de rhizomes d'Agropyron repens ( L.) Beauv. et d' Agrostis gigantea Roth 相似文献
12.
Summary. Seeds of Polygonum lapathifolium and P. persicaria were germinated in mid-March, -April or -May 1967 and mid-April, -May, -June or -July 1968 and planted out into fertilized field plots. Seed was collected from twelve individual plants for each month of sowing. Mean seed weight was least from May-sown plants in 1967 and from June-sown plants in 1968 for both species. May-sown plants of P. persicaria had the lowest percentage of trigonous seeds in both years. Viability and germination were influenced by month of sowing in both species. Month of sowing also affected inter-plant variation in the various attributes studied. In the 1967 experiment. May-sown P. lapathifolium plants produced seed that germinated more slowly than that from March- or April-sown plants; only a small percentage of the germinated seeds from the May sowing were able to emerge when shallowly planted in compost. Plant fresh weight was positively correlated with seed production and with seed weight, the correlation coefficients being larger for P. persicaria. Recherches sur les espèces de mauvaises herbes du genre Polygonum L. VI. Effets de l'environnement sur le poids de la semence, le polymorphisme et le mode de germination chez P. lapathifolium et P. persicaria Résumé. Des semences de Polygonum lapathifolium et P. persicaria furent mises à germer à la mi-mars, -avril, -mai 1967 et à la mi-avril, -mai, -juin ou -juillet 1968; les plantes furent repiquées en plein champ, dans des parcelles situées dans des terrains fertilisés. La semence fut récoltée individuellement sur douze plantes pour chaque mois de semis. Le poids moyen de la semence fut plus faible pour les plantes semées en mai en 1967 et pour celles semées en juin en 1968, pour les deux espèces. La date de semis eut également une influence sur la variation entre plantes quant aux divers caractéres étudiés. Dans l'expérience de 1967, le P. lapathifolium semé en mai produisit une semence à germination plus lente que celle des plantes semées en mars ou avril; un faible pourcentage seulement des semences germées provenant des semis de mai furent capables de lever lorsqu'elles furent plantées superficiellement dans un compost. Le poids frais des plantes montra une corrélation positive avec la production de semence et avee le poids de la semence, les coefficients de corrélation étant plus élevés pour P. persicaria. Untersuchungen über Unkrautarten der Gattung Polygonum L. VI. Umwelteinflüsse auf Samengewicht, Samenpolymorphismus und Keimungsverhalten bei Polygonum lapathifolium und P. persicaria Zusammenfassung. Samen von Polygonum lapathifolium und P. persicaria wurden 1967 Mitte März, Mitte April bzw. Mitte Mai und 1968 Mitte April, Mitte Mai, Mitte Juni bzw, Mitte Juli eingekeimt und in gedüngte Feldparzellen ausgepflanzt. Von 12 Einzelpflanzen der verschiedenen Saatzeiten wurden Samen gesammelt. Bei beiden Arien waren 1967 bei im Mai gesäten und 1968 bei im Juni gesäten Pflanzen die mittleren Samengewichte am geringsten. Die im Mai gesäten Pflanzen von P. persicaria hatten den niedrigsten Anteil an trigonoiden Samen in beiden Jahren. Die Lebensdauer und die Keimfähigkeit hingen bei beiden Arten vom Monat der Saat ab. Der Saattermin beeinflusste ausserdem die interpflanzenvariation bei den verschiedenen untersuchten Faktoren. In dem Versuch von 1967 keimten die Samen von im Mai gesätem P. lapathifolium langsamer als diejenigen von im März oder April gesäten Pflanzen; nur ein geringer Prozentsatz der im Mai gekeimten Samen war in der Lage, bei flaehem Auspflanzen in Kompost aufzulaufen. Das Pflanzenfrischgewicht stand in positiver Korrelation zur Samenproduktion und zum Samengewicht, wobei die Korrelationskoeflizicnten für P. persicaria grösser waren. 相似文献
13.
SHELDON C. NAVIE F. DANE PANETTA RACHEL E. McFADYEN STEVE W. ADKINS 《Weed Biology and Management》2004,4(3):154-167
The germinable soil seedbank was determined at two sites in central Queensland on four separate occasions between February 1995 and October 1996. These sites were infested with parthenium weed ( Parthenium hysterophorus L.), a serious invasive exotic weed. During this period, the seedbank varied between 3282 and 5094 seeds m−2 at the Clermont site, and between 20 599 and 44 639 seeds m−2 at the Moolayember Creek site. Parthenium hysterophorus exhibited a very abundant and persistent seedbank, accounting for 47–73% of the seedbank at Clermont and 65–87% of the seedbank at Moolayember Creek. The species richness and species diversity of the seedbank, and the seed abundance of many species, was lower at Moolayember Creek during spring (the time of year when the most dense infestations of the weed originate). Parthenium hysterophorus seedlings also emerged more rapidly from the soil samples than did those of all other species. Hence, it seems that various aspects of the weed's seed ecology, including abundance and the persistence of its seedbank and the rapid emergence of its seedlings, are major factors contributing to its aggressiveness in semiarid rangeland communities in central Queensland. The domination by P . hysterophorus of the seedbanks of these sites suggests that the weed is having a substantial negative impact on the ecology of these plant communities. The diversity of these seedbanks was found to be lower in comparison with that observed in other grassland communities that were not dominated by an invasive weed species. Hence, the prolonged presence of P . hysterophorus may have substantially reduced the diversity of these seedbanks, thereby reducing the ability of some of the native species to regenerate in the future. 相似文献
14.
Effect of seed age and cultivation on seedling emergence and seed decline of Avena fatua L. in winter barley 总被引：3，自引：0，他引：3
B. J. WILSON 《Weed Research》1985,25(3):213-219
Avena fatua was sown in a cultivation experiment in the autumn of 3 successive years. For each population seedling emergence and viable seeds in the soil were recorded for 4 years in crops of winter barley in which new seed production was prevented. About half of the seeds sown were recovered after 1 year. In subsequent years viable seeds in the soil declined more rapidly with tine cultivation than with ploughing. After 4 years up to 5% of the original seeds were still viable. One population exhibited greater seed dormancy than the other two populations, due it is thought to higher summer rainfall and the greater availability of moisture during seed maturation. Most seedlings emerged in the autumn and spring, between 12 and 18 months after sowing. A total of 950 seedlings emerged from 12 000 seeds sown; 21% of these seedlings came from new seeds (< 1 year old), 57% from seeds 1–2 years old, 14% from seeds 2–3 years old and 8% from seeds 3–4 years old. Autumn seedlings arose fairly evenly from all age groups while spring seedlings mostly came from the 1–2-year-old seeds. With tine cultivation total seedlings over 4 years represented 9–7% and with ploughing 6–2% of the original seeds sown. A. fatua was more persistent than in previous experiments in spring barley, which suggests that control measures would have to be applied for longer in a succession of winter cereals than spring-sown crops to reduce A. fatua to low populations. 相似文献
15.
The effect of sowing date on the infection of sugar-beet seedlings by Polymyxa betae was examined in a small-plot experiment on a naturally infested site. Seed was sown on seven occasions at weekly intervals from late March to early May. From each sowing, plant samples were taken at approximately weekly intervals over a period of 7 weeks. The extent of root infection by P. betae and the dry weight of plants was determined at each sampling date, and the progress of infection and rate of plant growth were examined against time and thermal time. Infection occurred sooner after sowing and the subsequent rate of fungal development was more rapid in late-sown than in early-sown plants. Early sowing allowed germination and growth of sugar beet at temperatures too low for fungal infection. The growth of late-sown plants appeared to be reduced by P. betae infection. The implications of these findings for the development of rhizomania disease are discussed. 相似文献
16.
R. J. H AGGAR 《Weed Research》1979,19(4):231-239
Changes in ihe species composition of a ryegrass pasture were examined over a 2 year period from a spring establishment. Seed of S23 perennial ryegrass was sown in main plots, eilher broadcast or drilled, at rates of 15, 25 or 35 kg/ha in a field experiment at Oxford. The whole area was oversown withfour weed grasses (Agrostis siolonifera.Holcus lanatus. Poa annua and P trivialis). Five cultural and three herbicide treatments were applied across the plots. These consisted of three levels of nitrogen (0. 50 and 100 kg N per ha), two companion species (Italian ryegrass and white clover) and 2.4-D, benazolin and methabenzihiazuron applications. Ten weeks after sowing, broad-leaved weeds accounted for nearly half the lotal dry-matter yield, except where controlled by the three herbicides. Grass yields were nol increased by herbicide treatment. The only cultural treatment checking broad-leaved weeds was ihe 35 kg/ha seeding rale. Seven months after sowing, the only treatment which had decreased the abundance of weed grasses was melhabenzthiazuron especially againsi A. stolonifera and Poa spp. Two years afler sowing, perennial ryegrass had only 34% ground cover and had been replaced largely by H. lanatus (38%), Poa spp, (15%) and A. stolonifera (7%), Where methabenzthiazuron had been used the ryegrass ground cover was 48%. with less P. trivialis and A. stolonifera. but H. lanatus was nol altered. White clover decreased H. lanatus cover. In two supplementary pot experiments, methabenzthiazuron sprayed pre-emergence damaged perennial ryegrass unless the seed was covered with at least 4 mm of soil. Only H. lanatmand F. rubra out of sixteen grasses were relatively resistant to methabenzihiazuron when applied at ihe tillering stage, confirming that this herbicide has potential for preventing the ingress of many unsown grasses in new leys. 相似文献
17.
In order to clarify the growth and reproductive success of seed‐derived Sagittaria trifolia individuals emerging at different times within a season, seeds were sown on May 16, June 16 and July 22 2010 and allowed to grow in pots under shaded and unshaded conditions. The timing of when the first inflorescence of each seedling appeared was recorded, as well as the number of seeds and tubers produced and the dry weight of each organ. In total, 220 seedlings were used, 23–59 in each treatment. As the sowing time was delayed, so too was the appearance of the first inflorescence. Additionally, the number of inflorescences, fruits and seeds produced by the unshaded plants significantly decreased with the sowing time. The total dry weight was significantly greater in the unshaded than in the shaded plants: the July‐sown, shaded plants grew very poorly. The relative resource allocation to the tubers was greater in the late‐emerging, shaded seedlings. Even in the shaded groups, except for the July‐sown plants, most of the plants set seed. Therefore, when addressing weed control in paddy fields, one should keep seedlings in mind, in addition to plants that have grown from tubers. 相似文献
18.
A long-term study was conducted during 4 consecutive years to determine the effects of herbicides on the major demographic parameters and on the dynamics of the populations of Avena sterith ssp. ludoviciana (Durieu) Nyman growing in winter wheat crops in Central Spain. The three herbicides tested bad different effects on the life cycle of the plant. Tri-allate was moderately effective in reducing seedling recruitment and seedling survivorship, but it resulted in adult fecundities similar to or higher than, those of the check plots. Difenzoquat was highly effective in reducing plant survivorship and it consistently reduced the reproductive capacity of the survivors. Flamprop-isopropyl L was not very effective in reducing plant survivorship, but it had the largest influence on adult fecundity. Overall, although the three herbicides were able to reduce substantially (59–95%) the production of new seeds, large numbers of seeds were returned annually to the soil in all the treatments. The annual application of any of the three compounds during 4 consecutive years had a marked effect on the long-term evolution of the populations of buried seeds in the soil, emerged seedlings, mature plants and new seeds produced. Continuous herbicide application resulted in a gradual depletion of the seed bank of A. sterilis in the soil. At the end of the 4-year period, buried seed populations in the herbicide-treated plots were (61–81%). lower than those at the beginning of the experiment, and 92–95% lower than those of the check plots at the same lime. However, the seed reserves present in the treated plots were Mill high enough to require some type of control programme. 相似文献
19.
Epidemics of the splash-dispersed pathogenic fungus Diaporthe adunca on its host, the perennial herb Plantago lanceolata , were followed during two consecutive years in transects at roadsides in the Netherlands. Epidemics of D. adunca were also studied on clones of a susceptible and a partially resistant genotype of P. lanceolata grown either in a pure stand or in a 1:1 mixture in small plots in the garden. The epidemics in the natural and experimental populations could be adequately described by logistic and Gompertz models, but large differences were found in final disease levels and relative growth rates. The effect of partial resistance on the epidemic in the mixture was less than in a pure stand, probably due to the provision of inoculum from the highly diseased susceptible genotype to the partially resistant genotype. In the garden focal and wind-direction effects were seen. In the natural populations the epidemics developed from numerous primary infected scapes making foci and wind-directions effects less conspicuous. 相似文献
20.
S. R. MOSS 《Weed Research》1987,27(5):313-320
Alopecurus myosuroides Huds. was studied over a 2-year period in winter wheat established after tine cultivations or direct drilling. Straw was removed by baling or spread and burnt. Seed production was either allowed or prevented by cutting and removing all vegetation at the end of the first year. Cultivation differences had no consistent effect on plant or seed populations. Straw burning destroyed about 50% of seeds and encouraged the germination of surviving seeds. Weed populations in the crop were lower on burnt than on baled areas. Where seed shedding was allowed, populations of seeds in soil and plants increased by up to nine-fold per year. Straw burning resulted in smaller population increases. Seed decline in the soil averaged about 80% per year, so that less than 6% of the weed seeds sown were still viable after 2 years’burial in the soil. Most of the seed decline occurred between July and October and was slightly greater on burnt than on baled areas. Only part of this seed loss was accounted for by germination and emergence of seedlings during summer and autumn. Plants emerging in the crop represented less than 26% of viable seeds present in the soil at time of drilling the crop. Few seedlings emerged in spring. The viability of shed seeds varied with year and with weed density. High infestations were associated with lower seed viability and also fewer heads per plant. 相似文献