Variation in reproductive characteristics of Eupatorium adenophorum populations in different habitats

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.     

Effect of fire on population dynamics of Mikania micrantha H.B.K. during early succession after slash-and-burn agriculture (jhum) in northeastern India

The population size of Mikania micrantha H.B.K. is considerably enhanced by fire in 2-, 4- and 8-year-old fallows developing after slash-and-burn agriculture (jhum) in northeastern India. The recruitment pattern in burnt and unburnt sites in each fallow differed. Seedling recruitment was restricted only to burnt sites in 2- and 4-year-old fallows, whereas it occurred in both burnt and unburnt sites in an 8-year-old fallow. Sexual reproductive potential of the species was affected by the age of the fallow and by fire in each fallow plot. These results are related to micro-environmental changes in the habitat as a consequence of fire in different fallow plots. Effet du feu sur la dynamique des populations de Mikania micrantha H.B.K. dans un mode de conduite alternatif coupe-brulage dans le nord-est de l'Inde L'importance des populations de Mikania micrantha a été considérablement augmentée par le feu dans des vieilles jachères de 2, 4 et 8 ans conduites selon la technique coupe-brûlage dans le Nord-Est de l'Inde. Le processus de reprise dans les zones brûlées et non brûlées a été différent pour chacune des jachères. La reprise de plantules n'a eu lieu que dans les zones brûlées pour les jachères vieilles de 2 et 4 ans. mais elle est survenue en tout lieu dans la jachère de 8 ans. Le potentiel de reproduction sexuée a été affectéà la fois par l'âge de la jachère et par le feu dans chaque parcelle. Ces résultats sont liés à des changements microenvironnementaux dans l'habitat, conséquence du feu dans les différentes parcelles en jachère. Der Einfluss von Feuer auf die Populationsdynamik von Mikania micrantha H.B.K. während der Frühentwicklung einer Folgevegetation nach Brandhackbau in NO-Indien Die Populationsdichte von Mikania micrantha H.B.K. wird nach Rodung und Abbrennen auf 2, 4 und 8 Jahre altem Brachland durch Feuer beträchtlich erhöht. Auf den einzelnen Brachflächen war die Wiederbesiedelung von abgebrannten und nicht abgebrannten Parzellen verschieden. Die Entwicklung einer Sämlingspopulation war auf 2 resp. 4 Jahre altem Brachland auf abgebrannte Flächen beschränkt, während auf 8 Jahre alter Brache sowohl auf abgebrannten als auch nicht abgebrannten Flächen die Entwicklung einer Sämlingspopulation stattfand. Die sexuelle Reproduktionskraft der Species wird durch die Dauer der Brache und die Wirkung des Feuers beeinflusst. Diese Ergebnisse stehen in Beziehungzu kleinflächigen Umweltveränderungen im Biotop, als Folge des Feuers und des Alters der Brache.     

The influence of crop rotation and soil tillage on seed population dynamics of A vena sterilis ssp. ludoviciana

The dynamics of seed populations of Avena sterilis ssp. ludoviciana (Durieu) Nyman in plots maintained under different crop rotations and tillage systems was studied over a 5-year period. The seed reserves buried in the soil were practically depleted during this period by using any of the three cropping systems evaluated. No significant differences were found between using a continuous barley rotation with annual application of herbicides and using a barley:fallow rotation with herbicides applied only as needed. The decline in seed populations was not affected by the tiliage system used during the fallow period (ploughing or no tillage). The tillage practices used in the various treatments, combined with the variable seed output from each treatment, resulted in different vertical distribution of the seeds in the soil profile. Shallow cultivation resulted in an accumulation of seeds in the upper soil layers; in contrast, a large proportion of the seeds were buried and maintained below 15 cm in the ploughed treatments. Although the seed distribution patterns produced by the various tillage systems had an effect on seedling recruitment, the largest changes in this parameter were associated with the different cropping sequences. Four times more seedlings were recruited in years under barley cropping than in those under fallow.     

Influence of Chromolaena odorata and Mucuna pruriens fallow duration on weed infestation

Summary Fallow management is a major strategy for weed control and soil fertility restoration in tropical farming systems. From 1995 to 1998, weed infestation was evaluated in plots managed under 0, 1, 2 and 3 year fallow durations of (1) a natural bush fallow dominated by Chromolaena odorata ; (2) a planted Mucuna pruriens fallow; and (3) a modified bush fallow without C. odorata . The study was conducted at the Nigerian Institute for Oil Palm Research (NIFOR), Benin City, Nigeria. The 3 × 4 factorial experiment was set up in a split plot arrangement. The three fallow types were the main plots and the four fallow durations were the subplots. Each year, the subplots were planted to maize ( Zea mays , cv. TZSR-W) as appropriate and harvested 14 weeks after planting for yield comparison. Continuous cropping and the modified natural bush fallow increased weed diversity and biomass. Irrespective of fallow type, weed infestation was more gradual in the first year of cropping after fallow than in subsequent cropping years. Regardless of cropping intensity, C. odorata and M. pruriens fallows promoted broad-leaved weeds, chiefly Ageratum conyzoides , Tridax procumbens and Phyllanthus amarus , whereas the modified bush fallow promoted grasses. Maize grain yield was higher in the C. odorata and M. pruriens fallows than in the modified bush fallow, but the yield difference diminished with cropping intensity.     

Cohort-dependent seedling recruitment, survival and reproductive capacity of Tribulus terrestris

Knowledge of the population biology of the summer annual Tribulus terrestris can provide valuable information for managing the risk of its colonising crop fields. Because of spring‐summer crop management practices, fields can exhibit bare ground in late April and early May. In this situation, four cohorts in 2000 and three cohorts in 2001 were censused and monitored throughout the vegetative and reproductive season, in order to evaluate the relationship between time of emergence, survival, vegetative growth and plant reproductive capacities. To a great extent, seedling survivorship depended on emergence timing; the earlier the emergence of the seedlings, the higher was the proportion of survivorship (64% and 4%, for early and late emergences). The time of emergence also influenced plant development; in both years, surviving individuals of the first cohorts presented significantly greater plant biomass and larger numbers of reproductive structures (60.5 fruits per plant) than those of later cohorts (0.8 fruits per plant). Reproductive meristem allocation was also highest in the earliest cohorts. Results showed that T. terrestris can increase its population size in fields if gaps of bare soil surface are available from mid spring to early summer.     

Changes in Organic Matter of a Ferrallitic Tropical Soil Degraded by Cropping Systems: The Case of Southern Senegal

Understanding of the mechanisms involved in the restoration of degraded soils is necessary in order to assess the sustainability of a cropping system. For this purpose, an 8-year experiment was set up to test the efficiency of four cropping systems involving applications of fertilizer and/or manure and incorporation of crop residues and/or fallows on the regeneration of a Haplic Acrisol degraded by about 90 years of traditional cropping (groundnut-millet rotation without any input). The supply of nitrogen by the soil and particle size and chemical distribution were measured and used to characterize the soil organic matter (SOM) after 2 and 8 years of treatments, and then related to nutrients uptake. Two of the four cropping systems tested that were expected to regenerate soil fertility (Q1 and Q2: 4-year rotations including a plowed-in fallow, incorporation of crop residues, and mineral fertilization) both had a depressive effect on SOM content, although the losses of total C and N observed during the experiment (e.g .,-23% N and -20% N for Q1 and Q2, respectively) were less than that for the control (traditional cropping B, -33% N). Only the multiyear fallow did not result in further degradation of SOM, without, however, enriching the soil. On the other hand, an annual application of 10 Mg dry matter of manure ha -1 , combined with fertilizer, markedly increased the SOM (total N increased by factor 2 after only 2 years), an effect that seemed, however, stabilized at the end of the 8 years. Only a strong (10 Mg dry matter ha -1 ) and annual supply of manure, associated with mineral fertilization, had a positive effect on SOM, but its durability is not established.     

Population dynamics of buried weed seeds as influenced by shifting and terrace cultivation in the humid subtropics of India

Change in the viable seed populations of three weed species, Galinsoga ciliata (Rafin) Blake, Polygonum alatum Buch. Ham. and Spergula arvensis L. in soil was studied in potato, radish, cabbage and cabbage+radish (mixed to gether) fields under shifting agriculture (locally called jhum) and terrace cultivation in northeast India from October 1988 to September 1989. The effect of weeding frequency on the viable weed seed populations of these weeds was also investigated. In most fields seed populations were smaller during the rainy season than during other seasons. Initially, the viable seed populations of all three weed species showed a significant (P<0.05) decrease with increasing soil depth in all crop fields under jhum cultivation. However, there was no clear trend in the terraced fields. At the end of the study period the trend was not clear in all crop fields under either jhum or terrace cultivations. In the ‘normally weeded plots’ the viable seed populations of S. arvensis and P. alatum recorded about a 2% increase in jhum fields, while in the terraced fields they showed a loss of 4% over the 1-year period. The ‘frequently weeded plots’ however, showed a sharp decline in viable seed populations in all crop fields. Dynamique des populations des graines de mauvaises herbes enfouies: influence de l'agriculture itinérante et de la culture en terrasses dans les zones humides sub-tropicales de l'Inde Les changements dans les populations de graines viables de trois espèces de mauvaises herbes, Galinsoga ciliata (Rafin) Blake, Polygonum alatum Buch. Ham. et Spergula arvensis L., ont étéétudiés dans des champs de pomme de terre, de radis, de chou et de chou et radis (en mélange) dans des conditions d'agriculture itinérante (appelée localement jhum) et d'agriculture en terrasses dans le nord-est de l'Inde, d'octobre 1988 à septembre 1989. L'effet de la fréquence de désherbage sur les populations de graines viables de ces mauvaises herbes a aussi étéétudié. Dans la plupart des champs, les populations de graines étaient plus réduites pendant la saison des pluies que pendant les autres saisons. Au début de l'étude, les populations de graines viables des trois espèces de mauvaises herbes montraient dans toutes les cultures jhum une décroissance significative (P<0.05) avec la profondeur dans le sol. Par contre, il n'y avait pas de relation claire dans les champs en terrasses. À la fin de l'étude, la tendance n'était claire dans aucun des champs, qu'il soient en culture jhum ou en terrasses. Sur la période d'un an qu'a duré l'étude, et dans les parcelles ‘normalement désherbées’, les populations de graines viables de S. arvensis et de P. alatum ont augmenté de 2% dans les champs jhum, alors que dans les champs en terrasses, elles ont chuté de 4%. Cependant, dans les parcelles fréquemment désherbées, les populations de graines viables décroissaient rapidement dans tous les champs. Populationsdynamik des Unkrautsamenvorrats im Boden unter dem Einfluß von Rodungs- und Terrassen-Kulturen in humid subtropischen Gebieten Indiens Veränderungen der Samenpopulation der 3 Unkrautarten Galinsoga ciliata (Rafin) Blake, Polygonum alatum Buch. Ham. und Spergula arvensis L. im Boden wurden in Kartoffeln, Rettich, Kohl und Mischbeständen von Kohl und Rettich bei wandernden Rodungskulturen (Jhum genannt) und Terrassenkulturen in Nordostindien zwischen Oktober 1988 und September 1989 untersucht. Die Wirkung der Häufigkeit des Jätens auf die Populationen lebensfähiger Unkrautsamen wurde auch untersucht. Auf den meisten Feldern waren die Samenpopulationen während der Regenzeit kleiner als in der übrigen Jahreszeit. Anfänglich nahm die Samendichte aller 3 Unkrautarten mit zunehmender Bodentiefe in allen Jhum-Kulturen signifikant ab (P<0.05). In den Terrassenkulturen jedoch waren die Verhältnisse nicht klar. Zum Ende der Untersuchungsperiode war sowohl bei der Jhum- als auch der Terrassenkultur die Verteilung der Samen im Boden gleich. Auf den Jhum-Feldern nahmen die Samenpopulationen von S. arvensis und P. alatum bei normalem Jäten um 2% zu. während sie bei der Terrassenkultur um 4% abnahmen. Bei häufigem Jäten jedoch nahmen die Samenpopulationen in allen Kulturen sehr deutlich ab.     

Rapid nitrogen and phosphorus homeostasis transformation in Eupatorium adenophorum during invasion

Exotic plants can compete well with native species because many invasive species are considered better nutrient users in both low‐ and high‐resource environments. However, whether invasive plants can outperform native plants at all stages of invasion is not very clear. We investigated the nitrogen (N), phosphorus (P) and N:P homeostasis of an invasive Eupatorium adenophorum and a co‐occurring native plant Artemisia argyi in an area across the five invasion stages of E. adenophorum. The N homeostasis (H_N) of E. adenophorum was higher than that of A. argyi, whereas the P and N:P homeostasis (H_P and H_N/P) were higher for A. argyi. For E. adenophorum, H_N decreased, but H_P and H_N/P increased with the invasion time. For A. argyi, H_N/P increased, H_P and H_N remained stable with the invasion time. The results demonstrated that E. adenophorum could maintain higher H_N during invasion stages when N was limited and could maintain higher H_N and H_P at invasion stages when P was more limited. This rapid nitrogen and phosphorus homeostasis transformation of invasive E. adenophorum during its invasion stages guarantees its stronger competitive ability over native species and promotes its invasion success.     

Seedling establishment and vegetative spread of Cirsium arvense (L.) Scop, in Victoria, Australia

Although large numbers or viable seeds of C. arvense arc formed in some districts of Victoria, the germination percentage declines rapidly in the first 2 years. No seedlings were established from seed artificially spread on pastures, although at two sites 6–8% and 12–6% of seed sown 0–5–1′0 cm deep into bare soil gave emerged seedlings, and 78% and 93% respectively of the seedlings survived. It is unlikely that C arvense is spreading rapidly by seed under the present management of permanent grassland. Patches of C. arvense were shown to have a pattern of development similar to plants such as Pteridium and Calluna that degenerate behind an advancing front. The annual rate of vegetative spread in pastures was about 150 cm and extremely variable (range 4–341 cm).     

Effects of two pathogens on the performance of Cirsium arvense in a successional fallow

Biological control of weeds by natural antagonists is of increasing interest. To reduce densities of the weed Cirsium arvense (creeping thistle) in a successional fallow, we applied spores of two pathogens, the biotrophic rust Puccinia punctiformis and the perthotrophic Phoma destructiva, for three consecutive years individually at different dates and combined. The proportion of systemically Puccinia punctiformis-infected C. arvense was not influenced by the treatments, but local rust infection was a good predictor of systemic infection in the following season. Artificial inoculations with P. destructiva increased the incidence of this pathogen in the third year as a result of synergistic effects, when co-inoculated with P. punctiformis. Inoculations with either pathogen had little effect on C. arvense shoot density, although there were transient reductions after combined inoculations with both fungi compared with the fungicide treatment. Cirsium arvense decreased from 60% to 5% cover within 3 years, while the cover of the co-occurring fallow vegetation increased. Under field conditions, with an already high degree of natural P. punctiformis infection, the effects of inoculations of the single pathogens were minor, but reductions in shoot density after combined inoculations indicate that this inoculation may have the potential to cause a decline of this weed.     

Growth and patterns of resource allocation in Eupatorium odoratum L. in the secondary successional environments following slash and burn agriculture (Jhum)

Biomass, nitrogen, phosphorus and potassium in Eupatorium odoratum L. (Asteraceae), an abundant early successional perennial weed, were studied in seral stages after slash and burn. Increment in individual biomass and nutrient uptake declined with increasing time after fallow. A higher proportion of the available resources was allocated to the supporting organs but a lower proportion to the photosynthetic organ in the older fields compared to recently fallowed fields. The allocation of biomass to reproduction, and also nutrient content, decreased during seral development. However, cost of reproduction to the plants (considered as the proportion of increment in biomass or nutrient uptake during the current growing season) was much higher in the older fields than the younger ones. Growth was adversely affected by low nutrient availability in soil in the recently fallowed fields but the allocation pattern remained unaffected. Biomass was not allocated in the same manner as nutrients. A higher proportion of nitrogen and phosphorus compared to that of biomass and potassium was devoted to reproduction in all the fields.     

Comparing rice germplasm groups for growth, grain yield and weed-suppressive ability under aerobic soil conditions

Germplasm and cultivars need to be selected as parents for breeding weed‐competitive aerobic rice in the tropics. Forty rice (Oryza sativa) cultivars belonging to the aus, indica and tropical japonica germplasm groups, or derived from crosses among them, were evaluated in adjacent weed‐free and weedy trials in aerobic soil conditions during the wet seasons of 2001–2003. The objectives of this study were to assess vegetative growth, grain yield under weed‐free (Y_F) and weedy (Y_W) conditions, and weed‐suppressive ability (WSA) of different germplasm groups. In the first 4 weeks after sowing, indica cultivars had faster growth in height, tillering and crop biomass than other groups. They also had high Y_F, Y_W and strong WSA. Aus cultivars were similar to the indica types in early growth and WSA, but were poor in Y_F. Tropical japonica groups and the group derived from indica/tropical japonica crosses were generally inferior to aus and indica groups in early growth and WSA. Both of their Y_F and Y_W were lower than that of the indica group. Therefore, indica germplasm seemed to be most suitable for breeding high‐yielding and weed‐suppressive aerobic rice for the tropics. The relationship of WSA with various traits within tropical japonica germplasm revealed that fast early growth, rather than plant erectness, is crucial to WSA.     

杂交稻自生苗中类似杂草稻的生物学特性

在自然条件下,种植不同时间籼型杂交稻后改种常规粳稻,对粳稻田中的杂交稻自生苗展开调查,分析杂交稻自生苗中出现类似杂草稻的频率及其生物学性状,测定杂交稻自生苗对粳稻产量的影响.结果表明,在粳稻田中籼型杂交稻自生苗可以转变成类似杂草稻,即存在籼粳亚种间异交产生杂草稻的可能;连续种植杂交稻3年后改种常规粳稻田块的杂交稻自生苗密度最高,对常规粳稻产量的影响最大.     

Weedy rice: An expanding problem in direct‐seeded rice in the Philippines

Weedy rice is morphologically similar to cultivated rice (Oryza sativa L.). It has biological characteristics that identify it as a weed. Its important weedy characteristics, that is, early and heavy seed shattering, makes it very difficult to control. Weedy rice has not been reported to be an important weed problem in transplanted, flooded rice. However, the shift to direct‐seeded rice (DSR) due to water issues and high costs of labor has increased reports of weedy rice becoming an expanding important problem in Vietnam, Malaysia, Thailand, and the Philippines. Experts believe that the growing adoption of DSR in Asian countries will result in the rise of weedy rice as one of the top troublesome weeds in rice production. Early and recent surveys in the Philippines have indicated the urgent need to increase awareness of weedy rice among farmers to allow the implementation of a number of effective location‐specific weed management strategies. These surveys and other studies conducted since weedy rice was first reported in 1991 confirmed that weedy rice and grass weed species caused major problems in DSR areas. About 35% of the 4.56 M ha harvested area in the country is planted with DSR. As cultivated and weedy rice are close relatives, it would be very difficult to implement management options very early in crop growth. However, a deeper understanding of the underlying traits of weedy rice can help develop a holistic approach toward effective and economic weed management.     

杂草稻对水稻生长及产量的影响

通过室内试验和田间试验明确了杂草稻对水稻生长、产量构成因子和产量的影响。水稻营养生长期,不同杂草稻密度对水稻基本苗、株高、单株鲜重、分蘖、倒二叶长与宽均没有影响。而水稻株高、有效穗数、穗长、一次枝梗数、穗粒数、千粒重、结实率、实际产量等均随杂草稻密度的增加而呈现下降趋势。杂草稻密度为1株/m2可导致水稻产量损失9.15%,当杂草稻密度达7株/m2时可导致水稻产量损失50%以上,杂草稻密度达到12株/m2时水稻产量损失可高达72.29%。     

Weed interference in maize, cowpea and maize/cowpea intercrop in a subhumid tropical environment. II. Early growth and nutrient content of crops and weeds

Early growth and nutrient content of crops and weeds from weed-free and weedy no-tillage maize (Zea mays L, cv. TZB), cowpea (Vigna unguiculata (L) Walp. cv. VITA-5) and maize/cowpea intercrop at populations of 40000, 50000 and 30000 + 40000 plants ha^?1 grown on a loamysand Oxic Ustropept in a subhumid tropical location were monitored in the early and late 1979 cropping seasons. In the first 6 weeks of growth in the early season, cropping pattern had no effect on weed growth; weeds did not suppress crop growth significantly until 5–6 weeks after sowing and total crop dry weights were not affected by cropping pattern. Three weeks after sowing, weeds from weedy crop plots had taken up two to four times as much nutrient (N, P, K, Ca + Mg) as was taken up by corresponding weed-free crops. In the late season, weed dry weight 6 weeks after sowing was depressed in the intercrop compared to monocultures and dry-matter production of the intercrop was higher than those of monocultures. The resource use index (RUI), defined as the amount of an environmental resource used by a weed-free crop divided by the combined amount of the same resource used by the corresponding weedy crop and the associated weeds, increased with age of crop and was higher for the intercrop than the monocultures only in the late season.     

Population dynamics of Eupatorium adenophorum Spreng. and Eupatorium riparium Regel in relation to burning

The population dynamics of Eupatorium adenophorum Spreng. and E. riparium Regel was studied in the field for 2 years, in relation to burning, by following the fate of individuals in permanent quadrats at short and regular time intervals. Both species showed increased population density and longevity of individuals on the burnt site. Adult and seedling populations of both species showed greater survival in the burnt plot. Eupatorium riparium survived better than E. adenophorum adults after burning. In the unburnt plot, however, the seedling survival of both species was nil. The heavy juvenile mortality of both species in the unburnt situation is attributed to the accumulation of a thick layer of pine needles and the growth of herbaceous vegetation. Moisture stress and low temperature in winter months also seem involved in the regulation of seedling population of these two weeds.     

Phenylalanine ammonia‐lyase and cinnamate 4‐hydroxylase genes' response to HHO in Eupatorium adenophorum

6‐Hydroxy‐5‐isopropyl‐3,8‐dimethyl‐4a,5,6,7,8,8a‐hexahydronaphthalen‐2(1H)‐one (HHO) is an allelopathic substance that is related to allelochemical metabolism in Eupatorium adenophorum. In this study, the full‐length complementary DNA of two phenylalanine ammonia‐lyase (PAL) genes and a fragment of the cinnamate 4‐hydroxylase (CA4H) gene from E. adenophorum (Ea) were cloned. The expression of all three genes was increased by the HHO treatment, with varying sensitivity: EaPAL2 > EaPAL1 > EaCA4H. Southern blotting suggested that there is a third member of the PAL gene family in this species.     

Effect of herbicides and doses on short- and long-term control of Eleusine tristachya

In Argentina, Eleusine tristachya has been recently reported as a problematic weed that can occur at high densities in spring and summer in fallows and in maize and soyabean. The reason for the increase in E. tristachya populations is that once the weed is established, it is difficult to eliminate because it produces a high number of seeds and plant regrowth occurs after herbicide treatments. The aim of this study was to determine the effect of post-emergence application of herbicides (glyphosate, haloxyfop-methyl and clethodim) at the seedling, vegetative and reproductive stages on the short-term (biomass 30 days after treatment—30 DAT) and long-term (tiller number and height and seed production—regrowth at 330 DAT) control of E. tristachya selected biotypes in outdoor pot experiments. Data fitted to a log-logistic model. For all the herbicides considered, at the seedling and vegetative stages, short-term control was achieved with low ED₅₀ and ED₉₀ values, whereas at the reproductive stage, ED₉₀ values were three- to sixfold (glyphosate), six- to 52-fold (haloxyfop-methyl) and five- to 13-fold (clethodim) higher. Long-term control at the recommended dose or lower was not possible at the reproductive stage as tiller regrowth and seed production occurred with all herbicides. It is advisable to control Eleusine tristachya when plants are small at the beginning of the growing season using the recommended herbicide dose. A delayed application will produce tiller regeneration the following year, and consequently, control would only be achieved applying an overdose, which can cause risks to health and the environment. We concluded that a management programme based on the combination of glyphosate with post-emergence graminicides applied at early stages will be effective to control future infestations.     

Weed seedling emergence in contrasting fodder crop systems following 30 years of cultivation in the lowlands of Northern Italy

Five fodder crop systems of different intensity (ranging from a double annual crop of Italian ryegrass + silage maize to a permanent meadow) were adopted for 30 years in the lowlands of Northern Italy under two input levels, differing mainly in their provision of organic fertiliser (manure). Herbicides were used in the maize crops included in all systems, except the meadow. After 30 years, the weed seedbank of all systems and input levels were assessed by the seedling emergence technique on soil samples from each plot. The cropping systems determined the abundance and composition of the weed assembly. Relatively few, frequent species made up the majority of the emerged seedlings in all systems, and there was no relationship between the total number of emerged seedlings and the mean number of species recorded in the different systems. Arabidopsis thaliana and Oxalis corniculata were abundant in the annual double crop and in the 3- and 6-year rotations that also comprised the annual double crop. These weeds, however, were unlikely to represent a major threat to the crops, due to their vigour and growth period. The permanent meadow tended to greater weed biodiversity than the other systems. The application of manure favoured the seedbank of species such as Lolium multiflorum, Digitaria sanguinalis and A. thaliana. Weed communities in the different systems were mainly determined by herbicide application, (through the ability of weeds to avoid its effects, determined by the weed life history and emergence period) and manure application (with its possible dual effect of spreading weed seeds and favouring nitrogen-responsive weeds).