The effects of seed mix and management on the abundance of desirable and pernicious unsown species in arable buffer strip communities

Buffer strips are refuges for a variety of plants providing resources, such as pollen, nectar and seeds, for higher trophic levels, including invertebrates, mammals and birds. Margins can also harbour plant species that are potentially injurious to the adjacent arable crop (undesirable species). Sowing perennial species in non‐cropped buffer strips can reduce weed incidence, but limits the abundance of annuals with the potential to support wider biodiversity (desirable species). We investigated the responses of unsown plant species present in buffer strips established with three different seed mixes managed annually with three contrasting management regimes (cutting, sward scarification and selective graminicide). Sward scarification had the strongest influence on the unsown desirable (e.g. Sonchus spp.) and unsown pernicious (e.g. Elytrigia repens) species, and was generally associated with higher cover values of these species. However, abundances of several desirable weed species, in particular Poa annua, were not promoted by scarification. The treatments of cutting and graminicide tended to have negative impacts on the unsown species, except for Cirsium vulgare, which increased with graminicide application. Differences in unsown species cover between seed mixes were minimal, although the grass‐only mix was more susceptible to establishment by C. vulgare and Galium aparine than the two grass and forb mixes. Annual scarification can enable desirable annuals and sown perennials to co‐exist, however, this practice can also promote pernicious species, and so is unlikely to be widely adopted as a management tool in its current form.     

Under‐sown cover crops and post‐harvest mowing as measures to control Elymus repens

Two potential control methods for Elymus repens, which do not disturb the soil, are post‐harvest mowing and competition from under‐sown cover crops. Our aim was to quantify the effect of cover crop competition and mowing on E. repens and to evaluate the potential for combining the two methods. We present a two‐factorial split‐plot experiment conducted at three locations in Sweden, in two experimental rounds conducted in 2011–2012 and 2012–2013. A spring cereal crop was under‐sown with perennial ryegrass, red clover or a mixture of the two (subplots). Under‐sown crops were either not mowed, or mowed once or twice post‐harvest (main plots). This was followed by ploughing and a new spring cereal crop the next year. Mowing twice reduced autumn shoot biomass by up to 66% for E. repens and 50% for cover crops compared with the control, twice as much as mowing once. Pure ryegrass and mixture treatments reduced E. repens shoot biomass by up to 40% compared with the control. Mowing twice reduced rhizome biomass in the subsequent year by 35% compared with the control, while the pure red clover treatment increased it by 20–30%. Mowing twice and treatments including red clover resulted in higher subsequent grain yields. We concluded that repeated mowing has the potential to control E. repens, but a low‐yielding cover crop has insufficient effect on rhizome biomass. Clover–grass mixtures are of interest as cover crops, because they have the potential to increase subsequent crop yield and even at low levels they reduce E. repens above‐ground autumn growth.     

Interacting effects of soil degradation and precipitation on plant productivity in NE Patagonia,Argentina

Our objective was to examine the effects of inter-annual variation of precipitation on productivity of two dominant species (Chuquiraga avellanedae, an evergreen shrub, and Nassella tenuis, a perennial grass) in two communities of contrasting soil degradation: a herbaceous steppe with shrubs (HSS) and a degraded shrub steppe (SS). Data were collected during two consecutive years with different annual precipitation. Aboveground productivity was determined nondestructively using a double sampling approach. The number of inflorescences per plant was recorded too. Perennial grass productivity was lower in SS than in HSS in both years, while shrub productivity was lower in SS only during the year of below average precipitation. With rising precipitation the perennial grass increased the number of inflorescences while the evergreen shrub augmented vegetative biomass. In summary, the effects of precipitation on plant productivity are community dependent; abiotic factors, such as superficial and sub-superficial soil characteristics, and biotic factors, such as leaf area index (LAI) or tussock sizes, may interact to influence the responses of species to precipitation. Our results suggest that if precipitation increased, this would favor the dominance of shrubs over grasses.     

EXPERIMENTS IN HAND-WEEDING OF CONIFER SEEDBEDS IN FOREST NURSERIES

Summary. In 3 years and in three nurseries, experimental plots sown with conifer seed were weeded by hand at intervals from 1½ to 12 weeks. Assessments of the seedlings at the end of each year showed a reduction in numbers and height only on plots left for 12 weeks between successive weedings. The total time taken to weed plots during the growing season was least for plots weeded at intervals of 3-4 weeks and greatest for plots weeded at the longest intervals. Data on the total weight of weeds, the total number of weeds, the species composition and the stage of weed growth at weeding are also given and discussed.
Essais de désherbage dans les pépinières     

Effect of weed control treatments on weeds, seed yield, yield components and nodulation in winter lentil

Good weed control is critical in winter lentil production. This study was conducted on the lentil cultivar Sazak 91 during the winter seasons of 1997–98 and 1998–99 to determine the most appropriate method for controlling weeds. Hand weeding (weed‐free control), weedy control (inoculated), weedy control (uninoculated), hand hoeing once, hand hoeing twice, trifluralin, imazethapyr, linuron, prometryn, phenmedipham + desmedipham, trifluralin + hand hoeing and linuron + hand hoeing treatments were evaluated and the effects of herbicides on nodulation in lentil were investigated. In the first year Convolvulus arvensis, Centaurea balsamita, Ranunculus arvensis, Cephalaria syriaca and Lathyrus spp., dominated whereas in the second year Hordeum vulgare, Adonis aestivalis and Centaurea depressa were the dominant weed species in the plots. Prometryn, hand hoeing, linuron and a combination of linuron + hand hoeing were found to be the most effective for control of weeds, resulting in the highest yield in winter lentil throughout the investigation. Trifluralin and imazethapyr had a phytotoxic effect on the lentil plants. None of the weed control treatments had any adverse effects on nodulation and Rhizobium leguminosarum inoculation was not found to have any effect on the competitive ability of the lentil plants.     

The influence of herbicides, nitrogen fertilizer, seed rate and method of sowing, on the establishment and long-term composition of a perennial ryegrass ley.

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.     

Can the occurrence of Senecio jacobaea be influenced by management practice?

Senecio jacobaea is a poisonous weed in grasslands of various countries (e.g. Great Britain, New Zealand, Central European states) and the further spread of the species into farmland must be prevented. To assess the influence of management practice and site conditions on the occurrence of S. jacobaea, we conducted a survey in the northern and central part of Switzerland. Botanical assessments were carried out on grassland plots with S. jacobaea occurrence and on neighbour plots without S. jacobaea. For these plots, we analysed the soil nutrients and the details of management practice, such as type and intensity of management and fertiliser application. The most important factors influencing the occurrence of S. jacobaea were related to management: There was a high risk for the occurrence of the species on parcels with low nitrogen fertilisation, continuous‐extensive grazing (set stocking) and a very open sward. Senecio jacobaea was not present in intensively managed meadows cut more than twice per year. As an exception, with a high propagule pressure from the vicinity, S. jacobaea was also found in intensively grazed pastures and in meadows of moderate management intensity (two cuts). We conclude that long‐term control of S. jacobaea can best be achieved by avoiding sward damage and by preventing the species’ seed formation in the pasture and local vicinity.     

The impact of landscape structure and sown grass margin strips on weed assemblages in arable crops and their boundaries

A paired-field study was made in southern England in arable fields, each with or without sown 6-m wide grass margin strips. Seven field pairs were located in each of small, intermediate and open landscapes, which were based on mean field size. Ground cover, plant species diversity and assemblages were assessed in crop centres, crop edges and non-crop field boundaries. The data were used to test for effects of sown grass margins, differences in field location, impacts on rare weed species and for landscape effects on weed assemblages. Significantly higher plant species diversity was found in boundaries protected by buffer strips. Annual weeds associated with field edges, notably Anisantha sterilis , were found at lower cover where perennial grass strips were present. Sown grass strips enhanced boundary plant diversity, particularly by increasing polycarpic species. Margin strips had a small influence on the weed flora of the crop edge, possibly reducing weed cover, but had no influence on floras of field centres. Field size and landscape context did not affect weed assemblages, which show marked field-to-field variability, though crop type was an important influence. Grass margins did not enhance rare arable weed species and may be a threat to them, if margins are sited where such species are known to occur in the seedbank. With this exception, grass strips are a positive influence on boundary flora diversity and reduce margin weeds in arable landscapes.     

Weed competition in willow coppice crops: the cause and extent of yield losses

Growth in 2-year-old willow Salix spp., grown in the short-rotation coppice (SRC) system on agricultural land, was compared in 30 weeded and 30 unweeded plots in each of 2 years after cutting. Non-destructive assessment methods of both crop and weed biomass were used. Coppice growth in year I was greater in the weeded plots than in the unweeded plots. In year II, coppice growth was not different between plots so that, over the 2-year study period, the coppice yield reductions with weeds reflected the losses in year I only. There was considerable variation in the amount of weeds in the unweeded plots. The relationship between the volume of weeds present and the extent of the coppice yield reduction over 1 and 2 years after cutting are described by linear models. Soil moisture and nutrient content, when measured in mid-summer, were not different between plots in either year. In year I, mid-summer coppice height was greater in the weedy plots, while stem numbers in both years and canopy density in year II were lower in the weedy plots. These results indicate that tall weeds competing for light and space in the first year of growth, rather than moisture or nutrient stress, caused fewer (and taller) stems to grow from the coppice stools, leading to the observed reductions in biomass.     

Pre-sowing herbicides in irrigated cotton (Gossypium barbadense L.) and ground nut (Arachis hypogaea L.) in the Sudan. I. Weed control and crop yields achieved with trifluralin and benfluralin.

Trifluralin in cotton and benfluralin in groudnut. incorporated pre-planting. gave satisfactory control of grass weeds and increased crop yields substantially. Oxadiazon as a pre-planting treatment did not give satisfactory additional control of dicotyledons resistant to the first two herbicides. A post-sowing mechanical ridging operation controlled some herbicide resistant weeds, but its effects depended on timing, weed species and growing conditions. Supportive hand weeding of resistant weeds (mainly dicotyledons) was most effective 4 weeks after crop emergence. Crop yields similar to clean weeded controls were achieved by combining trifluralin or benfluralin with moderate supportive hand weeding and re-ridging. Herbicide applications could be made several months before crop planting during the dry season, giving more effective use of spray equipment and operatives. Delays of up to 24 hours between spraying and incorporation by normal cultivation could be tolerated without loss of herbicidal activity.     

Chemical weed control in irrigated direct-seeded rice in the Sudan Gezira

Unrestricted weed growth resulted in serious yield losses (60–75%) in rice (Oryza saliva L.). Hand-weeding once at 2 weeks after crop emergence was ineffective, but weeding at 2 and 2 weeks after crop emergence brought yield losses down to 20%. Pre-emergence application of bifenox and oxadiazon (12 l) and post-emergence application of molinate + propanil gave crop yields comparable to that of the clean weeded control (91–129%). Grain yields obtained with pre-emergence application of oxadiazon (25 EC) and post-emergence applications of propanil, bentazone + propanil, and bifenox alone or as a tank mix with propanil or bentazone were considerably less than those obtained from the clean weeded plots. Bifenox, oxadiazon (12 l) and propanil + molinate gave adequate and persistent weed control (72–97%), and did not damage rice. Oxadiazon (25 EC) gave good weed control but resulted in a serious stand reduction. Post-emergence application of propanil, propanil + bentazone bifenox alone or as a tank mix with propanil or bentazone had no adverse effect on crop stand, but gave poor control of grasses (0–40%).     

Efficacy of chemical weed control in spring cereals in Finland

A national survey was conducted in Finland from 1982 to 1984 to determine the main weed species in spring cereals and the efficacy of herbicides on Finnish farms. The most common dicotyledonous weeds producing the highest biomass in spring cereals were Chenopodium album L., Galeopsis spp. L., Stellaria media (L.) Vill. and Lapsana communis L. The main grass weed was Elymus repens (L.) Gould. The average reduction of weed biomass by herbicide treatment was 75%. More reliable efficacy was obtained with herbicide mixtures than with MCPA alone.     

Control of Elymus repens by rhizome fragmentation and repeated mowing in a newly established white clover sward

Control of perennial weeds, such as Elymus repens, generally requires herbicides or intensive tillage. Alternative methods, such as mowing and competition from subsidiary crops, provide less efficient control. Fragmenting the rhizomes, with minimal soil disturbance and damage to the main crop, could potentially increase the efficacy and consistency of such control methods. This study's aim was to investigate whether fragmenting the rhizomes and mowing enhance the control of E. repens in a white clover sward. Six field experiments were conducted in 2012 and 2013 in Uppsala, Sweden, and Ås, Norway. The effect of cutting slits in the soil using a flat spade in a 10 × 10 cm or 20 × 20 cm grid and the effect of repeated mowing were investigated. Treatments were performed either during summer in a spring‐sown white clover sward (three experiments) or during autumn, post‐cereal harvest, in an under‐sown white clover sward (three experiments). When performed in autumn, rhizome fragmentation and mowing reduced E. repens shoot biomass, but not rhizome biomass or shoot number. In contrast, when performed in early summer, rhizome fragmentation also reduced the E. repens rhizome biomass by up to 60%, and repeated mowing reduced it by up to 95%. The combination of the two factors appeared to be additive. Seasonal differences in treatment effects may be due to rhizomes having fewer stored resources in spring than in early autumn. We conclude that rhizome fragmentation in a growing white clover sward could reduce the amount of E. repens rhizomes and that repeated mowing is an effective control method, but that great seasonal variation exists.     

Vegetation and seedbank response to Eragrostis lehmanniana removal in semi‐desert communities

Eragrostis lehmanniana (Lehmann lovegrass) is an invasive perennial bunchgrass in semi‐desert grasslands in the USA. We removed E. lehmanniana using glyphosate at three locations in south‐eastern Arizona in 2003 and 2004 to evaluate the community response. We also sampled the seedbank five times during the course of the experiment to characterise viable seeds at the sites. Two of the sites with histories of livestock grazing responded similarly to the continued removal of E. lehmanniana, with significant increases in native cover and species richness, mainly attributable to herbaceous annual species. Over the course of the study, progressively fewer E. lehmanniana seeds and higher numbers of native annual herb seeds were germinated from seedbank samples of treated plots. At the third site, characterised by a history of intense agricultural use and drier conditions than the other sites, there was a large decrease in E. lehmanniana cover in all plots, followed by an increase in aggressive non‐native species as well as native grasses. The seedbank at this site suggested potential for restoration, with native perennial grass species present in increasing quantities. The results of this study have implications for site restoration, should a means of permanently removing E. lehmanniana be found.     

Survival of seeds from perennial biomass species during commercial‐scale anaerobic digestion

Tall perennial grass species can be utilised as bioenergy feedstocks, but some are considered invasive species. Using biomass from such species as feedstocks for anaerobic digestion (AD) may introduce the risk of disseminating viable seeds onto agricultural lands during digestate application. To evaluate this risk, we investigated the survival rates of perennial grass seeds obtained from biomass species during AD. After removal from the digester, seeds were germinated and stained with tetrazolium chloride to determine viability. During three experimental runs, batches of 100 seeds from four species were exposed to 0, 2, 6, 12, 24, 48, 72 and 168 h of mesophilic (38°C) AD within a commercial‐scale digester. Seed viability of Phalaris arundinacea, Phragmites australis, Panicum virgatum and Solanum lycopersicum was reduced by 95% (LT₉₅) after 29, 52, 98 and 105 h of AD respectively. Commercial digesters that utilise perennial grasses as a feedstock typically have retention times ranging from 240 to 1480 h, which greatly exceeds the LT₉₅ values found in this study. Anaerobic digestion resulted in the rapid death of seeds in all species tested, suggesting unwanted dissemination of perennial grass species via digestate application to agricultural land is unlikely.     

Weed seed rain interception by grass cover depends on seed traits

Weed management requires a better understanding of the dynamics of the weed seedbank, which is a primary source of weeds in a field. Seeds reaching the ground after seed rain replenish the seedbank and therefore contribute to future weed infestations. Our investigation is based on the hypothesis that a permanent vegetation cover, such as a grassland, can prevent weed seeds from reaching the ground. Therefore, we developed an innovative experimental device to simulate in controlled conditions the seed rain of 12 weed species (Capsella bursa‐pastoris, Conyza canadensis, Myosotis arvensis, Papaver rhoeas, Poa annua, Polygonum aviculare, Ranunculus sp., Rumex obtusifolius, Sonchus asper, Stellaria media, Taraxacum officinale and Veronica persicaria). We quantified the interception of weed seeds by a grass cover. Grass cover height, seed size and seed appendage (e.g. pappus, wing or awn) increased seed interception, in contrast to seed weight and shape index. From these results, we established a linear model to predict weed seed interception by a grass cover as a function of their seed trait values. The relationship between the predicted interception and weed community dynamics observed in grasslands was negative for some species, indicating that other processes may be involved depending on weed species. The weed seed interception model will be incorporated into an existing model of weed population dynamics to simulate the impact of grassland insertion into arable crop rotations.     

Floristic composition and species diversity of weed community after 10 years of different cropping systems and soil tillage in a Mediterranean environment

Sustainable cropping systems based on low inputs have received much attention, even if they may lead to the establishment of a competitive weed flora. This study, conducted from 2011 to 2014 in a Mediterranean environment, evaluated the changes in weed community composition in two cropping systems [conventional (CONV ) and organic (ORG )] with different soil tillage [inversion tillage (IT ) and non‐inversion tillage (NoIT )] in a wheat–tomato–chickpea rotation that began in 2000. The treatments were replicated three times according to a randomised complete block design. The organic system was managed according to EU regulations. Inversion tillage consisted of mouldboard ploughing to a depth of 30 cm, while NoIT consisted of subsoiling to a depth of 20 cm. Weed control was based on herbicide application in CONV and mechanical weeding in ORG . The organic non‐inversion system showed the highest weed biomass (134, 128 and 195 g dry matter (DM ) m^?2 in wheat, tomato and chickpea, respectively) and weed density (66, 77 and 76 plants m^?2 in wheat, tomato and chickpea, respectively), as well as community richness. However, ORG always increased weed diversity, even if annual dicotyledon species were abundant in ORG ‐IT and perennial dicotyledon species in ORG ‐NoIT . The conventional system enhanced the relative frequency of both annual (CONV ‐IT ) and perennial (CONV ‐NoIT ) grasses. There was a negative correlation between density of perennial weeds and crop yield (r ² = 0.24, P  <  0.001). Therefore, in the Mediterranean environment, combining organic practices with non‐inversion tillage could lead to the establishment of perennial weeds that are difficult to control, thus requiring specific weed management practices.     

Weed infestation and tea growth under various weed management methods in a young tea (Camellia sinensis[L.] Kuntze) plantation

A field experiment was conducted in the low country of Sri Lanka, during the period 1994–1995 to investigate the severity of weed infestation and tea growth in relation to weed management methods in newly established tea ( Camellia sinensis [L.] Kuntze). Manual weeding (hand and slash weeding) at various intervals was compared with various herbicides, with or without mulching. Weed control with herbicides was superior to that of hand weeding at 6-week intervals or more. Weed control with oxyfluorfen at 0.29 kg ai ha⁻¹ + paraquat at 0.17 kg ai ha⁻¹ or glyphosate at 0.99 kg ai ha⁻¹ + kaolin at 3.42 kg ha⁻¹ were superior. Plots unweeded for 12 weeks or more produced significantly greater ( P  < 0.05) weed biomass than plots unweeded for 6 weeks. Although the least weed dry weight ( P  < 0.05) and the greatest number of weed species were recorded with hand weeding at 2 week intervals, there was no particular benefit on tea growth when compared with hand weeding at 6 and 12 week intervals. Inter row mulching in chemically treated plots was more favorable for tea growth than no mulching, while living weed cover in unmulched slash weeded plots suppressed tea growth. A combination of mulching and herbicides, particularly oxyfluorfen and paraquat, followed by hand weeding at least every 6–8 weeks was considered the most appropriate weed management system for young tea.     

Weed control in rose-scented geranium (Pelargonium spp)

Abstract: Field investigations were carried out during 1999 and 2000 to identify effective chemical/ cultural methods of weed control in rose-scented geranium (Pelargonium spp). The treatments comprised pre-emergence applications of oxyfluorfen (0.15, 0.20 and 0.25 kg AI ha(-1)) and pendimethalin (0.50, 0.75 and 1.00kg AI ha(-1)), successive hand weeding, hoeing and mulching using spent of lemon grass (at 5 tonnes ha(-1)) 45 days after planting (DAP), three hand-weedings 30, 60 and 90 DAP, weed-free (frequent manual weeding) and weedy control. Broad-leaf weeds were more predominant than grass and sedge weeds, accounting for 85.8% weed density and 93.0% weed dry weight in 1999 and 77.2% weed density and 93.9% weed dry weight in 2000. Unrestricted weed growth significantly reduced geranium oil yield, by 61.6% and 70.6% in 1999 and 2000, respectively. Pre-emergence application of pendimethalin (0.75-1.00 kgAI ha(-1)) or oxyfluorfen (0.25 kg AI ha(-1)), successive hand-weeding, hoeing and mulching and three hand-weedings were highly effective in reducing weed density and dry weight and gave oil yield comparable to the weed-free check. Application of oxyfluorfen (0.15 or 0.20 kg AI ha(-1)) and pendimethalin (0.50 kg AI ha(-1)) were less effective in controlling the weed species in geranium. None of the herbicides impaired the quality of rose-scented geranium oil measured in terms of citronellol and geraniol content.     

The influence of the soil management systems on aboveground and seed bank weed communities in olive orchards

The biodiversity of farmed landscapes is, in the context of agricultural intensification, a key aspect with regard to improving the sustainability of agroecosystems. Olive groves are undergoing rapid changes because of the spread of intensive farming systems, which may have negative environmental impacts. This paper reports a survey on the aboveground flora and seed banks in five olive groves located in Andalusia (Southern Spain). In this study, the following three management systems have been compared: no‐tillage, with the mowing of spontaneous weedy vegetation; no‐tillage, with the mowing of planted cover crops (Poaceae); and conventional tillage practices. Results showed that coverage and an abundance of vegetation are favored by spontaneous weedy vegetation with mowing management, while the richness of aboveground species was affected by landscape diversity and the presence of edges, which increases the richness and diversity of aboveground flora species in olive groves. Seed bank composition showed a low relationship with aboveground flora in the three cover crop management systems. The multivariate analysis performed pointed to those seed species that have a major influence on the aboveground flora communities of each of the three agricultural systems. The seed bank was clearly impoverished in terms of both abundance and species richness after the long‐term conventional tillage practices. We conclude that the intensive long‐term conventional tillage dramatically reduces weed communities in olive orchards and the subsequent ecosystem services provided by them.