The fungicide tridemorph as a selective herbicide for the control of Holcus lanatus in ryegrass and of Bonus sterilis in barly

The potential of the fungicide tridemorph selectively to control established plants of Holcus lanatus L. in ryegrass (Lolium perenne L) and Bromus sterilis L. in barley (Hordeum vulgare L.) was examined in glasshouse trails. A dose of 4.2 kg ha^?1 tridemorph gave selectively between H. lanatus and ryegrass similar to, but more costly than, that which would be provided by 1.2 kg ha^?1 asulam. B sterilis was more sensitive to tridemorph than was barley. Two additives, glycerol and the oil-surfactant mixture ‘PF’ enhanced this selectivity when tridemorph was applied at 2.1 kg ha^?1.     

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.     

Interactions between weeds of winter wheat under different fertilizer,cultivation and weed management treatments

Interactions between the weeds Bromussterilis L., Galium aparine L. and Papaver rhoeas L. were investigated over 3 years of continuous winter wheat (Triticum aestivum L.) across a factorial combination of organic and conventional fertilizer, and ploughing and hand-roguing contrasted with minimum tillage and herbicide. The species were sown separately and together at 50 seeds m^?2 per species at the start of the experiment in October 1989. In addition, there were weed-free and background-weed controls. Weed densities were monitored at roughly monthly intervals and crop yield recorded for three seasons. B. sterilis populations increased 10-fold under minimum tillage, but declined under ploughing. Densities of P. rhoeas remained largely low. G. aparine increased on the organically fertilized minimum-tillage plots, except where B. sterilis was present; the high densities of B. sterilis reduced the population size of G. aparine. Crop yield was influenced most strongly by the fertilizer treatment in the first season, but later the density of B. sterilis was by far the most important factor; the evidence of interactive effects of the different weed species on crop yield was weak at best. Interactive effects of arable weed species can be observed, but only at very high densities, and so are unlikely to be of widespread economic importance.     

Paraquat tolerant Lolium perenne L.: effects of paraquat on germinating seedlings

A cultivar of Lolium perenne L. (Causeway) selected for tolerance to foliar-applied paraquat was shown also to be tolerant at seed germination and establishment. When seeds were germinated in paraquat solutions (1, 3, 9, 27 ppm), Causeway was more than ten times as tolerant as a normal cultivar of L. perenne. When germination and survival were studied in a soil which had been sprayed with paraquat (0.0, 0.3, 0.9, 2.7 kg/ha) before sowing, Causeway was nearly three times as tolerant as a normal cultivar. Holcus lanatus L. was about equal to normal L. perenne, but Poa trivialis L. was less tolerant. Phytotoxicity was greater in a 10.5% organic than a 4.8% organic soil. It is concluded that the mechanism of paraquat tolerance operates in the non-photosynthetic tissues of germinating seedlings as well as in the photosynthetic tissues of older plants, although the degree of tolerance varies according to the mode and stage of application of the herbicide. There might be advantages in using a paraquat tolerant cultivar of L. perenne when direct drilling grass after sward destruction by paraquat.     

A survey of grass weeds in cereals in central southern England

A survey of grass weeds in cereals in nine areas of central southern England was made in summer 1981 with the primary purpose of determining the importance of Bromus sterilis. A total of 1477 fields of winter wheat, 715 of winter barley and 434 of spring barley were assessed by visually scoring the whole field for grass flower heads. In all, 19 species were found; their levels of infestation were scored. In winter cereals the most frequent species were Avena spp. in 32% of fields. Agropyron repens in 24%, Poa trivialis in 22% and Alopecurus myosuroides in 19%. Bromas sterilis was next most frequent in 9%. In spring barley the two most frequent species were Agropyron repens in 53% of the fields and Avena spp. in 52%. The third most frequent was Alopecurus myosuroides in 1 1%. Bromus sterilis was recorded in 12% of winter wheat and 4% of winter barley crops, but did not occur in spring barley. Of the 206 fields where it was present it occurred throughout the field in only 82 and it was confined to the headlands in the remainder.     

The selectivity of methabenzthiazuron between barley, perennial ryegrass and Poa trivialis

In field experiments methabenzthiazuron at 1.1 kg ai/ha applied pre-emergence gave good control of Poa trivialis L. in perennial ryegrass S23 which was undersown in spring barley (Zephyr); no significant damage to barley or perennial ryegrass resulted from 2.2 kg ai/ha. However this dose applied when barley had three to four leaves decreased the subsequent barley yield. In pot experiments in the glasshouse methabenzthiazuron was active mainly due to uptake through the soil. Much greater damage to barley and perennial ryegrass resulted when herbicide-treated soil was placed below seed level than above the seed. The difference was less marked with P. trivialis. The latter started to develop secondary roots near the soil surface earlier than either perennial ryegrass or spring barley.     

Selective regulation of germination and growth of annual weeds by crop residues

Residues from mature, harvested crops of sorghum (Sorghum bicolor Moench.), sunflower (Helianthus annuus L.), oilseed rape (Brassica napus L.), wheat (Triticum aestivum L.) and field pea (Pisum sativum L.), exhibited selective effects on weed germination and growth under field conditions. Weed species in the study included Avena fatua L., Avena sterilis ssp. ludoviciana (Durieu) Nyman, Echinochloa crus-galli (L.) Beauv., Phalaris aquatica L., Phalaris paradoxa L., Lolium perenne L., Vulpia myuros (L.) Gmel., Hibiscus trionum L., Polygonum aviculare L., Bilderdykia convolvulus (L.) Dumort. and Lamium amplexicaule L. All crop residues tested, and in particular wheat and pea residues, promoted the germination and growth of A. fatua and A sterilis ssp. ludoviciana. Other grass weeds, however, were inhibited by the presence of crop residue, the extent of inhibition being dependent on residue type. Germination response of dicotyledonous weed species was also a function of residue type, H. trionum numbers were significantly higher in plots where oilseed rape, sorghum or sunflower residue had been incorporated, while L. amplexicaule was inhibited by these residue types and stimulated by pea and wheat residues.     

The competitive interactions between winter barley and Avena sterilis are site-specific

Competition between winter barley and Avena sterilis is expected to depend on the specific conditions present in a given site. Considering that site conditions may be variable within a field, we hypothesised that the lower densities of A. sterilis frequently observed under more favourable soil conditions can be attributed to the improved growth and competitiveness of the barley crop under those conditions. Artificial populations of A. sterilis were established at three sites with different soil properties, both in the absence and the presence of a barley crop. Plant density, total biomass, dry weight per plant, seed production and seed per plant production were measured at different times in two growing seasons. Avena sterilis proved to be a generalist species when growing in monoculture, with similar seed production, regardless of the site conditions. However, when growing with the crop, differences in growth and seed production were observed at the different sites under some climatic conditions. The effect of the crop on A. sterilis biomass and seed production was more pronounced at the sites with finer textures and higher organic matter and nitrogen contents, suggesting that barley site‐specific competitive ability may contribute to limiting weed populations in favourable soils.     

Estimation of economic thresholds for weed control in winter wheat

Thresholds for winter wheat weed control have been determined for different herbicides or mixtures effective against individual weed species. For Avena sterilis L. subsp. ludoviciana (Durieu) Nyman the economic threshold was between 7 and 12 plants m^?2, for Alopecurits myosuroides Hudson and Lolium multiflorum Lam. it varied between 25 and 35 plants m^?2, while for Bromus sterilis L. the values were just under 40 plants m^?2. For Galium aparine L. the threshold was as low as 2 plants m^?2, while for Vicia sativa L. it was between 5 and 10 plants m^?2. Within the same species the different values of economic threshold result from the different costs and efficacy of herbicides. Nitrogen fertilization was important: in its absence, the competitiveness of B. sterilis and G. aparine was negligible, and it was not possible to calculate an economic threshold for some of the treatments which could not be justified economically. Estimation de seuils économiqu.es de désherbage chez le blé d'hiver Les seuils économiques de désherbage du blé d'hiver ont été determinés pour différents herbicides, seuls ou en mélanges, pour plusieurs espèces demauvaises herbes. POUT Avena sterilis L. subsp. ludoviciana (Durieu) Nyman, le seuil économique était compris entre 7 et 12 plantes m^?2. PourAlopecurus myosuroides Hudson et Lolium multiflorum Lam., il variait entre 25 et 35 plantes m^?2 et était juste au-dessous de 40 plantes m^?2 pour Bromus sterilis L. Pour Galium aparine L., le seuil était2 plantes m^?2 et était compris entre 5 et 10 plantes m^?2 pour Vicia sativa L. Les différences de seuil pour une même espèce sont dues aux différences de coût et d'ef-ficacité des herbicides. Le rôle de la fertilisation azotVe Vtait important: en son absence, le pou-voir compVtitif de B. sterilis et de G. aparineétait négligeable, et il n'était pas possible de calculer de seuil économique pour certains traitements, qui ne pouvaient se justifier économiquement. Bestimmung von wirtschaftlichen Schadensschwel-lenfiirdie Unkrautbekdmpfung in Winterweizen Für verschiedenen Herbizide und -mischungen wurden entsprechend ihrer Wirksamkeit gegenüber bestimmten Unkrautarten Schadensschwellen zur Unkrautbekämpfung inWinterweizen bestimmt. Für Avena sterilis L. spp. ludoviciana (Durieu) Nyman lag die Schadensschwelle zwischen 7 und 12 Pflanzen m^?2, fur Alopecurus myosuroides Hudson und Lolium multiflorum Lam. variierte sie zwischen 25 und 35 Pflanzen m^?2, während die Werte für Bromus sterilis L. bei knapp 40 Pflanzen m^?2 lagen. Bei Galium aparine L. war die Schadensschwelle ganz niedrig, nämlich 2 Pflanzen m^?2, während sie für Vicia sativa L. zwischen 5 und 10 Pflanzen m² betrug. Fiir ein und die-selbe Art ist die okonomische Schadensschwelle je nach den Kosten und der Wirksamkeit der Herbizide unterschiedlich. Die Stickstoffdün-gung ist zu beachten: wenn sie fehlt, ist die Konkurrenz durch Bromus sterilis und Galium aparine verachlässigbar, so daß keine gerechtfertigten ökonomischen Schadensschwellen berechnet werden konnten.     

The effect of asulam on two Lolium perenne swards containing Rumex obtusifolius

The effects of asulam applied in September 1970 at 0.55, 1.12 and 2.24 kg a.i./ha on Rumex obtusifolius (L.), Lolium perenne (L.), Other grasses and Trifolium repens (L.) growing in two swards in Wales were investigated. Good short-term control of Rumex was achieved by all rates of asulum although regeneration was occurring by the spring following treatment. Dry matter yields of L. perenne were slightly lowered by 2.24 kg a.i./ha 6 weeks after spraying but production in the spring following treatment was substantially greater than on untreated plots. Poa trivialis (L.) and Agrostis stolonifera (L.) were substantially reduced but invasion of the bare spaces by P. trivialis and P. annua (L.) seedlings tended to mask the success of this control. No harmful effects on T. repens were recorded.     

Secondary dispersal, spatial dynamics and effects of herbicides on reproductive capacity of a recently introduced population of Bromus sterilis in an arable field

An arable field was subdivided and subjected to either deep inversion ploughing or non‐inversion cultivation after viable seeds of Bromus sterilis had been sown into oilseed rape stubble. After sowing in isolated plots distributed within the field, sequences of cropping treatments for the establishment of two successive winter wheat crops were applied. Each subfield was split into an uphill and a downhill direction for soil cultivation. The field had a 10° slope. In the season following seed introduction, 2.6% of the introduced seeds had successfully germinated and established in the non‐inversion cultivation regime, when no effective graminicide was applied. Ploughing eradicated B. sterilis. Using differential global positioning system (DGPS) mapping of the whole field population, emerged plants were observed up to 8.7 m (uphill treatment) and 21.3 m (downhill treatment) of their initial source. The median distance seeds were transported was 2.3 m uphill and 4.8 m downhill. Post‐emergence application of the herbicide propoxycarbazone slightly reduced weed density and seed weight, and almost halved weed seed production. Application of fenoxaprop‐P‐ethyl was followed by higher density of plants, tillers and seeds of B. sterilis. Seed viability was unaffected by herbicide use. Thus, in the second wheat crop following seed rain, the weed population was dispersed more widely in the field, such that 20–30% of seeds were dispersed more than 5 m distance from the first year's foci of infestation. The relevance of soil cultivation to secondary dispersal of B. sterilis is discussed.     

The control of Holcus lanatus in perennial ryegrass swards by asulam.

Asulam was evaluated in three fields experiments for the control of Yorkshire fog (Holcus lanatus L.) in perennial rygrass(Lolium perenneL). It was used in 1976 on a 3 year-old ryegrass/timothy (Phleum pratense L.) sward in comparison with propyzamidc, in 1977 on a 9 year-old ryegrass pasture grazed at two stocking rates and in 1978 on an intensively managed ryegrass dominant sward. Asulam at 1.75 kg ha^?1 gave good selective control in all the field experiments and was more effective under higher than lower slocking rates. In laxly grazed swards it was most effective when sprayed in October. Propyzamide also controlled H. lanatus and increased yields of while clover (Trifolium repens L.) even at 0.25 kg ha^?1 but it damaged the sown grasses and increased the growth of broad-leaved weeds.     

Effect of crop density on competition by wheat and barley with Agrostemma githago and other weeds

The effect of Agrostemma githago L. and other naturally occurring weeds on biomass production and grain yield was studied in winter wheat and winter barley. Naturally occurring weeds had only a negligible effect on barley, but reduced wheat grain yield by 10% at a quarter of normal crop density. The interaction between the cereals and A. githago was studied in additive series employing different crop densities. Growth of this weed species was strongly dependent on crop density, which was more important for controlling weed growth than it was for obtaining a normal grain yield. Wheat and especially barley had a better competitive ability than A. githago. Wheat and A. githago utilized resources for growth better when grown in mixture than when grown in pure stands as the relative yield totals were significantly larger than unity.     

Characterization of the germination and emergence response to temperature and soil moisture of Avena fatua and A. sterilis

Seeds of Avena fatua L. and )A. sterilis L. were germinated under a wide range of temperatures (5–30°C) and osmotic potentials (?25 to ?1400 KPa) in order to characterize their responses to these two environmental factors. Although both species behaved similarly at moderate temperatures, different responses were observed at the two extremes. )A. sterilis germinated and emerged in a higher proportion than A. fatua at temperatures below 10°C but the opposite was true at temperatures above 20°C. Although the rates of these two processes were similar in both species up to 18°C, above this temperature the germination and emergence of )A. sterilis was considerably delayed in comparison with that of A. fatua. The effect of decreasing osmotic potentials in reducing the germination was more pronounced in A. sterilis than in A. fatua. However, no differences were observed in the emergence responses of either species. The adaptative advantages of these characteristics and their relationship with the geographic distribution of the two species is discussed.     

Germination of proximal and distal seeds of Poa trivialis L. from contrasting habitats

Seeds of Poa trivialis L. were collected from one grassland and two arable habitats. Seeds from the grassland population were less dormant than the arable populations. Distal (upper) seeds were consistently more dormant than proximal (basal) seeds. Dry storage at 4°C and 15°C for 4 weeks after shedding resulted in a slightly greater loss of dormancy than storage at 23°C. Germination was enhanced by subjecting seeds stored at 15°C to repeated hydration and dehydration cycles. Germination of P. trivialis seeds was density-dependent. Germination of distal seeds was particularly impaired at high densities. The ecological implications of these results are discussed in relation to seed survival strategies.     

Spatial and temporal patterns of Lolium rigidum–Avena sterilis mixed populations in a cereal field

Through a detailed case study of a two‐species (Lolium rigidum and Avena sterilis) weed community at contrasting scales, this paper examined factors that affect weed distribution across space and time in a commercial wheat field in north‐east Spain. A. sterilis showed relatively stable spatial distribution and spatial structure of its population over time at large scale, with well‐defined patches, although weed density rose quickly. L. rigidum showed poorly defined patches that were not stable across time. Interaction between species could explain to some degree the spatial distribution at large scale: a negative relationship was detected between the spatial structures of both weed populations. At fine scale, both species showed a clear interaction effect from primary dispersal (more important in A. sterilis) and secondary dispersal from combine harvesting (more important in L. rigidum).     

Herbicidal potential of pyrenophorol isolated from a Drechslera avenae pathotype

A pathotype of Drechslera avenae (Eidam) Scharif exhibited host‐specificity, being pathogenic to Avena sterilis L but not to a number of related or unrelated species tested. In culture, the fungus produces a metabolite which was identified as the macrodiolide pyrenophorol (5,13‐dihydroxy‐8,16‐dimethyl‐1,9‐dioxa‐cyclohexadeca‐3,11‐diene‐2,10‐dione). This compound at a concentration of 320 µM was phytotoxic to A sterilis and considerably less so to Avena fatua L. The phytotoxicity was expressed as leaf necrosis on seedling cuttings partially immersed in pyrenophorol solution and as ‘green islands’ on detached leaves on which droplets of the solution were placed. Seed germination and seedling growth of A sterilis were not affected. Pyrenophorol at concentrations up to 640 µM did not cause any symptoms of phytotoxicity to a number of other monocotyledons or dicotyledons tested, with the exception of Lycopersicon esculentum Miller on which leaf necrosis was observed after application of the substance through the vascular system to seedling cuttings. These findings are discussed in relation to the exploitation of such compounds of natural origin as wild oat herbicides. © 2000 Society of Chemical Industry     

Avena sterilis and Lolium rigidum infestations hamper the recovery of diverse arable weed communities

Intensification of agricultural practices has severely reduced weed diversity in arable fields, which affects the delivery of ecosystem services. However, in parallel, some species have benefited from intensive farming and have vastly increased their abundance, as is the case for Lolium rigidum and Avena sterilis in cereal fields. These highly competitive species severely reduce yields but can also compete with other weed species, and, when less intensive practices are applied, they might limit the recovery of weed diversity and the success of arable species reintroductions. A gradient of infestation was established in a winter wheat field in Catalonia (north‐eastern Spain) by sowing seeds of both species at three different densities to test their effects on the abundance, diversity and composition of the natural weed community. The emergence of seeds and the survival and biomass of transplanted seedlings of two rare species, Agrostemma githago and Vaccaria hispanica, were also evaluated. Avena sterilis and L. rigidum infestations reduced the diversity, abundance and biomass and changed the composition of the natural weed community, even at low infestation densities. Moreover, infestations of both species affected the overall performance of A. githago and V. hispanica. This study reveals that A. sterilis and L. rigidum are highly competitive and that their infestations might hamper the recovery of diverse weed communities. Their densities should be considered when selecting suitable sites for promoting diversity and reintroducing rare species.     

<Emphasis Type="Italic">Bacillus pumilus</Emphasis> SG2 chitinases induced and regulated by chitin,show inhibitory activity against <Emphasis Type="Italic">Fusarium graminearum</Emphasis> and <Emphasis Type="Italic">Bipolaris sorokiniana</Emphasis>

The possible role of chitinase in in vitro growth inhibition of the wheat pathogens Fusarium graminearum and Bipolaris sorokiniana by Bacillus pumilus SG2 was investigated. B. pumilus SG2, a chitinolytic bacterium producing two different chitinases, was previously isolated from the saline deserts of Iran. When grown in Spizizen salts medium with colloidal chitin, B. pumilus SG2 secreted two chitinases into the medium, resulting in growth inhibition of F. graminearum and abortion of hyphal elongation of B. sorokiniana. In contrast, when glucose was used as the carbon source, the chitinases were not expressed and antifungal activity of the B. pumilus SG2 was completely abolished. These results confirmed that expression of the B. pumilus SG2 chitinases is under the control of two types of regulation, special regulation by chitin and global regulation by glucose. We demonstrated that chitinases are the main components that caused hyphal inhibition activity of B. pumilus SG2. Hyphal inhibition of F. graminearum and B. sorokiniana was stable in agar for a minimum of 14 days.     

Apical leaf necrosis as a defence mechanism against pathogen attack: effects of high nutrient availability on onset and rate of necrosis

An outdoor experiment was conducted to increase understanding of apical leaf necrosis in the presence of pathogen infection. Holcus lanatus seeds and Puccinia coronata spores were collected from two adjacent and otherwise similar habitats with differing long‐term N fertilization levels. After inoculation, disease and necrosis dynamics were observed during the plant growing seasons of 2003 and 2006. In both years high nutrient availability resulted in earlier disease onset, a higher pathogen population growth rate, earlier physiological apical leaf necrosis onset and a reduced time between disease onset and apical leaf necrosis onset. Necrosis rate was shown to be independent of nutrient availability. The results showed that in these nutrient‐rich habitats H. lanatus plants adopted necrosis mechanisms which wasted more nutrients. There was some indication that these necrosis mechanisms were subject to local selection pressures, but these results were not conclusive. The findings of this study are consistent with apical leaf necrosis being an evolved defence mechanism.