Winter annual grassy weeds increase over‐winter mortality in autumn‐sown wheat

Over‐winter mortality, that is, winterkill, reduces cereal crop competitive ability and yield. While management and environmental variables are known to affect winterkill, the extent to which weeds contribute to increased winterkill is largely unknown. Winter annual weeds may increase winterkill through resource competition and by increasing incidence of and damage from plant pathogens that cause winterkill. We evaluated the impact of summer annual (Avena fatua) and winter annual (Bromus tectorum) weeds on the over‐winter survival rate of winter wheat over three winters, during which plots were covered with snow. Pink snow mould (Microdochium nivale), a winterkill pathogen known to infect B. tectorum and winter wheat, was common in wheat stands. In weed‐free treatments, mortality rates were initially near zero, but increased by nearly 45% in each subsequent winter, presumably due to an increase in snow mould disease in continuously cropped winter wheat. Whereas A. fatua infestation had no impact on crop survival rates, winter wheat survival in B. tectorum‐infested plots was 50% less than the weed‐free control in the second and third years of this study. Among B. tectorum‐infested plots, winter wheat over‐winter survival declined with increasing weed seed produced in the previous summer. Overall, this study demonstrated that winter annual weed infestations can reduce crop stand densities below replanting thresholds by reducing fall‐sown cereal winter survival. The effects of winter annual weeds on winter wheat may be meditated by increased proliferation of snow mould disease.     

Impacts of cropping system and management practices on the assembly of weed communities

Understanding how weed communities assemble as a function of biotic and abiotic filters and transform through time has important implications for the sustainable management of agronomic systems. In a three‐year study, we evaluated weed community responses to lucerne (Medicago sativa, perennial) vs. continuous spring wheat (Triticum aestivum, annual, CSW) and weed management practices where weeds in the CSW system were managed with three contrasting approaches (herbicide, tillage or sheep grazing). Our results indicated no differences in weed diversity between the perennial and annual crops or across the different management practices in CSW. However, there were differences in weed community composition. Lucerne, with the exception of the establishing year, impeded the growth and reproduction of several annual weeds, including Amaranthus retroflexus, Thlaspi arvense, Lamium amplexicaule and Chenopodium album, but favoured perennial broad‐leaved weeds such as Taraxacum officinale and Cirsium arvense. The replacement of herbicide treatments in pre‐plant and post‐harvest in CSW with soil tillage or sheep grazing selected for different weed communities beyond the second year of establishment. The weed species driving the differences in CSW systems were Androsace occidentalis, more common in CSW managed chemically; Asperugo procumbens, more common in CSW managed with tillage; and T. officinale and Lactuca serriola, more common in CSW managed with sheep grazing. Understanding how cropping systems modify weed communities is a necessary step to shift from reactive weed control programmes to predictive management strategies.     

Effects of surface treatments and application shanks on nematode, pathogen and weed control with 1,3-dichloropropene

BACKGROUND: Preplant fumigation with methyl bromide (MeBr) has been used for control of soilborne pests in high‐value annual, perennial and nursery crops, but is being phased out. In 2007 and 2008, research trials were conducted to evaluate the effects of surface treatments and two application shanks on pest control with 1,3‐dicloropropene (1,3‐D) in perennial crop nurseries. RESULTS: All 1,3‐D treatments controlled nematodes similarly to MeBr. Application of 1,3‐D with virtually impermeable film (VIF) reduced Fusarium oxysporum compared with unfumigated plots, but was not as effective as MeBr. Applications of 1,3‐D with VIF or 1,3‐D followed by metam sodium reduced Pythium spp., but 1,3‐D followed by intermittent water seals was comparable with the untreated plots. When sealed with high‐density polyethylene (HDPE) film or VIF, 1,3‐D generally was as effective as MeBr for reducing weed density and total weed biomass, but weed control was reduced by intermittent water seals and in unsealed plots subsequently re‐treated with additional 1,3‐D or metam sodium. CONCLUSION: Applications of 1,3‐D sealed with HDPE or VIF film or with intermittent water seals can control nematodes similarly to MeBr. However, additional management practices may be needed for effective pathogen and weed control if plastic film is not used. Copyright © 2011 Society of Chemical Industry     

Weed flora and seed yield in quinoa crop (Chenopodium quinoa Willd.) as affected by tillage systems and fertilization practices

The effects of tillage system and fertilization regimes on weed flora in quinoa (Chenopodium quinoa Willd.) were evaluated by means of two field experiments in 2011 and 2012. The experiments were laid out in a split-plot design with two main plots (conventional and minimum tillage) and four sub-plots (fertilization regimes). The results indicated that weed biomass and density in quinoa were influenced by the different fertilization and tillage treatments. Moreover, seed yield in conventional was 5%–13% higher than that of minimum tillage, probably due to the lower weed density and biomass. Concerning fertilization treatments, total weed density and biomass increased under manure application and inorganic fertilization. Tillage effects on weeds were species specific. The density of perennial weeds such as purple nutsedge (Cyperus rotundus L.) and the density of small-seeded weeds such as redroot pigweed (Amaranthus retroflexus L.) and common purslane (Portulaca oleracea L.) were significantly lower under the conventional tillage than under the minimum tillage system.     

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.     

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.     

Effect of non-ionic nonylphenol surfactants on surface physicochemical properties, uptake and distribution of asulam and diflufenican

The effect of non-ionic nonylphenol (NP) surfactants containing 4–14 ethylene oxide (EO) molecules on the distribution of asulam and diflufenican was investigated in Pteridium aquilinum L. Kuhn and Avena fatua L. The distribution of the herbicides was dependent on the EO content and concentration of surfactant and differed between plant species and herbicide. The surface properties of contact angle, droplet diameter and surface tension were examined. For solutions of asulam, the greatest reductions in contact angle, surface tension and greatest droplet diameter were obtained with surfactants of EO 6.5–10 (at 0.001–0.1%). For solutions of diflufenican, these responses were greatest when applied with surfactant of EO 4. Surfactants of EO 6.5–10 increased the uptake and translocation of [¹⁴C]asulam in P. aquilinum, particularly at surfactant concentrations of 0.01 % and 0.1 %. All surfactants increased uptake of [¹⁴C]asulam in A. fatua with no significant effects of surfactant EO number or concentration. For both species, there was a positive correlation between the optimum surface characteristics of the herbicide droplets and the uptake of asulam. With diflufenican, greatest uptake and translocation by mature frond tissue of P. aquilinum occurred at the highest concentration of surfactant EO 4; in A. fatua, however, uptake and translocation were not significantly affected by any of the surfactants.     

Site‐related set‐back by weeds on the establishment of 12 biomass willow clones

Ten commercial clones of willow and two breeding clones were studied for their ability to compete with weeds during the establishment year at three different sites in southern Sweden. Cuttings were planted according to commercial practice in April, and the two treatments, ‘Weeded’ and ‘Unweeded’, were laid out in a strip‐plot design. Weeds in the ‘Weeded’ treatment were removed mechanically and by hand hoeing. Willow plant shoot weight and plant mortality were measured after the first growing season to evaluate the initial effect of weeds. In addition, weed flora, weed aboveground biomass, soil properties, shoot damage and soil moisture were assessed during the growing season. Plant mortality was <1% in the ‘Weeded’ treatment at the three study sites, while in ‘Unweeded’ it was significantly higher, 2.7%, 24.6% and 37.4%. Weeds reduced willow plant shoot weight by 93.4%, 94.0% and 96.1% at the three sites. Only one site showed clonal differences in shoot growth reduction, as well as in plant mortality. These results show the importance of weed control in willow plantations, as growth of all clones tested were dramatically hampered by weeds during the first growing season, regardless of trial site conditions. Moreover, conditions at certain sites, such as soil properties in combination with weed cover, may cause high plant mortality during the establishment year in this perennial biomass crop.     

Cover crops and mulches influence weed management and weed flora composition in strip‐tilled tomato (Solanum lycopersicum)

This study was conducted in the Mediterranean environment of Central Italy from 2011 to 2013 with the aim of evaluating the effects of winter cover crops and their residues on weed composition in a cover crop‐tomato sequence. Treatments consisted of five soil managements (three cover crop species ‐ hairy vetch, phacelia, white mustard, winter fallow mulched with barley straw before tomato transplanting and conventionally tilled soil), two nitrogen fertilisation levels (0 and 100 kg N ha^?1) and two weed management levels (weed free and weedy) on tomato. Cover crop residues were arranged in strips on the soil surface and then used as beds for transplanting the tomato seedlings in paired rows. Rotary hoeing was performed in the bare strips between paired tomato rows. At tomato harvesting, the weed aboveground biomass and density was higher in nitrogen‐fertilised tomato than unfertilised tomato, except in hairy vetch and barley straw that showed similar values. Hairy vetch used as a cover crop and dead mulch was the most suppressive species with the highest production of residues, while phacelia and mustard were not suitable for controlling weeds. The tomato yield was high in nitrogen fertilised and weed‐free treatments, except in barley straw mulch, which showed similar values among the weed management treatments. The mulch strips caused variations in weed species composition that was mainly composed of perennial ruderal weeds, while in tilled soil, the weed flora was dominated by annual photoblastic weeds.     

Using the age shift method to determine gains from weed management for Pinus radiata in New Zealand

Understanding the effects of interspecific competition on long‐term growth of plantation forestry crops is critical to forest management decisions around methods used for weed control. A series of permanent sample plots (31) incorporating trees maintained either weedy or weed‐free until canopy closure were established across New Zealand between 2000 and 2002. We used the age shift method to characterise growth responses of Pinus radiata, in New Zealand, to interspecific competition over the first third of a typical rotation. Eight years after planting, age shifts between treatments ranged between ?0.60 years and +3.07 years. On average, the age shift due to weed control increased from 0.62 to 0.96 years between 4 and 8 years of age. This was due to divergent tree growth between weedy and weed‐free plots at 55% of the sites, while at 32% and 13% of sites, respectively, differences between treatments remained constant or decreased beyond age 4 years. The magnitude of the age shift was found to be related to the type of weed dominating early interspecific competition, with woody weeds associated with significantly greater age shifts. Continued divergence in tree growth between weedy and weed‐free treatments up to 8 years after planting at the majority of sites was an unexpected result and contrasts with previous literature. In situations where growth divergence continues beyond 2 years, managers should consider continued treatment of weeds to mitigate the detrimental impacts of on‐going competition.     

Image‐based thresholds for weeds in maize fields

Recent development of site‐specific weed management strategies suggests patch application of herbicides to avoid their excessive use in crops. The estimation of infestation of weeds and control thresholds are important components for taking spray decisions. If weed pressure is below a certain level in some parts of the field and if late germinating weeds do not affect yield, it may not be necessary the spray such places from an economic point of view. Consequently, it makes sense to develop weed control thresholds for patch spraying, based on weed cover early in the growing season. In Danish maize field experiments conducted from 2010 to 2012, we estimated competitive ability parameters and control thresholds of naturally established weed populations in the context of decision‐making for patch spraying. The most frequent weed was Chenopodium album, accompanied by Capsella bursa‐pastoris, Cirsium arvense, Lamium amplexicaule, Tripleurospermum inodorum, Poa annua, Polygonum aviculare, Polygonum persicaria, Stellaria media and Veronica persica. Relative leaf cover of weeds was estimated using an image analysis method. The relation between relative weed leaf cover and yield loss was analysed by nonlinear regression models. The competitive ability parameters and economic thresholds were estimated from the regression models. The competitive ability of weed mixtures was influenced by the increasing proportion of large size weeds in the mixtures. There was no significant effect of weeds which survived or established after the first herbicide application, indicating that early image analysis was robust for use under these conditions.     

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.     

Long‐term changes in weed occurrence,yield and use of herbicides in maize in south‐western Germany,with implications for the determination of economic thresholds

In 393 field experiments in Baden‐Württemberg region in south‐western Germany, herbicide efficacy, yield loss and crop tolerance of maize (Zea mays) were investigated between 1981 and 2011. The collected data served to determine changes in weed frequencies, in herbicide use, yield loss functions and economic thresholds (ETs). Over 60 weed species were reported. Chenopodium album and Galium aparine were the most frequent broad‐leaved weeds, the former becoming more frequent over time. Species of the genera Lamium, Polygonum, Veronica and Matricaria occurred in about every fifth trial. Alopecurus myosuroides and Echinochloa crus‐galli were the most frequent grass weeds; the former declining in frequency by 1.1% per year, the latter increasing by 1.5%. Results suggest a weed population shift towards thermophilic species. aceto‐lactate‐synthase and 4‐HPPD‐inhibitor herbicides became important in the 1990s. Pendimethalin and bromoxynil have been integral components of weed control since the 1980s. ETs, the point at which weed control operations provide economic returns over input costs, ranged between 3.7% and 5.8% relative weed coverage. Without weed control, no yield increase was found over 24 years. Yield increased by 0.2 t ha ^{? 1} year ^{? 1}, if weeds were controlled chemically. Despite intensive use of effective herbicides in maize, problematic weed species abundance and yield losses due to weed competition have increased in Baden‐Württemberg over a period of 30 years.     

Night‐time tillage revisited: the delayed soil desiccation process in night‐time tilled plots may promote unexpected weed germination

Night‐time tillage and sowing (photocontrol of weeds, soil cultivation in darkness) can reduce the germination and subsequent density of light‐sensitive weeds by excluding the short light flash during soil disturbance. In most experiments conducted from 1990 to 2004 worldwide, total weed density was reduced in night‐time tilled plots as expected. However, in a few field experiments, total weed density was significantly increased in night‐time compared with daytime tilled plots. We hypothesise that the desiccation process of the upper soil layer (roughly about 0–30 mm), from where most small seeded weeds emerge, may have been delayed in night‐time compared with daytime tilled plots, with significant effects on early seed germination processes. Daytime tillage was usually performed around noon, to capture high light intensities during soil tillage. However, around noon soil desiccation can be much higher than during the night. A few hours of relatively higher water availability for seeds in the upper soil layer during the night, before the next morning when soil desiccation usually increases again, may have favoured seed germination and subsequent weed emergence compared with daytime tillage, finally resulting in higher weed density in night‐time tilled plots. On the other hand, crop germination and emergence may also be higher under such conditions.     

The impacts of traditional and novel herbicide application methods on target plants,non‐target plants and production in intensive grasslands

Herbicides contribute significantly to agricultural intensification, but some negatively impact non‐target organisms. Much research has focused on reducing herbicide use through technological improvements in application and herbicide selectivity, but impacts on non‐target organisms are less well understood. Using experimental plots in silage systems, we investigated impacts of herbicides (both narrow spectrum targeting broad‐leaved plants and selective and non‐selective broad spectrum) applied using traditional techniques (blanket‐ and manual spot‐spraying) and a novel application technique (automated spot‐spraying) on non‐target plant richness/diversity, target weed presence (Rumex species) and production (DM yield). All herbicides reduced non‐target plant richness/diversity and sometimes target weeds (when applied using traditional methods). Automated spot‐spraying had fewer negative effects on non‐target organisms, but did not reduce target weeds. No differences in production levels among treatments were observed. The automated spot‐spraying technique requires further research and development. Our results indicate that 20–30% weed cover does not significantly alter production and so, as herbicides are expensive, their effects on non‐target organisms and the environment can be more significant than their benefits to production. We advocate more research into the relationships between weed infestation and production in grasslands, so that the propensity to overuse herbicides is reduced.     

Development of herbicide resistance in weeds in a crop rotation with acetolactate synthase‐tolerant sugar beets under varying selection pressure

The development of acetolactate synthase (ALS) tolerant sugar beet provides new opportunities for weed control in sugar beet cultivation. The system consists of an ALS?inhibiting herbicide (foramsulfuron + thiencarbazone‐methyl) and a herbicide‐tolerant sugar beet variety. Previously, the use of ALS‐inhibitors in sugar beet was limited due to the susceptibility of the crop to active ingredients from this mode of action. The postulated benefits of cultivation of the ALS‐tolerant sugar beet are associated with potential risks. Up to now, with no relevant proportion of herbicide‐tolerant crops in Germany, ALS‐inhibitors are used in many different crops. An additional use in sugar beet cultivation could increase the selection pressure for ALS‐resistant weeds. To evaluate the impact of varying intensity of ALS‐inhibitor use on two weed species (Alopecurus myosuroides and Tripleurospermum perforatum) in a crop rotation, field trials were conducted in Germany in two locations from 2014 to 2017. Weed densities, genetic resistance background and crop yields were annually assessed. The results indicate that it is possible to control ALS‐resistant weeds with an adapted herbicide strategy in a crop rotation including herbicide‐tolerant sugar beet. According to the weed density and species, the herbicide strategy must be extended to graminicide treatment in sugar beet, and a residual herbicide must be used in winter wheat. The spread of resistant biotypes in our experiments could not be attributed to the integration of herbicide‐tolerant cultivars, although the application of ALS‐inhibitors promoted the development of resistant weed populations. Annual use of ALS‐inhibitors resulted in significant high weed densities and caused seriously yield losses. Genetic analysis of surviving weed plants confirmed the selection of ALS‐resistant biotypes.     

Studies on the mode of action of asulam in bracken (Pteridium aquilinum L. Kuhn). III. Longterm control of field bracken.

The longterm control of bracken (Pteridium aquilinum) following applications of asulam was studied for 5 years al a site in the West of Scotland; there was no post-spray management. The time of treatment was found to be of considerable importance, satisfactory long-term control being obtained only when 4.4–8.8 kg/ha were applied around the stage of full frond expansion (26 July–16 August). Application of 4.4 kg/ha asulam on 26 July decreased frond density by 99, 95, 85, and 73% in the 4 years following treatment; about 50% recovery was observed in the fifth year. The latter may be partially due to the encroachment of rhizomes from the adjacent untreated plots and the lack of post-spray management. Examination of rhizomes dug from 1 m² areas showed that asulam killed more than 90% of the active frond buds and apices in the first year, but left undamaged 48% of the dormant buds on the deeper rhizome branches; the latter appeared to be the main source of reinfestation of treated plots in subseqquent years. The total number of living buds increased from 17% of the untreated in the first year to 38% in the fifth year; the majority of these buds were dormant. Formulation of asulam (4.4 kg/ha) with 1% ethylan CP only improved the reduction in frond density over a 4-year period by 10%. Recherches sur le mode d'action de l'asulame sur la fougère (Pteridium aquilinum L. Kuhn). III, Elimination durable de la fougère. Lélimination durable de la fougére (Pteridium aquilinum) a la suite d'applications d'asulame a éte etudiee pendant 5 annees dans une station de I'ouest de I'Ecosse; il n'y a pas eu d'autre intervention apres le trailement. W a ete constate que Vepoque du traitement avait une importance considerable, une elimination durable n'ayant pu etre obtenue qu'en appliquant 4,4 a 8,8 kg/ha d'asulame au stade de plein developpement des frondes (26 juillet-16 aout), L'application de 4,4 kg d'asulame le 26 juillet diminua la densite des frondes de 99, 95, 88, et 73% au cours des 4 annees suivant le traitement; une repousse d'environ 50% fut observee la cinquieme annee, Ce resultat final peut etre du en partie a I'empietement de rhizomes provenant des parcelles adjacentes non traitees et a I'absence d'intervention apres le traitement. L'examen des rhizomes extraits sur des surfaces de 1 m² montra que I'asulame avait tue plus de 90% des bourgeons et des apex des frondes en activite au cours de la premiere annee, mais n'avait pas endommage 48% des bourgeons dormants situes sur les ramifications les plus profondes des rhizomes; ce fait est apparu comme la cause principale de la reinfestation des parcelles traitees au cours des annees suivantes. Le nombre total des bourgeons vivants est passe de 17% des temoins la premiere annee a 38% la cinquieme annee; la majorite de ces bourgeons etaient dormants. La formulation de I'asulame avec 1% seulement d'etylan CP” a augmente de 10% la reduction de la densite des frondes au cours de la periode de 4 ans. Untersuchungen zur Wirkuttgsweise von Asulam bei Adlerfarn (Pteridium aquilinum L. Kuhn). III. Langfristige Bekdmpfung In einem Versuch in Westschottland wurde die langfristige Bekampfung von Adlerfarn (Pteridium aquilinum) nach Asulam-Behandlungen uber 5 Jahre untersucht. In diesen Versuchen wurden nach der Herbizidbehandlung keine weiteren Bekampfungsmassnahmen durchgefiihrt. Es konnte festgestellt werden, dass der Bekampfungszeitpunkt von erheblicher Bedeutung ist. Eine befriedigende langfristige Bekampfung wurde nur erzielt, wenn 4.4–8.8 kg/ha zum Zeitpunkt der vollen Wedelentwicklung (26, Juli-16. August) angewendet wurden. Eine Behandlung mit 4,4 kg/ha Asulam am 26, Juli fuhrte in den 4 Jahren nach der Applikation zu einem Ruckgang der Wedeldichte um 99, 95, 85 und 73%, und im fiinften Jahr betrug die Wedeldichte wieder etwa 50% der ursprunglichen. Das letztere lasst sich teilweise mit dem Eindringen von Rhizomen aus benachbarten unbehandelten Parzellen und dem Fehlen weiterer Massnahmen mach der Herbizidbehandlung erklaren. Die Untersuchung von I m² grossen Flachen zeigte, dass durch Asulam im ersten Jahr iiber 90% der aktiven Wedelknospcn und -apices getotet wurden, aber 48% der dormanten Wedelknospen und -apices der tieferliegenden Rhizomstijcke unbeeinfiusst blieben. Diese Organe scheinen die Hauptursache der Wiederverseuchung in den folgenden Jahren gewesen zu sein. Die Gesamtzahl an lebenden Knospen nahm, bezogen auf Unbehandelt, von 17% im ersten Jahr auf 38% im fiinften Jahr zu, die meisten Knospen waren aber dormant. Zusatz von 1% Ethylan CP zu Asulam (4,4 kg/ha) verbesserte im Beobachtungszeitraum von 4 Jahren die Wirkung (Verminderung der Wedeldichle) nur um 10%.     

Changes in Pteridium aquilinum growth and phototoxicity following treatments with lime, sulphuric acid, wood ash, glyphosate and ammonium nitrate

The comparative effects of lime, sulphuric acid, wood ash, glyphosate and ammonium nitrate on Pteridium aquilinum (L.) Kuhn growth and development were evaluated in a Scots pine (Pinus sylvestris L.) clear-cut stand in south-east Sweden over a 4-year period. P. aquilinum growth was effectively controlled following the application of glyphosate, but the other treatments generally had little effect on growth in terms of shoot density and length. Shoot length was positively related to the number of shoots on plots treated with ammonium nitrate but negatively correlated with the number of P. aquilinum shoots found on wood ash-treated and control plots. In a bioassay aspen (Populus tremula L.) seedling emergence and pH were significantly lower in humus treated with sulphuric acid, glyphosate, ammonium nitrate and in untreated humus as compared with the humus treated with lime and wood ash. The negative effect of humus on emergence of aspen seedlings may be caused by phytotoxic compounds at a lower pH level. Forest regeneration might be performed with shade-tolerant species such as Norway spruce (Picea abies (L.) Karst.) planted beneath a thin canopy of trees to prevent the rapid increase of P. aquilinum.     

Integrating preventive and curative non‐chemical weed control strategies for concrete block pavements

Reduction in herbicide use in non‐agricultural areas is being imposed by a growing number of governments, triggering the development of alternative strategies for weed prevention and control. This study aimed to determine the weed preventive abilities of different paving types, the required treatment frequency of non‐chemical weed control scenarios on these pavements and the associated weed species composition. A test parking area, constructed with four concrete paving types, was sown with a mixture of dominant weed species. Six scenarios with repeated use of a single weed control method (brushing with waste removal, hot air, selective application of hot water and three scenarios with flaming) and two scenarios with alternating use of brushes and hot air were applied to control the weeds during two growing seasons. Treatments were applied at well‐defined intervention moments, based upon weed development. Over 2 years, the paving types differed in weed coverage (up to a fourfold difference) and required varying treatment frequency (up to a 11‐fold difference) with lowest values for pavings with porous pavers. Within most paving types, up to 28% lower treatment frequencies were found for selective application of hot water, as compared with all other single method scenarios. Shifts in weed composition occurred in plots treated repeatedly with the same technique. Paving type determined the chances for the establishment of different weed species and alternating non‐chemical control methods with different modes of action offered the best opportunity to keep weeds under control.     

小麦田不同杂草群落及防除时间对小麦产量的影响

为明确小麦田不同杂草群落及防除时间对小麦产量的影响,于2013—2015连续两年在山东省聊城市高唐县小麦田中设无草对照区、禾本科杂草区、阔叶杂草区以及混合杂草自然发生区4种不同杂草群落以及不同的杂草防除时间,测定在不同条件下小麦产量及各项产量构成指标的情况。结果表明,阔叶杂草对小麦产量的影响大于禾本科杂草,冬小麦田杂草的最佳防除时间为4月1日之前,在此期间除草对小麦产量影响均不大,但之后防除或不除草会造成小麦严重减产甚至绝产,2014年4月15日除草可造成在阔叶杂草区和杂草混合生长区的小麦减产30.5%和32.6%,不除草可造成在禾本科杂草区、阔叶杂草区和杂草混生区的小麦减产8.6%、91.4%和94.3%,2015年趋势和2014年一致。从构成小麦产量的3个指标来看,杂草危害主要影响小麦的总穗数,其次为穗粒数,对千粒重影响最小。