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.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

Impact of Indian mustard growth and incorporation on annual weed population dynamics and communities

Biofumigation from Brassica cover crops may be used to control soilborne pests and weeds. A study was conducted to understand the influence of biofumigation on key processes of annual weed population dynamics. Five combinations of Indian mustard (M) and oat (O) cover crop treatments were assessed in a 3 year field study at two locations in Québec, Canada. Treatments included four spring/fall cover crop combinations (M/M, M/O, O/M, O/O) and a weedy check control with no cover crop. Prior to mowing and incorporation of cover crops, weed identification, count and biomass measurements were recorded to evaluate the total weed density, to calculate the relative neighbour effect (RNE) and weed diversity metrics and to perform principal co‐ordinates analyses. Indian mustard cover crops had no impact on weed establishment in 2014 due to low biofumigant potential compared to the oat cover crop. In 2015 and 2016, Indian mustard isothiocyanate (ITC) production increased and weed establishment within the Indian mustard cover crop decreased. Moreover, post‐cover crop incorporation decreased the next year spring weed emergence. Allelopathic interference of Indian mustard was significant when plant tissues produced more than 600 μg of allyl‐ITC g^?1. It is now possible to rationalise the use of Brassica cover crops and biofumigation for weed control with an enhanced understanding of the impact of biofumigation on key processes of weed population dynamics.     

Relationships between soil properties and the occurrence of the most agronomically important weed species in the field margins of eastern Arkansas – implications for weed management in field margins

The work presented in this study adds to previous research on the occurrence, distribution and growth habitat of common weeds along roadsides in the Mississippi River Delta region of eastern Arkansas, USA. It addresses the relationships between soil properties (i.e. defined as a group of individual soil characteristics or attributes such as P, K, Ca, Mn and other nutrients) and the most agronomically important weeds of which the occurrence at field margins accounted for ≥ 10% of the total sampling sites. These were three broad‐leaved weeds (Amaranthus palmeri, Ipomoea spp. and Sida spinosa) and four grass weeds (Echinochloa crus‐galli, Urochloa platyphylla, Sorghum halepense and Digitaria sanguinalis). Soil properties were used as explanatory variables for weed occurrence (presence–absence) using partition analysis; the occurrences of the weeds under examination were partitioned by the application of a decision‐tree method. The most important soil properties explaining the occurrence of these weeds in field margins were extractable soil nutrients, specifically sodium, boron and copper content, as well as soil physical attributes, in order of importance, bulk density, silt content, field moisture capacity, hydraulic conductivity, wilting point, available water and clay content. Soil chemical properties proved least reliable in explaining weed occurrence at roadside field margins. Knowledge of the relationships between soil properties and weed occurrence can add to our understanding of weed biology and hence enhance the efficiency of weed management strategies. For example, the occurrence of A. palmeri, in soils with high bulk density (>1.4 g cm^?3) and low organic matter content (<2.7%) and thus lower residual herbicide activity, will require integrated weed management of this species in field margins. This is of interest given the occurrence of herbicide resistance in roadside arable weeds, mainly A. palmeri, E. crus‐galli and S. halepense, in the Mississippi River Delta region of eastern Arkansas and other parts of the world.     

Combining mechanical rhizome removal and cover crops for Elytrigia repens control in organic barley systems

Mechanical weed control of perennial weeds in organic crop production over long post‐harvest periods is incompatible with the establishment of cover crops for improving soil quality and preventing nutrient leaching. We suggest a new concept that comprises uprooting and immediate removal of vegetative propagules located within the plough layer to allow for quick re‐establishment of a plant cover. A field experiment comparing the effects of conventional practices (stubble cultivation) with different combinations of rotary cultivation (One, Two or four passes) and cover crops (none vs. rye‐vetch‐mustard mixture) on Elytrigia repens rhizome removal, shoot growth and suppression of a subsequent barley crop was examined in two growing seasons. Four passes with a modified rotary cultivator, where each pass was followed by rhizome removal, reduced E. repens shoot growth in barley by 84% and 97%. In general, the cover crop developed poorly and did not affect barley or E. repens. Barley yield was only affected by treatments in the first season, where yield was negatively correlated with E. repens shoot biomass. The concept has potential for the control of severe E. repens infestations, but future research aimed at identifying more effective smother crops and less intensive methods of rhizome removal is needed.     

Summer cover crops for weed management and yield improvement in organic lettuce (<Emphasis Type="Italic">Lactuca sativa</Emphasis>) production

Over the last two decades, the demand for organic products has grown rapidly in the world due to increased concern about side effects of pesticides on the environment and human health. Studies were conducted in organic lettuce (Lactuca sativa L.) from 2004 to 2005 at the Black Sea Agricultural Research Institute in Samsun, Turkey, to determine the suppressive effects of summer cover crops on weeds. The experiment was arranged in a randomized complete block design with four replications. Treatments consisted of grain sorghum [Sorghum bicolor (L.) Moench.], sudangrass [Sorghum vulgare Pers. var. sudanense (Piper) Hitchc.], hairy vetch (Vicia villosa Roth.), grain amaranth (Amaranthus cruentus L.), pea (Pisum sativum L.) and bare ground with no cover crop. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 days after incorporation (DAI) of the cover crops. The cover crops produced between 1.2 and 3 t ha⁻¹ biomass and grain sorghum produced more dry matter than any other species in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer weed species, and lower weed density than the other cover crops in both years. Hairy vetch, grain sorghum, and sudangrass were the most effective cover crops and reduced total weed dry biomass by 90.3%, 87.4%, and 86.9% in 2004, and by 88%, 86.3%, and 85.2% in 2005, respectively. Cover crop residue suppressed many broadleaved weed species but failed to control grass weeds. Hairy vetch treatments produced the highest yield, followed by sudangrass and grain sorghum. Yields with grain amaranth and pea were similar to that of the control. These results indicate that hairy vetch, grain sorghum, and sudangrass can be used to suppress weeds in early season of organic lettuce production.     

An integrated approach to control glyphosate‐resistant Ambrosia trifida with tillage and herbicides in glyphosate‐resistant maize

Glyphosate‐resistant Ambrosia trifida is a competitive and difficult‐to‐control annual broad‐leaved weed in several agronomic crops in the Midwestern United States and Ontario, Canada. The objectives of this study were to compare treatments for control of glyphosate‐resistant A. trifida with tillage followed by pre‐emergence (PRE) and/or post‐emergence (POST) herbicides in glyphosate‐resistant maize and to determine the impact of A. trifida escapes on maize yield. Field experiments were conducted in 2013 and 2014 in grower fields infested with glyphosate‐resistant A. trifida. Tillage prior to maize sowing resulted in 80–85% control compared with no tillage. Tillage followed by PRE application of saflufenacil plus dimethenamid‐P with or without atrazine resulted in 99% control compared with ≤86 and 96% control with PRE herbicides alone at 7 and 21 days after application respectively. Tillage or POST‐only herbicides resulted in 4–14 A. trifida plants m^?2, whereas a PRE and POST programme had <3 plants m^?2. Maize yield was greatest (13.1–14.2 tonnes ha^?1) with tillage followed by PRE and POST herbicide programme. The relationship between maize yield and late‐season density of A. trifida escapes showed a 50% maize yield reduction irrespective of control measures when A. trifida density was 8.4 plants m^?2. It was concluded that the combination of tillage with PRE and/or POST herbicides reduced A. trifida density and biomass accumulation early in the season and provided an integrated approach for effective management.     

Aminopyralid soil residues affect rotational vegetable crops in Florida

BACKGROUND: Bahiagrass (Paspalum notatum Flueggé) is a poor host of several soilborne pests of vegetable crops; therefore vegetable crops are commonly grown in a rotation with bahiagrass pastures in Florida. The herbicide aminopyralid provides foliar and soil residual weed control and increases forage production in bahiagrass pastures; however, the soil residual activity of aminopyralid makes carryover injury likely in subsequent sensitive vegetable crops. Field research was conducted to determine the sensitivity of five vegetable crops to soil residues of aminopyralid. RESULTS: At an aminopyralid soil concentration of 0.2 µg kg^?1 (the limit of quantitation for aminopyralid in this research), crop injury ratings were 48% (bell pepper), 67% (eggplant), 71% (tomato), 3% (muskmelon) and 3% (watermelon), and fruit yield losses (relative to the untreated control) at that concentration were 61, 64, 95, 8 and 14% in those respective crops. CONCLUSIONS: The crops included in this research were negatively affected by aminopyralid at soil concentrations less than the limit of quantitation (0.2 µg kg^?1). Therefore, it was concluded that a field bioassay must be used to determine whether carryover injury will occur when these crops are planted on a site where aminopyralid has been previously applied. Copyright © 2011 Society of Chemical Industry     

Effects of alternative winter cover cropping systems on weed suppression in organically grown tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>)

Weed control is a major concern for organic farmers around the world and non-chemical weed control methods are now the subject of many investigations. Field studies were conducted in tomato (Solanum lycopersicum L.) from 2004 to 2006 at the Black Sea Agricultural Research Institute experiment field to determine the weed suppressive effects of winter cover crops. Treatments consisted of ryegrass (Lolium multiflorum L.), oat (Avena sativa L.), rye (Secale cereale L.), wheat (Triticum aestivum L.), gelemen clover (Trifolium meneghinianum Clem.), Egyptian clover (Trifolium alexandrinum L.), common vetch (Vicia sativa L.), hairy vetch (Vicia villosa Roth.) and a control with no cover crop. Treatments were arranged in a randomized complete block design with four replications. To determine the weed suppressive effects of the cover crops, weed density and total weed dry biomass were assessed at 14, 28, and 56 days after termination (DAT) of the cover crops from all plots using a 50 × 50 cm quadrat placed randomly in each plot. After cover crop kill and incorporation into soil, tomato seedlings variety ‘H2274’ were transplanted. Broadleaved weed species were the most prominent species in both years. Total weed biomass measured just prior to cover crop incorporation into the soil was significantly lower in S. cereale plots than in the others. The number of weed species was lowest at 14 DAT and later increased at 28 and 56 DAT, and subsequently remained constant during harvest. This research indicates that cover crops such as L. multiflorum, S. cereale, V. sativa and V. villosa could be used in integrated weed management programs to manage some weeds in the early growth stages of organic tomato.     

A review of the effects of crop agronomy on the management of Alopecurus myosuroides

This study reviews 52 field experiments, mostly from the UK, studying the effects of cultivation techniques, sowing date, crop density and cultivar choice on Alopecurus myosuroides infestations in cereal crops. Where possible, a statistical meta‐analysis has been used to calculate average responses to the various cultural practices and to estimate their variability. In 25 experiments, mouldboard ploughing prior to sowing winter cereals reduced A. myosuroides populations by an average of 69%, compared with non‐inversion tillage. Delaying drilling from September to the end of October decreased weed plant densities by approximately 50%. Sowing wheat in spring achieved an 88% reduction in A. myosuroides plant densities compared with autumn sowing. Increasing winter wheat crop density above 100 plants m^?2 had no effect on weed plant numbers, but reduced the number of heads m^?2 by 15% for every additional increase in 100 crop plants, up to the highest density tested (350 wheat plants m^?2). Choosing more competitive cultivars could decrease A. myosuroides heads m^?2 by 22%. With all cultural practices, outcomes were highly variable and effects inconsistent. Farmers are more likely to adopt cultural measures and so reduce their reliance on herbicides, if there were better predictions of likely outcomes at the individual field level.     

Apera spica-venti population dynamics and impact on crop yield as affected by tillage, crop rotation, location and herbicide programmes

Apera spica‐venti is a winter annual grass and, increasingly, a severe weed problem in autumn‐sown crops. Non‐inversion tillage has become more common in Denmark in recent years, but may accentuate problems with A. spica‐venti. These problems may be avoided, if selected preventive and cultural weed management practices are adopted. To this end, we conducted a 4‐year field study investigating the effects of crop rotation, tillage method, location and limited herbicide input on A. spica‐venti population dynamics and crop yield. Additionally, detailed studies were performed on the fate of A. spica‐venti seeds when incorporated to different soil depths. The location with a lighter soil texture, cooler climate and higher rainfall favoured A. spica‐venti growth and consequently crop yield loss, especially in the crop sequence comprised only of autumn‐sown crops and with non‐inversion tine tillage. Incorporating A. spica‐venti seeds in the soil improved their survival, explaining the higher A. spica‐venti proliferation seen with tine tillage as opposed to direct drilling. The rotations including an even mixture of spring‐ and autumn‐sown crops did not lead to noteworthy changes in the A. spica‐venti population, irrespective of tillage method. Thus, in many regions, management of A. spica‐venti will require rotations that balance autumn‐ and spring‐sown crops.     

Advancing cover cropping in temperate integrated weed management

The effects of cover crops on weeds and the underlying mechanisms of competition, physical control and allelopathy are not fully understood. Current knowledge reveals great potential for using cover crops as a preventive method in integrated weed management. Cover crops are able to suppress 70–95% of weeds and volunteer crops in the fall‐to‐spring period between two main crops. In addition, cover crop residues can reduce weed emergence during early development of the following cash crop by presenting a physical barrier and releasing allelopathic compounds into the soil solution. Therefore, cover crops can partly replace the weed suppressive function of stubble‐tillage operations and non‐selective chemical weed control in the fall‐to‐spring season. This review describes methods to quantify the competitive and allelopathic effects of cover crops. Insight obtained through such analysis is useful for mixing competitive and allelopathic cover crop species with maximal total weed suppression ability. It seems that cover crops produce and release more allelochemicals when plants are exposed to stress or physical damage. Avena strigose, for example, showed stronger weed suppression under dry conditions than during a moist autumn. These findings raise the question of whether allelopathy can be induced artificially. © 2019 Society of Chemical Industry     

Functional diversity of cover crop mixtures enhances biomass yield and weed suppression in a Mediterranean agroecosystem

Functional diversity of cover crop mixtures is thought to improve biomass production and weed suppression, two key agroecosystem services in organic systems. To test this hypothesis, we selected eight cover crop species belonging to four functional groups: (i) vining growing large-seeded legumes (field pea, common vetch), (ii) erect growing small-seeded legumes (crimson clover, squarrosum clover), (iii) grasses (barley, oats) and (iv) Brassicaceae (radish, black mustard). Nine cover crop mixtures were designed to create a gradient of diversity in terms of number of species and number of functional groups. A control treatment and all monocrops were included in the trial. Regarding cover crop biomass, mixtures outyielded monocrops by an average of 37%. Both functional identity and composition (i.e. trait complementarity) influenced biomass production and weed suppression provided by cover crops. Regression analysis showed that increase in both species diversity and functional diversity in cover crop mixtures improved the provision of agroecosystem services. Results from this study show that complementarity of species functional traits in cover crop mixtures can be used as a strategy to ensure high biomass production and good weed suppression in changing agroecosystems.     

Evaluation of herbicides against Phalaris minor in wheat in north-western Indian plains

Phalaris minor, the most serious weed in wheat in north‐western India, has developed extensive isoproturon resistance due to continuous isoproturon use. For its control, alternative herbicides (flufenacet, metribuzin and sulfosulfuron) at different application rates and timing were evaluated in wheat. In addition, herbicide carryover risk onto rotational crops (sorghum; maize and green gram, Vigina radiata) was also assessed. Isoproturon at 1 and 2 kg a.i. ha^?1 provided only 10.5% and 51.8%P. minor control respectively. Of the other herbicides, early post‐emergent [15–21 days after sowing (DAS)] flufenacet at 180–480 g a.i. ha^?1 provided acceptable control of P. minor, but failed to control broad‐leaved weeds and was phytotoxic to the wheat crop. Metribuzin at 210 g a.i. ha^?1 was effective in controlling both Phalaris and dicotyledonous weeds. Mixtures of both flufenacet and metribuzin at reduced rates were better than flufenacet for weed control and grain yield. The efficacy of flufenacet and metribuzin was drastically reduced with later growth stages of P. minor (four to five leaf). Whereas sulfosulfuron at 25–30 g a.i. ha^?1, applied either early post‐emergence (19 DAS) or post‐emergence (30–42 DAS), was quite effective. Overall, sulfosulfuron was the most effective treatment with regard to weed control and crop yield. However, maize and sorghum grown in rotation after harvest of sulfosulfuron‐treated wheat plots showed 65–73% crop biomass inhibition. The residual effect of sulfosulfuron was also noticed on Trianthema portulacastrum (Horse purslane), causing 73.5% dry matter reduction. By contrast, no carryover damage with flufenacet was observed on maize, sorghum and green gram. Glasshouse pot experiments and field trials investigating crop sensitivity to pre‐plant applications of sulfosulfuron found the decreasing order: sorghum > maize > green gram. The risk of carryover onto rotational crops should be considered when choosing alternative herbicides for P. minor control in wheat.     

UV-B radiation increases paraquat tolerance of two broad-leaved and two grass weeds in relation to changes in herbicide absorption and photosynthesis

Depletion of the protective ozone layer in the atmosphere leads to increasing UV‐B radiation on the earth's surface with potential effects on the response of plants to different stresses. Abutilon theophrasti, Amaranthus retroflexus, Digitaria sanguinalis and Chloris virgata are common weeds encountered in most arable fields in China. The effectiveness of herbicides used in controlling these weeds needs to be evaluated with increased UV‐B radiation. Seedlings of these four weeds were therefore grown under ambient and elevated UV‐B radiation to compare the efficacy of paraquat, a commonly used contact herbicide. Irrespective of species sensitivity to radiation, the elevated UV‐B radiation decreased the effectiveness of paraquat. Net photosynthesis rate was adversely affected except for D. sanguinalis, while the chlorophyll content was significantly reduced in A. retroflexus and C. virgata. UV‐B treatment increased the leaf surface wax and decreased the absorption of ¹⁴C‐paraquat in A. theophrasti, D. sanguinalis and C. virgata. These results suggest that the response of weeds to paraquat or the use of the herbicide may be affected by increased UV‐B radiation, to the extent that larger doses may be required to achieve desired effects. This may have damaging consequences for the environment.     

Potential impact of weedy Brassicaceae species on oil and meal quality of oilseed rape (canola) in Australia

Brassicaceae weeds are a widespread problem in Australian oilseed rape crops. The weeds not only compete for resources during crop growth, but also have the potential to reduce both oil and meal quality of the harvested crop. This study investigated oil and meal quality of weedy species from the Brassicaceae family that were collected throughout cropping regions of Australia. Eighty‐nine lines from 19 species were grown and evaluated in the same environment for their potential to contaminate Australian oilseed rape seed lots. Seed and flowering characteristics of each species were also examined. The glucosinolate concentration of most of the weedy species was greater than 100 μmol g^?1 of oil‐free meal, well above the threshold for meeting oilseed rape quality. Erucic acid content of 18 of the 19 weedy species also exceeded the oilseed rape quality standard of less than 2% erucic acid. This study highlights the potential of the weedy species to reduce the quality of Australian oilseed rape crops.     

Sensitivity of recently naturalised Digitaria spp. populations to 4‐hydroxyphenyl pyruvate dioxygenase‐ and acetolactate synthase‐inhibiting herbicides in maize

Until recently, Digitaria aequiglumis var. aequiglumis, native to South America, and Digitaria ciliaris subsp. nubica, native to Northeast Africa, were completely overlooked in Belgium due to their close morphological resemblance to Digitaria sanguinalis and Digitaria ischaemum. One of the possible reasons for their expansion in maize fields, besides for example the lack of crop rotation, might be a lower sensitivity to post‐emergence herbicides acting against panicoid grasses. Dose – response pot experiments were conducted in the glasshouse to evaluate the effectiveness of four foliar‐applied HPPD‐inhibiting herbicides (mesotrione, sulcotrione, tembotrione, topramezone) and two foliar‐applied ALS‐inhibiting herbicides (foramsulfuron, nicosulfuron) for controlling Belgian populations of D. aequiglumis and D. ciliaris subsp. Nubica, as well as local D. sanguinalis and D. ischaemum populations. In another dose–response pot experiment, the influence of growth stage at time of herbicide application on efficacy of topramezone and nicosulfuron for Digitaria spp. control was evaluated. In general, D. aequiglumis and D. ciliaris subsp. nubica populations were less sensitive to HPPD inhibitors than D. ischaemum and D. sanguinalis populations, except for D. aequiglumis treated with topramezone. Contrary to other herbicides tested, topramezone adequately controlled all D. aequiglumis populations at doses well below maximum authorised field dose. All species tested showed a progressive decrease in sensitivity to topramezone and nicosulfuron with seedling age. A satisfactory post‐emergence control of Digitaria species in the field will require appropriate choice of herbicide and dose, as well as more timely application.     

Total phenol,anthocyanin, and terpenoid content,photosynthetic rate,and nutrient uptake of Solanum nigrum L. and Digitaria sanguinalis L. as affected by arbuscular mycorrhizal fungi inoculation

Over the last decades, tillage, chemical fertilizers, and pesticides have reduced the beneficial fungal population size in arable soils. Though soil inoculation can be a practical way to restore arbuscular mycorrhizal fungi (AMF) population size, weeds may also be benefited, as well. This study was aimed to evaluate the effect of three AMF species (Funneliformis mosseae, Rhizoglomus fasciculatum, and Rhizoglomus intraradices) on photosynthetic rate, secondary metabolites content, reproductive organs percentage and nutrient uptake in Solanum nigrum L. and Digitaria sanguinalis L. weed species. Our results showed species variation in response to AMF inoculation, so that, while inoculation with R. intraradices fungal species decreased total biomass in S. nigrum plants significantly, it increased total biomass of D. sanguinalis plants by 26–49%. In addition, inoculation with F. mosseae species increased phenol, anthocyanin, and total terpenoid content in S. nigrum plants much more than D. sanguinalis. Increased photosynthetic rate, secondary metabolites content, and flowering percentage in AMF‐inoculated S. nigrum plants show the enhanced competitive ability and allelopathic potential of this weed when associated with AMF, which makes it a good competitor against other plant species in the environment.     

Manipulating crop row orientation and crop density to suppress Lolium rigidum

Light is an important resource that crops and weeds compete for and so increased light interception by the crop can be used as a method of weed suppression in cereal crops. This research investigated the impact of altered availability of photosynthetically active radiation (PAR) (from crop row orientation or seeding rate) on the growth and fecundity of Lolium rigidum. Wheat and barley crops were sown in an east–west (EW) or north–south (NS) direction, at a high or low seeding rate, in three field trials in 2010 and 2011 (at Merredin, Wongan Hills and Katanning, Western Australia). The average PAR available to L. rigidum in the inter‐row space of EW crops compared with NS crops was 78% to 91% at crop tillering, 39% to 56% at stem elongation, 28% to 53% at boot/anthesis and 41% to 59% at grain fill. Reduced PAR in the EW crop rows resulted in reduced L. rigidum fecundity in five of the six trials (average of 2968 and 5705 L. rigidum seeds m^?2 in the EW and NS crops). Availability of PAR was not influenced by seeding rate, but the high seeding rate reduced fecundity in three of the six trials (average of 3354 and 5092 seeds m^?2 in the crops with high and low seeding rate). Increased competitive ability of crops (through increased interception of PAR or increased crop density) was highly effective in reducing L. rigidum fecundity and is an environmentally friendly and low cost method of weed suppression.     

Weight loss in overwintering below‐ground parts of Sonchus arvensis under current and temperature‐elevated climate scenarios in Sweden

Weight loss in overwintering below‐ground parts of perennial weeds has been attributed to respiration, but neither its temperature dependence nor its relevance for biomass dynamics under changing climate conditions have been investigated. In two experiments, we quantified weight loss of the perennial weed Sonchus arvensis, by measuring weight changes over time of sprouting roots in dark rooms at temperatures of 4, 8 and 18°C. Dry weight loss rates were 0.47, 0.64 and 1.47% day^?1 at 4, 8 and 18°C, respectively, giving a half‐life time of 149, 110 and 47 days, respectively. A factor by which weight loss rates increase for every 10° rise in temperature (Q₁₀) was equal to about 2.3. Cumulative weight loss may comprise >40% of the below‐ground biomass during overwintering periods. Applying weight loss rates and Q₁₀ to elevated soil temperature projections showed that losses during winter seasons in central Sweden will remain basically constant, the effect of increased weight loss at higher temperatures being balanced by shorter winters. This implies that need for control of S. arvensis in a changing climate will persist, but that shorter winter seasons will provide a longer time window for control of S. arvensis prior to sowing crops.