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.     

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.     

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.     

Response of weed emergence to rate of Vicia villosa Roth and Secale cereale L. residue

Vicia villosa Roth (hairy vetch) or Secale cereale L. (rye) residue at 2 to 4 times the natural field rate reduced seedling emergence of a wide variety of weed species. However, the natural rate of residue was insufficient for control of most weed species. The form of the response of weed emergence to increasing rates of residue varied among species: emergence of some species showed a monotonic decline in response to increasing rates of residue whereas emergence of others increased at low rates before declining at higher rates. In addition to reducing number of seedlings, high rates of residue delayed the date of emergence. Seed size was generally not a good indicator of a species' ability to emerge through residue, although one very large seeded weed, Abutilon theophrasti. was especially insensitive to residue. V. villosa and 5. cereale did not differ greatly in their effect on weeds early in the growing season, but V. villosa decomposed more rapidly and allowed greater emergence later in the season. Effet de résidus de Vicia villosa Roth et de Secale cereale L. sur la levée des mauvaises herbes Des résidus de Vicia villosa Roth (Vesce velue) et de Secale cereale L. (seigle) à 2–4 fois la quan-tité normale réduisaient la levée d'un large spectre de mauvaises herbes. Cependant la quantité normale de résidus était insuffisante pour lutter contre la plupart d'entre elles. La réponse de la levée des mauvaises herbes à des quantités crois-santes de rVsidus différait selon les espèces. Pour certaines, la levée subissait un déclin monotone; pour d'autres, elle augmentait en présence de faible quantités de reésidus puis décroissait pour des quantités plus importantes. Ces dernières réduisaient la levée et la retardaient également. La taille des graines n'était généralement pas un bon indicateur de la capacité des espèces à lever au travers des résidus, bien qu'une trèAs grosse grains, Abutilon theophrasti Medic., était particu-lièrement insensible aux résidus. V. villosa et 5. cereale ne différaient pas beaucoup dans leur effet sur les mauvaises herbes en début de saison, mais V. villosa se décomposait plus rapidement et permettait des levees plus importantes en fin de saison. Wirkung von Emterückständen von Vicia villosa Roth und Secale cereale L. aufdie Keimung von Unkräutern Durch 2- bis 4 fache Ernteräckstände der Be-haarten Wicke (Vicia villosa) und des Roggens (Secale cereale) wurde die Keimung einer großen Zahl von Unkrautarten herabgesetzt. Normale Ernterückstandsmengen behinderten jedoch die Keimung nur unzureichen. Die Art und Weise der Reaktion der Keimung auf höhere Riick-stände war von Art zu Art verschieden: Die Keimung einiger Arten nahm mit zunehmender Menge an Ernterückständen gleichmäßig ab, während sie bei anderen bei niedrigen Mengen anstieg, urn dann bei höheren Mengen abzunehmen. Zusätzlich zur Verringerung der Keimpflanzendichte wurde bei hohen Rück-standsmengen die Keimung verzögert. Die Samengröße war im allgemeinen kein guter Indikator für die Fähigkeit einer Art, durch das Rückstandsmaterial zu keimen, obwohl eine Art mit großen Samen, Abutilon theophrasti, gegenüber diesen Rückständen besonders unempfindlich war. Die Rückstände der beiden Kulturpflanzen zeigten zu Beginn der Vegetationsperiode keine großen Wirkungsunterschiede, aber die Rückstände von Vicia villosa zerfielen schneller und ließen später eine stärkere Keimung zu.     

Effect of live hairy vetch and its incorporation on weed growth in a subtropical region

Two of the many benefits of including legume cover crops in a fallow cropping system are weed suppression and increased soil organic N. This study was conducted in order to examine the effect of hairy vetch (Vicia villosa) on weed growth and soil N through a fallow period in subtropical Okinawa, Japan. Together with an untreated control plot, hairy vetch was grown from November 2007 to April 2008 and subsequently incorporated into the soil. The weeds were allowed to develop uncontrolled for 2 months until the time when a cash crop would be planted. In the period after the incorporation of hairy vetch, the weed biomass in the hairy vetch (HV)+ plot was more than threefold greater than that in the HV? plot. Hairy vetch had a high tendency to uptake N in April before the incorporation of hairy vetch; the N uptake by the weeds was lower in the HV+ plot than in the HV? plot. After the incorporation of hairy vetch, the N uptake by the weeds in the HV+ plot was two‐to‐six times higher than that by the weeds in the HV? plot. The C/N ratios of hairy vetch and the weeds in the HV+ plot were lower than those of the weeds in the HV? plot. More than half of the hairy vetch residue and N in the residue had decomposed by 28 days after incorporation. The content of both the NH₄‐N and NO₃‐N in the HV+ soil was higher than that in the HV? soil. Moreover, the amount of NO₃‐N increased during the growing period of hairy vetch and decreased after the incorporation of hairy vetch. The fallow soil into which hairy vetch had been incorporated displayed a greater weed biomass and resulted in a higher inorganic N content than the soil that had not supported hairy vetch.     

Phenology and growth of Orobanche crenata Forsk (broomrape) in four legume crops

Studies were conducted in the field in 2 years comparing the phenology and growth of Orobanche crenata (Forsk) (crenate broomrape) in lentils (Lens esculenta L.) cv. Castellana, peas (Pisum sativum L.) cv. Orix, vetch (Vicia sativa L.) cv. comun and broadbean (Vicia faba L. cv. Alameda. First attachment of O. crenata to these crops took place 9–14 weeks after mid-November planting and earlier after later plantings, Differences in the first O. crenata attachment dates and in the duration of the underground growth period of O. crenata were much greater between years for any given crop than between crops in a given year: both attributes were apparently affected more by seasonal climatic conditions than by crop species, Furthermore, there was no consistent relationship found between crop growth stages and time after first attachment of the parante. This occurred in lentils and vetch while they were vegetative, in peas at late vegetative-early flowering stages, and at widely varying growth stages in broadbean, depending on planting dates and years. The maximum number of O. crenata plants successfully attached to each individual crop plant decreased in the order: peas > broadbean > lentil > vetch, with 21, 14, 10 and 8 per plant, respectively, averaged over the two seasons. Similarly, plant parasites: host dry weight ratio were 1.0, 0.7, 0.3 and 0.2 For each of these crops, respectively.     

Losses in grain yield of winter crops from Lolium rigidum competition depend on crop species, cultivar and season

The competitive abilities of eight winter crops were compared against Lolium rigidum Gaud, (annual ryegrass), an important weed of southern Australia, as a potential strategy to suppress weeds and reduce dependence on herbicides. Two cultivars of each species were chosen to represent the range of competitive ability within each crop and grown in field experiments in 1992 and 1993. The order of decreasing competitive ability (with the ranges of percentage yield reduction from L. rigidum at 300 plants m^?2 in parenthesis) was as follows: oats (Avena sativa L.), 2–14%; cereal rye (Secale cereale L.), 14–20%; and triticale (×Triticosecale), 5–24%; followed by oilseed rape, (Brassica napus L.), 9–30%; spring wheat (Triticum aestivum L.), 22–40%; spring barley (Hordeum vulgare L.), 10–55%; and, lastly, field pea (Pisum sativum L.), 100%, and lupin (Lupinus angustifolius L.), 100%. Differences in competitive ability of cultivars within each species were identified, but competition was strongly influenced by seasonal conditions. Competition for nutrients (N, P and K) and light was demonstrated. L. rigidum dry matter and seed production were negatively correlated with grain yield of the weedy crops. More competitive crops offer the potential to suppress grass weeds while maintaining acceptable grain yields. Ways of improving the competitive abilities of grain legume crops are discussed.     

THE EFFECT OF SUPERPHOSPHATE APPLICATION, 2,4-DB AND GRAZING ON BROOMRAPE (OROBANCHE MINOR SM.) IN A SUBTERRANEAN CLOVER PASTURE

Two 5-year trials were conducted in New South Wales on the control of broomrape (Orobanche minor Sm.), a plant parasite of subterranean clover (Trifolium subterraneum L.) and skeleton weed (Chondrilla juncea L.). Applications of superphosphate to two soils of low phosphorus status stimulated clover growth, which caused a reduction in the number of skeleton weed plants and a decrease in the broomrape population. Similar but less effective control was obtained when subterranean clover pasture was sprayed with 2,4-DB for skeleton weed control as soon as the clover seedlings had developed trifoliate leaves. In spring, sheep readily grazed the broomrape stems before flowering, causing death of the plants. Autumn application of super phosphate, coupled with grazing of the pasture by sheep, significantly reduced broomrape density.     

Assessment of trap crops for Lygus spp. in lettuce

The effectiveness of the use of trap crops for reducing herbivorous Lygus spp. (Heteroptera: Miridae) in a lettuce agroecosystem was evaluated in a series of field experiments in two locations in Sweden. Trap crop efficacy was determined by comparing Lygus densities in plots of lettuce with densities in adjacent plots of the cover crops Melilotus officinalis, Vicia sativa, Trifolium pratense and Medicago sativa, and the weed Artemisia vulgaris . All of the trap crops tested were more attractive to Lygus than lettuce, with between five- and 30-times as many adult Lygus on cover crops and more than 100-times more on A. vulgaris. Lygus rugulipennis was the dominant species on all plant species. These results suggest that a wide range of trap crops, including nitrogen-fixing cover crops, may be suitable for reducing populations of Lygus spp. in lettuce cropping systems.     

Orobanche palaestina: a potential threat to agricultural crops in Israel

Weeds of the genus Orobanche are obligatory chlorophyll-lacking root parasites that infect and severely damage many dicotyledonous agricultural crops in warm-temperate and subtropical regions of the world. The genus comprises over 100 species, at least six of which are notable weeds. Orobanche palaestina Reut. is an endemic Mediterranean species, previously reported to parasitize thistles [Notobasis syriaca (L.) Cass. and Cirsium phyllocephalum Boiss. & Bl.] and annual legumes in native Mediterranean habitats, mainly in disturbed places such as roadsides and waste sites. In recent years, we have observed a rapid expansion of O. palaestina populations adjacent to commercial agricultural fields in the Jezreel Valley of Israel. The ability of O. palaestina to infect crops was tested in pots under nethouse conditions. The experiments revealed that O. palaestina is able to parasitize agricultural crops. Safflower (Carthamus tinctorius L.), lettuce (Lactuca sativa L.), gazania (Gazania uniflora Gaertn.), vetch (Vicia sativa L.) and artichoke (Cynara scolymus L.) were found to be potential hosts for this parasite, and all of them, except vetch and artichoke, were preferred to thistle, the native host. Sunflower (Helianthus annuus L.) induced O. palaestina seed germination and root attachment, but the attached parasites could not reach maturity and died soon after the attachment stage. Tomato (Lycopersicon esculentum Mill.), carrot (Daucus carota L.), garland chrysanthemum (Chrysanthemum coronarium L.) and cabbage (Brassica oleraceae L.) were not parasitized by O. palaestina.     

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.     

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.     

Size and composition of the weed seedbank after 7 years of different cover-crop-maize management systems

The objective of this study was to obtain detailed information on the long‐term weed suppression potential of four winter soil cover types included in an arable crop system managed at various input levels. We used weed seedbank size and composition to assess weed suppression potential. A field experiment was established in 1993 as a split‐split‐plot design with four replications, including two tillage systems [a conventional system (CS) including ploughing in the cover crops and a low‐input system (LIS) including no tillage with surface mulching of the cover crops] in the main plots, three mineral nitrogen fertilization rates for the main crop in the sub‐plots and four soil cover types (main crop residue, rye, crimson clover and subterranean clover) in the sub‐sub‐plots. Seedbank sampling took place in winter 2000/01. The weed seedbank was analysed with the seedling emergence method. Data were analysed using anova and multivariate techniques. Results indicated that the seedbank density in the LIS was about five times higher than in the conventional input system. In the CS, use of a rye cover crop resulted in a lower seedbank density with respect to the crop residue treatment (?25%), whereas in the LIS the subterranean clover cover crop decreased weed seedbank density as compared with the other cover crops and the crop residue treatment (?22% on average). Differences in species composition were mainly related to tillage system. Implications for cover crop management and the development of sustainable cropping systems are discussed.     

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.     

Warum Untersaaten und Zwischenfr??chte wieder Bedeutung zur Unkrautregulierung in Europ?ischen Ackerbausystemen bekommen

Cover crops and under-sown crops have often been reported to have a positive impact on soil structure, soil living organisms and soil fertility. In many studies it was shown that they suppress weed populations. However, the percentage of winter annual cereals in European cropping system has strongly increased, which consequently reduced the time for growing cover crops. In this study, it was investigated if cover crops and under-sown have the capacity to reduce weed infestations also in rotations with a high percentage of winter annual cereals. Three field trials were conducted using at the University of Hohenheim from 2008 until 2010. Trifolium repens and Lolium perenne reduced weed density and weed biomass in Triticum aestivum and Triticum spelta, when they were sown as under-sown crops. Both under-sown crops had no negative effect on grain yield. Until 14 days after harvest, the under-sown crops developed a dense plant canopy. In the third experiment, Sinapis alba, Phacelia tanacetifolia, Avena strigosa and a mixture of Trifolium alexandrinum, Vicia sativa, Fagopyrum tataricum and Guizotia abyssinica were sown directly after harvest of winter wheat. Most of the cover crops emerged after few days and significantly reduced the density and biomass of emerging weeds. Sinapis alba resulted in a 93% reduction of above-ground weed biomass. Avena strigosa reduced root-biomass of weed by 97% and weed density by 90%. In order to achieve a significant weed suppression, cover crops need to emerged quickly and grow rapidly until the soil has been covered. The results of this study underline the potential of under-sown crops and cover-crops to support a sustainable and environmental friendly cropping system.     

Effect of sowing date and host resistance on the establishment and development of Orobanche crenata in faba bean and common vetch

The effect of early and late sowing dates on the establishment of Orobanche crenata Forsk. (crenate broomrape) in resistant and susceptible cultivars of faba bean (Vicia faba L.) and vetch (Vicia sativa L.) were studied over four seasons in southern Spain. Differences in establishment, development and shoot emergence of the parasite were compared. With resistant faba bean and vetch cultivars, there was reduced attachment and shoot emergence of O. crenata with all sowing dates. Susceptible cultivars were more severely affected by the parasite with early sowing. Orobanche crenata development was also delayed in resistant cultivars. Crop yield, estimated by the number of pods per plant, decreased with late sowings. The combined use of resistant cultivars and early sowing is a useful tool as part of an integrated control strategy. Resistant cultivars allow early sowing (with low O. crenata attack), thus avoiding yield losses due to the short crop cycle with late sowing.     

Effect of tillage, cover crop and crop rotation on the composition of weed flora in a sandy soil

The development of integrated weed management strategies requires knowledge of mechanisms that influence compositional changes in weed flora. A 9-year study was initiated in 1988 at Delhi, Canada, on a loamy sand soil to evaluate the effect of tillage systems [conventional (CT) and no-till (NT)] and cover crops (only in NT) on weed density, species composition and associations, and crop yield in a winter wheat ( Triticum aestivum L.)/bean/winter wheat rotation. Three bean types: soyabean ( Glycine max L. Merr.), white bean ( Phaseolus vulgaris L.) and kidney bean ( P . vulgaris L.) were included. The NT system included variations: rye ( Secale cereale L.) or maize ( Zea mays L.) cover crop, volunteer wheat disked after harvest and wheat stubble. Data were collected in 1994, 1995 and 1996. Tillage systems, cover crops and crop type had differential effects on weed densities, species composition and associations. Weed densities were not affected by tillage or cover crops in wheat but, in the beans, densities were greater in the CT than in the NT systems. Various associations of weed species with tillage system, cover crop and crop type were observed. Crop yields were not affected by tillage type or cover crop, except that soyabean yields were highest in plots with cover crops.     

Weed seed bank as affected by tillage,residue, and fertilization management under sweet corn-wheat cropping sequence in Iran

Soil weed seed bank is an important factor determining above-ground floristic composition and weed density in agricultural systems. The quantitative and qualitative measures of weed seed bank can help growers to predict the extent to which they are facing weed problems. Along with tillage, crop residues can affect the fate of weeds in the upcoming crops. To investigate such effects, we compared the effects of tillage systems [conventional tillage (CT), reduced tillage (RT), and no tillage (NT)], wheat residue retention, and nitrogen (N) rates (0, 69, 138, and 207 kg N ha⁻¹) on depth-related characteristics of the weed seed bank under a sweet corn-wheat sequence during 2014–2015 growing seasons in Shiraz, Iran. Soil bank was not affected by tillage systems but tended to be slightly higher under RT. The highest (898 seeds m⁻²) and lowest (322 seeds m⁻²) weed population at 0–10 cm depth were found when 138 kg N ha⁻¹ in 2015 and 207 kg N ha⁻¹ in 2014 were applied. Species richness and diversity were higher under NT and RT practices at the top layer, but CT system was more diversified at deeper depths. They were higher when crop residues were retained as well. Barnyard grass (Echinochloa crus-galli [L.] Beauv), common lambsquarter (Chenopodium album L.), common purslane (Portulaca oleracea L.), field bindweed (Convolvulus arvensis L.), flixweed (Descoreinia sofia [L.] Webb. & Berth.), henbit (Lamium amplexicaule L.), pigweeds (Amaranthus spp.), and stinking goosefoot (Chenopodium vulvaria L.) were the most common weeds found in all tillage systems and soil depths. Grasses were relatively lower than broadleaves regardless of treatments. Weed seed bank was mostly affected by weather conditions than treatments in this short-term experiment.     

Contribution of allelopathic effects to the overall weed suppression by different cover crops

Cover crops can suppress weeds within agricultural fields due to competitive and allelopathic effects. Glasshouse experiments were conducted to evaluate the relative proportions of allelopathic effects to the total weed inhibition. Six different cover crop species were combined with three weed species in the presence or absence of active carbon over a period of four weeks. Active carbon was used as an adsorbent for allelopathic substances in the soil. Our study revealed that the competition between cover crops and weeds shifted, possibly due to the minimisation of allelopathic effects by active carbon in the soil. We assume that the degree of cover crops allelopathic effects on weeds is species‐specific, both on the side of cover crops and on the weed side. The cover crops Raphanus sativus, Fagopyrum esculentum and Avena strigosa showed the highest allelopathic weed suppression with up to 28%. Additionally, Stellaria media turned out to be the most sensitive weed against allelopathic effects induced by all cover crops, except for Linum usitatissimum and Guizotia abyssinica. The knowledge about the contribution of competitive and allelopathic effects by cover crops would help to create cover crop mixtures with high weed suppressive ability.     

The effects of flax (Linum usitatissimum L.) and other crops as trap and catch crops for control of Egyptian broomrape (Orobanche aegyptiaca Pers.)*

Growing trap and catch crops to decrease infestation of Egyptian broomrape (Orobanche aegyptiaca Pers.) was tested in a 2-year field experiment supported by two pot experiments. Growing flax (Linum usitatissimum L.) in two successive winter seasons or one summer cropping with mung beans (Phaseolus aureus Roxbg.) reduced early infestation of the parasite and significantly increased tomato (Lycopersicum esculentum Mill.) vigour and production. However, the efficacy of using trap and catch crops for broomrape control in a heavily infested field was limited. Orobanche aegyptiaca attacked clover (Trifolium alexandrinum L.), flax and mung bean and developed inflorescences. Various sources of the parasite showed different degrees of virulence to flax, from heavy attack and severe damage, to sparse attachment with no production of flowering shoots. The virulent subspecies attacked flax all year round, causing severe damage. Vetch (Vicia saliva L.) var. Sadot was not parasitized by O. aegyptiaca. Effets du lin (Linum usitatissimum L.)et d'autres plantes cultivées comme plantes pièges et hôtes pour lutter contre l'orobanche égyptienne (Orobanche aegyptiaca Pers.) L'utilisation de plantes cultivées comme pièges et hôtes pour diminuer l'infestation par l'orobanche égyptienne (Orobanche aegyptiaca Pers.) a fait l'objet d'une expérimentation au champ sur deux ans ainsi que de deux expériences en pots. Si du lin (Linum usitatissimum L.) était cultivé sur deux saisons hivernales successives ou lors d'une saison estivale avec de l'ambérique (Phaseolus aureus Roxbg.), l'infestation précoce de la tomate (Lycopersicum esculentum Mill.) par le parasite était réduite, et sa vigueur ainsi que sa production étaient significativement augmentées. Cependant, l'efficacité des plantes cultivées pièges et hôtes pour lutter contre l'orobanche égyptienne dans des champs fortement infestés était limitée. Orobanche aegyptiaca attaquait le trèfle (Trifolium alexandrinum L.), le lin et l'ambérique, et développait des inflorescences. Différentes sources du parasite montraient des degrés variés de virulence à l'égard du lin, allant d'attaques importantes qui occasionnaient de sévères dommages, jusqu'à des infestations éparses qui ne produisaient pas de tiges florales. Les espèces virulentes attaquaient le lin tout au long de l'année et causaient des dommages importants. La vesce (Vicia sauva L.) variété Sadot n'était pas parasitée par O. aegyptiaca. Saat-Lein (Linum usitatissimum L.) und andere Kulturen als Fangpflanzen und Zwischenfrüchte zur Bekämpfung von Orobanche aegyptica Pers. In einem 2 ährigen Freiland- und 2 Gefäßversuchen wurden Fangpflanzen und Zwischenfrüchte zur Minderung der Verunkrautung mit Orobanche aegyptica untersucht. Nach dem Anbau von Saat-Lein (Linum usitatissimum L.) in 2 aufeinanderfolgenden Wintern oder einer Sommerkultur der Mungo-Bohne (Phaseolus aureus Roxbg.) war bei der Tomate (Lycopersicum esculentum Mill.) der frühe Befall durch den Parasiten herabgesetzt und Wachstum und Ertrag signifikant erhöht. Die Wirksamkeit des Anbaus von Fangpflanzen und Zwischenfrüchten zur Bekämpfung der Sommerwurz war jedoch auf stark verseuchten Feldern begrenzt. Orobanche aegyptica befiel Trifolium alexandrinum L., Saat-Lein und Mungo-Bohne und entwickelte Blüten. Die Virulenz verschiedener Herkünfte des Parasiten variierte von schwerem Befall und starkem Schaden bis schwachem Befall ohne Blütenbildung. Die virulente Unterart befiel den Lein das ganze Jahr über und führte zu schwerem Schaden. Die Sorte ‘Sadot’ der Saat-Wicke (Vicia sativa L.) wurde von O. aegyptica nicht befallen.