Germination Of Weeds Research Articles

The arid land invasive weed Nicotiana glauca R. Graham (Solanaceae): Population and soil seed bank dynamics, seed germination patterns and seedling response to flood and drought

Disturbances in plant communities provide opportunities for weed germination, propagation, spread, and invasion. When the population density of a weed increases, fast-tracked and appropriate control management strategies are required. The objectives of this study were to: (i) examine the population and soil seed bank dynamics of Nicotiana glauca; (ii) compare the germination patterns of invasive N. glauca seeds collected from two states in Australia, and (iii) investigate the impact of a flood in September 1997 and subsequent drought on N. glauca seedlings. The density of N. glauca followed a steep positive increment during the sampling time (September 1999 to October 2004). The increment pattern was similar in flooded fenced and unfenced plots. Plant density increased over much of the observation period, but had declined to 80 and 432 stems ha −1, respectively, by October 2004. Stem density recorded in October 2004 along two transects radiating from the central point of the newly created lake demonstrated that a significant number of stems appeared to be dead. A soil seed bank study revealed that seed density varied significantly ( p=0.0001) between flooded fenced (598.75±71) and flooded unfenced (327.5±66) plots. In contrast, no N. glauca seedlings were recruited from the soil collected from the control plots. Germination trials were undertaken on N. glauca seed collected from New South Wales. There was no significance difference detected between treatments light and temperature. Similarly, no interaction was found between light and temperature. A comparative study on seed germination patterns of N. glauca seeds collected from Ivanhoe, New South Wales, and the Flinders Ranges, South Australia, showed that temperature had a significant effect on N. glauca seed germination. The effect varied significantly with main variables (state, length and time) and also with different interactions, except state×light ( p=0.3840). N. glauca seedlings exposed to flood were found to withstand partial flooding for at least 58 days. Under waterlogged conditions, the seedlings showed stem hypertrophy and produced adventitious roots. Only one seedling was found dead in the drought treatment. In conclusion, it is clear that N. glauca invaded the area after a rare flood event and began to function as a casual weed. Established seedlings in the field can withstand extreme ecological events such as flood and drought. Understanding the plants’ ecological characteristics through a study such as this at an early rather than late stage in the invasion will help us to take appropriate control measures for this species.

Phytochrome-mediated long-term memory of seeds

The question is how long phytochrome, stored within the cytoplasm of plant diaspores, may stimulate their germination. This question arose from the observation that soil cultivations in darkness for weed control gave inconsistent results. Namely, after a single nighttime or daytime cultivation during spring and summer, differences in weed emergence became hardly detectable after a period of six weeks. However, after nighttime and daytime cultivations in late autumn, emergence differences persisted for up to nine months. To examine whether this differing memory effect is phytochrome-mediated, seeds of Chenopodium album and Stellaria media were sown in pots with wet peat, either in daylight or after sunset. In the latter, seeds were irradiated with far-red light for one day prior to being covered and buried. For more than two years the far-red irradiated seeds produced significantly reduced emergence, indicating that germination and emergence of weeds in the field may be supported by maternal far-red absorbing seed phytochrome B(fr) over several months or even years. This conclusion allows refining of the strategy of lightless tillage.

Weed and Crop Response to Colored Plastic Mulches in Strawberry Production

The phase out of methyl bromide has forced strawberry (Fragaria ×ananassa Duchesne) growers to consider the use of cultural methods such as colored mulches to enhance weed control. Black plastic mulch controls most weeds; however, black mulch often does not warm the soil as well as clear mulch. Soil warming with clear mulch is desirable for early season markets, but clear mulch does not control weeds. Neither black nor clear mulches combine the ideal weed control and soil warming characteristics required. Seven colored mulches, as well as clear, black and no mulch were evaluated in California organic and conventional strawberries to identify mulch factors associated with weed control and soil warming. Laboratory and greenhouse experiments were also conducted to isolate the effects of light transmittance through mulch on weed germination and growth. The effect of mulch color on transmittance of photosynthetically active light (400 to 700 nm) through mulches was the key weed control factor, and was more important than the effect of mulch color effect on weed germination. Satisfactory weed control was provided by all mulches except clear, blue and red-brown laminated. Clear and black mulches provided the greatest soil warming in sunny and cloudy climatic conditions, respectively, although plants in clear mulched conventional production system plots produced the highest yield of marketable berries. Green and brown plastic mulches provided the best combinations of soil warming and weed control benefits at all trial locations.

(416) Weed Management in Organic Sweet Corn

Organic weed control in direct seeded vegetables depends on management strategies that control weed germination or growth which depletes the weed seedbank. In 2004, a randomized complete-block experiment conducted on land transitioning to organic production examined the effects of tillage and control treatments on weed pressure in sweet corn [Zeamays (L.) cv. Silver Queen]. The two tillage treatments consisted of conventional (moldboard and rototill) and spader tillage. Weed control treatments included a weed free control, a spring-tine weeder, rolling cultivator, row flamer, stale seedbed, and corn gluten meal. In August, the weed infestation was primarily goose grass [Eleusineindica (L.) Gaertn.], crab grass [Digitariasanguinalis (L.) Scop.], giant foxtail (Setariafaberi Herrm.), and smooth pigweed [Amaranthushybridus (L.)] species. Dried weed weights indicated that smooth pigweed constituted about 80% of the total weed biomass in all but the control and flamer treatments. Plots managed with the spring-tine weeder or corn gluten had twice the weed biomass of those managed with the rolling cultivator and flamer. The rolling cultivator and control treatments produced equivalent husked corn yields (6.9 t·ha-1); yields were reduced by the other weed control methods. At 5.4 t·ha-1, yields in the flamer treatment were the lowest among all weed control methods. The flamer suppressed both weeds and the crop, which may preclude its utility for sweet corn production. Results demonstrated that the rolling cultivator provided the best weed control without negatively affecting potential yields.

Sharing a Signal for Good and Bad

The majority of terrestrial plants rely on symbiotic relationships to obtain necessary nutrients. One of these relationships is between the roots of plants and arbuscular mycorrhizal fungi (see Parniske). Akiyama et al. isolated and identified the so-far elusive chemical that is the signal, called branching factor (BF), released by plants to attract the fungi. The compound was determined to be a strigolactone, which belongs to a class of sesquiterpene lactones that also serve as seed germination stimulants for parasitic weeds. Natural and synthetic strigolactones stimulated the formation of hyphal branches in an in vitro bioassay. Strigolactones are unstable compounds that are released by plants under conditions of low phosphate availability, which are the same conditions that allow parasitic weeds to prevail. The sharing of the signal for symbiotic root colonization by fungi with seed germination of parasitic weeds may lead to new strategies for managing beneficial symbiotic relationships and preventing the invasion by parasitic plants. M. Parniske, Plant-fungal association: Cue for the branching connection. Nature 435 , 750-751 (2005). [PubMed] K. Akiyama, K.-i. Matsuzaki, H. Hayashi, Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi. Nature 435 , 824-827 (2005). [PubMed]

根寄生雑草 <i>O. minor</i>、<i>S. asiatica</i> 及び <i>S. hermonthica</i> の種子発芽と寄生に及ぼす色素生合成阻害剤の影響

根寄生雑草 <i>O. minor</i>、<i>S. asiatica</i> 及び <i>S. hermonthica</i> の種子発芽と寄生に及ぼす色素生合成阻害剤の影響

地表面で越冬した夏畑雑草種子の発芽に対する温度と光条件の影響

地表面で越冬した夏畑雑草種子の発芽に対する温度と光条件の影響

Allelopathic Potential and Systematic Evaluation of Organic Extracts from Canavalia ensiformis Leaves (Jack Beans)

This article describes the assessment of possible allelopathic potential of organic extracts obtained from leaves of Canavalia ensiformis under laboratory conditions. Furthermore, a systematic evaluation of these extracts was carried out using specific protocols developed in capillary electrophoresis (CE) to determine some groups of secondary metabolites. After the identification and quantification of compounds, the effects of compounds on germination of some common weeds was investigated, which are becoming a real problem in pastures in the state of Pará, Brazil.

Aspectos sobre el control de malezas compuestas en pastos dedicados a la ganadería de leche

Con el objeto de encontrar métodos de control oportunos y eficientes de Senecio inaequidens y Sonchus oleraceus, se desarrollaron una serie de observaciones sobre la ecofisiología y morfología de estas especies de malezas y se probaron algunos métodos de control cultural, químico y biológico. Los resultados mostraron que la edad de la semilla, la cantidad y calidad de la luz percibida, tienen una incidencia proporcional sobre la tasa de germinación. La relación entre la temperatura día/noche es inversamente proporcional a la producción de capítulos florales y hojas, con óptimos entre 20°/15° C. Al analizar la curva fenológica de S. inaequidens, se encontró que los 40 días es la época óptima de contro, mientras que a los 50 días la planta toma la forma de roseta y adquiere resistencia bioquímica a grandes grupos de herbicidas. Los resultados indican que el crecimiento y desarrollo de S. inaequidens se incrementa bajo condiciones de alta humedad del suelo, de allí que esta especie coloniza fácilmente bordes de canales y áreas inundadas en lotes agrícolas. En cuanto al control químico, S. inaequidens es una especie cuyo estado adulto es muy tolerante al amplio grupo de herbicidas derivados de los fenoxidos, del ácido benzoico, del ácido picolínico y de las isoxazolidinonas. Cuando se usaron algunos métodos mecá­nicos en la preparación del suelo, para el manejo del banco de semillas de malezas, el renovador de praderas redujo en un 23% el número de semillas; posteriormente se realizan dos pases de guadaña cada 45 días para cortar la floración de la maleza que emerge posteriormente; la reducción fue de 20% más. En cuanto al control biológico se encontraron dos especies de insectos: Homeosoma oconoquensis y Ensina hyallipennis, cuya actividad redujo en más de 50% las poblaciones de Senecio inaequidens y Sonchus oleraceus, siendo su incidencia y severidad mayor en el segundo semestre del año. La información generada permite suponer que los parámetros morfológicos y ecofisio­lógicos analizados servirían como herramientas de conocimiento que, integradas con algunos métodos de manejo cultural, biológico y químico, conformarían un modelo para el control de estas especies de malezas en praderas de trópico alto.

ENHANCED PEST MANAGEMENT WITH COVER CROP MULCHES

Living and dead plant vegetation on the surface of soils can provide opportunities for regulating pest populations in no-tillage production systems. Cover crops generate substantial quantities of surface vegetation and residue that can be managed to enhance control of pests. Research at the Beltsville Agricultural Research Center has shown that weed germination and emergence is inhibited by high levels of cover crop mulch, that small-seeded annual weeds are particularly susceptible to suppression by mulches, and that herbicide use can be reduced when cover crops are incorporated into cropping systems. Growing mixtures of legume and cereal cover crops is a particularly effective way to produce large quantities of cover crop residue for weed suppression. Mulches with a high surface area-to-soil area ratio and a low amount of internal empty space are most highly correlated with inhibition of weed emergence. Foliar diseases can be reduced by a cover crop mulch, primarily by preventing dispersal of pathogen propagules through splashing and/or wind-borne processes. Cover crops can suppress establishment of soil-inhabiting herbivores such as Colorado potato beetle by disrupting emergence and migration behavior. Reduction of weed and pest populations by cover crops has reduced or eliminated crop yield loss caused by these organisms. INTRODUCTION Holistic management principles and a shift to a systems approach for crop protection are vital to combating the escalating economic and environmental consequences of agricultural pests. In conventional pest management strategies, pesticides typically constitute the first line of defense. In contrast, an ecological-based, systems approach focuses on preventive practices and natural processes of population regulation with pesticides used only as therapeutic tools when needed. Emphasis is placed on maximizing the beneficial, desirable ecological processes within farming systems that can maintain weed and pest populations at low, manageable levels. Although agricultural systems are simplified compared to natural ecosystems, there are abundant opportunities to redesign and manage agricultural systems to reduce and eliminate pest outbreaks. No-tillage production systems offer several opportunities to regulate weed and pest populations. One of the biggest advantages to farming without tillage is the maintenance of plant residue on the surface of soils. The soil microclimate under residue avoids temperature extremes and maintains more uniform soil moisture that favors a wide array of organisms. These conditions lead to improvements in soil structure, tilth, nutrient holding capacity, and water-holding capacity as well as biological activity. These improvements to soil physical, chemical, and biological properties can act in a synergistic manner to create a soil that is more similar to that of natural ecosystems. The live and dead plant material associated with use of cover crops in no-tillage systems are particularly suited to natural suppression of weeds and pests. Generally, a more diverse biological and physical environment at the surface of soils such as that associated with cover crops offers opportunities for regulating and minimizing pest populations. Proc. XXVI IHC – Sustainability of Horticultural Systems Eds. L. Bertschinger and J.D. Anderson Acta Hort. 638, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA)

Temperature effects on germination of nineAmaranthusspecies

Germination of weed seed and time of emergence are greatly affected by temperature. The effects of temperature on seed germination of tumble pigweed, prostrate pigweed, smooth pigweed, Palmer amaranth, Powell amaranth, spiny amaranth, redroot pigweed, common waterhemp, and tall waterhemp were examined under constant and alternating temperature regimens at 5, 10, 15, 20, 25, 30, and 35 C. Averaged over all temperatures, alternating temperature regimens increased total germination of all species, except Powell amaranth, which germinated similarly under both constant and alternating temperatures. In addition, Powell amaranth seed exhibited the highest total germination across all temperatures compared with the other amaranth species. Prostrate pigweed seed demonstrated the lowest total germination. Optimal temperatures for maximum germination were greater than 20 C for all species, except prostrate pigweed. The alternating temperature regimen centering at 30 C was used to compare the germination rates of the nine species. Palmer amaranth and smooth pigweed attained complete germination on the first day. The rate of germination for these species was much more rapid than the otherAmaranthusspp., which took 3 to 8 d to reach 50% germination.

Growth Regulator Effects of Propiconazole on Redroot Pigweed (Amaranthus retroflexus)1

Nonfungicidal effects of agricultural fungicides on crop plants have been reported previously; however, there are few reports of nontarget effects of fungicides on weedy species. Field research trials in Oregon demonstrated that the growth of several broadleaf weeds was reduced after multiple applications of the fungicide propiconazole. Greenhouse experiments confirmed that preemergence applications of propiconazole reduced the biomass accumulation of several common broadleaf and grass weeds 15 to 63%. Laboratory experiments were performed on redroot pigweed, the most sensitive species, to examine the effects of propiconazole on germination and early seedling growth. Redroot pigweed germination and total seedling length (root plus shoot) were reduced at propiconazole concentrations above 37 and 0.36 mg/L, respectively. Growth-regulating effects of fungicides such as propiconazole on the germination and early growth of weeds may contribute to integrated weed management, especially when adequate moisture ensures the presence of germinating seeds and small seedlings throughout the growing season.Nomenclature: Propiconazole; redroot pigweed, Amaranthus retroflexus L. #3 AMARE.Additional index words: Fungicide, Lolium multiflorum, LOLMU, POAAN, Poa annua, nontarget effects, Senecio vulgaris, SENVU, sterol biosynthesis inhibitor.Abbreviations: DMI, demethylation inhibitor; POST, postemergence; PRE, preemergence; SBI, sterol biosynthesis inhibiting.

Essential oils from Mediterranean lamiaceae as weed germination inhibitors.

The essential oils obtained from rosemary (Rosmarinus officinalis L.), thyme (Thymus vulgaris L.), and savory (Satureja montana L.) and the four monoterpenes that are their major constituents have been analyzed by GC and GC-MS and tested for their allelopathic properties on the seeds of three different annual weeds (Chenopodium album, Portulaca oleracea, and Echinochloa crus-galli) and three crops (Raphanus sativus, Capsicum annuum, and Lactuca sativa), with the aim to evaluate in vitro their potential as germination inhibitors. The essential oil composition varied with the species, thymol being the main constituent (44%) of thyme and carvacrol (57%) that of savory oil. Differences in essential oil composition were observed within two different rosemary ecotypes, type A, with alpha-pinene (37%) and 1,8-cineole (23%), and type B, characterized by a 2-fold content of 1,8-cineole (47%). This latest essential oil inhibited completely the germination of weeds while concurrently displaying little effect on pepper. The other two oils showed less selective action. S. montana essential oil, with 57% carvacrol, is the most active compound, completely inhibiting germination both of crops and weeds. Borneol, one of the main constituents of the oil of rosemary type B, showed an activity comparable to that of the whole oil. Crop and weed seeds treated with 1,8-cineole showed germination values that were not significantly different from controls, even if a slowing of the germination process expressed in terms of a significant increase in mean germination time was observed. Monoterpene compounds also present in the essential oils mainly represented the volatile fraction released from the crops and their residues into the soil.

Swainsona sejuncta: a species of ornamental promise or a potential weed?

The potential for indigenous species to establish outside their natural range and become weeds is less well recognised than the potential for exotic species to become weeds. In this study, the weed potential of a native Australian legume, Swainsona sejuncta Joy Thomps., was assessed using weed risk assessment protocols (the 'Pheloung system') and germination experiments. The Pheloung system uncovered several traits indicating that S.�sejuncta has significant weed potential. These traits include production of the toxin swainsonine, a short generative time, production of large numbers of viable seeds, and formation of a dense canopy. The species appears to benefit from cultivation, and seedlings emerged along paths surrounding garden beds. The Pheloung system did not give a definitive outcome for rejection or acceptance (high or low weed potential, respectively) but indicated that further evaluation is required. However, if S. sejuncta naturalises outside its limited native range in the future, then the species would be considered to have a high weed potential. Experiments in addition to the Pheloung system showed that S. sejuncta germinated rapidly over a wide range of temperatures once the seed coat was broken, reflecting a high competitive ability. Consequently, cultivation and commercialisation of S. sejuncta as an ornamental plant is not recommended without further research.

紙マルチの分光特性

In order to evaluate the use of paper as a mulch for plant production, this research investigated the optical characteristics of two recycled papers (Emboss and Eco, beige 120 g/m2, and dark brown 55 g/m2, respectively) and a silver-polyethylene film (Silver, containing aluminum powder). We measured transmittance and reflectance of these materials as mulches under light controlled and open field (Tottori Sand Dune) conditions. Reflectance was defined as a ratio of reflective radiance of the mulch surface to that of the reflection standard surface.Used as mulches, all three materials would inhibit weed growth as they prevented the penetration of light at 660 nm, which stimulates weed germination. Mean transmittance at 400-700 nm for all three was less than 1%. The reflectance of Emboss and Eco was low for ultraviolet (350-400 nm). but high for visible (400-700 nm) and near infrared rays (700-2, 500 nm). The opposite was found with Silver. The radiances of the three mulches on fair and cloudy days were compared. The radiance of the three mulches on the cloudy day were high for ultraviolet but low for visible and near infrared rays. The light scattering property of each material was measured hemispherically at 5 angles: 30°, 60°, 90°, 120° and 150°. Silver reflected light more strongly in the direction against the angle of the sun. In contrast, Emboss generally reflected more light than Eco in all directions, both had no significant differences among the directions. Because Emboss reflects photosynthetically active radiation (400-700nm) at a wider angle than Silver, it may be better for plant photosynthesis.

Photobiologische Unkrautregulierung annueller Ackerunkräuter

AbstractPhotocontrol of weed germination of arable annual weedsField studies were conducted to test the effect of light during soil tillage on the emergence of common weed species. Soil tillage was conducted at night or during daylight. In 20 out of a total of 23 field experiments, weed density after nighttime tillage was reduced compared to conventional daytime tillage. The average reduction of weed density attributable to photocontrol was 28.4 %. Results of field trials in the literature suggest that the emergence of Chenopodium album, Matricaria species and Stellaria media is especially reduced by nighttime tillage practices, but photocontrol had almost no effect on the emergence of Galium aparine and Polygonum convolvulus. The level of reduction of weed emergence after nighttime tillage was very variable. Important factors affecting this variation were: (1) the different light sensitivities of weed species, (2) the different light sensitivities of populations within one species, (3) the dormancy status of the seeds in a natural seed bank, and (4) the variation of light sensitivity of seeds.

Ecological Management of Agricultural Weeds

Concerns over environmental and human health impacts of conventional weed management practices, herbicide resistance in weeds, and rising costs of crop production and protection have led agricultural producers and scientists in many countries to seek strategies that take greater advantage of ecological processes and thereby allow a reduction in herbicide use. This book provides principles and practices for ecologically based weed management in a wide range of temperate and tropical farming systems. After examining weed life histories and processes determining the assembly of weed communities, the authors describe how tillage and cultivation practices, manipulations of soil conditions, competitive cultivars, crop diversification, grazing livestock, arthropod and microbial biocontrol agents, and other factors can be used to reduce weed germination, growth, competitive ability, reproduction, and dispersal. Special attention is given to the evolutionary challenges that weeds pose and the roles that farmers can play in the development of new weed management strategies.

Effect of the Presence or Absence of Corn on Common Lambsquarters (Chenopodium album L.) and Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] Emergence1

A 3-yr study was conducted to establish if the presence of corn had an effect on the emergence patterns and total weed seedling density under growing conditions in southwestern Québec. Weed seedling emergence was monitored in permanent quadrats throughout the growing season in the presence and absence of growing corn. Common lambsquarters and barnyardgrass were prevalent in most site-years. The presence of corn did not affect the patterns of common lambsquarters and barnyardgrass emergence nor their total weed seedling density except in 1994. Corn canopy was probably not sufficiently developed to affect light levels or soil temperature needed for weed germination and, consequently, seedling emergence. In 1994, in the absence of corn, some soil crusting was observed on a fine-textured soil, and the total number of seedlings was reduced. The results of these weed emergence studies in corn can be extended to other crops growing with wide row spacing and relatively slow canopy closure similar to those of grain corn.Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; corn, Zea mays L. ‘Pioneer 3921’.Additional index words: Amaranthus retroflexus L., AMARE, crop competition, redroot pigweed, weed density, weed seedling emergence.Abbreviations: CHU, corn heat units; PAR, photosynthetically active radiation.

Integrated weed management: Quo vadis?

The different components of Integrated Weed Management (IWM), such as crop selection, crop husbandry, plant nutrition, crop protection, farm hygiene, and the site‐specific conditions, all are factors having an influence on the successful adoption of the basic IWM concept. Farmers’ field activities, directly or indirectly, affect germination and development of weeds as well as weed population dynamics. However, also important non‐agronomic parameters indirectly affect weed management. They include farm structure, farmers’ personal targets and preferences, the provision and communication of technical know‐how, economics, but also demands from society and in the area of ecology. In the light of the many additional important influences and interactions, rather than thinking in terms of IWM, it seems appropriate to view crop production as a whole process, probably best defined as Integrated Crop Management (ICM). Boiling down the mass of information and outlining a rational, straightforward, easy‐to‐apply and cheap approach for the site‐specific weed management is needed for the successful implementation of IWM principles within the framework of ICM.

Environmental factors affecting germination of apple of Peru

Abstract Laboratory and field experiments were conducted to determine the effects of several environmental factors on seed germination and seedling emergence of the invasive weed, apple of Peru. The anatomy of the seed was also investigated in this study. The anatomy of the seed is similar to that of an eggplant (Solanum melongena L.) seed. The seed is albuminous, and consists of a seed coat, endosperm, and an embryo. The seed coat, which consists of both outer and inner integuments, is relatively thick. Fresh and dry stored seeds exhibited strong dormancy. Hot water treatment did not affect the seed germination in the light, but significantly (P < 0.05) reduced the germination rate in the dark. Dry-heat treatment had no significant effect on seed germination in the dark, but it significantly (P < 0.05) increased the germination rate in the light. Cold stratification alone did not influence seed germination under constant temperature (25 C) but affected it under alternating temperature (25–15 C). However,...