Impact of mowing and weed control on broadleaf weed population dynamics in turf

Abstract

Various turf management activities may influence weed population dynamics and interfere with weed control. The effects of a biocontrol agent, Sclerotinia minor, a chemical herbicide, Killex?, and mowing height on broadleaf weed dynamics were examined in two turfgrass stands for two consecutive years. Mowing did not reduce the population densities of dandelion or the ground cover of broadleaf weeds. In the second year, mowing significantly reduced white clover density, but significantly increased broadleaf plantain density, particularly at the closest mowing height (3–5 cm). Apart from the close height, the S. minor and Killex? treatments were equally effective in suppression of dandelion, white clover, broadleaf plantain, and prostrate knotweed in the second year. Common mallow increased in the herbicide treated plots and other species including yellow woodsorrel, yellow toadflax and lambsquarters increased in abundance in plots mowed at the 3–5 cm height and in plots treated with Killex?. Significant differences between the Killex? and S. minor treatments on dandelion population dynamics were rarely present and did not favour either treatment. S. minor did not damage the turfgrass, but Killex? reduced turf quality in 25% of the plots. The application of S. minor with a regular, medium height (～7 cm) mowing regime was highly effective in controlling broadleaf weeds in temperate Kentucky bluegrass turf.     

Epiphytic survival of Pseudomonas viridiflava on tomato and selected weed species

A rifampicin-nalidixic acid mutant of Pseudomonas viridiflava (PV) was studied in the field and greenhouse with respect to its epiphytic survival on the roots and foliage of a susceptible (FM 6203) and resistant (Ontario 7710) tomato cultivar and 16 weed species. In the field, populations varied between years, which was attributed to differences in environmental conditions. Hot, dry conditions caused rapid decline or elimination of populations. Some hosts were more conducive than others in promoting epiphytic growth, and generally, roots were better survival sites than foliage. Some hosts such as johnsongrass, lambsquarters, pigweed, prickly sida, and red sorrel had no detectable populations of PV on foliage 2 weeks after inoculation. (Plants had been misted with a 10⁸ cfu/ml suspension until run off occurred.) PV was recovered at week 4 on the foliage of the two tomato cultivars, beggarweed, jimsonweed, morning glory, smooth vetch, and wild mustard, and was recovered until week 16 on roots of buckhorn plantain in the field and for the same period on the ground cherry in the field and greenhouse. In scanning electron microscopy studies, PV was observed to survive as microcolonies in depressions between epidermal cells, around trichomes, along veins, and sometimes around stomates of tomato and beggarweed. Bacterial cells sometimes were held together and to the leaf surface by fibril-like strands. These studies show that PV does have an epiphytic stage on both tomato and certain weed species. However, the epidemiological significance of the epiphytic stage is probably dependent on environmental conditions.     

Amylolytic activity of selected species of ruminal bacteria

A variety of species of ruminal bacteria were screened for the ability to grow in starch-containing medium and produce amylase. Of those tested, the highest levels of amylase were produced by Streptococcus bovis JB1 and Ruminobacter amylophilus H18. Other strains that grew well on starch and produced amylase included Butyrivibrio fibrisolvens A38 and 49 and Bacteroides ruminicola 23 and B14. Varying the carbohydrate source provided for growth resulted in changes in the growth rate and level of amylase produced by these strains. All strains grew rapidly in starch-containing medium, and the rates of growth were generally more rapid than those observed for maltose-grown cultures. For S. bovis JB1, B. ruminicola 23 and B14, and B. fibrisolvens 49 and A38, amylase was produced when growth was on maltose or starch, but this activity was greatly reduced in glucose-grown cultures. The distribution of amylolytic activity between cellular and extracellular fractions was sometimes affected by the carbohydrate provided for growth. If S. bovis JB1 and B. fibrisolvens 49 were grown on starch, amylase was largely associated with cell pellets; however, if grown on maltose these strains produced activities that were almost entirely present in the extracellular fluid fractions. Although not as dramatic, a similar shift in the location of amylase activities was noted for the two B. ruminicola strains when grown on the same substrates. Growth on maltose or starch had little influence on either the predominantly cell-associated activity of B. fibrisolvens A38 or the activity of R. amylophilus H18, which was equally divided between cell pellet and extracellular fluid fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Amylolytic activity of selected species of ruminal bacteria.

A variety of species of ruminal bacteria were screened for the ability to grow in starch-containing medium and produce amylase. Of those tested, the highest levels of amylase were produced by Streptococcus bovis JB1 and Ruminobacter amylophilus H18. Other strains that grew well on starch and produced amylase included Butyrivibrio fibrisolvens A38 and 49 and Bacteroides ruminicola 23 and B14. Varying the carbohydrate source provided for growth resulted in changes in the growth rate and level of amylase produced by these strains. All strains grew rapidly in starch-containing medium, and the rates of growth were generally more rapid than those observed for maltose-grown cultures. For S. bovis JB1, B. ruminicola 23 and B14, and B. fibrisolvens 49 and A38, amylase was produced when growth was on maltose or starch, but this activity was greatly reduced in glucose-grown cultures. The distribution of amylolytic activity between cellular and extracellular fractions was sometimes affected by the carbohydrate provided for growth. If S. bovis JB1 and B. fibrisolvens 49 were grown on starch, amylase was largely associated with cell pellets; however, if grown on maltose these strains produced activities that were almost entirely present in the extracellular fluid fractions. Although not as dramatic, a similar shift in the location of amylase activities was noted for the two B. ruminicola strains when grown on the same substrates. Growth on maltose or starch had little influence on either the predominantly cell-associated activity of B. fibrisolvens A38 or the activity of R. amylophilus H18, which was equally divided between cell pellet and extracellular fluid fractions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ecology of germination of weed seeds

Summary Merremia gangetia Linn. (Cuf) is one of the most important weeds invading cultivated lands of India. Temperature, both high (45° C) and low (15° C) exhibit a definite role in development of the weed, particularly during germination. Higher tempeeratures (45° C) during dry storage appeared to be the main factor in laboratory experiments as well as in nature. Low temperature induced secondary dormancy and its removal by incubation at 35° C helps to explain the ecological mechanism through which the weed endures winter conditions. Germination of buried seeds confirm that the atmospheric conditions were found to be more effective in upper layers of soil. Ecological adaptations of this weed via germination requirements are assessed in the paper.     

Ozone treatment inactivates common bacteria and fungi associated with selected crop seeds and ornamental bulbs

The use of disease-free seeds or bulbs is very crucial to ensure sustainable and profitable agricultural production. Seed-borne pathogens which are responsible for significant yield losses in various crops need to be successfully eliminated with appropriate seed treatments. In this study, we investigated the efficacy of gaseous ozone (O₃) and ozonated water treatments on the inactivation of seed-borne fungal and bacterial pathogens of widely cultivated vegetable and cereal seeds, and ornamental bulbs. We demonstrated that O₃ application to tomato and cucumber seeds inactivates Fusarium oxysporum f. sp. lycopersici, Fusarium oxysporum f. sp. radicis-lycopersici, Clavibacter michiganensis subsp. michiganensis, Pseuodomonas syringae pv. tomato, and Pseudomonas syringae pv. lachrymans, respectively, with no negative effect on seed germination rate. The sterilization capacity of O₃ has substantially increased when the seeds were soaked in water before the treatments. The saprophytic fungal load and the infection rate of Pectobacterium carotovorum subsp. carotovorum on several species and cultivars of ornamental bulbs were suppressed by O₃ treatment. A strong decrease in the infection rate of Tilletia caries was also shown in O₃-treated wheat seeds under field conditions. Overall, the current study indicated that O₃ treatment has great potential in ensuring the use of disease-free seeds or other propagation materials, which is indispensable at the beginning of crop production.     

Weed species and weed communities

Summary With weeds as with many plant species the main or first level factor determining the area of distribution is a (complex) climatic one. As they have an artificially enlarged area of distribution, they have a huge border area (in an ecological sense), where the climate is not optimal for them, and where they have a narrow ecological and sociological amplitude and are especially sensitive to some measures of modern intensified agriculture. In their northern border areas species of southern origin are restricted to calcarcous substrates and to agrestal and finally ruderal communities, while in their optimal climate they are indifferent to that soil factor and able to compete with other species even in natural vegetation types. Species presumably of origin in atlantic areas are restricted with increasing continentality to very poor and acid soils, as they cannot compete with other species on better sites any more, because of their physiological properties. Thus weed distribution demonstrates the complicated reaction of plant species to the complexes of soil-climatic factors and to the competition of other species. As far as weeds are concerned, species may be only relatively calciphilous, but genuinely calcifuge species, the control being climatic in the former case and physiological in the second.The measures of modern agriculture bring about a gradual extinction of sensitive species from the limit of their range towards their centre of distribution, where they can find refuge habitats in the natural vegetation. The sensitivity of such species (also against herbicides) seems to increase towards their limits. Resistant species occur with increasing densities after the removal of their competitors. In addition, they are able to enlarge their area and to invade sites, where they had not been able to compete before, or sites where they could not previously bear the environmental conditions together with the competition of the rich weed flora.As the complex climatic gradients responsible for the ranges of weed species show smooth transitions, the alteration of species composition in weed communities is also a gradual one. This is one of the problems of weed phytosociology briefly discussed.Nomenclature follows Ehrendorfer (1973), Phytosociological units according to Westhoff & Den Held (1969).Contribution to the Symposium on Plant Species and Plant communities, held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Field studies were partly supported by a grant of the Austrian Federal Ministry of Agriculture and Forestry.     

Naturally occurring phenanthrene degrading bacteria associated with seeds of various plant species

Seeds of 11 of 19 plant species tested yielded naturally occurring phenanthrene degrading bacteria when placed on phenanthrene impression plates. Seed associated phenanthrene degrading bacteria were mostly detected on caragana, Canada thistle, creeping red fescue, western wheatgrass, and tall wheat grass. Based on 16S rRNA analysis the most common bacteria isolated from these seeds were strains belonging to the genera Enterobacteria, Erwinia, Burkholderia, Pantoea, Pseudomonas, and Sphingomonas. These plants may provide an excellent source of pre-adapted bacterial-plant associations highly suitable for use in remediation of contaminated soil environments.     

Raptors as legitimate secondary dispersers of weed seeds

Although raptors are not usually seen as seed dispersers, we demonstrate their important ecological role as legitimate seed dispersers of weeds. On the oceanic island of Fuerteventura in the Canary Islands, up to 11 000 weed seeds from a total of 39 and 62 different plant species, respectively, were found in 300 and 319 pellets, respectively, of two native predatory birds, the Common Buzzard Buteo buteo and the Eurasian Kestrel Falco tinnunculus, which consumed European Rabbits Oryctolagus cuniculus and Barbary Ground Squirrels Atlantoxerus getulus, both invasive mammals that carried these seeds in their guts. Four and seven weed species appeared with a frequency of occurrence greater than 10% in the pellets of Kestrels and Buzzards, respectively. Despite the time interval between pellet collection and germination experiments, almost 10% of planted seeds germinated, even after passing through two digestive processes, one inside the mammal and another inside the raptor. Our study encourages a change of perspective in this regard, as raptors may be involved in complex interactive dispersal processes on a wider geographical scale.     

Nucleic acid homologies of selected bacteria, L forms, Mycoplasma species

Rogul, M. (Walter Reed Army Institute of Research, Washington, D.C.), Z. A. McGee, R. G. Wittler, and Stanley Falkow. Nucleic acid homologies of selected bacteria, L forms, and Mycoplasma species. J. Bacteriol. 90:1200-1204. 1965.-The molar per cent of guanine plus cytosine (G + C) in the deoxyribonucleic acids (DNA) of Proteus mirabilis, strain 9, and its stable L form was determined by thermal denaturation and found to be approximately 39.5% G + C. The DNA homologies of this bacterium and its L form were estimated by the agar-column technique and were equivalent in their abilities to anneal and form specific duplexes. The next series of comparisons were performed between two Mycoplasma species and their often suggested bacterial parent. The G + C ratios of M. gallisepticum (32.7%), M. gallinarum (28.1%), and Haemophilus gallinarum (41.9%) varied to a high degree. In the homologous system, the denatured DNA of H. gallinarum trapped in agar bound approximately 40% of its sheared, denatured, and H(3)-labeled DNA. In comparison, the nucleic acids of M. gallinarum and M. gallisepticum were incapable of binding the labeled DNA of H. gallinarum. These findings provided evidence that the two strains of Mycoplasma were not derived from H. gallinarum.     

稻田水面漂浮的杂草种子种类及动态

为了揭示杂草种子的漂浮动态,并为探寻生态控草方法提供理论依据,我们于2005年6-11月,在南京沧波门稻作区调查了水稻种植前及生长后期田问杂草群落以及稻田灌水期间水面漂浮的杂草种子的种类及漂浮时间.结果表明,在水稻种植前及生长后期田间出现有15科24种杂草;可漂浮于水面的杂草种子有17科26种,与田间发生的杂草种类相同的共有18种,占所有32种杂草的56.25%.这些杂草主要隶属于禾本科、蓼科、毛茛科、报春花科、莎草科、菊科和雨久花科.田埂附近漂浮的杂草种类及种子数量均高于田中间;各类杂草种子的漂浮能力不一,其中菵草(Beckmannia syzigachne)、泽珍珠菜(Lysimachia candida)、茴茴蒜(Ranunculus chinensis)、齿果酸模(Rumex dentatus)、蛇床(Cnidium monnieri)、鳢肠(Eclipta prostrata)和看麦娘(Alopecurus aequalis)等在田间水面漂浮能力较强.漂浮期间杂草种子除多集中于田埂附近,也附着于稻稞周围,并有互相结联的趋势.从整体上看,杂草种子漂浮2天后骤降,8天后基本全部沉降.显然,稻田生境的杂草种子大多可以漂浮于水面传播扩散.因此在灌水早期采取过滤或清除水上漂浮杂草种子可以减少杂草种子的输入和加速杂草种子从田间输出,减少杂草发生基数.     

Biological properties of bacteria of the species Shigella flexneri

Some biological properties of S. flexneri have been studied. The strains of this bacterial species have been shown to produce DNAase in 98.8 +/- 0.77% of cases and RNAase in 97.4 +/- 1.5% of cases. The capacity for the positive reaction with Congo red as early as after 24-hour incubation in the thermostat has proved to be characteristic of S. flexneri (91.1 +/- 3.6%). If stored at 4 degrees C in semiliquid agar, S. flexneri cultures have been found to retain their capacity for producing the above-mentioned enzymes as long as 10-13 years. All S. flexneri serovars under study, with the exception of serovar 6, have shown high activity in the manifestation of their properties.     

N-acylethanolamines in seeds of selected legumes

Seven molecular species of N-acylethanolamines were quantified in seeds from selected members of the legume family. Total concentrations for the 14 taxa studied ranged over approximately three orders of magnitude with no consistent overall relationship to phylogeny. Elevated concentrations observed in some species make them good candidates for natural sources of these compounds which are of increasing therapeutic interest in the modulation of the mammalian endocannabinoid system.     

Two types of ventilated porometers compared on broadleaf and coniferous species

Two ventilated porometers (diffusion and steady-state) were compared on four broadleaf and five coniferous species. The diffusion porometer gave consistently lower conductance values for both types of species, reflecting a direct stomatal response to low chamber humidity. At high conductance values, the porometers produced a linear and nearly equal response, but the diffusion porometer was less sensitive at low conductance values. This was due to lower air flow (20% of the velocity in the steady-state porometer) and water vapor sorption (by its acrylic plastic chamber). The broadleaf species had less variation (R² = 0.81) than did the coniferous species (R² = 0.61), but, with the latter, there was better correspondence between the two porometers, possibly due to sampling technique. Conductance values were clustered by species.     

The effect of temperature on viability of imbibed weed seeds

Imbibed seed of 10 common arable weeds were placed in trays in initially moist soil and, after imbibing for 2h, heated in ovens/incubators set to 31^oC, 42^oC, 56^oC, 75^oC or 100^oC for 0.5, 1, 2, 4, 8 or 16 days or at 102^oC, 155^oC, 204^oC or 262^oC for 0.5, 1, 2, 5, 7.5 or 10 min. After heating, seeds were incubated for 28 days at 10/20^oC or 20/30^oC on a 12 h dark/light regime, depending on species, and germination recorded. At the lower temperatures, germination of all species was prevented by temperatures of 75^oC or higher for periods of 0.5 days or more. Germination was lower after treatment at 56^oC than at 31^oC or 42^oC for all species except Rumex obtusifolius. The maximum temperature required to prevent germination varied among species and was of greater importance than the duration of heating. Germination was variable with duration of heating. At the higher temperatures, there was very little germination of any species after heating at 204^oC for 7.5 min or 262^oC for 5 min or more. Seeds were greatly buffered from the air temperature by 3 mm of soil, throughout the shorter duration of heating. The average temperature of the soil, over the 10 min heating required to prevent over 90% germination, varied among species and ranged from 48^oC for Avena fatua to 65^oC for R. obtusifolius. This work implies that composting systems maintained at 65^oC are unlikely to provide an efficient method of weed control. Recommendations for improvement of the laboratory technique are suggested.     

Drought tolerance of selected Eragrostis species correlates with leaf tensile properties

BACKGROUND AND AIMS: Previous studies on grass leaf tensile properties (behaviour during mechanical stress) have focused on agricultural applications such as resistance to trampling and palatability; no investigations have directly addressed mechanical properties during water stress, and hence these are the subject of this study. METHODS: Critical (lethal) relative water contents were determined for three species of grass in the genus Eragrostis varying in their tolerance to drought. Measurements were taken for leaf tensile strength, elastic modulus, toughness and failure load under different conditions of hydration, and light microscopy and histochemical analyses were undertaken. KEY RESULTS: Leaf tensile strength of fully hydrated leaves for the drought-intolerant E. capensis, the moderately drought-tolerant E. tef and the drought-tolerant E. curvula correlated well with drought tolerance (critical relative water content). Eragrostis curvula had higher tensile strength values than E. tef, which in turn had higher values than E. capensis. Measurements on the drought-tolerant grass E. curvula when fully hydrated and when dried to below its turgor loss point showed that tensile strength, toughness and the elastic modulus all increased under conditions of turgor loss, while the failure load remained unchanged. Additional tests of 100 mm segments along the lamina of E. curvula showed that tensile strength, toughness and the elastic modulus all decreased with distance from the base of the lamina, while again the failure load was unaffected. This decrease in mechanical parameters correlated with a reduction in the size of the vascular bundles and the amount of lignification, as viewed in lamina cross-sections. CONCLUSIONS: The results confirm that leaf mechanical properties are affected by both water status and position along the lamina, and suggest a positive correlation between leaf internal architecture, tensile strength, cell wall chemistry and tolerance to dehydration for grasses.     

Lamina-specific localization of silicon accumulation in two broadleaf tree species

Journal of Plant Research - Silicon (Si) accumulation differs greatly among plant species, as revealed by an increasing number of studies reporting whole-leaf Si concentration for a wide range of...     

Predation of annual grass weed seeds in arable field margins

Seeds of three species of annual grass weeds (Alopecurus myosuroides, Avena fatua and Bromus sterilis) were placed in field margins around arable fields in a randomised block split-plot design experiment. The field margin vegetation was either sown or naturally regenerated and either cut or uncut. The seeds were either placed in cages designed to exclude small mammals and birds or were uncaged. The proportion of seeds removed was monitored on 10 occasions and mean seed loss was analysed. In general, a greater proportion of weed seeds was removed from uncaged trays in uncut swards, suggesting predation by small mammals, which inhabit tall grass. This effect was mainly due to removal of seeds of the two large-seeded species (A. fatua and B. sterilis), with A. fatua being especially favoured. It is therefore likely that small mammals play a role in the population dynamics of major crop weeds by feeding on their seeds in field margins, especially when these are dense and uncut.