摘要:

SummaryDifference equation models incorporating density dependence are considered in the context of the description of the dynamics of weed populations over discrete generations. Their applicability is assessed in relation to modelling yield loss, two species and three species interactions and the influence of density independent control practices. Analysis indicates that whilst plant populations may show simple dynamical properties around equilibrium levels, convergent oscillations to equilibrium may result from the application of control measures. Such models are argued to have potential as robust qualitative predictors of weed species abundance.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00907.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryAmmonium‐containing fertilizers such as granular limestone ammonium nitrate (LAN) and liquid ammonium nitrate (AN) proved to be most effective in stimulating germination and emergence of wild oat in sandy and loamy soil. In pot experiments, rates as low as 25 kg N ha−1, significantly increased seedling emergence of wild oat. In sandy soil percentage emergence increased with increasing levels of LAN‐fertilizer up to 125 kg N ha−1which gave 76·1 % emergence after 60 days. In control pots where no nitrogen was applied, only 21·6% of seeds planted emerged after 60 days, In loamy soil, as for AN in both soil types, high levels of LAN initially delayed seedling emergence. This negative effect disappeared approximately 15 days after seeding, resulting in no significant difference in emergence of wild oat where 25 to 125 kg N ha−1was applied as LAN or AN. All these rates, however, increased seedling emergence between 25 and 35% compared to the no‐nitrogen treatments. Since the same rate of ammonia gas is not equally effective in breaking dormancy of semi‐ and deeply dormant wild oat seed, results of these experiments are not necessarily applicable to wild oat seeds differing in

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00908.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ZusammenfassungDie Zusammensetzung der Samenspeicher in Kulturfeldern im Mittelmeerraum hängt von unterschiedlichen Faktoren ab. Zum einen ist es die Bodenart, die aufgrund ihrer Struktur auf den Samenvorrat im Boden einwirkt. Weitaus grösser sind aber die Auswirkungen der anthropogenen Beeinflussung wie mechanische Bodenbearbeilung und chemische Behandlungen. Damit zeigen sich für mediterrane Kulturböden die gleichen Einflüsse auf den Samenspeicher wie im mittel‐europäischen

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00909.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryProduction of viable seeds occurred in immature capitula ofSilybum marianumfollowing simulated slashing and mowing. In the slashing treatment, capitula with 20 cm or less of stem attached produced viable seeds if cut off when at least half the florets were open, the proportion of viable seeds ranging from 0·3% in capitula at midanthesis to 12% in those at the end of anthesis. Following mowing, viable seeds were produced in full‐sized buds which were close to anthesis and in capitula at any stage of anthesis at the time of plant cutting, the proportion increasing from 0·1% in capitula at the start of anthesis to 30% in those at the end. Within a capitulum, anthesis usually lasted five days in irrigated plants. Ripe seeds were released about 17 days later. Seed production averaged 190 seeds for the primary capitulum and 114 in others. In a flowering season starting in early November and lasting about two months, individual plants had the potential to produce an average of 55 capitula, representing an output of 6350 seeds per plant, of which 94% were viable. In view of the prolonged flowering season and the large seed output ofS. marianum, it is argued that the restricted period of oviposition by the weevilRhinocyllus conicusand the low density of larvae per capitulum might limit its impact as a biological control agent for this weed in Austra

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00910.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryTwenty inbred maize lines, raised in a growth chamber, were treated with 0 or 1 ng g−1of chlorsulfuron which caused a variable reduction in root‐length. In a second experiment, all crosses (reciprocals included) among two tolerant lines (T: Va85 and Mes44) and two susceptible lines (S: B73 and B79) were raised in a growth chamber together with the parental lines and exposed to 0,0×5 or 1 ng g−1, The interaction of reciprocal effects x rates was not significant for all traits, The T × S hybrids showed an intermediate response between the T × T and S × S responses for root‐length and dry weight. Interaction (hybridsvs.parental lines) × rates was not significant for all traits. These results indicate that susceptibility to chlorsulfuron is not controlled by extra‐nuclear factors and that additive gene actions prevail. Four crosses (one T × T, two T × S and one S × S) were further investigated at nine rates from 0 to 1 ng g−1. The responses confirmed the intermediate behaviour of T×S hybrids, resulting in a GR20of 0×07, 0×55 and 0×94 ng g−1for S × S, T × S and T × T, respectively. In a third experiment, the four crosses previously considered were grown in the field with parental lines and treated at five rates from 0 to 1·12 g a.i. ha−1. Effects on shoot height and dry weight were consistent with root effects foun

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00911.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryA two‐species model was used to summarize results of four experiments with two component mixtures of barley (Hordeum vulgareL.), peas (Pisum sativumL.),Chenopodium albumL. andSinapis albaL. grown in pots in greenhouses. The results, covering a wide range of plant densities both in mixtures and pure stands, showed that the model was not always able to describe the relationship between the yield of a species and the densities of itself and its companion species. The deviations from the model were in all instances greatest for the least competitive species. The model that quantifies competition and niche differentiation appeared to be too general because competition between species was not independent of the wide plant density ranges used here. The results are discussed in relation to possible improvements of the model and an analogy between the principles of assessing crop weed competition and the assessment of the relative potency of herbicides in bioassay studies is put forwar

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00912.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryAdsorption and degradation rates of chlorsulfuron and metsulfuron‐methyl were measured in soil taken from depths of 0–20, 20–40 and 40–60 cm at eight sites. Adsorption of both herbicides was negatively correlated with soil pH, and positively correlated with soil organic matter content. When two soils with very high organic matter were excluded from the calculations, the correlations with organic matter content were no longer statistically significant but those with soil pH were affected only slightly. Degradation rates of both herbicides generally decreased with increasing depth in the soil and were positively correlated with microbial biomass and negatively correlated with soil pH. The possible significance of the results to persistence of the herbicides in the field is di

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00913.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryThe performance of fluazifop‐butyl againstElymus repens(L.) Gould was significantly influenced by the environmental conditions in which the plants had grown prior to treatment as follows: soil moisture deficit (greatest reduction of herbicide performance)>cool temperatures>low light intensity. The level of control under conditions in which none of these factors was reduced (so‐called ‘standard’ conditions) was similar to that observed for‘low light’regime plants. Significant effects of environment on spray retention, foliar uptake and amounts of herbicide translocated to the roots and rhizomes were observed. The lowest rates of herbicide uptake were found with plants grown under cool conditions, the greatest amount of basipetal herbicide translocation being associated with low light intensities. Rates of herbicide de‐esterification were much lower in plants grown under low light intensities, cool temperatures, or soil moisture deficits than in those plants grown under the ‘standard’ conditions. This result was confirmed by studies of herbicide deesterification using cell‐fr

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00914.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryInfluence of 2,4‐D on toxicity of diclofop‐methyl toAvena sativa(cv. Selma) andArena fatua at2·5 leaf stage has been evaluated under controlled conditions. Effects of 2,4‐D on the fate of diclofop‐methyl in cultivated oat have also been studied. Mixture with 2,4‐D reduced the toxicity of diclofop‐methyl to both species. When applied immediately after diclofop‐methyl treatment, 2,4‐D still reduced herbicide toxicity to wild oat. This reduction was smaller in cultivated oat. and was only observed at higher phytotoxicity. No interaction was observed when a 10‐day period separated the two applications. In mixture, 2,4‐D enhanced diclofop‐methyl penetration and diclofop acid conjugation in cultivated oat, and it slightly increased conjugation when applied separately. None of these effects clearly explain the reduction of diclofop‐methyl toxicity by 2, 4‐D in cultivated oat. Other processes are possibly involved and could be connected with the site of

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00915.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY