摘要:

SummaryThe outcome of crop‐weed competition should be predicted as early as possible in order to allow time for weed control measures. Maize grain yield losses caused by interference fromAmaranthus retroflexusL. (redroot pigweed) were determined in 1991 and 1992. The performance of three empirical models of crop‐weed competition were evaluated. Damage functions were calculated based on the weed density or relative leaf area of the weed. In the yield loss‐weed density model, values ofI(percentage yield loss at low weed density) were relatively stable for similar emergence dates ofA. retroflexusacross years and locations. Estimated maximum yield loss (A) was more variable between locations and may reflect environmental variation and its effect on crop‐weed competition, at least in 1991. The two‐parameter yield loss‐relative leaf area model, based onm(maximum yield loss caused by weeds) andq(the relative damage coefficient) gave a better fit than the single‐parameter version of the model (which includes onlyq). In both relative leaf area models, the values ofqvaried between years and locations. Attempts to stabilize the value ofqby using the relative growth rate of the leaves of the crop and weed were successful; however, the practical application of such relative leaf area models may still be limited owing to the lack of a method to estimate leaf area index quickly a

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01783.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA total of 74 independently run bioassays with soil incorporated metsulfuron‐methyl from 12 different laboratories was analysed by a logistic dose‐response curve to assess the precision of regression parameters and relate ED50to soil properties. The potency in terms of ED50of metsulfuron‐methyl inBrassica rapaL., which was used by all laboratories, varied between 0.05 and 3.9 g a.i. ha‐1. ED50was negatively correlated with pH and positively correlated with organic matter. The majority of laboratories had ED50within the interval 0.1‐1.0 g a.i. ha‐1. At one laboratory using three test species, the most sensitive species wasBeta vulgarisL. followed byBrassica rapaL. andLepidium sativumL. The coefficients of variation were smallest for the ED50and ED90response levels and largest for the ED10. The slope of the response curves had considerably lower coefficients of variation than the EDs. The results are discussed in relation to a previous collaborative bioassay study. Finally it is suggested that standardization of bioassays with herbicides could be achieved in the same way as standardization of chemic

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01784.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

RésuméL'étude écologique des mauvaises herbes des cultures de la région du Saïs (Maroc Central) est abordée par l'appréciation du pouvoir discriminant d'un ensemble de 26 descripteurs du milieu, en vue de la mise en évidence des descripteurs les plus “efficaces” vis‐à‐vis de la distribution des mauvaises herbes dans les cultures de cette région. Contrairement aux résultats enregistrés dans des études similaires conduites dans d'autres régions du Maroc, les résultats présentés ici, montrent la prépondérance des variables agronomiques (culture en place, travail du sol préparatoire au semis, date de semis, nature du précédent cultural) dans la distribution des mauvaises herbes. Ces résultats témoignent de la forte pression culturale qui s'exerce sur le milieu, en raison de l'intensification de l'agriculture pratiquée dans la région du Saïs. On examine ensuite la réaction des mauvaises herbes aux variations de quatre descripteurs agronomiques (culture en place, travail du sol, mode de désherbage et mode de fertilisation), susceptibles de faire ressortir l'influence de la culture en place et celle du type d'agriculture pratiqué, sur la distribution des mauvaises herbes. L'exploitation des quatre séries de profils écologiques conduit à la mise en évidence de quatre principaux groupes d'espèces liées, respectivement, aux cultures annuelles, aux cultures pérennes, aux jachères et aux milieux incultes de la région. Les différents groupes sont commentés en insistant plus parti‐culièrement sur le premier, étant donné la prépondéranc

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01785.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThree years of experiments with spring barley showed significant differences in weed suppression ability among varieties. Weed dry matter in the most suppressive variety, Ida, was 48% lower than the mean weed dry matter of all varieties, whereas it was 31% higher in the least suppressive variety, Grit. Ranking varietal responses to weed competition in terms of grain yield loss corresponded well to ranking weed dry matter produced in crop weed mixtures. There was no correspondence between the varietal grain yields in pure stands and their competitiveness, suggesting that breeding to optimize both yielding and competitive ability may be possible. Non‐linear regression models were fitted to canopy height and light interception data for each variety in all three years. The canopy height model provided a precise description of development and maximum canopy height of the varieties. A light interception model was developed to describe the light interception profiles of the varieties. A study of the estimated parameters showed significant correlation between weed dry matter, rate of canopy height development and the light interception profile. However, when estimates were standardized to eliminate the effect of year, there was no correlation between weed dry matter and the light interception profile parameters, indicating that varietal competitiveness was not related to this trait. A multiple regression analysis showed that a model comprising parameters of maximum canopy height, maximum light interception and temporal displacement of light interception provided a good description of the varietal difference

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01786.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryGlyphosate was applied at four rates under greenhouse conditions toAvena fatuaL. plants at four stages of seed development. Application at anthesis completely prevented the formation of viable seeds. Application five days after anthesis (DAA) of the terminal floret of the panicle significantly reduced seed production at all herbi‐cide rates used, and at 1.76 kg a.i. ha‐1no viable seeds were produced. When applied 10 DAA, only the highest rate of glyphosate resulted in substantial reduction in number of primary seeds, but seed viability suffered at all herbicide levels. Glyphosate applied 15 DAA still produced a significant decrease in primary and secondary seed production and biomass. Both the viability and the germination rate of seeds from treated plants were significantly affected. When the herbicide was applied to plants 5 DAA, no viable seeds were produced by plants surviving the highest rate, and all rates significantly reduced germination. Glyphosate applied 10 DAA significantly suppressed germination, with 1.76 kg a.i. ha‐1being the most effective rate. When applied to plants 15 DAA, only the highest rate of glyphosate significantly affected the overall germination of both primary and secondary seeds, but the normal imposition of dormancy was partially blocked in seeds from plants treated with 0.44 and 0.88 kg a.i. ha‐1. These findings are relevant to chemical summerfallow and crop desiccation pr

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01787.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

RésuméLa disponibilité et la dégradation de l'isoproturon dans le sol au cours du temps ont étéévaluées pendant 140 jours dans une expérience de laboratoire en conditions contrôlées à l'aide de la molécule marquée au14C sur le cycle. L'état de dégradation de la matière active a été suivi: après 65 jours, l'isoproturon extractible ne représente plus qu'une très faible part (0,6%). Le monodéméthyl‐isoproturon est mesurable dès le 15ème jour (2,6%). La mesure du14CO2 provenant de la dégradation du cycle benzénique et dégagé au cours du temps donne un total de 13,6% d'isoproturon minéralisés durant l'incubation. Parallèlement, les quantités de résidus extractibles (par l'eau puis par le méthanol) ou subsistant dans le sol quelle que soit leur forme (dosage par combustion) ont été successivement mesurées. Après 140 jours, 72% de la radioactivité apportée se trouve sous forme non extractible dans le sol. La demi‐vie de la matière active

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01788.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryCompetition between winter‐sown wheat andViola arvensisMurray orPapaver rhoeasL. was studied in two experiments in two successive years. The effects of varying crop and weed density were modelled in terms of weed biomass over time, weed seed production and crop yield. Biomass model parameters, representing maximum weed biomass and intra‐ and interspecific competition, were obtained for different assessment dates, enabling biomass levels to be predicted during the two growing seasons. Weed biomass declined, and its maximum level was reached earlier, with increasing crop density. Intraspecific competition was higher in the absence than in the presence of crop, increasing with time and with weed density. Halving the wheat population increased June biomass ofV. arvensisby 74% and ofP. rhoeasby 63%. Crop yield losses with increasing weed density were greater with low than with medium and high crop populations.P. rhoeaswas significantly more competitive thanV. arvensisin both years. Weed biomass in 1989 responded more to reductions in crop density following the milder winter of 1988/89 than in the previous year; however crop yields were less affected in 1989 due to summer drought, restricting late weed growth and competition. Weed seed production was related to weed biomass; the progressive lowering of crop density increased seed production, and both species were very prolific in the absence of crop. By combining models, seed production could be derived for a given competitive effect on the crop. Threshold weed populations, based on low weed levels that are not economic to control, could then be equated with the accompanying weed seed product

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01789.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryBenfuresate (2‐3‐dihydro‐3,3‐dimethylbenzofu‐ran‐5‐yl ethanesulfonate) is a selective herbicide for the control of purple nutsedge in cotton. Under outdoor conditions, purple nutsedge was sensitive to benfuresate incorporated in soil up to eight days after initiation of shoot sprouting from the tuber. Older seedlings recovered from the damage. During the period of susceptibility to benfuresate, young shoots more sensitive than the roots. Under controlled environmental conditions, benfuresate applied directly to apical buds developing from the tuber caused severe damage to the treated bud and induced abrupt development of axillary buds. Negligible amounts of the applied herbicide were translocated from the treated part to the other buds and roots. Application of the herbicide to fully developed leaves had no effect, probably because of its rapid metabolism and low basipetal mobility. Its relatively high volatility may also contribute to its low foliar post‐emergence activity. Tubers also absorbed herbicide vapours. Root uptake of14C‐benfuresate resulted in a rapid accumulation of14C in the shoot, which had no effect on the purple nutsedge plant, regardless of concentration. The herbicide is rapidly converted, mainly to a non‐phytotoxic polar product. These results may explain the high sensitivity of the weed to benfuresate at early growth stages, and the lack of sensitivi

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01790.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryIt is widely assumed that organisms that evolve resistance to a triazine suffer from a fitness deficit in the absence of that herbicide. Arguments for this view are examined, and previously published evidence is discussed. A simple model was developed to examine the genetics of resistance in triazine‐resistant plants, based on the assumption that a founder effect is in operation. The model examined the hypothesis that the extent to which plants in the sprayed population are related will increase rapidly under continual selection, even when there is a significant input of genes from non‐selected populations. The possible consequences of the above hypothesis on the validity of competition experiments are discus

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01791.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

RésuméLa dégradation chimique du chlorimuron‐éthyle et du chlorimuron a étéétudiée à 30°C au contact de quatre solides minéraux secs (kaolin, silice, bentonite H+, montmorillonite K10) et d'acides humiques solides. Dans tous les cas, on observe la coupure de la fonction sulfonylurée de la molécule conformément au processus précédemment observé en solution aqueuse acide. La cyclisation en saccharine du phényl‐sulfonamide formé n'est observée qu'au contact des minéraux peu acides (kaolin, silice) tandis que la pyrimidamine. autre produit d'hydrolyse, présente une certaine affinité pour les solides minéraux plus acides (bentonite H+, montmorillonite

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb01792.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY