摘要:

Summary:The dynamics of sprout emergence and rhizome populations ofSorghum halepense(L.) Pers. were followed in two field experiments. In addition, the herbicide dalapon was applied at various stages during rhizome development and the degree of control was evaluated. Rhizome biomass oscillated during the growth cycle, whereas the number of rhizome sprouts increased asymptotically until mid‐summer. Observed values were compared against those predicted from a thermal calendar model. The dynamics of the rhizome population was predicted accurately in both experiments, but only in one of them was the prediction of the sprout emergence satisfactory. The degree of control differed markedly between herbicide applications at various intervals during population development. Best results were obtained from applications when rhizome biomass was at a minimum. The time of minimum biomass was predicted by a thermal calendar model. The advantages of using the thermal calendar model to determine the time of herbicide application, and the possible influence of the distribution of the rhizome population in the soil profile on the predictions of the model, are discusse

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01699.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:Propagules ofCarduus acanthoidesare pappus‐bearing achenes. Flower production, potential achene output, seedbank and wind dispersal of propagules ofCarduus acanthoideswere analysed. Flower production was measured in four cohorts in 1986–87 and three cohorts the following reproductive season, when the potential achene output was estimated. Achene output was very large in all cases but early cohorts had a longer fruiting period and produced more flowers and fruits per plant. The seedbank was small and results from autumn and spring samples showed a low seed persistence in soil. In laboratory experiments greater landing and dispersion distances were reached at higher wind speeds, the major wind effect being that on the movement of propagules after landing. Barriers simulating vegetation almost completely stopped this movement after landing and the final distances reached were almost the same at all wind speeds. In field experiments achenes recovered in seed traps and seedling emergence show the same pattern of distribution around the parent plant. The implication of these results for the behaviour of thistle populations are discus

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01700.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:The effect of degree of water stress inAvena sativaon diclofop‐methyl efficacy was assessed. Within 24 h of applying stress by adding mannitol to the root medium (0 to 12.5%), the rate of leaf extension of the youngest leaves (leaves 3 and 4) decreased with increasing mannitol concentration. Without water stress, application of diclofop‐methyl had little effect on extension rate of leaves 3 and 4 during the first 4 days after spraying. Subsequently, it caused a significant decrease in the extension rate of leaf 4 with more pronounced effects on later leaves. Diclofop‐methyl had little effect on leaf extension rate of plants given mannitol. Shoot dry weight at harvest for unsprayed plants decreased with increased mannitol concentration and for sprayed plants it was greater without mannitol than with mannitol (all levels). However, at mannitol concentrations greater than 4%, shoot dry weight for sprayed and unsprayed plants was not significantly different. Sprayed plants exposed to 2–8.5% mannitol produced seed heads but those at zero mannitol did not. When the root medium of all treatments was flushed of mannitol one week after spraying, then main‐tained without mannitol, shoot dry weight at harvest for unsprayed plants decreased slightly with increased mannitol concentration applied initially. However, shoot dry weight for sprayed plants increased with increased mannitol concentration. Without mannitol two weeks after spraying, chlorophyll concentrations of leaves 3 and 4 were greater and water saturation deficit (WSD) values were lower for unsprayed plants than sprayed plants but there were no differences at 6.2% mannitol. It is proposed that tolerance to diclofop‐methyl byA. sativaas a result of water stress, is primarily due to a decreased rate of leaf expansion resulting in lower demand for membrane synthesis and less strain on membranes damaged by th

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01701.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:Populations of the winter annualEmex australiswere established by initiating irrigation at monthly intervals, beginning in mid‐summer. Natural seedling densities varied from 100 m−2when irrigation was begun during late January to almost 700 m−2when it began at the end of March. Densities were increased by sowing non‐dormant seeds, but most sown seeds became dormant when introduced before autumn. Plants which emerged after the earliest irrigation grew most rapidly. Those originating from the latest irrigation grew most slowly, in association with vigorous growth of other annual species. Because it minimizes interspecific competition, early commencement of irrigation, coupled with sowings of nondormant seeds is the best method for establishingE. australisduring summer. Maintenance of such populations may enhance the persistence of non‐aestivating biological control agents and/or boost their numbers prior to the onset of mass germination. This approach could also prove useful for other winter annuals which are targeted for biologica

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01702.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Zasammenfassung:Chenopodium albumL. gehört zu den Un‐krautarten, bei denen sich Resistenz gegen Herbizide, vor allem Triazine, häufiger entwic‐kelt. Um eine frühzeitige Erkennung herbi‐zidresistenter Populationen zu ermöglichen, wurden die Beziehungen zwischen den Sippen der polymorphen Art und ihrer Reaktion auf Herbizide ermittelt. Als grundlegende Vor‐aussetzung mußte die bestehende infraspezi fische Systematik vonCh. albumL. ssp.albumvar.album (sensuAellen, 1960) kritisch unter‐sucht und eine neue Gliederung auf Grund der Ergebnisse mehrjähriger Kulturversuche vorge‐nommen werden. Die genetische Stabilität mehrerer Merkmale wurde überprüft und die Infloreszenzformen als grundlegendes Merkmal verwendet. Bei Tests auf die Herbizidemp‐findlichkeit der Sippen ergab sich eine größere Toleranz bzw. Resistenz gegen Triazine bei dem Taxon mit trugdoldig‐scheinrispigen In‐floreszenzen. Die seit 1985 in der DDR nachge‐wiesenen triazinresistenten Biotypen vonCh. albumaus landwirtschaftlichen Kulturen gehörten ebenfalls zu dieser Sippe. Die mitCh. albumoft gemeinsam vorkommende und sehr ähnliche ArtCh. suecicumJ. Murr war hochempfindlich gegen Triazine. Versuche zur Kreuzresistenz ergaben eine allgemeine Resistenz gegen Triazine und Chloridazon, während Methazol, Pyridate, Bentazon, Meto‐bromuron und Bromuron voll wirksam waren. Die Wirkung von Metribuzin erschien abge‐schwächt. Ebenso reduzierte die Kombination von Bromuron und Fenuron mit Triazinen den Bekampfungserfolg. Triazinresistente Biotypen vonCh. albumreagierten langsamur auf das insgesamt gut wirksa

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01703.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:The growth and competitiveness of 12 annual weed species were studied in crops of winter wheat, in which weeds were sown to give a wide range of plant densities. Weed growth patterns were identified; early species which senesced in mid‐summer were less competitive than those with a growth pattern similar to that of the crop. Most species had little effect on crop yield in 1987, and this was attributed to a high crop den sity. Crop yield‐weed density relationships for all species in 1988 and forGalium aparinein 1987 were well described by a rectangular hyperbola. Species were listed in the following competitive order based on the percentage yield loss per weed m−2:Avena fatua>Matricaria perforata>Galium aparine>Myosotis arvenis>Poa trivialis>Alopecurus myosuroides>Stellaria media>Papaver rhoeas>Lamiumpur‐pureum>Veronica persica>Veronica hederi‐folia>Viola arvensis. Prediction of yield loss is discussed. The assumptions inherent in using Crop Equivalents (based on relative weights of weed and crop plants), are challenged; with intense competition, weed biomass at harvest failed to replace lost crop biomass, and harvest index was reduced. It is concluded that a competi tive index, derived from yield density relation ships, and expressed as the percentage yield loss per weed m−2, is more likely to reflect the com petitive ability of a species than an index obtained from plant weights in the g

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01704.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Summary:In a soil application,Torilis arvensiswas nearly as susceptible asLolium rigidumto simazine but was 18‐fold more tolerant to diuron. Treat ment with diuron inhibited photosynthesis inL. rigidumbut had only a limited effect inT. arvensisalthough chloroplasts isolated from both species displayed similar susceptibility.14C‐diuron degradation in plants was limited, with the formation of conjugates of mono‐methyl‐diuron inT. arvensisandN‐dealkylated derivatives of diuron inL. rigidum.14C‐diuron entered the roots and was translocated throughout the leaves ofL. rigidumbut was restricted to stems, leaf petioles and leaf veins ofT. arvensis. This difference in transport pattern is proposed to explain the tolerance ofT. arvens

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01705.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01706.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1990.tb01707.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY