摘要:

Summary:Two naturally‐established pure stands ofPortulaca oleraceaL. were used to study the effects of five disturbance schedules (early, midseason, late, repeated and no disturbance) on the development of purslane populations. In one stand disturbance was by rototilling and in the second stand by hoeing. In most disturbed plots, the re‐established stands had densities which were not significantly less than those of the control plots. These stands were composed of plants established by seed germination (seed plants) and by regeneration of roots on severed stems (stem plants) or shoots on root and stem bases (root plants). The composition of these stands depended on the type of disturbance. Undisturbed stands were composed predominantly of seed plants. Disturbed stands had fewer than 55% seed plants. Hoeing resulted in a greater proportion of stem plants and a lower proportion of root plants than rototilling. All disturbances resulted in decreased dry matter yields per unit area. The maximum yields for the controls in the two stands were similar, regardless of differences in density, mean dry weight, size class distribution and time of establishment. Early disturbance resulted in significant decreases in seed capsule production while disturbance late in the season had minimal effects on seed production. The implications for control of purslane in crops are discus

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00096.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Summary:Terbutryn (2‐ethylamino‐4‐(tert‐butylamino)‐6‐methylthio‐s‐triazine) was applied in June 1978, to two farm ponds (A and C) near Winnipeg. Canada, to give 100 μg/l water concentrations. The persistence of the herbicide and its degradation products was monitored over a 61‐week period following application. The half‐life of terbutryn m the water column ranged from 3 weeks in Pond C, which contained heavy growths of cattails (Typhasp.) and duckweed (Lemnasp.), to 30 days in Pond A. which was free from aquatic macrophytes, Terbutryn residues m sediment reached a maximum of 1.4 μg/g (dry wt) in Pond A and 0.5 μg/g in C. Maximum concentrations of N‐deethylated terbutryn (2amino‐4‐(tert‐butylamino)‐6‐methylthio‐s‐tria‐zine)(DET) were 14.4 μg/l in Pond A water after 61 weeks and 0.14 μg/g in Pond C sediment after 30 weeks. The maximum concentration of hydroxy‐terbutryn (2‐hydroxy‐4‐ethyl‐amino‐6‐(tert‐butylamino)‐s‐triazine) (HT) observed in pond water was 6.4 μg/l in Pond C after 7 weeks. HT was not detected in sediment (<0.05 μg/g) during the study. After 61 weeks, about 50% of the terbutryn that was added could still be accounted for in Pond A and 35% in Pond C. Terbutryn. DET and HT represented an estimated 71, 28 and 1%, respectively, of total terbutryn remaining in Pond A and 65, 29 and 6%, respectively, of that remaining in Pond C, 61 weeks after application, Terbutryn residues inTypharanged from 0.3 μg/g (dry wt) in the shoot to 3.3 μg/g in the roots. After 12 weeks, terbutryn residues in plants (Pond C)

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00097.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Summary:The response of etiolated cucumber (Cucumis sativusL. cv. National Pickling) cotyledons to fluridone was investigated in terms of inhibition of photosynthetic pigments, and utility as a bioassay. At a light intensity of 35 W/m2, chlorophyll levels were higher in the controls, than at either 12.9 W/m2, or 75 W/m2. Fluridone inhibition was also more pronounced at that intensity. Significant differences between treatments were established as early as 24 h after exposure to light, when at the lowest fluridone concentration of 0.001 μg/ml, chlorophylls and carotenoids were inhibited 25 and 35% respectively. The system's simplicity and sensitivity suggest its use as a bioassay. It is shown that simple monochromatic absorbances of acetone extracts can satisfactorily estimate chlorophylls and carotenoids. Concentrations of fluridone as minute as 10−9moles/ litre are easily delected, and the system could feasibly detect even lower leve

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00098.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Summary:Techniques of high‐volume spraying of weedy plants, have not changed greatly since their introduction in the late 19th century. improvements to the effieiency of the operation have been investigated, and the influence of atomizer type. pressure and formulation on the droplet spectra produced were assessed. The VMD (volume median diameter) decreased log linearly (r2>0.98 with all atomizers tested. whilst the volume of the small‐droplet component (<107 μm) increased linearly (r2) with increasing pressure. A comparison of the droplet spectra produced by three fan and three swirl cone atomizers showed that the fan atomizers gave significantly higher VMD's and lower volumes of small droplets than cone atomizers under comparable operating conditions. The influence of type and concentration of’formulation on the droplet spectra was variable with both the fan and cone atomizers The atomizer and pressure had the greater influence on the droplet spectra. but the effects of formulalion must also be considered if improvements are to be obtained in high‐volume

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00099.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Summary:Rales of linuron and metrihuzin breakdown in soil were studied in four laboratory systems: fresh soil incubated in polyethylene bags; air‐dry soil resetted and incubated in polyethylene bags; complete soil cores; a perfusion apparatus. The apparent order of reaction. estimated using a power rate equation, varied from 0.45 to 2.90 and was not consistent with respect either to the compounds or the incubation methods. It is possible that diffusion controlled processes may be involved in producing this variation. The results of six of the eight experiments could be fitted to the first order rate equation (P= 0.01). When the first order model was statistically valid, half‐life times were within 50% of the time for 50% disappearance calculated wiih the power rate expression but there were differences up to five‐fold in the times for 90% disappearance, calculated by the two methods. It is suggested that decomposition experiments giving orders of reaction greater than I require verification in more than one experimental

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00100.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Résumé:L'application durant 3 jours de doses létales d'atrazine, de MCPA, de dichlobénil, d'alachlore et de paraquat par voie racinaire et/ou par voie foliaire a permis de démontrer que la phytotoxicité des herbicides n'est pas nécessairement liée à une diminution d'ATP. L'atrazine administrée par voie racinaire provoque dans les feuilles une diminution de 57–88% de glucose et de fructose; de 70–97% de saccharose. Dans les ratines les pertes sont respectivement de 14–60% et 33–96%.L'atrazine par voie foliaire accentue davantage les pertes en glucides. Après traitement au MCPA, le glucose des feuilles croit de 250 a 890%; le fructose de 240 à 630%; le saccharose de 110 a 170%. Dans les racines, le glucose augmente de 150 à 420%; le fructose de 160 à 450% tandis que le saccharose diminue de 20–39%. L'alachlore diminue les sucres réducteurs des feuilles et les augmente dans les racines. Le diehlobénil fait baisser les glucides des feuilles les deux premiers jours et les fait croitre le troisième jour. Les auteurs proposent quelques formules permettant de caractériser la nature des herbicides d'après les rapports des teneu

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00101.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Summary:The effects of reduced‐cultivation Systems on weeds in cereals are reviewed. Increasing dependence of these Systems upon Chemical weed control together with changes in the soil physical environment are expected to modify existing weed floras. Annual‐grass weeds are likely to remain a problem with the use of minimal cultivations, particularly when early drilling is practised, while hitherto unimportant species may become more prevalent, e.g.Bromusspp. Furthermore, reduced cultivations may encourage the establishment of wind‐disseminated species. However, annual dicotyledonous species characteristic of arable land are expected to continue to de

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1981.tb00102.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY