摘要:

The effects of intraspecific competition on the growth, development and resource‐allocation ofPanicum repenswas studied under greenhouse conditions. Evidence of severe intraspecific competition and adjustments to plant growth as a response to stress caused by competition, was seen from fairly early stages. An eight‐fold difference in initial plant density per pot, did not produce a significant difference in the dry weight accumulation between densities by 16‐weeks. Increase in plant density resulted in a very significant decrease in dry weight accumulation on a per plant basis, as expected. In general, dry weight partitioning into rhizomes and inflorescences increased with time at all densities, with a concomitant decrease in the percent dry weight partitioned into roots and shoots. Under low density conditions more dry weight was partitioned into inflorescences than at higher densities, indicating a shift in resource‐allocation with changing density. However, the expected shift of dry weight partitioning towards rhizome production at the highest densities was not evident. Allocation of resources to rhizomes did not vary with density. Even the lowest density plants which were not subjected to competitive stress, and the plants at the highest density, all allocated about one fifth of their dry weights to rhizomes. Plants under the highest density stress showed a very significant reduction in the number of tillers they produced and tiller dry weights, on both per pot and per plant basis. The study provides several insights into the highly adaptive and competitive nature of the grass weed, which contribute greatly to its success as a species.

ISSN:0143-6147    

DOI:10.1080/09670878909371389

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In wheat fields, irrigated with treated sewage water, the performance of six herbicides: bromoxynil/MCPA; bentazon/ dichlorprop; diclofop‐methyl; tralkoxydim; pendimethalin and bromophenoxim; and some their combinations were assessed at two different locations around the city of Riyadh. The common weeds include:Loliumspp.;Phalarisspp.;Avenaspp.;Malvaspp.;Chenopodiumspp. and others. The best weed control treatments were: bentazon/dichlorprop followed by bromoxynil/MCPA for the broad‐leaved, and diclofop‐methyl followed by tralkoxydim for the grassy weeds. The combinations of bromoxynil/MCPA with either pendimethalin or tralkoxydim were far more effective against the broad‐leaved weeds, and significantly improved the wheat growth and yield, compared with the single treatments. However, bromoxynil/MCPA combination with diclofop‐methyl was less effective against the grassy and broad‐leaved weeds than each of them. Bromophenoxim showed an effective control of the whole weeds, with appreciable improvement in the wheat growth and yield.

ISSN:0143-6147    

DOI:10.1080/09670878909371390

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The marked resistance ofSpodopteraspp. to endotoxins ofBacillus thuringiensisincluding the well recognized standards HD‐1–1971 and HD‐1‐S‐1980 has necessitated the search for a new active strain that can be used as a standard reference in the bioassays of these lepidopterous insects. The high activity ofB. thuringiensisvar.entomocidusHD‐635 vs.Spodoptera littoralisand S.exiguawas found to fulfill these requirements. The sporeendotoxin complex of this strain, designated as HD‐635‐S‐1987, is proposed as a reference standard for bioassays againstSpodopteraspp. and is assigned arbitrarily the value of 10,000 iu/mg. Potencies of an active strain, i.e.B. thuringiensisvar.aizawaiHD‐133 and of a low‐active preparation, i.e. HD‐1‐S‐1980 were carried out in reference to the newly proposed standard. Comparative studies revealed the possible reduction of bioassay period to 4 days as time saving and fora priorijudgement on the activity of certain bioinsecticide preparations derived fromB. thuringiensis.

ISSN:0143-6147    

DOI:10.1080/09670878909371391

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0143-6147    

DOI:10.1080/09670878909371392

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Bifenthrin e.c. (15 ml a.i./100 litres water), carbosulfan e.c. (40 ml), cypermethrin e.c. (37.5 ml), deltamethrin + triazophos e.c. (72 ml) and dimethoate e.c. (80 ml) reduced theThrips tabaciLind., population for more than 2 weeks. Thereafter population increased at a similar rate in treated and untreated plots. Deltamethrin + trizophos, cypermethrin and carbosulfan were superior to dimethoate in increasing yield. Bifenthrin and no treatment produced similar yields. The former two insecticides were also superior to the remainder in increasing bulb weight.

ISSN:0143-6147    

DOI:10.1080/09670878909371393

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Up to 10% of yeast can be used to ensure regular and continuous supply of normal test insects for experimentation, but higher yeast levels will have adverse effects on the number of offspring and the developmental period.

ISSN:0143-6147    

DOI:10.1080/09670878909371394

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0143-6147    

DOI:10.1080/09670878909371395

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Commonwealth Institute of Entomology Guide to Insects of Importance to Man: I. Lepidopteraby J. D. Holloway, J. D. Bradley and D. J. Carter. Edited by C. R. Betts. C. A. B. International Institute of Entomology and British Museum (Natural History). 262 pp, 1987, Hardback edition £27.50, Paperback £16.00.

ISSN:0143-6147    

DOI:10.1080/09670878909371396

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0143-6147    

DOI:10.1080/09670878909371368

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor