摘要:

Field trials were conducted at three sites in Sierra Leone near Njala University College, to compare the weed vegetation before and after clearing operations and dryland rice yields on the same sites after zero, five‐year and 10‐year fallow periods respectively. The weed flora during the cropping period at all three sites bore some relation to the vegetation before clearing. Though there were no plant species common to all sites before farming began, the weed shift during the cropping period produced a number of such common species;Rottboellia exaltataL.,Pennisetum subangustumStapf & C. E. Harbbard,Calopogonium mucunoidesDesv.,Ageratum conyzoidesL. andPanicum laxumSw. were the most important. The five‐year fallow site had the greatest weed cover, height and biomass; next in order were the site under continuous cultivation and the 10‐year fallow site. Thus the latter site produced the highest rice yields, followed by the zero fallow site. Stam F‐34 (propanil + fenoprop) application was shown to bemoreeconomical than hand weeding on the zero‐ and five‐year fallow sites, but less so on the 10‐year fallow site.

ISSN:0143-6147    

DOI:10.1080/09670878209370665

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Seedbed preparation is difficult for hoe farmers because hoes make inefficient tillage instruments. Test were made in sorghum and millet fields in northern Nigeria to evaluate glyphosate and paraquat as substitutes for seedbed preparation by tillage. These chemicals were applied at rates of 0.5, 1.0 and 2.0 kg a.i./ha, in the period between weed and crop emergence. All treatments except 0.5 kg a.i./ha of paraquat gave acceptable yields. Glyphosate applied at a rate of 0.5 kg a.i./ha and paraquat at 1.0 or 2.0 kg a.i./ha, gave rise to similar crop yields. Sorghum grain yield after treatment with 1.0 kg a.i./ha of glyphosate was not significantly different from that obtained in hoe‐tilled fields. The addition of 0.5 kg a.i./ha of atrazine to some treatments did not result in improved crop yield or weed control.

ISSN:0143-6147    

DOI:10.1080/09670878209370666

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The present status of the imported and naturally occurring insects pests ofLantana camara L.a noxious exotic weed in Zambia, was determined by survey. Of the seven insect species imported in 1969–74, onlyTeleonemia scrupulosaStål has become established in Zambia and occurs today all over the country. Two other neotropical lantana insects, namelyOphiomyia lantanae(Froggat) andLantanophaga pusillidactylaWalk, have spread naturally into Zambia. In addition, 17 indigenous insect species were recorded as infesting lantana during the survey. The actual injuriousness of the insect complex to lantana was in all cases negligible, and it was concluded that insects will probably not contribute significantly to lantana control in Zambia.

ISSN:0143-6147    

DOI:10.1080/09670878209370667

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The introduction and rapid spread of the water hyacinthEichhornia crassipes(Mart.) Solms in the White Nile system of southern Sudan has produced serious problems for the use of that river as a resource. Not least of these is the increasing cost of chemical control of the weed in a very large and often inaccessible area. Biological control of the plant by the introduction of some of its natural insect enemies had been earlier suggested as an alternative method. A programme for the mass culture and release of insects in the Sudan commenced early in 1979. During the following two years three species,Neochetina eichhorniaeWarner,N. bruchiHustache (Col., Curculionidae) andSameodes albiguttalis(Warren) (Lep., Pyralidae) were reared and released. TheNeochetinaweevils became successfully established and are dispersing in the river system. Heavy infestations have been observed in some areas. The mothS. albiguttalishas apparently failed to establish so far, but it is considered that further releases will improve the chances of producing stable populations of this species.

ISSN:0143-6147    

DOI:10.1080/09670878209370668

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Reductions in cassava root yield were related to infestations of the crop by the cassava mealybug,Phenacoccus manihotiMat.‐Ferr. in field trials that combined several varieties, dates of planting and dates of onset of infestation. Reductions in root yields of up to 84.4% and 54.4% were measured in late‐ and early‐planted cassava respectively. There was a gradual increase in yield loss due to pest attack with every delay in planting. Root yields for December, February and April plantings were reduced by 2.6, 11.2 and 31.2% respectively when compared with the first planting in October. However a delay in the onset of mealybug infestation results in a decrease in yield loss. A correlation coefficient of r = 0.77 was obtained between root yield and date of initial pest infestation.

ISSN:0143-6147    

DOI:10.1080/09670878209370669

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Insecticidal control of cotton bollworms(Pectinophora gossyplella(Saund.),Heliothisarmigera(Hb.) andFarias vittella(F.)) was evaluated in the Southern Province of Sri Lanka for the period 1978–79. The standard schedule of 8–10 applications of 840 g a.i./ha monocrotophos was compared with monocrotophos (500 g a.i./ha); fenvalerate (100 and 200 g a.i./ha); permethrin (125 and 250 g a.i./ha); fenthion (1500 g a.i./ha); trichlorphon (900 g a.i./ha); methamidophos (840 g a.i./ha); profenofos (750ga.i./ha);profenofos + DDT(750ga.i./ha);and carbaryl (2240 g a.i./ha) in three trials with various schedules of application. Results were expressed as yield of seed cotton, percentage of damage to harvestable bolls and number ofP. gossypiellalarvae in opened bolls. Fenvalerate at the lower rate significantly reduced damage and larval infestation of bolls compared with the standard monocrotophos recommendation. It is suggested that fenvalerate or permethrin replace the monocrotophos recommendation since they are safer and give improved control.

ISSN:0143-6147    

DOI:10.1080/09670878209370670

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Preliminary laboratory and field trials of control methods for use against mole‐rats (Spalax leucodonNordm.) were carried out in northern Syria. Captive mole‐rats preferred either carrot or soaked wheat to potato, onion and other vegetables. Zinc phosphide was used on carrot, discs of which were dipped into the poison to give a bait containing 2.9–3.8% zinc phosphide, while fluoroacetamide was used at 2% on soaked wheat. Sites with moderate mole‐rat infestations were selected for field trials, two sites being treated with fluoroacetamide, one each with zinc phosphide and aluminium phosphide gassing tablets. Poisons were placed in mole‐rat tunnels close to the nest of each animal and prod‐hole censuses were carried out to measure mole‐rat activity before and after treatment. Activity was reduced by 65% after a single application of zinc phosphide whereas fluoroacetamide achieved 83% and 79% and aluminium phosphide gassing tablets 89% success. Complete control was achieved after a second application of the latter poisons. All of these poison methods were much more cost‐effective than even the best results achieved with the traditional digging method. Moreover, the efficiency of the digging method is greatly reduced at lower mole‐rat densities. European mole traps were found to be unsuitable for use against mole‐rats.

ISSN:0143-6147    

DOI:10.1080/09670878209370671

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The effects on plant pathology of the newInternational code of nomenclature of bacteriaand theApproved lists of bacterial namesare discussed. The use of pathovar nomenclature and theInternational standards for naming pathovars of phytopathogenic bacteriaand aList of pathovar names and pathotype strainsis also considered. The correct way to publish a new species or combination and a new pathover is described.

ISSN:0143-6147    

DOI:10.1080/09670878209370672

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Some previous treatments forPhytophthorabark canker of cocoa, in Papua New Guinea and elsewhere, are summarised and the new systemic fungicide metalaxyl, other non‐systemic fungicides and removal of outer bark by scraping are compared. Details are given of inoculation and reisolation techniques which gave rapid and reliable results for the study of cocoa canker. Metalaxyl was much superior to the other treatments under the conditions of these experiments and 0.25% a.i. metalaxyl effectively controlledP. palmivorain artifically induced cankers. Bark cankers very often start around bark damage made by the larvae of woodboring insects and 0.25% a.i. metalaxyl added to an aqueous dichlorvos/white oil mixture used to control these insects was also effective in eliminating the fungus. It was considered that scraping followed by natural desiccation, which effectively controls canker in W. Malaysia, would not be reliable under the wetter climatic conditions in Papua New Guinea. The current recommendations for canker control are given based on the above results.

ISSN:0143-6147    

DOI:10.1080/09670878209370673

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The downy mildews of maize, sorghum and pearl millet are among the most destructive diseases in the tropics and subtropics. The pathogens causing the diseases arePeronosclerospora sorghi, P. heteropogoni, P. philippinensis, P. sacchari, P. maydisandSclerospora graminicola.In spite of an increase in research on graminaceous downy mildews during the last decade, broad gaps in information still exist which prevent their adequate control. Information on seed transmission, collateral hosts as sources of inoculum and effects of environment on the conidial and oospore phases of these diseases is reviewed, and some of the important information gaps are discussed.

ISSN:0143-6147    

DOI:10.1080/09670878209370674

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor