摘要:

Tanzania is one of the largest producers of Upland cotton (Gossypium hirsutumL.) in Africa. The crop is raingrown by smallholders over a large ecologically diverse area with a variety of disease problems. The main diseases areFusariumwilt (Fusarium oxysporumf. sp.vasinfectum(Atk.) Sny. & Hans.) and bacterial blight (Xanthomonas malvacearum(E. F. Smith) Dowson).Fusariumwilt is established over much of the area close to Lake Victoria where the soils are sandy and acidic. The disease is seed borne but spread is reduced by issuing seed produced inFusariumfree villages. Bacterial blight has become less important due to success in breeding resistant varieties.Verticilliumwilt (Verticillium dahliaeKleb.) and root-knot nematode are potentially serious in some areas. Many other diseases occur at the seedling stage or on leaves and bolls but cause crop loss only under unusual environmental conditions or after insect damage.Alternaria macrosporais the most common cause of leaf spot andColletotricum gossypiithe main boll rot pathogen. Screening and selection for resistance toFusariumwilt is conducted in the glasshouse and on land artificially infested with high levels ofFusarium. Field selection for blight resistance involves assessment of naturally occurring leaf infection together with stem and boll inoculation.

ISSN:0143-6147    

DOI:10.1080/09670878109414165

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Between 1973 and 1979, studies were undertaken in North Thailand to quantify the impact ofCercosporaleaf spots,Mycosphaerella arachidisDeighton (Cercospora arachidicolaHori) andM. berkeleyiJenkins (Cercosporidium personatum(Berk. & Curt.) Deighton), and rust,Puccinia arachidisSpeg., on rainfed groundnut production and to examine control measures including comparisons of fungicides, spraying regimes (commencement time, interval and duration), varietal response to spraying and the addition of oils and wetting agents. Yield responses to fungicide treatments were between 50% and 113%. The most effective fungicide treatment was benomyl 50% w.p. in combination with maneb 80% w.p., used at application rates of 148 g and 1100 g a.i./ha/application. Chlorothalonil 80% w.p., zineb 75% w.p. and a commercial equivalent of benomyl + maneb were less effective. In years of average rainfall distribution, spraying could be left until 50 days after sowing for early wet season sowings. Spraying at 10 day intervals was superior to 15 or 20 day intervals. Yields continued to increase with spraying continued to 90 days but were only marginally economic for local varieties when continued beyond 80 days. Higher yielding groundnut varieties were proportionately more responsive. The addition of oils or wetting agents did not allow a reduction in fungicide application rates. Spraying for the control of the diseases under farming conditions was economical when assuming yield increments in response to disease control would be 50% of those achieved experimentally.

ISSN:0143-6147    

DOI:10.1080/09670878109414166

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Virus diseases are an important factor worldwide in crop production losses. Correct diagnosis of a disease is essential and in developing countries in the absence of modern facilities virologists regard infectivity tests as an important tool in identifying viruses. However compared with progress in other areas of plant virology infectivity assays lag behind. These tests should be carried out under optimum environmental conditions to permit symptom development. Environmental conditions should be standardised. Results of infectivity tests should be interpreted in relation to variation in the environment and the use of a known cultivar and its source. The use of an indicator host relates indirectly with variation in the environment and consequently symptom development. A suitable host must be used if the virus is to initiate infection. Plants used as indicator hosts must be genetically identical and from the same origin. Sensitive hosts are required to index seed batches in a well organised seed certification programme. There is a need for international seed and serum centres in strategic regions among developing countries and close collaboration between virologists to list genetically identical test plants for infectivity assays under their own conditions. Other factors to improve identification include an understanding of insect vectors. When used properly these tests can play a significant role in identification of virus strains and screening for resistance against virus diseases of economically important cash and food crops.

ISSN:0143-6147    

DOI:10.1080/09670878109414167

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Root-knot nematode,Meloidogyne incognita(Kofoid & White, 1919) Chitwood 1949, can limit production of French bean (Phaseolus vulgaris). The cheapest and best method of control is the use of resistant varieties. Although screening for resistance has been carried out in different parts of the world no such work has been carried out in India. The present study describes the screening and evaluation of 302 cultivars of French bean for resistance toM. incognitain replicated trials in the field and glasshouse under Indian conditions. Results showed 31 cultivars were resistant in both field and glasshouse conditions while 64 cultivars were moderately resistant. These 95 cultivars will be important to breeders interested in nematade-resistant cultivars of French bean.

ISSN:0143-6147    

DOI:10.1080/09670878109414168

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Euphorbia heterophyllaLinn., commonly known as wild poinsettia, is widespread in the tropics. It occurs as a major weed in six tropical countries, an important weed in 22 tropical countries and is present in a further 37 countries. It causes serious loss of yield and quality in a wide range of crops as it competes successfully by growing rapidly and forming a dense canopy over the crop. Dormancy is an important factor in the persistence of seed reservoirs in the soil and American and Nigerian work show light and temperature are important factors in germination. Pre-emergence herbicides do not give effective control for the whole growing season and as the weed becomes larger it is more difficult to control with post-emergence herbicides. In general the phenoxy-type herbicides give effective control, the triazines, ureas and uracils are variable and the acetanilides and anilines are poor. Some herbicide mixtures will suppressE. heterophyllalong enough to allow the establishment of the crop and minimise yield reduction but the best control has recently been obtained using a sequence of herbicides throughout the growing season.

ISSN:0143-6147    

DOI:10.1080/09670878109414169

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Field trials were conducted during 1978 and 1979 on Freeport sandy clay loam, Pasea clay loam and Cunupia clay soils to provide further data on the performance of pre-plant incorporated treatments of benfluralin (1.1 kg a.i./ha), butralin (4.0 kg a.i./ha), isopropalin (1.5 kg a.i./ha) and trifluralin (1.0 kg a.i./ha) and pre-emergence treatments of chlorthal-dimethyl (10.0 kg a.i./ha) and diphenamid (5.0 kg a.i./ha) for weed control in rainfed ‘Early Long Purple’ eggplant and to determine their influence on the yield, grading quality and chemical composition of eggplant fruit. Although the herbicide treatments generally gave better performance on Freeport and Pasea loams than on Cunupia clay, the results confirmed the reliability of the herbicide treatments on the three soils where no evidence of crop injury was observed. The herbicides generally provided satisfactory reduction of early weed growth, gave acceptable yields of good quality fruits and did not affect the protein, total carbohydrate or moisture contents of fruits. No residual injury to beans (Phaseolus vulgaris) and watermelon (Citrullus lanatus) from soil residues was observed.

ISSN:0143-6147    

DOI:10.1080/09670878109414170

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The climate, soil types, vegetation, land use and crops of The Gambia are briefly introduced. The most important weeds are commented on and a checklist of 219 species is appended. Methods of weed control in current use and which are undergoing research and development are described. They include hand cultivations, animal-drawn equipment, herbicides and fallow management. Current training of farmers and agricultural staff is mentioned.

ISSN:0143-6147    

DOI:10.1080/09670878109414171

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Strategies for the use of pheromones for the control of insect pests have generally been developed in countries of advanced technologies. In this paper the relevance of pheromones to the needs of agriculture in developing countries are discussed with particular reference to work by the Scientific Units of the British Overseas Development Administration.

ISSN:0143-6147    

DOI:10.1080/09670878109414172

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A comprehensive list of the insect prey of 47 species of Syrphidae from India and neighbouring countries is presented, including a total of 542 individual records. The introduction includes a detailed summary, with references, of different insect groups known to be preyed upon by syrphids from all over the world, this being the first time that such a summation has been attempted for the Syrphidae. Pertinent information on predacious syrphids, their role as biocontrol agents, and a short historical account of Indian work on their biology and ecology is provided. The syrphid-prey list details recorded information on the 47 species of syrphids for whom prey have been recorded. This includes the author's own rearings and other unpublished data from the CIBC Indian Station, which together total 46 new prey records. Incorrect prey data and doubtful predator identifications are indicated or corrected. The prey-syrphid index gives the syrphid species recorded as preying upon the 77 prey species listed. The list of references constitutes a bibliography of all papers citing prey information on Indian syrphids, as well as those providing data on different prey groups of world Syrphidae.

ISSN:0143-6147    

DOI:10.1080/09670878109414173

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The results of discriminative spraying of endosulfan and decamethrin from a Bell 47G-4A helicopter to fringing riverine forest habitats ofGlossina tachinoidesin the Komoe Valley, Upper Volta, are described. The insecticides, diluted with diesel oil were applied from the helicopter through a unilateral (left-side) arrangement of four rotary atomisers. Three experimental blocks were each sprayed twice at an interval of about one month, one with endosulfan at individual swath dosages of 100 g (a.i.)/ha, the second with endosulfan at 200 g (a.i.)/ha and the third with decamethrin at 12.5 g (a.i.)/ha. In spite of aerially applied dieldrin barriers there was extensive reinvasion byG. tachinoidesduring the inter-spray period, consequently conclusions were largely drawn from the data collected before and after the second cycle of insecticide applications. The reinvasion problem is discussed. Endosulfan at 200 g/ha was the most effective in controllingG. tachinoides. Other treatments were less, but probably adequately effective, although the decamethrin was more expensive. Detailed cost analyses are presented. Even though the track of the helicopter was about 15 m from the banks of the R. Komoe, contamination with insecticide was sufficient to adversely affect some aquatic non-target organisms. Decamethrin caused high mortalities of two aquatic prawns,Caridina africanaandMachrobrachium raridens. One year later fish andC. africanapopulations had recovered, but notM. raridens.

ISSN:0143-6147    

DOI:10.1080/09670878109414174

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor