摘要:

The dramatic increase in the use of pesticides has led to increasing political, social, human health, and environmental concerns. Accidents due to misuse among users have risen dramatically and speak to the need for the development of practical and useful communication programs and materials, particularly with small farmers. Three studies were designed to research and test the comprehensibility of sets of pictographs, pictures, and symbols depicting proper and improper procedures for using agricultural pesticides. Field testing was conducted with Mexican farm workers in California and small farmers and farm workers inEcuadorSouth America. Results indicate that, like language, the meaning of symbols and visual literacy will have to be taught if the goal of perfect comprehensibility is to be achieved. Furthermore, research on visual communication materials and information systems in this area must become an integral part of formal and nonformal educational efforts. These efforts must be undertaken not only by communication researchers but also in conjunction with technical personnel.

ISSN:0143-6147    

DOI:10.1080/09670878809371253

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Water hyacinth is the most serious aquatic weed in India, infesting more than 200000 ha of water surface. Successful biological control of this weed was achieved in a fully infested tank covering 20 ha at Bangalore. More than 95% of the infestation was cleared within 32 months by releases ofNeochetina eichhorniaeWarner. The insect also spread along a water channel and controlled water hyacinth infesting a nearby tank. Drying up of the tank after the insect population had spread throughout and increased to 3.1 adults/plant hastened weed control. Fresh plants emerging after rains were suppressed by the residual population of insects.N. eichhorniaealong withN. bruchiHustache is being supplied to centres throughout the country for multiplication and releases. Sustained efforts with these insects holds out promise of control of water hyacinth in India.

ISSN:0143-6147    

DOI:10.1080/09670878809371254

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Larviposition by the Tachinid fly,Sturmiopsis inferensTns. on sugarcane shoot borer larvae was studied. One adult female laid on an average 285 maggots (range 126–521). More than 90% of the maggots extruded were free of the enveloping chorion. Less than 4% were found to be unfertilized and undeveloped. The mean number of maggots laid per host was 1.21 and more than 70% were laid at the bore hole, the remaining being larviposited near the bore hole. Larviposition began on the sixth day after emergence of the female and mating, reached its peak during seventh to eleventh days and declined thereafter. Over 90% of the total number of maggots were deposited by the thirteenth day. Some maggots (9.52%) were not extruded but remained in the fly's uterus. The number of maggots laid at a bore hole varied from one to nine, but in more than 50% of the shoots only a single maggot was deposited. The flies preferred third, fourth and fifth instar larvae and shoots having only wet frass for larviposition, although larviposition did occur in shoots having second instar larvae and freshly formed pupae.

ISSN:0143-6147    

DOI:10.1080/09670878809371255

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Recent investigations have shown that the juvenile decline condition is widespread amongst young clove trees in Zanzibar and Pemba and causes a serious loss in production. In the past the condition, which affects young clove trees on both islands, has been attributed to pathological or agronomic causes. Results are presented which show that trees affected with the condition respond very favourably to the use of herbicide for ring weeding and the application of the fertilizer ammonium sulphate. It is suggested that juvenile decline is caused by weed competition for nitrogen; the role of other factors in contributing to the condition is discussed.

ISSN:0143-6147    

DOI:10.1080/09670878809371256

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

One hundred and thirty six weed species, belonging to twenty nine plant families were recorded from rice weed surveys carried out in four major rice‐growing districts of the low country Wet Zone of Sri Lanka, during two consecutive ‘Yala’ seasons in 1984 and 1985. In terms of abundance and distribution Moncotyledon weeds of the Poaceae and Cyperaceae, were found to be far more important than dicotyledon weeds.Isachne globosa(Thunb.) Kuntz., andIschaemum rugosumSalisb. of the Poaceae, andFimbristylis miliaceaVahlCyperus iriaL. andCyperus pilosusVahl, of the Cyperaceae, were the most abundant, widespread and troublesome rice weeds in all four districts surveyed. Of the dicotyledon weeds,Ludwigia hyssopifolia(G. Don) Exell emerged as the single most widespread and abundant species in all four districts, and a new weedLudwigia decurrensWalt. was found to be spreading rapidly in the area surveyed. Some indications of district to district differences in the floristic composition and abundance of the more important weeds were obtained, apparently due to factors such as local distribution of weeds, management practices, and cultivars of rice grown.

ISSN:0143-6147    

DOI:10.1080/09670878809371257

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Dissemination of weed seeds, weed seedlings, and shoots of perennial weeds along with transplanted rice(Oryza sativaL.) seedlings was observed in farmers’ fields in Guimba, Nueva Ecija, Philippines. The percentage of weed seedlings and shoots in bundles of rice seedlings to be transplanted into the field ranged from 4–5 to 14.2% in the wet season and from 3.0 to 8.7% in the dry season. Grasses comprised 63% of the weed seedlings in the wet season and 81% in the dry season. The number of weed seeds disseminated with the rice seedlings ranged from 271 to 683 per bundle. Mainly sedges and broadleaf weeds were disseminated in this manner. Possible ways of reducing dissemination of weeds with rice seedlings are suggested.

ISSN:0143-6147    

DOI:10.1080/09670878809371258

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The growth and development of three selections of torpedograss(Panicum repensL.), collected from different geographical locations in Sri Lanka were studied in order to understand the general patterns of growth and allocation ofresourcesto various component parts. In general, the ascendancy of the mother culm was short lived. The grass showed a high capacity for tillering, and it was evident that a few primary tillers arising from the base of the mother culm, and several rhizome tillers, arising from lateral buds on the nodes of rhizomes, became the dominant components of the shoot system accounting for more than 90% of the shoot. The selections from Colombo (CO) and Talawakele (TA) showed significantly more shoot growth than a selection from Galle (GA). In contrast, the GA selection produced a significantly greater amount of rhizome material by the end of 16 weeks, than CO or TA, indicating significant differences in the allocation of resources among the selections studied. The total lengths of rhizomes and the numbers of nodes borne on them were also greater in the GA selection, although the rhizomes of CO and TA were thicker and heavier. Both the TA and CO selections produced inflorescences at least 2 weeks before GA and by 16 weeks, had a greater number of panicles and spikelets, indicating differences in allocation of resources to seed production. The distinct differences recorded among the three selections studied raise the possibility of occurence of ‘ecotypes’ of the grass in geographically distant locations within the island.

ISSN:0143-6147    

DOI:10.1080/09670878809371259

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The distribution of two sweet potato potyviruses, FMV and SPLV, was assessed in three plants infected with both viruses and in one plant infected with FMV only. All leaves, the top and basal sections of the main stem, and branch sections were tested by ELISA. Both symptomless leaves and leaves showing symptoms including purple rings, chlorotic spots, mottle or discoloration were found to contain the viruses. However, neither could be detected in every leaf or stem piece. SPLV was found in a lower proportion of leaf and stem samples than FMV. This indicates that the two viruses are either very unevenly distributed within sweet potato plants or that the virus concentration in some parts is below the detectable level. Testing of each leaf is recommended for reliable virus indexing of small, meristem‐derived sweet potato plantlets, if the ELISA method is used. Additional indexing of all ELISA‐negative materials by grafting to susceptible indicator plants is nevertheless still necessary.

ISSN:0143-6147    

DOI:10.1080/09670878809371260

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Bacterial blight of cotton caused byXanthomonas campestrispv.malvacearumoccurs in most countries where the crop is grown. Once a serious disease, it has been successfully controlled in many African countries, including Zimbabwe, through the use of resistant varieties. However, as new cultivars are produced to meet the changing requirements of the spinning industry, there is a constant need for rigorous screening for blight resistance. In Zimbabwe, severe blight symptoms have occurred in selections derived from crosses with high quality introductions. This has emphasized the potential importance of the disease in susceptible cultivars and reaffirmed the commitment to regular screening for resistance in the country's cotton breeding programme. The paper describes the historical background to the production of blight resistant cottons in Zimbabwe and gives methods currently employed in screening for blight resistance.

ISSN:0143-6147    

DOI:10.1080/09670878809371261

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The major pulse crops of Pakistan are chickpea, lentil, mungbean, and urdbean. Diseases are a constant threat and often a limiting factor in the cultivation of pulse crops. Chickpea is attacked mainly by blight, wilt and root rot complex. The main diseases of mungbean and urdbean are yellow mosaic virus (YMV), leaf crinkle virus (LCV), cercospora leaf spot, bacterial blight and charcoal rot. Lentil is attacked by rust, wilt and blight. Details are given of the symptoms, distribution and control of the diseases of economic importance.

ISSN:0143-6147    

DOI:10.1080/09670878809371262

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor