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to reduce their dependency on pesticides (farmer field school approach or FFS) [Braun, A.R., G. Thiele and M. Fernandez (2000). Farmer field schools and local agricultural research committees: complementary platforms for integrated decision-making in sustainable agriculture. AgREN(105): 1-16]. The second case study involves the use of mass media to deliver a message related to reducing pesticide use in rice farming in Vietnam [Escalada, M.M., K.L. Heong, N.H. Huan and V. Mai (1999). Communication and behavior change in rice farmers' pest management: the case of using mass media in Vietnam. Journal of Applied Communications 83(1): 7-25]. The third involves the application of FFS to disease management in Andean potato fields [Nelson, R.J., R. Orrego, M. Mundt, M. Fredrix and N.V. Vien (2001). Working with resource-poor farmers to manage plant diseases. Plant Disease 85(7): 684-695]. These examples will be used to explore the ways in which the nature of the message interacts with the method of delivery and the success obtained.  Relevant considerations include the value that can be obtained from heeding the message (cost/benefit); the robustness of the point captured in the message; the existence and stability of an extension system; the nature of the relationship between the researcher, message delivery agent and the farmer in the development and implementation of the message; the manner in which the message is conveyed; the cost of delivering the message in relation to the primary and secondary benefits obtained; and the intended scale of impact.  

Understanding seedling infection by downy mildew pathogens in relation to improving vegetable transplant production systems

Tijs Gilles and Roy Kennedy

Warwick HRI, Wellesbourne, Warwick CV35 9EF, UK. E-mail: Tijs.Gilles@warwick.ac.uk

The downy mildew pathogens of brassicas (Hyaloperonospora parasitica, former Peronospora parasitica) and lettuce (Bremia lactucae) can cause considerable damage during production of transplants of these crops in glasshouses. These downy mildew pathogens can kill or stunt seedlings in glasshouses, and when apparently healthy plants with latent infections are transplanted into the field, B. lactucae can cause downy mildew epidemics in adult lettuce plants and H. parasitica can cause systemic infections causing damage to cauliflower curds. The best strategy to reduce yield losses is to control downy mildew during transplant production to reduce stunting or kill of transplants and the level of initial inoculum going out into the field. Detailed infection studies were done with both downy mildew pathogens in controlled-environment cabinets and in glasshouses. Interestingly, light and the mode of dispersal of sporangia greatly affected the level and rate of infection of B. lactucae and H. parasitica. When fresh sporangia were directly dispersed within water such as by splash-dispersal the rate of infection was very high regardless of light conditions. Infection rates were reduced when dry sporangia were dispersed through air and exposed to wetness after their deposition on cotyledons. Furthermore, the disease severity caused by infection with air-dispersed sporangia was significantly reduced by light. For H. parasitica, the level of reduction in disease severity by light was greatest at sub- (5°C) or supra-optimal temperatures (25°C), and least at the optimum temperature (15°C). These findings have led to novel ideas on how to reduce downy mildew development in transplants by adapting to different irrigation systems and by controlling irrigation times in relation to light and shading within glasshouses. An air-borne spore detection system is also in development, which specifically detects H. parasitica sporangia. Downy mildew control treatments could be applied when the sporangia of H. parasitica are detected in air and conditions are good for infection.

Biology, control & biological control:  a case study of broccoli head rot

Rob Harling, Scottish Agricultural College, UK

Head rot, caused by opportunistic infection with the bacterium Pseudomonas fluorescens, is a major disease of broccoli in temperate regions of the world.  An understanding of host/pathogen biology has had an impact on how growers manage the disease in the UK, for example in the way bactericides are applied.  Alternative strategies such as biological control are attractive options for bacterial diseases such as head rot which are difficult to control by conventional means. However, knowledge of how bacteria control their virulence genes by quorum sensing may result in the next major advances in disease control.

Providing advice on plant health in developing countries

Eric Boa, Global Plant Clinic, CABI Bioscience, Bakeham Lane, Egham, Surrey TW20 9TY, UK

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