Browsing by Author "Isard, S"

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    The influence of weather and microclimate on Dalbulus maidis (Homoptera: Cicadellidae) flight activity and the incidence of diseases within maize and bean monocultures and bicultures in tropical America
    (Annals of applied biology, 1992) Castro, V; Rivera, C; Isard, S; Gámez, R; Fletcher, J; Irwin, M
    Mixed cropping systems in tropical America have been shown to be less prone than monocultures to damage from pathogens carried by insects. This finding formed the basis for a series of experiments conducted in Costa Rica to evaluate the hypothesis that mixed cropping systems create a physical environment that influences vector movement and consequently the spread of leafhopper-borne pathogens. The principle finding of the study is that both the mixture of plants and planting density have little influence on the spread of pathogens by Dalbulus maidis, an oligophagus leafhopper which prefers maize, within maize and bean single and mixed cropping systems. Leafhopper flight activity proved similar for high and low density monocultures and bicultures. The number of leafhoppers immigrating to and emigrating from a field appears dependent on the size of the field, not the density of maize plants. Single and mixed crops with the same density of maize plants were equally prone to damage by pathogens carried by leafhoppers. The lower percentage infection in high density than in low density maize treatments resulted from fewer vectors per plant in the former.
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    The microclimate of maize and bean crops in tropical America: a comparison between monocultures and polycultures planted at high and low density
    (Agricultural and Forest Meteorology, 1991) Castro, V; Isard, S; Irwin, M
    This study characterizes the microclimates of maize and bean crops planted in monocultures and polycultures at two planting densities in Costa Rica. The hypothesis that the density and mixture of plants affects the microclimate within a field is evaluated as part of a larger study to identify environmental factors relevant to the spread of disease by insects in tropical agricultural systems. In general, the results support the findings of many previous studies that the density and morphological characteristics of the plants strongly influence the microclimate within an agricultural field. This research differed from most agricultural microclimate studies in that fields planted at two densities with different mixtures of plants were observed concurrently in tropical America.