Field studies on the spread of African cassava mosaic

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Abstract
SUMMARY: The spread of African cassava mosaic disease (ACMV) into healthy cassava fields was recorded at weekly intervals. In addition, 21 yellow water traps were placed in one field and the number of whiteflies caught was recorded twice a week. The number of Bemisia spp. feeding on cassava was also estimated. The results indicate that the pattern of disease spread is related to the pattern of infestation with Bemisia.Airborne whiteflies carried by the south‐west prevailing wind alighted preferentially on cassava plants along the upwind edges (south and west borders) of the plantings. The pattern of incidence of mosaic disease resembled that of whiteflies. Along the SW‐NE diagonal, there was a gradient of disease incidence with a maximum at the SW corner block. Similar gradients occurred in three different fields and they were maintained throughout the 6‐month study, although gradually flattening with time. There were indications that the reservoirs both of the virus and of the vectors were located some distance upwind from the experimental fields.