The spread of bunchy top disease by the banana aphid was studied in two established banana plantations, in the presence and absence of roguing operations for disease control. The probability P of a new infection occurring x metres from an estimated source of inoculum was described by a special case of Pearson's gamma probability functionPx = exp( – x / x) ÷ x, where the mean distance between all of 178 new infections and their estimated sources of inoculum was x = 17.2 m, irrespective of roguing. All except two of the new infections occurred within five standard deviations (5x = 86 m) of the source as predicted, with nearly two-thirds within 20 m. The results were confirmed by successfully predicting the number of new infections that were encountered within 10 m of sources of inoculum in five other banana plantations. The results are discussed in relation to quarantine measures aimed at limiting the spread of disease in established plantations.