THE RELATION OF POTATO LEAF ROLL VIRUS NET NECROSIS IN POTATO-TUBERS TO THE INTERVAL BETWEEN PLANTING AND INOCULATION

The green peach aphid, Myzus persicae, is a vector of potato leaf roll virus. Inoculated potato plants may develop tubers expressing net nec rosis at harvest or in storage, which can significantly reduce the cro p's commercial value. Insecticides have been traditionally used in a p rophylactic manner to suppress the aphid population in the field there by preventing inoculation and the advent of net necrosis. To analyze t he rationale of such an insecticide application decision, data generat ed by two field experiments were used to establish an empirical relati onship between the probability that a tuber will express net necrosis (NN probability) and the time after planting that inoculation occurs ( inoculation interval). In contrast to past studies, the data analyzed here allow for the investigation of the impact of inoculation dates oc curring over the entire growing season. This uncovers the previously u nknown empirical result that NN probabilities may peak before monotoni cally declining in the second half of the growing season. It implies t hat insecticide spraying might profitably be concentrated on inoculati on intervals generating peak probabilities, to 'flatten' the peaks to acceptable probability levels. The data also permitted a limited analy sis of the systematic ways that increasing storage periods may alter t he empirical relationship between NN probabilities and inoculation int ervals. (C) 1997 Elsevier Science Ltd.