Agricultural Systems 27 (1988) 215-224 Formulating Policy to Cope with Virus Disease in Citrus Orchards Ishai Spharim & Sarit Shalhevet* Division of R & D Economics, The Volcani Center, Agricultural Research Organization, Bet Dagan, Israel (Received 3 September 1987; revised version received 27 October 1987; accepted 28 October 1987) ABSTRACT Citrus tristeza virus ( CTV) is a serious disease of citrus trees. ,4 simulation model was constructed which simulates the behavior of an infected orchard under various treatment methods. The model estimates the damage for an infected orchard under each of these treatment methods. Then the treatment which causes the smallest damage is chosen. The optimal treatment depends on the specific grove conditions. For example, in young groves with low infection rates, eradication of infected trees and their replacement with new trees is recommended, whereas in old groves with high infection rates and short intervals from infection to death of tree, the grower is best advised to refrain from tree removal until it becomes unprofitable and then replace it. The latter strategy does not prevent the spreading of CTV by vectors, and therefore may cause a conflict of interests between the individual grower and his neighbors. The model is used to produce decision-supporting information, for two policy levels, the grove owner and the whole industry. It helps (1) to choose the best treatment for the single grove owner; (2) to define the conditions in which the owner's interests conflict with those of the industry as a whole--a situation in which government intervention is needed. INTRODUCTION Citrus tristeza virus (CTV) is a serious disease of citrus trees. It is transmitted from infected to healthy trees by aphid vectors. The distance of CTV dispersal varies from short distance transmission to neighboring trees to * To whom all correspondence should be addressed. 215 Agricultural Systems 0308-521X/88/$03"50© 1988 ElsevierApplied SciencePublishers Ltd, England. Printed in Great Britain