Host Free Period for Tomato Yellow Leaf Curl Virus Control

Tomato yellow leaf curl (TYLC) and tomato leaf curl (TLC) diseases, caused by a complex of whitefly-transmitted geminiviruses [e.g., species in the genus Begomovirus such as Tomato yellow leaf curl virus (TYLCV)], are among the most damaging diseases of tomato in tropical and subtropical regions of the world. These diseases are difficult to control, and farmers often use large amounts of insecticides to control the whitefly vector with little success. Thus, effective sustainable practices are needed for disease management. Characterization of the causal begomoviruses and their biological properties has revealed that they are not seed- or transovarially-transmitted and that they have relatively narrow host ranges (tomato is the primary host). This has led to the development, evaluation, and implementation of regional crop-free periods as a management strategy. This involves not growing tomatoes (and some other solanaceous plants), on a regional level, for a period of 2–3 months. The disruption of the continuous cropping of the primary host (tomato) results in a dramatic reduction in the virus’s level virus in the agroecosystem and, in some cases, an accompanying reduction in the whitefly population. This results in a ‘window’ of 4–8 weeks of low virus pressure after the host free period in which tomato crops can be planted and grown before the virus pressure becomes high. Two successful examples of the use of host-free periods in IPM programs for managing these diseases in developing countries will be presented. In addition, the biological, economic, and social aspects of developing and implementing a host-free period will be discussed.