Chapter 13 - Dynamics of diseases and insect pests of cashew tree

Abstract

Cashew is infested with a wide range of diseases and insects, which affect different parts of the crop ranging from the stems, leaves, inflorescences, apples (fleshy fruit) to the nuts, resulting in significant losses. The attack of a multitude of pests from seedling to fruiting stages is somewhat closely related. Some important diseases of cashew range from inflorescence blight (Lasiodiplodia theobromae), anthracnose (Colletotrichum gloeosporioides), damping-off (Fusarium sp., Sclerotium rolfsii), seedling dieback (Pythium sp., Fusarium sp., L. theobromae) to twig dieback (L. theobromae). Lasiodiplodia theobromae is a fungus common in many countries, widely distributed in tropics and subtropics, and also has a wide host range. This pathogen causes blight and dieback of cashew parts, which are major diseases. In this review, examples and case studies are taken mostly from cashew-growing areas in Nigeria. Survey of inflorescence blight in cashew trees in Nigeria showed variations in cultural isolates of Lasiodiplodia sp. This pathogen was spread across growing states with high incidences and severity in all farms. This disease caused significant crop losses to yield reduction in cashew. Economically important insect pests of cashew in Nigeria include Analeptes trifasciata, Selenothrips rubrocinctus, and Pachnoda cordata. Analeptes trifasciata caused significant damage to cashew production. Survey of A. trifasciata infestation showed the yield loss up to 54.8% in almost all cashew-producing states in Nigeria. Lasiodiplodia sp. and A. trifasciata distribution in Nigeria showed significant spread across major and minor growing areas with varying degree of severity depending on production status. However, the wide host range of Lasiodiplodia sp., its endophytic nature, and existence of strains are major hurdles to overcome in the development of effective disease management strategies.