Pg. 60-62 Litchi decline in South Africa – new or old problem?

Litchi decline has been reported in several countries over the past few years. Also in South Africa it seems to be a sporadic problem, associated with several pathogens and probably several predisposing biotic and abiotic factors. Different symptoms and possible causes are discussed with emphasis on recent observations throughout the litchi industry of South Africa. Management and research strategies, which focus on eliminating predisposing factors, are discussed.

Summary:

• Topic: Litchi decline in South Africa—whether it is a new issue or a long-standing problem.
• Scope: Decline has appeared in multiple countries recently; in South Africa, it appears sporadic and linked to several pathogens and likely multiple biotic and abiotic predisposing factors.
• Symptoms: Slow decline (die-back) and sudden death are described; affected trees show reduced vigor, poor/cancelled new growth, leaf drop, die-back of twigs, and potential temporary recovery before eventual death.
• Age pattern: Slow decline tends to affect older trees; sudden death more common in younger trees.
• Possible causes: Pathogenic infections of feeder roots, larger root systems, or trunk; but drought stress, anaerobic soil conditions from compaction or poor drainage, poor root structure, nutritional deficiencies, and chemical injuries (fertilizers/herbicides) can produce similar symptoms.
• Pathogens implicated: Clitocybe tabescens is highlighted as a major association; other species reported in various regions include Fusarium solani, Cylindrocladium, Phytophthora, Pythium, Rhizoctonia, and Diplodia, Leptosphearia, Phomopsis in different contexts.
• Pre-disposing factors: Poor drainage and soil conditions, inadequate irrigation during dry periods, and general soil/root health problems are repeatedly noted as contributing factors.
• Geographic comparisons: Similar decline patterns and pathogen associations described in Florida, the Philippines, Northern Vietnam, Australia, and China, with South Africa’s experience emphasized.
• Management focus: Strategies emphasize eliminating predisposing factors (e.g., improving drainage, soil conditions, and irrigation practices) alongside ongoing research to better understand pathogen roles and interactions.