Outbreak of pink disease in intensively managed Eucalyptus grandis plantations in India

An outbreak of pink disease caused by Corticium salmonicolor occurred in intensively managed Eucalyptus grandis plantations (104 ha) in High Ranges at Munnar, Kerala, Severe infection with multiple main-stem canker, bark splitting, gummosis, girdling, etc. occurred in Shenkulam plantation (40 ha), Kathippara plantation (24 ha), and Kaithachal Plantation (40 ha). In Shenkulam plantation, about 10 ha was under substantial disease pressure affecting >98% of the plants. In other areas disease incidence varied from 5 to 95%. The plants in valleys and on the bank of the reservoir showed 80-90% infection with medium to high disease severity. The l6-month-old plantation with >99% stocking was under intensive silvicultural management viz., chemical fertilisation, soil work, weeding, mechanical pruning of lower branches, etc. The plants showed an exceptionally excellent growth; in Shenkulam, the plant height ranged from 5.5 to 8.0 m (av. 6.75 m) and gbh ranged from 15 to 34 em (av. 25 em). In Kathippara the plant height ranged from 3.5 to 6.0 m (av. 4.5 m), gbh ranged from 9.5 to 23,0 em (av. 19 em). Environmental factors including site factors considered to be the major influencing ones for the sudden outbreak of the disease. Heavy rainfall (5055 mm per annum), high relative humidity due to the presence of a permanent water source (reservoir) nearby the plantation, conducive micro-climatic conditions brought about by the closed canopy formation in the plantation, etc. favoured the quick build-up of the pathogen inoculum, infection and its successive spread within and between the plants to an epidemic proportion. Increased host susceptibility due to the development of highly succulent bark in faster grown plants under high input management, pathogen virulence, etc. are the other possible contributing factors for the outbreak of the disease. Brush-on application of Bordeaux paste (10%) in moderately to severely affected plantations, Shenkulam (5 ha), Kathippara (3 ha), Kaithachal (2 ha) gave promising results, The economics of the fungicidal treatment was worked out and the total cost including labour and chemicals comes around Rs, 1.50 per plant. The paper highlights the economic importance of the epidemic, analyses the possible environment, host, pathogen and time factors for the disease outbreak, and suggests short-term as well as long-term strategies for combating the disease.