Spatial–temporal patterns of Ceratocystis wilt in Eucalyptus plantations in Brazil

Ceratocystis wilt, caused by Ceratocystis fimbriata, has become the most important disease in eucalyptus (Eucalyptus spp. and hybrids) plantations in Brazil. To further our understanding of the epidemiology of this disease, we surveyed eucalyptus plantations in the states of Minas Gerais and Bahia that were known to have Ceratocystis wilt or were thought to have been planted with infected rooted cuttings. There was generally higher disease incidence in the Minas Gerais plantations, which were on former Cerrado forest sites and likely had soilborne inoculum prior to planting eucalyptus. In such plantations, disease incidence was not evident before 20 months after planting but slowly increased up to 50% at 74 months. The symptomatic and killed trees were aggregated, perhaps from uneven distribution of inoculum in the soil. Also, the progression of cumulative disease incidence best fit a monomolecular model, which is typical of soilborne diseases (fixed level of initial inoculum with little or no secondary inoculum during the crop rotation). However, plots where some trees had been harvested during the rotation showed very high levels of disease incidence in the sprouts that arose from stumps, suggesting secondary spread of the pathogen on harvesting tools or machinery. Most of the Bahia plantations were on pastureland prior to eucalyptus cultivation, and the pathogen was likely introduced with infected nursery stock. In such plots, symptoms were evident as soon as 7 months after planting, and most of the mortality occurred within 12 months. The diseased trees on former pastureland sites were sometimes aggregated within planting rows, suggesting that bunches of infected nursery stock were planted together within the rows. Care should be taken in planting disease-free planting material and spreading the pathogen on tools, but on sites with soilborne inoculum, use of resistant clones may be the only management option.