Vertical spread of Puccinia psidii urediniospores and development of eucalyptus rust at different heights

Rust, caused by Puccinia psidii, is an important disease in eucalyptus nurseries and plantations in Brazil. In the field, eucalyptus plants taller than 3–4 m are not infected by the pathogen. We hypothesised that microclimatic conditions above 3 m do not favour either pathogen establishment or disease development. Therefore, we evaluated the effect of the height gradient on rust incidence, related to leaf wetness duration and the number of airborne urediniospores. Young eucalyptus plants were maintained at heights from 0.5 to 4.0 m, and disease was assessed weekly at all heights in five plant sets. Rust incidence reduced as height increased. The values of area under rust progress and rust incidence were negatively correlated (P ≤ 0.05) with height and positively correlated (P ≤ 0.05) with the number of both hours with leaf wetness and airborne urediniospores. Thus establishment and progress of eucalyptus rust were affected by leaf wetness duration and concentration of airborne urediniospores, which decreased as the height increased.