Wind dispersal of Puccinia psidii urediniospores and progress of eucalypt rust

Summary To identify and implement Puccinia psidii control strategies, it is essential to understand the role of environmental factors on rust-disease development and spread among eucalypt (Eucalyptus spp.) plantations. In this study, we evaluated the wind dispersal of P. psidii urediniospores and the progress of eucalypt rust in a field trial in Brazil. Urediniospores of P. psidii were trapped in a Burkard® spore trap from July 2004 to June 2005. To evaluate the progress of eucalypt rust, plots were established in March 2002 using a clonal hedge scheme. The incidence of both branches and leaves with rust was assessed weekly from February 2003 to October 2005. Disease progress was studied using time-series analysis. Urediniospores were trapped on 77% of the days sampled. The highest average urediniospore concentration was detected from July to November, and most of the urediniospores (58%) were trapped at night. Urediniospore concentration was negatively correlated with rainfall, light intensity, minimum, average and maximum temperatures and wind speed, whereas urediniospore concentration was positively correlated with leaf-wetness duration and relative humidity. From December 2004 to June 2005, average urediniospore concentration was 0.22 spores m−3 air h−1 and had no correlation with meteorological data. The highest average urediniospore concentration was associated with a combination of low average temperature, low light intensity, low wind speed, high relative humidity and high leaf wetness, which reflect conditions observed at night. The disease incidence was positively correlated with the urediniospores trapped at 12 days prior to disease assessment. According to the models obtained by the time series, a seasonal yearly effect was found on rust progress. Using our models, we were also able to forecast disease incidence up to 3 months after the last field assessment.