Influence of climate factors on Phakopsora euvitis Y. Ono airborne dispersal in grapevine crop

ABSTRACT

Grape rust, one of the most important diseases of Vitis spp., is managed in Brazil according to a calendar-based fungicide spray program. Despite the use of fungicides, the crop and the quality of grapes have shown significant losses due to rust. This disease causes leaf fall, unequal size and color of berries and loss in plant vigor in the following harvest. The aim of this study was to investigate the relationship between airborne urediniospore dispersal and weather parameters to improve the management of this disease. Thus, vineyards of the cultivar ‘Syrah’, susceptible to grape rust, were monitored to determine Phakopsora euvitis airborne dispersal dynamic. Wind vane spore traps were maintained at 0.5 m above the grapevine canopy and samples were collected every 24 h, while slides were changed at 9:00 a.m. A logistic regression model was developed to estimate the urediniospore dispersal probability. Higher urediniospore concentrations were observed between April and August, while in the remaining months the concentration was low or zero. The regression model of the airborne urediniospore concentration relative to the weather parameters was described as logit (Y) = 15.6668 - 0.6333 (temperature) + 0.4291 (wind speed), and a decision threshold of 0.47 was determined for predictive purposes.

Keywords
Vitis ; grape rust; risk; logistic model