Factors affecting uredospore production and dispersal in Tranzschelia discolor

Abstract

Uredosori of Tranzschelia discolor mature on infected twigs of susceptible peach varieties in July and uredospores are produced at a diminishing rate throughout most of the following growing season. Dry liberation of uredospores from sori on leaves occurs at a rate which increases logarithmically with the wind speed. The onset of heavy rain, or irrigation from overhead sprinklers, may cause a temporary 10-fold increase in the concentration of airborne uredospores within an orchard. In wind tunnel tests, bombardment of sori by water droplets caused liberation of uredospores at wind speeds below those normally required to release detectable quantities. The results emphasize the importance of directing control measures at prevention of the overwintering phases of the rust, which in peaches occur on twigs, and in almonds on rusted leaves retained throughout the short dormant period.