The phyllosphere is known for hosting a great diversity of fungi, yeasts and bacteria. These microorganisms interact with each other and with the host plant in the form of symbiosis, mutualism, commensalism, parasitism, competition or simply neutralism. Pseudomonas syringae is a ubiquitous epiphytic bacterium commonly found in these microbial communities. The phylogeny complex of P. syringae comprises 13 phylogroups, containing strains that are well-known pathogens and strains that apparently have limited capacity as pathogens. Emblematic among the pathogens are P. syringae pv. syringae (Pss) and P. syringae pv. actinidiae (Psa) belonging respectively to phylogroups 2 and 1. Bacterial blights of fruit trees caused by P. syringae lead to significant economic losses worldwide. With the expansion of bacterial blight of kiwifruit caused by P. syringae pv. actinidiae and bacterial blight of apricot caused by P. syringae pv. syringae, the identification of reservoirs of these pathogenic strains and an understanding of the role of the accompanying diversity of P. syringae in disease epidemiology are needed. Here we describe the structure of P. syringae populations on orchard ground covers based on a series of PCR that specifically identify most of the phylogroups of this species. This efficient technique allows us to link population structure on ground covers to those associated with trees and to the botanical diversity and location of the ground cover reservoirs. The overall goal of these analyses are to identify microbiological contexts that are unfavorable for disease and to conceive management strategies of ground covers to foster these microbiological contexts.