This study was conducted with the aim to know the possibility of other host of Pestalotia theae, the pathogen causing leaf blight of Pinus merkusii seedlings, and the possibility of topsoil as a source of the inoculum. The study covered: the search for potential host species of alternative pathogens, isolate and observe pathogens from nursery and pine forests, cross-inoculation of all pathogenic isolates found. The results showed that Ageratum conyzoidez and Paspalum conjugatum, two common weeds found in the nursery, were found to be hosts for P. theae. Isolate pathogens of both types of weeds have the same ability, in infecting pine seedlings, with isolates derived from seedlings and trees of pine. It turns out that P. theae is also the pathogen of the soil
