Huanglongbing disease caused by the bacterium Candidatus Liberibacter is transmitted from infected to healthy plants by the Asian citrus psyllid, Diaphorina citri Kuwayama. Infectivity by conidia of five strains of Hirsutella citriformis Speare applied by contact was evaluated in field bioassays against D. citri adults. Bioassays were in three orchards of Persian lime (Citrus aurantiifolia (Christm. et Panz.) Swingle var. latifolia Yu. Tanaka) and one Mexican lemon (Citrus aurantiifolia Swingle) orchard at Chiapas, Campeche, Quintana Roo, and Colima states in Mexico. Treatments remained bagged on citrus trees in the field for 21 days after application. The five strains were pathogenic to the Asian citrus psyllid; CHE-CNRCB 339 and INIFAP-Hir-2 strains killed the most (74.1 and 68.3%, respectively). Most mycosis (71.1%) was by CHE-CNRCB 339. Preliminary results in the field confirmed the potential of H. citriformis to control Huanglongbing in Mexico.