Globally, citrus is threatened by huanglongbing (HLB), and the lack of effective control measures is a major concern of farmers, markets, and consumers. There is compelling evidence that plant health is a function of the activities of the plant's associated microbiome. Using
Liberibacter crescens
, a culturable surrogate for the unculturable HLB-associated bacterium “
Candidatus
Liberibacter asiaticus,” we tested the hypothesis that members of the citrus microbiome produce potential anti-“
Ca
. Liberibacter asiaticus” natural products with potential anti-“
Ca
. Liberibacter asiaticus” activity. A subset of isolates obtained from the microbiome inhibited
L. crescens
growth in an agar diffusion inhibition assay. Further fractionation experiments linked the inhibitory activity of the fungus
Cladosporium cladosporioides
to the fungus-produced natural products cladosporols A, C, and D, demonstrating dose-dependent antagonism to
L. crescens
.