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Tagatose is a rare sugar that suppresses plant diseases, such as late blight of tomato, caused by <i>Phytophthora infestans</i>. Tagatose can be metabolized by some microorganisms and no information is available on its persistence on tomato leaves. The aim of this study was to assess the persistence of tagatose on tomato leaves under commercial greenhouse conditions. The amount of tagatose on tomato leaves and the inhibitory activity against <i>P. infestans</i> decreased seven days after spray application in the absence of rain wash-off. Potential tagatose-degrading bacteria were isolated from tomato leaves, and they belonged to <i>Acinetobacter</i> sp., <i>Bacillus</i> sp., <i>Comamonas</i> sp., <i>Enterobacter</i> sp., <i>Methylobacterium</i> sp., <i>Microbacterium</i> sp., <i>Pantoea</i> sp., <i>Plantibacter</i> sp., <i>Pseudomonas</i> sp., <i>Ralstonia</i> sp., <i>Rhodococcus</i> sp., <i>Sphingobium</i> sp., and <i>Sphingomonas</i> sp. Thus, indigenous phyllosphere microorganisms could partially metabolize tagatose laid on plant leaves after spray application, reducing the persistence of this fungal inhibitor on tomato leaves.