Ants cut leaves that contained both high or low levels of fungi, but they took longer to cut leaves from the high endophyte treatment. Moreover, the leaf preparation process by the ants significantly lowered the amount of fungi in leaf pieces before they were placed into the fungal garden. The Petri plate experiment also showed that the garden fungus reduced the growth rate for 28 of the 32 endophytic fungal strains that were tested, with a stronger effect for more rapidly growing endophyte strains. This suggests that, apart from the hygiene practiced by the ants, the garden itself can compete with incoming microbes.

"Fungi in the leaves were not welcome in the leaf cutter ants' garden," concluded Van Bael

I see leaf cutter ants almost daily, marching in line carrying bits of bright green leaf. Knowing that they are active gardeners and practice hygiene (!), makes them even more interesting to watch. Thanks for the clip!