Plant extracts have been considered for the control the leaf-cutting ants. The objectives of this study were to evaluate the survival leaf-cutting worker ants after topical application of Ageratum conyzoides (mentrasto) and Manihot esculenta (cassava) extracts; and to evaluate the effect of Manihot esculenta hexane extract via ingestion on the survival of the workers of Atta sexdens Forel 1908 isolated or not from their colonies, in order to verify whether the symbiotic fungus Leucoagaricus gongylophorus confers protection to the workers against the extract. First, ten medium workers were removed from their colonies and received the application of 1 μL of extract on the pronotum. The cassava extract (125 µg.mL-1) was diluted in a solution of honey with water for the ingestion bioassay. Five repetitions (ten ants inside a transparent plastic container) were performed in each of the four colonies used in the experiment. The numbers of dead ants were recorded daily until the control also died. The solution of the hexane Manihot esculenta extract gave a significant result at the concentration of 100 µg.mL-1, with 100% of mortatily after 4 days. The ants maintained with the symbiont fungus that ingested the cassava hexanic extract showed a lower mortality rate (40% at the end of 25 days) than the workers who were kept isolated (90%). The symbiosis between the ants and the fungus means more than a food source for leaf-cutting ants because it reduces the toxic effect on the ants when the ants remain in contact with the fungus and is offered an unsafe vegetable.