Charles and Patterson became primarily responsible for fungus research with the Pathological Collections after the organization of Plant Disease Survey in 1917.

Charles also conducted research and publish articles on the fungal pathogens that North American insects face.

[1] Her knowledge of agarics, specifically the identification of edible and poisonous fungi, meant that for many years she was the government expert.

However, eventually Charles' eyesight weakened to the point that she could no longer use a microscope but she continued writing.

[1] During her career she was author or co-author of over 37 books and scientific papers, as well as assisting other mycologists with descriptions of new species.