(Singular, Fungus) Molds, mildews, yeasts, mushrooms, and puff-balls, a group organisms that lack chlorophyll (i.e., are not photosynthetic) and which are usually non-mobile, filamentous, and multicellular. Some grow in the ground, others attach themselves to decaying trees and other plants, getting their nutrition from decomposing organic matter. Some cause disease, others stabilize sewage and break down solid wastes in composting.Fungicide: Pesticides which are used to control, prevent, or destroy fungi.