Which condition is characterized by a soot-like exterior on plants?

The condition characterized by a soot-like exterior on plants is sooty mold. This phenomenon occurs when fungal growth develops on the surface of leaves and stems due to the accumulation of honeydew, a sugary substance secreted by sap-sucking insects such as aphids or whiteflies. The dark, soot-like appearance is the result of the fungal spores that overlay this honeydew.

Sooty mold does not harm the plant directly, but it can impede photosynthesis by blocking sunlight from reaching the leaves. This can result in reduced plant vigor and health over time if the insect infestation is not managed. Unlike other choices, such as verticillium wilt, which is a vascular disease affecting the plant at a systemic level, or rust and rose mosaic virus, which affects plants through specific viral or fungal pathogens, sooty mold primarily results from environmental conditions related to insect activity.