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Exudate A substance (usually liquid) formed inside a plant and discharged from diseased or injured tissue. The presence of an exudate often aids in diagnosis (e.g., fire blight bacteria). ...

Facultative Parasite An organism that is ordinarily saprophytic but under proper conditions may be parasitic. ...

Facultative Saprophyte An organism that is ordinarily parasitic but under proper conditions may be saprophytic. ...

Fasciation A distortion of a plant caused by an injury or infection that results in thin, flattened, and sometimes curved shoots. ...

Flagellum A long hairlike or whiplike contractile filament protruding from certain bacterial cells and spores of fungi and that enable movement. ...

Flagging The loss of turgor and the drooping of plant parts, usually following a water deficit. The death of a branch in a tree where the leaves remain attached. In either case, the diseased portion stands out like a flag. ...

Fleck A small, white to translucent lesion (spot) visible through a leaf. ...

Frass Excrement of an insect, usually mixed with plant debris. ...

Fruiting Body Any of various complex, spore-bearing fungal structures. ...

Fumigant Vapor-active chemical used in the gaseous phase to kill or inhibit the growth of microorganisms or other pests. ...