Encyclopedia Article

Terms Used to Describe Plant Problems (including plant disease, insect damage and disorders)

Signs—the actual agent causing the symptoms. Examples of signs are presented underlined for example: (e.g., conk, frass, honeydew, etc.)

Symptom—visible response of a plant to a disease or insect (. Examples of symptoms are presented italicized: blight, spots, wilt, etc.).


Anthracnose—a type of sunken and or/discolored lesions on leaf, stem, or fruit lesions.

Bleeding—sap flowing from a wound, in some cases with a distinctive red tone.

Blight—general and rapid death of leaves, branches, twigs, or flower parts.

Blister—swollen, raised area on a leaf or other plant part.

Bronzing—a yellow or golden discoloration of leaves caused by a very high density of tiny spots or speckles that coalesce.

Canker—a localized wound or dead and discolored area on the bark, often sunken.

Conk—a fungal structure, usually formed by wood rot fungus, that commonly extends from the bark in a shelflike fashion.

Chlorosis—abnormally yellow leaf tissue.

Decline—plants growing poorly, often with small, discolored leaves; some defoliation and dieback may
be present.

Defoliation—loss of foliage; either leaf drop or disappearance of leaf tissue by chewing damage.

Dieback—progressive death of twigs or branches, beginning at their tips and advancing toward their base.

Emergence holes—randomly scattered, small, round holes through bark that connect to tunnels made by wood boring beetles inside wood.

Fecal specks or Frass—small, dark, shiny drops of dried excrement from insects on the surface of leaves or fruit; also known as varnish spots.

Gall—a swelling or overgrowth of plant tissue; may be caused by insects, mites, fungi, bacteria, or other organisms.

Gallery—a collection or pattern of small tunnels radiating from a single source, such as is made by certain insects.

Girdling roots—roots that are tightly coiled around the trunk of a tree, above or below ground.

Honeydew—a sticky fluid rich in sugars, excreted by certain insects such as aphids, scales, mealybugs, and whiteflies.

Leaf mining—damage within a leaf caused by an insect that lives inside the leaf and feeds between the upper and lower surfaces; may be a winding, narrow tunnel or an irregular blotch.

Leaf spot—a well-defined dead area on a leaf.

Lesion—a localized area of discolored, diseased tissue.

Necrosis–death of plant cells, usually resulting in darkening of the tissue.

Pustule—a small, blister-like swelling.

Rot—decay or decomposition of tissue.

Scab—roughened, crustlike areas on the surface of fruit, leaves, tubers, etc., usually slightly raised or sunken and cracked, giving a scabby appearance.

Skeletonization—results from the feeding pattern of certain leaf-feeding insects; only the leaf veins remain and the material between the veins is missing.

Scorch—browning of leaf margins or tips.

Shot-hole—a symptom produced by the dropping out of the dead center of a leaf spot, leaving a hole in the leaf.

Signs—the actual agent causing the symptoms. Examples are pathogen structures or insect bodies and their products. Often magnification is needed to observe signs.

Sooty mold—a dark, usually black fungus growing on honeydew secreted by insects, and producing a soot-like covering on leaves, stems, and fruit.

Symptom—visible response of a plant to a disease or insect (e.g., leaf yellowing or browning, spots on leaves, wilt, etc.).

Tent—a structure of silk constructed by leaf-feeding caterpillars.

Tunnel—linear holes within wood produced by beetle larvae or moth caterpillars as they feed.

Web—see “tent.”

Wilt—loss of rigidity and drooping of plant parts, generally caused by a disturbance in the water-conducting tissues (xylem) of a tree.

Window-paning—results from the feeding pattern of certain leaf-feeding insects; similar to skeletonization in that the material between the veins has been eaten, leaving the veins, but also leaving a thin translucent layer of the upper or lower epidermis.

Witches’ broom—a cluster of small twigs arising from the same point on a branch or trunk.

Original from the new edition of the publication Identifying Tree Problems available at the extension store to download for free