| sanitation | the removal and burning of infected plant parts, decontamination of tools, equipment, hands, etc. |
| saturated | full to capacity; in soil - very wet. |
| sawfly | not a fly - a primitive wasp. |
| scab | a roughened, crustlike diseased area on the surface of a plant organ or the common name of a disease in which such areas form. |
| scorch | "burning" of leaf margins as a result of infection or unfavorable environmental conditions. |
| sepals | one of the units comprising the calyx; a usually green foliaceous element subtending the corolla. |
| serrations | "tooth-like" edge at leaf margin. |
| sheaths | any elongated, more or less tubular structure enveloping an organ or part. |
| shepherds crook | appears like the handle or bent end of a walking cane. |
| shothole | a symptom in which small diseased fragments of leaves fall off and leave small holes in their place or small holes in wood resulting from beetle boring. |
| silica | silicon dioxide (SiO2) |
| skeletonize | feeding by certain insects which leads to the elimination of all or most of the leaf tissue - often leaving only the veins. |
| smut | a disease caused by the smut fungi, characterized by masses of dark, powdery spores. |
| sooty mold | a sooty coating on foliage and fruit formed by the dark hyphae of fungi that live in the honeydew secreted by insects such as aphids, mealybugs, scales, and whiteflies. |
| spikelets | (1) a secondary spike; (2) one part of a compound inflorescence which of itself is spicate; (3) the floral unit, or ultimate cluster, of a grass inflorescence comprised of flowers and their subtending bracts. |
| spikes | (1) a usually unbranched, elongated, simple, indeterminate inflorescence whose flowers are sessile; the flowers may be congregated or remote; (2) a seemingly simple inflorescence whose "flowers" may actually be composite heads (Liatris). |
| sporadic | irregular events such as insect population outbreaks that are largely unpredictable. |
| spores | comprised of a single gametophytic cell, it functions as the reproductive unit of fungi and some primitive plants. |
| stamens | the unit of the androecium and typically comprised of anther and filament, sometimes reduced to only an anther; the pollen-bearing organ of a seed plant. |
| sterile | barren, not able to produce seed. |
| stippling | the appearance of tiny white or yellow green spots on leaves resulting from mite, leafhopper, etc. feeding. |
| stipules | a basal appendage of a petiole, usually one at each side, often ear-like and sometimes caducous (falls of easily). |
| stolons | a horizontal stem that roots at its tip and there gives rise to a new plant. |
| succulent | bearing a thickened, juicy, soft, fleshy appearance (e.g., new leaves, or thick-leaved plants like cactus). |
| symptoms | the external and internal reactions or alterations of a plant as a result of a disease, insect, or mite. |
| systemic | spreading internally throughout the plant. |