TERMS AND DEFINITIONS
The following definitions were developed by WSSA committees. They are included here for the convenience of Herbicide Handbook readers and to encourage the use of standardized terminology in WAAS publications. Some terms are defined only in their specific weed science context, while recognizing that other definitions apply for common and general English usage. Soil terms were taken from a December 1, 1978 report of the WSSA Soil Terminology Subcommittee including J. Boehle, Jr. (chair), J. Alexander, E. Chamberlain, D. Finnerty, A. Hiltbold, C. Reick, and K. Savage (reviewed by D. E. Smika). Other terms were compiled by the WSSA Terminology Committee including T. R. Harger (chair), P. A. Banks, A. R. Bell, J. H. Dawson, W. R. Mullison, D. T. Patterson, and J. R. Teasdale (with assistance from J. B. Baker, D. E. Davis, L. M. Kitchen, and B. Truelove).
Absorption – The process by which a herbicide passes from one system into another, e.g., from the soil solution into a plant root cell or from the leaf surface into the leaf cell.
Acid equivalent (ae) – The theoretical yield of parent acid from a pesticide active ingredient which has been formulated as a derivative.
Acid soil – Soil with a pH value <7.0.
Acropetal – Toward the apex of a plant organ; generally upward in shoots and downward in roots. Opposite of basipetal.
Activation – The process by which a surface applied herbicide is moved into the soil where it can be absorbed by emerging seedlings. This is normally accomplished by rainfall, irrigation, or tillage. Activation does not imply any chemical change in the active ingredient.
Active ingredient (ai) – The chemical herbicide formulation primarily responsible for its phytotoxicity and which is identified as the active ingredient on the product label.
Acute toxicity – The quality or potential of substance to cause injury or illness shortly after exposure. See chronic toxicity.
Adjuvant – Any substance in an herbicide formulation or added to the spray tank to modify herbicidal activity or application characteristics.
Adsorption – The process by which an herbicide associates with a surface, e.g., a soil colloidal surface.
Agroecosystem – An ecosystem managed for crop production.
Alkaline soil – Soil with a pH >7.0.
Allelopathy – The adverse effect on the growth of plants or microorganisms caused by the action of chemicals produced by other living or decaying plants.
Anion exchange capacity – The sum total of exchangeable anions that a soil can adsorb. Expressed as moles or mmoles of positive charge per kg of soil (or other exchange material).
Apoplast – The total, non-living continuum in a plant, including cell walls, intercellular spaces, and the xylem vessels, that forms a continuous permeable system through which water and solutes may move.
Antagonism – An interaction of two or more chemicals such that the effect when combined is less than the predicted effect based on the activity of each chemical applied separately.
Antidote – (1) A chemical applied to prevent the phytotoxic effect of a specific herbicide on desirable plants (Synonymous with protectant). (2) A substance used as a medical treatment to counteract herbicide poisoning.
Available nutrient – That quality of a nutrient element or compound in the soil that can be readily absorbed and assimilated by growing plants.
Available water – The portion of water in a soil that can be absorbed by plant roots; considered by most workers as the amount of water decreased from field capacity to 1500 joules/kg.
Band treatment – applied to a linear restricted strip on or along crop rows rather than continuous over the field area.
Basal treatment – applied to encircle the stem of a plant just above the soil surface such that foliage contact is minimal. A term used mostly to describe treatment of woody plant.
Base-saturation percentage – The extent to which the adsorption complex of a soil is saturated with exchangeable cations other than hydrogen. It is expressed as a percentage of the total cation exchange capacity.
Basipetally – Toward the base of a plant organ; generally downward in shoots and upward in roots. Opposite of acropetal.
Bed – (1) A ridge or elevated strip of soil formed for planting crops above furrows on each side. (2) An area in which seedlings or nursery stock are grown for later transplanting in the field.
Bioassay – Quantitative or qualitative determination of herbicide by use of sensitive indicator plants or other biological organisms.
Biological control of weeds – Control or suppression of weeds by the action of one or more organisms, through natural means, or by manipulation of the weed, organism, or environment.
Biotic interference – The adverse effect of one organism or population in a common ecosystem on another by attracting, encouraging, or harboring one or more intermediate organisms.
Biotype – A population within a species that has a distinct genetic variation.
Blind cultivation – Cultivation before seeded crops emerge.
Boot or Booting – A growth stage of grasses (including cereal crops) when the upper leaf sheath swells due to the growth of the developing spike or panicle.
Broadcast rate equivalent – For band treatments, it is the amount of herbicide applied per unit area when only the band area is considered. All rates for band treatment should be expressed as the broadcast rate equivalent. Broadcast treatment – Applied as a continuous sheet over the entire field.
Brush control – Control of woody plants such as brambles, sprout, clumps, shrubs, trees, and vines.
Calcareous soil – Soil containing sufficient free calcium carbonate or calcium-magnesium carbonate to effervesce visibly when treated with cold 0.1 M HCI in water.
Caliche – A layer near the surface, more or less cemented by secondary carbonates of CA or Mg precipitated from the soil solution. It may occur as a soft then soil horizon, as a hard thick bed beneath the solum, or as a surface layer exposed by erosion.
Carcinogenic – Capable of causing cancer in animals.
Carrier – A gas, liquid, or solid substance used to dilute or suspend a herbicide during its application.
Cation exchange capacity (CEC) – The sum total of exchangeable cations that a soil can adsorb. Expressed as moles or mmoles of negative charge per kg of soil (or other exchange material).
Chemical name – The systematic Name of a chemical compound according to the rules of nomenclature of the international union of pure and applied chemistry (IUPAC), chemical abstracts service, or other organization. Chemical names presented in this handbook are those of the chemical abstracts’ service.
Chemotype – A group of organisms that produce the same profile for a particular class of chemicals such as chalcones, aurones, flavanols, etc.
Chiorosis – Loss of green color (chlorophyll) from foliage.
Chronic toxicity – The quality or potential of a substance to cause injury or illness after repeated exposure over and extended period of time.
Clay – (1) A soil separate consisting of particles <0.002 mm in equivalent diameter (2) A soil textural class; soil containing 40% or more clay, <45% sand, and < 40% silt.
Clay loam – A soil textural class; soil containing 27-40% clay and 20-45% sand.
Clod – A compact, coherent mass of soil ranging in size from 5-10 mm to as much as 20 or 25 cm; produced artificially, usually by the activity of man by tillage, digging, etc., especially when these operations are performed on soils that are either too wet or too dry for normal tillage operation.
Coarse-textured soil – The texture exhibited by sands, loamy sands, and sandy loams except very fine sandy loam.
Common name – A generic name for a chemical compound.
Community – The populations of species living in a common ecosystem.
Compatibility – The characteristic of a substance, especially a pesticide, of being mixable in a formulation or in a spry tank for application in the same carrier without undesirably altering the characteristics or effects of the individual components.
Competition – The active acquisition of limited resources by an organism which result in a reduces supply and consequently reduced growth of other organisms in a common environment. Concentration – For herbicides, the quantity of active ingredient or parent compound equivalent expressed as moles or mass per unit volume or per unit mass of the resulting solution or mixture. Expressions of percent should be avoided or used only for expressions of mass per mass.
Contact applicator – A device that applies a herbicide to plants by direct contact of the applicator and the plant.
Contact herbicide – An herbicide that causes injury to only the plant tissue to which it is applied, or a herbicide that is not appreciably translocated within plants.
Cracking – The time just prior to seedling emergence when the soil cracks and the surface is pushed upward by growth of the emerging seedling.
Crust – A surface layer on soils, ranging in thickness from a few millimeters to perhaps as much as 3 cm, that is much more compact, hard, and brittle when dry, than the material immediately beneath it.
Defoliant – A chemical that causes the leaves to abscise from a plant.
Desiccant – Any substance or mixture of substances used to accelerate the drying of plant tissue.
Dicot – Abbreviated term for dicotyledon; preferred in scientific literature over broadleaf to describe plants.
Dicotyledon (dicot) – A member of the Dicotyledoneae; one of two classes of angiosperms usually characterized by the following: two seed leaves (cotyledon), leaves with net venation, and root systems with tap roots.
Diluent – Any gas, liquid, or solid material used to reduce the concentration of an active ingredient in a formulation.
Direct application – Precise application to a specific area or plant organ such as to a row or bed or to the leaves or stems of plants.
Dispersible granule – A dry granular formulation that will separate or disperse to form a suspension when added to water.
Dormancy – A loose, finely granular, or powdery condition on the surface of the soil, usually produced by shallow cultivation.
Ecosystem – An ecological entity consisting of the biotic community and the non-living environment functioning together in an inseparable interacting system.
Ecotype – A population within a species that has developed a distinct morphological or physiological characteristic (e.g., herbicide resistance) in response to a specific environment and that persists when individuals are moved to a different environment.
Edaphic – (1) Of or pertaining to the soil. (2) resulting from or influenced by factors inherent a soil or other substrate, rather than by climatic factors.
Emergence – The event in seedling establishment when a shoot becomes visible by pushing through the soil surface.
Emersed plant – A rooted or anchored aquatic plant adapted to grow with most of its leaf-stem tissue above the water surface and not lowering or rising with the water level.
Emulsifiable concentrate (EC) – A single phase liquid formulation that forms and emulsion when added to water. See abbreviations and symbols section for the official GIFAP definition used elsewhere in this handbook.
Emulsifier – A substance that promotes the suspension of one liquid in another.
Emulsion – One liquid suspended as minute globules in another liquid (e.g., oil dispersed in water).
Encapsulated formulation – Herbicide enclosed in capsules (or beads) of material to control the rate of release of active ingredient and thereby extend the period of activity.
Environment – The sum total of all biological and physical factors affecting an organism, population, or community.
Epinasty – That state in which more raped growth on the upper side of a plant organ or part (especially leaf) causes it to bend or curl downward.
Exchange capacity – The total ionic charge of the adsorption complex active in the adsorption of ions. See Anion exchange capacity and cation exchange capacity.
Extender – A chemical that increases the longevity of a herbicide in soil.
Fertilizer – Any organic or inorganic of natural or synthetic origin that is added to a soil to supply one or more elements essential to the growth of plants.
Field capacity – The percentage (expressed on the basis of weight or volume) of water remaining in a soil 2 or 3 after having been saturated and after free drainage has practically ceased.
Fined-textured soil – Consisting of or containing large quantities of the fine fractions, particularly of silt and clay. Includes clay loam, sandy clay loam, silty clay loam, sandy clay, silty clay, and clay textural classes. Sometimes subdivided into clayey texture and moderately fine texture. See soil texture.
Floating plant – A free-floating or anchored aquatic plant adapted to grow with most of its vegetative tissue at or above the water surface and lowering or rising with the water level.
Flowable – A two-phase formulation containing solid herbicide suspended in liquid and that forms a suspension when added to water.
Formulation – (1) A pesticide preparation supplied by manufacturer for practical use. (2) the process, carried out by manufacturers, of preparing pesticides for practical use.
Frill treatment – placement of a herbicide into a series of overlap-ping ax cuts made through the bark in a ring around the trunk of a tree.
Genotype – The entire genetic constitution or set of genes possessed by an organism.
Germination – The process of initiating growth in seeds.
Granular – A dry formulation consisting of discrete particles generally <10 mm3 and designed to be applied without a liquid carrier. See Abbreviations and Symbols section for the official GIFAP definition used elsewhere in this handbook.
Green manure – A Plant material incorporated into the soil while green, or soon after maturity, for improving the soil.
Habitat – The physical location or type of environment in which an organism is normally found.
Hardpan – A hardened soil layer, in the lower A or in the B horizon, caused by cementation of soil particles with organic matter or with materials such as silica, sesquioxides, or calcium carbon-ate. The hardness does not change appreciably with changes in moisture content and pieces of the hard layer do not slake in water.
Head or Heading – A growth stage of grasses (including cereal crops) when the spike or panicle is emerging or has emerged from the sheath.
Herbaceous plant – A vascular plant that does not develop persistent woody tissue above ground.
Herbicide – A chemical substance or cultured biological organism used to kill or suppress the growth of plants.
Herbicide modifier – A chemical substance used with herbicides to change their herbicidal properties by a physiological mechanism. They include safeners, synergists, extenders, etc., but do not include compounds such as surfactants that may modify herbicidal activity by chemical or physical mechanisms.
Humus – (1) That more or less stable fraction of the soil organic matter remaining after the major portion of added plant and animal residues have decomposed. Usually it is dark colored. (2) Includes the F and H layers in undisturbed forest soils. See Soil organic matter.
Incorporate – To mix or blend a herbicide into soil.
Interference – For plants; the total adverse effect that plant exert on each other when growing in a common ecosystem. The term includes competition, allelopathy, biotic interference, and other detrimental modifications in the community or environment.
Invert emulsion – The suspension of minute water droplets in a continuous oil phase.
Joint or Jointing – A growth stage of grasses (including cereal crops) when stem internodes begin elongating.
Label – The directions for using a pesticide approved as a result of the registration process.
Lateral movement – Movement of a herbicide through soil, generally in a horizontal plane, from the original site of application.
Layby application – Applied and incorporated with or applied after the last cultivation of a crop.
LC50 – The concentration of a substance in air (inhalation toxicity), water (aquatic toxicity) or continual exposure in the diet that will kill 50% of the organisms in a specific test situation.
LD50 – The dose (quantity) of a substance that will be lethal to 50% of the organisms in a specific test situation. It is expressed in weight of the chemical (mg) per unit of body weight (kg) and the toxicant may be fed (oral LD50), applied to the skin (Dermal LD50), or administered in the form of vapors (Inhalation LD50)
Leaching – (1) The removal of materials in solution from the soil. (2) The downward movement of material(s) into a soil profile with soil water (material may or may not be in true solution and may or may not move from soil).
Lime, agricultural – A soil amendment consisting principally of calcium carbonate, but including magnesium carbonate and perhaps other materials used to neutralize soil acidity and furnish calcium and magnesium for the growth of plants.
Loam – A soil texture class; soil containing 7-27% clay, 28-50% silt, and <52% sand.
Loamy sand – A soil texture class; soil containing no more than 85-90% sand, and the percentage of silt plus 1.5 times the percentage of clay is not less than 15%; also, it contains not less than 70-85% sand, and the percentage of silt plus twice the percentage of clay does not exceed 30%
Loamy soil – Intermediate in texture and properties between fine and coarse-textured soils. Includes all textural classes with the words “loam” or “loamy” as a part of the class name, such as clay loam or loamy sand. See soil texture.
Macronutrient – A chemical element necessary in relatively large amounts (usually greater than 500 ppm in the plant) for the growth pf plants. These elements consist of C, H, 0, Ca, Mg, K, P, 5, and N.
Medium-textured soil – Intermediate between a fine- and coarse-textured soil. Includes very fine sandy loam, loam, silt loam, and silt textural classes.
Metabolite – A compound derived from metabolic transformation of an herbicide by plants or other organisms.
Micronutrient – A chemical element necessary only in extremely small amounts (usually <50 ppm in the plant) for the growth of plants. These elements consist of B, Cl, Cu, Fe, Mn, Mo, and Zn.
Mineral soil – A soil consisting predominantly of, and having its properties determined predominantly by, mineral matter. Usually contains <20% organic matter, but may contain an organic surface layer up to 30 cm thick.
Moisture tension (or pressure) – The equivalent negative pressure in the soil water. It is equal to the equivalent pressure that must be applied to the soil water to bring it to hydraulic equilibrium, through a porous permeable wall or membrane, with a pool of water of the same composition.
Monocot – Abbreviated term for monocotyledon; preferred in scientific literature over grass to describe plants.
Monocotyledon (monocot) – A member of Monocotyledoneae; one of two classes of angiosperms, usually characterized by the following: one seed leaf (cotyledon), leaves with parallel venation, root systems arising adventitiously and usually diffuse (fibrous).
Muck soil – (1) A soil containing between 20 and 50% of organic matter. (2) An organic soil in which the organic matter is well decomposed (USA usage).
Mulch – (1) Any material such as straw, sawdust, leaves, plastic film, loose soil, etc., that is spread on the surface of the soil to protect the soil and plant roots from the effects of raindrops, soil crusting, freezing, and evaporation, or to control weeds.
Mutagenic – Capable of causing genetic changes.
Nastic movement – Movement of the flat plant part (as a leaf or bud scale) that is oriented in respect to the plant rather than an external source of stimulation, is brought about by disproportionate growth of increase of turgor in the tissues of one surface of the part, and typically involves a curling or bending outward or inward of the whole part in a direction away from the more active surface.
Necrosis – Localized death of tissue usually characterized by browning and desiccation.
Neutral soil – A soil in which the surface layer, at least to normal plow depth, is neither acid nor alkaline in reaction. See Acid soil, Alkaline soil, Soil pH, and Soil reaction.
Niche – The functional role of an organism in an ecosystem.
Non-selective herbicide – An herbicide that is generally toxic to all plants treated. Some selective herbicides may become non-selective if used at very high rates.
Non-target species – A species not intentionally affected by a pesticide.
No-till – Planting crop seed directly into stubble or sod with no more soil disturbance than is necessary to get the seed into the soil.
Noxious weed – A plant regulated or identified by law as being undesirable, troublesome, and difficult to control. Precise definition varies according to legal interpretation.
Nyctinasty – A nastic movement (as the opening and closing of sunflower) that is associated with diurnal changes of temperature or light intensity.
Oncogenic – Capable of producing or inducing tumors in animals, either benign (non cancerous) or malignant (cancerous).
Organic soil – A soil that contains a high percentage (> 15 or 20%) of organic matter through out the upper and most weathered part of the soil profile (solum).
Overtop application – A broadcast or banded application applied over the canopy of crops such as by airplane or a raised spray boom of ground equipment.
Peat soil – An organic soil containing more than 50% organic matter. Used in the United States to refer to the stage of decomposition of the organic matter, “peat” referring to the slightly decomposed or undecomposed deposits and “muck” to the highly decomposed materials.
Pelleted formulation – A dry formulation consisting of discrete particles usually larger than 10 mm3 and designed to be applied without a liquid carrier.
Persistent herbicide – A herbicide that, when applied at the recommended rate, will harm susceptible crops planted in normal rotation after harvesting the treated crop, or that interferes with regrowth of native vegetation in non-crop sites for an extended period of time. See Residual herbicides.
Phenotype – The characteristics of an organism as determined by the interaction of its genetic constitution and the environment.
Phloem – The living tissue in plants that functions primarily to transport metabolic compounds from the site of synthesis or storage to the site of utilization.
Phytotoxic – injurious or lethal to plants.
Plant growth regulator – A substance used for controlling or modifying plant growth processes without severe phytotoxicity.
Population – In ecology, a group of individuals of any one species.
Postemergence (POST) – (1) Applied after emergence of the specified weed or crop. (2) Ability to control established weeds.
Preemergence (PRE) – (1) Applied to the soil before emergence of the specified weed or crop. (2) Ability to control weeds before or soon after they emerge.
Preplant application – Applied before planting or transplanting a crop, either as a foliar application to control existing vegetation or as a soil application.
Preplant incorporated (PPI) – Applied and blended into the soil before seeding or transplanting, usually by tillage.
Rate – For herbicides, a quantity of active ingredient or parent compound equivalent expressed as moles or mass per unit area of treated surface or per unit volume of the treated environment (for aquatic or vapor applications). Rates expressed as formulated product should not be used in scientific publications.
Recirculating sprayer – A sprayer system with the nozzle aimed at a catchment devise that recovers and recirculates herbicide not intercepted by plants.
Registration – The process designated by the federal insecticide, fungicide, and rodenticide Act (FIFRA) and carried out by the environmental protection agency (EPA) by which a pesticide legally approved for use in the U.S.
Residual herbicide – A herbicide that persists in the soil and injures or kills germinating weed seedlings for a relatively short period of time after application. See persistent herbicide.
Residue – That quantity of an herbicide or metabolite remaining in or on the soil, plant parts, animal tissues, whole organisms, and surfaces.
Safener – A substance that reduces toxicity of herbicide to crop plants by a physiological mechanism.
Saline soil – A non-sodic soil containing sufficient soluble salt to impair its productivity. The electrical conductivity of the saturation extract is greater than 2 decisiemens per meter (dS/m) at 25 C.
Sand – (1) A soil separate consisting of particles between 0.05 and 2.00 mm in equivalent diameter. (2) A soil textural class; soil containing 85% or more of sand; percentage of silt plus 1.5 times the percentage of clay shall not exceed 15%.
Sandy clay – A soil textural class; soil containing 35% or more clay and 45% or more sand.
Sandy clay loam – A soil textural class; soil containing 20-35% clay, <28% silt, and 45% or more sand.
Sandy loam – A soil textural class; soil containing either 20% clay or less, and the percentage of silt plus twice the percentage of clay exceeds 30%, and 52% or more sand; or <7% clay, <50% silt, and 43-52% sand.
Seed protectant – (1) A substance applied to seed before planting to control pests. (2) A substance applied to seed to prevent injury from herbicides by a physical mechanism such as absorption.
Selective herbicide – A chemical that is more toxic to some plant species than to others.
Silt – (1) A soil separate consisting of particles between 0.05 and 0.002 mm in equivalent diameter. (2) A soil textural class; soil containing 80% or more silt and <12% clay.
Silt loam – A soil textural class; soil containing 50% or more silt and 12-27% clay or it contains 50-80% silt and <12% clay.
Silt clay – A soil textural class; soil containing 40% or more clay and 40% or more silt.
Silty clay loam – A soil textural class; soil containing 27-40% clay and <20% sand.
Soil amendment – Any substance added to the soil that alters soil properties. Examples are gypsum, lime fertilizers, sawdust, etc.
Soil buffer compounds – The clay, organic matter, and compounds such as carbonates and phosphates that enable the soil to resist appreciable change in pH.
Soil bulk density – The mass of dry soil per unit bulk volume. The bulk volume is determined before drying to constant weight at 105 C.
Soil class – A group of soils having a definite range in a particular property such as acidity., degree of slope, texture, structure, land use capacity, degree of erosion or drainage, see Soil texture and Soil structure.
Soil fertility – The status of a soil with respect to its ability to supply the nutrients essential to plant growth.
Soil injection – Placement of the herbicide beneath the soil surface with a minimum of mixing or stirring of the soil as with an injection blade, knife, or tine.
Soil-layered – Placement of the herbicide beneath the soil surface in a continuous layer with a minimum of mixing.
Soil organic matter – The organic fraction of the soil: includes plant and animal residues at various stages of decomposition, cells and tissues of soil organisms, and substances synthesized by the soil population. Usually determined on soils that have been sieved through a 2.0-mm sieve. See humus.
Soil pH – The negative logarithm of the hydrogen-ion concentration of a soil. The degree of acidity or (alkalinity) of a soil as determined by means of a glass, quinhydrone, or other suitable electrode or indicator at a specified moisture content or soil-water ratio, and expressed in terms of the pH scale.
Soil reaction – The degree of acidity or alkalinity of a soil, usually expressed as a pH value. Descriptive terms commonly associated with certain ranges in pH are: extremely acid < 4.5; very strongly acid, 4.5-5.0; strongly acid, 5. 1-5.5; moderately acid, 5.6-6.0; slightly acid, 6. 1-6.5; neutral, 6.6-7.3; slightly alkaline, 7.4-7.8; moderately alkaline. 7.9-8.4; strongly alkaline, 8.5-9.0; and very strongly alkaline, >9.1.
Soil separates – Mineral particles, <2.0 mm in equivalent diameter, ranging between specified size limits. The names and size limits of separates recognized in the United States are: very coarse sand, 2.0-1.0 mm; coarse sand, 1.0-0.5 mm; medium sand, 0.5-0.25 mm; fine sand, 0.25-0.10 mm; very fine sand, 0.10-0.05 mm; silt, 0.05-0.002 mm; and clay <0.002 mm.
Soil structure – The combination or arrangement of primary soil particles into secondary particles units, or peds. These secondary units may be, but usually are not, arranged in the profile in such a manner as to give a distinctive characteristic pattern. The secondary units are characterized and classified on the basis of size, shape, and degree of distinctness into classes, types, and grades, respectively.
Soil texture – The relative proportions of the various soil separates in a soil as described by the classes of soil texture: sand, loamy sand, sandy loam, loam, silt loam, silt, sandy clay loam, clay loam, silty clay loam, sandy clay, and clay. Textural classes may be modified by the addition of suitable adjectives when coarse fragments are present in substantial amounts; for example, “stony silt loam”, or “ silt loam, stony phase”. The sand, loamy sand, and sandy loam are further subdivided on the basis of the proportions of the various sand separates present.
Soil type – the lowest unit in the natural system of soil classification; a subdivision of a soil series and consisting of or describing soils that are alike in all characteristics including the texture of the horizon.
Soluble concentrate – A liquid formulation that forms a solution when added to water. See Abbreviations and Symbols section for the official GTFAP definition used elsewhere in this handbook.
Soluble granule – A dry granular formulation that forms a solution when added to water. See Abbreviations and Symbols section for the official GIFAP definition used elsewhere in this handbook.
Soluble powder – A dry formulation that forms a solution when added to water. See Abbreviations and Symbols section for the official GIFAP definition used elsewhere in this handbook.
Solum (plural: Sola) – The upper and most weathered part of the soil profile; the A and B horizons.
Solution – A homogeneous or single phase mixture of two or more substances.
Spot treatment – A herbicide applied to restricted area(s) of a whole unit; i.e., treatment of spots or patches of weeds within a larger field.
Spray drift – Movement of airborne spray from the intended area of application.
Submersed plant – An aquatic plant that grows with all or most of its vegetative tissue below the water surface.
Surface soil – The uppermost part of the soil ordinarily moved in tillage, or it is equivalent in uncultivated soils and ranging in depth from 8 or 10 cm to 20 or 25 cm. frequently designated as the “plow layer”, the “AP layer”, or the “AP horizon”.
Surfactant – A material that improves the emulsifying, dispersing, spreading, wetting or other properties of a liquid by modifying its surface characteristics.
Susceptibility – The sensitivity to or degree to which a plant is injured by a herbicide treatment.
Suspension – A mixture containing finely divided particles dispersed is a soil, liquid, or gas.
Symplast – The total mass of continuous living cells in a plant connected by plasmodesmata and including the phloem.
Synergist – For herbicides; a non-herbicidal compound used to increase the phytotoxicity of an herbicide by physiological mechanism.
Systemic – Synonymous with translocated herbicide, but more correctly used to describe the property of insecticide of fungicides that penetrate and disperse through out a plant.
Tank-mix combination – Mixing of two or more pesticides or agricultural chemicals in the spray tank at the time of application.
Teratogenic – Capable of producing birth defects.
Tiller or Tillering – A growth stage of grasses (Including cereal crops) when additional shoots are developing from the crown.
Toxicity – The quality or potential of a substance to cause injury, illness, or other undesirable effects.
Toxicology – The study of the principles or mechanisms of toxicity.
Trade name – A trademark or other designation by which a commercial product is identified.
Translocated herbicide – An herbicide that is moved within the plant. Translocated herbicides may be either phloem mobile or xylem mobile. However, the term frequently is used in a more restrictive sense to refer to herbicides that are applied to the foliage and move downward through the phloem to underground parts.
Vapor drift – The movement of pesticides as vapor from the area of application after the spray droplets have impinged on the target.
Water content – The amount of water lost from the soil upon drying to constant weight at 105 C; expressed as either the mass of water per unit mass of dry soil or as the volume of water per unit bulk volume of soil.
Weed –a plant that causes economic losses or ecological damage, creates health problems for humans or animals, or is undesirable where it is growing.
Weed control – The process of reducing weed growth and/or infestation to an acceptable level.
Weed eradication – The elimination of all vegetative plant parts and viable seeds of a weed from a site.
Wetting agent – (1) A substance that serves to reduce the interfacial tensions and causes spray solutions or suspensions to make better contact with treated surfaces (see surfactant). (2) A substance in a wettable powder formulation that causes it to wet readily when added to water.
Wettable powder (WP) – A finely divided dry formulation that can be readily suspended in water. See Abbreviations and Symbols section for the official GIFAP definition used elsewhere in this handbook.
Xylem – The non-living tissue in plants that functions primarily to conduct water and mineral nutrients from roots to the shoot.