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Glossary of Terms

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Dairy ranching
The practice of keeping cows of relatively low milk yield, either indigenous or low-grade exotic crosses especially of dual-purpose breeds, who are parted from their calves in the evenings, milked out in the morning, and spend the day with their calves at foot; the cows are not milked in the evening.

Mother. Alternatively an artificial lake made by constructing a wall of earth or concrete, etc.

The adverse effect on plants or crops due to biotic or abiotic agents, resulting in a reduction of yield and/or quality. Compare with injury.

Dam catchment
Catchment area above a water storage reservoir.

Damping off
The rot of seedlings near soil level or prior to emergence (pre-emergence) or after emergence (post-emergence). Disease or necrotic symptom of disease in seedlings in which the seedling is decayed near the soil line and the seedling topples. Damping-off pathogens may also prevent seed germination and kill the sprout before it emerges from the soil.

A cladoceran (zooplankton) genus that is very common in lake ecosystems and is often used as a test animal for toxicity bioassays.

Data base
The total of all sampling points ('cases') assembled in a convenient form for retrieval and processing.

Data base management
A computerised system which manages data system according to a specific format.

Dauer larva
Nematode juvenile in which development is arrested during unsuitable conditions and resumes when conditions improve.

The least number of days, established by law, between the last pesticide application and the harvest date, as set by law to prevent exposure to a hazardous amount. Same as 'harvest intervals'.

The least number of days permitted by law, between the final pesticide application and the date an animal is to be slaughtered.

Diameter at breast height. This is a standard measure made on a tree that has been correlated with height, leaf area and volume for many tree species.

Digestible crude protein.

Digestible energy; see metabolisable energy.

Debt-servicing capacity
Annual whole farm net cash flow before deducting interest and loan repayments.

Ten-hooked larva that hatches from the egg of cestodarian tapeworm; also called a lycophora.

Plants or trees that shed leaves or awns at a particular season or stage (leaf loss may also be induced by drought etc.).

Decimal code
A detailed, computer-compatible scale describing growth stages in cereals.

Decimal reduction time
Time at a particular temperature to reduce the viable population by 90 percent.

Decision analysis
The logical and quantitative analysis of all the factors that influence a decision.

Decision tree
A decision making technique that shows a branching-off of events arising from different courses of action. The probability of the events occurring can be included in the decision branches.

A heterotrophic organism that utilises dead organic matter as food, decomposing it into more simple substances.

Removal or breakdown of any pesticide chemical from any surface or piece of equipment.

Lying along the ground.

To remove from an organism its commensalistic or mutualistic micro-fauna, for which the organism ordinarily serves as a host.

Deferred grazing
Withholding animals from a pasture for a period of time beyond the normal beginning of the grazing season. The simplest fodder conservation; an area is closed to livestock for the latter half to three-quarters of the rainy period and the pasture is allowed to grow into standing hay.

Deficiency disease
A disease resulting from lack of carbohydrates, proteins, amino acids, fatty acids, vitamins or trace minerals, or other essential constituents and elements of the diet.

Definitive host
Host in which a parasite achieves sexual maturity. If there is no sexual reproduction in the life of the parasite, the host most important to humans is the definitive host.

Deflector nozzle
See nozzle iv.

Increased stability of solids dispersed in a liquid by adding substances which form protective colloids.

Deflocculating agent
Material added to suspension to delay sedimentation.

Any substance or mixture of substances when applied to a plant causes the leaves or foliage to drop, with or without causing abscission.

Removal of shoots.

A compound which causes the leaves or foliage to drop from the plant.

Degenerate code
The genetic code is said to be degenerate because many amino acids are coded for more than one codon.

A general term applied to the breakdown of toxic components by biochemical processes into non-toxic products.

Degree of milling
Expression used to indicate the amount of bran removed in the milling process.

Degrees of freedom
The number of linearly independent observations in a set of n observations. The degrees of freedom are equal to n minus the number of restrictions placed on the entire data set.

The act of swallowing.

To split open along a natural line, especially when associated with discharge of contents, as in the opening of seedpods or the freeing of pollen by the anther.

Opening spontaneously when ripe, e.g. capsules, anthers.

The process of removing husk from the grain during milling.

The absence or loss of water.

Removal of water from a body or tissue; or the condition which results from loss of water.

A class of enzymes which oxidise substrates in the process of removing electrons and hydrogen atoms.

Cervical papillae located in the lateral fields near the base of the neck. Sensory papilla on each side near the anterior end of some nematodes.

Delayed action
As opposed to immediate effect. Some herbicide chemicals (2,4-D; 2,4,5-T; MCP, dalapon) provide a delayed response. Considerable time may elapse before maximum effect can be observed. Usually treated plants stop developing soon after treatment, then gradually die.

Delayed density dependent
A parasite will act as a delayed density dependent mortality factor on the host if its rate of increase is strongly correlated with host density in successive generations, as is assumed in Nicholson's theory.

Delayed hypersensitivity
Manifestation of cell-mediated immunity, distinguished from immediate hypersensitivity in that maximal response is reached about 24 hours or more after intra-dermal injection of the antigen; lesion site is infiltrated primarily by monocytes and macrophages.

A removal of a portion of a gene.

General term to refer to the planned administrative or technical results of a R & D tasks, project or programme.

Deliverables chart
An adaptation of the bar chart, the deliverables chart includes the identification of key results of technical work or completion of administrative tasks associated with the project like periodic activity and status reports to management.

Delphi technique
A forecasting technique carried out in the absence of a relevant database whereby individual experts anonymously give an opinion, and their reasons for it, and the opinions are then circulated and amended until a consensus is reached.

Form of parasitism in which one sex develops parasitically in the body of the opposite sex.

Deltoid (muscle)
A roughly triangular muscle connecting the spine of the scapula to the upper arm.

Interbreeding group in a population; also known as local population.

De minimis risk
A risk that is too small to be of societal concern; risks below 10-5 or 10-6 are generally viewed as de minimis in the United States of America.

Denatured protein
Protein whose properties have been altered by treatment with physical or chemical agents.

A tree diagram used as a graphical display to show the similarity of different entities.

To make anew.

The mass of substance per unit volume at a stated temperature. The units of volume and mass must be clearly stated e.g. grams per millimetre at 20°C. Number of individuals in relation the space in which they occur.

Density dependent
A proportionate increase in mortality (or decrease in fecundity) as population density increases.

Density-dependent factors
Factors whose effects on a population are dependent upon the density of that particular population; density dependence may be direct or inverse.

Density-gradient centrifugation
A centrifugation procedure in which partially purified virus is further clarified by movement through a gradient. Contaminating components may be separated from the virus particles by velocity centrifugation, usually in a low to high sucrose gradient, which separates components, according to their differing sedimentation coefficients, or alternatively, by isopynic centrifugation usually in caesium chloride or caesium sulphate gradients, which separates the components according to their differing buoyant densities.

Density independent
The percentage mortality or the survival varies independently of population density.

Density-independent factors
Factors whose effects on a population are not dependent upon the density of that particular population.

A fatal disease of larvae of the wax moth, Galleriam ellonella, caused by a virus.

A type of maize having kernels that contain both soft and hard starch and thus become indented at maturity.

Small, tooth-like projections.

By an examination of the lower incisors an estimate can be made of the animal's age; indigenous stock, however, do not erupt new teeth as quickly as exotics while intensively reared stock erupt teeth at a rather earlier age than ranch stock. With so many variables, ageing by teeth in the tropics is not usually reliable. Some ranchers report that there is a set-back when the central incisors are cast in hard dry conditions.

The reduction of nitrates to nitrites, ammonia and free nitrogen in the soil under anaerobic conditions, resulting in loss of nitrogen from ecosystems.

Virus disease transmitted by mosquitoes.

Dependent transmission
Transmission of a virus (by aphids) that only occurs when the vector feeds on a source plant that is jointly affected by a second virus. The second virus is referred to as a helper virus, and the virus that is not transmissible on its own is called the dependent virus.

Dependent variable
The predictand in a regression equation (plotted on the x axis). The variable of interest in a regression equation, which is said to be functionally related to one or more independent or predictor variables.

Deoxyribonucleic acid
DNA A polymer of nucleotides connected via a phosphatedeoxyribose sugar backbone; the genetic material of the cell. A polymer composed of the sugar deoxyribose and of nucleic acid bases arranged in such a fashion as to encode the inheritable traits of an organism; the genetic material of an organism.

Quantity of toxicant or the toxicant preparation deposited on a unit area of plant, plant part or other surface at a given application. May refer to the deposit of the total spray preparation, or may refer only to the amount of chemical left after the water evaporates.

Deposit, Spray
Amount and pattern of spray or dust deposited per unit area of plant surface.

The process by which dispersal units terminate their flight by landing on soil and plants, hosts and non-hosts.

Deposition velocity
Velocity at which spray impinges on target surface.

Depot fat
Fat reserves localised within the animal body and used in times of poor nutrition.

The loss in value of capital equipment as it becomes older.

Depreciation allowance
The sum of money which is deducted from income each year so that funds are available to replace equipment etc. when it is worn out.

Dermal toxicity
Toxicity of a material as a result of contact with the skin usually tested on the shaved belly of a rabbit; the property of a pesticide to poison an animal or human when absorbed through the skin.

Fungi that cause superficial mycoses.

A disease occurring in several genera of parasitic nematodes; characterised by necrotic cuticular lesions; the intestinal bacteria of the host mammals have been implicated as causal agents.

Descriptive statistics
That branch of statistics dealing with procedures for summarising the information in a set of measurements and for describing the characteristics of the set.

Deseasonalised series
A time series in which the seasonal component has been estimated and then removed from the series.

A chemical which kills vegetation by inducing rapid desiccation of plant tissue e.g. seed alfalfa or red clover pre-harvest are sprayed with dinitro and oils, usually the foliage is killed by contact action and often seed moisture is reduced, which aids harvest.

Accelerated drying of a plant or plant parts.

Design of an experiment
The sampling procedure that enables the gathering of a maximum amount of information for a given effort.

Epithelium from which the surface is peeling or scaling off. (epithelium)

Removal of the maize tassel, usually to prevent release of pollen in a breeding programme.

Wetting agents that increase the spreading of spray liquids and enable wettable powders to disperse readily in water.

A scalar value involving the sums of products of elements of a square matrix, used in eigenanalysis and in matrix inversion.

When the terminal or central flower of an inflorescence opens first and the prolongation of the axis is arrested.

Determinate growth
The type of development in which a plant ripens all of its seeds at approximately the same time.

A deterministic situation is one in which given inputs lead to predictable outputs.

Deterministic model
A model in which all the relationships are fixed and probability (random elements) does not enter so that a given input produces one exact prediction as an output; opposite of stochastic model.

The inactivation of destruction of a toxin by alteration, binding or breakdown of the toxic molecule. (1) A process, or processes, of metabolism which renders a toxic molecule less toxic by removal, alteration or masking of active functional groups. (2) To treat patients suffering from poisoning in such a way as to reduce the probability and/or severity of harmful effects.

To make an active ingredient in a pesticide or other poisonous chemical harmless and incapable of being toxic to plants and animals.

A measure of the expected harm or loss associated with an adverse event, usually in a manner chosen to facilitate meaningful addition over different events.

Dead organic material in the water column or on the bottom of a water body.

Animals that feed on dead plant or animal material.

That pattern or mode of parthenogenetic reproduction in which progeny of both sexes are produced by unmated females.

Posterior half of a cephaline gregarine protozoan.

In the life cycle of some mesostigmatid mites, a non-feeding stage that moults into the adult.

Incompletely developed larva that hatches from the egg of a chigger mite.

Development budget
A budget used in planning major changes for a farm which will take some time to reach full capacity.

Development phase
Stage of development or progress to reproduction.

Development work
Uses the results of applied research to create the form and substance of a new product, or process, or improve present ones.

Developmental zero
The temperature To at which a given developmental process would cease if the rate of the process was proportional to (T - To).

The difference between anticipated (planned) and actual results (see standard deviation).

The temperature at which a given parcel of air must be cooled (at constant pressure and constant water vapour) in order for saturation to occur.

Diabatic process
A diabatic thermodynamic process is one in which heat enters or leaves the system. Meteorological examples are evaporation, condensation, turbulent mixing, heat conduction, and emission and absorption of radiation. The established equivalent term 'non-adiabatic' is generally preferred because it better emphasises the nature of the processes involved.

Identification of the nature and cause of an illness, ailment of disease on the basis of its signs, symptoms, etiology, pathogenesis, physiopathology, morphopathology etc.; also the decision reached.

Diallel cross
The genetic intercrossing of parents in all combinations of two; all possible crosses among individuals in a group.

A physiological state of arrested development, generally resulting from physical stimuli, such as temperature and light, that provides an insect with a means of surviving unfavourable periods.

1. The thin sheet of muscle and fibrous tissue that separates the thorax from the abdomen. 2. Any thin dividing septum.

Diaphragm pump
See pump ii.

Diapolar cells
Ciliated somatodermal cells located between the parapolar and uropolar cells of a mesozoan.

Diatamaceous earth
A very abrasive, white powder prepared from naturally occurring deposits formed by the silicified skeletons of diatoms; used a diluent in pesticide dust formulations.

An inherited constitutional state whereby an individual is especially prone to a certain disease.

Diauxic growth
Growth occurring in two phases between which a temporary lag occurs.

A pair of haploid nuclei in a cell (derived from male and female thalli) which undergo simultaneous division (conjugate division) upon formation of each new cell. Typified in the diploid phase (dicaryophase) of basidiomycetes.

Forked regularly in two.

Having two cotyledons in each seed, e.g. beans, including flowering plants which are not monocotyledons, the majority of annual weeds and many perennial weeds.

Necrotic symptom of disease in which death of shoot tissues begins at the tip and progresses back towards the main stem.

Condition in which ecdysis processes are going on continuously and one ecdysis cycle grades rapidly into another.

Difference equations
Equations used in population models when changes occur over discrete time intervals (often a generation interval) and therefore have the merit of including some of the time delays which figure so prominently in the real world.

Differential centrifugation
Cycles of low and high speed clarification and sedimentation used in the purification of a virus.

Differential costing
A decision-making technique where only the relevant costs that are likely to differ between alternative courses of action are used for comparison.

Differential cultivar
A cultivar that distinguishes between physiologic races of a pathogen.

Differential equations
Equations used in population models when life cycles have generations that overlap completely and birth and death processes are continuous. Differential equations relate the rate at which the population is changing dN/dt, to the population value at any time N(t) (compare with difference equations).

Differential host
A plant which gives distinctive symptoms when infected with a specific virus, allowing the virus to be distinguished from others.

Differential medium
A culture medium which can be used to distinguish between different micro-organisms.

Differential stain
A staining technique which stains different organisms or tissues in different ways so that they may be distinguished e.g. the Gram stain.

Differential variety
A variety which gives reactions which distinguish between race-specific isolates of a pathogen (see race-specific, Laos analogous to biotype).

Cells with identical, or nearly identical genotype which have become distinct through developmental changes, e.g. muscle cells and liver cells have differentiated from common precursor cells but are phenotypically distinct.

A form of corporate strategy which involves producing products which differ from the competition in ways which buyers value.

The movement of matter or individualss out from a central location. Diffusion models are sometimes used for animal migration.

Digestible Organic Matter
(DMO) A measure of the nutritional value of food to an animal.

Digestible protein
The absorbed portion of protein that has been eaten.

A fungal compartment (often called a cell but fungi are generally better regarded as being coenocytic) containing two genetically distinct haploid nuclei.

Spores containing two sexually compatible nuclei per cell that are common in the basidiomycetes.

Any liquid or solid material serving to dilute or carry an active ingredient and may aid in mechanical application but does not directly influence toxicity e.g. water in sprays, oils in sprays, finely-ground inert materials in dust.

Dilution end-point
The lowest dilution in a serial dilution of a virus preparation, that will infect a mechanically inoculated plant.

Dilution rate
General term to describe the rate of additions to a population from birth and immigrations.

Acronym for 2,4-dihydroxy-7-methoxyl-1,4-benzoxazin-3-one, a naturally occurring compound that confers resistance to certain insect pests in maize.

Consisting of two parts.

A lake that turns over twice a year. A monomictic lake turns over once a year. Lake turnover is when the temperature distribution with depth is constant and where waters can and do mix between all depths of the lake.

Diminishing returns
The phenomenon where increases in variable inputs to a process results in smaller and smaller returns.

Of two forms, as may occur with branches etc.

Dimorphic fungus
A fungus which can exist either in unicellular yeast

A common designation for dinitro-phenols. These materials are used as contact chemicals, as crop defoliants or as a control for succulent annuals.

A group of yellow staining, synthetic organic compounds with acaricidal and insecticidal properties containing two nitro groups and a hydroxyl group in association with aromatic moieties.

Plants in which the male reproductive organs occur in one individual and the female organs in another.

Dioecious aphid
An aphid whose life cycle alternates between a primary and secondary host plant.

Diphasic temperature
A fluctuation in the temperature of an animal's body between a high and a low value.

An infectious disease caused by bacterium Corynebacterium diphtheriae, which establishes itself in the upper respiratory tract and elicits a potent exotoxin which spreads in the blood and may cause death.

Pertaining to a false membrane often covering a lesion in the intestine or lung passages, formed by the solidification of secretions from the lesion.

Having the appearance of a pair of cocci (i.e. spherical bacteria) which have divided incompletely.

Having two homologous chromosomes in pairs in the nucleus so that twice the haploid number is present, usually written as 2n.

Having nuclei associated in pairs.

Strigeoid metacercaria in the family Dislostomatidae.

Larval stage in the life cycle of the monogean Diplozoon.

Dip treatment
The application of a liquid chemical to a plant by momentarily immersing it, wholly or partially, under the surface of the liquid to coat the plant with the chemical. Also, the immersion of livestock in a liquid chemical (usually an insecticide) to control ectoparasites.

Direct cost
A cost which can be specifically allocated to a cost unit (product), say for example, any raw materials used or labour expended.

Direct count
Enumeration of micro-organisms and cells by counting them in a defined area or volume using a microscope.

Direct drilling
Drilling seed directly into soil without any mechanical seedbed preparation e.g. tilling since the previous crop.

Directed application
Placement of spray or dust, of for example a herbicide, so as to avoid or minimise contact with the crop e.g. as a row or bed or to the leaves or stems of weeds.

Direct fixed cost
A fixed cost which can be specifically identified with a product line or segment of activity.

Direct loss
Loss of crop yield by spillage or consumption by insects, rodents and birds.

Co-ordinating the application and expenditure of all resources required to complete a task, project or programme - including labour, supplies, facilities and money.

Directional selection
The adjustment, through natural selection, of a pest population to a change in for instance host resistance or of a host population to a change in the parasitic ability of its pests.

(1) An act of nature or an act of man which is or threatens to be of sufficient severity and magnitude to warrant emergency assistance. (2) A disruption of the human ecology which the affected community cannot absorb with its own resources.

Front plate of a sprayer nozzle having a central orifice.

Stage in plant succession which replaces a true climax because of some disturbance, e.g. fire.

Discoloured grains
Grains which have changed to a yellowish or brownish or black colour because of heat damage during storage or uneven parboiling e.g. rice.

An ascomycete whose fruiting body is an apothecium (e.g. Sclerotinia sclerotiorum).

A calculation used to estimate the present value of future cash flows.

Discounting factor
The value by which a future cash flow must be multiplied to calculate its present value.

Discrete distribution
A probability distribution that only has a finite or countably infinite number of possible values.

Discrete random variable
A random variable over a finite or a countably infinite number of points.

Discrete results
Characteristic of a R & D project component which makes it easy to isolate technical outcomes.

Disc, tarred
Tarred felt disc placed round base of Brassica plant to prevent oviposition by cabbage root fly.

A process, not a thing, that represents the response of an organism to injury that affects its normal structure, functions or economic value and is expressed in characteristic pathological responses called symptoms.

Disease assessment
Any method of disease estimate based on a pre-set standard.

Disease assessment keys
Diagrams of whole plants or individual organs showing different amounts of disease usually expressed on a percentage scale.

Disease cycle
The chain of events involved in disease development, including the stages of development of the pathogen and the effect of the disease on the host.

Disease (damage) rating
An estimate of relative intensity of pests and diseases by means of pre-set classes.

Disease escape
The failure of a host to become diseased because of separation, in space or time, of susceptible host tissues and the infective units of the pathogen.

Disease gradient
The change in incidence of a disease with increasing distance from the source of infection.

Disease incidence
The frequency of diseased or damaged individuals or their parts; commonly the portion of plant units diseased.

Disease intensity
The total amount of disease present.

Disease measurement
See disease assessment.

To free from infection by destruction of a pest established in or on plants or plant parts.

Agent that kills microorganisms e.g. a chemical or other agent that kills or inactivates micro-organisms in animals, seeds or other plant parts, chemicals used to clean or surface sterilise inanimate objects.

To kill pathogens that have not yet initiated disease, but that occur in or on such inanimate objects as soil, tools and so on, or that occur on the surface of such plant parts as seeds.

An agent that kills or inactivates pathogens in the environment or on the surface of a plant or plant organ before infection takes place.

Any harmful deviation from normal plant physiological processes due to abiotic factors.

Movement and spread of individual organisms out of a population (emigration) or into a population (immigration).

Dispersal unit
Seed plus associated tissues of flower, fruit or specialised leaves. Any device for spread and survival that can be recognised visually and counted.

Dispersibility (in relation to pesticides)
The ease with which a substance may be dispersed uniformly in a fluid.

In dispersal unit transport, the process by which the unit is actually moved from the point of formation to the point of landing; the middle process of the dispersal act consisting of takeoff, flight and landing, or liberation, displacement and deposition.

The transport of inoculum or pest from a diseased to a healthy plant.

Dissolved oxygen
Oxygen dissolved in water and used by aquatic organisms for respiration processes.

Away from the point of attachment.

Fluke with two suckers; oral and ventral.

Dispersal and spread of an organism to areas outside of its previous geographical range; 'geographical distribution' is synonymous with 'range'.

Disulphide bond
A bond formed between the sulphur atoms of two different organic compounds, such as cysteine; often responsible for joining different proteins or bending the primary amino acid sequence into a more complex structure.

Active during the daytime. Daily.

Diversity index
A measure of the number of species and the evenness of the distribution of population or biomass among species in an ecosystem.

Deoxyribonucleic acid, the macro-molecular polymer which carries the genetic hereditary message and controls all cellular functions in most forms of life. The twin strands, in the form of a helix, are composed of successive units of the sugar de-oxyribose, phosphate and the bases adenine, cytosine, guanine and thymine, through which the twin strands are cross-linked: adenine to thymine and cytosine to guanine.

DNA virus
A virus which contains DNA as its genetic material.

The amount of foreign material or impurities found in a sample of grain usually expressed as a percent.

Cutting and trimming the long hairs in a horse's tail or cutting off the tail of a sheep.

The process of recording the model equations, rationale, data sources, variables, code and experiments for purposes of information transmission.

The process of breeding for a given desirable characteristic found in the wild so as to increase, enhance and stabilise its occurrence in cultivated plants (Robinson, 1980).

Condition in communities or in vegetational strata in which one or more species, by means of their number, coverage or size have considerable influence upon or control of the conditions of existence of associated species.

A heritable character possessed by one parent of a hybrid which, when pure, will express itself in the hybrid to the apparent exclusion of the opposite or recessive character in the other parent. Also a species that comprises the majority of biota in an ecosystem.

Dominant eigenvalue
For Leslie matrices this is the sole eigenvalue that is a positive real number. Its value relative to 1.0 determines whether the population will grow or decrease in the long-term.

Dominant gene
A gene that is fully expressed in the phenotype of the heterozygote.

Dominant position
A market structure in which a single firm has a very large market share.

A linear differential equation model in which the flows between compartments depend on the compartment from which the flows come; the donor compartment.

Dorfman-Steiner condition
The condition that, for profit-maximisation, the advertising to sales ratio should equal the ratio of advertising elasticity to price elasticity.

Condition of relative inactivity as applied to seeds, tubers and perennial plants during the winter.

Temporary suspension of visible growth and physiological activity evidenced in many plants by loss of leaves.

Dormant spray
Chemical applied in winter or very early spring to plants that are not growing.

Dorsal plate
Dorsal plate on the body of a mesostigmatid mite.

The integral of concentration with respect to time. If the concentration is constant over a given time interval then the dosage is the product of concentration and time.

Dosage rate
The amount of active ingredient dispensed per unit area. It could be mixed with a wide range of quantities of carrier medium. The dosage is constant, but the application rate may vary.

Referring to the back or upper side of an organism.

From the back to the front of an animal; in the plane of the back and front, as distinct from the lateral or side plane.

The upper edge or, in animals, the back.

Dose: Dosage
Quantity of pesticide applied per individual (plant or animal), or per unit area, or per unit volume, or per unit weight.

Dosage-mortality curve
The curve resulting from plotting percentage mortality of test insects over a period of time against dosage of insecticide. Usually at least four or five doses are used as points to draw the curve.

Dose-effect curves
Demonstrate the relationship between dose and the magnitude of a graded effect, either in an individual or in a population. Such curves may have a variety of forms. Within a given dose range they may be linear but usually they are not.

Dose ratio
Ratio between successively increasing or decreasing dosages. Dose-response assessment The process of characterising the relationship between the dose of an agent administered or received and the incidence of an adverse health effect in exposed populations.

Dose-response curves
Demonstrate the relation between dose and the proportion of individuals responding with a quantal effect. In general, dose-response curves are S-shaped (increasing), and they have upper and lower asymptotes usually but not always 100 and 0%.

Double antibody sandwich
A method in enzyme-linked immunosorbent assay (ELISA) in which the reactants are added to the test plate in the order of antibody, virus, antibody-enzyme complex.

In plant breeding or genetics studies the progeny resulting from crossing two single crosses.

Double entry bookkeeping
The method of recording financial transactions whereby every item is entered as a debit in one account and a corresponding credit in another.

Doubling time
The time needed for a population to double.

Disease of horses and other equids caused by Trypanosoma equiperdum.

Time lost when no work is done on the R & D project.

Downy mildew
A plant disease in which the mycelium and spores of the fungus appear as a downy growth on the host surface; caused by fungi in the family Peronosporacae.

Draught animals
Animals used to provide power.

Drench treatment
The application of a liquid chemical to an area until the area is completely soaked.

Dressing out (D..O.%) (or K.O.%)
Dressing-out or killing-out percentage, calculated as the weight of carcass per 100 units of live weight.

Dressing percentage
The percentage of live weight which is represented by the CDW. This varies with the 'finish' of the animal from some 48% to 51-56%, the latter in extreme beef types well finished.

Movement of droplets/dust in natural air currents beyond the intended area of application.

Drift deposit
The volume (or mass) of chemical landing on unit horizontal area of the ground at a given downwind distance outside the field or target area.

Drift spraying
Method of applying pesticide aerosol sprays for control of flying insects.

To sow in furrows.

Driving variable
Environmental conditions that affect model behaviour without being affected by the model.

Droplet spectrum
Distribution (by number or volume of droplets) of spray into intervals of droplet size.

Dry farming
Producing crops, requiring some tillage, in sub-humid or semi-arid regions without irrigation.

The process of reducing the moisture content in the grain.

Dry period
The time from drying off to re-calving. The usual aim is two months for a cow and three months for first calvers before their second calf.

Dry rot
Rotting that proceeds at a rate that allows drying of the lesion to keep pace with lysis; rotting of apparently dry timber by Serpula (Merulius) lacrymans.

Dual-purpose cattle
Breeds of cattle with two productive outlets, e.g. females are economic market milk producers, males are good for beef. Also, though less frequently nowadays, for cattle combining draught and beef or draught and milk qualities.

Dummy variable
An artificial variable used to represent the level of a qualitative variable in a multiple regression analysis.

Wood frames used on concrete floors for stacking bags of rice. Prevents direct contact between the grain and the floor.

The first section of the small intestine.

Durable resistance
A term used to describe resistance that is long lasting and rarely circumvented by a given pathogen of the plant species under consideration.

A pesticide formulation in dry, finely-divided form (with particle size less than 30 µm) designed for application as a dry dressing without further preparation or dilution.

Dustable powder
A free-flowing powder pesticide formulation suitable for dusting.

Dust mulch
A loose, dry surface layer of a soil under cultivation.

Equipment for applying a pesticide formulated as a dust.

Water-soluble or water-dispersible organic colorants.

Dynamic catch
Proportion of spray collected by target.

Dynamic economic level
A term used to denote a seasonally changing relationship, between a pest insect and its host plant, such that the level of the pest population that is sufficient to cause damage varies according to the stage of plant growth and the season.

Dynamic pool
A model framework in which age, weight or size classes are lumped together into groups of average age, weight or size.

Dynamic programming
An optimisation problem over some planning horizon when decisions occur at discrete time stages and where each stage has a finite (usually small) number of decision options.

Dynamic spreading
The outward creep of surfactant cover the plant epicuticular wax beyond the edge of the drying pesticide droplet.

Changing over time; in contrast to static.

Dynamic-pool model
Type of optimum-yield model in which the yield is predicted from the components of growth, mortality, recruitment and fishing intensity; contrast with logistic-type model.

In population ecology the study of the reasons for changes in population size; contrast with statics.

A term given to a number of disorders marked by lesions of the alimentary canal and often attended by abnormal frequency and liquidity of faecal discharges.

Difficult or laboured breathing.