[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]
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.
Dam
Mother. Alternatively an artificial lake made by constructing a wall
of earth or concrete, etc.
Damage
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.
Daphnia
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.
Days-to-harvest
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'.
Days-to-slaughter
The least number of days permitted by law, between the final pesticide
application and the date an animal is to be slaughtered.
DBH
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.
DCP
Digestible crude protein.
DE
Digestible energy; see metabolisable energy.
Debt-servicing capacity
Annual whole farm net cash flow before deducting interest and loan
repayments.
Decacanth
Ten-hooked larva that hatches from the egg of cestodarian tapeworm;
also called a lycophora.
Deciduous
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.
Decomposer
A heterotrophic organism that utilises dead organic matter as food,
decomposing it into more simple substances.
Decontamination
Removal or breakdown of any pesticide chemical from any surface or
piece of equipment.
Decumbent
Lying along the ground.
Defaunate
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.
Deflocculation
Increased stability of solids dispersed in a liquid by adding substances
which form protective colloids.
Deflocculating agent
Material added to suspension to delay sedimentation.
Defoliant
Any substance or mixture of substances when applied to a plant causes
the leaves or foliage to drop, with or without causing abscission.
Defoliation
Removal of shoots.
Defoliator
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.
Degradation
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.
Deglution
The act of swallowing.
Dehisce
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.
Dehiscent
Opening spontaneously when ripe, e.g. capsules, anthers.
Dehusking
The process of removing husk from the grain during milling.
Dehydrated
The absence or loss of water.
Dehydration
Removal of water from a body or tissue; or the condition which results
from loss of water.
Dehydrogenase
A class of enzymes which oxidise substrates in the process of removing
electrons and hydrogen atoms.
Deirids
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.
Deletion
A removal of a portion of a gene.
Deliverables
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.
Delphoparasitism
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.
Deme
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.
Dendogram
A tree diagram used as a graphical display to show the similarity of
different entities.
De-novo
To make anew.
Density
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.
Densonucleosis
A fatal disease of larvae of the wax moth, Galleriam ellonella,
caused by a virus.
Dent
A type of maize having kernels that contain both soft and hard starch
and thus become indented at maturity.
Denticles
Small, tooth-like projections.
Dentition
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.
Dentrification
The reduction of nitrates to nitrites, ammonia and free nitrogen in
the soil under anaerobic conditions, resulting in loss of nitrogen from
ecosystems.
Denuge
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.
Deposit
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.
Deposition
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.
Depreciation
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.
Dermatophytes
Fungi that cause superficial mycoses.
Dermomyositis
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.
Desiccant
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.
Desiccation
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.
Desquamated
Epithelium from which the surface is peeling or scaling off.
(epithelium)
Detassel
Removal of the maize tassel, usually to prevent release of pollen in
a breeding programme.
Detergents
Wetting agents that increase the spreading of spray liquids and enable
wettable powders to disperse readily in water.
Determinant
A scalar value involving the sums of products of elements of a square
matrix, used in eigenanalysis and in matrix inversion.
Determinate
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.
Deterministic
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.
Detoxification
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.
Detoxify
To make an active ingredient in a pesticide or other poisonous chemical
harmless and incapable of being toxic to plants and animals.
Detriment
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.
Detritus
Dead organic material in the water column or on the bottom of a water
body.
Detrivores
Animals that feed on dead plant or animal material.
Deuterotoky
That pattern or mode of parthenogenetic reproduction in which progeny
of both sexes are produced by unmated females.
Deutomerite
Posterior half of a cephaline gregarine protozoan.
Deutonymph
In the life cycle of some mesostigmatid mites, a non-feeding stage
that moults into the adult.
Deutovum
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).
Deviation
The difference between anticipated (planned) and actual results (see
standard deviation).
Dew-point
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.
Diagnosis
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.
Diapause
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.
Diaphragm
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.
Diathesis
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.
Dicaryon
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.
Dichotomous
Forked regularly in two.
Dicotyledon
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.
Die-back
Necrotic symptom of disease in which death of shoot tissues begins
at the tip and progresses back towards the main stem.
Diecdysis
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).
Differentiated
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.
Differentiation
A form of corporate strategy which involves producing products which
differ from the competition in ways which buyers value.
Diffusion
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.
Dikaryon
A fungal compartment (often called a cell but fungi are generally better
regarded as being coenocytic) containing two genetically distinct haploid
nuclei.
Dikaryotic
Spores containing two sexually compatible nuclei per cell that are
common in the basidiomycetes.
Diluent
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.
DIMBOA
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.
Dimeric
Consisting of two parts.
Dimictic
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.
Dimorphic
Of two forms, as may occur with branches etc.
Dimorphic fungus
A fungus which can exist either in unicellular yeast
Dinitro
A common designation for dinitro-phenols. These materials are used
as contact chemicals, as crop defoliants or as a control for succulent
annuals.
Dinitrophenols
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.
Dioecious
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.
Diphtheria
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.
Diphtheritic
Pertaining to a false membrane often covering a lesion in the intestine
or lung passages, formed by the solidification of secretions from the lesion.
Diplococcoid
Having the appearance of a pair of cocci (i.e. spherical bacteria)
which have divided incompletely.
Diploid
Having two homologous chromosomes in pairs in the nucleus so that twice
the haploid number is present, usually written as 2n.
Diplokarya
Having nuclei associated in pairs.
Diplostomulum
Strigeoid metacercaria in the family Dislostomatidae.
Diporpa
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.
Directing
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.
Disaster
(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.
Disc
Front plate of a sprayer nozzle having a central orifice.
Disclimax
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.
Discomycete
An ascomycete whose fruiting body is an apothecium (e.g. Sclerotinia
sclerotiorum).
Discounting
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.
Disease
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.
Disinfect
To free from infection by destruction of a pest established in or on
plants or plant parts.
Disinfectant
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.
Disinfest
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.
Disinfestant
An agent that kills or inactivates pathogens in the environment or
on the surface of a plant or plant organ before infection takes place.
Disorder
Any harmful deviation from normal plant physiological processes due
to abiotic factors.
Dispersal
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.
Displacement
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.
Dissemination
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.
Distal
Away from the point of attachment.
Distome
Fluke with two suckers; oral and ventral.
Distribution
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.
Diurnal
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.
DNA
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.
Dockage
The amount of foreign material or impurities found in a sample of grain
usually expressed as a percent.
Docking
Cutting and trimming the long hairs in a horse's tail or cutting off
the tail of a sheep.
Documentation
The process of recording the model equations, rationale, data sources,
variables, code and experiments for purposes of information transmission.
Domestication
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).
Dominance
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.
Dominant
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.
Donor-controlled
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.
Dormancy
Condition of relative inactivity as applied to seeds, tubers and perennial
plants during the winter.
Dormant
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.
Dosage
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.
Dorsal
Referring to the back or upper side of an organism.
Dorso-ventrally
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.
Dorsum
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.
Double-cross
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.
Dourine
Disease of horses and other equids caused by Trypanosoma equiperdum.
Down-time
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.
Drift
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.
Drill
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.
Drying
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.
Dunnage
Wood frames used on concrete floors for stacking bags of rice. Prevents
direct contact between the grain and the floor.
Duodenum
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.
Dust
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.
Duster
Equipment for applying a pesticide formulated as a dust.
Dyestuffs
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.
Dynamic
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.
Dynamics
In population ecology the study of the reasons for changes in population
size; contrast with statics.
Dysentery
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.
Dyspnoea
Difficult or laboured breathing.
