---

---

[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]

Warble
Fly maggot of the family Hypodermatidae; also called a heel fly.

Warning
An advance notice of a pest or disease outbreak or to draw symbol, notice, attention to the toxicity of a pesticide product on container label.

Water activity (aw)
A measure of water content equivalent to percent humidity divided by 100.

Water column
The water in some water body treated as spatially homogeneous having light reduced with depth from the surface.

Water-soaked
A term used to describe a disease symptom in which an area of plant cells takes on a darker colour owing to the filling of intercellular air spaces with cell sap; sometimes indicative of the action of a toxin, particularly if the symptoms are at a distance from the invading organism.

Water soluble granules
A formulation consisting of granules to be applied as a true solution of the active ingredient after dissolving in water, but which may contain insoluble inert ingredients.

Water soluble powder
A powder formulation which forms a true solution of the active ingredient when dissolved in water but which may contain insoluble inert ingredients.

Water stress
Drought.

Water table
The upper limit of gravitational water in saturated soil.

Watery disintegration
Also called Wassersucht; a lethal disease of cockchafer grubs (Melolontha) caused by a virus.

Weather
Meteorological condition of the atmosphere, as warm, cold, wet, dry, windy, still, cloudy, clear etc.

Weathering
Summation of effects of all meteorological factors (rain, wind. etc.) tending to diminish persistence of pesticide spray deposits.

Weber-Fechner law
A law which states that visual acuity is proportional to the logarithm of the stimulus.

Weed
An aggressive, invasive, easily dispersed nuisance plant, one which commonly grows in cultivated ground to the detriment of a crop.

Weed allelopathy
The damage to crops by weed toxic exudates.

Weed assessment scales
Descriptive scales relating weed and crop densities.

Weed control
The process of limiting weed infestations so that crops can be grown profitably or other operations can be conducted efficiently.

Weed density
The total amount of weeds per unit area as determined by counting or weighing.

Weed eradication
The complete elimination from an area of all live plants, plant parts and seeds of a weed infestation.

Weedkiller
A chemical that will kill or inhibit the growth of weeds, a herbicide.
Contact - a weed-killer that kills only that part of the plant from which it comes into contact;
Hormone - a weed-killer that is similar to substances produced naturally by the plant which regulate the growth of the plant;
Residual - a weed-killer that is applied to the soil where it persists for some time, killing weeds as they germinate;
Selective - a weed-killer which, used correctly, causes no injury to the crop or no injury of any economic importance;
Total - non-selective weed-killer. A weed-killer which is used to kill all vegetation as opposed to one used selectively;
Translocated - a weed-killer which is absorbed by the plant and moves about within the plant before killing it.

Weed seeds, injurious
Weed seeds subject to statutory regulations.

Weeds perennial
Herbaceous plants that live for more than two years. Those living only for two years are called biennials.

Wet rot
Any rot in which the tissue is rapidly and completely disintegrated, with release of water from the lysed cells.

Wettable powder
Finely particulate inert material (eg. kaolin) containing pesticide that forms a stable (semi-permanent) suspension when added to water (may require tank agitation to maintain suspension).

Wetter, Wetting agent
Material that reduces contact angle of liquid on given surface. Used in pesticide formulations (see adjuvant and surfactant). Added to a spray to reduce the surface tension of the applied droplets.

White-bud
See fruit-bud stage x.

White corpuscle
Leucocytes. Cells which circulate in the blood but do not contain haemoglobin (the red colouring matter). They are of various types, some of which are concerned with destruction of circulating micro-organisms. They are very much fewer in number than the red blood corpuscles.

Whitehead
A bleached cereal ear containing little or no grain. Usually a result of attack by stem base or root pathogens, particularly Gaeumannomyces graminis (take-all).

White muscardine
A mycosis of various larval, pupal and adult insects, caused by the hyphomycetous fungus Beauveria bassiana.

Whitening
Process of removing the bran layer of grain during milling.

White rot
Rotting of wood in trees invaded by lignin-destroying fungi, leaving a white cellulose residue.

Whole farm budget
Budget showing the expected outcomes of a farm plan, as it affects the entire farm's 'profitability'.

Whole farm planning
Planning for the entire farm, as distinct from partial budget planning.

Wiggler
Mosquito larva.

Wild type
The phenotype characteristic of individuals of a species that predominate under natural conditions.

Wilt
Loss of rigidity and drooping of plant parts generally caused by insufficient water in the plant. Also, a disease characterised by loss of turgidity and collapse of leaves, typically caused by vascular infection by a fungus or bacterium.

Wilt disease
Nucleopolyhedrosis virus disease of lepidopteran larvae.

Wilt point
The water content of the soil (% vol vol-1) below which rooted plants are no longer able to extract water. Typical values range from 1-30 vol%.

Windrow
A row of hay or un-threshed grain raked up to dry.

Windrowing
Pushing plant material into a long narrow heap.

Wind shear
The rate of change of the vector wind with distance in a specified direction normal to the wind direction. Shear is an important property of the wind field, ie. shear at a well marked frontal surface may produce shearing instability.

Winter annual
A plant which germinates in the autumn, lives over winter, produces its seed during the following spring and then dies.

Winterbottom's sign
Swollen lymph nodes at the base of the skull, symptomatic of African sleeping sickness.

Winter wash
Pesticide application (usually ovicidal) on trees or bushes in dormant season.

Wire-worm
The larva of Elateridae (Coleoptera); long; slender; well-sclerotised, thoracic legs but no prolegs and few setae.

Witches broom
Abnormal broom-like growth or massed proliferation caused by the dense clustering of branches of woody plants.

Withers
In a horse or other animal, the highest part of the back, lying between the shoulder blades.

Wood vessel
A series of dead lignified cells with the end walls broken down to form a continuous tube for the conduction of water in the plant's vascular system.

Woody plants
Plants that develop woody tissues.

Wool
A mass of desiccated nematodes of Ditylenchus dipsaci found in or on some plants.

Work breakdown schedule
A list of R & D project tasks accompanied with task durations and dependent, or precursor tasks.

Work gate
An active energy processing unit that combines energy from two or more sources; used in Odum diagrams.

Wrap-around boundaries
The property of edge states that movement out of one edge of a grid results in movement into the edge states at the opposite end of the grid.