Agriculture Reference
In-Depth Information
The importance of understanding the above relationships became apparent during
the foot and mouth disease epidemic, which affected the United Kingdom (UK) in
2001. A highly virulent virus was infecting highly susceptible hosts (sheep and
cattle) under favourable environmental conditions. It was only when the human
factors were addressed by the strict policing of the movements of individuals and
vehicles, coupled with thorough disinfection, that the disease was brought under
control (Anon., 2002).
9.2.1 Environment
It is generally assumed that the environment is the driving force for diseases
(Hardwick, 2002). Smith and Hugh-Jones (1969) analysed the foot and mouth
disease outbreak of 1967 and concluded that weather played a greater part in the
spread of the disease than was previously recognised.
Meteorological data can be collected on the macro-scale at synoptic weather
stations (a network of weather stations measuring dry-bulb and wet-bulb
temperature, cloud amount and type, cloud base, weather type, visibility, wind
direction and speed and atmospheric pressure. The frequency of the observations
vary, but the main synoptic hours are 0000, 0600, 1200 and 1600 GMT). Synoptic
stations are generally sited at airfields which may be remote from the main arable
areas or in atypical cropping situations and may therefore give readings less relevant
to specific crops. The spatial scales are necessarily large. At the micro-scale, where
data can be generated from in-field monitors by the minute, the data are spatially
independent. The benefit of the micro-scale is that it can be identified with a specific
crop and is, therefore, influenced more by the microclimate from within the crop or
field.
The study of environmental factors play an important role in disease
epidemiology and therefore forecasting. Much research is expended on capturing
meteorological information and relating disease outbreaks to weather criteria. The
basic systems consider only rainfall, its frequency and intensity; the more
sophisticated include temperature, both maximum, minimum and mean, humidity,
leaf wetness, wind speed and direction and hours of sunshine. The duration of these
events and the period in which they fall, e.g. during night or day, are also important
elements of data requirement.
9.2.2 Inoculum
In considering any forecasting scheme, inoculum is important and its source will
greatly influence the type of forecasting scheme that is appropriate. These include
inoculum that arises from within the crop, carried on the seed or on the perennating
part of the plant, such as tubers and rhizomes. Seed certification schemes play an
important role in restricting this source and, where strictly applied, can eliminate seed
as a source of inoculum. Elimination of inoculum may involve micropropagation or
treatment by physical and/or chemical means. Volunteers (plants that grow from seed
or tubers left behind after harvest) carrying infection from the previous season can be
