Agriculture Reference
In-Depth Information
problem through to advising on control measures but it requires an understanding of
all of them for forecasting systems to work at all. This was highlighted in a review of
the subject by Miller and O'Brien (1952) where they stated “All sciences reach a point
where future real progress, as distinguished from mere accumulation of additional
information, depends on the organisation of the separate blocks of knowledge and
application of them to accomplish practical results. It will be seen that forecasting is
one of the ways of achieving such a synthesis. It is this inherent constructive feature
that makes the development of forecasting one of the most interesting and rewarding
phases of plant pathological investigation”. Miller and O'Brien (1952) also provided a
useful historical review of the subject using numerous examples from throughout the
world and covering a wide range of commodities.
9.2 WHAT IS FORECASTING?
Forecasting is partly about defining the conditions under which a pathogen, when in
contact with a susceptible host, can infect and become established. However,
forecasting schemes have to have as their components data on, and an understanding
of, the epidemiology and aetiology of the diseases and pathogens. Forecasting
provides an indication when the disease is likely to go 'critical' and therefore have
an economic impact. With some diseases, it is important to be able to predict the
first occurrence of the disease, where subsequent control would be difficult due the
absence of, for example, effective chemicals to eradicate the disease once
established. For other diseases, a certain level may be tolerated, particularly on parts
of the plant that make little contribution to yield or quality and, therefore,
forecasting is about predicting when that disease is likely to affect the vital parts of
the plant or critical periods in its development.
Understanding the components of the 'disease tetrahedron' (Fig. 9.1) (Zadoks
and Schein, 1979), the interaction between host, inoculum, environment and human
activity is essential for devising suitable forecasting systems.
Figure 9.1. The 'Disease tetrahedron', illustrating the relationships between environment, host,
pathogen and human activity (after Zadoks and Schein, 1979).
