Agriculture Reference
In-Depth Information
Table 1.1
Estimated loss potential and actual losses
due to pathogens (fungi and bacteria) in six major
crops worldwide in 2001-2003 (adapted from Oerke,
2006, © Cambridge University Press, reproduced with
permission).
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(Oerke, 2006). Loss rates can be looked at in terms of potential loss and actual loss.
Potential loss compares yields in a system without any form of crop protection treat-
ment, with yields from a system with a similar intensity of crop production, but receiv-
ing crop protection treatments. Actual losses are those sustained despite the use of crop
protection (Oerke, 2006). The effi cacy of crop protection can be calculated as the per-
centage of potential losses prevented. Table 1.1 illustrates the potential and actual losses
as a result of disease for a range of crops. Potential losses range from 8.5% for cotton to
21.2% for potatoes, while actual losses range from 7.2% for cotton to 14.5% for potatoes
(Table 1.1). These fi gures indicate the importance of crop protection in reducing potential
losses in all of these crops. It is important to note here that disease-induced crop losses and
the effi cacy of crop protection practices will vary with geographical area, as a result of dif-
ferences in cropping intensity, climatic conditions and cropping systems (Oerke, 2006).
A comparison of the actual losses due to disease in wheat and maize in the period
1964-2003 shows increases in crop losses from 9.1% to 12.6% in wheat and from 9.4%
to 11.2% in maize (Table 1.2). In contrast, although the actual losses due to disease in
cotton increased from 9.1% to 10.5% from 1964 to 1990, actual losses dropped to 7.9%
by 2003 (Table 1.2). According to Oerke (2006), the differences in the estimates of actual
crop losses over this period are likely to be the result of several factors, including:
•
Increased fertiliser use, further increasing susceptibility to some pathogens
The use of varieties with high yield potential, but high susceptibility to pathogens
•
Large-scale cropping of genetically uniform plants, providing ideal conditions for
•
rapid pathogen spread
Expansion of crops into less suitable regions with higher incidence of other
•
pathogens; here, less well-adapted, but high-yielding varieties replace well-adapted
local varieties
The import and spread of pathogens into regions without the natural restrictions
•
(e.g., climate, natural enemies) of the region of origin.
Globally, agricultural production has grown faster than the human population over the
past few decades (Hazell & Wood, 2008). In most parts of the world, this has been
