Agriculture Reference
In-Depth Information
Currah (2002). These sources have been drawn on in the preparation of this
chapter.
The application of new technologies to plant pathology, in particular, has
resulted in rapid progress in recent years. Diagnostics are being made faster
and more precise by new molecular methods that identify pathogens by their
DNA or RNA sequences, and also by the development of rapid immunological
tests for pathogens (Ward
et al.
, 2004). With these techniques, rapid and
accurate diagnoses can be made without the need for highly trained specialists.
These methods are also opening up new fields of study relevant to plant disease.
For example, it is becoming possible to investigate the interactions between
mixed species of microbes, including pathogens and their antagonists, on leaf
surfaces or close to roots. In addition, the rapid detection and quantification of
airborne pathogen spores, along with automated electronic monitoring of the
microclimate in crops, can input real-time data into weather-based models for
predicting pathogen infection and epidemic development. These predictions
enable fungicides to be applied only when they are beneficial.
In developed economies vegetable producers are required by supermarket
buyers to supply high-quality, blemish-free produce and, at the same time, there
is public and political pressure to reduce pesticide usage. Needless to say, these
two requirements are often in conflict and can be reconciled only by developing
more sophisticated methods of crop protection based on scientific knowledge. As
an example, the models for forecasting required fungicide application, mentioned
above, can reduce unnecessary spraying. Such technologies are incorporated
within programmes of 'Integrated Pest Management' (IPM), which aim to
control weeds, pests and diseases by using pesticides in conjunction with other
aspects of crop protection, including cultural methods, resistant varieties and the
encouragement of beneficial organisms.
Surveys of actual pesticide use on commercial bulb onion crops in the UK
indicate a modest increase in the amount of pesticides applied in recent years
(total kg/ha active ingredients (AI)) but a large increase in the number of
applications, particularly of herbicides and fungicides (Thomas, 2003).
Between 1986 and 1999 the mean number of herbicide sprays per crop
increased from around five to nine to ten, but the weight of AIs applied
increased by only 19% (Grundy
et al.
, 2003). The reason for this was a
continuing trend towards more 'repeat low-dose' herbicide treatments. In the
same period the mean number of fungicide sprays increased from about three
to five to six (Thomas, 2003). Improvements in application technology -
whereby less pesticide gets wasted on non-target surfaces - and better
chemicals, which are effective at lower concentration, are both tending to limit
increases in amounts applied despite increases in the number of applications.
In contrast, there is a growing market for 'organic' vegetables grown without
using chemical pesticides. The main limitation for large-scale 'organic'
production of allium vegetables is the need for many hours of hand-weeding to
produce satisfactory crops (Melander and Rassmusen, 2001).
