DISEASE FORECASTING - The Epidemiology of Plant Diseases - page 256

Forrer (1992) reported that, apart from EPIPRE, decision support systems have had
little impact in Europe. One of the major deficiencies is observational weakness, for
example in yellow rust where observations are required early in the season (Young
et al ., 2003). The requirement is for accurate disease diagnosis - expertise not
always present in farmers or indeed their consultants. Forrer (1992) proposed the
integration of immunodiagnostics in the decision-making process to simplify the
accuracy of disease identification.
Integrating observations, meteorological data and agronomic factors such as field
history, cultivar performance and inputs into a computer-based system for general
use is now possible with improved and readily available computer power at
relatively reasonable costs. DESSAC (Decision Support System for Arable Crops)
has been developed in the UK to provide the industry with sufficient detail to allow
the user to make better informed decisions (Parsons et al ., 2004).
9.8 OILSEED RAPE
Compared to potatoes and cereals, oilseed rape is a relative new crop for forecasting
disease. Disease/yield loss relationships have only relatively recently become
understood (Sansford 1995a and b; Sutherland et al ., 1995).
9.8.1 Light leaf spot
Data on disease incidence and severity collected from crop surveys gathered
between 1977 and 1993 (Fitt et al ., 1994, 1996; Gladders et al ., 1995) have been
used to propose a prediction scheme for forecasting high-risk seasons for light leaf
spot (caused by Pyrenopeziza brassicae ). Gladders et al . (1995) found a good
correlation between the incidence of light leaf spot on the pods in July and the
incidence of light leaf spot on leaves in the following March. This has been
proposed as part of the seasonal risk index for a more comprehensive forecasting
scheme including an initial crop risk index - to identify crops at risk at the
beginning of the season and an index to refine decisions as the season progresses
(Fitt et al ., 1996). The seasonal risk element is the strongest of the three and the crop
risk and progressive risk elements require further refinement. However, the use of
the seasonal risk element on its own is a start and can give more confidence on spray
recommendations required in the autumn in advance of disease symptoms being
reported.
9.8.2 Canker
Canker (caused by Leptosphaeria maculans ) of winter oilseed rape is a disease
which affects the stem bases leading to premature ripening and, in severe cases,
lodging. Early phoma leaf spot epidemics are a major cause of yield loss but can be
managed economically with fungicides applied in autumn and winter. Conversely,
phoma epidemics developing from December onwards may have little effect on