Agriculture Reference
In-Depth Information
Fig. 5.16.
The relationship between the number of lesions of
Botrytis squamosa
counted on onion leaves and the concentration of airborne conidia derived from
spore trapping between 10.00 and 12.00 am in field trials in Quebec, Canada in
1999 and 2000. The solid line represents the linear regression and the broken lines
the upper and lower 95% confidence band. An airborne inoculum concentration of
10-15 conidia/m
3
was found to be the appropriate threshold for initiating fungicide
sprays to prevent the disease (from Carisse
et al
., 2005. Courtesy of
Plant Disease
).
Spray programmes initiated only when the concentration of spores exceeded
10-15/m
3
resulted in fewer than half the number of sprays compared with a
conventional routine spray programme in Quebec, Canada, with no increase in
disease severity, mainly because of delays in the start of spraying (Carisse
et al.
,
2005). A technique has been developed for monitoring fungal pathogen spore
concentrations using a novel spore trap to capture and quantify them by
measuring colour intensity in an enzyme-linked immunosorbent assay (see
Fig. 5.17). This technology makes it possible for the concentration of particular
pathogen spores to be monitored within mixed-species aerial spore populations
by non-experts.
By combining these improved methods of spore trapping with meteoro-
logically based models for sporulation and infection potential, more precise
forecasts of the need for fungicide sprays will be possible. Thereby, the number of
fungicide applications could be reduced, with a consequent reduction in
pollution, cost and risk of development of fungicide-resistant pathogens. These
technologies need integrating within farm management systems. Currently, it is
often regarded as easier to manage men and equipment in large farming
operations using routine spray programmes rather than spraying according to
disease risk forecasts where the timing of sprays is more episodic.