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Stated briefly, the conditions necessary for the wide-scale development of a damaging disease are (Berger 1977):
1. The virulent race of the pathogen (fungi, bacteria, or virus) must b present in low frequency in the host (crop).
2. The host (crop) that is susceptible to this race must be widely distributed in a region.
3. Environmental conditions must be favorable for the development of the pathogen.
The extensive cultivation of genetically and horticulturally homogenous crops, a typical tendency in many modern agricultural systems, favors the circumstances allowing disease to proliferate to epidemic levels.
Large plantings adjacent to main foci are particularly vulnerable, and host-rich interstices make remote locations more accessible to invasion.
These elements work together to create a disease triangle; plant disease is the outcome of their interactions and occurrence. In fact, the disease won't spread unless there is an active pathogen, a good host, and favorable environmental factors for the pathogen's infection, colonization, and reproduction.
The intensification of agriculture includes several practices which favor plant disease:
Enlargement of fields.
Aggregation of fields.
Increase in the density of host crops.
Decrease in the diversity of the species and at the varietal level of host populations.
Increase of monoculture and/or short rotational patterns.
Use of fertilization, irrigation, and other crop environmental modifications.
In general, three epidemiological techniques can be used to reduce disease-related losses:
Delay or eliminate the first inoculum (X0), or both, from showing up at the start of the season.
During the growth season, slow down or reduce the pace of diverse development (r).
Reduce the length of time the crop is exposed to the pathogen by utilizing short-season cultivars or fertilization and irrigation techniques that don't inhibit crop development.
Epidemiology and Disease Management.
BY
K H Akhil Srinivas. (KHAS).
