Forecasting of Plant Diseases | Botany

In this article we will discuss about the forecasting of plant diseases.

Forecasting of plant diseases is predicting the occurrence of disease in an epi­phytotic form in a particular area. Plant diseases vary in incidence from season to season due to differences in the nature and amount of inoculum, environmental condi­tions, numbers and activity of vectors, and other factors which affect the development and spread of pathogens.

Reliable forecasting of the likely incidence of plant diseases can save a great deal of money provided it can be done sufficiently early to organize effective control measures. This will also avoid wasting time and money on unnecessary control measures. Early forecasting gives crop growers sufficient time to rearrange their crop schedules and to avoid susceptible crop in a season when disease is likely to be severe.

The aim of disease forecasting should also be to arrange control measures before the inoculum is likely to infect the crop. It is thus very important that forecasts should be correct so that an effective disease warning system is reliable to the crop growers.

Forecasting Methods:

A rational method of disease forecasting method should be based on:

(i) Factors (microclimatic) which influence the initial appearance and subsequent spread of inoculum

(ii) Thorough knowledge of the life cycle of the pathogen

(iii) The ways in which the pathogen perennates

(iv) Rough estimate of the quantities of inoculum expected to be disseminated through propagating stock, soil, air, vectors, etc.

(v) Mechanism of host infection

(vi) Knowledge of the sus­ceptibility of the host plant at different stages of growth

(vii) Meteorological data (macroclimatic conditions) of the area.

Methods of disease forecasting may be:

(i) empirical, in which correlation bet­ween the results of disease surveys and the corresponding weather conditions in a particular area has to be related to the biology of host plant and pathogen

(ii) fundamental, in which the effects of different weather conditions (moisture, tem­perature, etc.) on plant and pathogen, separately and together, are investigated in the laboratory and conclusions tested under field conditions. Besides these, many methods are based on a survey of the viable inoculum available at the beginning of the crop season.

These methods provide an early warning but have the disadvantage that many other factors may subsequently modify the course of expected outbreak, e.g., unsuitable weather may prevent disease development despite the presence of ample inoculum.

Again other forecasting systems are based on weather conditions during the crop season, but these assume the presence of sufficient inoculum and will be irrelevant if this is not available. Forecasting systems should therefore take account of inoculum sources as well as the weather conditions which affect the deve­lopment and dissemination of inoculum.

Hence forecasting methods should be basi­cally based on:

(i) Weather conditions during the intercrop period, particularly as affects survival of inoculum;

(ii) Weather conditions during the crop season;

(iii) The amount of disease in the young crop; and

(iv) The nature of propagating organs of the pathogen in the air, soil, or planting material.

Weather conditions during the intercrop period are usually related to survival of the pathogen or its vectors bet­ween crops. Intercrop weather which reduces pathogen or its vectors is likely to mini­mize inoculum sources for the following crop. Weather conditions during the crop season are important in the development and spread of inoculum.

The effects of weather conditions on plant diseases are complex, influencing not only the events of the infection cycle, but also the resistance of the plant, its ability to throw off or survive attacks, and the numbers and activity of any vectors of the pathogen.

Hence the results of laboratory experiments on the pathogens are not always a completely reliable indication as to what happens under more varied conditions of the field.

Detailed observations over a number of years may be necessary before forecasting systems based on weather conditions can be prepared. Some diseases originate from inoculum blown in from distant sources and information on the incidence of the disease in such areas, if known can be useful in forecasting the date and severity of the disease in the area expected to receive inoculum.

This may be supplemented by spore trapping to determine when the inoculum will be arriving in large quantities. Such study should be supported by the knowledge of the circulation of the air currents which is responsible for the transport of inoculum.

The distribution and concentra­tion of soil borne pathogens can be estimated by suitable laboratory experiments and the data collected may be utilized for both forecasting and controlling of diseases.

Some pathogens are partly or exclusively seed-borne and the degree of seed-borne infection can be estimated in the laboratory by germinating seeds under conditions suitable for disease development.

According to virulence of infection or contamina­tion the propagating materials may be rejected or treated to destroy contaminating pathogen to render them safe for sowing. In such a case both forecasting and control are combined.