2. Survey of plant diseases is useful
i . To know the prevalence of the disease in a season in a crop
of a particular area.
ii. To correlate the disease incidence with the weather factors,
biological factors and soil factors.
iii. To forecast the disease and inform about the outbreak of the
disease to the crop growers.
iv. To assess the damages caused by diseases.
v. To find out the occurrence of new diseases.
vi. To workout the management practices in the control of the
diseases
3. Methods of survey
1. Fixed plot survey
Two villages / division or block for each crop
Two one acre fields / village
In each field of one acre - five sampling plots (1m x 1m size) are
selected and they should be three metres away from the bunds.
In each plot twenty representative plants / leaves are selected and
observed for the disease incidence utilizing the standard score
chart having 0-9 grades for foliar diseases.
Per cent disease index (PDI) is worked out using standard formula.
4. For systemic diseases like viral and phytoplasma
diseases, root rot, wilt, damping-off, sugarcane smut,
green ear, etc, percentage of disease incidence is
worked out.
In the case of vector-borne diseases, the number of
vectors per tiller / plant has to be observed and included
in the report.
Survey on the crop diseases are done every week, the
report is prepared.
5. 2. Roving survey
For each Union / Block, four representative villages for individual
crops are selected. In each village two fields are fixed.
In each field, observe 100 plants / leaves and score them for the
disease intensity by walking across starting from South-West
corner to North-East corner.
The percentage of disease / per cent disease index is calculated
by using the standard formula.
As in the fixed plot, roving survey is also made at every week.
6. Disease surveillance report
The weekly data collected from fixed plot survey and
roving survey by the Assistant Director of Agriculture in a
block are sent to the Joint Director of Agriculture in
respective districts with any one of the following.
a. White card: It contains disease / pest surveillance details
of a particular block / division / district.
b. Yellow card: It should be sent when the disease / pest
occurrence reached half of the level of economic threshold
level (ETL)
c. Red card: It should be sent when the disease / pest
occurrence exceeded the economic threshold level (ETL).
7. Disease surveillance programme in Tamil Nadu
Pest and disease surveillance programmes are in existence and
the Indian Government has a set of staff for disease surveillance.
Among different states, Tamil Nadu has an organized pest and
disease surveillance programmes which is functioning effectively
throughout the state.
Officials of Departments of Agriculture and Department of
Horticulture and Plantation Crops and the Plant Pathologists and
Entomologists in TNAU are involved.
The departmental staff collect the data from different villages in
respective districts and the scientists (Plant pathologists and
Entomologists) collect the data in the respective research station /
Agricultural College.
8. Weekly reports for the district are prepared for each district by the
Deputy Director (Plant Protection) at JDA office in consultation with
the Plant Pathologist, Entomologist and send them to the TNAU
for analysis and compilation at state level.
The pest/ disease surveillance report should accompany the
details on the daily weather data viz., minimum temperature,
maximum temperature, relative humidity, rainy days, rainfall, wind
velocity, etc.
The weekly survey reports from different districts are compiled,
analysed at the Directorate of Centre for Plant Protection Studies
(CPPS), TNAU, Coimbatore and the consolidated report for the
state is sent to the Agriculture Secretary and Director of
Agriculture, Govt. of Tamilnadu for pest & disease forecast and
follow up action.
9. Based on the prevailing weather data, the message on the
severity level of the disease and management measures to be
adopted are disseminated to the farmers through mass media
like newspaper and All India Radio.
Leaflets are also distributed to the farmers for adoption.
If the disease is in epidemic form, materials are mobilized by
staff for immediate and effective control of the disease in a short
span of time.
