Nematode Pests of Horticultural Crops and their Management (1+1)

Practical 1

Exercise: 1

Survey = latin word; Sur= over, vey=Video i.e. to see over
Definition
Survey: To move over a specific place for some observation.
Surveillance: Repeated or sequential survey of some place/ locality for some observation to ascertain the changes /fluctuations in the objects of study e.g. in this case to ascertain the changes in plant status due to suspected nematode infestation.

Principle of Survey:
Principle of survey relates that no management practice should be followed against a pest unless its presence is confirmed at the population level that exceeds the economic threshold to make the management tactics economically desirable.

Objectives of Survey:
1) To obtain a general idea about the occurrence of nematode fauna in a particular crop/ locality.
2) To obtain information regarding distribution and frequency of a particular disease or a nematode species in a given crop/ locality.
3) To have an idea about association of one or more nematode species and their population densities during different periods of time.

Kinds of Survey:
1) Qualitative Survey: includes identification of different species of nematodes.
2) Quantitative Survey: involves the estimation of population of one or more nematode species present.

Types of Survey:
1) Random: Samples are collected from any crop at any place suspected to be infested.
2) Planned: It is further of two types
a. Extensive Survey: A vast area is taken in to consideration to obtain a preliminary assessment of nematode population.
b. Intensive Planned: A particular area is surveyed to obtain accurate and detailed knowledge about the pest status in that region and some times in a particular crop.

Methods of Survey: Five steps are involved.
1) Collection of plant and soil samples and recording of relevant information like locality, crop, crop status, soil type, previous crop (optional), time of collection, collector’s name etc.
2) Storage of samples at around 5°C in temperate regions, 10–16°C in warmer regions of the middle latitudes and 16–18°C in the tropics and subtropics.
3) Processing of samples for nematode extraction
4) Estimation of nematode population of different genera
5) Identification of important and prevalent species for further studies.

Presentation of Survey Data: After identification, the data accumulated during survey can be represented in number of ways:
1) Mapping
2) Quantitative indexing (1 to 5); 1= rare or 1% infestation, 2= infrequent or 2% infestation, 3=Frequent i.e. 3-10% infestation, 4= Abundant i.e. 11-50% infestation, 5= Very abundant i.e. >50% infestation.
3) Gall indexing (in case of root-knot nematode infestation) 1 to 5.

The frequency and Density of nematode population can be calculated by using following formulas:

No. of samples infested with a particular species
Absolute Frequency = ------------------------------------------------------------------------ x 100
Total number of samples collected

Frequency of a particular species
Relative Frequency = ------------------------------------------------------------------------ x 100
Sum frequency of all species

Total of all individuals in a sample
Relative Density = ------------------------------------------------------------------------- x 100
No. of individuals of a particular species in the sample