Crop
Losses to rodent pests in Kerala: A pre-harvest survey in select crop fields and
survey on grain storage losses
(Abstract)
The situation in
Kerala is not different from the rest of the world; may be it is even worse.
Annual crops such as rice, tubers, and banana are affected adversely by rodents.
Production of tuber crops such as cassava in the State has gone down steeply
during the past decade. The fall is mainly due to the rat problem, specifically
of Bandicoots. In perennial crops such as coconut and cocoa where the damage is
cumulative, the problem is even more serious. But little information on actual
losses by rodents is available in the State, except the results of a few studies
and surveys done during the early seventies (Koya, 1975). Studies on pests of
agriculture in the State were mainly centered on insect pests. In fact, no
extensive study on rodent pests and their damages has taken place in the State.
There are more
than 6,000 different kinds of rodents. Nearly 600 of these belong to the genus, Rattus
and are called 'rats', though many other rodent species are commonly referred to
as rats. The term 'mouse' is applied to smaller rodents.
The present
study is undertaken to conduct a survey of the damages caused by rodents,
principally rats, to the different crops in the central Travancore area. The
study is conducted in multicrop. mixed farming systems, and monoculture crop
fields which come under small holder eco-systems.
Loss
of stored grain to rodents is a serious problem, experienced throughout the
world. In Kerala, no such scientific studies are undertaken those provide
reliable data. The extent of stored grain losses depends upon the distribution,
abundance, and species composition of the rodent populations involved.
Techniques for estimating rodent populations and the loss to grain storages are
well established (Mian et al, 1987).
The present study includes analysis
of the grain storage losses in houses and shops of Kerala.
The major objectives
of the study are the following.
(i)
assessment of
the extent of damage caused by rodents to various crops in the central
Travancore area;
(ii)
assessment of the crop damage caused by
rodents to different crops in a multicrop, mixed farming ecosystem;
(iii)
identification of the pest species of rodents
associated with crops in the area;
(iv)
enquiry into the extent of damage in houses,
small-scale storages, shops and farm-granaries, caused by rats; and
(v)
comparison of the value of loss with the
standard cost of different control measures, and to suggest efficient control
strategies.
Integrated Pest Management Programme
(IPM)
Even through
Integrated Pest Management (IPM), is widely discussed in relation to the
management of rodent damage problems, only minimal field research on the
integration of methods and evaluation of programmes has taken place. A few
practical IPM programmes are in routine use for rodent damage problems in field
crops. Smith and Calvert (1978) defined IPM as broad, ecologically-based control
systems that use and manipulate plant protection tactics in an effective and co-ordinated
way. More complex definitions have come up, but theirs remain broadly the most
applicable to all plant pest situations, including those involving rodents.
Smith (1970) recognised two decades ago that chemical pesticides would continue
to provide powerful tools in IPM programmes and that the hope for
'revolutionary' approaches to pest control should not be a basis for rejecting
effective chemical techniques. Although IPM is increasingly promoted as an
'alternative' to the use of chemical pesticides, in fact and in practice,
pesticides, effectively and selectively used, remain an important component of
most successful IPM programmes. This will most certainly be the case for the
foreseeable future for programmes to manage rodent damage to field crops.
Nonetheless, in every pest situation there are many opportunities to improve the
effectiveness, selectivity, and environmental compatibility of rodent damage
control programmes by developing, evaluating, and using IPM approaches.
Development of
IPM approaches to reduce or prevent crop damage by rodents presents some special
problems that require consideration (Marsh, 1981; Fall, 1991). The species are
all highly responsive to changes in environmental conditions, making it
essential to develop a thorough understanding of the specific ecological,
phenological, and climatic factors that influence rodent population behaviour in
particular crop situations. Such rodents enjoy longer periods of life than crop
cycles, have the capability for relatively long range movements across different
habitats, and can reproduce rapidly whenever adequate food and cover are
available. Most rodent damage problems must be studied and evaluated in fields
owned by farmers rather than on small plots or experiment stations. The same
rodents often damage a variety of crops in the same area, shifting from one
field to another as crop fields near to dwellings or storage structures are
common for a number of problem species. In some cases, more broad-based
integrated programmes addressing community problems may be more practical and
sustainable than specific crop-oriented approaches.
Many of the
techniques, materials, and practices available for rodent damage control
programmes have the potential for affecting other wildlife adversely and
reducing biotic diversity. Although farmers cannot be expected to divert
agricultural lands or suffer crop damage to maintain wildlife populations, one
need only consider the impact of such desperate rodent control practices as
burning or destroying habitat adjacent to croplands or poisoning of irrigation
water, to recognise that the utility and impacts of rodent control operations
need careful evaluation. If other wildlife species are determined to have a
measurable role in predatory mammals or birds around crop fields, then they may
be a useful part of an IPM programme. Even if `natural controls' are not
demonstrated as practical components of crop damage prevention, IPM programmes
should be developed with the dual objectives of minimising crop damage and
environmental effects (Fiedler, 1994).
Developing
integrated rodent pest management programmes for small holders is more complex
than for plantation crops. The major problem is organising large number of
farmers; and developing simple methods (Richards
and Buckle, 1986).
In the Kerala
context, IPM is the only promising way of pest control. Pollution due to the
excessive use of insecticides and rodenticides has reached a disastrous level in
the State. Besides, the present rodent control measures - chiefly the mechanical
and chemical - are found to be a total failure due to the unscientific
implementation. Proper integration of the various control measures giving thrust
to indigenous techniques and minimising the use of chemical control measures, is
needed. Factors such as rodent population dynamics, seasonal variation, crop
diversity, inter-crop migration of rodents and the social and ecological
dimensions should be considered. Extensive research programme for a minimum
period of five years, covering the whole State should be conducted before or as
part of designing the IPM for rodents, in Kerala. Only the implementation of IPM
and the sustaining efforts for developing IPM strategy can become effective to
curb the rat menace. Further research to chalk out an IPM programme for the
State is needed since Kerala is a conglomeration of 'small holder ecosystems'.
*Punnen Kurian is Lecturer in
Zoology, St. Mary’s College, Manarcaud, Kottayam.