The farmers should make habit to use pesticides only when needed

By Dr. S. M. Alam, M. A. Khan
 and Dr. R. Ansari
Nuclear Institute of Agriculture,
Tandojam, Pakistan
Aug 14 - 20, 2000

Plant protection: More than one hundred years ago, a chemically synthesized crop protection product used to control pests for the first time in the history of insecticide in Germany. The product under the trade name "Antinonnin" launched in 1892 to combat a forest pest known as nun moth larvae, Lymantria monacha, which ravaged Germany's forests and other crops in the experimental field in many other areas of German Empire. Report says that they first infested the spruce forests of Upper Bavaria. The naked branches and stumps were all that was left of almost 3,000 of the 8,000- hectare Ebersberg forest near Munich, and another 3,000 hectares suffered from severe damage. People tried desperately to stop the rampage of these insatiable pests. Thousands of helpers dug out more than 170 kilometers of trenches around the Ebersberg forest and spread some 350,000 kilograms glue on 34,000 meters of trap posts and boards. It was a milestone in the history of chemical crop protection because this chemical was proved effective to control attack of this insect. Many historical records attest to the desperate efforts of the old users to combat the pests and pathogens that threatened their crops. Since that times many varieties of insecticides were manufactured, prepare and used in the experimental fields to overcome the insects attack on the crops. This insecticide was in use up to 1974 and after that the German manufacturer stopped its production. The occurrence of pernicious insect pests and diseases is a constant threat to our agricultural economy. It is painful to contemplate the extent of insect damage alone on national basis. The use of pesticides is very common by the farmers in these days.

The farmers community have become aware of the importance of pest control and the demand for pesticides has been continuously on the increase year after year all over the country. The expanding use of pest killing chemicals pesticides is no doubt effective and beneficial. However, as a result of their excessive and indiscriminate application a number of side effects such as problems of resistance, crop tolerance and pollution have come to light. The chemicals being poisonous material have given rise to yet another problem of residual toxicity, which can be fatal to man and his animals. The financial aspect of chemical control is all the more important since the annual expense of huge foreign exchange resources on the import of pesticides is rather difficult for a developing country like Pakistan.


In the view of these facts, the results obtained from the exclusive use of pesticides cannot be considered as completely satisfactory. There is, therefore, an urgent need to organize an integrated approach in carrying out pest and disease control programmes. For this purpose, it would be necessary for our economic Entomologists and other agricultural scientists to conduct biological studies on plant pests and pathogens in different ecological zones with a view to establishing economic injury levels of each pest on different crops throughout the season. In most of the developing countries, yields are very adversely affected due to serious rampage by crop devouring field insects or by the secret and silent enemies the diseases. There is no end to their destruction from the experimental fields. Even after harvesting the crops, the produce is generally attacked by them even in well-protected godowns of the country. Under these conditions, adoption of proper crop protection techniques becomes a pre-requisite for a progressive, productive and prosperous agriculture. Current methods of pest and disease control mainly rely  on the outright killing of harmful organisms with suitable chemicals. This single approach has not only proved inadequate but, also found insufficient from economic and environmental viewpoint. However, useful pesticides may be, there is today a widely and wisely held view that it will be necessary to develop and deploy other methods in conjunction with chemicals for ideal pest control. The objective of this integrated pest control is to keep the pest population below the economic injury level rather than complete pest eradication. Though it is a gigantic task yet it offers great prospects of improved pest control with minimum adverse environmental impact at comparatively low cost to the farmers. Success in this field would depend on the extend of our knowledge about the biology, ecology and physiology of insects.

In Pakistan, generally throughout the growing season various food and cash crops in the field are attacked by innumerable pests and diseases, which cause a colossal loss to agricultural production annually and thus a substantial loss in the economical growth of the country. The government agencies as well as the farmer communities have been making all out efforts and possible ways, to surmount over or solve the problems ever since which happening for the last many decades mainly through chemical control. The results, although quite promising, yet the problem remains almost as threatening to the crops as ever. By spending millions of rupees annually in this context in foreign exchange, hardly 15-20 % area is being covered and the rest still needs plant protection coverage to keep the crops free from the ravages of pest and disease complex. Now there is an urgent need to search out alternative methods to control fully or as far as possible the pests attack on the agricultural crops. Thus, it is also important to find out a suitable method for technique to reduce the abnormal crop situation caused by varieties of insects to the agricultural crops.

In the past decades, synthetic, organic pesticides have been the main weapon or the technique used by a man against his pests and their uses have made a major contribution to greatly increased yields of many crops in many parts of the world, specially in the developing countries. Pesticides also provide great possibilities for helping to increase agricultural production in the developing world. On the other side, over-reliance on chemical pesticides has, i) created well-known pollution problems ,ii) made some pests more abundant, and have put an adverse effect on non-targeted organisms, iii) generally created new pests and, iv) led to pest resistance pesticides. There is no doubt, that insecticides will continue to play an important role in insect control, but that alternative measures should have to be developed to a greater extent in order to get benefit from their application.

Crop protection has received a great deal of attention within agricultural development projects and research stations, and much information is available on the component technologies involved. However, crop protection is only one of many concern in the lives of farmers in developing countries. A wider appreciation of the crop production and overall farming system is needed from the prospective of the resource poor farmer in order to help the development of appropriate crop protection techniques. When developing crop protection programme, it is essential to recognize the wider political and policy context with in which programme will be expected to work. A modern pest control method known as "Integrated Pest Management- (IPM)", is being widely assessed by developing countries to form the basis for their crop protection programme. This approach seeks to provide farmers with a choice to control applying techniques against the pest complex, which can be fitted into their production system and which are safe and environmentally friendly.

Integrated pest management is defined as a pest management system that in the context of the associated environment and the population dynamics of pest species, utilizes all suitable techniques and methods in as compatible a manner as possible and maintains the pest populations at levels below those causing economic injury. It generally refers to the management of single pest species on specific crops or in particular places. In a more general sense, it applies to the co-ordinated management of all pest populations in the agricultural environment. Integrated pest management a multi-faceted approach, usually involving several control strategies. Integrated pest management is an enlightened pests control strategy that has evolved is most effective long-range procedure for the control of insect pest engaged in the agricultural fields.

Control measures: The major components of insect pest management currently available and proved effective are biological control, cultural control, physical control, chemical and regulatory control. In addition to these microbial control, pheromones and insect growth regulators are considered to a potential tools in IPM programme. This programme requires a high level of scientific management background. The necessary points to be kept in mind are, i) the general biology, distribution and behaviour of insects, ii) an approximation of the pest population levels that can be tolerated without significant crops loss, iii) a rough evolution of time and place of occurrence and significance of the major predator, parasites and pathogen pests, iv) information on the impact of pesticides on natural enemies.

i) Biological control: The struggle for existence between the insect pest and their natural enemies continues between until a balance of nature" is arrived at. This balance is vary delicate and is likely to be disturbed by man made activities. The natural enemies i.e., parasites and predators under normal conditions are not only to be saved from destruction but must be augmented and fostered through known methods of artificial rearing and release in addition to other method which promote their action. Full information on the parasite and predators of different pest species and the factors which promote their activity is necessary.

ii) Cultural control: Some of the common practices which can be of use in pest management programme are crop rotation, field station, growing of invaluable trap crop, uniform planting development of resistant varieties, deep ploughing and soil exposures, flooding of fields through controlled irrigation, modification in sowing and harvesting dates etc. All these practices combined or individually reduce the chances of pest multiplication. The cultural practices as mentioned above are by and large quite important in case of plant diseases, caused by the fungi, bacteria, viruses, nematodes etc. Infected seed and diseased plant debris serves as important source of primary inoculum. The elimination of these sources through cultural practices is, therefore, quite significant and is being strongly emphasised in many diseases. The use of healthy seed, and destruction of diseased plant material deserve special mention in this respect. Crop rotation is useful in some soil borne diseases in order to exhaust the dormant inoculum lying in the soil. Similarly, removal of weeds and clean cultivation is important because weeds some time may act as alternate host for the disease causing organism or they can serve as carriers of some virus diseases. Some other practices such as regulation of time of sowing, manuring and irrigation etc, serve to control those diseases which are sensitive to environmental conditions.

iii) Physical control: Putting up light traps during the growing season of the crop the moth population. Many insects are attracted to light by natural instinct. This habit can be utilized to collect the population and the pest potential can be reduced in some cases. This method can also assist in forecasting the pest infestation on the basis of adults attracted to light from time to time.

iv) Sterile male technique: The use of sterile-male technique without affecting the natural enemies is another approach for the control of some insects which are not migratory and live in a restricted habitat. The male population can be lowered with the help of sex attractants and thereafter irradiated sterile males can be released, which will be needed only in small number in view of depleted population of wild animals.

v) Chemical control: Use of hormones and pheramones and other such chemicals is of recent origin. These chemicals influence some physiological traits of the insects which can possibly be used in disturbing the usual life cycle. More basic research and application on an exploratory levels are needed to evaluate the practical utility of chemos-terilants, hormones, pheramones etc. Use of insecticides with proper doses and care may also solve this problem.

Recommendations for integrated pest control cotton: Cotton is a very important cash croup cultivated on vast areas of land in the provinces of the Punjab and Sindh. It contributes a very large amount to the national product in terms of foreign exchange. It feeds textile as well as oil industries by providing raw material. Improved varieties of cotton are now being cultivated and long staple cotton varieties have almost replaced with the new ones. In order to save cotton crop from pest attack there was a need to spray insecticides 4 times in a single crop season against 15 to 20 in USA and Gautemala and 10 to 12 sprays in Australia, but our number has lately risen to almost 10 in cotton growing provinces of Pakistan. Cotton plant suffers from ravages of insect pest throughout its growth period. Diseases are taking heavy toll of the crops all over the world. The losses caused by diseases in Asia have been estimated to 15%. The losses in seed cotton yield in Pakistan is very high. A number of insects success to attack the plant right from seedling to maturity stage. During early stages of its developments, the leaf eating and sucking complex attacks it and later on with crops reaches its maturity.

The cotton crop is delicate and subject to attack by a host of pest complex. A number of disease recorded in cotton are bacterial blight, root rot, boll rot, anthracnose, wet rot, sooty mold, leaf curl, nematode root knot, myrothecium leaf spot, cercospora leaf spot, alternaria leaf spot, etc. The cotton leaf curl virus (CLCV), and white fly. Cotton white fly is one of the serious pests of cotton in Sindh. Beside cotton, it attacks several other host plants and breed throughout year, building up its populations in a short span of time. These diseases in cotton crop are carried over chiefly through infested seed, plant debris, through organisms, excess irrigation water at the later stages of growth, fungi, and other diseases. Host pest such as boll worm, white fly, jassid, aphid, thrip and mites. In order to effectively check these pests integrated control is recommended.

1)            Removal of stubbles and stalks. The cotton growers may be asked to uproot the cotton stubbles and stalks immediately after final picking, 2" below soil level. The cotton sticks must be removed from the field and burnt immediately after collection. By this practice, the hibernating larvae are either killed or exposed to the predating birds.

2)            Malvaceous or Solanaceous plants and other weeds which can attract and harbour the pest should be removed as soon as possible. A weed-free crop is relatively less subjected to the attack of pest complex.

3)         Hairy varieties which show resistance should be evolved and grown for reducing jassid attack. Hairy sheath served as a protective cordon for the inner delicate parts of the leaves.

4)         Release of predators like Scymnus nubilans Muls. (Coccinellidae: Coleoptera) and Chilomenes sexmaculata Fabr. (Coccinellidae: Coleoptera) can reduce aphid population, if possible. Due to their voracious feeding they generally do not take long to bring down the aphid population to a safe level.

5)           Heliothus (Heliotus armigera), an American boll worm and other boll worms cause serious damage.

The following measures may be undertaken:

a)            Fumigation with methyl bromide or phostoxin or solar treatment for 4-5 consecutive days before sowing to eradicate hibernating larvae of pink boll worm.

b)         Seed supplying agencies should also fumigate cotton seeds with the above mentioned chemicals in the sarne way. This treatment should be given a legal backing if necessary.

c)         Proper clearing and regular sanitation programme by the ginning factories can reduce the boll worm infestation considerably. All trash in ginning factories must be burnt to destroy one of the best hibernating niches of the pest.

d)         Picking of egg masses: Picking of egg masses may reduce and eliminate chances of attack of boll worm. This could easily be achieved by deploying the local manpower even the primary school children which are available in abundance in the rural areas.

e)         To minimize the chances of mite 'infestation, other Malvaceous, Solanaceous and Cucurbitaceous plants and weeds should not only be removed from the cotton fields but from their vicinity as well.

f)          In order to control the pink boll worm a sex attractant 'Hexalure' or 'Propylure' may be used, if possible. The males will be attracted in large numbers and the population of this pest can be reduced.

g)         The following parasites may also be tried against the Bollworms, if possible.

(i)            Trichogramma sp. (Trichogrammatidae: Hymenoptera)

(ii)            Goryphus nursei (Ichneumonidae: Hymenoptera)

(iii)            Brachymeria tachardiae (Chalcididae,: Hymenoptera),

(iv)       Actia aegyptia (Tachinidae: Diptera)

(v)        Bracon lefroyi (Braconidae: Hymendptera)

h)         Release of predatory mite Typhlodromus sp. may be carried out to control the Spider mite infestation, if possible. Mite infestation results in defoliation of the crop and heavy damage.

 i)            Chemical control which comes as a last resort to check the pest infestation should only be undertaken, when it reaches an alarming stage. Dusting with BHC or baiting with aldrin may be carried out to check grass-hopper and crickets when necessary. Other insecticides as described in the literature may be used for specific pests as recommended. Some of the other pesticides suitable for use in cotton are diamthoate, methamidophos monoprotophos, endosulphan, thiodicarb, acetamipride, imidachloropride etc. may also solve the problem.

Cotton crop suffers from a number of diseases but the root rot, angular leaf spot or premature defective opening of bolls. For root rot, it is necessary to, i) sow cotton at right time of the season, ii) and to use resistant variety if available. For angular leaf rot, i) use of healthy seed obtained from healthy bolls is very important, to ii) destroy the diseased plant debris when the crop is over, iii) to rogue out the affected and dead seedlings and, iv) to disinfect the seed with fungicides. For premature defective opening of bolls, i)close plantation by increasing rate of seed may also be preferred.