Potato

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Potato Agronomy

Potato is a temperate crop grown under subtropical conditions in India. The economically useful part (the tuber) is a modified stem. This necessitates special care while carrying out cultural operations. The tubers are invariably used as planting material therefore seed preparation and its handling becomes very important. Since the tubers are formed underground, land preparation needs to be done so as to promote a healthy environment both for the roots as well as the growing tubers. Use of tubers as planting material also necessitates greater skill in planting so as to economize of seed and get maximum possible yield. Further potato has sparse root system at the same time it is a heavy feeder of nutrients as well as very sensitive to drought. Therefore, fertilization and irrigation is more intense in potato than other crops. Since it is heavily fertilized and supplied with water as and when required it is natural that potato is exposed to greater competition from weeds than would have been the case otherwise. In addition weeds play a more important role as carriers of vectors of potato pests and diseases and so weeding and earthing up are very important cultural practices in potato. Potato is exposed to very serious pests and diseases. Some of the pests/diseases are so serious that the whole crop is washed out in a few days if timely action is not taken, therefore, adequate and timely plant protection is required. Haulms cutting, harvesting and sorting and grading are some of the other cultural operations which needs special attention in potato due to it being a bulky vegetative organ with more than 80% moisture. Further, potato is used as such as a vegetable, however it is a semi-perishable commodity. About 80% of the produce is produced in the northern indo-gangetic plains, where the summer season sets in soon after its harvest. Unless proper care is taken while harvesting and grading as well as during storage heavy losses can occur. Cold storage are the major method of storage but low cost alternate storage structures have also been developed. A clear understanding of the storage requirement is necessary for proper storage with minimum loss as well as cost. It needs to be processed for getting added returns. Therefore processing is a big industry in potato. Properly timed cultural operations are expected to make potato cultivation profitable as well help meet the nutritional security of the people of the country.

Climate :Potato is a temperate climate crop, however it grows under a diverse range of climatic conditions. It is grown only under such conditions where the temperature during the growing seasons is moderately cool. The vegetative growth of the plant is best at a temperature of 24°C while tuber development is favored at 20°C. Hence, potato is grown as a summer crop in the hills and as a winter crop in the tropical and subtropical regions. The crop can be raised up to an altitude of 3000 m above the sea level.

Land Preparation :Land preparation is crucial to potato since it provides suitable environment for the growth of both roots and tubers. Proper tillage ensures the proper development of roots as well as helps proper retention and movement of water and nutrients to the roots. Moreover, tillage is also practiced to control the weeds as well as to cover the emerging stolons and tubers to prevent them from turning into aerial stems/turning green. The number and type of cultivation that is required for achieving these objectives is the deciding factor. Tillage in case of potato mainly falls into two classes pre planting tillage and post emergence tillage. In India, more so in the northern Indo Gangetic plains, the growing season is short and so only two main tillage categories as mentioned above is followed.

In the northern Indo Gangetic plains the autumn season is the main potato season. An early crop is also taken in many places to take advantage of the high prices of the early crop. At some places especially in the western Indo Gangetic plains a late winter/spring crop is also raised. The date of planting is temperature dependent. In the main crop, planting starts when the maximum temperature is between

030-32 C while in the case of the late winter crop planting coincides with the period when minimum temperature is above frosting temperatures and start warming up. Apart from the time of planting, yield is also affected by the method of planting. The method adopted is also dependent to a certain extent upon the weather/season so that the adverse effect of temperature/moisture could be mitigated and maximum use of resources can be made.

Planting material:Healthy whole, cut or mini tubers

Spacing :Inter-row spacing : 0.60 to 0.91 mIntra-row spacing : 0.15 to 0.45 mOptimum plant density : 30,000 to 53,200 plants/Acre

Seeding rates :Varies with cultivar, market, moisture, planting date, seed size, seed age and cost of production. Generally 600kgs to 1200 kgs /Acre.Seeding depth 5 to 10 cm.

Fertilization :Potato is a short duration shallow rooted crop. Therefore, it is highly responsive to fertilization. As in the case of other crops Nitrogen is the first limiting nutrient in potato also. Phosphorous and potash are also very important in the case of potato. Phosphorus due to its effect on the root system and potash due to its effect on translocation of photsynthate. Apart from these major nutrients, calcium and sulphur is also becoming limiting and potato responses to both have been observed. Zinc, iron, manganese, magnesium, copper and boron are the micronutrients found limiting in potato growing soils and potato responses to them have also been observed in India.Apply mineral fertilizers based on the targeted yield, leaf analysis results, fertilizer experiment results, leaf deficiency symptoms, nutrient uptake, soil analysis results, and nutrient recycling.

Nutrient uptake :3 – 4 kg N1 – 1.5 kg P O2 5

4 – 6 kg K O2

0.2 kg CaO per ton of tuber yield0.3 kg MgO per ton of tuber yield.

Optimum leaf nutrient levels :10,000 – 15,000 ppm N0.17 – 0.22% P7.0 – 8.0% K0.15 – 0.30% Mg0.4 – 0.6% Ca0.15 – 0.20% S10 – 20 ppm B2 – 4 ppm Cu20 – 40 ppm Mn20 – 50 ppm Fe10 – 20 ppm Z

Fertigation Schedule Recommendation

Base Fertilizers :Potassium Sulphate – 120 kgs / AcreSingle Super Phosphate – 420 kgs / AcreAmmonium Nitrate – 72 kgs / Acre

Application Time

Recommended Fertilizers ( Kgs/Acre)

N

K O2

Ca

13:0:46

Calcium Nitrate

( CN)

60% Emergence

-

60

9.2

-

11.4

1 week latter

64

-

8

30

-

2 weeks latter - 60 9.2 - 11.4 3 weeks latter 64 - 8 30 - 4 weeks latter - 60 9.2 - 11.4 5 weeks latter 64 - 8 30 - 6 weeks latter

-

60

9.2

-

11.4

7 weeks latter

64

-

8

30

- 8 weeks latter

64

-

8

30

- 9 weeks latter

64

-

8

30

-

Total 384 240 84.8 180 45.6

Irrigation :Irrigation refers to the practice of artificial supply of water to the crop. In the northern Indo Gangetic plains potato is grown during the autumn season which receives negligible rainfall, hence underground tube wells are used for irrigation while in some places like Maharashtra lift irrigation is practiced.

Potato is very sensitive to water stress. Therefore, it requires water to be supplied through irrigation wherever rainfall is not sufficient to meet the crop needs. As regards when irrigation has to be done, this would depend upon the method of irrigation adopted as well as the scheduling criteria. Normally time interval approach is adopted in autumn season in the northern Indo Gangetic plains. In this case irrigation is scheduled at an interval of 8-10 days initially when the temperatures are warm and later the interval is increased to 12-15 days as the winter sets in and the temperatures cool down. Irrigation on the basis of cumulative pan evaporation has also been advocated in potato. In this case irrigation scheduling when the cumulative pan evaporation reaches 20 mm is recommended.Normally surface irrigation is adopted. Beds are prepared over 8-10 furrows of 6-8 m length and water is let into the bed till the water level reaches 3/4th of the ridge height, if the water level is more then aeration is affected. About 50 mm water is applied at each irrigation through surface method. It is difficult to apply lesser depth of water through this method and this is a big disadvantage of this system in addition to conveyance loss, which is also relatively high in this case.Sprinkler irrigation system can also be profitably adopted for potato. In this case the conveyance losses are minimal and depth of irrigation can be maintained to the required depth. However it is a high pressure irrigation system and requires energy for conveyance as well as pumping. The investment cost therefore is high. In late blight prone areas this system has to be used with caution during the favorable period for late blight incidence.Drip system is another system of irrigation found suitable for most crops and also potato. With this system also conveyance losses are minimum and required depth of irrigation can be applied even daily. This is a low pressure system and so the energy requirement is lesser than that for sprinkler system. However, the initial investment is very high due to close spacing of the plants which increases the requirement of pipes for main lines, laterals emitters etc. which makes the cost exorbitant.

Weed Control :Weeds affect crop growth and yield in a variety of ways. They compete with the crop for space, water and nutrients. However in potato they are more serious because potato is a short duration crop and fast early growth is essential for high yield. Presence of weeds at early stages will slow down early growth due to competition for space, water and nutrients while presence of weeds at harvest would make it difficult to expose the tubers thus increasing the cost of harvesting as well as cumbersome. Weeds also harbor vectors of potato pests and diseases which make pest and disease control difficult unless weeds are controlled. Weed control traditionally is done through cultural methods in potato. However, in some situations chemical weed control is advantageous while in some other situation a combination of the two i.e. integrated weed controls is desirable. For an effective weed control strategy, the weeding operation should be properly timed as well as the cropping system i.e. crop sequence or inter cropping system should also be borne in mind.

Earthing up :As the name itself indicates earthling up refers to the practice of remaking up the ridge by bringing soil from the furrow and putting it back on the ridges. Thus it refers to the practice of making up the ridges in an inter cultural operation. This operation is normally done at stolonization stage because if done later stolons and roots are liable to be damaged. In the case of manual cultivation, earthing up is done using hand tools like Khurpa. Where bullocks are used for earthing up, a bullock drawn plough is used for earthing up while in the case of mechanical cultivation, a ridger is used for earthing up.

Plant Protection :Plant protection refers to the practices adopted for controlling the pests and diseases attacking the potato crop. Potato crop is infested by a variety of fungal, bacterial and viral diseases. As regards pests, some pests attack the foliage while some attacks the tubers. Many of the diseases in potato are soil/seed borne and so once infected is very difficult to control them. Similarly viruses affect the seed quality and so has a chain of implications. Thus proper diagnosis and control of pests and diseases is of utmost importance. Some of the important pests and diseases attacking the potato crop are late blight, early blight, wart, common scab, black scurf, bacterial wilt, soft rot / black leg, viruses, cutworm, white

grub, aphids, leaf hoppers, tuber moth, mites, potato cyst nematode, root knot nematode etc. Not all pests and diseases are present everywhere. Some of them are more widespread than the other while some are very localized e.g. Wart is one such disease, which is confined to the Darjeeling hills while golden nematode is another such pest, which is confined to the Nilgiri hills.

Late Blight :Late blight is the most important fungal disease of potato in perhaps most of the potato growing regions of the world. In India, it is very widespread in the hills where the disease is very severe but in the plains it is less severe or not of regular occurrence. The problem with this disease is that it spreads very fast and unless it is identified early, control is difficult. A multi pronged strategy for control of late blight is desirable for effective control.

Early Blight :It is a problem in the kharif crop in the plateau areas. These diseases occur only during specific growing conditions and can managed through a combination of cultural and chemical methods.

Management :Effective management strategy would involve a combination of different methods viz chemical, crop husbandry methods and host resistance etc. in an integrated manner so as to reduce both foliar and tuber infection. The chemical method would involve use of both contact and systemic fungicides. As regards contact fungicide Mancozeb is the most common while metalyxl is the most common systemic fungicide.

Cultural practices: Cultural methods aim at eliminating or reducing the initial inoculum load in seed tuber and other sources. Care should be taken to avoid tuber infection by covering the tubers with a thick ridge, minimizing irrigation after the blight has set in and by cutting the infected haulms. The tubers should be harvested after proper skin curing and diseased tubers should be sorted out before storage. Elimination of refuse piles in hills could also help to minimize disease inoculum. It has been estimated that the onset of epidemic can be delayed by 3 to 6 weeks if all primary infection from early potato can be eliminated.

Wart :Wart is caused by Synchytriunendo bioticum a member of Chytridales. It causes great damage to potato seed industry in the hills. The disease once established is difficult to eradicate since the resting spores of the pathogen remain viable for many decades.Rough warty mostly spherical outgrowths or protuberances appear on buds and eyes of tubers, stolons, or underground stems or at stem base. Wart may appear occasionally on above ground stem, leaf or flowers. Underground galls are white to light pink when young that become brown or light black with age. Above ground galls are green to brown or black. The wart tissues are soft and spongy. Tubers may get completely replaced by warts, which desiccate or decay at harvest.

Management :Potato wart is restricted to Darjeeling and adjoining hills in India. The disease has been successfully managed by sanitation, long crop rotation, growing resistant and immune varieties and by enforcing strict quarantine legislation in Darjeeling hills. Control of the disease is possible by cultivation of wart immune varieties.

Application of fungicides and chemical to soil is costly and not practical. Inter cropping potato with maize, or rotational crops such as bean and radish have been found to reduce population of viable resting spores in soil.

Scab:Common Scab is very wide spread soil/tuber borne disease. It does not cause yield loss but disfigures the tubers with the result there is economic loss. It is caused by Streptomyces sp. The symptoms ranges from abrasions of skin, russettings, corky lesions around lenticels which may be star shaped or irregularly circular, irregular concentric corky rings around lenticels, raised rough corky pustules and 3-4 mm deep pits surrounded by hard corky tissues. Use of healthy seed is the first requirement for control of the disease.

Management :Treating the seed tubers with organomerculrial compounds (0.015% for 20 minutes) or boric acid (3% for 30 minutes) before or after cold storage is recommended.Keeping the soil at optimum moisture content right from tuber initiation also checks the disease development.Crop rotation with wheat, peas, oats, barley, lupin, soybean, sorghum, bajra and green manures checks the disease.

Black Scurf :The affected tubers appear shabby with black mass sticking on the tubers which leads to lower economic return. Normally yield losses to the extent of 25% in the hills and 10% in the plains have been reported.The emerging sprouts when infected develop cankers causing girdling of the stem bases. The affected plants show upward rolling of leaves with pinkish or purplish margin.The roots and emerging stolons also get infected having rottage of cortical tissues. Therefore infected plants have poor root system and infected stolons give rise to deformed tubers.The tubers from infected plants show dark brown to black irregular lumps sticking on the surface of tubers.Tubers may also show skin cracks, crater like depressions, pitting, stem end necrosis and shape deformity.

Bacterial wilt / brown rot :Bacterial wilt/brown rot is the most destructive bacterial disease of potato. Besides potato, the pathogen Ralstonia solanacearum (formerly Pseudomonas solanacearum and more recently, Burkholderia solanacearum) also causes lethal vascular wilt diseases in more than 200 plant species belonging to at least 50 different plant families including several crops like potato, tomato, chilli, brinjal, pepper, ginger and others. It is very widespread in southern India. Since the disease affects the vascular bundles, the symptoms of the disease is seen in the field as drooping of foliage as in the case of water stress. Control of bacterial wilt is difficult but it can be managed so that the loss is minimized.

Soft rot of potato caused by bacteria is a serious problem of potatoes in storage as well as transit while in the field it causes black leg. Soft rot of tubers and black leg or stem rot is mainly caused by coliform bacteria called Erwinia carotovora ssp. carotovora, E. carotovora ssp. atroseptica, E. chrysanthemi. The same pathogen also causes the black leg in fields. Losses caused by bacterial decay in seed and storage are very common. Extreme tuber losses of more than 80% have also been recorded in poorly ventilated transport system. Soft rot of potato can be observed at any stage right from tuberization in field until it reaches the market and /or consumer.

The disease is not only present in the cool, temperate climates but also in the warm, tropical potato growing region of the world. The incidence of the disease is greater in the tropics due to high temperature and humidity. For management of the disease a combination of methods including avoidance, exclusion and eradication are to be practised.

Management of bacterial wilt : Management of the disease due to some races is by adopting 2-3 years crop rotation. On the contrary wilt caused by the heterogeneous solanaceous race 1, which is most prevalent throughout the Indian sub-continent, is really difficult to manage.

Avoidance : Avoidance by using healthy seed: The pathogen perpetuates through two distinct ways viz. infected tubers and field soil. Latently infected but looking healthy tubers are the most important carriers of R. solanacearum. High load of inoculums is carried in vascular tissues, on surface and in lenticels and not eradicated by low temperatures in the long period of cold storage. Such infections go unnoticed. Carryover of the pathogen in seed tubers has played very significant role in disease epidemics and its local, continental and intercontinental spread. Therefore introduction of inoculums in the field can be best avoided by use of healthy seeds. Wilt can also be effectively managed by use of healthy seeds in infested soils. Use of healthy seeds alone for planting in infested soil reduces wilt incidence by 44% to 94%.

Avoidance of congenial conditions for disease development. In North-eastern and North-western hills, wilt does not appear in summer crop before July. Therefore planting potato crop in second week of February and harvested in June reduces wilt incidence to a negligible extent.Field inoculum can be brought down considerably by physical and chemical manipulations and soil amendments.

Exclusion by physical and chemical means :Raising the soil temperature to 85°C for 15 minutes by steam application effectively eliminated the pathogen from the soil up to the depth of 30-40 cm. Thus wilt incidence was negligible. Raising the soil temperature by covering the field with polythene film has been found to be effective in reducing the wilt.

Soil disturbance has deleterious effect on survival of the pathogens. One to two deep ploughing of the field during summer in plains and winter ploughing in hills reduces the wilt incidence to an extent of 70%. These ploughing expose the infected root remnants, plant debris, and bacteria glued in soil in the form of pellets to desiccating sunshine.

Use of soil disinfectants and broad-spectrum toxic chemicals such as chloropicrin, DD mixture, ethylene di-bromide, sulphur followed by lime and zinophos have been found to check the disease. Application of bleaching powder @ 12 kg/ha mixed with fertilizer or soil drenching before or after first earthing up reduced the bacterial wilt incidence by 80% and also increased potato yield.

Soil amendments also help in wilt management. It is a popular perception that acidic or alkaline soil is not conducive to the bacterial wilt pathogen.

Exclusion by means of crop rotations: Planting non-host rotational crops also brings down incidence of bacterial wilt. It helps in exclusion of the pathogen by way of starving, increasing antagonist activity and reducing multiplication of the pathogen. Successful reduction in wilt incidence has been obtained by following crop rotations with wheat, maize, oat, barley, sun hemp, finger millet and vegetables like cabbage, onion, garlic and others. Among the above rotational crops, roots of finger millet remains free

from R. solanacearum. However, all other plants carried root infection as small necrotic lesions without systemic colonisation. Therefore, these crops can help reducing the pathogen build up without completely eradicating it.

Virus Disease :Viruses being intracellular pathogens employing host machinery for their propagation cannot be controlled through chemical means as in the case of fungal and bacterial diseases. There are many viruses infecting the potato crop and depending upon their nature causes varied symptoms. Their control is more a management aspect and constitutes a very important component of plant health management (PHM) such that the losses are below the economic threshold. The different components of the management strategy are quarantine which is applicable in case of viruses not present in India, cultural practices to ensure sanitation, forecasting and control of vectors of the viruses, using virus resistant varieties, eliminating viruses in cases where the sample size is small and very importantly, using healthy seed. In most cases combination of methods may have to be used in an integrated manner.The common symptoms of viral diseases in potato are mosaics of various kinds like leaf mottle, mild/rugose mosaic. The mosaics is characterized by irregular normal green and cholorotic areas on top leaves, the cholorotic areas may be faint or severe depending upon the severity of the disease.

Management :Cultural practices :Cultural practices involve sanitation (removal of infected debris), use of certified planting material, growing crop during vector-free/low vector period, crop rotation, use of barrier crops to check spread of the vector and virus, isolation of the crop, etc. Tospo virus causing stem necrosis disease in central and western parts of India can be avoided by delaying planting from September end/October beginning to last week of October/1st week of November in the northern Indo Gangetic plains. Some weeds like Solanum nigrum, Datura metel, D.stramonium and Polygonum spp. act as reservoirs of many potato viruses and their eradication can help in the management of viral diseases. Disinfection of implements before use for cultural practices particularly in seed plots is also helpful in checking the spread of contagious viruses like PVX, PVS and the viroid PSTVd from one field to another.

Cut Worms :Cutworms are polyphagous insects of cosmopolitan distribution. Two species are Agrotisipsilon (Hfn), A segetum Schiff., widely distributed in plains and hilly regions, respectively. The larvae (caterpillars) of cutworms damage the crop by cutting the young plants at the base and later on by feeding on shoots and leaves. After tuberisation, they feed on tubers by making deep and irregular galleries in them thus reducing the market value of infested tubers. In badly infested fields tuber damage may vary from 12-40 %.

Management :Cultural and mechanical : Deep ploughing of potato fields during summer months in the plains exposes the immature stages to high temperature and to predatory birds. Similarly, deep ploughing of fields during autumn in the hills also minimizes cutworms population. Light traps installed in and around potato fields attract the adults of cutworms, and helps in mass collection and destruction of the moths.

Chemical : Chlorpyrifos 20 EC is recommended at 0.05% concentration for the cutworm control. The first spraying with either of these insecticides should be given soon after noticing the attack on the crop. This may be repeated once after 20-30 days of first spraying if the damage persists.

Biological: Broscus punctatus Dist and Liogryllus bimaculatus Linn have been reported to be the parasitises of cutworms larvae. Macrocentrus collaris (Spin), Neteliaocellaris (Thomson), Coelichneumon sp. nrtruncatulus Thomson , Periscepsiacarbonaria Panzer and Turanogoniachinensis Wiedemann also parasitise A. ipsilon and A. segetum under natural field conditions. Entomogenous fungus, Metarrhizium anisopliae (Meld.), pathogenic bacteria Bacillus thuringiensis Berliner and entomophilic nematode, Stinernema (Neoaplectana ) sp. are also well known as dominant regulatory factors for cutworm populations from various parts of the country. Integrated management: The cutworms can be successfully managed by adopting the following IPM

schedule : -- Deep ploughing of potato fields during summer months in the plains and in autumn in hilly areas. -- Light traps be installed in/around potato fields to attract the moths of cutworms for mass collection and destruction.-- Spraying of crop and drenching the ridges with chlorpyrifos 20EC @ 2.5 lit/ha after noticing 2% plant damage in the fields.-- Conservation of natural enemies of cutworms by spraying the crop and ridges with biopesticides (Bt @ 109 spores /ml)

White Grubs : White grubs are distributed throughout the country. The damage to potato is caused by the grubs only, which feed on rootlets, roots and tubers. The white grubs infested tubers, have poor market value. The grubs damage the tubers without any symptoms on the foliage. Thus, the farmer remains unaware of the damage to tubers until harvest. The damage is more severe in the years following high adult activity. In Shimla hills, yield losses to potato crop have been reported to be as high as 85%.

Management :Cultural and mechanical : In the endemic areas, autumn ploughing in hilly areas not only exposes the grubs to adverse conditions (low temperatures) but the exposed grubs also become prey of the birds. The use of nitrogenous fertilizers, especially ammonia and urea, at higher doses kill the first instar grubs. Besides, the light traps may also be used for collecting the beetles during night. The beetles can also be collected by shaking or jerking the host plants during night. The fallen beetles should be collected and destroyed by putting them either in kerosinized water or by burning. The host trees of adults (beetles) should be lopped or pruned and sprayed with contact insecticides before the emergence of beetles in June / July.

Chemical : Infestation of white grubs can effectively be managed by applying insecticides to the soil at earthing up of potatoes when the grubs are young and delicate. Soil treatment with granules of fensulfothion / quinalphos / phorate / carbofuran or isofenphos @ 2.0 units / ha. at earthing is recommended for the control of grubs. At the time of beetle's emergence, spraying of host trees with carbaryl, fenitrothion, monocrotophos, endosulfan or quinalphos at 0.04% may register effective control of beetles that are responsible for next generation grubs damaging potatoes.

Biological : A number of bio-control agents are known to manage white grubs in different parts of the country. These should be encouraged either by conserving the existing populations or by introducing and establishing the known bio-control agents obtained from new localities. Some of the potential bio-control agents are : coliids, Campsomeris collaris F., Scolia aureipennis Lepeletier and S.spustulata Magr., pathogen like Bacillus popillae Dutky, Metarrhizium anisopliae (Metch.), Beauveria brongniartii (Sacc.) Petch, Isyr.and B. tenella (Del.), and entomophilic nematode, Steinernema sp.

Integrated management : The IPM schedule suggested for the management of cutworms has also been found beneficial for the management of white grubs in potatoes. Besides, other practices viz., removal of alternate/collateral hosts of the beetles from the vicinity and within potato crop, spraying of the beetle hosts and bunds with contact insecticides and early harvesting of potatoes in areas prone to white grubs.The larval stages live in the soil from July-November and initially feed upon roots of living plants, ingesting at the same time large quantities of soil and dead organic matter and afterward feed upon tubers. Emergence of adults starts with the onset of first monsoon showers in June onwards. Understanding the life cycle of white grubs makes it easy to manage them.

Aphids :constitute a major group of pests infesting potato crop. They are extremely important being vectors of many potato viruses. Both the adults and nymphs suck the leaf sap. Aphids transmit potato virus Y (PVY) and potato leaf roll virus (PLRV).The aphids start appearing on potato crop in the North- Western plains of India from the second week of November, and in the Eastern plains in early December, reaching the critical level (20 aphids per 100 compound leaves) by the end of December in the former and during1-2nd week of January in the latter area. In the North- Western higher hills i.e. from Kashmir to Kumaon and in North-Eastern hills, the critical level generally reaches by the end of July. In the plateau region of Maharashtra, aphid infestation remains almost negligible in Kharif crop while on Rabi crop, it appears in the second week of November and critical level reaches by the third week of December. The management of aphids involves monitoring its appearance and then controlling them through use of chemicals.

Management : Chemical : In the higher hills, where potatoes are grown as rain-fed crop under long-day conditions, only foliar systemic insecticides such as methyl-demeton, dimethoate, thiometon or monocrotophos etc., at 0.03% concentration are recommended for controlling aphids on seed crop. The first spray may be given soon after seeing 1-2 aphids/100 compound leaves on the crop and subsequent 1-2 sprays be given after 10-15 days depending upon the aphids' pressure. Under irrigated conditions, application of granular systemic insecticides like phorate 10G or carbofuran 3G @ 1.0 -1.5 kg /ha is effective for 40-50 days. Granular insecticides applied at planting will not be effective to protect the crop throughout the crop season. Therefore, one or two need- based sprays with any of the above mentioned foliar systemic insecticides at 10 to15 days interval would be needed during the later stages of crop.

Biological : Allograpta favana (Wiedemnn), Episyerphus balteatus (De Geer), Ischiodon scutellaris (Fabricius), S.scripta (Linnaeus), Sphaerophoria indiana Bigot; Leucopisfu midilarva Tanas, Menochilus sexmaculatus(Fabricus) among the predators and: Aphelinus sp. and Aphidiuscolemani Viereck among the parasitoids have been reported to be promising. At Shimla, Aphelinussp has been found to parasitize 100 per cent M.persicaeunder glass houses conditions.

Integrated management : The integrated management strategies for vectors (mainly aphids) are the need of hour. There is a need to evolve strategies for primary and secondary potato seed growing areas. Some of the approaches suggested are:-- Planting early bulking and/or maturing cultivars to help seed production programme in areas having short aphid-free periods so that the seed crop may escape the population pressure of aphid vectors.

-- Introduction and conservation of bio-agents that can establish themselves quickly in the crop season and help in checking the initial buildup of the vectors.-- Application of effective insecticides at the right time in recommended manner.-- Adjustment of planting and harvesting in different potato seed producing areas in a manner that the crop faces none or minimum population-pressure of vectors.

Leaf hoppers : The leafhoppers can damage the potato crop both as vector and direct pest. The species like Alebroidesnigro scutulatus Dist. and Serianaequata Singh damage the crop as vectors of phytoplasmal diseases, viz. purple top roll (PTR) and marginal flavescence (MF). These are predominantly present at/around Shimla from May to August.Amrascadevastans causes direct damage to potato crop as a pest and is widely distributed over all the potato growing regions in India. However, it regularly causes serious damage to early planted potato crops normally grown in Western Uttar Pradesh, Haryana and Punjab. On the other hand, it is graded as sporadic pest in Maharashtra and Karnataka. Being polyphagous it feeds on cotton, okra, brinjal, sunflower and holy hock. Both the adults and nymphs cause damage by sucking the sap from the foliage and depleting the cell content. The first symptom of its attack could easily be seen as black spot at the tip of leaf and/or end of each lateral vein let. Often the entire margin of infested leaf may roll upward which subsequently turns brown and looks as if scorched by fire or drought. These brown margins continue to increase in width until a narrow strip of leaflet along the mid rib remains green while the rest of the portions shrivel and die. Normally the older leaves below the growing tips burn first. However, upon heavy infestation, every leaf succumbs rapidly and dies much before the normal development of tubers is completed. On an average, the pest is responsible for 90-100% foliage damage. This type of foliage damage is popularly known as 'hopper burn' and leads to 20-30% yield losses to early-planted potato crops in the western Gangetic plains.

Management of leaf hoppers : Cultural and mechanical : The practice of adopting suitable crop rotations with non-host crops in pest prone areas and providing proper isolation to potato crop from susceptible hosts are most useful management components for

thprotecting the potato crop. Delayed planting undertaken on 25 September for early crop and during middle of October for the main crop reduces the incidence and impact of the pest.

Chemical : Sprays of monocrotophos @ 0.60 kg / ha. in 1000 liters of water is most effective. First spray may be given immediately after the appearance of pest and if needed spray may be repeated after 10 days. However, in the crops already treated with systemic insecticides against aphids, no additional spray is required for leaf hoppers.

Integrated management : In North-western plains, management components like clean cultivation, isolation of potato crop from

thalternate hosts, delayed planting on around 25 September in early crop and during mid October in main crop, encouragement of natural enemies and need based insecticide sprays are quite effective.

Potato Tuber moth :The potato tuber moth, Phthorimae aoperculella (Zeller), (Lepidoptera: Gelechiidae) (PTM) is a native of South America and is the most obnoxious pest of potato both in fields and the country stores. In areas where the pest is left unmanaged, the losses to potatoes kept in the country stores may be as high as 70 %. Due to inadequate cold storage capacity, raising more than one crop in a year and non-adoption of recommended control measures, PTM has the status of a serious/key pest. Prolonged dry and hot weather is quite conducive for PTM multiplication. PTM larvae damage the crop foliage and also stems, exposed tubers in field and stored tubers in the country stores with estimated losses to the tune of 26% and 56 %, respectively. In infested tubers, the feeding tunnels are packed with black excretory pellets and the larvae are inside the tunnels. PTM can be controlled effectively only through a combination of different methods.

Nematodes :

Root-knot nematode infests the roots and tubers of potato plants leading to the hindrance in normal functions of nutrient and water uptake / translocation. Infested plants are dwarfed, chlorotic and have stunted foliage and poor root development. The galls on roots are small and often go unnoticed but tubers have warty growth or rough surface that reduces their market value.

Management :Cultural practices : -- Deep ploughing and sun drying of fields during summer months help in drying of infective stages of larvae.

nd-- Planting of potato crop during the 2 week of October in autumn and in early January for the spring can limit RKN infestation on tubers.-- Burning of trash in field before planting helps not only by sterilizing the soil but also enriching it.-- Growing one row of trap plants like Tagetespatula and T. erecta (African marigold) in between 2 or 3 rows of potatoes improves the crop performance by reducing RKN infestation.-- RKN are being polyphagous in nature having a wide host range yet a few crops are free from M. incognita infestation allowing crop rotation with a non-host, like maize, wheat, millets, beans etc. for reducing RKN infestation.-- Potatoes harvested from RKN infested field should not be used as seed for subsequent crop. Movement of the soil and water from infested fields to RKNs free fields should also be avoided. Besides, the field should be kept free from weeds as RKNs have a wide host range and most of the weeds help them.

Chemical management : An effective control of RKN can be achieved either through carbofuran @ 3 kg / ha. or aldicarb @ 2 kg / ha. or ethoprop @ 10 kg / ha. preferably in two equal splits i.e. half at planting and remaining half at earthing time.

Biological control : A large number of biotic agents such as fungi, bacteria, predacious nematodes, protozoan etc. are reported for managing the RKNs. However, an efficient use of these bio-agents has not yet been possible.

Integrated approach : The IPM schedule consisting of soil solarization, adjusting planting dates, growing trap plants like Tagetus spp rotation with non host crops, conservation of natural enemies (bacteria, fungi etc.) and need based application of nematicides helps in control of nematodes in the soil.

Harvesting :In the case of potato in the northern plains, the crop can be harvested before full maturity to take advantage of the market prices. In the case of the seed crop also after the tubers are fully grown the haulms remain active for some time. The skin maturity does not take place as long as the haulms do not completely die away. Since this takes a lot of time which can otherwise be used for growing another crop, haulms cutting is done. Haulms cutting is a must for the seed crop and for the crop whose produce is likely to be stored for a long time either in cold stores or in country stores because only after haulms cutting the tuber skin starts maturing and a mature tuber skin is essential to avoid bruising of the tubers during harvest. In the case of the early crop or in the crop which is sold and consumed within a few days after harvest, halums cutting is not essential. Therefore generally in the main crop, haulms cutting is done about 4-5 days after the last irrigation and the fields left as such for tuber skin maturity and drying of the field. About 8-10 days after haulms cutting, the tuber skin would be hard enough to withstand harvesting. Generally haulms cutting is done by hand implement like sickle but contact herbicides like Diquat have also been recommended.

Post Harvest :Potato harvest is a critical cultural practice. The time of harvest and the method of harvest are some of the critical decisions to be made. The time of harvest is decided by the method of disposal of the produce. If the crop is a ware crop for immediate disposal, then the crop is harvested any time depending upon the market prices. However, if the crop is for either seed or ware but is to be stored then harvesting has to be scheduled depending upon the time of haulm cutting. For processing also scheduling of harvesting is a critical operation because the crop in this case has to be harvested at its physiological maturity and early as well as late harvest impairs the tuber quality.

Potatoes grown on improperly prepared fields are damaged while harvesting mechanically and have poor storage quality. Therefore, proper management of pre-storage factors that affect the keeping quality of potatoes is essential for getting good returns.

Grading :Grading is a critical operation in potato, which is required for easy marketing and to get a good price for the produce. Normally for house hold consumption, medium sized tubers are preferred. In the case of the seed crop, small to medium sized tubers are preferred while in the case of processing large sized tubers are generally preferred. Grading is done both by hand as well as graders. Various types of graders of various capacities are available in the market.

Storage :About 80% of the potato production in India is in the Indo Gangetic plains. The produce is harvested in January/February and summer sets in soon after. Therefore, proper storage is a must to minimize losses since potato is a semi perishable crop. It has been estimated that under tropical and sub-tropical conditions, losses due to poor handling and storage can amount to 40-50%. The losses during storage can be physiological as well as pathological in nature. Proper agronomic practices would minimize physiological losses while adequate pest and disease management is essential for minimizing pathological losses during storage, various biochemical changes in the carbohydrate content, nitrogen fractions, enzyme systems etc. take place in the tubers. These affect the quality of the stored tubers. Therefore, the method of storage is an important consideration. Normally for seed purposes it is advisable to store in cold stores since the seed quality is not impaired. However, for processing storage

0under warmer temperatures of 10-12 C is preferable. In this case sprout inhibition becomes important. TCNB, MH, CIPC and some natural substance and even irradiation have been found effective. Sometimes due to lack of space and/or cost, potatoes are also stored in country stores and many improvised country stores are being adopted in many parts of the country.