Potato

Insect Management

Sucking Pests Tuber Moth

Potato aphids and their management

  • As vectors of viral diseases, aphids Myzus persicae and Aphis gossypii play a vital role in limiting disease free potato seed production.
  • Thus regular replacement of seed with virus free seed stocks is essential failing which crop yields are reduced by more than 50 per cent.
  • In the Indo-Gangetic plains, 90 per cent of potato crop is raised in autumn season and the main vector appears later in the growing period, migrating from the secondary host plants.
  • The potato crop, however, is raised throughout the year in the country either in the plains, plateau or in the hills.
  • For achieving success in potato cultivation, we must have the right kind of variety and virus free seed stocks to start with because viruses cause degeneration of the crop in subsequent generation.
  • The main viruses infecting the crop are PVX, PVS, PVA, PLRV and PVY.
  • Amongst these, PLRV and PVY are the most destructive and aphid transmitted.
  • In Jalandhar (plains), yield losses in potato due to PVY and PLRV were between 13.9 to 20.1 and 7.5 to 15.7 per cent in autumn season and 44.0 to 57.2 and 38.8 to 60.0 per cent in spring crop.

Role of aphids in virus transmission

  • Viruses differ in their mode of insect transmission.
  • In older system viruses were described as either non-persistent, semi-persistent or persistent, depending upon whether ineffectively was retained by the vector for minutes, hours to several days, or weeks.
  • In the newer system viruses were classified as stylet-borne or circulative, terminology descriptive of the mechanism by which transmission occurs.
  • More recently the term non-circulative has been proposed to encompass both non-persistent and semi-persistent transmissions, since some viruses may be acquired and inoculated via the food canal of the maxillary stylet.
  • The aphids after feeding on the infected plant may retain the infection even after molting and often for entire rest of the life.
  • Opinions differ as to the multiplication of PLR virus in the body of the vector.
  • The aphid clones, which are efficient in transmitting leaf roll virus, may not necessarily be efficient in transmitting virus Y and vice versa.
  • The nymphs and adult apterous forms of M.persicae and A.gossypii are more efficient in transmitting PVY than adult Alta.
  • The late instars and adult apterae are more efficient in transmission of different strains of PVY than the adult Alta.
  • The environmental factors influencing aphid transmission of PLRV and PVY under Indian conditions have been studied.

Aphid dispersal and settling

  • Dispersal of the aphids is affected by many factors.
  • Before trying to elucidate these factors, it is worthwhile to differentiate the movements for host alteration and that for migration.
  • Host alternation refers to the movement between host plants to ensure the survival of aphids.
  • Migration refers to the movement of individuals, with or without host alteration, over considerable distances.
  • Host alternating species like M.persicae has two or more different species of plants of different families to complete sexual and asexual phases of their life cycle.
  • In temperate countries they shift to peach trees during autumn to tide over the severe winter through egg stage.
  • In India, however, they form sexuals and lay eggs on peach trees in small numbers at an odd time i.e., February.
  • In temperate regions of the world. M.persicae moves to primary hosts instead of other summer secondary hosts during autumn season under long, cold nights and short days.
  • Not all aphids leave the secondary hosts in this situation provided suitable food supply continues there.
  • In short, the aphid has three main periods of long flight during the year in temperate countries i.e., one in spring from primary to secondary host, then dispersal amongst various secondary host plants and finally in autumn migration back to the primary host plants for over wintering.

Monitoring and forecasting of aphids

  • Knowledge of aphid monitoring is important for deciding whether, when and how to grow and protect seed potato crops.
  • Sampling methods for monitoring of populations in the field have been reviewed.
  • Various types of traps are in use all over the world.
  • Some of them are based on attracting aphids while in flight by desirable colours such as yellow.
  • These are described below:

Traps

Water trap or colour type:

  • Moericke developed a simple and inexpensive, yet very reliable trap based on detailed study of the colour vision of green peach aphid (M.persicae). Tin dishes (46x26x8 cm) are painted with a yellow colour base and filled with water (Fig. ). Holes are left near the rims for drainage of excess water during rainfall.

Sticky trap

  • These traps consist of 30x12 cm cylinders painted yellow and coated directly with a grease banding preparation. These have been subsequently improved and standardized. Transparent plastic sheets bearing sticky grease were utilized to cover the metallic cylinder as and when required. Sticky traps are efficient in locating the frequency of aphid flights and have been in operation for the last many years at Rothamsted Experimental Station, Harpendun, UK.

Flat sticky traps :

  • Flat sticky traps are approximately 930 sq.cm in area and are coated with grease banding compounds. These were used in studying Brassica aphid in UK.
  • Recent studies have modernized the sampling techniques.
  • Frequent sampling of the air by sucking it at various heights is done in order to find out the aphids in motion in air at different altitudes.
  • This can divulge the dispersal and migration of aphids as they commence moving in or out.

Aphid critical level

  • To save the crop fromvirus infection it is desirable that the hauls should be cut at a time when the number of aphids reaches the critical level i.e., 20 aphids/100 leaves.
  • Moerick's yellow water traps have been found to help and save substantial scarifies yield in Dutch seed industry due to safely delaying the harvest when aphid build up is below the critical level.
  • Level of 20 aphids/100 leaves developed over fifty years ago in UK holds well in Indian conditions too.
  • The basis of accepting this threshold in the seed plot technique was that the aphid build up on potato crop under Indian plains during autumn season normally remains low upto the end of December by which time the crop is already mature hence the degeneration rate is assumed to be low.
  • Primary seed production areas of north western India where the population of M.persicae remains low till the maturity of the crop, permit the realization of maximum yields.
  • But in the secondary seed producing areas of eastern plains where the aphid population becomes high early in the crop season, there is likelihood of losses in yield of the medium and late maturing varieties which are still in active stage of tuberisation, and every day adds about 3 q/ha.
  • Thus if the haul cutting is delayed by 8 to 10 days it would increase the yields by over 20-25 q/ha.

Aphid population in relation to seed production in different agroclimates

  • In Karnataka, aphid is found on potato throughout the crop seasons.
  • In rabi crop, it generally appears in 1st week of January at
  • Belgaum and crosses the critical level by next week.
  • In kharif crop, it appears from the beginning of August and crosses this level within a week.

M. persicae populations on potato in Karnataka

Districts Appearance Critical Levels Peak levels Free Periods
Bangalore August First week August second week September-March April-July
Belgaum January first week; July fourth week January second week; August second week January-March, September-October April-June; April-June
Chick magalur (KR Hills) Nil Nil Nil Throughout the year
Dharwar August first week August second week September-October November-July
Hassan March first week July second week March second week July last week March last week July-September October-February
Kolar August first week August August October

  • In the area where low aphid period is limited, seed crop can be raised for local use by prolonging this period with the application of systemic insecticides.
  • This will make the farmers of these regions self sufficient in seed.
  • The areas which remain under high aphid population are not suitable for growing seed potatoes as in spite of pesticide application the incidence of vector transmitted viruses remains high.

Control measures

  • Since M.persicae has been reported to develop resistance to all major classes of insecticides and with the increased use of these, the number of cases of resistance has increased considerably, therefore, pesticides as means of controlling it or other potato aphids should be used judiciously.

Cultural control

  • Cultural control of the pest/vector is another important component of management.
  • This has been demonstrated as best in potato crop.
  • Potato was probably the first crop in India, where a single component of integrated pest management was advocated and has since been very successful.
  • The name given was, however, different i.e., "Seed Plot Technique".
  • The component was "Planting Season", the seed potato cropping season was shifted from "the spring" to "autumn season" in the plains and during the period, the vector's population remained low/or below the critical level.
  • This has revolutionized the potato seed production programme in India.
  • Besides, this also included rouging of diseased and off-type plants at least twice during the crop, viz., 40 and 70 days after planting, vine-killing or haul killing by end of December to first fortnight of January to prevent spread of potato viruses infection by vectors.
  • Since the population of aphids remain below the critical level (20 aphids/100 leaves) during this period in most part of Indo-Gangetic plains of India.
  • Application of fertilizers and plant products also regulate M.persicae build up.

Chemical

  • However, the role of application of insecticides cannot be totally ignored in potato seed crop.
  • As M.persicae generally appears after 15th November in the north western Indian plains it is suggested that granular systemic insecticides like phonate 10G @ 1.0 kg a.i./ha be applied at first earthing up.
  • This ensures protection against aphids between 45 to 55 days.
  • One need based subsequent foliar systematic insecticidal spray would be advantageous.
  • For ware potato crop, there is no need of insecticidal application for the control of aphids as its population does not attain pest status.

Bio-Control

  • The current thrust in plant protection is also through the use of bio-control agents.
  • In India, M.persicae is attacked by over 24 predators, (Syrphids, Chrysopids, Cocinellids), 22 parasitoids (Aphidiidae, aphelinidae) and 5 entomopathogenic fungal pathogens (74).
  • But only a few of these bio-agents have been attacking.
  • M.persicae and A.gossypii.
  • Though no serious effort has been made in utilizing these natural enemies yet some reports are available.
  • Under laboratory conditions Aphelinus sp. Caused 100 per cent mortality to M.persicae.
  • Similarly, A.colemani Vierck was observed to kill 70 per cent of the aphids under field conditions in Karnataka. M.persicae population was again suppressed by 78 per cent by the release of six second instar larvae/plant of Chrysopa sp. On tobacco.
  • Some predators are also known to regulate its population.
  • In primary seed producing area, the main problem is of late arrival of these bioagents when the damage by the vector has already been done.
  • To overcome these problems, research is needed in selecting out such bio-agents which can establish in the early phase of the vectors development and which do not allow these aphids to cross the critical level.
  • In ware crop, use of these agents will be of immense value.
  • The other management strategies should include use of pheromones, plant products, repellents and even bio-technological approaches to combat these aphids.
  • Pheromones are odorous molecules used by insects as powerful communication devices.
  • In addition, there are alarm pheromones, which help aphids to protect from predators and trail pheromones among socially organised insects.
  • The pheromone released by aphids through the pair of cornices (siphunculi) is known as alarm pheromone, the main chemical component of this alarm pheromone is (E) B-fernesence.
  • It is released by aphids to warn fellow/nearby aphids to stop feeding and move away from that side to avoid predators.
  • The aphids thus get disturbed and even drop from the plants.
  • Thus the alarm pheromones may be tried with insecticides in the field to ward off aphids from the crops.
  • Many plant products and chemicals are also known to act as deterrents for various aphid species.
  • Transgenic plants are now available in most of the crops, though not yet in India.
  • Efforts are needed in the creation of genetically altered plants for aphids.
  • High levels of resistance have been found in many Solanum species.
  • The wild Bolivian potato species, Solanum berthaultii has been gifted with the types of glandular trichomes on its foliage; type A short trichome with a four-lobed membrane-bound gland at its apex; type B, a long trichome with an ovoid gland at its tip.
  • As soon as the aphids land on the foliage, they encounter type B- hairs, which coat them with sticky exudate and also agitate them.
  • The aphids now react with type A- trichomes, which result in immobilisation, cessation of feeding and ultimate death.
  • As a male parent, S.berthaultii is being crossed with cultivated potato, S.tuberosum to get resistant cultivars.
  • Thus integrated aphid vector management strategies are the need of hour since individual control measures are of little value.
  • There is a dire need to evolve strategies for primary and secondary potato seed growing areas.

Some of the approaches suggested would be:

  • Breeding of early maturing cultivars in seed production programme so that these are not exposed to the aphids/vectors and escape their attack.
  • Introductions of such bio-agents, which can get establish early in the crop season, and thus which could check the initial build up of the vector.
  • Application of suitable insecticides at the right time.
  • Adjustment of planting and harvesting times in different potato seed producing areas in such a manner so that vectors attack is minimum.

Leaf Hopper

Symptoms

  • Folding of leaf margins and leaves turn to light red colour.

Control

  • Dimethoate 30EC, 17 ml in 10 liters of water.

Lady bird beetle

Symptoms

  • Half moon shaped leaves and they appear like net.

Control

  • Carbaryl 50 W.P @ 40 g in 10 lit of water.

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Potato Tuber Moth (Phthorimea opercullata)

Nature of damage

  • The damage is caused by the caterpillar, which bore into tuber feeding inner substances and rendering them unfair for seed and human consumption.
  • In addition, they make them susceptible for bacterial attack, which leads them to rotting.
  • The attacked tubers can be distinguished by black excreta near eyes.
  • Losses to tuber may occur from 30-70 per cent.
  • In fields, the caterpillar mines the leaves and bores into the stem and sometimes also expose tubers, but this type of damage is, however, negligible as compared to the stores.
  • The pest is carried over through infested tubers from place to place.
  • This pest is world wide in distribution.
  • In Australia it severely attacks potato plants in fields as well as tubers.
  • It was probably introduced in India from Italy in about 1900.
  • One life cycle is completed in 17-25 days and there may be 8-9 generations during, one storage season.
  • The pest remains active throughout the year and found on plants from November-March as leaf miners or bores the terminal shoots, petioles, tubers, etc., in fields and from March to October in storage.

Control

  • Seed tubers should be planted at proper time i.e., during first fortnight of November or even earlier at a depth of about 100 mm instead of 60 mm and through ridging of hills 30-50 days after transplanting.
  • Affected tubers, from the field with black spots in or around eyes, should be picked up and rejected before storage.
  • Store the potato in dry, well ventilated space where temperature does not exceed 21oC and should be covered with 5-25 mm of dry cool sand and sand should be changed fortnightly to remove pupating caterpillars.
  • Produce should not be left over in fields after harvest but should be immediately bagged to avoid egg lying.
  • Dusting the tubers with 1 per cent malathion dusts at an interval of one month @ 200 gm/quintal.
  • Spraying the infested crop with Bacillus thuringiensis B. @ 2.5 litres/ha is found effective.
  • Spraying the infested crop with 0.07 per cent endosulfan 35 EC or 0.05 per cent chlorfenvinphos (birlane) 24 EC or 0.05 per cent bidrin EC @ 700 litre water/ha proves effective in controlling the pest. After the harvest tubers may be fumigated with carbon bi-sulphide @ 2-3 kg/100 cubic meters of air space in container for 12-14 hours.

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Karnataka