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Potato tuber moth (PTM) - Phthorimaea operculella Zeller (Gelechiidae: Lepidoptera)

PTM is a native of South America which was introduced to India in 1906 with seed potatoes imported from Italy.

              Phthorimaea opercullela

Distribution: Cosmopolitan in distribution.

Host range: Major pest of Potato but has also been reported from crops like egg plant, tomato, tobacco, etc.

PTM damage on foliage

Nature of damage and symptoms:

•         Damage is caused by larvae.

•         Larvae mine the leaves, petioles and terminal shoots causing wilting.

•         After tuberization, the larvae enter into the tubers and feed on them. Larvae tunnel into the pulp which ultimately becomes unfit for use as seed or for human consumption.

•         The feeding tunnels are packed with black excretory pellets and the larvae are inside the tunnels.

•         The infested tubers are further exposed to microbial infection which leads to rotting.

•         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 per cent.

            PTM damage in tuber

Identification

•         The eggs are oval and measure less than 1mm in diameter.

•          Newly emerged larvae are gray, yellowish white with brown head.

•         Adult is a small grayish brown moth.

Life cycle:

• The female moth lays eggs on the underside of leaves or on exposed tubers near the eye. Each female can lay 150-200 eggs (Fig below).
• Incubation period is 3-7 days.
• Larval period is 15-20 days.
• Full grown caterpillars come out of the tubers/ foliage and pupate in silken cocoons either in dried leaves, soils, over the stored tubers or in cracks and crevices in the store. Pupal period lasts for 11-12 days.
• Total life cycle is completed in 20-30 days at optimum conditions of 22-28ºC temperature and 60-70% relative humifdity.
• There are 8-9 overlapping generations in a year.

                                                                       Figure. Life cycle of PTM

Management

1.      Planting seed tubers at a depth of 10 cm as against the traditional planting depth of 6 cm reduce its damage to a great extent.

2.      The fields should be ridged after 6 to 7 weeks of planting so that the tubers are burried at least 25cm below the soil surface.

3.      In areas where PTM population remains quite high and severe tuber damage is expected, ridging should be done twice so that the tubers are not exposed at any time for egg laying and infestation.

4.      Timely and adequate irrigations minimize soil cracking and thereby reduce the risk of tuber exposure to PTM attack or their laying eggs.

5.      This problem is quite common in areas where potato crop is taken in heavy soils. Harvested tubers must be removed from the field as early as possible and should not be kept overnight in the field.

6.      Leftover tubers, after harvest, should also be collected. All the plant debris including the weeds belonging to family solanaceae should also be collected and destroyed.

7.      The crops like tomato, tobacco, chillies and brinjal should not be grown in the vicinity of potato fields, particularly in PTM prone areas. 

8.      Store healthy (PTM free) potatoes in cold stores with 2-3 cm thick layers of chopped dried leaves of either of Lantana camara, Soapnut, Neem, Eucalyptus spp.

9.      Installation of PTM sex pheromone traps @ 20 traps/ha for mass trapping of male moths.

10.  Spraying the crop with Bt (10⁹ cfu/ml) @ 3ml or GV @ 4 LE/lit of water.

11.  Spray of crop with quinalphos @ 0.375 kg or acephate @ 0.5 kg a.i./ha.

12.  for seed potatoes dusting with cypermethrin dust @500 gm/ton of potato in storage.

13.  CIPC (Isopropyl N-(3-chlorophenyl) carbamate) is a sprout suppressant commonly used on ware potatoes (seed purpose) in country stores and is found effective against PTM damage in country stores when applied @30ppm.

            Potato tubers stored with dried lantana leaves                   No treatment                                                CIPC treated tubers

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