Potato

Potato Tuber Moth

Phthorimaea operculella

Insect

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In a Nutshell

  • Larvae mine the young leaves and tunnel into the tubers.
  • When the larvae leaves the tunnels, fungi, bacteria and mites take over.
  • The tubers rot and have an unpleasant smell.

Can also be found in

3 Crops
Potato
Tobacco
Tomato

Potato

Symptoms

This insect can feed on a variety of solanaceous crops but potato is favored. The larvae attack potato leaves, stems, petioles, and tubers (in field or in storage). They eat the internal leaf tissue without touching the epidermis, forming transparent blisters. Stems can be weakened or broken, causing the death of the plant. The larvae enter the tuber through the eye and make slender tunnels along the surface or dig deep irregular galleries into the flesh. Larval frass is visible at the entry points which are open to fungal and bacterial diseases.

Recommendations

Organic Control

Extracts of orange peel, and of the species Pithuranthos tortosus or Iphiona scabra, among many other plants, reduced the fecundity of the moth. Parasitoids wasps of the species Bracon gelechiae, Copidosoma koehleri or Trichogramma significantly reduced pest numbers. Predators include ants and lady birds. Applications of either granulovirus or Bacillus thuringiensis can result in 80% mortality within a fortnight. In some countries, damage during storage can be reduced by covering the sacks with the foliage of Eucalyptus or Lantana.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Insecticides of the group of organophosphates can be sprayed on leaves. Pyrethroids can be applied to seeds as repellent to prevent the attack of the larvae.

What caused it?

Adults moths have a gray stretched body with extended antennae, narrow brown forewings scattered with dark spots, and light-gray hindwings with long fringes. It is mostly nocturnal and attracted to light. Eggs are laid singly or in batches on the leaves or on exposed tuber buds in dry soil. They fail to hatch when kept at temperatures below 4°C for long periods. Larvae have dark brown heads and light-brown to pink bodies. They bore into petioles, young shoots or leaf veins and later into the tubers, making irregular galleries. 25°C is the optimum temperature for their life cycle but tolerance ranges between 15 and 40°C. Cracks in dry soils favor the survival of the larvae.

Preventive Measures

  • Use seed tubers from healthy plants.
  • Check for resistant or tolerant varieties.
  • Plant seed potatoes deep into the soil, in 5 cm depth or more.
  • Monitor their presence and mass-catch the moths with light or pheromone traps.
  • Control weeds and volunteer plants in and around the field.
  • Water the field regularly to avoid soil cracking.
  • Harvest as soon as possible when maturity is reached.
  • Bury rejected tuber piles or destroy them.
  • Clear the fields thoroughly of plant debris and mulch.
  • Keep the storage sacks and facilities clear of insects.
  • Store potatoes at temperatures between 7 and 10°C.

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