POTATO TUBER MOTH

PHTHORIMAEA OPERCULELLA “POTATO TUBER MOTH”

otato tuberworm Phthorimaea operculella , also known as potato tuber moth or tobacco splitworm, is an oligophagous pest (an insect feeding on a restricted range of food plants) of crops belonging to the family Solanaceae (mainly potatoes [Solanum tuberosum L.], tomatoes [Solanum lycopersicum L.], and tobacco [Nicotiana tabacum L.]). Phthorimaea operculella has been a minor pest of tobacco for more than 100 years.

Damage on a potato inflicted by the potato tuberworm, Phthorimaea

The potato tuberworm affects production, reduces quality of the produce, and increases the risk of infection by plant pathogens. The common name potato tuberworm is given to its damaging larval stage. There are two species in different genera with similar names: Tecia solanivora and Symmetrischema tangolias . Tecia solanivora .

Distribution

Potato tuberworm is a cosmopolitan pest. It occurs widely in Africa (Ethiopia, Egypt, Kenya), Asia (Iran, Syria), Europe, Americas (Latin America, Andes of Peru and Bolivia), and Oceania (Australia and New Zealand)

Host Range

Potato tuberworms are mainly associated with potatoes; however, they have been observed feeding on other plants such as tomatoes, eggplants (Solanum melongena L.), peppers (Capsicum spp.), tobacco, and wild solanaceous plants like Jimson weed or datura (Datura stramonium L.) .

Damage

Larvae feed on potato leaves, stems, petioles, and more importantly potato tubers in the field and in storage. The newly hatched larvae create mines on leaves by feeding on leaf tissue while leaving the upper and lower epidermis of the leaf intact. They prefer feeding on young foliage . Typical damage results from larvae boring tunnels in tubers. Larvae depositing their excreta make tubers unfit for consumption. Potato tuber eyes become pink due to deposition of silk and excrement by potato tuberworm infestation. Severe infestations result in yield and quality losses during storage where previously infested tubers are stored with healthy potato tubers . This generally destroys the entire crop of stored potatoes.

Damage on potato tuber caused by Phthorimaea operculella

Most economic damage occurs to potato tubers in storage conditions in developing countries and is caused by larval feeding. Presence of even one larva is sufficient to spoil and destroy a tuber. Rapidly moving caterpillars penetrate the tubers, form galleries coated with silken threads and eject frass outside the tuber. On leaves, caterpillars form galleries and then penetrate other plant parts. After two to three weeks, caterpillars leave the plant (caterpillars can move through cracks in soil) and pupate on walls of potato bags lying in potato fields. Fungi, bacteria, and mites can develop inside the tunnels made by the larvae, which causes the tubers to rot and emit an unpleasant smell.

Stored crop losses in potatoes ranging from 50% in Yemen and Peru, 86% in Tunisia, Algeria, and Turkey, 90% in Kenya, and 100% in India and the Philippines have been reported. In Egypt, potato tuber moth has caused up to 100% losses to potato plants in fields as well as in storage . Potato tuber moth is also a pest of tomatoes where larvae damage the leaves, stem and the unripe fruits.

Monitoring

Monitoring of potato tuber moth is a critical part of its management. Pheromone traps that attract males have been effective for monitoring potato tuber moth populations. Monitoring is one of the most important components of an integrated pest management (IPM) plan for potato tuber moth. Monitoring gives an indication of insect presence, population and distribution, and allows for timing of pesticide applications for its management. IQ water traps baited with the pheromone can be used for attracting and monitoring adult male populations. These traps are easy to use and clean between readings. Four traps per quadrant of a circle, about 50 ft from the periphery of the circle are suggested for monitoring in field. No economic threshold level (ETL) has been determined for crop damage or yield loss in fields. However, checking traps twice a week is suggested and pesticide application is recommended in case of high population (e.g., 15 to 20 moths/trap/night)

Management

The most common method of control of Phthorimaea operculella is pesticides . The development of pesticide resistance, resurgence of pest populations, and potential detrimental effects of synthetic pesticides on non-target organisms has led to the adoption of integrated pest management (IPM) strategies. It is important to know the biology and distribution of a pest for an IPM program to be successful.

Field Management

Cultural control

Weeds and volunteer plants can act as alternate hosts for potato tuberworms, and should be eliminated from fields and surrounding areas. Deep planting and good coverage of potato seeds with soil more than 2 inches during hilling helps protect damage by adults and larvae. Discard infested tuber seeds; only use healthy seed tubers for planting. Vines should not be used for covering tubers as they wilt after some time and larvae and moths can penetrate the cover to reach underlying tubers.

Harvest soon after crop maturity. Moth populations are maintained in plant and tuber debris in the field in the absence of main crop. Therefore, timely field cleanliness is an important preventive measure. Cull piles should be destroyed to reduce overwintering stages of potato tuberworm. Avoid leaving harvested tubers overnight in the field as these potatoes could act as egg laying sites for potato tuber moth .

 Soil management and irrigation

Irrigation is the most effective preventative method under dry conditions . Enough irrigation should be provided to not allow cracks to develop deeper than two inches in the soil. It is recommended that fields should be irrigated after vine desiccation to avoid cracks in the soil and that harvest of tubers occurs as soon as the skin sets.

 Resistant varieties

Host plant resistance enables plants to avoid, tolerate or recover from pest infestations . The efficacy of other control methods can be increased using resistant potato cultivars thus reducing use of insecticides.

 Biological control

Natural enemies of potato tuber moth can be used as a part of an IPM program. The parasitoids, Copidosoma koehleri and Bracon gelechiae Ashmead (Hymenoptera: Braconidae) have been used with some success in South America and Australia, respectively.

 Bio-pesticides and natural chemicals

Bacillus thuringiensis (Bt) formulations have proved effective for potato tuber moth control in various parts of world .

 Chemical control

Chemical control might be necessary when adults or larvae are present. For chemical recommendations for commercial growers or home gardens, consult your local county Extension service and be sure to follow all local laws regarding pesticide use.

Storage Management

Potato tuberworm is a year-long problem under storage conditions due to continuous breeding of this pest. The length of life cycle of potato tuberworm is highly dependent on temperature. So, storage temperature should always be kept below 52°F. Monitoring in storage situations relies on the use of pheromone traps. Under storage conditions, cultural control options involve elimination of damaged tubers. Screens should be installed at entry points to exclude moths.

Sanitation of storage facility walls, floors, and ceiling is very important. Treat facility with an approved pesticide, if this pest was detected the previous year. Use new or thoroughly sanitized potato sacks, crates or other containers. Bt spray can be used on tubers which are mainly used for human consumption, and pyrethroids on tubers used for seed purpose.

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POTATO TUBER MOTH

PHTHORIMAEA OPERCULELLA “POTATO TUBER MOTH”

How to control POTATO TUBER MOTH ?

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