Potato Tuberworm

Family: Gelechiidae

About the Potato Tuberworm

Reproduction and Life Cycle

The potato tuberworm will overwinter as pupae, eggs, or larvae, either in the soil, old potato piles, leaf debris, or even on walls of storage rooms. There can be up to 8 generations per year, depending on what the climate is like; there tends to be 2 generations in North America. The eggs are placed on foliage or tubers that the moth can reach through cracks in the soil. Females lie between 60 to 200 eggs within 4 days. The eggs will be laid either in clusters or individually. In 5 days, the eggs will hatch. Larvae take about 14 days to complete their instars, feeding off of host plants. When they pupate, this stage will take between 10 and 30 days to be completed. The adults will emerge as fast fliers and can live for 7 to 14 days. They are only active at dusk and dawn and their diet manly consists of plants nectar. They will mate within the first day. Females are known to be larger in size in comparison to the males.

Potato Tuberworm Identification and Habitat

Identification

The adult potato tuberworm is a moth with a wingspan of about 10 to 12mm long. When the moth is resting, their fringed wings are hugged in close to their body, making them look slender. The wings are gray with slightly darker spots, usually a gray-brown. The hindwing has scales that are almost like hair, found along the outer and inner margins. The eggs are oval; they have a smooth texture, and are white to yellow in colour. The larvae are about 10 to 12mm long with a yellow-white body and a brown prothorax and head. Each segment of the abdomen has bristles and tiny black dots. As the larvae mature, they will change to a green or pinkish colour. Pupae are about 12mm long, narrow and are typically white. The cocoon surrounding the pupae will become hard to spot as it gets covered in soil and plant residue.

Habitat

This pest can be found in many different parts of the world, but is believed to have originated in either South or Central America. The moths can fly for about 0.15 miles, often allowing them to find new tubers or plants to lay their eggs on. Mainly potato tuberworms will only travel far distances if they are transported. They can be found in storehouses for potatoes, potato fields, on tobacco plants, and tomato plants. These moths are mainly found between the months of April and October. They will eat tubers (both in storage and in field), leaves, stems, and green tomatoes. The larvae prefer eating foliage that is young, or bore tunnels into potatoes. When the larvae feed on the tubers, they leave behind their excreta, making the potatoes inconsumable and thus greatly affecting the crops yield. When this happens, potato eyes will appear pink in colour. Also, from the holes the larvae created, bacteria, mites, and fungus can enter the tuber and causes it to rot.

Potato Tuberworm Management and Control Methods

Cultural Control

There has been no economic threshold established for this pest. However, if you do notice a major infestation, then you should exercise the use of an integrated management method of both cultural and chemical control practices to provide you with the best results. For preventative measures, make sure to keep your fields weed-free to avoid this pest from using the weeds as an alternate host. Deep potato planning with good coverage (typically create hills that are at least 2 inches high of soil) to help deter the adults from laying their eggs on the potatoes and thus keeping the larvae from burrowing into them. Never use potato seeds that are infested, as this will promote new infestations. Harvest you crop soon after maturity. Also, always be sure to remove plant debris from your field, as adults can still live off of the residue and promote the potato tuberworms to overwinter. If the season is dry, make sure to irrigate in order to keep cracks from forming above the tubers; these cracks give the adults an entry way to lay their eggs. Lastly, when storing tubers keep them in a storage area that has a temperature below 52 degrees Fahrenheit and always make sure the floors, walls and ceiling are cleaned properly to avoid this pest overwintering there. You can also place screens at the entry points to keep moths from flying in.

Chemical Control

A natural chemical that can be used to help keep potato tuberworm populations in check is a Bacillus thuringiensis formulation. This pesticide can be used on potatoes for human consumption as well. Most insecticides that contain carbomates, pyrethroids, or organophosphates can reduce adult populations. Typically, application is most successful when done at dusk when the adults are active. These chemicals will not have much of an effect on the larvae, making multiple applications often necessary. Other insecticides that have been found to be effective on the tuberworm larvae: indoxacarb, novaluron, and spinosad. Be sure to always carefully read the label for cautions and proper application.

Latin / Alternative Potato Tuberworm Names

• - Phthorimaea operculella
• - Potato splitworm
• - Tobacco splitworm
• - Potato tuber moth
• - Potato tuberworm moth

Sources