Q. My tomatoes appeared to have some kind of leafminer attack this year. By the end of the season, the plants looked pretty ragged, and the fruit seemed to be affected, too. Can you tell me more about this pest and how I can avoid problems with it next year?
A. Although there are leafminers that attack tomatoes and related plants, there was an unusual infestation of tomato pinworm in mid-Atlantic states this year. There have been reports of damage from Delaware, Maryland and New Jersey. Early larval stages tunnel into tomato leaves and create a blotchy mine that is easily mistaken for the handiwork of a leafminer.
Tomato pinworm does not overwinter in colder areas of the country and is more common in southern states, Mexico, Haiti, the Bahamas, Cuba and Hawaii. In colder areas, they are more common in greenhouse-grown tomatoes because they are able to overwinter. Infestations in home gardens usually result from transplants that are shipped in from southern states or from nearby greenhouses, though adult moths can be blown north on wind currents.
The adult is a rather nondescript, small grayish-white moth that lays its eggs on the undersides of the leaves of tomato plants (occasionally eggplant, potato and weeds in the nightshade family). Adults are active at night, so they go unnoticed.
When the eggs hatch, the small yellow-gray larvae mine into the leaf and create a blotch-type mine that has a papery appearance. Older larvae may be yellow, green or gray with dark purple spots. They fold leaves over or web leaves together, and live and feed inside. Older larvae also tunnel into the stems and fruit. In large infestations, they can cause significant damage to the fruit, although it is usually confined to the core and the rind. Mature larvae drop to the ground and pupate near the soil surface. There are multiple generations a year, with seven to eight common in their native range.
Infestations can be more severe in home gardens and in organic production where regular pesticide applications are less likely. Insects that feed inside plant tissue are more difficult to control than those that feed externally. Management focuses on prevention and sanitation. Be sure to clean your garden out thoroughly this fall. To be on the safe side, bag and dispose of spent tomato plants with the trash rather than composting them. Even though they will not survive a "normal" Pittsburgh winter, do not take the chance.
Carefully inspect transplants for signs of pinworm and avoid purchasing those that are symptomatic. Once plants are in the garden, monitor your garden regularly for signs of mined or folded leaves. Pick them off and send them out with the trash. The only insecticides I could find suitable for home gardeners are products containing spinosad such as Captain Jack's Deadbug Brew. While spinosad is not a systemic product, it does move into the leaves enough to provide some control of leafminers. It may help control the small larvae.garden
Send questions to Sandy Feather by email at email@example.com or by regular mail c/o Penn State Extension, 400 N. Lexington Ave., Pittsburgh 15208.