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Lesser appleworm

The lesser appleworm or plum moth (Grapholita prunivora) is a native to Minnesota and found over most of the state. Lesser apple worm has a wide host range that includes many apples, plums, hawthorn fruit, and June berries. They feed inside plums and can be abundant in some orchards.

Identification

Adult lesser appleworm moths are about 1/4 inch long and dark brown with grayish orange bands on their wings. The larvae are creamy white to pink caterpillars with a brown head capsule. The caterpillars look quite similar to codling moth larvae, but are about half the size at maturity. Mature larvae are about 1/3 inch long when mature.

Plums with caterpillars exude a waxy substance after the larvae enter the fruit. Less appleworm larvae make small capsules just below the surface of the fruit and rarely feed much deeper than 1/2 inch.

Damage

Unlike plum curculio, lesser appleworms are most common in ripe fruit, but the fruit is typically edible. Since the capsules created by the moths are small, the damaged area can be cut out of the plum, provided there is only one caterpillar per plum.

Important biology

Lesser appleworms have two generations per year per year in Minnesota. The moths overwinter as larvae in cracks in the tree trunk and in leaf litter on the orchard floor. The larvae pupate in early spring, and the adults typically emerge the first week of June. Females lay their eggs on the surface of the fruit or on leaves near young fruit. The larvae search for fruit after emerging and begin mining the fruit just below the skin. First generation larvae often pupate in the tree or even in the fruit. Adults of the second generation emerge in early August in Minnesota and their offspring are most likely to infest ripe plums.

Management

Lesser appleworms can be monitored with pheromone traps, but the traps are expensive and not widely available. The Minnesota Department of Agriculture does have apple growers monitor for lesser appleworms each year using pheromone traps, and the results can be accessed in the IPM newsletter, published weekly for much of the growing season. The IPM newsletter can be seen at: http://www.mda.state.mn.us/en/plants/pestmanagement/ipm/fruit-veg-ipm.aspx

The traps only indicate when adults are present and are not a good estimate of how numerous they are at a given location. A gardener can also inspect the ripe fruit at the end of summer for the waxy secretions.

Once it is determined that lesser appleworm is present, each gardener needs to decide how much damaged fruit is acceptable for them. If minimal damage is the goal, then spray plum trees during the second flight of adult moths in early August. Effective insecticide sprays to treat lesser appleworm are acetamiprid, carbaryl and malathion.


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