Proactive Fruit Pest Management: Plum Curculio

While the name plum curculio may suggest that it primarily infests plums, this insect can infest most, if not all, of the tree fruits grown in Iowa, including apples, cherries, peaches, pears, and plums.

Recognizing Damage

Damage from plum curculio can vary depending on when it is noticed. Early-season damage is typically seen as crescent-shaped lesions on the fruit surface caused by egg laying (Figure 1). Later in the season, particularly on apples, damage may appear as raised scars with more irregular coloration (Figure 2). Plum curculio larvae are white grubs with brown heads and can feed on both the flesh and seeds of the fruit (Figure 3). Many infested stone fruits will drop before harvest, and in some cases, fruit may prematurely color.

Understanding the Plum Curculio Life Cycle

Adult plum curculio are mottled brown, weevil-like beetles (Figure 4) and can be difficult to scout. Adults overwinter in or on the ground, and as fruit develops, they begin moving into trees to lay eggs in the fruit. Once eggs are laid, management options are limited, so control efforts are focused on the adult stage. Historically, the Midwest has had only one generation of plum curculio to manage. However, in southern portions of the Midwest, there is evidence that two generations may now occur in some locations.

Targeting Adult Plum Curculio After Petal Fall

One thing to keep in mind is that fruit pest management needs to be timely and proactive rather than only reactive. Many home growers begin fruit pest management too late to provide effective control of plum curculio. Although the fruit damage or drop associated with plum curculio may not be easily noticed until summer or even fall, management of plum curculio should begin after complete petal fall. However, insecticides should not be applied during bloom to protect pollinators. In the Midwest, most plum curculio management concludes approximately four weeks after petal fall. Growers with multiple fruit crops that bloom over an extended period may find management particularly challenging and may need to target applications at petal fall for each specific crop rather than relying on a single blanket application. Because bloom timing varies from year to year, management decisions should be based on plant growth stages rather than calendar dates. In central Iowa, many plums and peaches are already at petal fall by mid-April, while pears may be at full bloom and apples may be just beginning to bloom, thus requiring species-specific timing of plum curculio control.

Additional Resources

Midwest Fruit Pest Management Guide

Spray Schedule for Home Apple Trees

Using Pesticides Safely in the Home and Garden

Plum Curculio Damage and Management video