In Oklahoma and throughout the eastern United States, the plum curculio is one of the most important insects attacking fruit. In particular, it is extremely detrimental where stone fruits (such as peaches, plums, and apricots) are interplanted with pome fruits (such as apples and pears). The host range of the plum curculio includes apple, pear, nectarine, plum, cherry, peach, apricot, and quince. It can also survive on hawthorn, wild plum, and crab apple.
The plum curculio is usually more abundant on fruit trees adjacent to woods, fencerows, and trashy fields.
The adult is a small, rough snout beetle, 1/4 inch long and generally mottled with brown, black, and gray colors. The forewings (elytra) of the beetle have four pairs of ridges, but because the middle humps are the largest, only two parallel ridges are apparent. Eggs are pearly white. Larvae are yellowish white with a brown head, lack legs, and are 1/4 inch long when fully grown. Adult curculios do not like strong light and prefer the dense shade of the tree's inner canopy.
Several types of damage occur. 1) Damage to peaches include crescent-shaped scars on the fruit from egg laying activity of adults early in the spring or bumps from feeding injury that protrude from the fruit at harvest. Heavily damaged fruit may be gnarled, knobby, and scarred. 2) Internal injury is caused by larvae tunneling throughout the fruit. Most fruit damaged in this way will drop to the ground by June. Premature dropping of fruit during May, June or even later in the season is often the result of larval activity within the fruit or adult feeding on the fruit. 3) Feeding punctures are made by adult beetles in the fall just prior to overwintering. These punctures are characterized by small holes in the skin of the fruit and may have a hollowed-out cavity extending into the flesh.
In addition to these three direct forms of injury, plum curculio adults can inadvertently infect fruit with spores of brown rot fungus. This occurs during the oviposition (egg-laying) process. Infested fruits usually fall prematurely; however, with some hosts (like cherries or peaches) the fruit can mature with disease infection and remain on the tree until harvest.
Clear fallen leaves and dropped fruits from under fruit trees on a regular basis to reduce hiding places for adult curculios and to keep larvae from reaching the soil to pupate. Adult curculios can be killed with insecticide. Spraying is most effective if done right after petal drop, the time when adult curculios are actively crawling on branches and beginning to lay eggs. Once the eggs and larvae are in the fruit, no amount of spraying will deter them.