A4160 Plum Curculio Annie Deutsch and Christelle Guédot lum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Identification Curculionidae), is one of the most Plum curculio is a type of weevil (snout Pcommon and detrimental pests of apple beetle). Adults have a distinctive, long, in Wisconsin and can cause significant curved snout, characteristic of weevils damage to tree fruit. Along with apple, it (figure 1). Adults are about 1/6 to 1/4 of an attacks pear, quince, and stone fruits such inch long and are speckled gray, brown, as plum, cherry, peach, and apricot. and black. They have four pairs of ridges along the back, although only one pair Plum curculio is a native beetle, distributed is readily apparent. Eggs are minute throughout the eastern and midwestern (approximately 1/50 of an inch long), white, United States and Canada. In its natural and oval shaped. The full-grown larva environment, it survives in wild plum, is 1/4 to 1/3 of an inch long, with a legless, native crabapple, and hawthorn. Many C-shaped, cream-colored body and brown wild crabapples and stone fruits occur in head (figure 2). Plum curculio pupae are woodlots and fencerows, which, along with about the size of full-grown larvae and are neglected or abandoned fruit trees, can white to tan in color. host plum curculio populations. All of these FIGURE 2. Plum curculio larvae inside a plants are potential sources of infestation peach. for cultivated trees. In the winter, the adult Life cycle beetles seek protection in wooded areas Plum curculio overwinters as an adult laying 100 to 500 eggs in their lifetime. with an abundance of fallen leaves from beetle among fallen leaves in wooded Egg-laying occurs for 3 to 5 weeks after deciduous trees or shrubs. Most orchards areas or hedges. Overwintering plum the end of bloom. Eggs typically hatch in that receive insecticide applications do not curculio adults will migrate into orchards about 1 week. have resident plum curculio populations, early in the season. When temperatures Larval development varies by fruit type. In as the adults tend to overwinter outside are below 70°F, they typically walk into the apple and pear, after hatching, almost all the orchards. In this situation, damage orchard and climb up tree trunks. When larvae are soon killed by the firmness of to cultivated trees is more common temperatures are warmer, they often the young fruit tissue as it develops. Often adjacent to the overwintering habitats. fly into orchards. Early spring activity of the only injury to the fruit is the crescent- In abandoned, low-sprayed, or poorly overwintered adult females is somewhat shaped surface scar where the egg was sprayed sites, plum curculio can overwinter unpredictable and depends on the number laid. Larvae that are most likely to survive within the orchard. and timing of warm days in the spring. and develop are those in dropped fruit. Usually females move to fruit trees about In stone fruit, when the egg hatches, the the time the trees are blooming, but in larva bores through the fruit and feeds some years this may be delayed as long as internally until fully grown. Therefore, 2 to 3 weeks after bloom. Factors causing larvae are able to fully develop within this delay include cold temperatures, high hanging fruit. winds, and low humidity, which forces the In both types of fruit, larvae progress beetles to remain in the soil searching for through four larval stages (instars) over moisture. the course of about 16 days. When Female plum curculio beetles lay eggs fully mature, they leave the fruit and just below the fruit skin. The female uses pupate 1 to 2 inches down in the soil. her mouthparts to cut an approximately The new generation of adults will 3/16-inch-long, shallow slit in the surface of emerge approximately 30 days after the fruit and then deposits a single egg pupation (typically early August through in the center of the flap of tissue created mid-September) and feed on the surface by this slit. After pushing the egg under of fruit for a short period of time before the slit with her snout, she cuts crescent- looking for overwintering sites. Plum shaped slits on either side of the egg curculio adults spend around 300 days of (figures 3 and 4). Females are capable of FIGURE 1. Plum curculio adult. the year in their overwintering sites. PLUM CURCULIO FIGURE 3. New plum curculio oviposition scar FIGURE 4. Plum curculio oviposition scar on on a tart cherry, early season. an apple, midseason. FIGURE 5. Plum curculio egg-laying scars on a FIGURE 6. Late season adult plum curculio mature apple. The scars are a result of early damage. season damage caused by overwintering plum curculio adults. rotting internally as the larva develops and survive the upcoming winter. The beetles Damage feeds within the fruit. While there may be chew round holes about 3/16-inch in Damage from plum curculio occurs multiple egg-laying scars on a single fruit, diameter and 3/16-inch deep into the fruit primarily to the developing fruit. The typically only one larva develops inside (figure 6). Often the feeding damage from egg-laying scars on the surface of newly each fruit. In all targeted fruit species, the second-generation adult beetles is developing fruit are often the first visual infested or damaged fruit often fall from near the stem end of the fruit. Fruit feeding symptoms of plum curculio damage. As the tree. by the new generation of adults occurs the fruit grows and expands, so does In addition to damage from laying eggs, from late summer until temperatures drop the scar created by the slit, resulting in plum curculio adults may feed on the in the fall. Insecticide sprays throughout a large, semicircular lesion on the fruit base of flowers prior to egg-laying. After the summer targeting other fruit pests surface (figure 5). In apple, where the pollination, fruit develop from this part of frequently contribute to keeping plum plum curculio egg is often killed, this the flower, so flowers damaged in this way curculio levels low later in the season, surface scar may be the only type of injury may result in lumpy and misshapen fruit at preventing widespread damage. apparent on the fruit. In stone fruits, such harvest. Late-season damage can be higher in as plum or apricot, the egg-laying scars unsprayed, low-sprayed, or organically In late summer, the new generation of look identical to those on apple, but a drop managed orchards. of clear to amber-colored sap may weep adult plum curculio may feed at the surface from the wound. The sap is due to the fruit of fruit to gain sufficient nourishment to 2 UNIVERSITY OF WISCONSIN-EXTENSION Options for commercial orchards program, keep in mind that sprays for plum Control curculio may also control or give partial In many regions, including Wisconsin, plum Due to the size of commercial orchards, the use of insecticides is the most practical control of other mid-season pests such as curculio damage can be severe. Before leafrollers, codling moth, and plant bugs. treatment begins, orchards should be and effective control method. Timing Before using a particular insecticide, it scouted to check for the slit-like egg-laying of pesticide applications is critical for is important to understand the way the scars on developing fruit, especially successful plum curculio management. product kills insects (also known as the along orchard edges near potential Scouting should begin towards the end mode of action). Rotating chemical modes overwintering sites. Documented history of the bloom period using the methods of action is important to reduce the of the pest within an orchard is also very mentioned above. Typically, the period for likelihood of insecticide resistance for both important to identify areas that tend to control of plum curculio is during the first plum curculio and other insect pest species have higher populations each year. In areas few days of warm and humid weather after in the orchard. Keep in mind that multiple with large plum curculio populations, petal fall. Low temperatures will extend products may contain the same chemical. tapping tree branches over a white sheet the treatment window because the beetles When choosing different products, check and searching for beetles that fall off can will not develop as quickly. Numerous the active ingredients list on the label to work to determine if adult plum curculio conventional and organic-approved make sure they contain an insecticide with are present. However, this technique can insecticides are available for commercial a different mode of action than the one be unreliable, so it should only be used orchards and provide good activity against used previously. along with searching for damaged fruit. plum curculio: Plum curculio is equally active during the • Carbamates (e.g., Sevin) Chemical registrations vary by year, day and night, so damage may be detected • Diamides (e.g., Exirel) state, and crop. For products currently in orchards that have been previously available for plum curculio control, refer • Neonicotinoids (e.g., Actara, Assail, scouted, but the beetles themselves were to the current year’s Midwest Fruit Pest Belay) not found. Management Guide. The publication can • Organophosphates (e.g., Imidan) be purchased or downloaded for free at Pest management strategies will vary for https://ag.purdue.edu/hla/Hort/Pages/ backyard fruit trees versus commercial • Oxadiazines (e.g., Avaunt) sfg_sprayguide.aspx. As always, make orchards. In all settings, elimination of • Pyrethroids (e.g., Asana, Danitol, sure to read the label and follow all label wild, abandoned, or neglected fruit trees Mustang Max, Permethrin, Warrior) directions before using any pesticide.