Department of Entomology

Southeastern Apple Production ENTOMOLOGY

Plum Curculio

Conotrachelus nenuphar (Herbst)

Description

Plum curculio (PC) are weevils, approximately 1/4 inch long, with a long, curved snout about one third of the length of the body. The body itself is brown-gray and warty. Full-grown larvae are 1/3 inch long, legless, and white with brown heads.

Adult and egg-laying scar

Adult and larva

Life History

PC adults overwinter in leaf litter in and around orchards. In the spring when the daily maximum temperature exceeds 70ºF (near bloom and/or petal fall), adults emerge, mate, and lay eggs under fruit skin. Eggs hatch within a few days of being laid and larvae feed in the apples. These apples nearly always fall to the ground, where the fully-developed larvae migrate to the soil and change into pupae. This second-generation usually emerges and lays eggs from mid-June through July. There are two generations per year.

Damage

PC is a sporadic pest in the Southeast but occasionally becomes serious. A PC female uses her snout to cut a crescent-shaped slit beneath each egg she lays in order to keep the growing apple from crushing the egg. This slit becomes a 'D'-shaped scar as the apple grows. Larvae may create tunnels, and heavily infested fruit may become knotty or fall to the ground. Later in the season, adult beetles may create numerous round punctures in fruit skin.

Crescent egg-laying scar

Older 'D'-shaped scars

Scarred feeding site

Internal tunneling

Monitoring and Control

PC activity is correlated with weather conditions after bloom: infestation tends to occur the first day after petal fall when high temperatures exceed 70° F. After bloom check fruit twice weekly for feeding and egg-laying scars. Typically, an insecticide at petal fall and first cover (if adult emergence is protracted) is used for control. However, additional insecticides should be applied if any new damage is observed.

PC Degree-Day (DD) Model: A degree-day model can help growers prepare for PC emergence and determine the end of adult movement in the spring. Once buds swell, note the second date when air temperature exceeds 70ºF (biofix) and begin accumulating daily degree days (DD) (base 50ºF) using the table below (base 50°F). Adults enter orchards from 50 to 400 DD after biofix. Damage occurs from 100 to 700 DD after biofix. Summer generation adults begin emerging after 1,100 DD and can cause damage until harvest.

Insect and Mite Management Overview
Insect and Mite Index

Southeastern Apple Production
Mountain Horticultural Crops Research & Extension Center
455 Research Drive
Mills River, NC 28759
Phone: 828.684.3562 ~ Fax: 828.684.8715
Email: jim_walgenbach@ncsu.edu

Web Crafters: Anne S. Napier and Steve Schoof
Email: steve_schoof@ncsu.edu

Updated March 22, 2007