Apple IPM - Plum Curculio

Plum Curculio (Conotrachelus nenuphar)

Overview:

The plum curculio (PC) is generally considered the single most destructive insect pest in orchards. The most recognizable type of wound caused by PC is the half-moon scar produced by ovipositing females. Prior to depositing her egg, the female first uses her mouthparts to cut a small crescent-shaped flap in the fruit skin; then, she turns around to deposit an egg. When eggs hatch, larvae tunnel into fruitlets and begin to feed. Larvae complete four instars inside the fruit in about 16 days. PC-infested fruitlets generally drop to the ground prematurely. When an egg is not viable, or a female cuts into a fruit but does not deposit an egg, the scar remains and can be seen at harvest, often making the fruit unmarketable.

ID/Life Cycle:

The plum curculio (PC) is a typical snout beetle, 1/4 inch-long, dark brown in color. The wing covers have four bumps and black, grayish-white patches. Full-grown larvae are 1/3 inch (7.5mm) long, legless, and white with brown heads. PC overwinters in the adult stage, primarily in forest leaf litter. In the spring, adults become active and migrate back into the orchards where they feed upon vegetative tissue and developing fruits. Soon after fruit set, the females start laying eggs. The female will make a small slit in the skin of the fruit, into which she deposits an egg. This injury leaves a distinctive crescent-shaped scar. This hole protects the egg as the fruit develops and expands. The grub can be found inside infested fruit during June and early July. Summer-generation PCs emerge from the soil during July and August and primarily feed on fruit. There is one generation per year in northern latitudes.

Damage:

In New England, PC is one of the most serious insect pests of apples and among the most destructive insect pests of peaches. It also attacks plum, pear, cherry, and apricot. In spring, orchard border rows near woods are often the first to show injury. The grubs immediately begin feeding and working their way into the center of the fruit. Infested apples usually fall to the ground about the same time as June drop. If the apple doesn’t fall to the ground, the larva probably did not hatch or the grub did not develop. However, the distinctive crescent-shaped egg scar will be present at harvest time. No more than 1% fruit injury at harvest should be tolerated.

Management Strategies

Monitoring:

Fruitlets should be monitored beginning at petal fall to determine if egg-laying injury is occurring. If fresh oviposition scars are observed, a first cover spray should be made to the entire block. Cool, wet weather will prolong PC activity. Continue to monitor for fresh scars. If more are found, a second cover spray targeting perimeter-row trees will be needed.

A monitoring system that makes use of attractive lures, termed the ‘trap tree’ approach, has been developed. It involves baiting the branches of one perimeter-row tree with a synergistic two-component lure. By examining the fruit solely on the odor-baited tree for signs of fresh PC injury this monitoring technique has proven effective at determining, in a timely manner, whether perimeter-row insecticide sprays against PC are required after the whole-block petal fall spray.

For more information, see Fact Sheet on “Effective Plum Curculio Monitoring Using Lures”

Cultural/Biological

• Eliminate wild or untended trees in the vicinity of the orchard to reduce the pest population.
• Prune in dormant season to maintain an open canopy to promote air circulation and improve spray coverage.
• For small-scale plantings, remove dropped fruit to help decrease the population.

Chemical

• Refer to the New England Tree Fruit Management Guide for specific materials and rates recommended for managing Plum Curculio.
• A full-block spray by the time of petal fall is needed given the ability of overwintered PCs to penetrate into the interior of the blocks.
• Apply follow-up cover sprays, targeting perimeter-row trees, as needed until activity ceases, usually 1 to 3 applications are made. Keep monitoring for fresh PC damage.
• Rotate insecticides from different IRAC groups to reduce the chance of resistance development in the pest.
• Do not apply insecticides until bloom is completely finished to reduce unwanted pollinator exposure to insecticides.
• For organic production: kaolin clay (Surround WP) is an OMRI-listed material that can also be complementary to conventional management strategies. Applied in suspension in water, kaolin clay produces a dry white film layer of interlocking microscopic particles on the surface of leaves, stems, and fruit after evaporation of the water.
• Kaolin acts as a physical barrier preventing insects from reaching vulnerable plant tissue. It acts as a repellent by creating an unsuitable surface for feeding or egg-laying.
• Surround applications begin at petal pall and are reapplied weekly to maintain coverage and deter egg-laying.

Date: March 2020

Additional information available on the MYIPM app: https://apps.bugwood.org/apps/myipmseries/