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Ministry of Agriculture, Food and Rural Affairs

Plum curculio

Plum curculio adult (Bernard Drouin, Ministry of Agriculture, Fisheries, and Food, QC) Adulte du charançon de la Oviposition scars Fresh damage
Click to enlarge.

Beginner

Scientific Name
Conotrachelus nenuphar

Identification
Eggs:

  • 0.6 mm long,
  • White,
  • Elliptical,
  • Deposited under the fruit skin.

Larvae:

  • Cream-coloured,
  • C-shaped,
  • Legless, with a distinct brown head capsule,
  • There are four larval instars, with mature larvae reaching 6-9 mm in length.
  • Larvae are rarely seen in fruit left on the tree

Pupae:

  •  5–7 mm in length,
  • White or cream coloured,
  • Soil dwelling.

Adults:

  • 4-6 mm long,
  • Dark brown with grey and white dorsal patches
  • Bent antennae arise from an elongated beak-like snout,
  • Four distinctive humps on their elytra (wing covers).

Damage:

  • Heaviest near the orchard perimeter,
  • Females create crescent-shaped oviposition scars on the fruit which remain at harvest,
  • Summer feeding creates rounded cavities that act as entry sites for decay organisms,
  • Fresh damage often has sap oozing out of the fruit,
  • Damaged fruit remaining on the tree is scarred and malformed.

Often Confused With

  • Other weevils- The presence of four distinctive humps on their elytra (wing covers) helps distinguish adults from other weevils.

Period of Activity
Plum curculio adults migrate into orchards from pink through petal fall. Adults do not begin to damage fruit until after petal fall. There is one generation of plum curculio in Ontario so damage usually stops at the beginning of early summer. However in southern regions (Virginia south) with 2-3 generations, plum curculio is present in orchards through harvest.

Scouting Notes
Monitoring of plum curculio adults is difficult since they respond poorly to olfactory or visual traps. More research is required to develop an effective bait for migrating plum curculio adults.

Monitor wild fruit trees adjacent to or near orchard perimeters for feeding and oviposition scars beginning at bloom. Examine apple trees in border rows every two to three days for signs of fresh injury. Continue monitoring until first injury is detected.

Thresholds
Once first injury is detected apply an insecticide.

Advanced

Scientific Name
Conotrachelus nenuphar

Identification
Eggs are 0.6 mm long, white and elliptical, and are deposited under the fruit skin. Larvae are cream-coloured, C-shaped and legless, with a distinct brown head capsule. There are four larval instars, with mature larvae reaching 6-9 mm in length. Pupae are 5–7 mm in length, white or cream coloured, and soil dwelling. Adults are 4-6 mm long, dark brown with grey and white dorsal patches. Their bent antennae arise from an elongated beak-like snout. They have four distinctive humps on their elytra (wing covers).

Adults damage fruit in two ways: 

    • Females create crescent-shaped oviposition scars on the fruit which remain at harvest;
    • Summer feeding on the apple pulp creates rounded cavities that act as entry sites for decay organisms.

Plum curculio damage is generally heaviest near the orchard perimeter. Oviposition damage is more economically significant than feeding damage. It is difficult to assess the impact of plum curculio on fruit loss, because fruit damaged in the early season is often aborted during natural fruit abscission (June drop). Fresh damage often has sap oozing out of the fruit.

Damaged fruit remaining on the tree is scarred, malformed and unsuitable for fresh market sale. If uncontrolled, plum curculio can reduce the crop by up to 85%. 

Often Confused With

  • Other weevils- The presence of four distinctive humps on their elytra (wing covers) helps distinguish adults from other weevils.

Biology
The plum curculio overwinters as an adult under leaf debris, brush piles and stacked wood near or adjacent to orchards. Adult activity and migration back into the orchard begin in the spring following sustained warm weather (mean temperatures of 15.5ºC or higher) and light rain. This usually occurs around bloom in apple and lasts for up to six weeks, with the greatest migration occurring within the period of up to 14 days after petal fall. Some research suggests weather patterns (sunny/cloud) affect whether beetles migrate into the orchard by crawling or flying. If weather is cool at bloom time and petal fall, adults may not migrate into the orchards until after petal fall

Adults mate and feed on developing leaves, blossoms and fruitlets. Females usually lay eggs in the fruit several weeks after emerging, once fruit set has occurred. Females cut a cavity into the fruits’ skin with their snout, depositing an egg in the hole. A crescent-shaped slit cut around the oviposition site helps prevent the egg from being crushed by rapidly expanding fruit.

Eggs hatch in three days at temperatures of 25°C, and may take as long as 12 days to hatch at 18°C. Emerging larvae feed inside the fruit, causing some of the infested apples to drop prematurely. Larvae continue to develop in fallen fruit. Mature larvae exit fruit and burrow into the soil to pupate. Infested apples that fail to drop expand and crush developing larvae.The complete lifecycle from egg to adult takes about 50-55 days. Plum curculio has a single generation a year in Ontario. A second generation occurs in more southern areas. Early varieties with dense foliage and yellow skinned cultivars are most heavily attacked.

Period of Activity
Plum curculio adults migrate into orchards from pink through petal fall. Adults do not begin to damage fruit until after petal fall. There is one generation of plum curculio in Ontario so damage usually stops at the beginning of early summer. However in southern regions (Virginia south) with 2-3 generations, plum curculio is present in orchards through harvest.

Scouting Notes
Monitoring of plum curculio adults is difficult since they respond poorly to olfactory or visual traps. More research is required to develop an effective bait for migrating plum curculio adults.

Monitor wild fruit trees adjacent to or near orchard perimeters for feeding and oviposition scars beginning at bloom.  Examine apple trees in border rows every two to three days for signs of fresh injury. Continue monitoring until first injury is detected.

Thresholds
Once first injury is detected apply an insecticide.

Management Notes

  • There are few effective cultural or biological controls to help manage plum curculio. Regular winter pruning to open up the canopy improves spray coverage. Some research suggests plum curculio is attracted to fresh pruning cuts. If possible, complete pruning prior to significant green tissue development to allow pruning cuts to heal over.
  • Researchers in Quebec have shown border sprays are effective as the sole strategy against plum curculio in special cases. Border sprays alone may be effective if:
    • European apple sawfly is not present
    • Spring temperatures were not too far from “normal”
    • The orchard is relatively uniform in shape, roughly square in shape, and if the trees are large.
  • The efficacy of border sprays using any non-organophosphate (OP) insecticides has not been assessed and consequently, their use is currently not recommended.
  • For information on what products are OP insecticides, see OMAFRA Publication 360, Guide to Fruit Production.
  • Plum curculio emergence and damage is affected by spring weather conditions, and models are effective for predicting when migration into the orchard may be extended, and when additional sprays may be needed to protect the crop. 
  • Researchers at Cornell University developed an oviposition model to determine when control sprays after petal fall are no longer necessary to protect fruit from plum curculio damage.
  • This model is based on the assumption that residues from control sprays after petal fall only need be maintained on fruit and foliage until about 40% of the oviposition cycle is complete. This is predicted by the model to occur at 154 DDC (base temp 10°C) after petal fall.
  • In order to use the degree day model strategy, treat the entire orchard at petal fall with a broad-spectrum insecticide. Begin calculating the accumulation of DD after petal fall (using base temp 10°C). Additional sprays for plum curculio are not necessary when the date of accumulation of 154 DDC falls within 10-14 days after a previous spray. See OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :