WSU Tree Fruit Research & Extension Center

Tree Fruit Market Diseases

Saturday, September 23, 2017

WSU-TFREC/Postharvest Information Network/Tree Fruit Market Diseases/plum



Conotrachelus nenuphar Herbst

Occurrence and importance
The plum curculio is a moderately destructive pest of apple fruits in States east of the Rocky Mountains. Fruits seriously injured by the insect's feeding and egg-laying activities fall to the ground or, if harvested, are culled out on the packing line. Lightly injured fruits, however, will occasionally appear on the market, especially in lower commercial grades.

Symptoms
Two kinds of insect punctures produce injury: those for feeding and those for deposition of eggs. Early in the growing season, adult curculios puncture the skin of young fruits and eat out small cavities beneath. When these fruits become mature, the punctures appear as small, round russeted scars. When abundant, these injuries cause the apples to be badly deformed and misshapen. More typical injury is produced by egg-laying punctures, shaped as crescent slits in the skin. As the apples grow, the injured areas expand and by maturity are more or less shield-shaped russeted scars. In the fall, adult curculios of the new generation often feed on ripening fruits, mostly around the calyx and stem ends. These feeding punctures do not heal. They appear as small, dark-brown cavities which may permit the entrance of decay organisms.

Causal factors
Adult plum curculios are small, hard-shelled beetles with long snouts. They hibernate in trash in orchards or in brushland or wasteland nearby and begin to return to the apple trees about the time these come into bloom. Most of the egg laying and feeding is done during a period of 4 to 6 weeks after petal fall; a limited amount of feeding is done in the fall. Many of the larvae in the fruits are killed by the pressure of the rapidly growing tissues, but enough of the larvae survive in fallen fruits to maintain the infestation.

Control measures
Plum curculio is controlled by spraying. The spray program should follow the recommendations of the State agricultural experiment station or extension service.

No photos available for this section.

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