Notes on Stone Fruit Insects &
Mites
Plum curculio
Identification
Plum curculio (PC) is a small (6 mm), rough, grey-brown weevil that creates
a characteristic crescent-shaped egg-laying scar on the surface of fruit.
New egg-laying scars reveal moist fruit flesh, while older scars are calloused
and brown. PC larvae feed inside the fruit and are sometimes confused
with OFM. PC larvae do not leave the frass that is typically found in
the entry wound created by OFM larvae. Both pests however, leave a clean
exit hole.
Period of activity
Plum curculio adults overwinter in wooded areas adjacent to orchards.
They become active in the spring after warm weather and rain. Adults emerge
over a three to six week period that begins just after bloom. Egg laying
and fruit injuries begin within two weeks of emergence.
Monitoring and thresholds
Apricots, cherries and plums located along borders of an orchard are
good indicator plants for PC activity. Observe fruit along the outside
two to three rows of the orchard next to wild hosts. Apply controls when
new injury is found. Monitor five to seven days after insecticide application
to determine the need for re-application. The best way to limit PC damage
is to set up a rigorous monitoring program in areas with previous damage.
When conditions are right in the spring, check developing fruit frequently
and carefully or enlist the services of a crop consultant. PC is quite
sporadic and often confined to border areas. Various kinds of traps are
commercially available for monitoring PC. These include "Circle"
traps and "pyramid" traps. Both trap types work best in areas
with high resident PC populations and are most useful to tell when PC
first migrate into an orchard.
Management notes
Since these insects often enter orchards from rough or bush areas, a
border spray of two to four rows may provide sufficient control.
The window for control for PC is narrow. Problems can become worse each
year if the pest is not adequately controlled. The first spray for oriental
fruit moth often, but not always, comes at a good time for control of
PC. However, adult PC emerge over a long period and are actively laying
eggs for more than a month. Ongoing monitoring for new damage is the key
to successful control.
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