March 2022 - 26

Adult plum curculio.
Small peach just before shuck split. Photos: Brett Blaauw
How to protect young peaches from plum curculio
By Emily Cabrera
University of Georgia
With the onset of warmer, longer days,
an array of pink blooms from peach,
cherry and plum trees break forth - the
first signs of spring. And while most of us
enjoy this seasonal shift, fruit tree growers
prepare their orchards for the relentless,
annual migration of insect pests.
Of these spring pests, plum curculio is
the most destructive insect that attacks
early-season fruit.
" If you have fruiting trees, especially
peaches, now is the time to ramp up your
monitoring efforts for plum curculio
to determine if and when management
decisions will need to be made, " urged
University of Georgia (UGA) College of
Agricultural and Environmental Sciences
peach entomologist Brett Blaauw.
Plum curculio is the most economically
important pest in the commercial peach
industry in Georgia, Blaauw explained,
but can also cause considerable damage
in home orchards because the majority
of homeowners don't have access to
effective insecticides or simply don't know
good preventative measures for reducing
populations each year.
Plum curculio, or Conotrachelus
nenuphar (Herbst), is a snout beetle
native to North America and is found
east of the Rocky Mountains in the U.S.
and Canada. Their long snouts puncture
young fruit during feeding and egg laying,
leaving characteristic crescent-shaped
scars on the skin of peaches. While plum
curculios have a wide range of hosts,
they prefer pome and stone fruits such as
apples, pears, peaches and plums.
Shuck split
In Georgia, overwintering adults
emerge and begin their migration into
orchards around the time of shuck split,
typically March through April. You can
learn to recognize shuck split in your
orchard by monitoring trees after they
have bloomed. Pollinated blooms will
begin developing young fruit, which will
be covered in a papery shuck - a remnant
of the flower.
As the fruit grows, the shuck will
split and eventually fall off. Shuck split
is a critical time period for making
management decisions as plum curculio
targets these young fruits and, once
established, can become exponentially
more difficult to control throughout the
growing season.
There are two generations of plum
curculio each season. Adult females begin
laying eggs in the spring, and within 5-8
weeks, adults emerge to begin feeding on
fruit and foliage before depositing eggs
and beginning a second generation.
Controlling curculios
If unmanaged, both generations can
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cause differing, yet significant economic
Most peaches infested by plum curculio
early in the season drop prematurely,
whereas larger peaches, infested after pit
hardening begins, generally stay on the tree
until ripe. These ripe fruits become infested
with larvae and have to be discarded.
First- and second-generation adults
continuously feed until cooler weather
arrives, when they begin seeking
overwintering sites, where they will lay in
wait for the next season.
Trapping and degree day (DD)
calculations help refine the management
of plum curculio. Once maximum
daily temperatures reach 70˚ F for two
consecutive days from February to early
March, growers can begin keeping track
of and accumulating growing degree days
using a base temperature of 50˚ F.
Adults continue to migrate into the
orchard from 50-500 DD, much of March
and April in central Georgia, so this is the
period when fruit should be protected by
insecticide sprays. Summer adults emerge
from the soil after 1,000 DD, which is
usually sometime in late May through
harvest of late-ripening cultivars.
Blaauw suggests making these early
season applications of insecticides to
protect the young, developing fruits
from adults laying first-generation eggs.
Typically, sprays are applied between
petal fall and shuck split. Two or three
additional sprays at 10- to 14-day
intervals are needed to assure control of
the overwintered population.
For commercial production, rotate
highly effective materials like phosmet,
thiamethoxam, clothianidin or
indoxacarb with pyrethroids, such as
For homeowners, products such as
kaolin clay can be applied to trees to
create a physical barrier against attack.
Other tools for small-scale production are
the use of fruit bags that protect growing
fruit throughout the season and eliminate
the need for weekly pesticide applications.
At the end of the season, proactive
measures for minimizing damage in
subsequent years will begin immediately
following harvest. Blaauw recommends
closely mowing ground cover to reduce
habitat for adults that are seeking out
overwintering sites. And always be sure
to clear out wild plum thickets and
other alternative hosts nearby to reduce
migration from outside sources.
To learn more about setting traps
and monitoring for plum curculio, read
Extension Circular 1224, " Plum Curculio:
An Incessant Pest of Peaches " at https://
For more information on peach
management, visit the UGA Peach
Blog (
peaches/). FGN

March 2022

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