USING NEW TOOLS TO MANAGE THE PLUM CURCULIO
(Harvey Reissig, whr1@nysaes.cornell.edu
Entomology, Geneva)
Biology and Traditional Chemical Control Programs
The plum curculio, Conotrachelus nenuphar (Herbst) (PC), is
a native pest of stone and pome fruits that has plagued orchardists since
the first settlers planted fruit trees. The PC flourishes in wild, unsprayed
habitats, because population levels and fruit infestation levels are not
regulated effectively by natural enemies. In natural habitats, unsprayed
apple and plum fruit is usually heavily damaged by this pest. Therefore,
the prospects of developing an effective biological control for PC by
conserving natural enemies in commercial apple orchards does not appear
to be feasible.
Plum curculio adult
Adult PC overwinter under ground debris, often along hedgerows or along
the borders of woodlots. Although a few adult PC may overwinter in commercial
orchards, the majority survive in adjacent overwintering sites. In the
spring, as soon as ambient temperatures begin to reach 50°F, adult
PC emerge from their overwintering quarters and begin to move into orchards.
Beetles can be found in apple orchards even before apples bloom, but the
adults are usually most numerous after blossoms begin to open. New adults
may continue to immigrate into orchards for a 4—6-week period in
early spring. Although adults are present in apple trees during Bloom,
developing apple fruit is not susceptible to PC injury until after petals
have dropped from the young fruitlets. After Petal Fall, beetles damage
apples either by feeding (making holes in the apple with their beak-like
mouthparts) or by ovipositing (cutting crescent-shaped oviposition scars
in the fruit).
Dried sap produced by plum curculio feeding and oviposition wounds
on apple
There is only one generation of PC annually. Since there are no resident
populations of PC in most commercial apple orchards in NY, it is only
necessary to control overwintering adults during their oviposition cycle.
Usually, feeding damage from surviving adults emerging late in the summer
is not found in commercial orchards.
PC activity and oviposition are greatly affected by temperature.
Adults are relatively inactive when temperatures remain below 50°F.
During cool springs, adult movement and oviposition may be lengthy (4—6
weeks), but in warmer seasons, the oviposition period may be relatively
short (2—3 weeks). Growers using traditional chemical control programs
usually apply a protective insecticide to the whole orchard to maintain
a protective residue on apple fruit and foliage during the entire PC oviposition
cycle in the spring. Since insecticide residues are usually effective
for 10—14 days, depending upon the amount of rainfall, traditional
control programs usually require an initial spray at Petal Fall, followed
by 2—3 insecticide sprays depending upon the weather and precipitation
during the spring.
Control and Management Options
Compared with many other insect pests, the PC is not highly mobile
and capable of dispersing uniformly throughout an entire orchard during
one growing season. Damage from curculio tends to be extremely spotty,
and is usually confined to the outer rows of commercial orchards. Since
most PC problems result from immigration into orchard borders from outside
sources, past history of damage is very useful in deciding whether or
not any particular orchard or portions of an orchard are likely to be
severely injured by this pest. Sprays of broad spectrum insecticides,
such as organophosphates, applied to control PC will also provide control
of the first generation of codling moth. Traditionally, growers in NY
who treated entire orchards with organophosphate insecticide sprays for
plum curculio have not had to apply special sprays against the first generation
of codling moth. Growers opting to control PC with reduced insecticide
schedules should also be aware that this strategy may require more consideration
of management of the first generation of codling moth. In addition, growers
in the Hudson Valley and Champlain Valley should also be aware that petal
fall sprays of organophosphates have also usually prevented early season
damage from the European sawfly.
Standard Control, Timing of Sprays Using PC Oviposition Model
Most studies in western NY have shown that applying a spray of insecticides
at the Pink bud stage is no more effective in protecting apples from PC
damage than starting control sprays at Petal Fall. However, some trials
in the Hudson Valley have suggested that a Pink spray does help in preventing
subsequent PC fruit injury in programs in which additional treatments
are applied at Petal Fall. Although growers realize that initial post-bloom
sprays for plum curculio control should begin at Petal Fall, they are
often unsure how many additional sprays will be necessary to maintain
protective chemical residues to prevent subsequent damage throughout the
PC oviposition cycle, which varies according to temperatures and weather
patterns after Petal Fall.
Recently, researchers at the Geneva Station have developed an oviposition
model to determine when control sprays after Petal Fall are no longer
necessary to protect fruit from PC 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, which is predicted by the model to occur at 340 DD
(base temp 50°F) after Petal Fall. A more detailed discussion of
this model and its validation can be found in the article published in
the New York Fruit Quarterly Vol. 2, No 2: "Timing Insecticide Applications
for Controlling Plum Curculio Using a Predictive Model". No one knows
exactly why it is not necessary to apply PC control sprays after 40% of
the oviposition cycle is complete. This parameter was chosen from initial
experiments designed to compare the effectiveness of different schedules
of control sprays after Petal Fall in protecting fruit from PC injury.
Probably, this strategy works because, after 40% of PC oviposition is
complete, adults usually are not moving into the orchard from outside
sources, or moving around within orchards from tree to tree. Therefore,
by this time, adults residing in treated trees have already been killed
by insecticide residues and are unable to complete the remainder of their
normal oviposition cycle.
In order to use this strategy: (1) Treat the entire orchard at Petal
Fall with a broad spectrum insecticide. (2) Start calculating the accumulation
of DD after Petal Fall (Base temp 50° F). (3) No additional sprays
are necessary whenever the date of accumulation of 340 DD falls within
10—14 days after a previous spray.
This conventional strategy is probably only necessary for commercial
apple orchards in which PC fruit damage has been observed frequently,
or for orchards thought to be particularly vulnerable to infestation from
codling moth or the European apple sawfly. Usually, orchards that chronically
suffer fruit damage from PC are relatively small blocks located next to
abandoned orchards or surrounded by woods or woodlots, which are favorable
sites for overwintering of PC adults. Some larger orchards bordered by
woods on one or more sides may also be at risk for chronic infestations
of PC.
Petal Fall Spray, Oviposition Model Border Sprays
This program is similar to the previous program, except that after
the Petal Fall spray is applied, additional sprays as determined by predictions
from the oviposition model are applied only to the border rows of the
orchard (outer 2—4 rows). When using this strategy, it is difficult
to treat the ends of orchards in which rows are perpendicular to hedgerows
or wooded areas. The only practical way to protect these edges is to drive
along the edge of the end trees, with only one side of an airblast sprayer
activated to attempt to blow spray back into the block to cover as many
trees near the end of the row as possible. Usually, depending upon the
size and spacing of trees, at least 2—4 of the end trees in each
row will be adequately covered by the single-sided sprayer application.
Using this strategy assumes that any PC that have migrated into an orchard
prior to Petal Fall will be killed by the Petal Fall spray, and any additional
adults coming in after Petal Fall will be killed by border row sprays
before they can damage fruit in the outer rows of treated trees or migrate
into the interior of the block. This strategy will probably be effective
in controlling plum curculio in typical commercial apple orchards that
have had no previous history of observed fruit damage from plum curculio
at harvest.
Border Sprays, Petal Fall and Oviposition Model
In this program, only the border rows and end trees within each row
are treated at Petal Fall for control of the PC. Subsequent sprays are
applied only to border rows and end trees according to oviposition model
predictions. This strategy can be used in orchards having no previously
observed history of plum curculio damage in which there is a desire to
use only selective pesticides to encourage the buildup of natural enemies
for biological control of mites and other foliar pests. In orchards in
which this strategy is used, it may be necessary to consider applying
a limited program of selective insecticides for control of the first generation
of codling moth. It is also a good idea to closely examine fruit from
both border rows and interior rows for damage at harvest from PC. If traces
of PC damage are observed in fruit harvest evaluations, it may be necessary
to apply one of the more conservative PC control programs during the subsequent
growing seasons until PC damage is eliminated.
WHITE APPLE LEAFHOPPER STOPPER
(Art Agnello, ama4@nysaes.cornell.edu
Entomology, Geneva)
WALH nymphs can be numerous in some blocks, especially in the eastern
part of the state. Provado has proven itself effective against this pest,
and a petal fall application also gives leafminer control. Furthermore,
it will have an added effect on green aphid populations, which could be
problematic, depending on the availability of succulent green tissue.
Growers using Sevin in their thinning sprays will get some control at
the 1 lb rate. Alternative choices for control include Thiodan and Lannate;
Agri-Mek or Carzol used for mites now will also do the job, but Carzol
will be harmful to predator mites. The damage potential of this first
generation should be evaluated carefully before deciding on the need for
a specific control of this pest.
BROTHERS UNDER THE SKIN
(Art Agnello ama4@nysaes.cornell.edu,
Entomology, Geneva)
Codling Moth
Most New York apple growers have traditionally ignored the potential
threat to their crop posed by this widely endemic orchard resident, as
the regular OP sprays for plum curculio and apple maggot between petal
fall and mid-August make fruit infestations by codling moth relatively
rare. During the past few years, however, with the advent of trapping-based
spray decisions for apple maggot, and a resulting decrease in cover sprays
in some cases, there have been more opportunities for an unwelcome return
of the worm in the apple, which is all the more unacceptable because it
is a fairly easy problem to prevent.
Internal apple injury caused by codling moth larva
To that end, we will again publicize suggested codling moth treatment
windows this season, for those growers who don't necessarily spray certain
blocks for maggot each year, and who have evidence (or suspicion) that
codling moth is starting to pose a significant threat.
The Michigan model for predicting this insect's development gives
fairly accurate predictions of codling moth activity in N.Y. As many as
two insecticide applications may be made for each of the two generations
per year, depending on the severity of pressure. Degree days are accumulated
from the date of first sustained moth catch, and the first spray is applied
at 250 DD (base 50°F), which corresponds with predicted 3% egg hatch.
A second spray may be applied 10—14 days later. If pressure is not
too severe, one spray will suffice, applied instead at 360 DD after the
biofix date (which we're calling May 13 in Geneva and May 2 in Highland).
To control the second generation, the timing is 1260 DD after this same
biofix date. We will be providing regular updates to identify imminent
spray dates.
Oriental Fruit Moth
(This just in from Debbie Breth of the Lake Ontario Fruit Team:)
Oriental fruit moth trap catches in peach orchards in the Niagara
region appeared to have peaked on May 8. A predictive model from Ontario
would have called for a spray 6 days later. However, trap catches are
increasing with the resumption of warm weather, and it is unclear when
the "true" peak will have occurred. Therefore, she recommends that growers
apply control sprays no later than shuck split, regardless of model predictions.
Of primary concern is terminal shoot damage in non-bearing blocks. In
some bearing orchards it may be necessary to control the first generation
to prevent a buildup of numbers in subsequent generations that can attack
the fruit.
Oriental fruit moth internal injury to apple.
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