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Managing Pesticide
Resistance on Avocados
Eduardo Humeres, Joseph Morse, Alan Urena,
Lindsay Robinson, Pam Watkins, Paul Flores, Darren Anderson
University of California Department of Entomology
Riverside, CA
Presentation
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What is pest resistance?
Key avocado pests
Management of key avocado pests
Avocado pest resistance
Summary
Pest Resistance
The development of resistance to a
pesticide is perceived in a number of
ways (McKenzie, 1996):
• Farmers, horticulturists or agricultural
advisers
• Recognize resistance as a decrease in the
effectiveness of control of a pest provided by
a chemical
• Geneticist
• Attempts to define the heritable basis of the
resistance phenotype
• Toxicologist
• Observes the change from susceptible to
resistance as a shift in dosage-mortality lines
Proportion of population
A
B
Early in resistance
evolution
Resistant individuals
at low numbers
Fitness
Concentration
Selection
(= pesticides sprays)
A
Proportion of population
Seleção
Concentration
B
Proportion of population
A
Distribution
after
resistance has
evolved
Concentration
B
Key Avocado Pests
Avocado Thrips
Scirtothrips perseae (Thysanoptera: Thripidae)
Biology
(Hoddle & Morse 2004)
Avocado Thrips: food source
Avocado Thrips Damage
Avocado Fruit Set
Persea Mite
Male
Female
Oligonychus perseae (Acari: Tetranychidae)
Biology
(Hoddle, 1999)
Avocado Persea Mite Damage
• Hass cultivar most damaged
• Mites occur mainly on the underside of the leaves
along the midrib, main veins and leaf depressions
• Lower epidermal, spongy parenchyma and
palisade cells of the leaf tissue are destroyed and
large necrotic areas on the leaf result from feeding
(Aponte & McMurty, 1997)
Avocado Pests Fluctuations
JAN
FEB
MAR
APR
Avocado Thrips
MAY
JUN
JUL
AUG
Persea Mite
SEP
OCT
NOV
DEC
Management of Key
Avocado Pests
Context of Chemical Control Research with
Avocado Pests
Avocado Thrips
• Worldwide, few examples of complete biological control of
pestiferous thrips species (chemical intervention often
required)
• Scirtothrips citri (Citrus thrips)
• Scirtothrips aurantii (South African citrus thrips)
• Scirtothrips dorsalis (Chili or yellow tea thrips)
Avocado Persea Mite
• Considerable research has focused on control using
augmentative releases of various predaceous mite
species
• Released mites do not appear to persist from year to
year
• Generally, cost of effective annual augmentative
releases is considered prohibitive
• General observation – avocado thrips and persea
mite can build to economically injurious levels
quickly under ideal conditions
• Optimal weather conditions (cool coastal
weather)
• Presence of leaf, leaf flushes or young fruit
(avocado monoculture = a banquet)
• Low endemic levels of biological control agents
Thus, an integrated approach is needed with key avocado pests
An Integrated Approach to
Avocado Pests Management
• Classical biological control - search in native range of
avocado thrips and persea mite for effective natural
enemies, import and release them
• Monitor field populations / natural enemies and apply
selective treatments only as needed, based on economic
thresholds (potential for fruit damage)
• Monitor field populations for pesticide resistance
development
• Continue to search for new selective chemical control
materials
Should I Spray for Avocado Pest Control?
• Suggest growers might employ a knowledgeable
pest control advisor to assist in monitoring / spray
decisions
• Monitor immature avocado thrips on young leaves,
then move to fruit when the thrips do
• Monitor for adult persea mite on mature leaves
• Good treatment decisions are tricky - several factors
are involved:
• Tree size and health (vigor), grove topography
• Timing (leaf flushes), weather
• Natural enemy levels
• Grower tolerance for fruit scarring (short-term economics
versus natural enemy and thrips susceptibility
maintenance)
• Leaf drop tolerance for persea mite feeding (increases
when > 7.5-10 % of the leaf surface is damaged)
• Spray equipment availability
• Many groves do not require an avocado thrips or
persea mite treatment in a particular year
Monitoring for Avocado Thrips in Spring
• Use a 10-14X hand or head lens to count the
number of immature avocado thrips on the
undersides of leaves prior to fruit set
Monitoring for Avocado Thrips in Spring
• Study by Phillips and Faber on Hass avocados in
Ventura Co.
When 3-5 thrips are
found per leaf
Resulting %
fruit scarring
97 days before fruit set
26-38%
75-36 days before fruit set
18-28%
During fruit set
6-15%
Monitoring for Avocado Thrips in Spring
• Avocado thrips do best under moderately cool
temperatures (68-76 °F)
• Under hot conditions (> 90 °F), populations crash
• Smaller fruit are more susceptible to damage by
avocado thrips
• As fruit become larger (1.5 inches or more in
diameter) - large numbers of thrips are needed to
cause significant levels of fruit scarring
Monitoring for Persea Mite
(Machlitt, 1998)
Number of persea mites per leaf =
Total no. of mites counted is divided by 10 (average no. mites per leaf) x 12 (correlation factor)
2004 Section 18 Allowing Agri-Mek Use
• Agri-Mek available 1999-2004 under a Section 18
Emergency Exemption for avocado thrips
• 1999-2003: two applications per season allowed by air or
ground
2004 Section 18 Allowing Agri-Mek Use
• Initial decision by EPA (Feb. 17) was to deny the
2004 (Year 6) Section 18 request due to the
availability of a registered alternative (Success
registered in 2000)
• Request submitted by CAC 9/03
• Economic analysis 11/5/03
• Additional data 2/6/04
• Analysis of data from 23 UC field trials prepared 2/16/04
2004 Section 18 Allowing Agri-Mek Use
• Only last-minute CAC intervention and CA-DPR
supporting a “Crisis Exemption” resulted in a
compromise with EPA (Feb. 18, 2004)
• A single Agri-Mek application was allowed in 2004 and
only by air
• Monthly conference calls (Guy Witney, Steve Peirce,
Joseph Morse) with Syngenta to make sure full
registration will be obtained for 2005
• Appear on track for registration Feb., 2005
• We have not yet seen the draft Section 3 label
• Suspect will allow 2 applications per year
• Unclear what filter strip requirements will be
Pesticides available for avocado thrips
• ABAMECTIN
- Agri-Mek 0.15 EC
• SPINOSAD
- Success 2 SC
- Entrust 80%
• SABADILLA
- Veratran D 0.2%
2004 Section 18 Language
• ABAMECTIN - Agri-Mek 0.15 EC
• 10 - 20 fl oz / acre
• Add 0.25 - 4 % NR-415 oil in 50 or more gpa
• Single application per season; 12 h REI, 14 d PHI
• Application allowed only by air
• See Section 3 label for 2005 restrictions and reporting
requirements
• ABAMECTIN - Agri-Mek 0.15 EC
• Agri-Mek relatively slow in killing avocado thrips
• Quite persistent in leaves, with control persisting
6-10 weeks or more
• Also effective in suppressing persea mite
populations
• pH of water should be 5-9, better above 6
• SPINOSAD – Success 2 SC
• 4 - 10 fl oz / acre
• Add 0.25% or more NR-415 oil by air or ground
• In order to delay thrips resistance development, do not
apply Success more than 2 times per year; 4 h REI, 1 d
PHI
• Do not apply more than 29 oz Success (0.45 lb spinosad)
per acre per crop
10 oz + 10 oz + 8.8 oz = 0.45 lb ai
• 1.25-3 oz Entrust 80% + an organically approved oil
(http://www.omri.org/OMRI_brand_name_list.html )
• SPINOSAD – Success 2 SC
• Similar chemistry as Agri-Mek (both are termed
macrocyclic lactones and are produced from
Actinomycetes in fermentation vats)
• Efficacy against Lepidoptera but almost no mite
activity
• More rapid kill of avocado thrips than Agri-Mek but
less persistent in leaves
• Do not acidify the spray tank as with Veratran D
(ph 7-9 is optimal)
Success Residual Activity with NR-415 Oil on Avocado
Thrips, Field/Laboratory Bioassay; Bonsall, CA 1999
Corrected mortality (%)
100
80
Wate r control
Success 6 oz
Succ + 0.25%
Succ + 0.50%
Succ + 1.0%
Succ + 2.0%
Succ + 4.0%
60
40
20
0
1
7
14
21
29
Age of residues (days)
35
• SABADILLA – Veratran D
• 10-15 lb Veratran D 0.2% in 10-40 gpa by air or 20100 gpa by ground; If 200 gpa is used, increase to
20 lb per acre; 24 h REI
• Botanical pesticide made from the ground seeds of a lilylike plant from Venezuela
• Screen size should be 20 mesh or larger (to avoid
plugging)
• Acidify water to pH 4.5 (citric acid or other) prior to
adding Veratran D
• SABADILLA – Veratran D
• Do not use additives (is a stomach poison and may
reduce thrips feeding activity)
• More effective in warm weather (when thrips are actively
feeding)
• Not persistent (50% gone after 4 days, control may last
1-3 weeks)
Avocado Pest
Resistance
Pesticide Resistance –
A Major Concern with Avocado Pests
• Loss of persea mite susceptibility to Agri-Mek
seen in a Ventura Co. avocado grove
(Humeres & Morse 2005a, in press)
• Avocado thrips resistance to Veratran D seen in
two Ventura Co. avocado groves
(Humeres & Morse 2005b, submitted)
Pesticide Resistance –
A Major Concern with Avocado Pests
• History of citrus thrips resistance on citrus
• Loss of citrus thrips susceptibility to Agri-Mek seen
in a Ventura Co. citrus grove with concurrent loss
in susceptibility to Success
• Avocado thrips resistance monitoring recently
initiated
History of Citrus Thrips Pesticide Resistance Development
Pesticide
Tartar emetic
DDT
Veratran D
Dieldrin
Malathion
Dimethoate
Carzol
Baythroid
Agri-Mek
Success
Year First Used
Commercially
1939
1946
1948
1953
1954
1969 a
1972 b
1991
1994
1998
Year Pesticide
Resistance Appeared
1941
1949
??
1954
1961
1980
1986
1996
?? (2004)
?? (reports investigated)
a Registered for use on non-bearing citrus in 1962.
b
Not used extensively until dimethoate resistance appeared in the early 1980’s.
Current Citrus Thrips Resistance Monitoring
• Agri-Mek registered for use against citrus thrips in
1994
• Citrus grove in Ventura County sprayed 8 times with
Agri-Mek for citrus bud mite control
• 1 spray in 1997, 1 in 1998, 2 in 1999, 2 in 2000, 1 in
2001, 1 on 28 April 2003
• Lesser citrus thrips control observed in 2002 and 2003
• Colony started October, 2003
• Bioassay done June. 2004
Avocado Thrips Resistance Monitoring
• We have recently initiated field monitoring
• If you have a grove without past exposure to Agri-Mek
and Success
• Or a grove with substantial past exposure to Agri-Mek
and/or Success and observed a lack of field control,
• Please contact Dr. Eduardo Humeres:
[email protected] or (951) 827-5443
(Please note we are limited in how many tests we can do)
Avocado Thrips Bioassay
Munger Cells
Munger Cells
Transfer early second
instar larvae
Avocado Thrips Resistance to Veratran D
• In contrast to citrus and citrus thrips (no
resistance suspected; material used on
citrus since 1948), clear resistance to
Veratran D seen in one avocado thrips
population in Ventura Co.
• Grove 4 in Ventura Co.: 10.9-fold resistance
developed after 6 Veratran treatments over
two years
Resistance reversion
• Study the reversion of avocado thrips
resistance to sabadilla in the Camarillo
(Grove 4) strain
Reversion of avocado thrips resistance to sabadilla in the Camarillo strain
19 AUG 1999
03 NOV 2003
09 DEZ 2003
30 JAN 2004
Resistance reversion
• The observed reversion of resistance does
not tell us how long adequate control with
Veratran D would persist
• How quickly would the population regain
resistance ?
Persea Mite Bioassay
California
Adult Female
Plastic box bioassay
Persea mite
Persea Mite Pesticide Susceptibility Testing
• Agri-Mek first available under the avocado thrips
Section 18 in 1999
• 7 groves monitored for persea mite susceptibility to
Agri-Mek in 2003
• One grove in Oxnard treated 7 times over 2000 2003 showed a loss of persea mite susceptibility to
Agri-Mek
• 4 treatments spring 2000-2004 for avocado thrips
• 3 treatments fall 2000-2003 for persea mite
Persea Mite Field Pesticide Susceptibility - Agri-Mek
LC50 Log(mg [AI]/liter)
1
b
ab
a
a
a
Bonsall-2
Gole ta
a
a
0.1
Rainbow Bonsall-1
Santa
Paula
Strain
Fallbrook
Oxnard
We must find an alternative to
Agri-Mek for Persea Mite
• Acramite (bifenazate)
– Crompton
• Zeal (etoxazole)
– Valent
• FujiMite (fenproximate)
– Nichino
• Kanemite (acequinocyl)
– Arvesta
• Envidor (spirodiclofen)
– Bayer
• Standard: Agri-Mek
– Syngenta
Summary
Evidence for Concern Regarding Avocado
Pest Resistance
1. Avocado thrips resistance to Veratran D detected
in two groves in Ventura Co.
2. Loss of persea mite susceptibility to Agri-Mek seen
in a Ventura Co. avocado grove
Evidence for Concern Regarding Avocado
Thrips Resistance to Agri-Mek
3. History of citrus thrips developing resistance to 5
classes of chemistry (8 chemicals) since 1941
4. Loss of citrus thrips susceptibility to Agri-Mek seen
in a Ventura Co. citrus grove (with concurrent loss
of Success susceptibility)
5. Only Success (same class of chemistry as AgriMek) and Veratran D currently available as
alternatives for avocado thrips
Avocado Thrips Management
• Agri-Mek is a remarkably effective material for
avocado thrips control with minimal detrimental
impact on natural enemies
• Few effective alternative control materials are likely
to become available
• We must conserve avocado pest susceptibility
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Limit Agri-Mek sprays to once per year maximum
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Find an effective alternative for persea mite control
This research was supported in
part by grants provided by the
California Avocado Commission
Acknowledgments
• Pest Control Advisors: Jim Davis, Charlie
Gribble, Matt Hand, Dave Machlitt, Mark
Nyberg, Tom Roberts
• UC Cooperative Extension: Gary Bender,
Ben Faber, Eve Oevering, Phil Phillips
• CAC: Steve Peirce, Guy Witney
• Many cooperating avocado growers