1. Managing Pesticide Resistance on Avocados

2. Eduardo Humeres, Joseph Morse, Alan Urena,
Lindsay Robinson, Pam Watkins, Paul Flores, Darren Anderson
University of California Department of Entomology
Riverside, CA

3. Presentation What is pest resistance? Key avocado pests
Management of key avocado pests
Avocado pest resistance
Summary

4. Pest Resistance

5. Farmers, horticulturists or agricultural advisers
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

6. Toxicologist
Observes the change from susceptible to resistance as a shift in dosage-mortality lines

7. Early in resistance evolution A B Proportion of population
Resistant individuals at low numbers
Fitness
Concentration

8. Seleção Proportion of population A B Concentration Selection
(= pesticides sprays)
Seleção
Proportion of population
Concentration

9. Distribution after resistance has evolved
Proportion of population
Concentration

10. Key Avocado Pests

11. Scirtothrips perseae (Thysanoptera: Thripidae)
Avocado Thrips
Scirtothrips perseae (Thysanoptera: Thripidae)

12. Biology
(Hoddle & Morse 2004)

13. Avocado Thrips: food source

14. Avocado Thrips Damage

15. Avocado Fruit Set

18. Oligonychus perseae (Acari: Tetranychidae)
Persea Mite
Male
Female
Oligonychus perseae (Acari: Tetranychidae)

19. Biology
(Hoddle, 1999)

20. 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)

24. Avocado Pests Fluctuations
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
Avocado Thrips
Persea Mite

25. Management of Key Avocado Pests

26. 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)

27. Released mites do not appear to persist from year to year
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

28. Optimal weather conditions (cool coastal weather)
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

29. 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

30. 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

31. 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 > % 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

32. 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

33. Monitoring for Avocado Thrips in Spring
Study by Phillips and Faber on Hass avocados in Ventura Co.
When 3-5 thrips are Resulting %
found per leaf fruit scarring
97 days before fruit set %
75-36 days before fruit set 18-28%
During fruit set %

34. 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

35. 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)

36. 2004 Section 18 Allowing Agri-Mek Use
Agri-Mek available under a Section 18 Emergency Exemption for avocado thrips
: two applications per season allowed by air or ground

37. 2004 Section 18 Allowing Agri-Mek Use
Initial decision by EPA (Feb. 17) was to deny the (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

38. 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

39. Pesticides available for avocado thrips
ABAMECTIN - Agri-Mek 0.15 EC
SPINOSAD - Success 2 SC
- Entrust 80%
SABADILLA  - Veratran D 0.2%

40. 2004 Section 18 Language ABAMECTIN - Agri-Mek 0.15 EC
fl oz / acre
Add % 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

41. ABAMECTIN - Agri-Mek 0.15 EC
Agri-Mek relatively slow in killing avocado thrips
Quite persistent in leaves, with control persisting weeks or more
Also effective in suppressing persea mite populations
pH of water should be 5-9, better above 6

42. Add 0.25% or more NR-415 oil by air or ground
SPINOSAD – Success 2 SC
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 oz = 0.45 lb ai
oz Entrust 80% + an organically approved oil
( )

43. 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)

44. Success Residual Activity with NR-415 Oil on Avocado Thrips, Field/Laboratory Bioassay; Bonsall, CA 1999
Corrected mortality (%)
Age of residues (days)

45. SABADILLA – Veratran D
10-15 lb Veratran D 0.2% in gpa by air or 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 lily- like 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

46. 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)

47. Avocado Pest Resistance

48. 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)

49. 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

50. History of Citrus Thrips Pesticide Resistance Development
Year First Used Year Pesticide
Pesticide Commercially Resistance Appeared
Tartar emetic
DDT
Veratran D ??
Dieldrin
Malathion
Dimethoate a
Carzol b
Baythroid
Agri-Mek ?? (2004)
Success ?? (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.

51. 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

54. 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:
or (951)
(Please note we are limited in how many tests we can do)

55. Avocado Thrips Bioassay

56. Munger Cells

57. Munger Cells

58. Transfer early second instar larvae

59. 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

61. Resistance reversion
Study the reversion of avocado thrips resistance to sabadilla in the Camarillo (Grove 4) strain

62. 19 AUG 1999
03 NOV 2003
09 DEZ 2003
30 JAN 2004
Reversion of avocado thrips resistance to sabadilla in the Camarillo strain

63. 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 ?

64. Persea Mite Bioassay

65. California

68. Adult Female

69. Plastic box bioassay
Persea mite

70. 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 showed a loss of persea mite susceptibility to Agri-Mek
4 treatments spring for avocado thrips
3 treatments fall for persea mite

72. We must find an alternative to Agri-Mek for Persea Mite
Acramite (bifenazate)
Zeal (etoxazole)
FujiMite (fenproximate)
Kanemite (acequinocyl)
Envidor (spirodiclofen)
Standard: Agri-Mek
Crompton
Valent
Nichino
Arvesta
Bayer
Syngenta

73. Summary

74. Evidence for Concern Regarding Avocado Pest Resistance
Avocado thrips resistance to Veratran D detected in two groves in Ventura Co.
Loss of persea mite susceptibility to Agri-Mek seen in a Ventura Co. avocado grove

75. Evidence for Concern Regarding Avocado Thrips Resistance to Agri-Mek
History of citrus thrips developing resistance to 5 classes of chemistry (8 chemicals) since 1941
Loss of citrus thrips susceptibility to Agri-Mek seen in a Ventura Co. citrus grove (with concurrent loss of Success susceptibility)
Only Success (same class of chemistry as Agri-Mek) and Veratran D currently available as alternatives for avocado thrips

76. 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
Limit Agri-Mek sprays to once per year maximum
Find an effective alternative for persea mite control

77. This research was supported in part by grants provided by the California Avocado Commission

78. 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