RLara CAPCA Final - University of California, Riverside · 2011-05-23 · 11/10/2010 1 A Simple...
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11/10/2010 1 A Simple Sampling Plan for Persea Mite in Avocado Orchards Ricky Lara University of California, Riverside Entomology Department Topics • Persea Mite Biology • Economic Importance • Economic Importance • Estimating Persea Mite Densities • Half-Vein Method • Absence-Presence Method • Method Evaluation H t C ll tA d L • How to Collect Avocado Leaves • Conclusions • Future Research
Transcript of RLara CAPCA Final - University of California, Riverside · 2011-05-23 · 11/10/2010 1 A Simple...
11/10/2010
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A Simple Sampling Plan for Persea Mitein Avocado Orchards
Ricky LaraUniversity of California, Riverside
Entomology Department
Topics
• Persea Mite Biology
• Economic Importance• Economic Importance
• Estimating Persea Mite Densities• Half-Vein Method
• Absence-Presence Method
• Method Evaluation
H t C ll t A d L• How to Collect Avocado Leaves
• Conclusions
• Future Research
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Persea Mite Biology
• 5 stages
• Feeding on leaf undersurface
• Feeding areas turn into necrotic (dead) spots
• Defoliation and fruit sunburn
• Population buildup in late summer
Counting Mites is Time Consuming!
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CAC 2005
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Control Strategies
Biological Control:• predatory mites,
Neoseiulus californicusNeoseiulus californicus
Pesticides: • Abamectin, new pesticides
coming soon• Threshold ≥100 mites per leaf
Persea Mite!
How do you estimate density of persea mites?
Questions
1. Is there a method to estimate persea mite densities on avocado leaves?
2. How reliable (accurate) is this method in the field and under lab conditions?
3 Are there other methods to estimate persea3. Are there other methods to estimate perseamite densities?
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Half-Vein Method
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Work in Avocado Orchards
Flagging TreesField Observations Distance Between Trees
Bring Leaves to Lab Count Mites!Systematic Leaf Collection
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Half-Vein Method Evaluation
Orchard N Leaves Observed Mean Half-Vein (Microscope) % Error
1 1608 8 4 471 1608 8 4 47
2 240 37 34 8
3 240 42 21 50
4 240 49 29 40
5 247 77 30 61
6 239 205 100 51
7 240 208 110 47
8 240 307 171 44
8 240 342 212 38
9 260 528 214 60
Half-Vein Method Evaluation
Orchard N Leaves Observed Mean Handlens/Optivisor % ErrorOrchard N Leaves Observed Mean Handlens/Optivisor % Error
1 1608 8 3 62
6 239 205 68 67
7 240 208 63 70
9 260 528 134 75
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Evidence for Relationship
4500
5000
af
y = 18.44x + 24.978R² = 0.71
1500
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. of
Per
sea
Mit
es o
n L
ea
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0 50 100 150 200 250
Tota
l N
o
No. of Persea Mites on Left Half Vein
Questions1. Is there a method to estimate persea mite densities
on avocado leaves?
Answer: Yes the half vein methodAnswer: Yes, the half vein method
2. How reliable (accurate) is this method in the field and under lab conditions?
Answer: Accuracy is low; 40-60% error. Method Still involves counting!
3. Is there another method to estimate persea mite densities that involves less counting and is reliable?
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Absence-Presence Method
• Absence/presence of persea mite on 0.9
1
pleaves
• Use proportion of infested leaves to estimate the density of persea mites 0.1
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av
es
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Mean No. Persea Mites per Leaf
Theoretical Relationship
Visualizing the Relationship
0.9
1.0
0.9
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y = 0.1704ln(x) + 0.2886R² = 0.9386
0 0
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eave
s
0.0
0 20 40 60Mean No. of Persea Mites per Leaf
(Ventura 1997)
Collected DataTheoretical
0
0 100 200 300 400 500 600
Mean No. Persea Mites per Leaf
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Data Summary
County Year Trees No. of Leaves No. of Sets Mites Counted
Ventura 1997 42 6,469 16 88,372
Orange 1999 66 5,280 8 232,548
Orange 2000-01 42 17,220 41 74,267
Orange 2003/05 9-17 4,190 31 151,092
Ventura, Santa Barbara (SB)
2009 30 1,207 5 205,584
Ventura, SB, Orange
2010 30-402 2,348 4 249,350
Total: 36,714 105 1,001,213
Proportion vs. Mean Density
1.0
1 M
ite)
0.4
0.6
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on
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ves
Infe
sted
(≥1
100 mite threshold
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po
rtio
Observed Mean Density of Persea Mites
100 mite threshold
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1.0
≥1 M
ite)
Mean-Proportion Model
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ves
Infe
sted
(≥
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Observed Mean Density of Persea Mites
100 mite threshold (can be customized)
Absence-Presence Sampling Model
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e) Area above Upper Stopline:
20
30
40
Lea
ves
Infe
sted
(≥1
Mit
e pp pSpray against persea mite
recommended
Area below Lower Stopline: Spray not recommended
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No
. of
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No. of Leaves Inspected
Minimum leaf sample
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How would it work in the field?
40
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Randomly Select Leaves (20 minimum)
Look at Undersurface Search for Persea Mites
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Present: 1 Absent: 0 Calculate Proportion Infested
Make a Decision
How Reliable Is the Method?
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tio
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ility
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Mean No. of Mites Per Leaf
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How Many Leaf Samples?
900
1000100 mite threshold
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ber
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f S
amp
les
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Minimum
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Mean No. of Mites Per Leaf
1.0
≥1 M
ite)
Mean-Proportion Model
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ves
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sted
(≥
70 mite threshold
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Observed Mean Density of Persea Mites
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Alternate Threshold
1
n
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bili
ty o
f Ta
kin
g N
o A
cti
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70 mite threshold
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bab
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Alternate Threshold
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er o
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eaf
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ple
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m
Mean No. of Mites Per Leaf
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Conclusion
3. Is there another method to estimate persea mite densities that involves less countingmite densities that involves less counting and is reliable?
Answer: Yes, a reliable absence-presence method can be customized for the avocado system.
Currently fine tuning the method: How to collect leaves in an orchard?
Collecting Avocado Leaves
1. Are mite counts higher on specific cardinal points on a tree (N E S W)?tree (N, E, S, W)?
2. Are mites on a tree influencing mite densities on other neighboring trees?
Goal: Reduce bias in estimating mite densities!
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Correlation between neighboring trees?
How Many Trees Do I Skip?
Tree 1 Tree 2 Tree 3Selected Tree
Skip no trees
Skip every other tree
Skip 2 trees
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Results of Spatial Analyses
Orchard Cardinal Effect? p-value Outcome Spatial Correlation? Trees To Skip p-value
7 No 0.30 No 0 0.50
8 Yes 0.004 E>N, W Yes 1 0.039
4 No 0.21 Yes 1 0.023
3 Yes 0.01 W>N Yes 3 0.047
6 Yes 0 004 S W>N Yes 3 0 00026 Yes 0.004 S,W N Yes 3 0.0002
9 No 0.080 Yes 4 0.047
Conclusions1. Are mite counts higher on specific cardinal
points on a tree?
Answer: Yes in some orchards cardinalAnswer: Yes, in some orchards cardinal directions have higher mite counts but there isn’t a consistent pattern across all orchards.
2. Are mites on a tree influencing mite densities on other neighboring trees?g g
Answer: Yes, in some orchards there is spatial correlation. To obtain an independent sample you should skip at least 4 trees.
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Future Research
• Combine the absence presence method with the• Combine the absence-presence method with the spatial work to design a cost-effective sampling scheme:
• Invest less time counting mites and have a reliable estimate of persea mite levels during the growing season
Potential Sampling Schemes
Corner to Corner Zig-Zag Perimeter
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Take Home Message
• Counting persea mites on leaves is a tedious process!process!
• The Half-Vein method underestimates mean mite densities
• A statistically reliable Absence-Presence method can reduce the counting effort in the field
Mit t i fl d iti th• Mite counts can influence densities on other trees and this needs to be accounted for in the sampling scheme
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ThanksFunding: NSF AGEP UCR Cota Robles FellowshipUC Hansen TrustWestern Region IPM
Collaborators:UCR Statistics DepartmentCalifornia Avocado CommissionSteve Naranjo (USDA-ARS)Various PCAs and Growers
Lab Assistance:Ruth Amrich, Allison Bistline, Mike Lewis, Naseem Saremi, Martin Castillo, John Jones, Nick Salvato
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