mid-south tarnished plant bug sampling methods f. musser, a. catchot - msu r. bagwell - lsu s....
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Mid-South Tarnished Plant Bug Sampling Methods
F. Musser, A. Catchot - MSU
R. Bagwell - LSU
S. Stewart- U. Tenn.
G. Lorenz, G. Studebaker J. Greene- U. Ark.
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Existing Situation
• Boll weevil eradication and Bt varieties lead to fewer sprays targeted at weevils and worms, more for TPB
• Most scouts use a plant count, but there is no standard whole plant sampling procedure
• Lack of confidence in TPB thresholds after first bloom
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Objectives• Identify efficient and accurate TPB sampling
methods in mid-season cotton• Verify or adjust current TPB thresholds• Standardize recommended scouting
procedures and thresholds in the mid-south
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2005 Sampling Methods
• 120 commercial fields in TN, MS, LA, AR
• 4 sites in each field
• 5 direct sampling methods (# bugs, time)
• 4 indirect sampling methods (damage, time)
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2006 Sampling Methods
• 60 commercial fields in TN, MS, LA, AR
• 4 sites in each field
• 3X per day (6-9 AM, 11 AM-2 PM, 4-7 PM)
• 3 direct sampling methods (# bugs, time)
• 4 indirect sampling methods (damage, time)
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Sampling Methods• 5 direct sampling methods (# bugs, time)
– Sweep net (25 sweeps with a 15” sweep net)– Drop cloth (5 row ft. on a black drop cloth)– Modified whole plant (25 plants)
• Terminal, 2 squares, 1 bloom, 1 boll
– Squares (25 squares) –in 2005 only– Blooms (25 white blooms) – in 2005 only
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Methods• Four indirect sampling
methods (damage, time)– Damaged squares (25 squares)– Dirty blooms (25 blooms)– Internal boll damage (25 bolls)– External boll damaged (25 bolls)
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Average Number of Plant Bugs per Sample
Average Number of Plant Bugs per Sample
0
0.5
1
1.5
2
2.5
3
3.5
4
2005 2006 2005 2006 2005 2006 2005 2005
Drop Cloth Sweep Net Whole Plant Squares Blooms
Sampling Method and Year
Pla
nt
bu
gs
per
sam
ple
Nymphs
Adults
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Average Number of Plant Bugs per Sample by State, 2006
Average Number of Plant Bugs per Sample by State, 2006
0
0.5
1
1.5
2
2.5
3
3.5
4
All AR LA MS TN All AR LA MS TN All AR LA MS TN
Ins
ec
ts /
sa
mp
ling
un
it
Nymphs
Adults
Drop Cloth/5 row ft.
Whole Plant/25 plants
Sweep Net/25 sweeps
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Average % DamageAverage % Damage
0
2
4
6
8
10
12
14
16
18
Dirty Squares Dirty Blooms External Bolls Internal Bolls
Sampling Method
% d
am
ag
e
2005
2006
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Average % Damage by State, 2006Average % Damage by State, 2006
0
5
10
15
20
25
All AR LA MS TN All AR LA MS TN All AR LA MS TN All AR LA MS TN
State and Sampling method
% d
amag
e
Dirty Squares Internal BollsExternal BollsDirty Blooms
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Average Time for One SampleAverage Time for One Sample
0
2
4
6
8
10
12
DropCloth
SweepNet
WholePlant
DirtySquares
DirtyBlooms
ExternalBolls
InternalBolls
Sampling Method
Min
ute
s p
er s
amp
le u
nit
2005
2006
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Average Number of Bugs Found Per Minute
Average Number of Bugs Found Per Minute
0
0.5
1
1.5
2
2.5
3
3.5
2005 2006 2005 2006 2005 2006
Drop Cloth Sweep Net Whole Plant
Year and Sampling Method
Pla
nts
bu
gs
/ m
inu
te
Nymphs
Adults
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Average Damaged Fruit Observed Per Minute, 2006
Average Damaged Fruit Observed Per Minute, 2006
0
1
2
3
4
5
6
7
8
9
Dirty Squares Dirty Blooms External Bolls Internal Bolls
Sampling method
dam
age
/min
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Time of Day Variation
0
0.5
1
1.5
2
2.5
AM Noon PM Ave. AM Noon PM Ave. AM Noon PM Ave.
Method and Time of Day
Inse
cts
/ sa
mp
lin
g u
nit
Adults
Nymphs
Drop Cloth/5 row ft.
Whole Plant/25 plants
Sweep Net/25 sweeps
p=0.133
p=0.033
p=0.020
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Sampler Impact by Method
Method F- value P-valueDrop Cloth 3.08 <0.0001
Sweep Net 2.77 <0.0001
Whole Plant 3.51 <0.0001
Dirty Squares 1.69 0.0380
Dirty Blooms 2.26 0.0025
Ext. Bolls 5.63 <0.0001
Int. Bolls 3.34 <0.0001
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Black vs. White Drop Cloth
TPB Stage White Black % difference
Adults 1.17a 0.98a -16
Nymphs 7.43a 9.55b +29
Total 8.60a 10.53b +22
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Other Factors Altering Bias Both Years
Factor Change
Wind ↓ PB with ↑ wind using whole plant sampling
Factors monitored: temperature, wind speed, cloud cover, plant height, nodes, NAWF
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Sampling Equivalencies
1 TPB per 2 row ft on a black drop cloth equals
Method EquivalentSweep Net 12 TPB/100 sweeps
Modified whole plant 9 TPB/100 plants
Dirty squares 8 /100 squares
Dirty blooms 14 /100 blooms
External bolls 12 /100 bolls
Internal bolls 9 /100 bolls
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Correlations of sampling methods
• Created a PB score based on all 7 sampling methods (PB score = 1 at threshold)
• Correlated each sampling method to the composite score
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Correlation of sampling methods to each other
Method Correlation (R)
2005 2006
Drop Cloth 0.788 0.773
Sweep Net 0.859 0.811
Whole plant 0.851 0.827
Dirty Squares 0.758 0.780
Dirty Blooms 0.820 0.816
External Bolls 0.758 0.711
Internal Bolls 0.775 0.685
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Sweep Net (Adults) -0.313
Sweep Net (Nymphs) -0.41
Drop Cloth (Adults) -0.334
Drop Cloth (Nymphs) -0.262
TPB per 25 sweeps -0.4
Drop Cloth -0.31
% Square Retention 0.587
Nymphs per 25 squares -0.432
% Dirty Squares -0.638
% Internal Square Damage -0.489
% Boll Damage (Small) -0.365
%Boll Damage (Medium) -0.475
%Boll Damage (Large) -0.404
%Boll Damage (Total) -0.452
Dirty Blooms per row ft. -0.303
% Dirty Blooms -0.357
Shed Squares 0.031
Shed Bolls -0.057
Method R Method R
Correlations with Yield
Jeff Gore
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0
2
4
6
8
10
SweepNet
DropCloth
Whole Plt DirtyBlooms
DirtySquares
Ext Bolls Int Bolls
Sampling method
# s
am
ple
s n
ee
de
d
20052006
Sampling Precision, 2006# samples needed to make a correct decision 80% of the time
when the actual pest density is 20% > threshold
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0
10
20
30
40
50
60
70
SweepNet
DropCloth
WholePlt
DirtyBlooms
DirtySquares
Ext Boll Int Boll
Sampling method
Min
ute
s n
ee
de
d 2005
2006
Sampling Efficiency, 2006Minutes needed to make a correct decision 80% of the time
when the actual pest density is 20% > threshold
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Sampling Methods Summary• Overall
– Sampler variability is great in all sampling methods but dirty squares appears to be least variable
• Direct Sampling methods– Sweep net is most efficient for adults– Drop cloth most efficient for nymphs, esp. black drop
cloth– Sweep net and drop cloth similar for total bug efficiency– Counts by all methods decrease during the hottest part
of the day (3-6 PM), but drop cloth least affected– Sweep nets catch fewer when foliage is wet
• Indirect sampling methods– Dirty blooms most efficient
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Acknowledgements
• Funding: Cotton Incorporated
• Cooperation– Extension agents, consultants and cotton
growers who facilitated data collection in commercial fields