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.

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

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

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)

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)

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Acknowledgements

• Funding: Cotton Incorporated

• Cooperation– Extension agents, consultants and cotton

growers who facilitated data collection in commercial fields