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 FOURTH EDITION

PROTECTIVE
RELAYING
P R I N C I P L E S A N D A P P L I C AT I O N S
 FOURTH EDITION

PROTECTIVE
RELAYING
P R I N C I P L E S A N D A P P L I C ATI O N S
 FOURTH EDITION

PROTECTIVE
RELAYING
P R I N C I P L E S A N D A P P L I C ATI O N S

Boca Raton London New York

CRC Press is an imprint of the

Taylor & Francis Group, an informa business
CRC Press
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Contents
Preface to the Fourth Edition...................................................................................xxi
Preface to the Third Edition................................................................................. xxiii
Preface to the Second Edition.................................................................................xxv
Preface to the First Edition...................................................................................xxvii
Author....................................................................................................................xxix

Chapter 1 Introduction and General Philosophies.................................................1

1.1 Introduction and Definitions.......................................................1
1.2 Typical Protective Relays and Relay Systems............................ 5
1.3 Typical Power Circuit Breakers.................................................. 8
1.4 Nomenclature and Device Numbers......................................... 11
1.5 Typical Relay and Circuit Breaker Connections...................... 16
1.6 Basic Objectives of System Protection..................................... 17
1.6.1 Reliability.................................................................... 19
1.6.2 Selectivity....................................................................20
1.6.3 Speed...........................................................................20
1.6.4 Simplicity.................................................................... 21
1.6.5 Economics................................................................... 21
1.6.6 General Summary....................................................... 22
1.7 Factors Affecting the Protection System.................................. 22
1.7.1 Economics................................................................... 22
1.7.2 Personality Factor........................................................ 22
1.7.3 Location of Disconnecting and Input Devices............ 23
1.7.4 Available Fault Indicators........................................... 23
1.8 Classification of Relays............................................................ 23
1.8.1 Protective Relays......................................................... 23
1.8.2 Regulating Relays........................................................24
1.8.3 Reclosing, Synchronism Check,
and Synchronizing Relays...........................................24
1.8.4 Monitoring Relays.......................................................24
1.8.5 Auxiliary Relays..........................................................24
1.8.6 Other Relay Classifications.........................................24
1.9 Protective Relay Performance..................................................25
1.9.1 Correct Operation........................................................25
1.9.2 Incorrect Operation.....................................................25
1.9.3 No Conclusion.............................................................26
1.9.4 Tracking Relay Performance.......................................26
1.10 Principles of Relay Application................................................26
1.11 Information for Application.....................................................28
1.11.1 System Configuration..................................................28

v
vi Contents

1.11.2 Impedance and Connection of the Power

Equipment, System Frequency, System Voltage,
and System Phase Sequence........................................ 29
1.11.3 Existing Protection and Problems............................... 29
1.11.4 Operating Procedures and Practices........................... 29
1.11.5 Importance of the System Equipment Being
Protected...................................................................... 29
1.11.6 System Fault Study...................................................... 29
1.11.7 Maximum Loads and System Swing Limits............... 30
1.11.8 Current and Voltage Transformer Locations,
Connections, and Ratios.............................................. 30
1.11.9 Future Expansion........................................................ 30
1.12 Structural Changes within the Electric Power Industry........... 30
1.13 Reliability and Protection Standards........................................ 32
1.13.1 Regulatory Agencies................................................... 33
Bibliography........................................................................................34

Chapter 2 Fundamental Units: Per-Unit and Percent Values............................... 37

2.1 Introduction.............................................................................. 37
2.2 Per-Unit and Percent Definitions.............................................. 37
2.3 Advantages of Per Unit and Percent......................................... 38
2.4 General Relations between Circuit Quantities......................... 38
2.5 Base Quantities.........................................................................40
2.6 Per-Unit and Percent Impedance Relations.............................. 41
2.7 Per-Unit and Percent Impedances of Transformer Units.......... 42
2.7.1 Transformer Bank Example........................................44
2.8 Per-Unit and Percent Impedances of Generators...................... 45
2.9 Per-Unit and Percent Impedances of Overhead Lines..............46
2.10 Changing Per-Unit (Percent) Quantities to Different
Bases. . ............................................................................. 46
2.10.1 Example: Base Conversion with Equation 2.34.......... 47
2.10.2 Example: Base Conversion Requiring
Equation 2.33............................................................ 48
Bibliography........................................................................................ 49

Chapter 3 Phasors and Polarity............................................................................ 51

3.1 Introduction.............................................................................. 51
3.2 Phasors...................................................................................... 51
3.2.1 Phasor Representation................................................. 51
3.2.2 Phasor Diagrams for Sinusoidal Quantities................ 53
3.2.3 Combining Phasors..................................................... 53
3.2.4 Phasor Diagrams Require a Circuit Diagram............. 54
Contents vii

3.2.5
Nomenclature for Current and Voltage....................... 54
3.2.5.1 Current and Flux.......................................... 54
3.2.5.2 Voltage......................................................... 55
3.2.6 Phasor Diagram........................................................... 56
3.3 Circuit and Phasor Diagrams for a Balanced Three-Phase
Power System............................................................................ 56
3.4 Phasor and Phase Rotation....................................................... 58
3.5 Polarity..................................................................................... 58
3.5.1 Transformer Polarity................................................... 58
3.5.2 Relay Polarity.............................................................. 61
3.6 Application of Polarity for Phase-Fault Directional
Sensing.............................................................................. 63
3.6.1 90°–60° Connection for Phase-Fault Protection.........64
3.7 Directional Sensing for Ground Faults: Voltage
Polarization...........................................................................66
3.8 Directional Sensing for Ground Faults: Current
Polarization........................................................................ 67
3.9 Other Directional-Sensing Connections................................... 68
3.10 Application Aspects of Directional Relaying........................... 69
3.11 Summary.................................................................................. 70

Chapter 4 Symmetrical Components: A Review................................................. 71

4.1 Introduction and Background................................................... 71
4.2 Positive-Sequence Set............................................................... 72
4.3 Nomenclature Convenience...................................................... 73
4.4 Negative-Sequence Set............................................................. 73
4.5 Zero-Sequence Set.................................................................... 74
4.6 General Equations.................................................................... 74
4.7 Sequence Independence........................................................... 75
4.8 Positive-Sequence Sources....................................................... 76
4.9 Sequence Networks.................................................................. 78
4.9.1 Positive-Sequence Network......................................... 78
4.9.2 Negative-Sequence Network.......................................80
4.9.3 Zero-Sequence Network.............................................. 82
4.9.4 Sequence Network Reduction.....................................84
4.10 Shunt Unbalance Sequence Network Interconnections............ 85
4.10.1 Fault Impedance.......................................................... 85
4.10.2 Substation and Tower-Footing Impedance.................. 86
4.10.3 Sequence Interconnections for Three-Phase Faults....... 86
4.10.4 Sequence Interconnections for Single-Phase-to-
Ground Faults.............................................................. 87
4.10.5 Sequence Interconnections for Phase-to-Phase
Faults........................................................................... 88
viii Contents

4.10.6 Sequence Interconnections for Double-Phase-to-

Ground Faults.............................................................. 89
4.10.7 Other Sequence Interconnections for Shunt
System Conditions.......................................................90
4.11 Example: Fault Calculations on a Typical System Shown
in Figure 4.16............................................................................ 91
4.11.1 Three-Phase Fault at Bus G......................................... 93
4.11.2 Single-Phase-to-Ground Fault at Bus G......................94
4.12 Example: Fault Calculation for Autotransformers................... 95
4.12.1 Single-Phase-to-Ground Fault at H Calculation.........97
4.13 Example: Open-Phase Conductor.............................................99
4.14 Example: Open-Phase Falling to Ground on One Side............99
4.15 Series and Simultaneous Unbalances..................................... 102
4.16 Overview................................................................................ 103
4.16.1 Voltage and Current Phasors for Shunt Faults.......... 103
4.16.2 System Voltage Profiles during Faults...................... 104
4.16.3 Unbalanced Currents in the Unfaulted Phases
for Phase-to-Ground Faults in Loop Systems........... 107
4.16.4 Voltage and Current Fault Phasors for
All Combinations of the Different Faults.................. 108
4.17 Summary................................................................................ 111
Bibliography...................................................................................... 112
Appendix 4.1 Short-Circuit MVA and Equivalent Impedance.......... 113
Appendix 4.2 Impedance and Sequence Connections for
Transformer Banks............................................................................ 115
Appendix 4.3 Sequence Phase Shifts through Wye–Delta
Transformer Banks............................................................................ 122
Appendix 4.4 Impedance of Overhead Lines.................................... 125
Appendix 4.5 Zero-Sequence Impedance of Transformers............... 141

Chapter 5 Relay Input Sources........................................................................... 145

5.1 Introduction............................................................................ 145
5.2 Equivalent Circuits of Current and Voltage Transformers..... 145
5.3 CTs for Protection Applications............................................. 150
5.4 CT Performance on a Symmetrical AC Component.............. 150
5.4.1 Performance by Classic Analysis.............................. 151
5.4.2 Performance by CT Characteristic Curves............... 151
5.4.3 Performance by ANSI/IEEE Standard Accuracy
Classes....................................................................... 151
5.4.4 IEC Standard Accuracy Classes............................... 155
5.5 Secondary Burdens during Faults.......................................... 155
5.6 CT Selection and Performance Evaluation for Phase Faults.....157
5.6.1 CT Ratio Selection for Phase-Connected Equipment.....157
5.6.2 Select the Relay Tap for the Phase–Overcurrent
Relays........................................................................ 157
Contents ix

5.6.3 Determine the Total Connected Secondary Load

(Burden) in Ohms...................................................... 158
5.6.4 Determine the CT Performance Using the
ANSI/IEEE Standard................................................ 158
5.6.4.1 When Using a Class T CT......................... 158
5.6.4.2 When Using a Class C CT and
Performance by the ANSI/IEEE Standard.....159
5.6.4.3 When Using a Class C CT and
Performance with the CT Excitation
Curves........................................................ 160
5.7 Performance Evaluation for Ground Relays........................... 161
5.8 Effect of Unenergized CTs on Performance.......................... 161
5.9 Flux Summation Current Transformer................................... 163
5.10 Current Transformer Performance on the DC Component......... 164
5.11 Summary: Current Transformer Performance Evaluation...........165
5.11.1 Saturation on Symmetrical AC Current Input
Resulting from the CT Characteristics and the
Secondary Load........................................................ 165
5.11.2 Saturation by the DC Offset of the Primary
AC Current................................................................ 166
5.12 Current Transformer Residual Flux and Subsidence
Transients................................................................................ 167
5.13 Auxiliary Current Transformers in CT Secondary Circuits........168
5.14 Voltage Transformers for Protective Applications................. 169
5.15 Optical Sensors....................................................................... 170
Bibliography...................................................................................... 172

Chapter 6 Protection Fundamentals and Basic Design Principles..................... 173

6.1 Introduction............................................................................ 173
6.2 Differential Principle.............................................................. 173
6.3 Overcurrent–Distance Protection and the Basic
Protection Problem................................................................. 176
6.3.1 Time Solution............................................................ 177
6.3.2 Communication Solution........................................... 178
6.4 Backup Protection: Remote versus Local.............................. 178
6.5 Basic Design Principles.......................................................... 179
6.5.1 Time–Overcurrent Relays......................................... 179
6.5.2 Instantaneous Current–Voltage Relays...................... 182
6.5.3 Directional-Sensing Power Relays............................ 184
6.5.4 Polar Unit.................................................................. 184
6.5.5 Phase Distance Relays............................................... 185
6.5.5.1 Balanced Beam Type: Impedance
Characteristic............................................. 185
6.5.6 R–X Diagram............................................................. 186
6.5.7 Mho Characteristic.................................................... 186
x Contents

6.5.8 Single-Phase Mho Units............................................ 189

6.5.9 Polyphase Mho Units................................................ 190
6.5.9.1 Three-Phase Fault Units............................ 190
6.5.9.2 Phase-to-Phase Fault Units........................ 192
6.5.10 Other Mho Units....................................................... 192
6.5.11 Reactance Units......................................................... 194
6.6 Ground Distance Relays......................................................... 194
6.7 Solid-State Microprocessor Relays........................................ 196
6.8 Summary................................................................................ 198
Bibliography...................................................................................... 198

Chapter 7 System-Grounding Principles........................................................... 199

7.1 Introduction............................................................................ 199
7.2 Ungrounded Systems.............................................................. 199
7.3 Transient Overvoltages........................................................... 203
7.4 Grounded-Detection Methods for Ungrounded Systems.......204
7.4.1 Three-Voltage Transformers......................................204
7.4.2 Single-Voltage Transformers.....................................206
7.5 High-Impedance Grounding Systems....................................208
7.5.1 Resonant Grounding..................................................208
7.5.2 High-Resistance Grounding......................................209
7.5.3 Example: Typical High-Resistance Neutral
Grounding................................................................. 210
7.5.4 Example: Typical High-Resistance Grounding
with Three Distribution Transformers...................... 215
7.6 System Grounding for Mine or Other Hazardous-Type
Applications............................................................................ 218
7.7 Low-Impedance Grounding................................................... 218
7.7.1 Example: Typical Low-Resistance Neutral
Reactor Grounding.................................................... 221
7.7.2 Example: Typical Low-Resistance Neutral
Resistance Grounding............................................... 222
7.8 Solid (Effective) Grounding................................................... 223
7.8.1 Example: Solid Grounding........................................ 223
7.8.2 Ground Detection on Solid-Grounded Systems........ 225
7.9 Ferroresonance in Three-Phase Power Systems..................... 225
7.9.1 General Summary for Ferroresonance for
Distribution Systems................................................. 229
7.9.2 Ferroresonance at High Voltages.............................. 229
7.10 Safety Grounding................................................................... 230
7.11 Grounding Summary and Recommendations........................ 231
Bibliography...................................................................................... 233
Contents xi

Chapter 8 Generator Protection/Intertie Protection for Distributed

Generation......................................................................................... 235
8.1 Introduction............................................................................ 235
8.1.1 Historical Perspectives.............................................. 235
8.1.2 Bulk Power Generators............................................. 237
8.1.3 Distributed Generators.............................................. 238
8.1.4 Potential Problems..................................................... 239
8.2 Generator Connections and Overview of Typical
Protection........................................................................ 240
8.3 Stator Phase-Fault Protection for All Size Generators........... 242
8.3.1 Differential Protection (87) for Small kVA
(MVA) Generators..................................................... 242
8.3.2 Multi-CT Differential Protection (87) for All
Size Generators......................................................... 243
8.3.3 High-Impedance Voltage Differential Protection
for Generators............................................................246
8.3.4 Direct-Connected Generator Current Differential
Example.....................................................................246
8.3.5 Phase Protection for Small Generators That Do
Not Use Differentials................................................ 247
8.3.6 Unit Generator Current Differential (87)
Example for Phase Protection...................................248
8.4 Unit Transformer Phase-Fault Differential
Protection (87TG)................................................................... 250
8.5 Phase-Fault Backup Protection (51 V) or (21)........................ 251
8.5.1 Voltage-Controlled or Voltage-Restraint
Time–Overcurrent (51 V) Backup Protection........... 251
8.5.2 Phase Distance (21) Backup Protection..................... 252
8.6 Negative-Sequence Current Backup Protection..................... 252
8.7 Stator Ground-Fault Protection.............................................. 253
8.7.1 Ground-Fault Protection for Single Medium or
Small Wye-Connected Generators (Type 1a: See
Figures 8.3 and 8.11)................................................. 253
8.7.2 Ground-Fault Protection of Multiple Medium
or Small Wye- or Delta-Connected Generators
(Type 2: See Figures 8.2 and 8.12)............................ 254
8.7.3 Ground-Fault Protection for Ungrounded
Generators................................................................. 255
8.7.4 Ground-Fault Protection for Very Small, Solidly
Grounded Generators................................................ 256
8.7.5 Ground-Fault Protection for Unit-Connected
Generators Using High-Impedance Neutral
Grounding (Type 1b: See Figure 8.5)........................ 256
xii Contents

8.7.6 Added Protection for 100% Generator Ground

Protection with High-Resistance Grounding............ 257
8.7.7 High-Voltage Ground-Fault Coupling Can Produce
V0 in High-Impedance Grounding Systems................... 259
8.7.8 Ground-Fault Protection for Multidirect-Connected
Generators Using High-Resistance Grounding..............261
8.8 Multiple Generator Units Connected Directly
to a Transformer: Grounding and Protection......................... 261
8.9 Field Ground Protection (64).................................................. 262
8.10 Generator Off-Line Protection............................................... 262
8.11 Reduced or Lost Excitation Protection (40)........................... 262
8.11.1 Loss of Excitation Protection with Distance (21)
Relays........................................................................ 262
8.11.2 Loss of Excitation Protection with a Var-Type
Relay..........................................................................266
8.12 Generator Protection for System Disturbances
and Operational Hazards........................................................266
8.12.1 Loss of Prime Mover: Generator Motoring (32)....... 267
8.12.2 Overexcitation: Volts per Hertz Protection (24)........ 267
8.12.3 Inadvertent Energization: Nonsynchronized
Connection (67)......................................................... 268
8.12.4 Breaker Pole Flashover (61)....................................... 268
8.12.5 Thermal Overload (49).............................................. 269
8.12.6 Off-Frequency Operation.......................................... 269
8.12.7 Overvoltage............................................................... 270
8.12.8 Loss of Synchronism: Out-of-Step............................ 270
8.12.9 Subsynchronous Oscillations.................................... 271
8.13 Loss of Voltage Transformer Signal....................................... 272
8.14 Generator Breaker Failure...................................................... 273
8.15 Excitation System Protection and Limiters............................ 273
8.15.1 Field Grounds............................................................ 274
8.15.2 Field Overexcitation.................................................. 274
8.15.3 Field Underexcitation................................................ 275
8.15.4 Practical Considerations............................................ 275
8.16 Synchronous Condenser Protection........................................ 276
8.17 Generator-Tripping Systems................................................... 276
8.18 Station Auxiliary Service System.......................................... 276
8.19 Distributed Generator Intertie Protection............................... 277
8.19.1 Power Quality Protection.......................................... 278
8.19.2 Power System Fault Protection.................................. 283
8.19.3 System Protection for Faults on Distributed
Generator Facilities...................................................284
8.19.4 Other Intertie Protection Considerations.................. 285
8.19.5 Induction Generators/Static Inverters/Wind Farms...... 285
8.19.5.1 Induction Generators................................. 285
8.19.5.2 Inverters..................................................... 286
Contents xiii

8.19.5.3 Wind Farms............................................... 288

8.19.6 Practical Considerations of Distributed Generation...... 289
8.20 Protection Summary............................................................... 291
Bibliography...................................................................................... 292

Chapter 9 Transformer, Reactor, and Shunt Capacitor Protection..................... 295

9.1 Transformers........................................................................... 295
9.2 Factors Affecting Differential Protection............................... 297
9.3 False Differential Current...................................................... 298
9.3.1 Magnetization Inrush................................................ 298
9.3.2 Overexcitation...........................................................300
9.3.3 Current Transformer Saturation................................ 301
9.4 Transformer Differential Relay Characteristics..................... 301
9.5 Application and Connection of Transformer
Differential Relays.................................................................. 303
9.6 Example: Differential Protection Connections for a
Two-Winding Wye–Delta Transformer Bank........................304
9.6.1 First Step: Phasing.....................................................304
9.6.2 Second Step: CT Ratio and Tap Selections...............306
9.7 Load Tap-Changing Transformers.........................................307
9.8 Example: Differential Protection Connections
for Multiwinding Transformer Bank......................................308
9.9 Application of Auxiliaries for Current Balancing.................. 311
9.10 Paralleling CTs in Differential Circuits................................. 311
9.11 Special Connections for Transformer Differential Relays..... 313
9.12 Differential Protection for Three-Phase Banks
of Single-Phase Transformer Units........................................ 315
9.13 Ground (Zero-Sequence) Differential Protection
for Transformers..................................................................... 316
9.14 Equipment for Transfer Trip Systems..................................... 317
9.14.1 Fault Switch............................................................... 317
9.14.2 Communication Channel........................................... 318
9.14.3 Limited Fault-Interruption Device............................ 318
9.15 Mechanical Fault Detection for Transformers....................... 318
9.15.1 Gas Detection............................................................ 318
9.15.2 Sudden Pressure........................................................ 319
9.16 Grounding Transformer Protection........................................ 319
9.17 Ground Differential Protection with Directional Relays....... 321
9.18 Protection of Regulating Transformers.................................. 324
9.19 Transformer Overcurrent Protection...................................... 324
9.20 Transformer Overload-through-Fault-Withstand Standards.......328
9.21 Examples: Transformer Overcurrent Protection.................... 330
9.21.1 Industrial Plant or Similar Facility Served by a
2500 kVA, 12 kV: 480 V Transformer with 5.75%
Impedance................................................................. 331
xiv Contents

9.21.2 Distribution or Similar Facility Served by a

7500 kVA, 115: 12 kV Transformer with 7.8%
Impedance................................................................. 335
9.21.3 Substation Served by a 12/16/20 MVA,
115: 12.5 kV Transformer with 10% Impedance....... 337
9.22 Transformer Thermal Protection............................................ 339
9.23 Overvoltage on Transformers................................................. 339
9.24 Summary: Typical Protection for Transformers.....................340
9.24.1 Individual Transformer Units....................................340
9.24.2 Parallel Transformer Units........................................ 341
9.24.3 Redundancy Requirements for Bulk Power
Transformers.............................................................344
9.25 Reactors.................................................................................. 345
9.25.1 Types of Reactors...................................................... 345
9.25.2 General Application of Shunt Reactors.....................346
9.25.3 Reactor Protection.....................................................346
9.26 Capacitors............................................................................... 347
9.27 Power System Reactive Requirements................................... 347
9.28 Shunt Capacitor Applications.................................................348
9.29 Capacitor Bank Designs......................................................... 349
9.30 Distribution Capacitors Bank Protection............................... 350
9.31 Designs and Limitations of Large Capacitor Banks.............. 351
9.32 Protection of Large Capacitor Banks..................................... 354
9.33 Series Capacitor Bank Protection........................................... 359
9.34 Capacitor Bank Protection Application Issues.......................360
Bibliography...................................................................................... 361
Appendix 9.1 Application of Digital Transformer
Differential Relays............................................................................ 362

Chapter 10 Bus Protection................................................................................... 371

10.1 Introduction: Typical Bus Arrangements............................... 371
10.2 Single Breaker–Single Bus..................................................... 373
10.3 Single Buses Connected with Bus Ties.................................. 373
10.4 Main and Transfer Buses with Single Breakers..................... 374
10.5 Single Breaker–Double Bus................................................... 377
10.6 Double Breaker–Double Bus.................................................. 378
10.7 Ring Bus................................................................................. 378
10.8 Breaker-and-Half Bus............................................................. 378
10.9 Transformer–Bus Combination.............................................. 379
10.10 General Summary of Buses.................................................... 379
10.11 Differential Protection for Buses............................................ 379
10.11.1 Multirestraint Current Differential........................... 381
10.11.2 High-Impedance Voltage Differential....................... 383
10.11.3 Air-Core Transformer Differential............................ 384
10.11.4 Moderate High-Impedance Differential................... 385
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 MP-313
NOVEMBER 1958

PECAN DISEASES AND

INSECTS
AND THEIR CONTROL
TEXAS AGRICULTURAL EXPERIMENT STATION ...
TEXAS AGRICULTURAL EXTENSION SERVICE
College Station, Texas

2
 Key to Pecan Diseases

DISEASES OF THE LEAVES

Olive spots on underside page Scab
5
Downy, buff, or greenish-yellow lesions page Downy Spot
7
Small, reddish-brown to gray spots on page Brown Leaf
underside 6 Spot
Dark brown to black lesions on veins and page Vein Spot
stems 6
Tiny white tufts of fungal growth on page Articularia
underside 9 Leaf Mold
Small olive green velvety spots. By page Leaf Blotch
midsummer, black pimple-like dots appear 7
in the spots
Leaflets yellowish, mottled, narrowed and page Rosette
crinkled with reddish-brown spots, may 8
be perforated
Broomy type of twig growth, bunching of page Bunch
leaves 8 Disease
DISEASES OF THE NUTS
Small black sunken or raised spots which page Scab
may fuse to cover entire surface of shuck 5
Pink spore masses on shuck surface page Pink Mold
9
DISEASES OF THE ROOTS
Galls of various sizes on larger roots page Crown Gall
7
 Splitting and deterioration of bark of page Cotton Root
infected roots, strands of buff-colored 10 Rot
fungal growth may be present
NONPARASITIC PLANTS ON THE LIMBS AND BARK
Whitish-gray mosslike masses on the bark page Lichens
9
Accumulations of grayish strands hanging page Spanish Moss,
from limbs and twigs or ball-like growth 9 Ball Moss
on limbs and branches
 Key to Pecan Insects

INSECTS ATTACKING THE NUTS

Olive-green caterpillars up to ½ inch page Pecan Nut
long feeding in the nuts, or later in the 10 Casebearer
season, in the shucks
White caterpillars up to ⅜ inch long page Hickory
tunneling in the shucks 11 Shuckworm
White legless grubs feeding in the nuts page Pecan Weevil
in late summer 12
Green or brown bugs sucking the sap page Stink Bugs and
from the nuts 12 Plant Bugs
INSECTS ATTACKING THE FOLIAGE
Soft-bodied yellow insects producing page Aphids
honeydew or small black insects causing 13
yellow blotches on the foliage
Tiny green arthropods in webs near the page Mites
midrib, leaves appear scorched 13
Caterpillars feeding in gray cases about page Pecan Leaf
½ inch long in the spring; small winding 14 Casebearer
blotches produced in the leaves in the
summer
Olive-green caterpillars tunneling in the page Pecan Nut
shoots in the early spring 10 Casebearer
Tiny caterpillars in light brown cigar- page Pecan Cigar
shaped cases about ¼ inch long 15 Casebearer
Galls on the leaves, twigs and nuts page Pecan
14 Phylloxera
Leaves eaten in the early spring by a page Sawfly
light green caterpillar which leaves the 14
 midribs and veins intact
Beetles feeding on the foliage at night page May Beetles
15
Caterpillars in large white webs page Fall Webworm
encasing entire branches 15
Caterpillars with long soft hairs feeding page Walnut
in colonies on the foliage without 16 Caterpillar
producing webs
Dark gray, active caterpillars up to 3 page Pecan Catocala
inches long feeding on the foliage in 16
early spring
Masses of frothy white foam enclosing page Pecan
tiny, light green insects in the spring 16 Spittlebug
Tiny greenish caterpillars feeding in the page Pecan Bud Moth
terminals and axils of the buds on 16
young pecan trees
INSECTS ATTACKING THE LIMBS, TRUNK AND
TWIGS
Beetle girdling twigs and limbs in late page Pecan Twig
summer and fall 17 Girdler
Holes about ⅛ inch in diameter in dying page Red-shouldered
limbs 17 Shot-hole Borer
White borers with an enlargement page Flatheaded
behind the head tunneling underneath 17 Borers
the bark of trunk and limbs
Limbs encrusted with scales, which page Obscure Scale
closely resemble the color of the bark 18
 CONTENTS
Key to Pecan Diseases 2
Key to Pecan Insects 2
Spray Schedule for the Control of Pecan Diseases and Insects 4
Introduction 5
Pecan Diseases and Their Control 5
Scab 5
Brown Leaf Spot 6
Vein Spot 6
Leaf Blotch 7
Crown Gall 7
Downy Spot 7
Bunch Disease 8
Rosette 8
Lichens 9
Articularia Leaf Mold 9
Pink Mold 9
Spanish and Ball Moss 9
Cotton Root Rot 10
Pecan Insects and Their Control 10
Pecan Nut Casebearer 10
Hickory Shuckworm 11
Pecan Weevil 12
Stink and Plant Bugs 12
Aphids 13
Mites 13
Pecan Leaf Casebearer 14
Pecan Phylloxera 14
Sawflies 14
May Beetles 15
Pecan Cigar Casebearer 15
 Fall Webworm 15
Walnut Caterpillar 16
Pecan Catocala 16
Pecan Spittlebug 16
Pecan Bud Moth 16
Twig Girdler 17
Red-shouldered Shot-hole Borer 17
Flatheaded Borers 17
Obscure Scale 18
Application of Fungicides and Insecticides 18
Spray Equipment 18
Literature Cited 19

4
 SPRAY SCHEDULE FOR THE CONTROL OF
PECAN DISEASES AND INSECTS

Insect or
Name of spray disease to Spray
and time of be materials, per
application controlled 100 gallon Remarks
Prepollination Scab, downy [A] If phylloxera is a
Zineb, 2 pounds
spray, when spot, vein problem, see page
first leaves are spot 14.
one-third grown
First cover Scab, downy Zineb, 2 pounds
spray, when tips spot, vein
of small nuts spot, leaf
have turned blotch,
brown and nut brown leaf
casebearer eggs spot
are observed
Pecan nut 3 pounds 50
casebearer, percent wettable
pecan leaf DDT, or 1 pound
casebearer 25 percent
wettable
parathion, or 1
pint nicotine
sulfate plus 2
quarts summer
oil, or 5 pounds
40 percent
wettable
toxaphene, or 3
 pounds 25
percent wettable
malathion
Rosette Zinc sulfate, 2 If rosette is a
pounds problem, include
zinc sulfate in
spray.
Second cover Scab, downy Zineb, 2 pounds
spray, 3 to 4 spot, vein Zinc sulfate, 2
weeks after first spot, leaf pounds
cover spray blotch,
brown leaf
spot
Rosette
Third cover Scab, brown Zineb, 2 pounds If aphid or mite
spray, 3 to 4 leaf spot, infestations are
weeks after liver spot, severe, use
second cover aphids, insecticides
spray mites recommended on
page 13.
Walnut If walnut
caterpillar, caterpillars or fall
fall webworms are a
webworm problem, use
insecticides
recommended on
pages 15 and 16.
Rosette Zinc sulfate, 2
pounds
Fourth cover Pecan weevil 6 pounds 50 For control of
spray percent wettable weevils, apply
DDT spray when as
many as three
weevils can be
 jarred from a tree.
If scab is present
add 2 pounds
zineb to DDT
spray.

[A]
Zineb. Zinc ethylene bis dithiocarbamate. Manufactured by Rohm
& Haas Co., trade name Dithane Z-78: E. I. DuPont Co., trade
name Parzate.
5
 Pecan Diseases and Insects and
Their Control
David W. Rosberg and D. R. King

Respectively, associate professor, Department of Plant Physiology

and Pathology, and associate professor, Department of
Entomology.

The pecan tree must be protected from attack by the many

destructive diseases and insects that affect it to produce a bountiful
nut crop.

The diseases that affect the pecan, especially those caused by fungi,
are rapidly spread throughout the trees in an orchard in the early
spring. During this season of frequent rains, the spores of the
disease fungi germinate and invade the young tender tissues of the
shoots, leaves and nuts. Under conditions of prolonged damp
weather, when the humidity remains high, the disease organisms
reproduce at a rapid rate and cause severe shedding of leaves and
nuts.

Pecans are attacked by more than 20 species of insects that cause

damage to leaves, nuts, twigs, buds, branches and even the bark.
The development of commercial pecan acreages has provided ideal
conditions for the increase in severity of both disease and insect
damage because of the abundant food supply in a concentrated
planting of pecans. In its natural habitat the pecan is less subject to
the devastations of diseases and insects.

The many destructive insects and diseases must be controlled for

successful pecan production. The pecan grower must also
understand the nature and habits of the various disease and insect
pests that threaten his crop and use certain cultural practices which
help to reduce damage from diseases and insects.
 Pecan Diseases and Their Control
The diseases which affect the pecan are of four different types:
namely fungus, bacterial, virus and physiological. The fungus
diseases, the most numerous and widespread, are caused by small
microscopic molds. Approximately 12 different fungus organisms
cause harmful diseases of the pecan.

The bacterial disease organisms, unlike the disease producing fungi,

are single celled and can be seen only under a microscope. Bacterial
diseases are fewer and of less economic importance than fungus
diseases.

Virus diseases are caused by extremely small agents which can be

seen only under special ultra-microscopes such as the electron
microscope. Plant viruses are protein substances, but their exact
nature is unknown.

Physiological disorders (sometimes called physiological diseases) are

caused by a variety of environmental conditions. A physiological
disorder in a pecan tree may result from infertile soil, excessive
moisture, or the absence or degree of available nutritional mineral
elements to the growing tree. These various environmental factors
have special adverse effects, manifested by specific symptoms
caused by insufficient levels of a given nutritional mineral element or
elements, which are easily corrected by supplying the tree the
necessary mineral elements either through soil application or foliage
sprays.

SCAB
Pecan scab, caused by the fungus Cladosporium effusum (Wint.)
Demaree, is the most destructive disease of pecans in Texas. The
fungus invades the young rapidly growing shoots and leaves and
later the developing nuts. Severely infected nuts on highly scab-
susceptible varieties fall or fail to develop, resulting in a total nut
crop loss. Early season defoliation often occurs in seasons of
frequent rains and high humidity which facilitate the rapid
development and spread of the scab fungus.

The scab fungus overwinters in infected shoots and in old shucks

and leaves in the trees. In the spring when temperature and
moisture conditions become favorable, the fungus begins to grow in
the shoot lesions, old leaves and shucks, and within a few days
produces great numbers of spores. These spores are spread by wind
and rain to newly developed leaves where they germinate and
invade the tender tissues, initiating primary infection. The fungus
produces a great abundance of spores on the surface of these
primary infection sites and spreads throughout the tree and infects
young shoots, leaves and nuts.

On the leaves, primary infection lesions occur on the lower leaf

surfaces and are characteristically olive brown, somewhat elongated
in shape and vary in size from a barely discernible dot to lesions
one-fourth inch or more in diameter. Frequently, adjacent lesions
coalesce, forming large very dark lesions. Primary scab lesions
commonly occur on or along the leaflet veins but often may be
found between the veins on the underleaf surface. On the nuts, scab
lesions appear as small black dots, which are elevated or sunken in
older infections. Adjacent lesions on the nuts may coalesce 6
forming large sunken black lesions, Figure 1. When infection is
severe, the entire nut surface is black in appearance, development is
arrested and the nuts drop prematurely.
Figure 1. Scab lesions on leaves and nuts of Delmas variety. Note concave lesions
and overall scabby appearance of severely infected nuts.
Pecan varieties vary in their susceptibility to scab disease. Among
the highly susceptible varieties are: Burkett, Delmas, Schley, Moore,
Halbert and most western varieties. Moneymaker, Success and Curtis
are moderately resistant. Mahan, Stuart and Desirable varieties are
highly resistant to the scab fungus. However, this character of
resistance varies, depending on the area of the state, local
environmental conditions and the particular strain of the scab fungus
present.

Scab disease development is favored by rainy periods and cloudy

days when the humidity remains high and leaf surfaces are wet.
Under these conditions, spores of the fungus in contact with the wet
leaf surface of a pecan leaflet or nut germinate rapidly, invade the
tender tissues and initiate infection within 6 hours. Lesions resulting
from these infection sites, become visible to the naked eye within 7
to 14 days, depending on environmental conditions. A period of
warm dry weather after infection occurs may retard lesion
development.

Control.—The control of pecan scab disease depends primarily on

the protection of tender leaf, nut and shoot surfaces with proper
application of an effective fungicide. A protective film of fungicide
chemical prevents scab fungus infections by killing the spores
immediately after their germination, thereby preventing invasion of
susceptible tissues. Unfortunately, once the fungus has invaded the
tissues it becomes protected from chemical attack and produces
spores in great abundance. Therefore, thorough coverage of leaf,
nut and shoot surfaces with a fungicide chemical must be
[6] [10] [11]
maintained to prevent secondary infections, ( , , ).

Sanitation measures, such as removal of old attached shucks and

leaf stems in trees and plowing or disk harrowing under fallen leaves
and shucks help reduce primary infections. See spray schedule, page
4, for scab disease control.

BROWN LEAF SPOT

The brown leaf spot disease fungus Cercospora fusca (Heald and
Walf) Rand affects only mature leaves and usually does not appear
until the latter part of May or mid-June. Primary lesions develop on
the lower leaf surfaces as small dots, which gradually enlarge and
become reddish brown with a grayish cast. The shape of the lesions
may be circular or irregular, especially where two or more lesions
develop adjacent to one another, Figure 2. In seasons favorable for
brown leaf spot development pecan trees may be completely
defoliated within 3 to 4 months if the disease is not controlled. Most
pecan varieties which are maintained in a vigorous state of growth
are resistant to brown spot disease.

Control.—See spray schedule, page 4.

VEIN SPOT
Vein spot disease is caused by the fungus Gnomonia nerviseda. The
symptoms of the disease are similar to the leaf lesion symptoms of
scab disease, but vein spot disease, unlike scab disease, affects 7
only the leaves. Lesions of vein spot disease develop on the
veins or stems of leaflets and leaves, are usually less than one-
fourth inch in diameter and are characteristically dark brown to
black. Leaflets and leaf stems which are severely affected drop,
resulting in premature defoliation.

The fungus lives in fallen leaves over the winter. The following spring
when temperature and moisture conditions are favorable, spores
formed in special structures called perithecia are forcibly discharged
into the air and carried by wind currents to the newly formed spring
foliage, initiating primary infections.

Control.—See spray schedule, page 4.

LEAF BLOTCH
Leaf blotch disease is caused by the fungus Mycosphaerella
dendroides (Cke.) Demaree and Cole. The disease occurs mainly in
trees of poor vigor, which may be due to neglect, infertile soil,
rosette or overcrowding. Nursery trees are particularly susceptible to
the disease.
The fungus overwinters in fallen leaves. In the early spring, large
numbers of spores produced in the old leaves on the ground are
carried by wind currents to the young leaves in the tree, where they
germinate and rapidly invade the tender leaf tissue.

The disease symptoms first appear on the undersurface of mature

leaves in early summer, as small olive-green velvety spots. By
midsummer black pimplelike dots become especially noticeable in
the leaf spots after the surface spore masses have been removed by
wind and rain, giving the diseased areas of the leaves a black, shiny
appearance. When the disease is severe, infected leaflets are killed,
which causes defoliation of the trees in late summer or early fall and
results in reduced tree vigor and increased susceptibility to disease
and insect attack.

Control.—Leaf blotch disease can be controlled effectively in the

early spring by disking under old fallen leaves that harbor the fungus
pathogen.

In areas where a spray program for the control of scab disease is

carried out, leaf blotch usually is not a damaging disease. In
localities where leaf blotch disease occurs in the absence of other
pecan diseases, two applications of fungicide will control the disease
effectively. The first spray should be applied after pollination when
the tips of the nutlets have turned brown and the second spray
application should be made 3 to 4 weeks later. See spray schedule,
page 4.

CROWN GALL
Crown gall disease, caused by the bacterium Agrobacterium
tumefaciens (E. F. and Town.) Conn., often is damaging to pecan
trees. Nursery trees as well as trees in bearing pecan orchards are
susceptible to the disease.
Figure 2. Brown leaf spot diseased pecan leaflet showing typical symptoms.
Lesions are circular to irregular in shape.

The development of galls is confined primarily to larger roots near

the base of the tree trunk, although small roots may become
infected and galls develop on them. The smaller galls are under the
soil surface and cannot be detected unless the soil is carefully
removed from around the roots, Figure 3. Large galls, often 10 to 18
inches in diameter, develop on larger roots and may protrude well
above the surface of the soil.
Figure 3. Crown gall disease symptoms on young infected pecan tree.

Galls on nursery trees develop at or below the soil surface on the

taproot and larger secondary roots.

Control.—All infected nursery trees should be dug and immediately

burned. Crown gall-diseased orchard trees sometimes can be saved
by digging the soil from around large roots and removing the
exposed galls. Where galls were removed, the damaged root
surfaces should be painted with a creosote-coal tar mixture (one
part creosote to three parts coal tar) to prevent spread of the
[9]
disease . Cultivation of the soil around the trunk base of infected
trees should be avoided to prevent root wounds and spreading of
the crown gall pathogen.
DOWNY SPOT
Downy spot disease, caused by the fungus Mycosphaerella caryigena
(Ell. and Ev.) Damaree and Cole, attacks all pecan varieties. Only
leaves are susceptible to the disease. Primary infection of new 8
leaves in the spring occurs from spores produced in specialized
fruiting bodies in old overwintered leaves. The downy spots appear
usually during the summer months on the lower surfaces of leaflets.
The downy character of the lesions is due to the production by the
fungus of thousands of minute spores on the surface of each spot.
The spores are spread by wind and rain to adjacent leaves and to
neighboring trees. After spore dissemination is complete, the lesions
visible from both leaf surfaces are one-eighth to one-fourth inch in
diameter and greenish yellow. Later in the season the lesions turn
brown due to the death of the leaf cells in the diseased area.

Moneymaker and Stuart varieties are most susceptible to downy spot

disease although all pecan varieties are moderately to slightly
susceptible.

Control.—Disk under old fallen leaves in the early spring before the
leafbuds begin to swell. This practice covers the leaves with soil and
prevents the discharge of spores into the air, thereby controlling
primary infection of new leaves. In seasons when heavy rains make
early spring disking impossible, downy spot disease can be
controlled by spraying the trees as indicated in the spray schedule
on page 4.

BUNCH DISEASE
Although the cause of bunch disease is not known, evidence
indicates it is an infectious disease, which suggests that the causal
agent may be a virus.
Trees affected with bunch disease show the bunching symptom,
which is due to excessive growth of slender succulent twigs from
lateral buds that normally remain dormant. In moderately affected
trees one or several branches will show the “bunch” growth
symptom. Bunching in severely affected trees may involve all main
branches which produce thick masses of sucker-like growth and few,
if any, nuts.

Observations indicate that the Stuart variety is the most resistant to

bunch disease.

Figure 4. Rosette die-back symptoms of pecan tree showing severe zinc deficiency.

Control.—There is no known effective control for bunch disease.

Early detection of the first symptom of bunch and pruning out of the
affected branch may prevent spread of the disease throughout the
tree. When the tree is severely affected, and limbs are involved, the
tree should be destroyed to protect nearby healthy trees from
infection.
For propagation purposes, all bud or scion wood should be taken
only from bunch disease-free trees.

ROSETTE
Rosette is a nutritional deficiency disease caused by certain soil
conditions which make zinc unavailable to the pecan tree. All pecan
trees require zinc for growth.

Trees showing the first symptom of zinc deficiency have yellowed

tops. The individual leaflets when examined are yellowish and
mottled. The next season the foliage may be yellowish and the
leaflets narrowed and crinkled. More severely affected trees produce
foliage which is a yellowish to reddish-brown overall color, and the
leaflets are very narrow with reddish-brown spots and may be
perforated. Shoots are much shortened and the leaves are produced
in compact bunches of dense foliage.

Trees affected by rosette for several seasons have many dead shoots
and small branches from the dying-back of each season’s growth,
Figure 4. Such trees are greatly stunted, of poor vigor and produce
few, if any, nuts.

Control.—Rosette is controlled readily by applying zinc sulfate to the

tree either as a foliage spray or in the dry form as a soil application.
Where a disease and insect spray control program is being carried
out, zinc sulfate may be added to the spray mixture.

Foliage spray. Two pounds zinc sulfate (36 percent) per 100
gallons of water.

First application: after pollination when tips of nutlets turn brown.

Second application: 3 to 4 weeks later.

Third application: 3 to 4 weeks later.

Soil application. Application of zinc sulfate to the soil, particularly

in a large orchard is a more expensive operation, but it provides
longer protection against rosette.

In highly alkaline soils, or soils that readily fix zinc and make it
unavailable to the tree, foliage spray applications of zinc sulfate are
more economical because of the excessive rates required to supply
available zinc through the soil.

Rate of application of zinc sulfate: Mildly rosetted trees—apply 5

pounds zinc sulfate (36 percent) annually for 2 to 3 years. Severely
rosetted trees—apply 5 to 10 pounds zinc sulfate (36 percent)
annually until rosette symptoms disappear.

Time and method of application: Apply zinc sulfate to the soil 9

around trees in late February or early March. Broadcast zinc
sulfate under the tree from the trunk to several feet beyond the limb
canopy. Disking, harrowing, or any operation that mixes the zinc
sulfate with the soil, is desirable to prevent washing away and
surface soil fixing of zinc.

LICHENS
Lichens commonly are found growing on the branches and trunks of
pecan trees, especially in humid areas and river bottom orchards
having poor air drainage.

Lichens are nonparasitic to the pecan tree, but merely attach

themselves to the bark surfaces. Lichens grow equally well on rocks,
fence posts, bricks and other objects. There are several types of
lichens that occur on pecan trees, none of which are damaging
except perhaps in appearance to the trees in cases of extremely
heavy infestations, Figure 5.
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