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1985 The mpI act of Individual Species and Complexes of Pest Arthropod Species on Soybean Grown on Various Row Spacings (Insect Pest Complexes, Non-Conventional Row Spacing). Jaime Yanes Jr Louisiana State University and Agricultural & Mechanical College
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Recommended Citation Yanes, Jaime Jr, "The mpI act of Individual Species and Complexes of Pest Arthropod Species on Soybean Grown on Various Row Spacings (Insect Pest Complexes, Non-Conventional Row Spacing)." (1985). LSU Historical Dissertations and Theses. 4081. https://digitalcommons.lsu.edu/gradschool_disstheses/4081
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University Micixjfilms Inter national 300 N, Zeeb Road Ann Arbor, Ml 48106 8517764
Yanes, Jaime, Jr.
THE IMPACT OF INDIVIDUAL SPECIES AND COMPLEXES OF PEST ARTHROPOD SPECIES ON SOYBEAN GROWN ON VARIOUS ROW SPACINGS
The Louisiana State University and Agricultural and Mechanical Ph.D. Col. 1985
University Microfilms
International300 N. Zeeb Road. Ann Arbor, Ml 46106 THE IMPACT OF INDIVIDUAL SPECIES AND COMPLEXES OF PEST ARTHROPOD SPECIES ON SOYBEAN GROWN ON VARIOUS ROW SPACINGS
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy
in
The Department of Entomology
by Jaime Yanes, Jr. B.S., Oklahoma State University, 1979 M.S., Oklahoma State University, 1981 May 1985 ACKNOWLEDGEMENTS
The author expresses his sincere appreciation to his major professor, Dr. David J. Boethel, for his guidance, encouragement, and patience throughout his endeavors as a Ph.D. candidate. His timely advice and friendship was much appreciated.
Appreciation is also expressed to other members of the author's graduate advisory committee, Drs. L. D. Newsom and Jerry B. Graves,
Department of Entomology; Dr. Kennth L. Koonce, Department of
Experimental Statistics; and Dr. Gerard T. Berggren, Department of Plant
Pathology and Crop Physiology. Thanks are given to all of the committee members for their critical review and helpful suggestions. A special thanks to Dr. Koonce for his counsel and assistance with statistical analyses.
The author would like to thank Mr. Robert Thevis, a cooperating farmer, for use of his land and equipment where the study was conducted.
Sincere appreciation is expressed to Noel Troxclair, Ruth Healy, Sherry
Bagent, Kenny, Chris and Tim Daigle, Margaret and Patti Sheng, Matt
Scheck, Oliver Raffray, and Allan Stewart for their valuable technical assistance. The author also thanks Dr. Thomas C. Sparks and his wife
Sandi for their assistance and use of their computer graphics equipment.
In addition, the author expresses his sincere appreciation to Monique
Ardoin for typing the dissertation.
A special thanks to his parents Clyde and Virginia Lechlider and his in-laws Jack and Fran Spiers for their support and encouragement throughout his graduate studies.
Most of all, the author's greatest appreciation goes to his wife,
Celeste, who sacrificed a great deal for little in return. Her love, understanding and encouragement was given unselfishly. TABLE OF CONTENTS
PAGE
ACKNOWLEDGEMENTS ...... ii
TABLE OF CONTENTS ...... iv
LIST OF TABLES ...... vii
LIST OF FIGURES ...... xlv
ABSTRACT ...... xvi
INTRODUCTION ...... 1
LITERATURE REVIEW ...... 3
I. ROW SPACING EFFECTS ON SOYBEAN YIELD...... 3
II. ROW SPACING EFFECTS ON SOYBEAN INSECTS...... 4
III. ECONOMIC INJURY LEVELS AND ECONOMIC THRESHOLDS ...... 7
A. Definitions ...... 7
B. Methods Of Establishing Economic Injury Levels .... 7
C. Economic Injury Levels Reported In The Literature.. 10
D. Benefits From Use of Economic Injury Levels In Pest Control...... 12
E. Present Research Needs ...... 12
MATERIALS AND METHODS ...... 15
I. SITE ESTABLISHMENT AND PRODUCTION PRACTICES ...... 15
II. ESTABLISHING POPULATIONS OF INDIVIDUAL SPECIES AND COMPLEXES OF INSECT PEST SPECIES...... 15
A. Experimental Design ...... 15
B. Subterranean Insects ...... 15
C. Above-ground Insects ...... 16 PAGE
III. SAMPLING ...... 17
A. Subterranean Insects ...... 17 B. Above-ground Insects ...... 19
IV. DEFOLIATION...... 19
V. YIELD ...... 20
VI. STATISTICAL ANALYSES ...... 20
RESULTS AND DISCUSSION ...... 21
I. SOIL SAMPLE ANALYSES ...... 21
II. POPULATIONS OF ABOVE GROUND INSECTS ...... 55
A. Row Spacing Effects ...... 55
B. Soil Treatment Effects...... 59
C. Foliar Treatment Effects ...... 65
1. Bean leaf beetle ...... 65
2. Colaspis beetle ...... 65
3. Soybean nodule fly ...... 72
4. Banded cucumber beetle ...... 79
5. Southern green stink bug ...... 79
6. Soybean looper ...... 88
7. Threecornered alfalfa hopper ...... 91
8. Geocorls spp...... 98
9. Nabis spp...... 98
10. Lebia analis ...... 105
11. Summary ...... 105
III. DEFOLIATION MEASUREMENTS ...... 114
IV. YIELD ...... 118
A. Response To Row Spacing ...... 118
v PAGE
B. Response To Subterranean Insects ...... 118
C. Response To Above-ground Insects ...... 124
CONCLUSIONS ...... 133
LITERATURE CITED ...... 135.
APPENDIX ...... 143
VITA ...... 146 LIST OF TABLES
TABLE PAGE
1. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and.untreated)...... 22
2. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and.untreated)...... 23
3. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion applied to the foliage..*.... 25
4. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion applied to the foliage...... 26
5. Effects of soil treatments with Isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with Bacillus thuringiensls applied to the foliage...... 28
6. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with Bacillus thuringiensis applied to the foliage...... 29
7. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with chlorpyrifos applied to the foliage...... 31
vii TABLE PAGE
8. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with chlorpyrifos applied to the foliage...... 32
9. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within untreated subplots...... 33
10. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within untreated subplots...... 34
11. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion plus permethrin applied to the foliage...... 36
12. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion plus permethrin applied to the foliage...... 37
13. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos...... 39
14. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of Isofenphos and chlorpyrifos...... 40
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion applied to the foliage...... 41
viii Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations. Hamburg. Louisiana. 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion applied to the foliage......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with Bacillus thuringiensis applied to the foliage......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with Bacillus thuringiensis applied to the foliage......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with chlorpyrifos applied to the foliage......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with chlorpyrifos applied to the foliage......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within the untreated sub-plots......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within the untreated sub-plots......
Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion plus permethrin applied to the foliage.... TABLE PAGE
24. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion plus permethrin applied to the foliage,... 50
25. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Comparison between 51 cm and 76 cm row spacing...... 51
26. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Comparison between 51 cm and 76 cm row spacing...... 52
27. Seasonal means for insect populations following selective insecticide treatments: 76 cm row spacing vs. 51 cm, 198 2 ...... 56
28. Seasonal means for insect populations following selective insecticide treatments: 76 cm row spacing vs. 51 cm, 198 3 ...... 57
29. Seasonal means for insect populations following selective insecticide treatments: Isofenphos and chlorpyrifos soil treatment vs. control, 1982...... 60
30. Seasonal means for insect populations following selective insecticide treatments: Isofenphos and chlorpyrifos soil treatment vs. control, 1983...... 61
31. Seasonal means for insect populations following selective insecticide treatments: Isofenphos soil treatment vs. chlorpyrifos, 1982...... 63
32. Seasonal means for insect populations following selective insecticide treatments: Isofenphos soil treatment vs. chlorpyrifos, 1983...... 64
33. Seasonal means for bean leaf beetle populations, across all row spaclngs and soil treatments, in response to selective Insecticide applications, 1982...... 66
34. Seasonal means for bean leaf beetle populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 67
x TABLE PAGE
35. Seasonal means for Colaspls louisianae populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 70
36. Seasonal means for Colaspls louisianae populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 71
37. Seasonal means for soybean nodule fly populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 75
38. Seasonal means for soybean nodule fly populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 76
39. Seasonal means for banded cucumber beetle populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 80
40. Seasonal means for banded cucumber beetle populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 81
41. Seasonal means for southern green stink bug populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 84
42. Seasonal means for southern green stink bug populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983...... 85
43. Seasonal means for soybean looper populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 89
44. Seasonal means for soybean looper populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 92
45. Seasonal means for threecornered alfalfa hopper populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 198 2 ...... 94
46. Seasonal means for threecornered alfalfa hopper populations, across all row spacings and soil treatments, in response to selective insecticide applications, 198 3 ...... 95
xi TABLE PAGE
47. Seasonal means for Geocorls spp. populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 99
48. Seasonal means for Geocoris spp. populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983. 100
49. Seasonal means for Nabis spp. populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1982...... 103
50. Seasonal means for Nabis spp. populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1983...... 104
51. Seasonal means for Lebia analis populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982...... 108
52. Seasonal means for Lebia analis populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983...... 109
53. Evaluation of selective foliar insecticides for manipulation of insect complexes, 1982...... 112
54. Evaluation of selective foliar insecticides for manipulation of insect complexes, 1983...... 113
55. Mean leaf area index, across all row spacings and soil treatments, in response to insect pest complexes, 1982. ... 116
56. Mean leaf area index, across all row spacings and soil treatments, In response to insect pest complexes, 1983. ... 117
57. Mean yield across all soil and foliar treatments, in response to row spacing, 1982...... 119
58. Mean yield across all soil and foliar treatments, in response to row spacing, 1983...... 120
59. Mean yield across all row spacings and foliar treatments, in response to soil treatments, 1982...... 122
60. Mean yield across all row spacings and foliar treatments, in response to soil treatments, 1983...... 123
61. Mean yield across all row spacings and soil treatments, in response to insect pest complexes, 1982...... 126
xii TABLE PAGE
62. Mean yield across all row spacings and soil treatments, in response to Insect pest complexes, 1983...... 127
63. Mean yield in response to Insect pest complexes on soybean planted on 51 cm and 76 cm row spacings, 1982...... 130
64. Mean yield in response to insect pest complexes on soybean planted on 51 cm and 76 cm row spaclngs, 1983...... 131
xiii LIST OF FIGURES
FIGURE PAGE
1. Mean population levels for bean leaf beetle following selective insecticide applications, 1982...... 68
2. Mean population levels for bean leaf beetle following selective insecticide applications, 1983...... 69
3. Mean population levels for Colaspls louisianae following selective insecticide applications, 1982...... 73
4. Mean population levels for Colaspis louisianae following selective insecticide applications, 1983...... 74
5. Mean population levels for soybean nodule fly following selective insecticide applications, 1982...... 77
6. Mean population levels for soybean nodule fly following selective insecticide applications, 1983...... 78
7. Mean population levels for banded cucumber beetle following selective insecticide applications, 1982...... 82
8. Mean population levels for banded cucumber beetle following selective insecticide applications, 1983...... 83
9. Mean population levels for southern green stink bug following selective insecticide applications, 1982...... 86
10. Mean population levels for southern green stink bug following selective insecticide applications, 1983...... 87
11. Mean population levels for soybean looper following selective insecticide applications, 1982...... 90
12. Mean population levels for soybean looper following selective insecticide applications, 1983...... 93
13. Mean population levels for threecornered alfalfa hopper following selective insecticide applications, 1982...... 96
14. Mean population levels for threecornered alfalfa hopper following selective insecticide applications, 1983...... 97
15. Mean population levels for Geocorls spp. following selective insecticide applications, 1982...... 101
16. Mean population levels for Geocoris spp. following selective insecticide applications, 1983...... 102
xiv FIGURE PAGE
17. Mean population levels for Nabis spp. following selective insecticide applications, 1982...... 106
18. Mean population levels for Nabis spp. following selective insecticide applications, 1983...... 107
19. Mean population levels for Lebia analis following selective insecticide applications, 1982...... 110
20. Mean population levels for Lebia analis following selective insecticide applications, 1983...... Ill
xv ABSTRACT
During 1982 and 1983, selective soil and foliar Insecticides were applied to soybean, Glycine max (L.) Merrill, planted on narrow (51 cm) and wide (76 cm) row spacings to manipulate soybean insects. Individual species and complexes of arthropod species were manipulated in plots to determine the effects of subterranean and above-ground insects on soybean growth and yield potential. Selective insecticides used in a selective manner proved to be an effective tool for studying insect pest complexes.
Sub-threshold levels of individual pest species, in combination, had a significant negative impact on yield. In addition, in 1982, the plots in which soybean looper, Pseudoplusia includens (Walker), populations approached the economic threshold, exhibited yield reductions comparable to those plots containing sub-threshold levels of several pests. Threecornered alfalfa hopper, Spissistulus festinus
(Say), populations of one-half and 1.8 times the economic threshold in
1982 and 1983, respectively, were associated with the lowest yields compared to all other pest species and complexes.
Yields due to row spacing were not consistent, with higher yields on 51 cm row spacing in 1982 and 76 cm row spacing in 1983. Significant interactions in yield were found between row spacing and the insect complexes maintained, suggesting that present economic thresholds established on conventional row spacings may need to be revised for narrow row spacings. No yield differences were found due to soil
xv i insecticide treatments.
Although responses to row spacing were detected for several insect species, the differences were of such a small magnitude that further study is warranted before definitive conclusions can be drawn. INTRODUCTION
Insect feeding may occur on soybean, Glycine max (L.) Merr., from the time it is planted until physiological maturity is reached in the fall. All parts of the plant may be attacked simultaneously by one or more species. Insects are an important cause of economic loss to soybean producers. In 1978 and 1979, losses plus cost of control of arthropod pests in Louisiana soybean were estimated at §151 million and
§72 million dollars, respectively (Milam 1980). Losses plus cost of control in Louisiana in 1980 were §39 million dollars (Southern 1982) and in 1981 were §40 million dollars (Southern 1983). The development of management strategies for soybean insect pest populations has been the goal of intensive research in the United States for 25 years.
One of the major tactics for soybean pest control is by chemical means. Presently, insecticides are being used excessively and unwisely in many soybean producing areas in the world. Prophylactic treatments of some highly persistent chlorinated hydrocarbons and broad spectrum materials have often been applied even before yields became threatened
(Turnipseed and Kogan 1976).
The concept of economic injury levels and economic thresholds is an important tool for the efficacy of any pest management program and is essential for the decision making process at the farm level. The establishment of dependable economic thresholds has been a major concern of soybean entomologists for the past decade. Determination of economic thresholds for treatment of a single pest species is relatively simple,
1 2
and reasonably satisfactory thresholds presently exist in many states
(Kogan 1984). Since most insect pests occur in complexes of two or more
species, economic thresholds for single species are unrealistic.
Simultaneous infestations of different Insect species and sequential
infestations of the same or different species occur in the field
throughout the growing season. The impact of these pest complexes is not known. In addition, very little research has been done in this area.
Increases in soybean yields have been seen in the U.S. soybean producing areas when row spacings are narrower than the conventional 102 cm (Cooper 1980, Boquet et al. 1983). Yield increases such as these have resulted in an increase in the number of farmers planting on narrow rows. Little is known as to what effect narrow rows have on the present economic injury levels for insect pests which were established on the wider, conventional row spacings.
The objective of this study was to determine the impact of individual pests and complexes of insect pest species on the growth and yield potential of soybean grown on a narrow and conventional row spacing. LITERATURE REVIEW
I. ROW SPACING EFFECTS ON SOYBEAN YIELD
Soybean yields in the north Central U.S. have been consistantly
higher when planted on narrow (50 cm or less) as compared to
conventional (90 to 102 cm) row spacings (Weber et al. 1966, Cooper
1977, Ryder and Beuerlein 1979, Cooper 1980, Costa et al. 1980,
Safo-Kantanka and Lawson 1980). Results from similar studies in the
southern U.S. have been inconsistent. Some southern researchers have
found increased yields following planting on narrow rows (Smith 1952,
Frans 1959, Carter and Boerma 1979, Parker et al. 1981); however, others reported no yield enhancement from narrow rows (HaTtwig 1957, Caviness
1966).
Increased yields were reported for all narrow row spacing studies conducted in Louisiana except those in the northern part of the state.
Five soybean cultivars were grown in Louisiana on 50 and 100 cm row spaclngs and results showed that planting on 50 cm rows afforded higher yields; however, yields were not consistent on 25 cm rows and were found to be dependent on the variety (Boquet et al. 1982). Similarly, Boquet et al. (1983) reported significantly higher yields on 25 and 57 cm row spaclngs over 102 cm conventional row spacings with yield increases on the narrow row spacings being greater as planting date was delayed.
Similar results were found by Williams and Noor (1973) on studies of row spacing and planting date in Louisiana.
Soybeans planted on 18 and 48 cm row widths, in Arkansas, were
3 found to produce 15% higher seed yield than the conventional 96 cm row
spacing (Beatty et al. 1982). Kollenkark et al. (1982) studied the
effects of row width, planting date, and cultivar on the agronomic
characteristics of soybean canopies. They reported that the three
variables affected the percent.soil cover, leaf area index, biomass, and
developmental stage of the soybean.
Soybean yield components at each node were determined following
variations in row width and plant density. Results from Herbert and
Litchfield (1982) demonstrated that the number of pods per plant and per
node was the yield component that was affected the most by row spacing
or plant density — pod number per plant increased as row spacing
became narrower and decreased as plant density within the row increased.
Cooper (1971, 1980), in studies involving row spacing, planting date, varieties and seeding rate, found that at the same seeding rate,
plants on narrow row spacings lodged more than those on wider rows. On wider rows, early competition within the row served to thin the population to one that resisted lodging. In contrast, thinning did not
occur on narrow rows; therefore, the equally competitive plants
developed to maturity and set seed resulting in increased lodging problems. Lodging can reduce soybean yields.
II. ROW SPACING EFFECTS ON SOYBEAN INSECTS
Relatively little information exists on the effects of row spacing on soybean insects. With the Increased popularity of farmers planting soybean on narrow rows, for yield advantages, little is known of effects on pest and beneficial insect populations.
Andrewartha and Birch (1954) suggested that two of the most 5
important factors limiting animal populations is the distribution of
plants and the amount of time needed by the animal to search for food.
Dethier (1959) found that the population growth rate of certain
Lepidoptera was dependent on the distance to the nearest host plant.
Some researchers have reported the effects of narrow row spacing on
soybean Insect pests. Sprenkel et al. (1979) found the populations of most foliage-feeding lepidoptera such as the green cloverworm,
Plathypena scabra (F,), corn earworm, Heliothis zea (Boddie), and
soybean looper, Pseudoplusia includens (Walker) were generally higher in plots planted on narrow row spaclngs. Similarly, Buschman et al. (1981)
reported higher populations of green cloverworm and velvetbean caterpillar, Anticarsia gemmatalis Hubner, in narrow row plantings; however, soybean looper and cabbage looper, Trichoplusia ni (Hubner), populations were inconsistent in 18 and 91 cm row spacings.
A survey conducted in 1500 North Carolina soybean fields by Bradley and Van Duyn (1980) showed that damage threshold levels of the corn earworm, Heliothis zea (Boddie), developed in only 2.8% of the closed canopy fields. In contrast, 22% of the open canopy fields developed threshold levels of corn earworm. Therefore, the reseachers indicated closed canopy fields were less desirable for oviposition by the corn earworm. Similar studies in Maryland by Joshl and Sheikh (1979) reported results that conflicted with the findings of Bradley and Van
Duyn (1980). They found no differences in pod damage by the corn earworm on 23 and 91 cm row spacings; however, on plots with 11 cm row spacings, pod damage was reduced.
Two researchers have indicated a greater abundance of the potato leafhopper, Empoasca fabae (Harris), on wider, more conventional row 6
spacings compared to narrow row plantings (Sloderbeck 1977, Mayse 1978).
In contrast, higher numbers of soybean thrips, Serlcothrips
variabilis (Beach), black alate aphids, Aphis craccivora and
Rhopaloslphum maidis, and green cloverworm were seen on 24 cm row
spacings compared to the wider 96 cm spacing (Mayse 1978). Troxclair
and Boethel (1984) reported higher populations of the leafhopper,
Scaphytopius acutus (Say), on 51 cm rows compared to row spaclngs of 91
cm. No differences were found for Mexican bean beetles, Epilachna varivestis (Mulsant), or redlegged grasshoppers, Melanoplus femurrubrum
(De Geer), on various row spacings in Indiana (Sloderbeck and Edwards
1979).
The effect of row spacing on beneficial Insects has been documented by several workers. Mayse (1978) reported significantly higher populations of Orius insidiosus, Nabis spp., and syrphid larvae in 24 cm as compared to 96 cm row spacings. He attributed the higher numbers to a more favorable microclimate, more prey population, easier prey capturabllity, and more desirable oviposition sites. Similarly, Nabis spp., 0. Insidiosus and spiders reached higher populations on narrow row spaclngs in North Carolina (Sprenkel et al. 1979). McPherson et al.
(1982) found significantly greater numbers of Geocoris spp. and spiders on drilled soybean in Richmond County, Virginia; however, the trends were not consistent in other counties.
The influence of row spacings on the entomopathogen, Nomuraea rileyi (Farlow) Sampson was studied by Sprenkel et al. (1979). These researchers found higher numbers of N. rileyi-killed lepidopterous larvae in narrow rows. They suggested more favorable microclimatic conditions in the narrow spacings may have attributed to the rapid 7
spread of the entomopathogen.
III. ECOMONIC INJURY LEVELS AND THRESHOLDS
A. Definitions. The success of any integrated pest management program is based on the establishment of economic injury levels and economic thresholds for pests (Stern 1973, Kogan 1976, Todd and Pitre
1979, Kogan 1984). Stern et al. (1959) first proposed the concepts of economic injury level (EIL) and economic threshold (ET). Economic injury level is defined as, "the lowest number of insects that will cause economic damage". Economic threshold refers to the pest population level at which control measures should be taken to prevent the pest from reaching the economic injury level. Without the use of
EILs as a foundation for the decision-making process in pest management, too much reliance is often placed on chemical insecticides for pest control (Pitre et al. 1979). Since the early 1970's, a main concern for soybean entomologists has been the establishment of reliable EILs for direct and indirect pests (Kogan 1976). The EIL concept integrates the concepts of biology and economics. Headley (1972) defines the EIL concept and provides an economic analysis of the concept.
B. Methods Of Establishing Economic Injury Levels. The development of EILs may be accomplished by several methods. Three empirical methods, based on visual estimations of crop loss, were discussed by
Stern (1966). The methods included: 1) quantitative measurements of the number of pests per unit area and assessment of pest numbers needed to cause economic crop damage; 2) observed physiological and morphological abnomalities (recognized as damaging to the plant) as a basis for threshold determination; and 3) utilizing marketing standards 8
Involving examination of the crop at harvest or shipment, the crop must
pass shipment examination or not be sold (eg. crops used for human
consumption).
A fourth method discussed by Stone and Pedigo (1972) combines
insect feeding data, obtained by entomologists with cost, marketing and yield data of agronomists and economists. Factors influencing the ET
levels can be manipulated in the laboratory using this deductive approach. Thus, the researcher may consider variations in market value, insecticidal costs, application costs, plant tolerance, plant populations, and insect feeding behavior in the calculation of EILs.
Many experimental approaches have been used in developing EILs
(Kogan 1976). By using naturally occurring pest populations, measurements on pest population levels can be recorded during outbreaks and the resulting damage can be correlated with population levels. A disadvantage of this approach is that the researcher has no control over the time and location of the pest outbreak. A study conducted by Miner
(1966) in Arkansas used this method to estimate damage by various levels of stink bugs.
A controlled outbreak may be obtained by utilizing artificial infestations of Insect pests. In this approach, plots are artificially infested with laboratory or field collected insects in numbers that will produce different levels of damage. Damage is then measured after a period of time. Although this approach affords a more controlled outbreak, disadvantages such as rearing/collecting large numbers of
Insects and effects from natural predation or parasitization may interfere with this method.
Use of field cages to confine insects on plants has been the most 9
widely used technique in pest population/damage research. This approach has been used on soybean for the potato leafhopper, Empoasca fabae
(Ogunlana and Pedigo 1974), the soybean looper (Sitchawat 1974), and for stink bugs (Daugherty et al. 1964, Todd and Tumlpseed 1974).
Researchers have attempted to manipulate or regulate certain soybean insect pests by means of selective insecticides or selective dosages to determine the damage potential of pest complexes. Although
Kogan (1976) stated that this method has not been successful in yielding useful data, he provided no examples in his discussion of any attempts made. Contrary to his statement, reports in the literature exist on studies where insects were successfully regulated by chemical means.
Tugwell et al. (1972) utilized differential applications of methyl parathion to establish various Infestation levels of threecornered alfalfa hoppers, Splssistilus festinus (Say), in EIL studies.
Similarly, Sparks and Newsom (1984) applied various insecticides in early season/late season combinations to establish different population levels of threecornered alfalfa hopper in Louisiana. Chemical insecticides were used on strawberry to reduce tarnished plant bug,
Lygus lineolaris (Palisot de Beauvois), to different levels in order to establish an action threshold level (Schaefers 1981). Ingram et al.
(1981) used diflubenzuron to prevent defoliation by the velvetbean caterpillar, Anticarsia geimnatalis Hubner, in studies to relate defoliation with CC^ exchange rates and reproductive growth of soybean.
Resistant isolines may provide a means for pest population manipulation. Various population levels of the potato leafhopper,
Empoasca fabae, were established utilizing soybean isolines that differed in the type and density of trichomes. Density and type (normal 10 or curly) of the trichomes determined the adequacy of the isoline as a host (Kogan 1976).
Damage simulation has been used in experiments to simulate the effect of insect pod and foliage feeders by means of depodding (Thomas et al, 1974a) and hand defoliation (Hammond and Pedigo 1982). In this method, surrogate damage is Inflicted on the plant in the absence of natural pest populations. There are many advantages for this approach such as: the ability to control the degree of injury; the ability to assess crop loss in the absence of pest populations; and the flexibility of studying insect injury in relation to the biology of the plant crop response (Poston et al. 1983), The disadvantage, however, is the criticism regarding the accuracy of damage simulation with respect to actual insect injury.
C. Economic Injury Levels Reported In The Literature. EILs have been established for insect pests feeding directly on soybean pods and seeds. The standard procedure involves the establishment of three or four infestation levels at critical stages in plant growth. Natural infestations of the green stink bug, Acrosternum hilare (Say), were utilized by Miner (1966) to determine EILs in Arkansas. Economic injury levels have been developed for various species of stink bugs: A. hilare and Euschistus servus (Say) (Daugherty et al, 1964); Nezara viridula
(L.) (Todd and Turnipseed 1974); A. hilare (Yeargan 1977); and A. hilare, E. servus, E. tristigmus (Say), and N. viridula (McPherson et al. 1979)-. In certain areas, Heliothis zea (Boddie) is a serious pod feeder and studies have determined the ET for H. zea in Arkansas to be
10 per row meter (Mueller and Engroff 1980). 11
Economic injury levels for specific soybean pests have been
documented. Gould (1963) established a EIL for Japanese beetle,
Popillla japonlca Newman, foliage injury in Indiana. Establishment of
EILs for several lepidopterous species at various soybean growth stages
was made by Thomas et al. (1974a). Stone and Pedigo (1972) first
described a useful method for development of EILs using a deductive
approach. This approach was later defined mathematically by Ruesink
(1975). The static model proposed by Ruesink can only be applied to
foliage injury and certain assumptions are made such as: 1) no new
leaves are formed while defoliation takes place; 2) defoliation is
Instantaneous; 3) the relationship between yield loss and defoliation is
based on results from simulated defoliation (which differs from actual
insect damage). Although the static model has rigid restrictions and
cannot respond to fluctuating environmental conditions, Kogan (1976)
stated that the model is a good initial approximation aiding in the
implementation of pest management programs at the farm level.
In order to establish reliable EILs involving the dynamic nature of pest/crop systems, Kogan (1984) suggests the Bystems approach to pest management discussed in Shoemaker (1980). This approach may involve
integrating pest population simulation and plant growth simulation models so that the dynamic interactions can be included into the system.
Rudd et al. (1980) utilized the systems approach In a model for determination of economic injury levels. In it, they integrated the LSU
soybean looper model and the LSU soybean crop growth model to calculate the treatment threshold based not only on the current pest population level but also on the date populations were measured and the leaf area estimated to remain if control measures are not taken. 12
Rudd (1980) developed a simple plant growth model for use in
soybean pest management model studies. This model, based on the
relationship between dry matter production and leaf area, explains the
effects of defoliation, depodding, and planting dates. Rudd states that
the model has been validated with plant growth data andresponds much
like real soybean systems to simulated damage.
Gandour (1977) utilized a model to construct treatment thresholds
for the southern green stink bug, Negara viridula (L.), and the brown
stink bug, E. servus. Her model took into consideration factors such as
the variety, the condition of the crop, time of year, cost of control,
projected price of soybean and projected yields. Similar economic
injury level studies for stink bug species are described in Marsolan and
Rudd (1975, 1976).
D. Benefits From Use of Economic Injury Levels In Pest Control.
The establishment of acceptable ETs in a pest management program can
benefit by reducing the total number of insecticidal applications needed
(Newsom 1980). In the Midwestern U.S., a 10 percent increase in the
accepted ET may result in at least the same percentage decrease in the
area treated (Kogan 1984). A reduction of 50-75 percent of the number
of insecticidal sprays was seen in Brazil after utilizing ET's similar
to those developed in the U.S. (Kogan et al. 1977).
E. Present Research Needs. According to Newsom (1980), reasonably
satisfactory EILs have been established for only eight species of insect
pests on soybean. Damage from these eight species comprise 83,2% of the
total amount of insect damage to soybean in the U.S. (Kogan 1980).
Although the EILs serve as a basis for the current pest management programs for soybean, all have been developed for single species of 13 pests. Numerous complexes of pests generally occur In most of the
soybean areas (Turnipseed 1972a). Researchers have expressed the urgent need for development of EILs for complexes of pest species (Pitre et al.
1979, Newsom 1980, Poston et al. 1983) and have discussed the difficulty
that is involved. Presently, no EIL exists for pest complexes on soybean.
In the past, when two or more species produced similar damage (such as the velvetbean caterpillar, soybean looper, and green cloverworm), they were considered together in establishing EILs as were the pod feeding stink bugs, Acrosternum hilare, Euschistus servus, and Nezara viridula (Newsom 1980). Attempts have been made to simulate the combined effects of foliage and pod injury in soybean (Thomas et al.
1974a); however, no experimental evidence has been shown to support the results. Newsom (1980) cited the typical problem that occurs in much of the acreage of soybean in Louisiana each year — the crop Is under simultaneous attack by the following pest species during pod filling: bean leaf beetle adults and larvae; southern green stinkbug and threecornered alfalfa hopper adults and nymphs; soybean looper and velvetbean caterpillar larvae; and several diseases. In addition, various weed species may compete with the crop. Newsom stated, "Any one species of this complex is capable of causing severe damage with heavy loss in yield." Presently, no answers are available to the farmer when he asks what control measures should be initiated when two or more pest species occur at the same time at a certain level below the EIL, In addition, although it is suspected that sub-threshold levels of individual pests occurring in combination cause yield losses and that numerous authors have stressed that a need for EILs for pest complexes 14
exists, the literature is still devoid of published data demonstrating
that yield losses do occur.
Present EILs established for single species of insect pests ignore
the fact that certain pest species have indirect and/or direct effects
on more than one portion of the host attacked (Newsom 1980). Newsom
gives the example of the bean leaf beetle •— the EIL established was
based on defoliation and pod feeding; however, no consideration was
given to the damage resulting from larval feeding on the nodules
(leading to a reduction in nitrogen fixation) or the transmission of bean pod mottle virus by the adult. The development of EILs becomes
even more complex when considering the effects of a pest or pest
complexes on nitrogen fixation of soybean. Newsom et al. (1978)
recently reported that foliage feeders, stem feeders, nodule feeders and
fungal pathogens affect the nitrogen-fixing capacity of soybean.
With the increased interest of planting on narrow row spacings,
little is known as to what effect narrow rows have on the present economic Injury levels which were established on conventional row spacings. MATERIALS AND METHODS
I. SITE ESTABLISHMENT AND PRODUCTION PRACTICES
The study was conducted in 1982 and 1983 near Hamburg,
Avoyelles Parish, La., on the farm of a cooperating grower. The experimental area consisted of 7.5 ha of a field planted to
'Centennial* soybean. Seedbed preparation, pre-emergence herbicide, and post-emergence herbicide practices followed those recommended by the Louisiana Cooperative Extension Service (Anon. 1982, 1983).
II. ESTABLISHING POPULATIONS OF INDIVIDUAL SPECIES AND COMPLEXES OF INSECT PEST SPECIES
A. Experimental Design. To characterize the damage potential of individual pest species and complexes of pest species, selective soil and foliar pesticides were used to manipulate soybean insect populations. The experiment was designed as a split plot design with three replications. Main plot treatments consisted of the row spacing/soil treatment combinations (6 per replication), whereas subplot treatments consisted of foliar treatments (5 per main plot).
Thus, a total of 90 experimental units were utilized in each year of the study. The planting dates were May 5 and 11 for 1982 and 1983, respectively.
B. Subterranean Insects. Combinations of two row spacings (51 cm and 76 cm) and three soil insecticide treatments [isofenphos
(Amaze®) at 68 g AI/305 m of row (2.2 kg Al/ha and 1.5 kg Al/ha for
15 51 cm and 76 cm row spacings,respectively), chlorpyrifos (Lorsban®)
at 34 g AI/305 m of row (1.1 kg Al/ha and 0.7 kg Al/ha for 51 cm and
76 cm row spacings, respectively), and an untreated check] were
randomly assigned to the six main plots in each replication and
applied in-furrow at planting. The soil insecticide treatments
provided control for 1st generation larvae of the bean leaf beetle
(BLB), Cerotoma trifurcata (Forster): Colaspis beetle (COL),
Colaspis loulslanae (Blake): and soybean nodule fly (SNF), RiveIlia
quadrifasciata (Maquart). In addition, since isofenphos has been
reported to have systemic activity against bean leaf beetle adults
(Newsom 1980, unpublished data), the isofenphos was directed toward
control of larval stages of the 1st generation of all the aforementioned soil insect pests plus adults of the bean leaf beetle.
C. Above-ground Insects. For manipulation of above-ground pests, each of the six main plots was split into five plots, each measuring 32 rows X 61 tn (0.25 ha) for the 51 cm row spacing and 24 rows X 61 m (0.27 ha) for the 76 cm row spacing for 1982; plot lengths in 1983 were decreased to 46 m for both row spacings. The foliar insecticides randomly assigned to the plots for manipulation of various pests and pest complexes were as follows: Treatment #1 - methyl parathion, 0.56 kg Al/ha, for soybean looper (SBL),
Pseudoplusia includens (Walker); Treatment #2 - Bacillus thuringiensis (Dipel®), 0.56 kg Al/ha for banded cucumber beetle
(BCB), Diabrotica balteata (LeConte), bean leaf beetle, soybean nodule fly, southern green stink bug (SGSB), Nezara viridula (L.), threecornered alfalfa hopper (TCAH), Spissistilus festlnus (Say), beneficial insects - Geocoris spp. (GEO), Nabis spp. (NAB), and
Lebia analis DeJean (LEB); Treatment #3 - chlorpyrifos (Lorsban®),
0.56 kg Al/ha for building up populations of threecornered alfalfa
hopper; Treatment #4 - untreated check for all insect species; and
Treatment if5 - permethrin (Ambush®) 0.11 kg Al/ha plus methyl
parathion, 0.56 kg Al/ha, for complete control of all insect
species. Foliar insecticides were applied weekly beginning at the
V5 developmental stage (Fehr et al. 1971) and continued until the
plants reached physiological maturity (R7) when insect populations
became insignificant.
Foliar treatments were applied in 1982 using a three-point
hitch tractor-mounted sprayer with a 6 m spray boom that delivered
145 1/ha of finished spray at 32 psi. In 1983, a Hahn Hi-Boy®
sprayer equipped with a 15 m spray boom was utilized. The sprayer
delivered 131 1/ha of finished spray at 25 psi.
The entire experiment received four and five applications of
benomyl (Benlate®) at 1.12 kg Al/ha in both 1982 and 1983,
respectively, for control of fungal pathogens. Benomyl was applied
every three weeks during the season except when conditions were
favorable for plant disease outbreaks (plots were then treated
every other week).
III. SAMPLING
A. Subterranean Insects. The methodology described by Lambert
(1981) was utilized to sample populations of subterranean pests and associated damage. Samples were taken June 24, July 19, and August 23 in 1982 and June 20, July 28, and September 9 in 1983. Sampling dates were selected to coincide with the period of the life cycles of the soil insects when immature insects were present. Stages of the life cycles were estimated by correlating weekly sweep samples of soil pests with published biological data for these pests. On the June 24, 1982 sampling date, two samples were taken in each main plot consisting of a row spacing/soil insecticide treatment; however, for the other sampling dates, one sample was taken in each of the ninety plots.
For each sample, two adjacent plants were selected at random and cut ca. 5 cm from the ground. A soil core sampler (8.9 cm dia.
X 12.7 cm deep) was inserted over the base of the plants, and the root system and adjacent soil was removed.
Insects and plant components were separated from the soil using a soil elutriator (Byrd et al. 1976). Material washed from the sample was collected on a 40 mesh sieve and rinsed under an aerated faucet to remove any remaining soil. The taproot portion of the sample and the remaining material in the sieve were removed and floated in a saturated salt solution. Bach sample was observed under an illuminated magnifying glass and then a dissecting microscope. Parameters measured for each sample were the number of bean leaf beetle larvae, pupae, and eggs, soybean nodule fly larvae, pupae, and pupal cases, Colaspis larvae, total nodules and damaged nodules. Nodules were considered to be damaged if they contained larvae, emergence holes, or were partially eaten. Nodule data were expressed on a per hectare basis and were calculated using actual stand counts in each plot. B. Above-ground Insects. Foliage inhabiting insects were sampled weekly beginning when the plants were in the V4 stage with a
38 cm diameter sweep net. On each sample date, 50 sweeps per plot were taken using procedures described by Kogan and Pitre (1980) for sweeps across one row. The following insects were monitored: larvae of the soybean looper; adults of the bean leaf beetle, banded cucumber beetle, Colaspis beetle, soybean nodule fly; nymphs and adults of the threecornered alfalfa hopper, southern green stink bug, Geocoris spp., Nabis spp.; and adults of the carabid, Lebia analis.
IV. DEFOLIATION
To determine the defoliation due to foliage feeding pests, leaf area indices (LAI) were determined twice each year. The initial sample was taken at R3 which corresponds to maximum LAI (Rudd 1980)
(before defoliation), and the second was taken later in the season after the peak populations of foliage feeders (after defoliation), generally late R6. The difference between LAI on the two sampling dates estimated the amount of defoliation that occurred in each treatment. These defoliation amounts then were adjusted to the amounts in the methyl parathion plus permethrin treatment in which all insects were controlled. Decreases in LAI in the latter treatment were presumed to be due to senescence and natural leaf drop.
One row-meter of plants was removed from each plot and brought to the laboratory for determination of LAI. Leaves were removed from each sample and processed on a LI-COR® model LI-3100 leaf area
meter. The LAI for each plot was calculated by methods described by
Sparks and Newsom (1984).
V. YIELD
Yields were taken from each plot utilizing a small plot combine
(Hege 125B). Two rows in the central area of each plot were
harvested (55 m and 40 m in length for 1982 and 1983, respectively).
Yields were standardized at 13% moisture content.
VI. STATISTICAL ANALYSES
Data from the soil sample analyses were subjected to analysis
of variance procedures and orthogonal comparisons were made between
the soil insecticides vs. the untreated control and between soil
treatments of isofenphos and chlorpyrifos. To stabilize the
variance for weekly insect counts, a logarithmic transformation was
performed. Transformed data were analyzed by date and season.
Appropriate orthogonal comparisons were made and means separation was performed using Tukey's studentized range test [Steel and Torrie
(1980)]. Yield and defoliation data also were subjected to analysis
of variance and Tukey's studentized range test. RESULTS AND DISCUSSION
I. SOIL SAMPLE ANALYSES
In-furrow soli Insecticide treatments were applied under optimal field conditions in both years of the study. In 1982, environmental conditions were favorable following planting, aiding early season activity of the soil insecticides. Environmental conditions following planting in 1983 were not as favorable with rainfall estimated to have been ca. 31 cm for a period of ten days after planting. It was suspected that heavy rainfall leached some of the insecticide from the soil surrounding the plants, thus reducing the efficacy of the treatments.
Tables 1 and 2 compare the two chemical soil treatments (isofenphos and chlopyrifos) with the untreated check in terms of their effects on parameters measured in both years. No differences were found for the total number of nodules/ha on any dates sampled. Thus, insecticide treatments had no phytotoxic effect on nodule number. Although a trend was seen in lower numbers of damaged hodules/ha on treated samples in
1982, no differences were found except for the August 23 sample where more damaged nodules/ha were counted in the untreated control resulting in a ca. 3% more damaged nodules/ha for samples on August 23. On June
19, although no differences were seen in the damaged nodules/ha for treated and untreated plots, a significant (P<0.05) reduction in the percentage of damaged nodules/ha occurred in treated plots compared to plots receiving no soil treatment. Significant differences (P< 0.05)
21 Table 1. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated)
June 24______June 19______August 23______
Isofenphos and Isofenphos and Isofenphos and Parameter______Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )-? . . 229.69 284.10 608.34 575.35 425.57* 427.81 Damaged nodules/ha (£/10 )~ 19.21 26.82 61.82, 87.39 19.50* 37.14 % Damaged nodules/ha— 8.47* 9.60 10.93; 16.12 4.94 9.69 Soybean nodule fly larvae 0.13* 0.50 0.00 0.10 0.10 0.00 Soybean nodule fly pupae 0.11 0.30 0.01 0.00 0.10* 0.03 Soybean nodule fly pupal cases 0.20 0.40 0.24 0.13 0.41 1.87 Colaspis larvae 0.00 0.00 0.05 0.20 0.03 0.10 Bean leaf beetle larvae 0.00 0.00 0.13 0.33 0.00 0.03 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.80 1.30 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.06 0.27
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis.
fv3 ho Table 2. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) .—
June 20 July 28 September 9
Isofenphos and Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )t k / 92.52 100.93 295.85 273.20 333.35 350.74 Damaged nodules/ha (?/10 )— 1.51 1.80 13.38 11.50 54.34 58.84 % Damaged nodules/ha— 1.93 1.94 4.67 4.43 16.37 17.08 Soybean nodule fly larvae 0.01 0.00 0.07 0.07 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.33* 0.33 0.33 0.33 0.88 0.53 Colaspis larvae 0.08 0.20 0.11 0.20 0.02 0.03 Bean leaf beetle larvae 0.16 0.03 0.03 0.03 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.01 0.03 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.03 0.03 0.95 1.97 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. 24
were found for SNF larvae, pupae, and pupal cases on two dates In 1982 and COL larvae In 1983; however, the populations were too low to adequately assess the treatment effects. In addition, more SNF pupal
cases were detected in untreated plots compared to those having
Insecticide treatments. Eastman (1976) In studying the effects of nodule-feeding bean leaf beetle larvae on treated soybean, was the first
to discover larval soybean nodule fly feeding on soybean nodules In
Louisiana. Her findings were important from the standpoint that nodule damage previously thought to be attributed to BLB larval feeding may also have resulted from SNF feeding. Presently, no reports exist on methods for determining whether nodule damage is due to BLB or SNF.
Ineffectiveness of the soil insecticides in 1983 is reflected by the nonsignificance of virtually all parameters measured (Table 2).
It waB established that the soil insecticide treatments were effective for protecting nodules from soil pests. Orthogonal comparisons were made testing soil treatments against the control, within each of the foliar treatments. Foliar treatments were used to regulate populations of certain complexes of above-ground Insects at more or less desired levels. Tables 3 and 4 compare the soil insecticides against the untreated check in response to methyl parathion foliar treatments in which soybean looper populations were regulated at
73 and 19% ET for 1982 and 1983, respectively. Data for 1982 represent only two sampling dates since samples were taken only on main plots (row spacing/soil treatment combinations) on June 24. Cumulative seasonal nodule damage for 1982 was found to be significantly less (P< 0.05) for treated vs. untreated plots on the August 23 sample.
The numbers of BLB larvae and hatched eggs were significantly Table 3. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos and untreated) within sub-plots treated with methyl parathion applied to the foliage.—
July 19______August 23
Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control
Total nodules /ha (X 667.60 698.50 430.66* 486.84 Damaged nodules/ha (jj/10 )— 45.80 97.43 15.67* 38.47 % Damaged nodules/ha— 6.96 15.94 2.93 8.04 Soybean nodule fly larvae 0.00 0.17 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.08 0.17 0.33 1.17 Colaspis larvae 0.08* 0.17 0.00 0.00 Bean leaf beetle larvae 0.08 0.50 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00* 0.00 Hatched bean leaf beetle eggs 0.41 0.50 0.17 2.00 Unhatched bean leaf beetle eggs 0.24 1.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 4. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isofenphos, chlorpyrifos and untreated) within sub-plots treated with methyl parathion applied to the foliage.—
June 20 July 28 September 9
Isofenphos and Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos IControl
Total nodules/ha (X *0^)^^ / 81.03 106.24 305.41 302.35 313.57 378.51 Damaged nodules/ha (X .10 )— 2.11 1.03 14.11 13.76 46.51 48.20 % Damaged nodules/ha— 2.72 1.60 4.81 3.11 14.19 13.61 Soybean nodule fly larvae 0.00 0,00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.67 0.17 0.25 0.67 0.58 0.50 Colaspis larvae 0.08 0.50 0.00 0.17 0.00 0.00 Bean leaf beetle larvae 0.83 0.00 0.08 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.08 0.17 0.66 1.67 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
a / * — Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. 27
(P< 0.05) lower in treated plots on July 19 and August 23, respectively.
Similar results were reported by Lambert (1981) who found a reduction in
numbers of adult and immature bean leaf beetle, damaged nodules and
percentage of nodules damaged following soil treatment with isofephos.
Foliar methyl parathion treatments held soybean looper populations at
about 73% ET and controlled adult soil pests (BLB, SNF, COL, BCB).
Thus, damage to nodules would be from overwintering populations of soil
pests that colonized fields and oviposited before weekly foliar
treatments were initiated.
Orthogonal comparisons of the soil insecticides vs. the untreated
control, in response to B. thuringiensis foliar treatments are shown in
Tables 5 and 6. B. thuringiensis was utilized to control the
lepidopterous insect pest complexes and allowed the adults of BLB, COL,
SNF, BCB, NV, TCAH to develop uncontrolled above-ground. None of the parameters measured were significant (P> 0.05) on July 19 for the 1982
season. On August 23, ca. 7% fewer damaged nodules/ha were found for plots receiving soil insecticide compared to the control. Plots, in which species of non-lepldopterous insects were allowed to develop uncontrolled above-ground had a slightly higher percentage of damaged nodules/ha (5.6%) than plots in which soybean looper alone was allowed to go uncontrolled (Table 3, 2.9%). This higher damage may reflect additional Injury by the small number of soil insects that escaped control from foliar applications. In 1983, samples taken on September 9 showed a significantly higher percentage of damaged nodules/ha; however, as mentioned above it was suspected that soil treatments in 1983 were ineffective due to heavy rainfall; thus, it is doubtful the difference Table 5. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations) Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within sub-plots treated with Bacillus thuringiensis applied to the foliage.—
July 19 August 23
Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )-t- , , 611.75 698.51 390.63 416.30 Damaged nodules/ha )~ 93.30 97.43 18.01. 46.31 % Damaged nodules/ha— 15.89 15.95 5,60 12.72 Soybean nodule fly larvae 0.00 0.17 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.08 0.67 0.16 1.83 Colaspis larvae 0.00 0.17 0.00 0.00 Bean leaf beetle larvae 0.17 0.50 0.00 0.00 Bean leaf beetle pupae 0,00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 1.75 0.50 1.92* 1.17 Unhatched bean leaf beetle eggs 0.00 0.00 0.16 1.00
Parameter means followed by are significantly different (P<0,05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 6. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isophenophos, chlorpyrifos, and untreated) within sub-plots treated with Bacillus thuringiensis applied to the foliage.—
June 20 July 28 September 9
Isofenphos and Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )-g ^ , 89.77 119.70 263.71 302.36 341.68 307.50 Damaged nodules/ha (X/10 )— 1.29 1.84 16.77 13.76 53.38. 68.69 % Damaged nodules/ha— 2.31 1.48 6.01 3.11 14.71 21.99 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 °-00* 0.00 Soybean nodule fly pupal cases 0.33 0.00 0.16 0.17 1.15* 0.17 Colaspis larvae 0.08 0.00 0.00 0.17 0.50 0.00 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.17 0.00* 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.08 0.00 0.00 4.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. 30
in damage resulted from effects of soil treatment.
Tables 7 and 8 summarize results from orthogonal comparisons between insecticide soil treatments and the untreated control, within chlorpyrifos foliar treatments. Foliar treatments of chlorpyrifos allowed populations of threecornered alfalfa hopper to go uncontrolled while giving effective control of other Insect pests. According to the analysis, no significant differences were found (P> 0.05) between treated vs. untreated soil treatments for any nodule parameters measured in both years. Hicks et al. (1984) reported a decrease in nodule number and nitrogen fixation following stem girdling by TCAH (8 TCAH per plant). The populations above-ground (discussed later) may not have reached levels high enough to cause similar reductions. On August 23,
1982 a significant (P< 0,05) difference was seen for lower numbers of
COL larvae in treated plots.
Results from orthogonal comparisons between chemical soil treatments and the untreated control, within the untreated foliar treatment, are shown in Tables 9 and 10. The untreated control allowed populations of all insect species present in the field to go uncontrolled. Thus, the tables for the following orthogonal comparisons demonstrate the effect of soil treatments alone without the influence of foliar insecticides manipulating populations of above-ground insects.
In 1982, approximately twice as many damaged nodules/ha were found on
July 19 in plots receiving no chemical soil treatment compared to those treated with insecticide. This is reflected in the significantly higher
(P< 0.05) percentage of damaged nodules/ha on the same date for treated plots (12.52%) compared to untreated plots (22.63%). A similar pattern Table 7. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos and untreated) within sub-plots treated with chlorpyrifos applied to the foliage.—
July 19 August 23
Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 W , . 582.10 572.21 388.08 485.33 Damaged nodules/ha (£yl0 )“ 38.53 82.13 18.04 34.44 % Damaged nodules/ha— 9.23 17.20 4.60 7.61 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.08 0.17 Soybean nodule fly pupal cases 0.33 0.67 0.41* 1.67 Colaspis larvae 0.16 0.00 0.08 0.33 Bean leaf beetle larvae 0.17 0.17 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 1.16 0.50 0.16 0.83 Unhatched bean leaf beetle eggs 0.41 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 8. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isophenophos, chlorpyrifos, and untreated) within sub-plots treated with chlorpyrifos applied to the foliage.—
June 20______July 28______September 9_____
Isofenphos and Isofenphos and Isofenphos and Parameter______Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )-g- ^ . 89.31 93.07 295.28 298.70 295.07 345.32 Damaged nodules/ha (X/10 )— 1.62 3.07 16.34 12.42 54.92 63.23 % Damaged nodules/ha— 2.31 3.51 5.70 5.26 18.61 18.65 Soybean nodule fly larvae 0.00 0.00 0.08 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.16 0.17 0.25 0.33 0.33 0.17 Colaspis larvae 0.00 0.17 0.33 0.33 0.08 0.00 Bean leaf beetle larvae 0.00 0.00 0.08 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00. 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.16 0.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 9. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (isofenphos, chlorpyrifos, and untreated) within untreated sub-plots.—
July 19 August 23
Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )■£ , , 616.80* 546.27 432.45 415.39 Damaged nodules/ha fg . 10 )— 60.76* 129.13 24.71* 39.95 % Damaged nodules/ha— 12.52* 22.63 5.92 11.05 Soybean nodule fly larvae 0.00 0.33 0.00 0.00 Soybean nodule fly pupae 0.08 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.33* 0.17 0.25 2.50 Colaspis larvae 0.00* 0.50 0.08* 0.17 Bean leaf beetle larvae 0.00 0.83 0.00 0.17 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.33 1.00 1.50 1.50 Unhatched bean leaf beetle eggs 0.75 1.50 0.17 0.33
Parameter means followed by * are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 10. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isophenophos, chlorpyrifos, and untreated) within untreated sub-plots.—
June 20 July 28 September 9
Isofenphos and Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )t . / 93.38 81.59 279.81 257.80 354.20 375.19 Damaged nodules/ha (jt/10 )— 1.03 4.27 10.41 9.85 67.91 84.40 % Damaged nodules/ha— 1.14 0.55 4.02 4.28 19.98 22.52 Soybean nodule fly larvae 0.08 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.15 0.00 0.40 0.17 1.25 1.33 Colaspis larvae 0.08 0.33 0.80 0.33 0.16 0.17 Bean leaf beetle larvae 0.00 0.17 0.00 0.17 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.08 0.00 0.00. 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 1.75 4.17 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons {Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. 35 was seen for percentage of damaged nodules/ha on August 23. All other differences, though significant (P< 0.05), in 1982 and 1983 were too small to interpret as having any significant effects on plant growth and development; however, a trend was shown for lower BLB and COL populations in treated plots.
Tables 11 and 12 reflect orthogonal comparisons between treated vs. the untreated control, within methyl parathion plus permethrin foliar treatments. The only differences found were on August 23, 1982 where ca. 5% fewer damaged nodules/ha were estimated in plots having insecticidal soil treatment compared to those which were untreated.
Soil pest populations above-ground had no Influence on nodule damage since these populations were controlled with weekly foliar treatments of methyl parathion plus permethrin. These data reflect damage caused by soil pests alone.
As a general rule, results from Tables 1-12 showed that the chemical soil treatments were significantly different (P< 0.05) than the untreated control for parameters measured. In addition, when the soil treatment was a check (untreated) and foliar treatments consisted of methyl parathion, chlorpyrifos or methyl parathion plus permethrin, these combinations reflected the amount of protection to nodules afforded by foliar treatments. Thus, for these treatments, any damage would be from overwintering populations of soil pests that colonized and oviposited before weekly foliar treatments were initiated or the small percentage of adults that escaped control with foliar applications. As discussed later, overwintering populations were very low prior to foliar applications; therefore, nodule damage and the impact of soil pests on soybean growth and development was minimal. Table 11. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications (Isofenphos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion plus permethrin applied to the foliage.®
July 19 August 23
Isofenphos and Isofenphos and Parameter ______Chlorpyrifos Control______Chlorpyrifos Control
Total nodules/ha (X lO6)^, , 551.99 507.04 474.23 405.49 Damaged nodules/ha (?/10 )— 55.87 53.15 21.03. 29.54 % Damaged nodules/ha— 9.30 10.67 4-83* 9.01 Soybean nodule fly larvae 0.00 0.00 0.00 0.16 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.42 0.50 0.33 2.17 Colaspis larvae 0.00 0.17 0.00 0.00 Bean leaf beetle larvae 0.25 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.16 0.00 0.33 1.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00
/ A — Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957). V / — Module data taken from soil core samples expressed on a per hectare basis. Table 12. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications (isophenophos, chlorpyrifos, and untreated) within sub-plots treated with methyl parathion plus permethrin applied to the foliage.—
June 20 July 28 September 9
Isofenphos and Isofenphos and Isofenphos and Parameter Chlorpyrifos Control Chlorpyrifos Control Chlorpyrifos Control
Total nodules/ha (X 10 )t . . 109.11 99.86 325.00 245.88 362.17 347.19 Damaged nodules/ha (X/10 )— 1.50 2.64 9.31 7.28 48.97 29.69 % Damaged nodules/ha— 0.77 2.57 2.85 3.72 7.41 8.60 Soybean nodule fly larvae 0.00 0.00 0.24 0.33 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.33 0.67 0.58 0.33 0.33 0.50 Colaspis larvae 0.16 0.33 0.00 0.00 0.00 0.00 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.25 0.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. 38
Tables 13 and 14 summarize the overall effect of isofenphos compared to chlorpyrifos soil treatments. In 1982, the sample taken on
July 19 showed that plots treated with isofenphos had significantly (P<
0.05) fewer damaged nodules/ha resulting in ca. 10% less damaged nodules/ha. On August 23, all three parameters measured on nodules were significant. Again, plots treated with isofenphos had less nodule damage; however, total nodules/ha were higher on plots treated with isofenphos for this date and the September 9 sample taken in 1983. Soil pest parameters shown to be statistically different (P< 0.05) did not differ by a large amount.
Tables 15-24 show the relationship between the soil insecticides when tested within each of the five foliar treatments. As shown in the tables, isofenphos gave more effective control of below-ground pests of soybeans than did chlorpyrifos.
Tables 25 and 26 summarize the data from the soil sample analyses in respect to row spacing for both seasons. No differences were found for any soil pest parameters measured. However, significant differences
(P< 0.05) were shown for nodule data. Higher numbers of nodules per hectare occurred on plots planted on 51 cm rows compared to those on 76 cm rows for all sample dates in both years.. Although the number of damaged nodules per hectare were significantly (P< 0.05) higher for the narrow row spacings on the first and last sampling dates in 1982 and the last sampling date in 1983, the percentage of damaged nodules per hectare was the same across both row spacings on all sampling dates. In addition, although there were more damaged nodules per hectare in narrow rows, more healthy nodules would exist in the narrow rows when considered from a per hectare basis. Relatively little is known about Table 13. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos.—
June 24 July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos fib/ Total nodules/ha (X 10 )r u/ 208.85 250.53 590.57* 626.19 479.49* 371.65 Damaged nodules/ha )~ 12.68 25.14 34.77* 88.79 13.97* 25.03 % Damaged nodules/ha- 7.49 10.89 5.53 16.04 2.78 7.11 Soybean nodule fly larvae 0.25 0.00 0.00 0.00 0.00 0.03 Soybean nodule fly pupae 0.83 0.83 0.00 0.03 0.00 0.03 Soybean nodule fly pupal cases 0.17 0.17 0.13 0.37 0.27 0.63 Colaspls larvae 0.00 0.00 0.00 0.10 0.03 0.03 Bean leaf beetle larvae 0.00 0.00 0.03 0.23 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00. 0.00 0.00. 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.23 1.23 0.20 1.43 Unhatched bean leaf beetle eggs 0.00 0.00 0.23 0.40 0.03 0.10
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis.
to VO Table 14. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos.—
June: 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )t b / 97.28 87.77 314.47 277.22 376.22* 290.46 Damaged nodules/ha (&/10 )” 0.92 2.10 11.83 14.94 58.53 50.15 % Damaged nodules/ha— 1.21 2.66 3.68 5.68 15.65 17.11 Soybean nodule fly larvae 0.03 0.00 0.07 0.07 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00* 0.00 Soybean nodule fly pupal cases 0.33 0.33 0.30 0.37 1.03* 0.43 Colaspis larvae 0.03 0.13 0.20 0.03 0.00 0.30 Bean leaf beetle larvae 0.33 0.00 0.03 0.03 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.03 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.07 0.00 0.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.90 1.03
a/ * — Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957),
Nodule data taken from soil core samples expressed on a per hectare basis. Table 15. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion applied to the foliage.—
July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )g , , 636.79 721.66 471.85 389.48 Damaged nodules/ha (3/10 )— 35.67 55.93 9.51 21.81 % Damaged nodules/ha— 5.31 8.63 1.70 5.87 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.17 0.00 0.33 0.33 Colaspis larvae 0.00 0.17 0.00 0.00 Bean leaf beetle larvae 0.00 0.08 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.33 0.17 0.17 0.17 Unhatched bean leaf beetle eggs 0.67 0.17 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 16. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenophos and chlorpyrifos within sub-plots treated with methyl parathion applied to the foliage.—
June 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos 6 li/ Total nodules/ha (X 10 W . < 98.34 63.73 341.84 268.99 407.39 219.76 Damaged nodules/ha (g .10 )— 0.88 3.34 14.24 13.98 57.26 35.77 X Damaged nodules/ha~ 1.01 4.38 3.62 6.01 12.69 15.69 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.67 0.67 0.00 0.33 0.83 0.33 Colaspis larvae 0.00. 0.17 0.17 0.17 0.00 0.00 Bean leaf beetle larvae 1.67 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.17 1.17 0.17 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 17, Effects of soli treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and , chlorpyrifos within sub-plots treated with Bacillus thuringiensis applied to the foliage.—
July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10^)^, . 651,92. 571.58 495.46 309.41 Damaged nodules/ha )“ 51.57* 135.04 11.99* 24.02 % Damaged nodules/ha— 7.47 24.34 2.45 8.75 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.00 0.00 0.00 0.33 Colaspis larvae 0.00 0.00 0.00 0.33 Bean leaf beetle larvae 0.00 0.33 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00* 0.00 Hatched bean leaf beetle eggs 0.67 2.83 0.17 3.67 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.33
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 18. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isophenophos and . chlorpyrifos within sub-plots treated with Bacillus thuringiensis applied to the foliage.—
June 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )t v/ 113.19 66.35 271.42 265.01 367.25 316.10 Damaged nodules/ha (&/10 )— 12.03 13.78 18.22 15.32 64.54 42.23 % Damaged nodules/ha— 1.59 3.03 6.32 5.70 16.73 12.68 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 o.oo* 0.00 Soybean nodule fly pupal cases 0.50 0.17 0.00 0.33 2.00* 0.33 Colaspis larvae 0.17 0.00 0.17 0.17 0.00 1.00 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00* 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.17 0.83 3.17 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
g/ * — Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 19, Effects of soil treatments with isofenphos and chlorpyrifos on nodules and Insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with chlorpyrifos applied to the foliage.—
July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 Jt u/ 469.26 695.00 471.85 389.48 Damaged nodules/ha (?/10 )— 29.32 76.97 9*51* 21.81 % Damaged nodules/ha— 5.28 13.19 1.70 5.86 Soybean nodule fly larvae 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.17 0.50 0.33 0.33 Colaspis larvae 0.00 0.33 0.00 0.00 Bean leaf beetle larvae 0.17 0.17 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 2.33 0.17 0.17 Unhatched bean leaf beetle eggs 0.00 0.83 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957),
Nodule data taken from soil core samples expressed on a per hectare basis. Table 20. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with chlorpyrifos applied to the foliage.—
June 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 hr ,, 88.59 90.02 295.58 294.97 332.89 257.45 Damaged nodules/ha (^/10 )“ 1.31 1.94 13.03 19.65 58.60 51.23 % Damaged nodules/ha— 1.44 3.18 3.77 7.63 17.14 20.07 Soybean nodule fly larvae 0.00 0.00 0.00 0.17 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.00 0.33 0.50 0.00 0.17 0.50 Colaspis larvae 0.00 0.00 0.67 0.00 0.00 0.17 Bean leaf beetle larvae 0.00 0.00 0.17 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.33 0.00 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
a/ * — Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 21. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated .with soil applications of isofenphos and chlorpyrifos within the untreated sub-plots.—
July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules /ha (X 10 )-r 690.27* 543.34 501.30 363.60 Damaged nodules/ha (j£/10 )— 22.98. 98.55 19.35* 30.19 % Damaged nodules/ha— 3.37 21.67 3.28 8.57 Soybean nodule fly larvae 0.00* 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.17 0.00 0.00 Soybean nodule fly pupal cases 0.17 0.50 0.33 1.67 Colaspis larvae 0.00 0.00 0.00 0.17 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00. 0.00 Hatched bean leaf beetle eggs 0.17 0.50 0.67 2.33 Unhatched bean leaf beetle eggs 0.50 1.00 0.17 0.17
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 22. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated .with soil applications of isofenphos and chlorpyrifos within the untreated sub-plots.—
June 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )*r . . 94.20 92.56 282.71 276.92 366.16 342.25 Damaged nodules/ha )“ 0.22 0.18 6.55 14.27 78.17 57.66 % Damaged nodules/ha— 0.55* 1.78 2.46 5.58 22.59 17.38 Soybean nodule fly larvae 0.17 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00* 0.00 Soybean nodule fly pupal cases 0.00 0.33 0.50 0.33 2.00 0.50 Colaspis larvae 0.00 0.17 0.17 0.00 0.00 0.33 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.17 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0,00 1.83 1.67 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 . 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 23. Effects of soli treatments with Isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Main plots treated with soil applications of Isofenphos and chlorpyrifos within sub-plots treated with methyl parathion plus permethrin applied to the foliage.—
July 19 August 23
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )■? . , 504.61 599.36 539.34 409.12 Damaged nodules/ha CX/10 )— 34.31 77.45 15.63 26.44 % Damaged nodules/ha— 6.24 12.37 2 -99* 6.67 Soybean nodule fly larvae 0.00 0.00 0.00 0.17 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.17 0.67 0.33 0.33 Colaspis larvae o.ooA 0.00 0.00 0.00 Bean leaf beetle larvae 0.00 0.50 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.33 0.00 0.67 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957). b/ Nodule data taken from soil core samples expressed on a per hectare basis. Table 24. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1983: Main plots treated with soil applications of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion plus permethrin applied to the foliage
June 20 July 28 September 9
Parameter Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos Isofenphos Chlorpyrifos
Total nodules/ha (X 10 )-r , , 92.05 126.17 380.79 289.22 407.42 316.92 Damaged nodules/ha (|£/10 )— 0.98 2.01 7.11 11.48 34.06* 63.88 % Damaged nodules/ha— 1.48 0.96 2.24 3.46 9.08 19.73 Soybean nodule fly larvae 0.00 0.00 0.33 0.17 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.50 0.17 0.17 1.00 0.17 0.50 Colaspis larvae 0.00 0.33 0.00 0.00 0.00 0.00 Bean leaf beetle larvae 0.00 0.00 0.00 0.00 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.33 0.17 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
3./ * — Parameter means followed by are !significantly different (P<0.05) than the other treatment mean in the row for each date as determined by orthogonal comparisons (Cochran and Cox 1957).
Nodule data taken from soil core samples expressed on a per hectare basis. Table 25. Effects of soil treatments with isofenphos and chlorpyrifos on nodules and insect populations, Hamburg, Louisiana, 1982: Comparison between 51 cm and 76 cm row spacing.—
•
June 24 July 19 August 23
Parameter 51 cm 76 cm 51 cm 76 cm 51 cm 76 cm
Total nodules/ha (X 10 )-g- ^ , 303.14* 192.51 744.68 450.05 527.40* 325.24 Damaged nodules/ha (X ,10 )— 28.69 14.27 76.95 63.68 31.84 18.92 % Damaged nodules/ha— 10.35 8.19 10.94 14.13 6.71 6.34 Soybean nodule fly larvae 0.17 0.33 0.04 0.02 0.00 0.02 Soybean nodule fly pupae 0.11 0.22 0.02 0.00 0.00 0.04 Soybean nodule fly pupal cases 0.05 0.44 0.40 0.29 1.07 0.78 Colaspis larvae 0.00 0.00 0.09 0.11 0.06 0.04 Bean leaf beetle larvae 0.00 0.00 0.22 0.18 0.00 0.02 Bean leaf beetle pupae 0.00 0.00 0.00 0.00 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.60 0.78 0.96 1.00 Unhatched bean leaf beetle eggs 0.05 0.00 0.29 0.40 0.09 0.18
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date.
Nodule data taken from soil core samples expressed on a per hectare basis. Table 26. Effects of soil treatments with isofenophos and chlorpyrifos on nodules and.insect populations, Hamburg, Louisiana, 1983: Comparison between 51 cm and 76 cm row spacing.—
June 20 July 19 September 9
Parameter 51 cm 76 cm 51 cm 76 cm 51 cm 7 6 cm
Total nodules/ha (X 10 . W , . 110.21 79.88 350.52 226.08 412.18* 266.13 Damaged nodules/ha (X/10 )~ 1.25 1.96 14.32 11.20 66.83 44.85 % Damaged nodules/ha— 1.43 2.46 4.23 4.96 16.32 16.90 Soybean nodule fly larvae 0.02 0.00 0.07 0.07 0.00 0.00 Soybean nodule fly pupae 0.00 0.00 0.00 0.00 0.00 0.00 Soybean nodule fly pupal cases 0.27 0.31 0.29 0.38 0.76 0.58 Colaspis larvae 0.16 0.13 0.08 0.20 0.04 0.17 Bean leaf beetle larvae 0.02 0.22 0.04 0.02 0.00 0.00 Bean leaf beetle pupae 0.00 0.00 0.02 0.02 0.00 0.00 Hatched bean leaf beetle eggs 0.00 0.00 0.02 0.04 1.00 1.60 Unhatched bean leaf beetle eggs 0.00 0.00 0.00 0.00 0.00 0.00
Parameter means followed by are significantly different (P<0.05) than the other treatment mean in the row for each date.
Nodule data taken from soil core samples expressed on a per hectare basis. the distribution of soil pests sampled in the experiment except for the
bean leaf beetle. Kogan et al. (1974) found that BLB adults followed a negative binomial distribution; therefore, the damage data shown may be
slightly overestimated.
To summarize the results from the soil sample analyses for 1982 and
1983, the data demonstrate that soil treatments, in 1982, were effective in establishing differential amounts of nodule damage. However, results from the 1983 season were erratic and showed no trends. As stated above, environmental conditions immediately following planting/soil treatment application were unfavorable for activity of the soil insecticides. Heavy rainfall accumulated to 31 cm for a period of ten days after planting; therefore, the majority, if not all, of the soil
Insecticide was leached from the soil and was unavailable for activity against soil pests. Because of this, the following summary will be based on soil sample analyses data for the 1982 growing season only.
Orthogonal comparisons between the combined soil insecticide treatments vs. the untreated check show a trend toward less nodule damage on plots treated with soil Insecticides (Tables 1 and 2).
Analyses of the soil insecticides vs. the control, within each of the five foliar treatments show that manipulation of the above-ground soil pests influenced the degree of damage. For example, on the July 19 sample, plots treated with soil insecticides and sprayed weekly with methyl parathion (SBL), chlorpyrifos (TCAH), or methyl paration plus permethrin (no insects) had a lower average percentage of damaged nodules/ha (8.50% combined) than when sprayed weekly with B. thuringiensis (non-lepidopterous insects) or the untreated control (all insect pests) (14.21% combined). Thus, when above-ground soil pests 54
were allowed to develop unabated throughout the season, nodule damage was greater than when soil pests were controlled. Lambert (1981)
reported less nodule damage due to BLB and SNF In plots treated with
Isofenphos compared to the untreated check. Similarly, Layton (1983) used cages to contain various population levels of BLB and found apparent differences in nodule damage for plots devoid of BLB compared to those having BLB populations. He also found a significant reduction in the nitrogen fixing capacity of infested plants due to nodule damage.
In the studies conducted in 1982 and 1983, near Hamburg, certain soil insect parameters were found to be significant, although sometimes by only small numerical differences. Distinct trends were shown for fewer
BLB larvae and eggs and COL larvae in soil insecticide-treated plots when foliage was sprayed with B. thuringiensis or left untreated.
After establishing that soil treatments were effective against soil pests when compared to the check, analyses revealed differences between
Isofenphos and chlorpyrifos. Treatments with isofenphos resulted in less nodule damage by soil pests than treatment with chlorpyrifos (Table i3).
When comparing Isofenphos and chlorpyrifos within the foliar treatments, virtually no differences were seen in the parameters measured when methyl parathion, chlorpyrifos or methyl paration plus permethrin was applied to the foliage. Applications with these chemicals controlled above-ground soil pests throughout the season, thus reducing their impact. In contrast, foliar applications of B. thuringiensis (non-lepidopterous Insects) and the untreated control allowed populations of soil pests above-ground to develop uncontrolled which in turn influenced nodule damage. Significantly higher (P< 0.05) 55
amounts of nodule damage were seen following treatments of _B.
thuringiensis and the untreated control (Tables 17 and 21). In
addition, a trend was seen for more bean leaf beetle eggs In these same
treatments for soil treatments of chlorpyrifos.
Row spacing had no effect on populations of the soil pests (Tables
25 and 26). However, differences were seen in the parameters for nodule
data. More plants are present on a hectare of soybean planted on 51 cm
rows as compared to those on 76 cm rows. Because of this, more
nodules/ha would be expected to be found on narrow rows. Our data show
this to be the case. In addition, the data reflect that more damaged
nodules per hectare were found in 51 cm row spacings; however, more
healthy nodules were left. The percentage of damaged nodules per
hectare, however, was equal for both row spacings.
II. POPULATIONS OF ABOVE-GROUND INSECTS
A. Row Spacing Effects. Insect populations above-ground were
analyzed by date and over the entire season. Before seasonal analyses
were performed on each insect species, dates on which the insect was
nonexistent (determined by the weekly sweep samples) were deleted. The
number of dates used for analyses (18 total dates sampled in 1982) were
as follows: 15 dates - BLB, TCAH, GEO, LEB, and NAB; 12 dates - BCB; 9
dates - COL; 8 dates - SNF; 5 dates - SBL; and 4 dates - SGSB. Of the
17 total dates sampled in 1983, the following were the number of dates
used for seasonal analyses: 17 dates - BLB, TCAH, GEO, LEB, NAB, AND
COL; 15 dates - SNF; 14 dates - SGSB; 12 dates - BCB; and 11 dates SBL.
Tables 27 and 28 summarize the effects of row spacing on seasonal means of above-ground insects. Soybean looper populations were 56
Table 27. Seasonal means for Insect populations following selective insecticide treatments: 76 cm row spacing vs. 51 cm, 1982.
a / Mean Number Per 50 Sweeps — Insect 76 cm rows 51 cm rows * Soybean looper 7.22 8.31 k Threecomered alfalfa hopper 8.31 10.21
Southern green stink bug 1.10 0.93 * Banded cucumber beetle 1.43 1.31 * Bean leaf beetle 3.11 2.63
Colaspis louisianae 2.77 2.97
Soybean nodule fly 3.31 3.23
Geocoris spp. 1.55 1.46 * Lebla analls 0.74 0.44
Nabls spp. 0.49 0.46
/ k “ Means followed by are significantly different (P<0.05) than the other treatment mean in a row. 57
Table 28. Seasonal means for Insect populations following selective insecticide treatments: 76 cm row spacing vs. 51 cm, 1983.
a / Mean Number Per 50 Sweeps — Insect 76 cm rows 51 cm rows * Soybean looper 1.74 2.06 * Threecornered alfalfa hopper 10.94 11.96 A Southern green stink bug 0.52 0.74 * Banded cucumber beetle 3.36 3.11 * Bean leaf beetle 3.65 3.35
Colaspis loulsianae 3.34 3.31
Soybean nodule fly 0.75 0.62 A Geocoris spp. 0.73 0.86
Lebla analis 1.06 1.09
Nabls spp. 0.61 0.59 a / * — Means followed by are significantly different (P<0.05) than the other treatment mean in a row. 58
significantly different between row spacings (P< 0.05) for both years of
the study. Although a trend showed higher numbers of SBL on narrow row
spacings, the differences were too small to draw conclusions. Larval
SBL, in 1982, were significantly (P< 0.05) higher in 51 cm rows for one
date and in 1983 for 3 dates; most dates corresponded to the time of low
populations except for one date in 1983 when SBL populations peaked.
Sprenkel et al. (1979) observed higher populations of SBL in narrow row
soybeans than in wider row soybeans; however, our results were more
similar to those of Buschman et. al (1981) who found significantly
higher SBL on narrow rows but the differences were too small to test
effectively.
Significantly (P< 0.05) higher numbers of TCAH were sampled from
narrow rows than wide rows in both years. In 1982, when analyzed by
date, TCAH were significantly (P< 0.05) higher on 51 cm rows on 7 of the
15 dates analyzed; however, in 1983, populations differed significantly
on only one date. Although the differences were only 1-2 TCAH per 50
sweeps, significant (P< 0.05) differences occurring on half of the dates
suggest a strong trend for higher numbers of TCAH on 51 cm rows than on
76 cm rows.
Banded cucumber beetle populations were observed to occur in higher numbers on 76 cm rows than narrow rows. When compared by date,
significantly (P< 0.05) higher numbers of BCB were found on 76 cm rows for 1 date in 1982 and 3 dates in 1983.
Similar results were found in both years for bean leaf beetle populations. Significantly (P< 0.05) higher numbers of BLB were found on 76 cm rows than on 51 cm rows. Analyses by date showed this trend to be significant (P< 0.05) on 3 and 2 dates for 1982 and 1983, 59
respectively. Although the numbers of BLB and BCB were different between the wide and narrow row spacings, the differences were again
small, thus making definite conclusions tenuous.
Differences were found for other insects but these differences were not consistent for both years. In 1982, the predaceous carabid. Lebia analis, was significantly (P< 0.05) higher on wide rows than on narrow
rows. Three out of 15 dates analyzed were significant (P< 0.05) when analyzed by date. Differences in seasonal means of LEB between row spacings were very small thus, these differences may not be large enough to justify conclusions being drawn. In 1983, significantly (P< 0.05) higher populations of southern green stink bug and Geocoris spp. were found on 51 cm rows. Analyses by date showed SGSB and GEO populations to be higher on the narrow rows on 1 date. Troxclair and Boethel (1984) reported seasonal SGSB populations to be higher on narrow (51 cm) row spacings in Louisiana soybean.
In summary, the response of insects to row spacing showed a consistent trend of more SBL and TCAH on 51 cm rows and more BCB and BLB on 76 cm rows, for both years. Populations of GEO and SGSB were higher on 51 cm rows in 1982, whereas LEB adults prefered the wider rows in
1983. Of the insects exhibiting a response to row spacing, the TCAH showed the strongest trend for narrow rows because of the larger number of dates populations were found to be significantly higher (P< 0.05) on
51 cm rows compared to 76 cm rows and from results from seasonal analyses.
B. Soil Treatment Effects. Orthogonal comparisons between the isofenphos and chlorpyrifos soil treatments vs. the untreated control are shown in Tables 29 and 30. These tables compare seasonal means for 60
Table 29. Seasonal means for insect populations following selective insecticide treatments: Isofenphos and chlorpyrifos soil treatment vs. control, 1982.
a/ Mean Number Per 50 Sweeps — Insect Isofenphos and chlorpyrifos Control
Soybean looper 7.86 7.57
Threecomered alfalfa hopper 9.18 9.41
Southern green stink bug 0.88 1.27
Banded cucumber beetle 1.33 1.44 * Bean leaf beetle 2.51 3.58 * Colaspis louisianae 2.56 3.50
Soybean nodule fly 4.53 3.64
Geocoris spp. 1.51 1.51 * Lebia analis 0.52 0.72
Nabis spp. 0.49 0.45
a/ * — Means followed by are significantly different (P<0.05) than the other treatment mean in a row as determined by orthogonal comparisons (Cochran and Cox 1957). 61
Table 30. Seasonal means for Insect populations following selective insecticide treatments: Isofenphos and chlorpyrifos soil treatment vs. control, 1983.
HP fl/ Mean Number Per 50 Sweeps — Insect Isofenphos and chlorpyrifos Control
Soybean looper 1.98 1.74
Threecornered alfalfa hopper 11.31 11.31 * Southern green stink bug 0.57 0.75
Banded cucumber beetle 3.33 3.06 * Bean leaf beetle 3.00 4.49 * Colaspls louisianae 3.17 3.63
Soybean nodule fly 0.67 0.72
Geocorls spp. 0.81 0.88
Lebia analls 0.98 1.27 * Nabis spp. 0.57 0.66
/ ^ — Means followed by are significantly different (P<0.05) than the other treatment mean in a row as determined by orthogonal comparisons (Cochran and Cox 1957). 62 above-ground insects in soil insecticide-treated plots with means in the untreated plots. These comparisons reflect the efficacy of the activity of soil insecticides on the Insects.
In 1982, bean leaf beetle, Colaspis beetle, and Lebia seasonal populations were significantly (P< 0.05) lower on plots treated with soil insecticides (to control soil pests) compared to untreated plots in which soil pests were allowed to develop uncontrolled. When analyzed by date, significantly (P< 0.05) fewer BLB and COL adults were found for soil insecticide-treated plots on 2 and 3 of 17 dates analyzed, respectively. Lower numbers of BLB and COL above-ground were reflected by lower nodule damage and numbers of these soil pests below-ground.
(Table 11). As stated above, soil sample data for 1983 was questionable due to unfavorable weather conditions resulting in the ineffectiveness of soil insecticides.
Tables 31 and 32 show results of orthogonal comparisons between isofenphos and chlorpyrifos soil treatments in response to their effect on above-ground insects. As shown in Table 31, four insect species had significantly fewer numbers in isofenphos-treated plots than plots treated with chlorpyrifos. Bean leaf beetle and Colaspis beetle populations were lower throughout the season on isofenphos plots.
Analyses by date showed this trend to be significant (P< 0.05) on 6 dates for BLB and 3 dates for COL (all of which occurred early in the season, shortly after each generation appeared). These results demonstrated that isofenphos not only had a greater effect on early generations of soil pests but also had systemic activity against above-ground populations of early season BLB and COL. Isofenphos has been reported to have systemic activity against BLB adults (Newsom 1980, 63
Table 31. Seasonal means for insect populations following selective insecticide treatments: Isofenphos soil treatment vs. chlorpyrifos, 1982.
3./ Mean Number Per 50 Sweeps — Insect Isofenphos Chlorpyrifos
Soybean looper 7.87 7.86
Threecomered alfalfa hopper 9.51 8.86
Southern green stink bug 0.80 0.96
Banded cucumber beetle 1.20 1.47 * Bean leaf beetle 1.73 3.29 * Colaspis louisianae 1.86 3.27 * Soybean nodule fly 2.89 3.28
Geocoris spp. 1.45 1.55 * Lebia analis 0.29 0.76
Nabis spp. 0.48 0.49
a/ * — Means followed by are significantly different (P<0.05) than the other treatment mean in a row as determined by orthogonal comparisons (Cochran and Cox 1957). 64
Table 32. Seasonal means for Insect populations following selective Insecticide treatments: Isofenphos soil treatment vs. chlorpyrifos, 1983.
3/ Mean Number Per 50 Sweeps — Insect Isofenphos Chlorpyrifos
Soybean looper 1.99 1.98
Threecornered alfalfa hopper 11.51 11.11 A Southern green stink bug 0.66 0.48
Banded cucumber beetle 3.04 3.62
Bean leaf beetle 2.60 3.40
Colaspis louisianae 3.02 3.32
Soybean nodule fly 0.72 0.62
Geocoris spp. 0.70 0.80
Lebia analis 0.91 1.06
Nabls spp. 0.56 0.59
a/ * , — Means followed by are significantly different (P<0.05) than the other treatment mean in a row as determined by orthogonal comparisons (Cochran and Cox 1957). 65
unpublished data). Populations of soybean nodule fly and Lebia spp. were significantly (P< 0.05) lower in isofenphos plots than in
chlorpyrifos plots.
C. Foliar Treatment Effects. Seasonal analyses for each insect
are given in Tables 33-52. Figures 1-20 illustrate insect population means by sampling date. Applications of selective foliar insecticides were successful in regulating populations of individual species and
complexes of insect species at desired levels.
1. Bean leaf beetle - Seasonal means for bean leaf beetles are given in Tables 33 and 34. Weekly treatments of B. thuringiensis and
the untreated check were successful in allowing development of
significantly (P< 0.05) higher populations of BLB than in other plots in both years. When analyzed by date, significantly higher numbers of BLB developed on plots treated with B.t. and the untreated check than in other plots for 15 of the 18 dates sampled. Bean leaf beetle population fluctuations for the untreated check and B. thuringiensis treatments peaked at 17 and 20 per 50 sweeps, respectively in 1982 and 19 and 15 per 50 sweeps, respectively in 1983 (Figs. 1 and 2). The economic threshold for BLB in Louisiana is 100 per 50 sweeps (Tynes et al. 1984); therefore, peak populations of BLB in 1982 and 1983 were ca. 18% and
17%, respectively, of the economic threshold (ET). The other foliar treatments were effective in controlling the BLB.
2. Colaspis beetle - Bacillus thuringiensis (B.t.) and the untreated check were successful in allowing development of significantly
(P< 0.05) higher populations of Colaspis beetles than in other treatments throughout the season for both years (Tables 35 and 36). The other foliar treatments were effective in controlling the COL. The B.t. 66
Table 33. Seasonal means for bean leaf beetle populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1982.
a / Foliar Treatment Mean Number Per 50 Sweeps —
Bacillus thuringiensis —^ 4.88 a c/ Control — 4.43 a A l Methyl parathion — 2.89 b e/ Chlorpyrifos — 1.20 c
Methyl parathion plus permethrin — 0.94 d a/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 2 « non-lepidopterous insect pests c / — Complex 4 = all insect pests A l — Complex 1 ** soybean looper e/ — Complex 3 “ threecornered alfalfa hopper f ! — Complex 5 = no Insects 67
Table 34. Seasonal means for bean leaf beetle populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983.
a/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 5.50 a c/ Bacillus thuringiensis — 5.08 a
Methyl parathion — 3.70 b g/ Chlorpyrifos — 1.95 c
Methyl parathion plus permethrin — ^ 1.27 d
— Means followed by the same letter are not significantly different (P<0.05; Tukey’s studentlzed range test [Steel and Torrle (1980)]).
— ^ Complex 4 = all insect pests c/ — Complex 2 = non-lepidopterous insect pests
— Complex 1 *= soybean looper e/ — Complex 3 = threecornered alfalfa hopper f / — Complex 5 = no insects 68
A \
. A / | , v \ JULY 1 MJtUtT loCT
Figure 1 Mean population levels for bean leaf beetle following selective Insecticide applications. 19B2. Legend! Hethyl parathion *------* ; Bacillus thuringiensis o 0 [ Chlorpyrifos D " — U i Untreated check A— A ; Methyl parathion plus peraethrln . 69
JUKI I JULY I JkUtUST I UFT
Figure 2. Kean population lavela for bean leaf beetle following aelective Inaectldde application^ 1963. Legend: Hethyl parathion *------* ; Badllua thurlnalenaia o ; Chlorpyrlfoa D — -- 0 {""Untreated check i • t s Hethyl parathion plua pemethrln * ...... * • 70
Table 35. Seasonal means for Colaspis loulsianae populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1982.
g/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 5.99 a c/ Bacillus thuringiensis — 5.37 a
Methyl parathion — ^ 2.35 b g/ Chlorpyrifos — 0.34 c f/ Methyl parathion plus permethrin — 0.32 c
Q./ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]). V / — Complex 4 = all insect pests c/ — Complex 2 = non-lepidopterous insect pests
— Complex 1 = soybean looper g/ — Complex 3 = threecornered alfalfa hopper f / — Complex 5 = no insects 71
Table 36. Seasonal means for Colaspis louislanae populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983.
a l Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 5.61 a c / Bacillus thuringiensis — 5.47 a
Methyl parathion — 3.96 b e/ Methyl parathion plus permethrin — 0.79 c f / Chlorpyrifos — 0.79 c a/ — Means followed by the same letter are not significantly different (P<0.05; Tukey’s studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 4 » all Insect pests c/ — Complex 2 = non-lepidopterous insect pests
— Complex 1 = soybean looper e/ — Complex 5 = no insects
— Complex 3 *= threecornered alfalfa hopper 72 treatment and untreated check were utilized to manipulate COL populations at higher levels than in other treatments. When analyzed by
date, these two treatments maintained significantly (P< 0.05) higher numbers of COL on 14 and 7 dates than other treatments in 1982 and 1983, respectively. Significantly (P< 0.05) higher numbers of COL were maintained in B.t. and check plots than plots having other treatments throughout the season. Methyl parathion treatments demonstrated intermediate control over adults (Figures 3 and 4). From the graphs, it appears that the COL had one generation each year with adults from the overwintering population emerging early in the season. Rolston and
Rouse (1965) observed that the grape colaspis Colaspis brunnea (F.), not
JC. flavida Say as had been previously thought, had one complete generation a year in Arkansas and, in favorable situations, a large, partial second generation. Maximum population peaks for COL in the study for 1982 and 1983 were ca. 18 and 25 per 50 sweeps, respectively.
Presently, no economic injury level exists for the colaspis beetle.
3. Soybean nodule fly - Seasonal means for soybean nodule fly are summarized in Tables 37 and 38. In 1982, the two foliar treatments used to maintain the non-lepidopterous Insects and all insect species showed significantly higher populations of SNF; however, this difference was very small numerically as shown in Figures 5 and 6. Analysis by date showed the B.t. treatment and untreated check to be significantly different (P< 0.05) from other treatments on only 2 dates. Thus, it is concluded that foliar treatments were unsuccessful in manipulating SNF populations in 1982. Similarly, foliar treatments were unsuccessful at controlling SNF in 1983 (Table 38);however, populations were very low
(ca. 2.5 per 50 sweeps, maximum). Thus, impact of SNF in the 1983 73
21
Figure 3. Mean population levels for Colaspis loulslanae following selective Insecticide applications! 1982! Legend: Hethyl parathion ; Bacillus thuringiensis o------o ; Chlorpyrifos O— — D s Uncreated cheek i------d ; Methyl parathion plus petmthrln *!..!.!* . s Mft m K c w ■ ft3 PC
2!
4
3
2
1 /\
Figure A. Heen population levela for Colaapia loulalanae following selective Insecticide applications, 1983. legend: Hethyl parathion *------* ; Bacillus thurlnalenala o------o ; Chlorpyrifos □ --- D ; Untreated check A------d > Hethyl parathion plus permethrln * > 75
Table 37. Seasonal means for soybean nodule fly populations, across all row spacings and soil treatments, In response to selective insecticide applications, 1982,
Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 4.19 a c/ Bacillus thuringiensis — 3.73 a
Methyl parathion — 3.15 b £ / Methyl parathion plus permethrin — 2.90 be
Chlorpyrifos — ^ 2.38 c a/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 4 = all insect pests c / — Complex 2 = non-lepidopterous insect pests
— Complex 1 = soybean looper c/ — Complex 5 = no insects f / — Complex 3 = threecornered alfalfa hopper 76
Table 38. Seasonal means for soybean nodule fly populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983.
a / Foliar Treatment Mean Number Per 50 Sweeps —
Chlorpyrifos — ^ 0.80 a c/ Bacillus thuringiensis — 0.80 a
Control —^ 0.70 a e/ Methyl parathion — 0.58 a
Methyl parathion plus permethrin — 0.56 a
— Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 3 = threecornered alfalfa hopper c/ — Complex 2 = non-lepidopterous insect pests
— Complex 4 = all insect pests g / — Complex 1 = soybean looper f / — Complex 5 - no insects 77
15
IS C b M► 8 e bbj
Bt
0 15 IE
9 6 3 0 AUIV1T
Figure S. Hein population lovcle for aoybeen nodule fly following eilective Ineectldde appllcatloni, 1 9 8 ! . Legend: Hethyl perethion * * ; B e d Hu e thurlnglenele o o ; Chlorpyrlfoa d ~ 'D ; tint rented check A------6 ; Hethyl parathion plue penethrln * * . 78
0 9
0.3
1.5
1.2
0.9
0.6
0.3
£ w m» 8 1.5 fi*■ 4 at mw 9m 0.5 ar t4 1.6
0.6
0.2
1.8
1.2 0.9
JULY u r r
Figure 6 Keen population level* for soybean nodule fly following selective Insecticide applications, 1983. Legeng: Hethyl parathion * ■* ; Bacillus thurltiflleaelB o------o ; Chlorpyrifos □---— □ ; Untreated check A------A ; Methyl parathion plus pernethrln *•««••»* . 79
experiment was considered to be of no significance.
4. Banded cucumber beetle - Tables 39 and 40 summarize the
seasonal means for banded cucumber beetle. Populations of BCB were
achieved at relatively high levels when B.t. was used and in the
untreated check. However, as seen in both years of the study, methyl
parathion (used to manipulate SBL) was ineffective against BCB. This
resulted in population levels which were similar to those where
non-lepidopterous insects and all insects species were maintained
(Figures 7 and 8). In 1982, BCB populations were relatively low and
reached peak populations of ca. 7 per 50 sweeps. Population levels were
slightly higher in 1983 where they peaked at ca. 11 per 50 sweeps. The
ET for BCB is 200 adults per 50 sweeps. Thus, the populations
experienced in our study were 3.5% of the ET in 1982 and 5.5% of the ET
in 1983. Although BCB was not controlled in plots maintaining SBL, the
small populations detected would not have had any impact on confounding
the SBL data.
5. Southern green stink bug - Seasonal populations of southern
green stink bug were maintained at significantly (P< 0.05) higher levels
following B.t. treatments and the untreated check than when treated with
other foliar treatments (Tables 41 and 42). Thus, B.t.
(non-lepidopterous insects) and the untreated check (all insects) were
successful in allowing SGSB populations to increase to relatively high
levels. The other foliar treatments were so effective in controlling
the SGSB that maximum population levels for 1982 and 1983 were 1.25 and
0.6 stink bugs per 50 sweeps, respectively (Figures 9 and 10).
Populations of SGSB peaked at ca. 6 stink bugs per 50 sweeps in 1982 and
ca. 5 per 50 sweeps in 1983. Time of peak populations occurred in late 80
Table 39. Seasonal means for banded cucumber beetle populations, across all row spacings and soli treatments, in response to selective Insecticide applications, 1982.
a l Foliar Treatment Mean Number Per 50 Sweeps — L / Methyl parathion — 2.20 a c / Control — 1.77 a J / Bacillus thuringiensis — 1.79 a g/ Methyl parathion plus permethrin — 0.70 b f / Chlorpyrifos — 0.40 b
a/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 1 = soybean looper c l — Complex 4 = all insect pests Al — Complex 2 = non-lepidopterous insect pests g/ — Complex 5 = no Insects
— Complex 3 = threecornered alfalfa hopper 81
Table 40. Seasonal means for banded cucumber beetle populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983.
Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 4.85 a c/ Methyl parathion — 4.37 a
Bacillus thuringiensis — 3.95 a e/ Chlorpyrifos — 1.81 b f / Methyl parathion plus permethrin — 1.23 b
Sif — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 4 = all Insect pests c/ — Complex 1 = soybean looper
— Complex 2 = non-lepidopterous insect pests e/ — Complex 3 m threecornered alfalfa hopper f / — Complex 5 = no Insects 82
e
M ft 1.2 Wfcl m*
■ ft.M 0.6 MK a■ a X
8
1.5
0.5
AUBUST lEfT
Figure 7. Mean population levels for banded cucuaber beetle following selective Insecticide applications, 1982. Legend: Methyl parathlon *----- * ; Bacillus thurlnglenaia o— — o ; Chlorpyrlfos Q 0 ; Untreated check 6------0 » Methyl parathlon plus penaethrln * ..... * . 83
Figure 6. Mean population lavela for banded cucuaber beetle • following selective Insecticide applications, 19B3. Legend: Methyl parathlon *------* ; Bacillus thurlntlensla o------o ; Chlorpyrlfos □---—D Untreated check Methyl parathlon plus pernethrln 84
Table 41. Seasonal means for southern green stink bug populations, across all row spacings and soil treatments, in response to selective Insecticide applications, 1982.
a/ Foliar Treatment Mean Number Per 50 Sweeps — b / Bacillus thuringiensis — 2.38 a c / Control — 2.25 a
Methyl parathlon plus permethrin — 0.19 b e/ Chlorpyrifos — 0.12 b
Methyl parathlon — 0.10 b
— Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 2 = non-lepidopterous Insect pests c / — Complex 4 - all insect pests d / — Complex 5 * no insects e/ — Complex 3 = threecornered alfalfa hopper
— Complex 1 = soybean looper 85
Table 42. Seasonal means for southern green stink bug populations, across all row spacings and soil treatments, In response to selective Insecticide applications, 1983,
a/ Foliar Treatment______Mean Number Per 50 Sweeps —
Control — ^ 1.36 a c/ Bacillus thuringiensis — 1,12 b
Chlorpyrifos —^ 0.33 c e/ Methyl parathlon— 0.19 c f/ Methyl parathlon plus permethrin — 0,16 c b J Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]). b/ Complex 4 = all insect pests c/ Complex 2 = non-lepidopterous insect pests
Complex 3 = threecomered alfalfa hopper e/ Complex 1 = soybean looper
f/ Complex 5 = no insects 86
G S 4 3 2 1 0 r I MH# «t• 3 0.6 ft.E u fe3
1
0 .B
0.6
0.2
1.5
0.5
Figure 9. Kean population leveln for aouthem green atlnk bug following eelectlvc lnaectlclde applications, 1982. Legend: Methyl parathlon * * i Baclllua thurlnglenala o ■ o ; C h l o r p y r l f o a D -- □ ; Uncreated check ft ■ i ; Hethyl parathlon plua panethrln * ..... * . 6
5
4 3
1 0 1 i m * 0.6
K 0.4 M m *5 DC
0.7 0.6 0.5 0.4 0.3
0.3
\a . . r v JULY I AUGUST KPT
Figure 10, Mean population levels for southern green stink bug following selective Insecticide applications* 1963* Legend: Methyl parathlon * * ; Bacillus thurlnglenals o o ; Chlorpyrlfoa 0 □ ; Untreated check A— A ; Methyl parathlon plus peraethrln *••••■•* » 88
September (R6 developmental stage) with the greatest increase occurring
earlier in the month. These results are in agreement with findings of
Shumann and Todd (1982) who reported that SGSB peak oviposition occurred in R4 soybean, had the greatest increase in populations during R5 and peaked in population in R6. The economic threshold for SGSB in
Louisiana is 18 stink bugs per 50 sweeps; therefore, populations reached a maximum of ca. 33% of the ET in both years for treatments in which high populations were maintained for SGSB.
6. Soybean looper - Foliar treatments of methyl parathion allowed for the maintenance of relatively high soybean looper populations. In
1982, significantly higher populations of SBL were successfully maintained throughout the season following applications of methyl parathlon than in other treatments (Table 43). Populations began to
Increase in mid-August and peaked in late August for plots treated with methyl parathion (Figure 11). Several researchers have studied the effects of methyl parathion on soybean pests. Shepard et al. (1977) reported that the removal of natural biotic agents (Nabis spp., Geocoris spp., and spiders) in soybean by treatment with methyl parathion and methomyl caused resurgence of green cloverworm, Heliothis spp., soybean looper, velvetbean caterpillar, and mexican bean beetle. Similarly,
Livingston et al. (1978) found a resurgence in soybean looper populations following treatments of methyl parathion with various fungicides. They noted that populations of predators were lower in treated plots compared to the untreated check. Morrison et al. (1979) reported that numbers of Orius lnsidiosus (Say), Geocoris punctipes
(Say) and Mabis spp. were inversely related to corn earworm numbers following methyl parathion treatments on soybean. As shown in Figure 89
Table 43. Seasonal means for soybean looper populations, across all row spaclngs and soil treatments, In response to selective insecticide applications, 1982.
o / Foliar Treatment Mean Number Per 50 Sweeps —
Methyl parathion —^ 17.00 a c / Control — 9.50 b
Bacillus thuringiensis — 7.59 c e/ Chlorpyrlfos — 4.02 d
Methyl parathion plus permethrin — 0.74 e fl/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 1 = soybean looper c/ — Complex 4 = all insect pests
— Complex 2 = non-lepidopterous insect pests g/ — Complex 3 = threecornered alfalfa hopper f / — Complex 5 = no insects 90
30
c IB wm m» s
it hi ■m K.a
3
Figure 11. Mean population levels for eoybean looper folloving ■elective Insecticide applications, 19B2. Legend: Methyl perethlon *------* ; Beclllue thuringianele o ■■■ ■■■■0 ; Chlorpyrlfoi D □ ; Untreated check t------1 ; Methyl perethlon plum peraethrln *•<••••* • 91
11, peak populations of SBL on methyl parathion-treated plots were ca.
55 per 50 sweeps (73% of the economic threshold; ET = 75 per 50 sweeps).
These peak populations were almost twice the natural peak populations found in the untreated check (40% of the ET). This finding corresponds with previous reports that SBL counts in methyl parathion-treated plots always exceeded those from untreated plots by as much as 100% (Shepard et al. 1977). Peak populations of SBL, in plots established with SBL only, occurred at a period slightly ahead of peak populations of SBL in the untreated check, thus reflecting the influence of beneficial insect species. B. thuringiensis treatments did not totally control SBL and allowed populations to reach ca. 29% of the ET.
In 1983, populations of SBL achieved significantly (P< 0.05) higher levels in plots treated with methyl parathion than in other plots; however, these populations were lower than in 1982 with the peak populations reaching 14 per 50 sweeps (ca. 19% ET) (Table 44, Figure
12).
7. Threecornered alfalfa hopper - Seasonal means for threecornered alfalfa hopper are shown in Tables 45 and 46. Treatments with chlorpyrifos were successful in establishing significantly (P< 0.05) higher populations of TCAH than in all other treatments. Overall population levels were considerably higher in 1983 than in 1982 (Figures
13 and 14). Peak numbers of TCAH reached 25 per 50 sweeps (50% ET) in
1982 whereas 1982 populations peaked at ca. 90 per 50 sweeps (180% or
1.8 times the ET) when treated with chlorpyrifos. When analyzed by date, these populations were significantly higher on 10 dates in both years of the study. Utilization of chlorpyrifos to establish higher population levels of TCAH has proven to be successful (Layton 1977, 92
Table 44. Seasonal means for soybean looper populations, across all row spacings and soil treatments, in response to selective insecticide applications, 1983.
a / Foliar Treatment Mean Number Per 50 Sweeps —
Methyl parathlon — ^ 3.44 a c/ Control — 2.37 b J / Bacillus thuringiensis — 1.93 b g/ Chlorpyrifos — 1.42 c f/ Methyl parathion plus permethrln — 0.34 d
— Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 1 ** soybean looper c j — Complex 4 = all Insect pests
J / — Complex 2 *= non-lepidopterous insect pests g/ — Complex 3 *= threecornered alfalfa hopper f / — Complex 5 *= no insects 93
B
5 t
s kic h .
hi•E a ma pc
IS
1 ! 0 0
Figure 12* Keen population levels for soybean looper following aelactlve Insecticide applications* 1983* Legend: Methyl parathlon * ■ * ; Bacillus thurlnglenala o 1" o ; Chlorpyrifo* O P ; Untreated chick 0------1 ; Hithyl parathlon plus peroechrln *•»«»*** . 94
Table 45. Seasonal means for threecornered alfalfa hopper populations, across all row spaclngs and soil treatments, In response to selective Insecticide applications, 1982.
a l Foliar Treatment Mean Number Per 50 Sweeps —
Chlorpyrifos — ^ 13.94 a c/ Control — 10.21 b
Bacillus thuringiensis ~ 9.46 b e/ Methyl parathion — 6.81 c
Methyl parathion plus permethrin — 5.90 d fl/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 3 = threecornered alfalfa hopper c/ — Complex 4 = all insect pests
— Complex 2 = non-lepidopterous insect pests
0 / — Complex 1 «= soybean looper f / — Complex 5 = no insects 95
Table 46. Seasonal means for threecornered alfalfa hopper populations, across all row spacings and soil treatments, In response to selective Insecticide applications, 1983.
fl/ Foliar Treatment______Mean Number Per 50 Sweeps —
Chlorpyrifos — ^ 24.47 a
Control — 9.65 b
Bacillus thuringiensis — 9.44 b p/ Methyl parathion — 8.41 c
Methyl parathion plus permethrin — 5.28 d a/ Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrle (1980)]): b/ Complex 3 = threecornered alfalfa hopper c j Complex 4 = all insect pests
1/ Complex 2 •= non-lepidopterous insect pests e/ Complex 1 “ soybean looper
£ I Complex 5 *= no insects 96
IB |------
Figure 13. Mean population lavtls for thro*com*rod alfalfa hoppar following aelectlva Insecticide applications, 1982. Legend: Methyl parathlon *■■ ■ ■ * t laclllui thurlnalanala o ■— 1 o ; Chlorpyrifos U-— 0 ; Untraatad chack 8------4 ; Hathyl parathlon plua penathrln * ..... * • 97
Figure M . Hean population levels for threecornered alfalfa hopper folloving aclectlve Inacctlclde applications, 1983. Legend: Hethyl parathlon *------* i Bacillus thurlnglensla o o j Chlorpyrifos 0---- —D Uncreated cheek Hethyl parathlon plus pernethrln 98
Sparks and Newsom 1984). For both years of the study, populations of
TCAH on plots maintained for non-lepidopterous insects (B.t.) and all insects (untreated check) were very similar in fluctuations with a peak in 1982 of ca. 17 per 50 sweeps (34% ET) and a peak in 1983 of ca. 26 per 50 sweeps (52% ET). Although the treatments of methyl parathion
(SBL) and methyl parathion plus permethrin (no insects) did not provide total control of TCAH, seasonal populations were the lowest for these two treatments compared to other treatments. The maximum populations of TCAH reached ca. 36% of the ET, for both treatments in 1982. In the following year, TCAH populations peaked at 56% ET, for plots treated with methyl parathion, and 28% ET, for plots treated with methyl parathion plus permethrin.
8. Geocoris spp. - Treatments of B.t. (non-lepidopterous insects) and the untreated check afforded higher numbers of Geocoris spp. throughout the season (Tables 47 and 48). Populations of GEO were lower in 1983 than in 1982 (Figures 15 and 16). GEO populations were effectively controlled using methyl parathion, chlorpyrifos, and methyl parathion plus permethrin. In 1982, plats maintaining GEO had peak populations in early and mid-season; however, as shown in the Fig. 15, populations were virtually non-existent at the time corresponding to peak SBL populations (2nd week in Sept.). Thus, GEO had little impact on SBL populations in 1982.
9. Nabis spp. - Seasonal means for Nabis spp. are shown in Tables
49 and 50. Significantly higher (P< 0.05) populations of NAB were found in plots treated with B.t. and the untreated check than in plots subjected to other treatments during both seasons. These populations fluctuated throughout the season and persisted during SBL population 99
Table 47. Seasonal means for Geocoris spp. populations* across all row spacings and soil treatments* in response to selective insecticide applications, 1982.
a/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 3.31 a c/ Bacillus thuringiensis — 3.31 a
Chlorpyrifos — 0.35 b g/ Methyl parathion — 0.34 b f / Methyl parathion plus permethrin — 0.23 b g/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 4 = all insect pests c/ — Complex 2 = non-lepidopterous insect pests
— Complex 3 ■ threecornered alfalfa hopper ©/ — Complex 1 = soybean looper f / — Complex 5 = no insects 100
Table 48. Seasonal means for Geocoris spp. populations, across all row spaclngs and soil treatments, In response to selective Insecticide applications, 1983.
fl j Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 1.66 a C / Bacillus thuringiensis — 1.31 a
Methyl parathion — 0.43 b g/ Chlorpyrifos — 0.37 be f / Methyl parathion plus permethrin — 0.20 c fl./ — Means followed by the same letter are not significantly different (P<0.05; Tukey’s studentized range test [Steel and Torrie (1980)]). b / — Complex 4 = all Insect pests c/ — Complex 2 * non-lepidopterous insect pests
— Complex 1 = soybean looper e l — Complex 3 = threecornered alfalfa hopper f / — Complex 5 = no insects 14 12 10 B 6 4 2 0
10
B 6
4 2 0
EW au in
ua a. IklK • ■ 0.6 at:» DC
2.5
0.5
urr
Figure 15. Mean population lavele for Ceocorla app. following selective Insecticide applications, 1982. Legend: Hethyl parathlon * — . a ; laclllua thurlagispels o------o i Chlorpyrlfo* 0 — — tJ Untreated check 6------A ; Hethyl parathlon plus peraethrln *..... * • e
5
4 3 2 1 0
3.5
1.5
0.5
r 1 • o.e •» 8 Q.6
0.4 uX am xa
1.4
0.6
1.4
0.6
0.2
Figure 16. Mean population leveln for Ceocorle app. following selective insecticide applications, 1983. Legend: Methyl parathlon *------* ; Bacillus thuringiensis o ■ o ; Chlorpyrifos D — — D s Untreated check 6------d ; Methyl parathlon plus permethrin * ..... * • 103
Table 49. Seasonal means for Mabis spp. populations) across all row spacings and soil treatments) in response to selective insecticide applications, 1982.
fl/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 0.82 a c/ Bacillus thuringiensis — 0.74 a
Chlorpyrifos — 0.31 b e/ Methyl parathion — 0.30 b
Methyl parathion plus permethrin — 0.22 b
3 —/ Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
~ Complex 4 *= all insect pests c/ — Complex 2 = non-lepidopterous insect pests
— Complex 3 =. threecornered alfalfa hopper e/ — Complex 1 = soybean looper
— Complex 5 = no insects Table 50. Seasonal means for Nabis spp. populations, across all row spacings and soil treatments, In response to selective Insecticide applications, 1983.
a/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 1.04 a c / Bacillus thuringiensis — 1.00 a
Chlorpyrifos — ^ 0.40 b 0/ Methyl parathion — 0.38b f / Methyl parathion plus permethrin — 0.19 c a / — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]). V / — Complex 4 = all insect pests c/ — Complex 2 = non-lepidopterous insect pests
— ^ Complex 3 «= threecornered alfalfa hopper c/ — Complex 1 = soybean looper f / — Complex 5 = no insects 105
increases in late September and early August for 1982 and 1983, respec
tively (Figures 17 and 18). Slight increases in NAB populations toward
the end of the 1982 and 1983 season reflect the response of Nabids to
increasing SBL populations. Peak populations of NAB in 1982 were ca. 2
per 50 sweeps for B.t. and untreated-check and for 1983 were ca. 3.5 per
50 sweeps.
10. Lebla analis - Significantly (P< 0.05) higher Lebia analis
populations were found in plots sprayed with B.t. and in the untreated
check (Tables 51 and 52, Figures 19 and 20). As seen in Figure 19,
these two treatments peaked at ca. 3.5 LEB per 50 sweeps. Methyl
parathion (SBL maintained) did not appear to be totally effective in
1983 in controlling LEB.
11. Summary - Tables 53 and 54 summarize the relative efficacy of
the foliar insecticides and demonstrate the success in maintaining the
desired populations of individual species and complexes of insect
species. Although the initial goal was to maintain soybean loopers,
solely, by utilizing methyl parathlon, certain other Insect species
(SNF, BCB, and TCAH) were not totally controlled by the material.
Soybean looper populations increased to 73% of the ET during 1982.
Included with SBL were one-third ET of TCAH. . In 1983, plots treated with methyl parathion maintained not only low populations of SBL (19%
ET) but also slightly more than half the ET of TCAH. Non-lepidopterous
insects were successfully established following B.t. treatments.
Although SBL larvae were not entirely controlled with this treatment
(28% and 12% ET in 1982 and 1983, respectively) the small population
levels had minor impact on the effects of the non-lepidopterous insect complex. Other Insects maintained in this complex were one third ET of 106
1.5
0.5
0.5
4 £ wM m» s
•tc «X xa K ■dbesStS&e.
a.5
0.5
JULY
Figure 17. Heen pDpulstlon levels for Hsbls epp. following ■elective Insecticide sppllcetlons, I9BZ. Legend: Hethyl perethlon *------* ; Beclllus thuringiensis o o ; Chlorpyrifos □ ---— 0 j~t)ntreoted check b — A ; Hethyl prrsthlon plus permethrin * ..... * . 107
3
fcl! U M» 8
K m m 0.3 Mi K
1.2
0.9
o.e
0.3
o.e
0.5
0.4
0.3
JULY ■EFT
Figure 18. H e m population levels for Mabie epp. following ■elective lnaectlclde applications, 1983. Legend: Methyl parathion *------* ; Bacillus thurlnalenala o o j Chlorpyrlfoa □— ---□ f~Untreated check fi & } Methyl parathion plui penethrln *.... * . 108
Table 51. Seasonal means for Lebla analis populations, across all row spaclngs and soil treatments, in response to selective insecticide applications, 1982.
flV Foliar Treatment Mean Number Per 50 Sweeps —
Bacillus thuringiensis — ^ 1.22 a c / Control — 1.10 a
Methyl parathion — 0.50 b e l Chlorpyrifos — 0.07 c f/ Methyl parathion plus permethrin — 0.07 c
3/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 2 = non-lepidopterous insect pests c/ — Complex 4 = all insect pests
— Complex 1 = soybean looper e/ — Complex 3 - threecornered alfalfa hopper
— Complex 5 = no insects 109
Table 52. Seasonal means for Lebla ana11s populations, across all row spaclngs and soil treatments, In response to selective Insecticide applications, 1983.
fl/ Foliar Treatment Mean Number Per 50 Sweeps —
Control — ^ 1.90 a c j Bacillus thuringiensis — 1.57 b
Methyl parathion —^ 1.11 c e/ Chlorpyrifos — 0.55 d f / Methyl parathion plus permethrin — 0.26 e
Sif — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentlzed range test [Steel and Torrie (1980)]).
— ^ Complex 4 = all insect pests c/ — Complex 2 *= non-lepidopterous insect pests
— Complex 1 = soybean looper e/ — Complex 3 = threecomered alfalfa hopper f / — Complex 5 = no insects 110
3.5 a.a
0.7
3.5 a.e e.t
0.7
r g 0.34
* 0.10
*^ 0.12 aI 3■t 0 .0G a« 3.5
0.7
O.B
0.6
0.2
FlBtir* 19 . Mean population lavala for Labia analla followinj aelactlva lnaactlclda appllcatlona( 1982. Lagtnd: Methyl parathion * * t ■aelllua thatinllannla o - < } Chlorpyrlfoa 0 — -- U ; Dntraatad chack 6------0 i Hathyl parathion plna paraathrln * ..... * • Ill
3.5
2.5
1.5
0.5
c 5 Mw & s at £ hi* 3 mX
3.5
2.5
1.5
0.5
0.9
0.6
0.3
JULY H P T
Figure 20. Kean population levele for Labis analla following aelectlve Insecticide applications, 1983. Legend; Methyl parathion *------* i Bacillus thurlnalenele o— — — o ; Chlorpyrlfoe P ■■■ □ “ Untreated check i A ; Methyl parathion plus peraethrln *...... * . Table 53. Evaluation of selective foliar insecticides for manipulation of insect complexes, 1982. -
(l)-7 (2)-7 (3)— 7 (4)-7 (5)— 7 Methyl Bacillus Methyl parathion Insect parathion thuringiensls Chlorpyrifos Control plus permethrin
c/ BLB - 18% ET 18% ET
COL 18 per 50 18 per 50
SNF 12 per 50 12 per 50 12 per 50 12 per 50 12 per 50
BCB 3.5% ET 3.5% ET 3.5% ET
SGSB 33.3% ET 33.3% ET
SBL 73% ET 28% ET 40% ET TCAH 36% ET 34% ET 50% ET 34% ET 36% ET
— Population peaks expressed as the percentage of the economic threshold (% ET) or mean number per 50 sweeps. J2,/ Numbers in parentheses denote complex labels. c/ — Acronyms: BLB, bean leaf beetle; COL, Colaspis Louisianae; SNP, soybean nodule fly; BCB, banded cucumber beetle; SGSB, southern green stink bug; SBL, soybean looper; and TCAH, threecornered alfalfa hopper. Table 54. Evaluation of selective foliar Insecticides for manipulation of insect complexes, 1983. - 1
C D - 7 (2)— 7 (3)^7 (4)— 7 (5)— 7 Methyl Bacillus Methyl parathion Insect parathion thuringiensis Chlorpyrifos Control plus permethrin
BLB^7 17% ET 17% ET
COL 25 per 50 25 per 50
SNF 2.5 per 50 2.5 per 50 2.5 per 50 2.5 per 50 2.5 per 50
BCB 5.5% ET 5.5% ET 5.5% ET
SGSB 33.3% ET 33.3% ET
SBL 19% ET 12% ET 12% ET
TCAH 56% ET 52% ET 1.8 times ET 52% ET 28% ET s/ — Population peaks expressed as the percentage of the economic threshold (% ET) or mean number per 50 sweeps. Numbers in parentheses denote complex labels. Acronyms: BLB, bean leaf beetle; COL, Colaspis Louisianae; SNF, soybean nodule fly; BCB, banded cucumber beetle; SGSB, southern green stink bug; SBL, soybean looper; and TCAH, threecornered alfalfa hopper. 114
SGSB and TCAH, 18% ET of BLB and various other Insects as shown In
Tables 53 and 54.
Chlorpyrifos treatments were effective in establishing high levels
of TCAH. The soybean nodule fly was not totally controlled by any of
the treatments. Populations of SNF were statistically the same for all
treatments; therefore any damage from SNF was presumed to be consistent.
Populations of TCAH peaked at 25 per 50 sweeps <50% ET) in 1982 before levels decreased due to an entomopathogenlc fungus, presumably Beauvaria basslana. This pathogen was not present in 1983, thus populations increased to a maximum of 90 per 50 sweeps which was 1.8 times the ET.
The untreated control was aimed at maintaining relatively high populations of all Insects. In 1983, insect population levels for plots treated with B.t. (non-lepidopterous insects) and the untreated check
(all insects) were the same (Table 54). The 1982 population levels were also the same for B.t. plots and the untreated check except for a higher
(40% ET) level of SBL in plots which were untreated (Table 53).
Foliar treatments of methyl parathion plus permethrin were utilized to control all insects; however, as discussed earlier SNF populations were not totally controlled by any treatment. In addition, this treatment had little effect on TCAH where peak populations were 36% and
28% ET for 1982 and 1983, respectively.
III. DEFOLIATION MEASUREMENTS
The first leaf area samples taken were on August 3 which corresponded to the time of maximum leaf area (full bloom). In addition, foliage-feeding lepidoptera were not present at this time. As expected, no significant (P> 0.05) differences were seen in leaf area 115 index (LAI) for any of the complexes of insects (Table 55).
As discussed earlier, soybean loopers reached a maximum population of ca. 73% ET following treatments of methyl parathion in 1982. A second leaf area sample was taken following colonization of the field by
SBL and subsequent defoliation. Results from the second sample showed that the highest LAI resulted from complete control of insects (Table
53, Complex 5). The lowest LAI was found in plots maintaining complexes
1 (SBL-73% ET and TCAH-36% ET) and 3 (TCAH - 50%). The percent defoliation was calculated by taking the difference between the two sampling dates and adjusting values for natural leaf drop. As shown in
Table 55, plots maintaining complex 1 experienced the greatest amount of defoliation (35.5%). Turnipseed (1972b) reported that the control of insects was uneconomical unless defoliation exceeded 35% through blooming or 20% thereafter. The defoliation experienced in the study exceeded the critical stage reported by Turnipseed. Defoliation by complexes 3 and 4 was statistically the same as that for complex 1.
Since foliage-feeding insects were eliminated in complex 3, defoliation observed was most likely due to early senescence resulting from adverse effects of chlorpyrifos. Sparks and Newsom (1984) reported premature yellowing of soybean foliage in plots receiving weekly applications of chlorpyrifos. They determined that chlorpyrifos had a phytotoxic effect on soybean causing an early senescence of plants. Other than the chlorpyrifos treatment, none of the treatments caused noticeable phytotoxic effects.
Leaf area Indices in 1983 were generally lower than those in 1982
(Table 56). No significant differences were shown in LAI in response to foliar insecticide treatments. Populations of SBL were lower in 1983 116
Table 55. Mean leaf area Index, across all row spacings and soil treatments, in response to insect pest complexes, 1982.
Leaf Area Index —
Percent . Foliar Treatment______August 3 September 15 defoliation**
Methyl parathion plus permethrin — ^ 6.2 a 3,5 a 0.0 c c / Bacillus thuringiensis — 6.5 a 2.5 b 16.7 b
Control — 6.3 a 2.1 be 22.1 ab
Chlorpyrifos — 6.9 a 1.8 cd 29.7 ab
Methyl parathion — 6.6 a 1.4 d 35.5 a
fl/ — Means in columns followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]).
— ^ Complex 5 = no insects c/ — Complex 2 = non-lepidopterous insect pests
— Complex 4 « all insect pests e/ — Complex 3 *= threecoraered alfalfa hopper
— Complex 1 ** soybean looper
^ Percent defoliation adjusted to the amounts in the methyl parathion plus permethrin treatments where all Insects were controlled, since decreases in LAI in this treatment were due to senescence and natural leaf drop. 117
Table 56. Kean leaf area index, across all row spacings and soil treatments, in response to Insect pest complexes, 1983.
Leaf Area Index — Foliar Treatment August 18
Bacillus thuringiensis — ^ 4.6 a c / Methyl parathion plus permethrin — 4.6 a
Methyl parathion 4.3 a e f Control — 4.1 a
Chlorpyrifos — 4.1 a
a/ — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]). Ti / — Complex 2 = non-lepidopterous insect pests c/ — Complex 5 = no insects
— Complex 1 = soybean looper g/ — Complex 4 * all insect pests
— Complex 3 = threecornered alfalfa hopper 118
and did not reach high enough population levels to cause defoliation;
therefore, a second LAI sample was not taken in 1983, No significant
LAI differences were found in regard to row spacing,
IV. YIELD
A. Response To Row Spacing. Tables 57 and 58 summarize the effect
of row spacing on yield of soybean. In 1982, plots planted on 51 cm row
spacings yielded significantly (P<0.05) more than when planted at
conventional row widths. This was reflected in an average yield
Increase of ca. 358 kg/ha. These findings are in agreement with reports
from southern researchers who found increased yields following planting
on narrow rows (Smith 1952, Frans 1959, Carter and Boerma 1979, Parker
et al. 1981).
In 1983, higher yields on narrow rows did not occur. Plots
on 76 cm rows had higher yields than those on 51 cm rows by an average
of ca. 280 kg/ha. Other reports in the southern U.S. showed no yield
enhancement from narrow rows (Hartwlg 1957, Cavlness 1966).
B. Response To Subterranean Insects. Results from soil sample
analyses demonstrated that the soil treatments were effective in establishing different levels of soil insect pests in 1982. High amounts of rainfall occurring over a 10-day period following planting
contributed to the ineffectiveness of soil treatments in 1983. When
compared to the untreated check, soil insecticides provided control of early-season soil pests resulting in less damage to the nodules. The effects of above-ground foliar treatments, in conjunction with soil
treatments showed that plots treated with soil Insecticides and sprayed weekly with methyl parathion, chlorpyrifos or methyl parathion plus 119
Table 57. Mean yield across all soil and foliar treatments, in response to row spacing, 1982.
Row Spacing Yield (kg/ha)— ^
51 cm 3207.6 *
76 cm 2849.5
* Means followed by are significantly different (P<0.05) than the other column mean. 120
Table 58. Mean yield across all soil and foliar treatments, In response to row spacing, 1983.
Row Spacing Yield (kg/ha)— ^
51 cm 2498.2 *
76 cm 2778.0
a / * — Means followed by are significantly different (P<0.05) than the other column mean. 121
permethrin (to control soil pests) had less nodule damage than plots
treated with B.t. or the untreated check (for maintenance of soil pests
above-ground). Comparison of the two soil insecticides revealed that
isofenphos treatments showed a trend for more activity against soil pests than did chlorpyrifos treatments.
Tables 59 and 60 summarize the results of the yield data in
response to soil treatments. Treatments of isofenphos afforded more protection from soil pests than other soil treatments; however, significant (P<0.05) yield differences were not found between soil treatments.
The maximum population levels attained above-ground by the bean leaf beetle and soybean nodule fly (nodule-feeding pests) in 1982 were
18% of the ET for bean leaf beetle and 12 per 50 sweeps for the soybean nodule fly. The largest number of BLB larvae sampled from the soil was
0.33 larva per soil core in 1982 (Table 1). Since each soil core sample contained soil material from two plants, then the number of larvae per plant was 0.16. Valdbauer and Kogan (1975) developed a sampling technique for BLB eggs and found that 77% of the eggs were within 2.5 cm of a soybean plant. A study by Eastman (1976) found that the average number of nodules damaged by a single BLB larva was 11. The highest average number of BLB larvae in the experiment was 0,16 per plant which translates to ca. 2 nodules per plant damaged by the BLB. The greatest number of nodules per plant in 1982 were found on the July 19 sample where the average total nodule numbers per plant exceeded 150; thus, in
1982, the average damage by bean leaf beetles resulted in ca. 2 damaged nodules out of 150 per plant. Soybeans are known to add new nodules and lose old ones almost continually during the season (Bergersen 1958). 122
Table 59. Mean yield across all row spacings and foliar treatments, in response to soil treatments, 1982.
Soil Treatment Yield (kg/ha)-/
Isofenphos 3068.4 a
Chlorpyrifos 3010.7 a
Control 3006.4 a
&/ — Means followed by the same letter are not significantly different (P<0.05; Tukey’s studentized range test [Steel and Torrie (1980)]). 123
Table 60. Mean yield across all row spacings and foliar treatments, in response to soil treatments, 1983.
Soil Treatment Yield (kg/ha)— ^
Isofenphos 2791.1 a
Chlorpyrifos 2563.7 a
Control 2559.7 a a t — Means followed by the same letter are not significantly different (P<0.05; Tukey's studentized range test [Steel and Torrie (1980)]). 124
Thus, the plant may be more tolerant of nodule damage at times without
effects on yield. Certain BLB populations (much higher than those
encountered in 1982 and 1983) established by Layton (1983) resulted in
no yield diffences. Populations of soybean nodule fly were relatively
low (12 per 50 sweeps) above-ground and below ground (.5 larva/soil
core, maximum average). Since no means are available to determine
whether nodule damage resulted from BLB or SNF, then damage must be
considered combining the effects of the two. The percentage of damaged
nodules/ha., on July 19, 1982, for the untreated check was 16.1% (Table
1), whereas plots receiving isofenphos had nodule damage of 5.5% (Table
13). Lambert (1981), who studied the nodule damage resulting from SNF and BLB, found no yield differences when 27.7% nodules were damaged in
the untreated check compared to 10.6% damage in plots treated with
isofenphos.
C. Response To Above-ground Insects. Selective insecticides applied on a weekly basis, were relatively successful in manipulating individual species and complexes of insect species. Tables 53 and 54 summarize the effectiveness of the treatments and the maximum populations attained by the various complexes of insects. Treatments of methyl parathion (complex 1) maintained not only SBL (as originally planned) but also populations of TCAH. Treatments with chlorpyrifos
(complex 3) were effective in the establishment of high TCAH populations. For the most part, all insect populations maintained in
the untreated check were statistically the same as those treated with
B.t. Treatments of methyl parathion plus permethrin (complex 5) were effective in controlling all insects except TCAH (36% and 28% ET for
1982 and 1983, respectively). 125
Tables 61 and 62 summarize yield results In response to the
complexes of insects maintained. In 1982, the maximum yield was
attained when all insects were controlled (actually 36% ET of TCAH).
This treatment reflects the maximum yield potential of the soybean in
absence of Insects. The yield for this treatment was significantly
greater (P<0.05) than that of the other treatments. When all insects were maintained (complex 4) or non-lepidopterous insects maintained
(complex 2), a significant (P<0.05) yield reduction was seen for plots
containing these complexes compared to plots having complete Insect
control (complex 5). No significant (P>0.05) yield differences were
found between plots maintaining complex 2 and complex 4 since both
complexes maintained virtually the same levels of insect species, except
for SBL which were slightly higher in complex 4. Although none of the
individual Insect species in complexes 2 or 4 reached ET, the combination of individual species at sub-threshold levels resulted in a
significant (P<0.05) yield reduction compared to plots having complete
insect control. Plots maintaining complex 1 (SBL and TCAH) had yields which were significantly lower (P<0.05) than plots having complete insect control. Peak populations of SBL (73% ET) resulted in a 35.5% defoliation level (Table 55). Turnipseed (1972b) reported that after bloom, soybeans can tolerate up to 20% defoliation without significant yield loss. The defoliation that occurred in methyl parathion-treated plots exceeded the lower limit established by Turnipseed, Plots maintaining all insect pests (complex 4), non-lepidopterous insects
(complex 2), and SBL (complex 1, 73% ET) had comparable yield reductions compared to plots devoid of insects. These data illustrate that sub-threshold levels of individual insect species, in combination, can 126
Table 61. Mean yield across all row spacings and soil treatments, In response to Insect pest complexes, 1982.
Foliar Treatment Yield (kg/ha)— ^
Methyl parathion plus permethrin — ^ 3530.1 a c/ Control — 3198.2 b
Bacillus thuringiensis — 3146.1 b e/ Methyl parathion — 3049.0 b i f Chlorpyrifos — 2219.2 c a / — Means followed by the same letter are not significantly different (P<0.05; Tukey’s studentized range test [Steel and Torrie (1980)]).
Complex 5 = no insects c/ — Complex 4 = all insect pests
— Complex 2 = non-lepidopterous insect pests g/ — Complex 1 = soybean looper
Complex 3 = threecornered alfalfa hopper 127
Table 62. Mean yield across all row spacings and soil treatments, In response to Insect pest complexes, 1983.
Foliar Treatment Yield (kg/haV^/ h / Methyl parathion plus permethrin — 3018.9 a c/ Methyl parathion — 2909.5 a
Bacillus thuringiensis ~ 2744.0 ab 0/ Control — 2622.4 b
Chlorpyrifos — 1895.9 c a/ — Means followed by the same letter are not significantly different (F<0.05; Tukey's studentize.i range test [Steel and Torrie (1980)]).
— ^ Complex 5 = no insects c / — Complex 1 ■> soybean looper
— Complex 2 *= non-lepidopterous insect pests 0 / — Complex 4 = all insect pests f / — Complex 3 *= threecornered alfalfa hopper 128 result in a yield reduction similar to that caused by an individual insect (SBL) reaching ET levels. The lowest yield was found in plots maintaining TCAH. Population reached 50% of the ET resulting in a
1310.9 kg/ha. decrease in yield compared to plots having complete Insect control. The decrease is actually more than what was attributed to TCAH since Sparks and Newsom (1984) reported that weekly treatments of chlorpyrifos resulted in a 368.7 kg/ha decrease in yield resulting from phytotoxicity effects on soybeans. Thus, yield reduction due to TCAH was estimated to be 942.2 kg/ha. No other phytotoxic effects were observed for the other treatments. The possibility may have existed for deleterious or stimulatory effects of treatments, other than the chlorpyrifos treatment, on soybean growth and yield; however, there are no reports in the literature that document this.
In 1983, maximum yield was found in plots maintaining complex 5.
Although this treatment was utilized to control all insects, the TCAH was not totally controlled. Yields for this treatment were not significantly (P<0.05) higher than all of the treatments as seen for
1982 data. Plots maintaining complex 1 had population levels in 1983 different than 1982, in that SBL and SNF populations were much lower and
TCAH numbers were higher (Table 54). Yields due to complex 1 were 109.4 kg/ha. less than that for complex 5 and were not significantly different due to lack of defoliation by SBL. Populations maintained by B.t. treatments and the untreated check (complex 2 and 4, respectively) were virtually identical from a numerical standpoint. No differences in yield were found between the two treatments; however, the untreated check plots had significantly lower yields than plots controlling all insects by 396.5 kg/ha. Complex 3, maintained with chlorpyrifos had the 129
lowest yields with a decrease In yield of 754.3 kg/ha (adjusted 368.7
kg/ha for phytotoxcity according to Sparks and Newsom (1984)).
Populations of TCAH reached levels of 1.8 times the ET in 1983, which
was higher than levels in 1982. Although populations of TCAH were
higher in 1983, the yield decrease between chlorpyrifos treated plots
and plots where insects were controlled was less than that found in
1982. Early season TCAH populations were higher in 1982 than in 1983
(Figures 13 and 14), The early season populations of nymphs in 1982 may
have caused more damage to the soybean than in 1983 and had the potential to peak in the late season at levels much higher than those
found in 1983; however, as mentioned earlier, a disease decimated 1982
TCAH populations resulting in a decrease in late season populations.
Tables 63 and 64 summarize yield data based on the row spacings and
insect pest complexes which were established. Significant (P<0.05)
interactions were found for yield between the row spacing and plots established with SBL alone and all insect pests, in 1982. When plots were planted on 51 cm rows and populations of SBL or all insect pests were allowed to develop uncontrolled, significantly higher (P<0.05) yields were achieved than in plots planted on 76 cm row widths and maintained with the same complexes. The interactions observed in 1982 were primarily due to the impact of relatively high population levels of
SBL.
In contrast, 1983 population levels of SBL were very low, thus the pattern seen in 1983 was not consistent with that of 1982. In addition, yields on plots planted on 76 cm rows were higher than those on 51 cm row widths in 1983. High populations of TCAH were present in 1983. As shown In Table 64, significant interactions (P<0.05) were found for 130
Table 63. Mean yield in response to insect pest complexes on soybean planted on 51 cm and 76 cm row spacing, 1982.—
Yield (kg/ha)
Foliar Treatment 51 cm 76 cm
Methyl parathion —^ 3240.1* 2857.9 c/ Bacillus thuringiensis — 3277.9 3014.4
Chlorpyrifos — 2354.1 2084.3
g/ Control — 3586.8* 2809.7
Methyl parathion plus permethrin — 3579.0 3481.2
/ ^ — Means followed by are significantly different (P<0.05) than other treatment means in the row. b/ Complex 1 = soybean looper c/ Complex 2 = non-lepidopterous insect pests d/ Complex 3 = threecomered alfalfa hopper ej Complex 4 « all insect pests
£/ Complex 5 = no insects 131
Table 64. Mean yield In response to insect pest complexes .on soybean planted on 51 cm and 76 cm row spacing* 1983. —
Yield (kg/ha)
Foliar Treatment 51 cm 76 cm
Methyl parathion —^ 2775.0 3044.0 c/ Bacillus thuringlensis — 2571.9* 2916.1
Chlorpyrifos — 1731.2* 2060.6 e/ Control — 2544.5 2700.3 f / Methyl parathion plus permethrin — 2868.5* .3169.2
/ A — Means followed by are significantly different (P<0.05) than other treatment means in the row.
— ^ Complex 1 = soybean looper c / — Complex 2 = non-lepidopterous insect pests
— Complex 3 = threecomered alfalfa hopper
C-/ — Complex 4 >= all insect pests f l — Complex 5 = no insects yield for row spacings and foliar treatments. When plots were established with complex 2 - non-lepidopterous insects, complex 3 -
TCAH, or complex 5 - no insects and planted on 76 cm rows, yields from plots where these complexes were maintained were higher than the yields from plots where the same complexes were established on 51 cm row spacings.
Although yield data were not consistent for row spacings for both years, the significant interactions (P<0.05) found between row spacings and insect pest complexes suggest that present EILs may need to be revised based on the row spacing. However, the inconsistency in the results over the two years of the study Indicate further research is needed concerning this aspect. CONCLUSIONS
1. Selective insecticides used in a selective manner proved to be a
good tool for studying insect pest complexes. These findings are in
disagreement with Kogan (1976) who stated that use of selective
Insecticides to determine the damage potential of pest complexes has not been successful in yielding useful data.
2. Although none of the individual insect species reached economic
threshold (in plots maintaining the non-lepidopterous insect complex and all insects in a complex), the sub-threshold levels of the individual species, in combination, had a significant impact on soybean yield. In addition, in 1982, plots maintaining soybean looper population levels near economic threshold had comparable yield reductions to plots maintaining sub-threshold levels of non-lepidopterous insects and all insect pests. This illustrates that sub-threshold levels of several insects, together in a complex, can result in similar reductions in yield caused by a single insect pest approaching the economic threshold level.
3. Threecornered alfalfa hopper populations of one-half and 1.8 times the economic threshold for both years, resulted in the lowest yields compared to other treatments. This illustrates the importance of the threecornered alfalfa hopper as a pest of soybean, and the findings further support the research of Sparks and Newsom (1984) who evaluated the pest status of threecornered alfalfa hopper in Louisiana.'
133 134
4. Yields due to row spacing were not consistent both years with higher yields on 51 cm rows, in 1982, and 76 cm rows, in 1983.
Significant interactions in yield were found between row spacing and insect pest complexes established, suggesting that present economic thresholds established on conventional row spacings may need to be revised for narrow row spacings.
5. Although higher populations of soybean loopers and threecornered alfalfa hoppers were found on 51 cm row spacing and banded cucumber beetle and bean leaf beetle populations found on 76 cm row spacings, the differences detected were of such a small magnitude that further study is warranted before definitive conclusions can be drawn concerning the response of these species to various row spacing.
6. Isofenphos soil treatments were more effective in protection against soil pests; however, due to low soil Insect pressure, yield differences were not seen. LITERATURE CITED
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Table 1. Analysis of variance table.
Source Degrees of freedom
Model 41 Error 48 Corrected total 89
Source Degrees of freedom
Block 2 Soil treatments 2 Row spacings 1 Soil treatment * Row spacing 2 Block * soil treatment * row spacing 10 Foliar treatments 4 Soil treatment * foliar treatment 8 Row spacing * foliar treatment 4 Soil treatment * row spacing * foliar treatment 8 145
Table 2. Orthogonal comparisons used for soil sample data analyses.
Soil treatments of isofenphos and chlorpyrifos vs. the untreated control.
Soli treatments of isofenphos and chlorpyrifos within sub-plots treated with methyl parathion.
Soil treatments of Isofenphos and chlorpyrifos within sub-plots treated with Bacillus thurlngiensis.
Soil treatments of isofenphos and chlorpyrifos within sub-plots treated with chlorpyrifos.
Soil treatments of Isofenphos and chlorpyrifos within untreated sub plots .
Soil treatments of Isofenphos and chlorpyrifos within sub-plots treated methyl parathion plus permethrin.
Soil treatments of Isofenphos vs. chlorpyrifos.
Soil treatments of isofenphos vs. chlorpyrifos within sub-plots treated with methyl parathion.
Soil treatments of isofenphos vs. chlorpyrifos within sub-plots treated with Bacillus thuringiensis.
Soil treatments of isofenphos vs. chlorpyrifos within sub-plots treated with chlorpyrifos.
Soil treatments of isofenphos vs. chlorpyrifos within untreated sub-plots.
Soil treatments of isofenphos vs. chlorpyrifos within sub-plots treated with methyl parathion plus permethrin. VITA
Jaime Yanes, Jr., the son of the late Jaime Yanes, Sr. and Virginia
R. Yanes, was born on December 30, 1957 in Washington, D. C. He attended Friendly Sr. High School, in Oxon Hill, Maryland, and graduated
in May, 1975.
After high school graduation, he attended Oklahoma State
University, in Stillwater, where he pursued a B.S. degree in Forestry.
He received his B.S. degree in December, 1979. Immediately following graduation, he entered graduate school to pursue an M.S. degree. In
July, 1981 an M.S. degree in Entomology was conferred.
In August 1981, he moved to Baton Rouge to pursue a Ph.D. degree in
Entomology. On June 25, 1983, he and Celeste Ann Spiers were married.
Presently, he is a candidate for the degree of Doctor of Philosophy in Entomology at Louisiana State University.
146 EXAMINATION AND THESIS REPORT
Candidate: Jaime Yanes, Jr.
Major Field: Entomology
Title of Thesis: The Impact of Individual Species and Complexes of Pest Arthropod Species on Soybean Grown on Various Row Spacings
Approved:
Major /Professor and Chairman
Dean of the Gradu.aduate School Sci
EXAMINING COMMITTEE:
tj \f~ / ? ^ r r r ^ - P
Date of Examination: