Biotic Stress and Yield Loss

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humidity. Because the relative humidity is variable at different canopy heights, insectdistribution can also vary in these canopies. For instance, Isichaikul et al. 3 demonstratedthat rice canopies near ground level were more favorable for the distributionand survival of brown planthopper nymphs because of a relatively more humidmicroenvironment than upper canopies. 3Most soil-inhabiting insects are adapted to moist and high relative humidityenvironments. These insects are more affected by changes in moisture stress thanfoliar insects. Insects, such as Collembolans, have less control over evaporative waterloss compared to foliar insects that strictly regulate water loss from their bodies. Ifthe duration of moisture stress is extended, soil-inhabiting insects may suffer fromdesiccation.The survival of corn rootworm, Diabrotica spp., and other soil inhabiting insectsdepends on soil moisture and soil texture. 4, 5 Soil texture determines the rate at whichthe soil moisture changes. In rapidly drying soils, larval mortality is higher becauseof faster desiccation than in less rapidly drying soils. 5 Consideration of soil moisturefor some insect pests, such as corn rootworms, may be an important criterion beforepest management action is taken.8.2.2 INDIRECT IMPACTS8.2.2.1 Changes in MicroenvironmentAn insect’s microenvironment primarily is influenced by precipitation, temperature,and the type and density of vegetation. 6, 7 Changes in the level of soil moisture stressthat plants experience can greatly modify insect microenvironments. Additionally,moisture stress impacts the microenvironment and insect populations by altering thegrowth and suitability of plants.Moisture stress results in elevated leaf temperatures as plants fail to cool viatranspiration. Closure of the stomates in moisture-stressed plants reduces transpirationalwater loss, limiting CO 2uptake for photosynthesis. Because of reduced photosyntheticrates, moisture-stressed plants maintain smaller canopy size. If canopiesfail to close, direct radiation can enter through plant canopies. Consequently, arthropodsthat live on moisture-stressed plants may experience warmer microclimate thanwell watered plants because of direct radiation and high leaf temperatures.High temperatures in moisture-stressed canopies may increase the metabolic andreproductive rates of some insects, leading to population build-up. 8–11 However, elevatedplant canopy temperatures resulting from moisture stress may not be conducivefor insects adapted to canopies with high relative humidity. Moisture-stressed plantscreate increased vapor pressure deficits, causing rapid water loss from insects.Changes in microenvironment may impact arthropods and their natural enemiesin different ways. Sometimes the microenvironment is more favorable to the naturalenemies than the herbivores, or vice versa. It is also possible that changes in microenvironmentact on insect population indirectly by altering the fitness of natural enemies.Indeed, in most cases the direct impact on insect fitness from changes inmicroenvironment is less than the impact from natural enemies. Therefore, thegeneralization that moisture stress leads to build-up of some arthropod pests should
e considered with caution, because of the indirect impact of microenvironment onnatural enemies.In agricultural ecosystems, understanding the insect microenvironment is essentialto design effective pest management strategies. Microenvironments with low relativehumidity generally may not be suitable to deploy fungal pathogens as biologicalcontrol agents. Comparisons of canopy microenvironment and the immediate cuticularmicroenvironment of grasshoppers suggest that the latter may be more importantin using Beuvaria bassiana for biological control. The role of ambient relativehumidity was less important than the relative humidity at the cuticular levels of themigratory grasshopper for the development of this fungus, demonstrating that it canpotentially be used even in areas with low relative humidity. 12 However, the cuticularrelative humidity depends on ambient relative humidity and practical use of thispathogen for pest management has not been confirmed.Other cultural practices that can impact insect microenvironment and also determinechanges in insect pest populations are irrigation management 13 and croppingsystems (i.e., monoculture vs. polyculture). 148.2.2.2 Changes in Plant Nutritional QualityAs insects approach host plants, determining the suitability of a host plant and furtheracceptance to resume feeding are essential processes that take place at theinsect–plant interface. Insect herbivores determine the nutritional quality of their hostplant, and sustained feeding will only ensue if the host plant can provide essentialnutrients needed for the growth and development of insects.The nutritional suitability of host plants can be influenced by environmental factors,such as soil moisture and nutrients available for plant growth and development.Changes in the levels of nitrogen alter the suitability of plants to herbivores. Also, thelevel of moisture stress plants experience can alter the composition of essentialelements and can affect plant nutritional quality. 15In moisture-stressed plants, the concentration of solutes is assumed to increase,improving their nutritional quality. Mattson and Haack 11 suggest that improved nutritionalquality of plants in response to moisture stress occurs because of increases inthe concentration of carbohydrates, proteins, and minerals compared to unstressedplants, which are not saturated with these compounds that are essential for arthropodgrowth. However, improved plant nutritional quality may not occur following moisturestress 16, 17 and may not affect insect fitness.Although changes in the nutritional quality of host plants occur after moisturestress, high canopy temperature and low relative humidity also may occur after moisturestress. Changes in these latter parameters may have a greater impact on insect fitnessand their natural enemies than changes in the nutritional quality of host plants.8.2.3 MOISTURE STRESS AND INSECT OUTBREAKSTemporal and spatial changes in insect populations, including cyclic outbreaks ofpest-species, have been attributed to environmental factors, primarily extremes in
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Biotic Stressand Yield Loss
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Library of Congress Cataloging-in-P
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PrefaceThe idea for this book came
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EditorsRobert K. D. Peterson, Ph.D.
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ContentsChapter 1Illuminating the B
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1Illuminating the Black Box:The Rel
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increase plant tolerance, through p
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the action of a stressor on a plant
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The magnitude and duration of injur
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Plant part injuredrefers to the pla
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cific competition, while agricultur
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2Yield Loss and PestManagementLeon
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direct relationships between the ac
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In keeping with the theme of this b
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egressions. Actually, the title “
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REFERENCES1. Teng, P. S., Crop Loss
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3Techniques for EvaluatingYield Los
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number of species and stage of cutw
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especially if buried in soil, can d
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elationships for some pests. When m
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injury can be precisely controlled
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day. 81, 99 However, except for an
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the literature most likely are actu
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20. Ba-Angood, S. A., and Stewart,
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60. Stewart, J. G., McRae, K. B., a
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99. Shields, E. J., and Wyman, J. A
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4.3.3.1.3 Third generation European
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ing on the developmental stage at t
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4.2.2.1.2 Temperature stressPlant s
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chronic injury. Acute injury result
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ows, roadsides, or small grain fiel
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numbers are present. Stink bugs, Eu
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Oligonychus pratensis, feed on corn
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ECB2. 224.3.3.1.4 The impacts of Eu
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stalk borer, Papaipema nebris, is a
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period prolonged with sufficient co
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Arthropod injuries to developing ea
Page 76 and 77: esponses to herbivory have been obs
Page 78 and 79: Midwest, Purdue University CES and
Page 80 and 81: 59. Bailey, W. C., and Pedigo, L. P
Page 82 and 83: 5Phenological Disruptionand Yield L
Page 84 and 85: ity by animal consumers is the agro
Page 86 and 87: ously, structural components (e.g.,
Page 88 and 89: FIGURE 5.2 Generalized alfalfa grow
Page 90 and 91: 601, 1972.9. Gordon, C. H., Derbysh
Page 92 and 93: do we know about how biotic stresso
Page 94 and 95: ing both large and small leaf veins
Page 96 and 97: population. Whole plants may respon
Page 98 and 99: temporally and spatially, are more
Page 100 and 101: some systems have allowed for a tra
Page 102 and 103: injury guilds would center on the f
Page 104 and 105: apple leaves, HortScience, 19, 815,
Page 106 and 107: 7The Influence of Cultivarand Plant
Page 108 and 109: unit ground area, and it indicates
Page 110 and 111: without considering plant architect
Page 112 and 113: photosynthesis. Regardless of the n
Page 114 and 115: light interception. 45 Skeletonizin
Page 116 and 117: Light interception, which intrinsic
Page 118 and 119: var. Consequently, use of a single
Page 120 and 121: 19. Jarosik, V., Phytoseiulus persi
Page 122 and 123: 62. Caviness, C. E., Registration o
Page 124 and 125: 8Drought Stress, Insects,and Yield
Page 128 and 129: temperature and precipitation. Prop
Page 130 and 131: compared to well watered soybeans.
Page 132 and 133: Changes in plant hormones, such as
Page 134 and 135: plays a key role in promoting plant
Page 136 and 137: In soybeans, a leaf area index (LAI
Page 138 and 139: 15. Schulze, E. D., Water and nutri
Page 140 and 141: 52. Meyer W. S., and Walker, S., Le
Page 142 and 143: 9The Impact of Herbivoryon Plants:
Page 144 and 145: conditions of stress are themselves
Page 146 and 147: are common, defenses to avoid herbi
Page 148 and 149: plant tissue, resulting in gall for
Page 150 and 151: found on cucumbers in polycultures
Page 152 and 153: compensatory response. Also, more v
Page 154 and 155: Costa Rica, and there are several g
Page 156 and 157: ivory from white cabbage butterfly
Page 158 and 159: made, while larger vertebrate herbi
Page 160 and 161: important consequences to plant fit
Page 162 and 163: de Entomol., 38, 421, 1994.32. Kare
Page 164 and 165: chlorophyll content in spider mite
Page 166 and 167: 114. Karban, R., and Strauss, S.Y.,
Page 168 and 169: 10Stephen C. WelterCONTENTSContrast
Page 170 and 171: Although literature is drawn from a
Page 172 and 173: and wheat acres receiving some type
Page 174 and 175: pattern to be true. 109 Because rel
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used in the experiment influenced t
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artificially elevated nitrogen leve
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annual, landrace cultivars, or mode
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settings are coupled with genotype
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10. Kennedy, G. G., and Barbour, J.
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53. Panda, N., and Heinrichs, E. A.
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97. Gross, K. L., and Soule, J. D.,
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143. Davidson, J. L., and Milthorpe
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11Crop Disease andYield LossBrian D
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The conditions listed above are opt
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to associate the effects of disease
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general relationship between LAI an
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Biomassproduction(total dryweight)R
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Y RUE(t)RI(t)[1 X]dt [11.12]wher
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sue. The most accurate prediction o
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tion. Two weeks before harvest, the
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15. Spitters, C. J. T., Van Roermun
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57. Richardson, A. J., Wiegand, C.
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they were cheap, convenient, and ef
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dW / W dtcauses and consequences of
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(a)(b)Maize yield (Mg ha -1 )987654
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Recall that c is a constant, so by
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where the subscripts c and w repres
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0.6Fraction yield loss0.40.2Eq. 16,
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the leaf area index (LAI). Incorpor
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can no longer be tolerated and, the
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cide. Steckel et al. 68 showed that
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A eq ∑ jN eq,ji 1YL n,j [12.31]1
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samples per field. Thomas 85 sugges
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external factors such as annual wea
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38. Boznic, A. C., and Swanton, C.
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weeds, Weed Sci., 44, 856, 1996.79.
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competition and weed management. 3-
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per unit biomass (1/W i)(dW i/dt) o
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of light interception). Algorithms
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where G a,iis the water limited pla
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13.4 COMPETITION FOR SOIL NITROGENA
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As with soil water, Equations 13.10
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partitioning of nitrogen to leaves.
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and stems to optimize photosyntheti
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influence of enhanced UV-B conditio
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Systems Approaches at the Field Lev
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