Biotic Stress and Yield Loss

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numbers are present. Stink bugs, Euschistus spp., Nezara viridula, and chinch bugs,Blissus leucopterus leucopterus, are known to remove plant fluids from vascular tissuesat the base of corn plants. Injury from these insects can range from temporaryreductions in plant vigor to stunted corn growth and serious plant malformation.22, 27–29Chinch bugs feed on a wide range of grass species including wheat, barley, rye,oats, corn, sorghum, and numerous weeds. Among preferred hosts, corn often figuresprominently in pest population build-ups. Chinch bug levels are correlated withmeteorological conditions, with economically important populations being associatedwith above-normal temperatures and below-normal rainfall. 26 Chinch bug injuryto corn can occur from spring brood infestations on early corn plantings, but morecommonly occurs when small grains (which serve as host for a majority of springpopulations) begin to mature and chinch bug nymphs move into neighboring cornfields. A second generation of chinch bugs will then develop within the corn crop.Chinch bugs feed in large numbers at the base of corn plants, obtaining food andwater from the phloem elements. As a result of chinch bug feeding, vascular bundlesbecome clogged, thereby restricting water and nutrient transport within the plant. 26Injury symptoms associated with chinch bug feeding range from reductions in plantheight (stunting) to the presence of curved or twisted stems, then severe leaf malformationand dead leaves. 29 Younger plants (V2 stage) are more susceptible to chinchbug injury than are older plants (V5 stage), which require greater chinch bug numbersto sustain serious injury. 29, 30 Following chinch bug feeding at the V2 and V5growth stages, ear weight and ear length decreases with increasing insect numbers.Infestations ranging from 2 to 20 chinch bugs per plant elicited yield responses. 29Several stink bug species are also known to cause injury to corn. The brown stinkbugs, Euschistus servus and E. servus euschistoides, the onespotted stink bug,Euschistus variolarius, and the southern green stink bug, Nezara viridula, have beenobserved feeding on most corn growth stages. 22, 27, 28 Like chinch bugs, many adultand nymphal stink bugs move into corn fields from small grains or other host plantsupon harvest, removal by herbicide use, mowing, or other means.Stink bugs feed in the vascular elements of the plant by puncturing plant tissuesand removing water and nutrients. The volumes of plant sap removed by stink bugfeeding are generally of little consequence, even with heavy infestations. During thefeeding process, these insects also inject enzymes into the plant that assist in digestionof tissue. 22 It is the presence of these enzyme toxins (and direct injury from puncturingmouthparts) that produces the majority of corn injury. Plant tissues at or nearthe feeding puncture often undergo partial or complete destruction, producing holesthat are ringed with yellow or brown tissue. Puncture injury also may appear as elongateholes in expanding leaves that have unrolled after injury is incurred. 22 In addition,plant deformities including irregular twisting or growth of stalks and leaves, andexcessive tillering, may result from enzyme toxins introduced through stink bugfeeding. Plant death also may occur from heavy feeding on smaller plants. 28Injury to corn from brown or onespotted stink bug feeding is most significant inyounger (V2) plants. 22, 28 Severe wilting of corn seedlings can occur when eight stinkbugs per plant are confined to plants for two days. 27 Four or more stink bugs per plant
for a period of 13 days resulted in high plant mortality. 27 On smaller plants, asidefrom mortality, excessive plant tillering is the most apparent response from stink bugfeeding, with 39 to 52% of plants exposed to stink bugs (one stink bug per plant) producingtillers. 28 Due to excessive tillering, silk development was delayed and meanextended leaf height and grain weights per ear were reduced in stink bug injuredplants. 28 Significant plant injury also has been observed for corn injured in late vegetativeand early reproductive stages (V15 to R2). 27 In older corn plants (V15), twoadult southern green stink bugs per plant were sufficient to cause reductions in earweight and length. 27 Overall yield decreases resulting from southern green stink bugfeeding on larger corn were attributed to production of fewer ears rather than reductionin kernel weight. 27 Ear deformity from stink bug feeding was also observed, butonly when insects were intentionally confined to ears for extended periods. 274.3.2.3 NematodesA variety of species of plant parasitic nematodes can be found in every acre of farmlandsoil. Nematodes are microscopic roundworms that feed on plant roots by withdrawingthe liquid contents from individual plant cells. In sufficient numbers, feedingby plant parasitic nematodes can cause severe injury to corn. Symptoms of nematodefeeding injury can include yellowing or distortion of foliage, stunting, and/or wiltingof plants, resembling symptoms brought on by low fertility, drought conditions, orsoil compaction. 22Plant parasitic nematodes are capable of injecting enzymes and other substancesinto the plant cells. These substances may be toxic, killing the cells, altering theirgrowth, or predisposing the plants to injury by other agents. In corn, common plantresponses to toxic enzymes introduced by nematodes include: (1) suppressed orclubbed roots from which fine feeder roots arise, giving the appearance of a witchesbroom (dagger nematodes, Xiphinema americanum, and needle nematodes,Longidorus breviannalatus), and (2) brown streaks of discoloration on roots (lesionnematodes, Pratylenchus hexincisus). 22 In addition, feeding wounds left by nematodesmay provide portals for bacterial and fungal pathogens not otherwise able toenter corn roots.Attack from plant parasitic nematodes can occur throughout the growing season,and rescue treatments currently do not exist for nematode pests. Combinations ofeffective crop rotation (to a non-host crop) and effective utilization of soil nematicidesat planting are most appropriate under heavy infestations. Once plant parasiticnematodes are confirmed as the causal agent for symptoms observed in the field,management tactics are likely warranted. Nematode populations at numbers too lowto cause visual responses (but possibly causing subtle yield depressions) in the corncrop are normally neither detected nor treated.4.3.2.4 Spider MitesSpider mite feeding can have serious effects on corn. This is particularly true whenenvironmental conditions such as hot, dry weather or soil compaction enhance plantstress. The twospotted spider mite, Tetranychus urticae, and Banks grass mite,
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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
Page 14 and 15: increase plant tolerance, through p
Page 16 and 17: the action of a stressor on a plant
Page 18 and 19: The magnitude and duration of injur
Page 20 and 21: Plant part injuredrefers to the pla
Page 22 and 23: cific competition, while agricultur
Page 24 and 25: 2Yield Loss and PestManagementLeon
Page 26 and 27: direct relationships between the ac
Page 28 and 29: In keeping with the theme of this b
Page 30 and 31: egressions. Actually, the title “
Page 32 and 33: REFERENCES1. Teng, P. S., Crop Loss
Page 34 and 35: 3Techniques for EvaluatingYield Los
Page 36 and 37: number of species and stage of cutw
Page 38 and 39: especially if buried in soil, can d
Page 40 and 41: elationships for some pests. When m
Page 42 and 43: injury can be precisely controlled
Page 44 and 45: day. 81, 99 However, except for an
Page 46 and 47: the literature most likely are actu
Page 48 and 49: 20. Ba-Angood, S. A., and Stewart,
Page 50 and 51: 60. Stewart, J. G., McRae, K. B., a
Page 52 and 53: 99. Shields, E. J., and Wyman, J. A
Page 54 and 55: 4.3.3.1.3 Third generation European
Page 56 and 57: ing on the developmental stage at t
Page 58 and 59: 4.2.2.1.2 Temperature stressPlant s
Page 60 and 61: chronic injury. Acute injury result
Page 62 and 63: ows, roadsides, or small grain fiel
Page 66 and 67: Oligonychus pratensis, feed on corn
Page 68 and 69: ECB2. 224.3.3.1.4 The impacts of Eu
Page 70 and 71: stalk borer, Papaipema nebris, is a
Page 72 and 73: period prolonged with sufficient co
Page 74 and 75: 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
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light interception. 45 Skeletonizin
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Light interception, which intrinsic
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var. Consequently, use of a single
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19. Jarosik, V., Phytoseiulus persi
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62. Caviness, C. E., Registration o
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8Drought Stress, Insects,and Yield
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humidity. Because the relative humi
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temperature and precipitation. Prop
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compared to well watered soybeans.
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Changes in plant hormones, such as
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plays a key role in promoting plant
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In soybeans, a leaf area index (LAI
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15. Schulze, E. D., Water and nutri
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52. Meyer W. S., and Walker, S., Le
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9The Impact of Herbivoryon Plants:
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conditions of stress are themselves
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are common, defenses to avoid herbi
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plant tissue, resulting in gall for
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found on cucumbers in polycultures
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compensatory response. Also, more v
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Costa Rica, and there are several g
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ivory from white cabbage butterfly
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made, while larger vertebrate herbi
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important consequences to plant fit
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de Entomol., 38, 421, 1994.32. Kare
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chlorophyll content in spider mite
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114. Karban, R., and Strauss, S.Y.,
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10Stephen C. WelterCONTENTSContrast
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Although literature is drawn from a
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and wheat acres receiving some type
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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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