Biotic Stress and Yield Loss

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ows, roadsides, or small grain fields with insects migrating into corn fields inlate spring as food supplies dwindle or other host plants begin to mature. Becauseof this migratory behavior, armyworm injury often appears first at field edges.Exceptions can occur in reduced-till corn fields where cover crops or weedyconditions may provide attractive food sources for armyworm egg laying, resultingin a more even distribution of armyworm damage throughout the field. Armyworminjury gives the corn plant a ragged appearance, because leaf margins and whorlareas are consumed. With severe armyworm injury, most of the leaf area may beconsumed.Fall armyworm infestations typically develop from midsummer through harvest.Moths are attracted to late-maturing, late-planted corn fields for egg laying, distributingtheir eggs throughout the field. Injury from fall armyworm feeding appears asragged holes in leaves, rather than ragged edges on leaf margins. In addition, fallarmyworms may feed on tassels and corn ears later in the season.Foliar injury to corn from both armyworm and fall armyworm consists of simpleleaf tissue removal. The effects of foliar injury from fall armyworm infestationsin corn are cumulative for vegetative growth stages with longer periods of injury havinggreater impacts on yield. 23 Corn plants are able to compensate for foliar injuryincurred over short periods of time. Plant responses to feeding injury appear to be linear,with no one time period during vegetative growth being more critical in causingyield reductions than any other. 23, 24 Corn yield reductions of 7 to 45% have beenobserved as a result of 100% fall armyworm infestations during periods of vegetativegrowth. 23–25 Yield reductions from fall armyworm leaf feeding injury incurred nearertassel stage were not observed to be significant. 254.3.1.3 Grasshoppers and Other General Foliage FeedersGrasshoppers, Melanoplus spp., and many other general foliage feeders that attackcorn produce injury similar to that described for armyworm—removing leaf tissuefrom above-ground portions of plants. Injury from grasshoppers is often more severein years when adverse conditions reduce natural vegetation and force them into cultivatedcrops. In addition, dry conditions can reduce the natural mortality ofgrasshopper eggs, increasing resident populations. 22Grasshopper injury can be devastating. They will feed on corn in many growthstages, but prefer the reproductive stages. They are known to attack all above-groundparts of the corn plant, including leaves, silks, and ear tips, potentially reducing yieldthrough both indirect (reductions in plant vigor, pollination disruption) and direct (earand seed damage) losses. When grasshopper populations are high, they may consumeall above-ground plant parts except leaf mid-ribs, pruned ears, and stalks, giving thefield the appearance of having suffered severe hail injury. 224.3.2 VASCULAR FEEDING INJURYVascular feeding injury to corn is initiated by arthropod and nematode pests withpiercing or sucking mouthparts. They remove sugars and other nutrients from thephloem and other vascular elements within leaves, stems, and roots, often resulting
in significant damage to the crop. 26 Corn plant development and subsequent grainyields can be negatively impacted through general reductions in plant vigor by thesepest-induced stresses. With higher pest populations, water and nutrient deficiencieswithin the plants may become evident. Slowed growth, wilting, and plant discolorationmay become obvious, while external injuries go relatively unnoticed.Symptoms may mimic those observed for some plant diseases, herbicide injuries ornegligent fertility programs.In addition, vascular feeding injury may include the effects of arthropod ornematode toxins deposited into plants during feeding. While actively feeding, manysucking pests inject enzymes into the host plant to assist in digestion of plant tissues.These enzymes are toxins and when injected into plants, often result in partialdestruction of plant tissues or plant deformities, such as irregular twisting or growthof stems and leaves. These secondary plant responses to the arthropod feeding oftenhave more devastating impacts on development and yield than does the removal ofresources.4.3.2.1 Corn Leaf AphidThe corn leaf aphid, Rhopalosiphum maidis, is a common pest of corn and numerousgrass weeds in corn-growing regions. The insect removes plant fluids from thephloem tissues of whorl corn leaves. Corn leaf aphid rarely occurs in densities largeenough to result in physiological yield losses. However, when heavy infestationsoccur, corn leaves may wilt, curl, and/or develop patches of yellow discoloration(chlorosis). 22Corn leaf aphids also deposit a sticky substance called “honeydew” on hostplants (as a part of feeding). This honeydew often fosters the growth of molds, givingthe top leaves and tassels a black sooty appearance. With excessive honeydew,tassels can become covered to the extent that anthesis is impeded, resulting invarying degrees of plant barrenness. 26 Although aphid outbreaks and excessive honeydewcan hinder pollen-shed in commercial fields, the phenomenon is primarilyof concern in seed production fields where pollen levels are already reduced by detasselingpractices.Aphid numbers necessary to cause yield reductions in corn will vary based onthe interval between pest infestation and plant development to the tassel stage. Thedegree of environmental stress (water stress) under which the corn crop is beinggrown will also play a role in the amount of aphid injury that can be tolerated.Generally, fewer aphids are required to justify control treatments when the intervalbetween infestation and tassel stage is lengthened (15 to 30 aphids per plant).Likewise, fewer aphids are required to justify control measures when plants are experiencingstressed conditions (10 to 15 aphids per plant). 224.3.2.2 Chinch Bugs and Stink BugsHemipteran pests of corn can have devastating effects on yield when sufficiently high
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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
Page 12 and 13: 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 64 and 65: numbers are present. Stink bugs, Eu
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
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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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