Spectral reflectance from a broccoli crop with vegetation or soil as background: influence on immigration byBrevicoryne brassicae andMyzus persicae |
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Authors: | Michael J Costello |
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Institution: | (1) Laboratory of Biological Control, University of California, 94720, CA, USA;(2) Present address: University of California, Cooperative Extension, 1720 S. Maple Ave., 93702 Fresno, CA, USA |
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Abstract: | Light reflectance in five wavebands of the spectrum was measured from broccoli (Brassicae oleracea var.botrytis L].) interplanted with leguminous cover crops (cover crop background) or broccoli grown as monoculture (bare soil background),
and fertilized with compost or synthetic fertilizer. AlateBrevicoryne brassicae (L.) andMyzus persicae (Sulzer) (Homoptera: Aphididae) were monitored in yellow pan water traps and on broccoli leaves. Reflectance intensity was
higher with a background of bare soil at all wavebands except blue (400–455 nm) in the early-season. Intensity decreased as
broccoli canopy cover increased at all wavebands except blue and green (515–550 nm), declining-most dramatically in the yellow
(550–590 nm). Highest late-season intensities were in plots with bare soil background and fertilized with compost (those stressed
for nitrogen). Few differences in spectral composition, expressed for each waveband as a percentage of total intensity, were
recorded. Numbers of alatae were lowest in cover crop background plots in the early season, reached equivalency with bare
soil background by mid-season, and showed highest positive correlations with intensity in the yellow (550–590 nm). Results
correspond to laboratory findings that aphids are attracted to higher intensity light, especially in the yellow waveband,
and support a phototactic explanation for aphid orientation in the field. |
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Keywords: | crop background reflectance light aphids Myzus persicae Brevicoryne brassicae living mulches intercropping |
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