Japanese beetle Popillia japonica Newman: foliar feeding on wine grapes in Virginia
Boucher, T. Jude
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The natural infestation level for 1985 of the Japanese beetle, Popillia japonica Newman, in the Shenandoah Valley of Virginia failed to reduce berry quality, yield or shoot growth in a commercial vineyard. Intensive postveraison foliage feeding by Japanese beetle resulted 1n fruit with lower soluble solids and higher total titratable acidity at harvest, but did not affect pH, sugar per berry, berry weight, yield, leaves per vine or shoot length. Intensive previraison feeding also resulted in fruit with higher total titratable acidity. All other parameters were unaffected. In a separate experiment with 0, 10, 20, and 33% leaf removal, no relationship was shown between leaf area loss and soluble solids, total titratable acidity or pH. Data from one season of damage by the beetle indicate that control measures may not be warranted in some years. In a third experiment, grape leaves on potted vines were artificially damaged by removing leaf disks with a paper punch. The leaves showed an increased loss of efficiency (measured in net photosynthesis, Pn) for the remaining tissue as leaf area loss (LAL) increased. This loss of efficiency in the remaining leaf area at low levels of damage was more pronounced after 12 days than after either 1 or 5 days. The additive effect on Pn of both LAL and lowered efficiency predicted the total shutdown of Pn at 60% damage at 1 and 5 days after treatment, but not at 12 days.
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