IMPACT OF TAEDIA-SCRUPEUS (HEMIPTERA, MIRIDAE) FEEDING ON CLUSTER DEVELOPMENT IN CONCORD GRAPES

Taedia scrupeus (Say) feeds on grape clusters and shoots early in the growing season. The impact of nymphal and adult feeding was assessed a t the individual shoot level by confining nymphs within sleeve cages a t 4 different times: prebloom, bloom, postbloom, and prebloom to postb loom. Prebloom feeding significantly reduced the number of berries per cluster and average berry weight, resulting in a 68% reduction in clu ster weight. When nymphs were allowed to feed from prebloom to postblo om, cluster weight was reduced by 71%. Feeding only during bloom and p ostbloom did not affect cluster weight. Prebloom feeding reduced the n umber of florets per cluster, berries per cluster, and berry weight. T he whole-cine impact of T. scrupeus was examined in a commercial Conco rd vineyard, where 3-vine experimental units were treated with carbary l to remove T. scrupeus or were left untreated. Unsprayed vines, with a mean density of 20 T. scrupeus per vine, yielded 10.4 kg per cine, a nd sprayed vines without injury yielded 14.1 kg per cine. The yield co mponent most strongly affected was the number of clusters per vine, wh ich averaged 165.4 and 131.8 per vine in sprayed and unsprayed vines, respectively. Each T. scrupeus nymph was associated with 0.18 kg of cr op loss, suggesting that as few as 0.5 nymphs per vine can cause econo mic injury. Where treatment of vineyards to prevent T. scrupeus injury is warranted, it must be applied during the prebloom period.