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Updated: August 8, 2017
Tarnished plant bugs appear when fruit buds form and plants begin to bloom. Feeding on buds and immature berries causes deformed berries. Plant bugs are more serious in small fields bordered by woods and fencerows, where weeds are plentiful.
Deformed berries can be caused by a variety of reasons, and it is important to be able to diagnose the causes of the various deformities. Raspberry fruits are clusters of drupelets attached to a central receptacle. Each drupelet is made up of a hard seed and a sugary, soft, fleshy portion. If the fruit appears abnormally small, then a fertility, plant vigor, or virus problem should be suspected. If the fruit is of normal size but has abnormally few drupelets with no deformed drupelets, then poor pollination should be suspected. If, however, there are abnormally few fully developed drupelets and the remaining drupelets are shriveled and seed like, then plant bug feeding should be suspected.
Apply an insecticide when more than 20 to 25 plant bugs are noted per 50 flower clusters. Pay particular attention to field borders.
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