We monitored egg parasitism and larval populations of Pieris rapae (L.) and Trichoplusia ni (Hübner) in cabbage plots treated with point and broadcast releases of Trichogramma brassicae Bezdenko, and we investigated whether weekly sugar sprays improved egg parasitism rates. We also compared yield and pest densities in cabbage treated with Bacillus thuringiensis (Dipel), methomyl (Lannate), or point releases of T. brassicae to an untreated control, and investigated the economics of these control strategies. Egg parasitism was highest in the point release treatment (46%), and parasitism in the broadcast and the broadcast sugar spray treatments (31 and 24%, respectively) did not differ from the control. Weekly applications of sucrose did not increase egg parasitism or decrease larval pest populations. Releases of T. brassicae did not significantly reduce P. rapae and T. ni larval populations, and plant damage and cabbage head weight were unaffected in the T. brassicae treatments relative to the control. In addition, the cost of applying the T. brassicae wasps was not recouped with significant yield improvements relative to the control. Methomyl and Bt consistently suppressed P. rapae and T. ni populations below action thresholds in a cost-effective manner.
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