173 CRANBERRY PLANTS COMPENSATE FOR UPRIGHT TIP DESTRUCTION BY CRANBERRY TIPWORM
Cranberry tipworm (Dasyneura vaccinii Smith) lays its eggs in the upright tips of cranberry (Vaccinium macrocarpon Ait.) plants. Feeding damage by newly hatched maggots leads to characteristic cupping of leaves in the upright tip. This damage is readily apparent to growers and has led to concern that damaged tips would not form terminal flower buds for the following season. Insecticide sprays and cultural practices intended to control this insect are generally ineffective. While studying the incidence of return bloom in cranberry uprights (Strik, B. C., et al. 1991. HortScience 26:1366-1367) heavy cranberry tipworm injury with little apparent effect on yield was noted. We initiated a three year study to examine the potential for cranberry plants to recover from tipworm injury and found that cranberry plants recover completely (no effect on flower bud production) from tipworm injury as long as the injury occurs before mid-August. Only 25% recovery from late-season infestations was found. However, such infestations seldom affected more than 5% of the upright tips. Based on our data, we calculated a maximum 6% loss of flower buds to cranberry tipworm in a year of high late-season infestations.