P-289 - Relative susceptibility of northern highbush blueberry flower and fruit stages to infection by Botrytis cinerea

Botrytis blight and fruit rot, caused by Botrytis cinerea, result in significant losses for the Pacific Northwest highbush blueberry industry. Timing of management, e.g., fungicide applications, is critical, but vulnerability of blueberry flower and fruit stages to infection has not been well established. Toward this objective, a screenhouse trial was conducted with three-year-old potted ‘Draper’ plants in a randomized complete block design with five replicates. Flowers and fruit at nine phenological stages ranging from green flower bud to 75% blue fruit were spray inoculated with a 10⁶ conidia/ml suspension. Prior to inoculation, senesced petals were removed from a subset of plants at the green fruit stage to assess potential mitigation of B. cinerea infection. Flowers inoculated at full bloom were 9.6 times as likely to become infected one week after inoculation compared to those inoculated at the green bud stage (P = 0.04), based on one year of data analyzed with generalized mixed linear models. No other significant differences in infection risk were observed between full bloom and other stages. Green fruit with senesced petals were twice as likely to become infected one week after inoculation compared to fruit with senesced petals removed (P = 0.03). The first year of data indicate that stages around full bloom may be similarly susceptible to B. cinerea infection and that petals may support early establishment of B. cinerea. If this finding is supported in subsequent trials, removing senesced petals to interrupt the disease cycle may be a new management strategy.