Effective vegetative growth management is essential in cranberry ( Vaccinium macrocarpon Ait.) production, as excessive canopy growth can compromise yield potential, fruit quality, and long-term bed health. This study evaluated the gibberellin biosynthesis inhibitor prohexadione-calcium (Pro-Ca) for its potential to control canopy growth in the cultivar ‘Stevens’. Pro-Ca rates of 83, 125, 250, and 375 mg l -1 and different application frequencies were evaluated over two years. The treatments effectively suppressed runner elongation and density, with the 125 mg l -1 rate providing maximum efficacy. Expanding treatment intervals from two to three weeks, or increasing applications from two to three, did not affect efficacy. In contrast to runners, upright growth was largely unaffected. Supplemental evaluations in the cultivar ‘Mullica Queen’ confirmed this lack of upright growth response. An exploratory hormone-profiling analysis did not detect clear differences in gibberellin, auxin (IAA), or cytokinin profiles associated with tissue type or Pro-Ca treatment that could explain this contrasting response. The two lowest Pro-Ca rates tested did not significantly affect yield, and key fruit quality traits, including titratable acidity, anthocyanin content, and total soluble solids, were generally unaffected. Four fungal genera commonly associated with cranberry fruit rot ( Coleophoma, Physalospora, Phomopsis, and Botrytis ) were identified in non-marketable berries; however, Pro-Ca treatments had minimal to no effect on non-marketable berry counts. Finally, carryover assessments indicated that prior-year Pro-Ca treatment may reduce runner density, but generally had no effect on runner length or yield. Overall, Pro-Ca shows potential as a canopy growth regulator for cranberry cultivars with excessive runner growth and warrants further evaluation.
Jayasinghege et al. (Fri,) studied this question.