2019 ASHS Annual Conference

Huanglongbing (HLB)-affected trees often display prolonged flowering period. Typically, in Florida, the flowering period in sweet oranges expands from late-January to mid-April with multiple waves of bloom. Such extended period of flowering results in difficulty for grove management especially, for the management of flower-associated fungal pathogens such as Colletotrichum acutatum, the causal agent for postbloom fruit drop (PFD). Gibberellins (GA) are well known to suppress flowering in citrus trees. Therefore, it can be a useful tool to manipulate flowering for better disease management. Hence, the objective of this study was to evaluate the potential of GA in synchronizing flowering in HLB-affected sweet orange cultivar Valencia. Trees were applied with GA five times from September to January at the rate of 20 g active ingredient per acre with surfactant and were compared to trees treated with surfactant only. The experiment was replicated at two separate locations, known to have close to 100% HLB infection and the history of PFD. The GA application resulted in a 55 to 60% reduction in floral intensity and a shift of full bloom by almost 2 weeks compared to untreated control trees. The flowering in GA-treated trees was more synchronized, with all the flowering activity occurring in period of 4 weeks whereas the flowering in control trees spread for about 6-7 weeks. Overall, the results of this research suggest that GA can be effectively used to alter the flowering pattern to benefit grove management.