Timing and intensity of flowering of sweet orange [Citrus sinensis (L.) Osbeck] as a function of local weather factors and crop under central Florida conditions

Under Florida conditions, flower bud induction is caused by low-temperature stress during the winter. High temperatures during spring bring about influorescence differentiation, followed by anthesis. A study was conducted to quantify the flowering response of citrus trees to low temperatures and crop load. Selected branches of mature sweet orange ‘Valencia’ and ‘Hamlin’ trees, carrying two levels of crop load, were tagged and then exposed to fall-winter inductive conditions. Floral induction was interrupted during the wintertime (November to February) twice monthly of different sets of branches. Treatments consisted of different flower induction levels. Phenological response to season, induction, and crop load treatments was evaluated in terms of bud sprouting and flowering response (including floral distribution). Phenological response was related to weather information using regression analysis. The factors that determined the phenological response of an individual bud to environmental conditions included cultivar, position of the bud along the shoot, shoot age, induction level, and crop load. Hours in the high temperature ranges decreased the sprouting of vegetative buds, while low temperatures increased the sprouting of reproductive buds. Crop load decreased the sprouting of reproductive buds and increased the sprouting of vegetative buds. Low temperatures and crop load were the two most important factors affecting floral intensity.; A second study was conducted that analyzed the effect of Florida's irregular winter weather on date of peak flowering, which may vary from mid-February to mid-April. Historical weather and flowering records (from 1959 to 2000) were used to develop mathematical models to predict the occurrence of peak anthesis and explain the presence of multiple bloom periods. Models that use average temperature, number of hours within temperature ranges, and degree-days were established to predict bloom date. These models, although accurate under Florida conditions, may not be used in other citrus production areas. Periods of relatively high temperatures occur during the winter and spring in Florida. Furthermore, insufficient high temperatures during differentiation and flower bud expansion also prevent extrapolation to tropical environments.; A Decision Support System (DSS) was developed to provide growers with recommendations for their citrus production practices. Best management practices often require that a given practice be applied at a specific stage of phenological development. Because of the variable flowering dates that occur, the proper timing of any given production practice may vary by as much as 2 months. The DSS includes modules for phenological development and for the scheduling of production practices. Mathematical models developed from this research were implemented to drive the phenology component. The phenological component was integrated with other expert systems, to aid in the decision making process of citrus growers.