f o r t h e crop
Seasons of Change Fall and Winter Are Deceptively Important in Florida Blueberry Fields WITH THE ONSET OF THE FALL AND WINTER SEASONS, many changes are taking place in blueberry fields, including physiological changes in the plants and management changes in fertilization and irrigation practices. Flower bud initiation and development are important processes occurring now (although not readily apparent) that will likely have a direct effect on berry yields the following year. The first indications of flower bud initiation are usually visible (with the aid of a microscope) during late August for some cultivars, or in September for others. One study conducted at the Plant Science Research and Education Unit (PSREU) in Citra showed differences between “Emerald” and “Jewel” in the timing of flower bud primordia development. For “Emerald” a significant number of buds contained floral structures by early September. However, for “Jewel,” buds with floral structures were not found until October. In both cases, the number of buds with floral structures continued to increase through the final measuring date of mid-November. In general, flower bud initiation and development is believed to continue throughout the fall and early winter. Certain environmental conditions are needed for these processes to occur satisfactorily. Shorter day lengths combined with cooler night temperatures are important environmental cues that initiate the onset of dormancy (in deciduous production) and stimulate flower bud initiation in many crops, including blueberry. A study conducted at the University of Florida demonstrated that short day lengths (long uninterrupted dark periods) combined with cool temperatures stimulated greater flower bud development in southern highbush
Table 1. Effect of temperature and photoperiod on flower bud number per plant of ‘Misty’ southern highbush blueberry. Photoperiod Short day + night interrupt1 Short day2
21 (C) 0.6b 38.0a
TEMPERATURE
28 (C) 0.0b 8.6b
8-hour photoperiod followed by 16-hour dark period. 8-hour photoperiod followed by 16-hour dark period with one hour of light interrupt. From Timothy M. Spann. 2001. Environmental influences on flower bud initiation in Vaccinium species. Thesis. University of Florida.
1 2
blueberry (SHB) (Table 1). Table 1 clearly shows the importance of photoperiod and temperature on flower bud development in “Misty” SHB. Note that a short photoperiod was a requirement for flower bud development and high temperature (28 Co) had a strong inhibitory effect on flower bud development, even under short photoperiod conditions. Although “Misty” is no longer commonly grown, these traits appear to be common to most, if not all, SHB cultivars. Research at UF has also demonstrated that healthy leaves are needed during the processes of flower bud initiation and development. Figure 1 shows the effects of removing leaves early in the fall (September) vs maintaining healthy leaves throughout
the fall (until December). Not only were there more flower buds, but the flower buds were more completely developed (individual buds contained more florets) when healthy leaves were present throughout the fall, versus when leaves were removed in early fall. In this study, leaves were manually removed at various times, but one can imagine that early fall defoliation from one of several leaf spot diseases could have a similar deleterious effect on flower bud initiation and development. Summer pruning, leaf disease and pest management, and a sound fertilization/irrigation program are key management practices that lead to healthy fall foliage. As mentioned earlier, with the onset of fall and winter, blueberry plants enter continued on page 24
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