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Jeffrey G. Williamson* and E. Paul Miller

Poor fruit set and sub-optimum berry size are potential yield- and profit-limiting factors for southern highbush (Vaccinium corymbosum) blueberry production in Florida. The cytokinin N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) has increased fruit size and fruit set of a number of fruit crops including rabbiteye blueberry. The purpose of this study was to determine the effects of CPPU applied at different rates and phenological stages of bloom and/or fruit development on fruit size, set, and yield of southern highbush blueberry. `Millennia' and `Star' southern highbush blueberry plants located on a commercial blueberry farm in Alachua County, Fla., were treated with 5 or 10 ppm CPPU at various stages of development ranging from full bloom to 20 days after full bloom. In contrast to findings with rabbiteye blueberry, fruit set in this study of southern highbush blueberry was not affected by any of the CPPU treatments when compared to the controls. Nor was total fruit yield affected by CPPU treatments. The most noticeable potential benefit found in this study was an increase in mean fruit fresh weight from CPPU treatments. However, cultivars responded differently to CPPU with respect to mean fruit fresh weight. For `Millennia', only one CPPU treatment increased mean fruit weight compared to controls. However, for `Star', all but one CPPU treatment increased mean fruit fresh weight. Several CPPU treatments resulted in delayed fruit ripening for `Star' but not for `Millennia'. For `Star', the treatments that most consistently delayed fruit ripening tended to have greater fruit fresh weights.

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Jeffrey G. Williamson and D. Scott NeSmith

The effects of flower bud removal treatments on growth of young rabbiteye (Vaccinium ashei Reade) and southern highbush (V. corymbosum hybrids) blueberry plants were evaluated. Treatments consisted of pruning, hand stripping, and hydrogen cyanamide applications. The growth index of rabbiteye plants after the first spring growth cycle was unaffected by any of the flower bud removal treatments. However, the effects of flower bud thinning were cultivar specific for southern highbush blueberry plants. ‘Misty’ plants showed increases in total plant dry weight and in root, leaf, and stem dry weights from hand thinning and hydrogen cyanamide sprays. Conversely, ‘Santa Fe’ showed no increased growth response from any of the flower bud removal treatments. Flower bud mortality increased as hydrogen cyanamide spray concentration increased and was greater when applications were delayed so that flower buds were more advanced. Hydrogen cyanamide may have potential as an alternative to labor-intense flower bud removal practices such as hand stripping or pruning on young blueberry plants during establishment.

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Jeffrey G. Williamson and E. Paul Miller

Bearing `Misty' and `Star' southern highbush blueberries were grown on pine bark beds and fertilized at three rates using granular and liquid fertilizers with a 3–1–2 (1N–0.83K–0.88P) ratio. Granular fertilizer was applied 8 times per year at 4-week intervals beginning in April and continuing through October. Liquid fertilizer was applied with low volume irrigation 16 times per year at 2-week intervals during the same period. During the growing season, irrigation was applied at 2- to 3-day intervals in the absence of rain. A 2 cultivar × 2 fertilizer type × 3 fertilizer rate factorial arrangement of treatments was replicated 8 times in a randomized complete-block design. All fruits were harvested from single-plant plots at 3- to 4-day intervals. Canopy volume was not affected by fertilizer type, but fruit yield was slightly greater for granular than for liquid fertilizer treatments. In 2003, fruit yield of 2.5-year-old `Misty' and `Star' plants increased with increasing fertilizer rates up to the highest rate tested (50 g N/plant/year). Similarly, in 2004, fruit yields increased with increasing fertilizer rates up to the highest rate (81 g N/plant/year). Root distribution was limited to the 12-cm-deep layer of pine bark with very few roots penetrating into the underlying soil. The positive growth responses of blueberry plants to high fertilizer rates in pine bark beds suggests that soluble fertilizer was leached through the pine bark layer into the soil below the root zone. More frequent, lighter applications of soluble fertilizers, use of slow-release or controlled-release fertilizers, and careful irrigation management may improve fertilizer use efficiency of blueberry plantings on pine bark beds.

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Jeffrey G. Williamson and E.P. Miller

In 1998, representative canes of mature, field-grown, `Misty' and `Sharpblue' southern highbush blueberry were hand-defoliated on 4 Sept., 2 Oct., 6 Nov., 7 Dec., or not defoliated. The experiment was repeated in 1999. Randomized complete-block designs with 11 (1998) or 10 (1999) replications were used. The early defoliation treatments (4 Sept. and 2 Oct.) resulted in reduced flower bud number per unit length of cane for `Misty', but not for `Sharpblue', when compared with later defoliation treatments or controls. A similar response to early defoliation was found both years for both cultivars. The later defoliation treatments (6 Nov. and 7 Dec.) had no significant effect on flower bud number compared to controls. Early defoliation had a negative effect on flower bud development for both cultivars. Flower buds that developed on canes defoliated on 4 Sept. or on 2 Oct. had smaller diameters than flower buds on canes defoliated on 6 Nov., 7 Dec., or on non-defoliated canes. Fruit fresh weight per unit cane length was less for the September and October defoliation treatments than for the December defoliation treatment or controls. These results support the need for summer pruning and a effective summer spray program to control leaf spot diseases that often result in early fall defoliation of southern highbush blueberries grown in the southeastern United States.

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Jeffrey G. Williamson and D. Scott NeSmith

Greenhouse and field experiments were conducted to determine the effects of the growth regulator N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) on fruit set, berry size, and yield of southern highbush blueberry (Vaccinium corymbosum hybrids). The experiments were conducted over a period of several years in Georgia and Florida. CPPU sprays were capable of increasing fruit set and berry weight of southern highbush blueberry, although the responses to CPPU treatment were variable and appeared to be influenced by factors such as rate, spray timing, and cultivar. In Florida, high natural fruit set may have prevented increased fruit set from CPPU. A slight delay in berry maturity was noted in several experiments. Spray burn occurred on several occasions and may be related to factors such as cultivar, rate, spray volume, and use of surfactant.

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Wendy L. Wilber and Jeffrey G. Williamson

The effects of fertilizer rate and composition on growth and fruiting of ‘Misty’ and ‘Star’ southern highbush blueberry were evaluated in a containerized production system using pine bark medium. Two fertilizer analyses (12N–1.8P–46.6K and 12N–5.2P–9.9K) and three fertilizer rates were used. Plant growth and fruiting were unaffected by fertilizer analysis. Growth and fruit yield of ‘Star’ increased linearly with increasing fertilizer rate. For ‘Misty’, plant growth and yield were reduced at the highest fertilizer rate as a result of a high incidence of blueberry stem blight associated with that treatment. Flower bud density was highest for the ‘Misty’ plants receiving the high fertilizer rate and this may have resulted in excessive fruit set leading to stress-induced blueberry stem blight. Optimum fertilizer rates for young southern highbush blueberry plants grown in containerized pine bark systems appear to be cultivar-specific and similar to fertilizer requirements in soil culture.

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Jeffrey G. Williamson and Jonathan H. Crane

A wide variety of temperate, subtropical, and tropical fruit crops are grown commercially in Florida. Farm size ranges from large commercial operations exceeding 100 acres to small 1- or 2-acre “estate” farms. Irrigation and fertilization practices vary widely with crop, soil type, and management philosophy. However, many growers are adopting practices such as microirrigation, fertigation, and other technologies, which, if properly used, should reduce water and fertilizer inputs and minimize leaching and runoff of fertilizers and pesticides. Although fertilizer and irrigation recommendations exist for major crops such as avocado (Persea americana), mango (Mangifera indica), and blueberry (Vaccinium spp.), there is little research-based information specific to Florida for many minor crops, including muscadine (Vitis rodundifolia), blackberry (Rubus spp.), sapodilla (Manilkara zapota), guava (Psidium guajava), papaya (Carica papaya), and others. Even where recommendations exist, refinement of irrigation and fertilization practices is needed because of changes in technology.

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Rebecca L. Darnell, Nicacio Cruz-Huerta and Jeffrey G. Williamson

Low night temperatures and/or high source-sink ratios increase ovary swelling and subsequent fruit malformation in many sweet peppers (Capsicum annuum), including bell pepper. Although this response has been correlated with increased ovary carbohydrate accumulation, evidence for this is limited. Furthermore, it is unknown how the combined effects of night temperature and source-sink ratio affect ovary carbohydrate accumulation and ovary swelling. The objectives of the present work were to determine night temperature and source-sink effects on ovary swelling, net carbon exchange rate (CER), and soluble sugar and starch concentrations in bell pepper ovaries at anthesis. Source-sink and temperature effects were tested by comparing fruiting (low source-sink ratio or high sink demand) with non-fruiting (high source-sink ratio or low sink demand) ‘Legionnaire’ bell pepper plants grown at 22/20 °C [high night temperature (HNT)] or 22/12 °C [low night temperature (LNT)] day:night temperatures. Flowers that opened after imposition of the temperature and fruiting treatments were harvested at anthesis. Ovaries from harvested flowers were weighed and analyzed for non-structural carbohydrates. Leaf gas exchange measurements were performed every 3 days. Ovary fresh weight of flowers harvested at anthesis was highest in non-fruiting plants under LNT and lowest in plants grown under HNT regardless of fruiting status. Mean CER averaged over the experimental period was significantly higher in fruiting plants under HNT compared with all other treatments. There were no significant interactions between night temperature and fruiting status on ovary soluble sugar or starch concentrations. Low night temperature increased glucose, fructose, and starch concentration and decreased sucrose concentration in the ovary wall compared with HNT. There were no differences in soluble sugar or starch concentrations in the ovary wall between fruiting and non-fruiting plants. Thus, although both low temperature and high source-sink ratio (i.e., non-fruiting plants) resulted in ovary swelling, the mechanisms appear to differ. Whereas LNT effects on ovary swelling were associated with increased ovary carbohydrate accumulation, this association was not apparent when ovary swelling occurred in response to high source-sink ratios.

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Jeffrey G. Williamson, Karen E. Koch and William S. Castle

Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] seedlings were budded with `Hamlin' orange [Citrus sinensis (L.) Osb.] and subjected to 3 bud forcing treatments: (1) topping [T] by removing the seedling above the bud union; (2) lopping [L] by cutting half way through the seedling above the bud union and breaking the rootstock over; or, (3) bending [B] the seedling top over and tying it to the base of the plant. As scion buds emerged and grew, plants were sacrificed for dry weight measurements; also, the portion of the rootstock seedling above the bud union was exposed to 14CO2 at 3 stages of scion development. Plants with seedling tops attached (B,L) gained more dry weight and fibrous roots than T seedlings. Scion elongation was greater for B plants than for T plants. Plants usually flushed twice regardless of bud forcing treatment. No treatment differences were noted for time of flushing or scion bud emergence. Labeled photosynthate from attached rootstock leaves was translocated to scions during both flushes suggesting that recently fixed C enhanced scion growth for B and L plants.