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Blueberry (Vaccinium spp.) summer pruning can increase yield by promoting healthy fall foliage to support the reproductive development. However, there has been little research to examine the effects of timing and intensity of summer pruning in subtropical conditions. The objective of this study was to determine the effects of summer pruning timing and intensity on reproductive traits of mature ‘Jewel’ and ‘Emerald’ southern highbush blueberry (SHB) plants (V. corymbosum L. interspecific hybrid) in subtropical Florida. The effect of pruning time was evaluated by removing 30% of the canopy in June or July. The effect of intensity was evaluated by pruning either 30% or 60% of the canopy in June, followed by removal of the upper 5 cm of regrowth (‘‘tipping’’) in July. Both timing and intensity used nonpruned plants as a control. The same plants were evaluated over three consecutive seasons (June 2011–May 2014). Main effects of pruning time, intensity, and tipping were evaluated. Tipping did not affect the reproductive traits evaluated. ‘Emerald’ reproductive traits were unaffected by either summer pruning time or intensity over the 3-year study. ‘Jewel’ yield was unaffected in the first year, but was increased by 48% and 65% in years 2 and 3, respectively, in the 30% pruning treatment compared with the nonpruned control. Lack of pruning in ‘Jewel’ decreased inflorescence bud number compared with moderate pruning likely due to more diseased foliage that increased defoliation. Thus, pruning effects on reproductive traits were cultivar dependent. Leaving ‘Jewel’ plants unpruned for two or more seasons reduced inflorescence bud number and yield. Pruning blueberry (Vaccinium spp.) bushes is an important cultural practice (Mainland, 1989; Shutak and Marucci, 1966; Williamson et al., 2004) that, if done properly, results in a balance between plant vigor and cropping, and ensures new growth for the following season’s crop (Yarborough, 2006). The overall objectives of pruning are to obtain optimal and stable yields of high-quality fruit and to increase the plant life span (Pescie et al., 2011). Pruning renews the canopy and increases productivity of blueberry bushes by stimulating vegetative and reproductive growth. Pruning practices vary in different production regions based on climate, growing conditions, and blueberry species. SHB (V. corymbosum interspecific hybrid) is the major species of blueberry grown in Florida and other mild winter areas. High temperatures and a long-growing season characterize the climate where SHB are typically grown, and summer pruning after fruit harvest stimulates healthy vegetative growth through the end of the growing season by removing older foliage that would otherwise serve as source of inoculum for leaf diseases (Kovaleski et al., 2015a; Patten et al., 1991; Williamson et al., 2004). This is important as the fall foliage supports inflorescence bud development and increases carbohydrate reserve accumulation to support early fruit development the following growing season (Lyrene, 1992; Swain and Darnell, 2001, 2002; Williamson and Miller, 2002). Although summer pruning is an important commercial practice for SHB production, there has been little research examining the effects of timing and intensity of summer pruning on reproductive growth of this species. Ba~nados et al. (2009) compared no pruning and both early and late summer pruning in southern and northern (V. corymbosum) highbush blueberry cultivars. Early summer pruning increased inflorescence bud number in ‘O’Neal’ and ‘Star’ SHB compared with late summer pruning, whereas the nonpruned control had an intermediate inflorescence bud number. However, both summer pruning times decreased inflorescence bud number in ‘Elliott’, a northern highbush cultivar, compared with no pruning. Summer pruning effects on blueberry yield are also inconsistent. Williamson and Darnell (1996) found that no pruning and early summer pruning in ‘Sharpblue’ SHB increased the yield compared with late summer pruning in Florida. However, Pescie et al. (2011) found that summer pruning alone reduced yield of ‘O’Neal’ SHB compared with summer followed by winter pruning or compared with nonpruned plants in Argentina. Summer followed by winter pruning also increased fruit size in ‘O’Neal’ compared with no pruning (Pescie et al., 2011). Yield and fruit size in rabbiteye blueberry (Vaccinium virgatum) were increased by summer followed by winter pruning compared with winter pruning alone in North Carolina (Mainland, 1989). However, in Georgia, yield decreased in summer or winter pruned rabbiteye blueberries compared with nonpruned plants, although fruit size was greater in the pruned treatments compared with nonpruned (Austin, 1997). Krewer et al. (2004) found no differences in yield or fruit size between summer pruned and nonpruned rabbiteye blueberry in Georgia. The intensity of pruning plays a role in yield of blueberry bushes. Heavy summer pruning decreased yield of rabbiteye blueberry compared with moderate and no pruning in Louisiana, but had no effect on fruit size (Spiers et al., 2002). Davies (1983) found moderate pruning, regardless of season, produced the highest yields compared with heavy and nonpruned rabbiteye blueberries in Florida. Austin and Bondari (1989) reported that yield and fruit size of ‘Tifblue’ rabbiteye blueberry were similar among light, moderate, and heavy pruning intensities over a 5-year period in Georgia. Most summer pruning studies in blueberries have been carried out in climates far different from those found in subtropical blueberry production regions, and few studies have been done with SHB, which is expanding in acreage in the southeast United States and California, and warmer regions of Argentina and Chile (Ba~nados, 2004, 2009). The hypothesis tested in this research was that summer pruning increases reproductive growth and yield in SHB compared with no pruning. The objectives of this study were to determine the effects of timing and intensity of summer pruning on inflorescence bud number, number of fruits set per inflorescence bud, yield, and quality of berries in SHB. Materials and Methods ‘Emerald’ and ‘Jewel’ SHB plants, field planted at the UF-IFAS Plant Science Research and Education Unit in Citra, FL in 2006, were used in this experiment. ‘Emerald’ bushes are high yielding, with large, firm, flavorful berries that ripen from midApril to mid-May in north-central Florida (Lyrene, 2001a, 2008). ‘Jewel’ produces smaller, more tart berries, and generally Received for publication 5 June 2015. Accepted for publication 17 Aug. 2015. This work was supported by the Specialty Crop Block Grant Program, contract number 018005, USDA-AMS, the Florida Blueberry Growers’ Association and the National Institute of Food and Agriculture. Corresponding author. E-mail: jgrw@ufl.edu. 1486 HORTSCIENCE VOL. 50(10) OCTOBER 2015 yields less than ‘Emerald’ (Lyrene, 2001a, 2001b; Williamson and Lyrene, 2004). The planting was on raised pine bark beds and the plants were spaced 0.9 m by 2.7 m in-row and between rows, respectively. Fertilizer was applied at an annual rate of 2000 kg·ha of 12N–1.7P–6.6K, evenly distributed every 20 d fromMarch through October. The plants received irrigation throughmicrosprinklers at a rate of 9.5 mm·d from mid-February through mid-October and 7.1 mm·d from mid-October through mid-February; and overhead irrigation provided frost protection. Hydrogen cyanamide (1.5% v/v) was applied in late December to defoliate plants and aid in fulfilling the chilling requirement. Pruning treatments to assess effects of timing, intensity, and shoot tipping were imposed after fruit harvest in Spring 2011. To determine effects of pruning time, 30% of the canopy was removed in June (early) or July (late). To determine pruning intensity effects, either 30% (moderate) or 60% (heavy) of the canopy was removed in June, both followed by shoot tipping in July. Both timing and intensity treatments were compared with a nonpruned control. The effect of shoot tipping was assessed by comparing tipping vs. no tipping in July on plants that received moderate pruning in June. Pruning treatments, as well as tipping, were done mechanically, pruning the top and sides of plants with a hand-held hedge trimmer PP2822 (Poulan PRO; Charlotte, NC.). Tipping consisted of removal of about the top 4 cm of regrowth. In 2012 and 2013, the treatments were pruned 5 cm above the cut from the previous year (followed by tipping when appropriate), therefore, achieving about the same initial pruned plant size for each treatment. The experiment was a randomized complete block design (RCBD), with four plant plots (one guard plant on each side and two central data plants) and six replications per cultivar. Because the field consisted of alternating rows of ‘Emerald’ and ‘Jewel’, each cultivar was evaluated independently for pruning intensity, timing, and tipping and direct comparisons between the two cultivars were not made. Data were collected for three seasons starting with the first pruning in 2011, using different seasons as repeated measures. Pairwise comparisons were made to test the main effects of timing, intensity, and tipping. Following shoot growth cessation in the fall, five shoots per plant originating from regrowth after the pruning treatments—or in the case of the nonpruned control, the entire year’s shoot growth—were randomly selected for assessment of the total number of inflorescence buds per shoot, inflorescence bud density (number of inflorescence buds per centimeter), and number of fruits per inflorescence bud. For inflorescence bud density, the total length of the regrowth shoot was used for the pruned treatments, whereas for the nonpruned control the entire year’s shoot growth was used. The number of fruits per inflorescence bud was assessed the week before first harvest to assure only fruits that set were included, and was done by counting the number of

Effects of Timing and Intensity of Summer Pruning on Reproductive Traits of Two Southern Highbush Blueberry Cultivars