Pruning blueberries is a recommended practice to maintain the balance between vegetative vigor and reproductive growth (Mainland, 1989; Shutak and Marucci, 1966; Williamson et al., 2004; Yarborough, 2006). Pruning improves light penetration into the canopy, adjusts leaf:fruit and shoot:root ratios (Rana et al., 2011; Ryugo, 1986), improves harvest efficiency, and reduces limb breakage (Austin, 1997; Clark and Matheny, 2010; Hrotkó, 2013). Lack of pruning, however, results in excessively tall, hard-to-pick bushes (Krewer et al., 2004; Pescie et al., 2011; Strik et al., 2003) and decreases vigor and node number in regrowth shoots (Pescie et al., 2011).
Low-chill subtropical production areas use southern highbush blueberry (SHB) cultivars and rely on high prices obtained for early-season fruit (Lyrene, 1992; Williamson and Lyrene, 2004a, 2004b). Summer pruning after fruit harvest is used in these areas to stimulate healthy vegetative growth for the remainder of the growing season (Patten et al., 1991; Williamson et al., 2004). Healthy foliage must be maintained in blueberry during the long growing season after fruit harvest to support optimal flower bud development and carbohydrate reserve replenishment (Lyrene, 1992, 2005; Williamson and Miller, 2002). These carbohydrates are used to supply the intensive sink demand of flowering and early fruit development the next growing season (Swain and Darnell, 2001, 2002). However, both timing and severity of summer pruning must be considered to obtain desired results (Rana et al., 2011). Early or heavy summer pruning can result in excessive regrowth, late pruning can reduce cold-hardiness, and lack of pruning can reduce the amount of regrowth (Mika and Piatkowski, 1989; Pescie et al., 2011; Williamson and Darnell, 1996).
Several studies have been done on summer pruning in blueberry (Austin, 1997; Austin and Bondari, 1989; Bañados et al., 2009; Davies, 1983; Krewer et al., 2004; Mainland, 1989; Pescie et al., 2011; Spiers et al., 2002; Williamson and Darnell, 1996); however, few studies describe the effects on vegetative traits. In Chile, early summer pruning of southern and northern highbush (V. corymbosum) blueberries increased lateral shoot number and length compared with late pruning (Bañados et al., 2009). Williamson and Darnell (1996) reported that regrowth and canopy volume of ‘Sharpblue’ SHB was greater when plants were pruned early after harvest compared with plants pruned later. Although severe pruning also increased regrowth compared with moderate and no pruning, regrowth volume was not enough to compensate for the loss in canopy volume resulting from pruning. Austin and Bondari (1989) found no differences in plant height measured 1 year after different pruning treatments in ‘Tifblue’ rabbiteye blueberry grown in Georgia, regardless of season or intensity of pruning. Similar results were found by Krewer et al. (2004) in ‘Climax’ rabbiteye blueberry. Mainland (1989), however, found that winter followed by summer pruning decreased rabbiteye blueberry plant size compared with winter pruning in North Carolina. In Louisiana, summer pruning of rabbiteye blueberries resulted in more and longer shoots compared with no pruning (Spiers et al., 2002). Summer pruning of blueberry appears to have more positive effects in climates with longer growing seasons (Bañados et al., 2009; Williamson and Darnell, 1996); however, proper timing and intensity of pruning remain to be determined.
Pruning reduces disease levels possibly by reducing inoculum levels, decreasing moisture retention inside the canopy, and increasing pesticide coverage (Hanson et al., 2000). Furthermore, pruning can promote vigor of the plant, increasing the productivity and survival even in the presence of disease (Smith, 2006a, 2006b; Williamson et al., 2004). Summer pruning can be useful in controlling leaf diseases such as septoria leaf spot (Septoria albopunctata) and blueberry leaf rust (Pucciniastrum vaccinii), which are emerging problems with the expansion of SHB production (Scherm et al., 2001). These leaf diseases cause marked reductions in photosynthesis (Roloff et al., 2004), fruit set, and yield (Ojiambo et al., 2006) and often cause severe defoliation (Lyrene, 1992; Ojiambo and Scherm, 2005a). However, the wounds caused by pruning can increase plant susceptibility to other diseases, most notably stem blight (Botryosphaeria dothidea, Lasiodiplodia theobromae, and Neofusicoccum ribis) (Milholland, 1972), which has been identified as the disease with the greatest economic impact in the Florida blueberry industry (Wright and Harmon, 2010). Although pruning appears to be associated with disease incidence, there are no studies that have examined the effect of timing and intensity of summer pruning on diseases in blueberry.
Most summer pruning studies on blueberries have been done in climates far different from those found in the subtropical blueberry production regions, and few studies have been done with SHB, which is expanding in acreage in the southeast United States and California, warmer regions of Argentina and Chile, and Mexico (Bañados, 2004, 2009). Furthermore, most studies have little information on the effects of pruning on vegetative growth or disease incidence and severity. The hypothesis tested in the current research was that summer pruning stimulates vegetative regrowth and reduces disease incidence in SHB. The objectives of this study were to determine the effects of timing and severity of summer pruning on vegetative growth, defoliation, incidence of leaf spots, and incidence and severity of stem blight in SHB.
Austin, M.E. & Bondari, K. 1989 Fertilizer rate and hedging intensity influences on the yield and fruit size of rabbiteye blueberry, cultivar Tifblue Fert. Res. 18 233 243
Bañados, M.P. 2009 Expanding blueberry production into non-traditional production areas: Northern Chile and Argentina, Mexico and Spain Acta Hort. 810 439 444
Clark, J.R. & Matheny, N. 2010 The research foundation to tree pruning: A review of the literature Arboricult. and Urban For. 36 110 120
Davies, F.S. 1983 Pruning, yield and morphology of 3 rabbiteye blueberry cultivars in Florida Proc. Fla. State Hort. Soc. 96 192 195
Hanson, E., Hancock, J., Ramsdell, D.C., Schilder, A., Vanee, G. & Ledebuhr, R. 2000 Sprayer type and pruning affect the incidence of blueberry fruit rots HortScience 35 235 238
Kovaleski, A.P., Williamson, J.G., Olmstead, J.W. & Darnell, R.L. 2015 Inflorescence bud initiation, development, and bloom in two southern highbush blueberry cultivars J. Amer. Soc. Hort. Sci. (in press)
Krewer, G., Stanaland, D., NeSmith, S. & Mullinix, B. 2004 Post-harvest hedging and pruning of three year pruning trial on ‘Climax’ and ‘Tifblue’ rabbiteye blueberry Small Fruits Rev. 3 203 212
Lyrene, P.M. 2001a Blueberry plant called ‘Emerald’. U.S. Patent No. PP12,165. 23 Oct. 2001
Lyrene, P.M. 2001b Blueberry plant named ‘Jewel’. U.S. Patent No. PP11,807. 13 Mar. 2001
Mainland, C.M. 1989 Managing the growth and fruiting of rabbiteye (Vaccinium ashei Reade) blueberries with pruning and growth regulators Acta Hort. 241 195 200
McFadyen, L.M., Robertson, D., Sedgley, M., Kristiansen, P. & Olesen, T. 2011 Post-pruning shoot growth increases fruit abscission and reduces stem carbohydrates and yield in macadamia Ann. Bot. (Lond.) 107 993 1001
Ojiambo, P.S. & Scherm, H. 2005a Survival analysis of time to abscission of blueberry leaves affected by septoria leaf spot Phytopathology 95 108 113
Ojiambo, P.S. & Scherm, H. 2005b Temporal progress of septoria leaf spot on rabbiteye blueberry (Vaccinium ashei) Plant Dis. 89 1090 1096
Ojiambo, P.S. & Scherm, H. 2006 Optimum sample size for determining disease severity and defoliation associated with septoria leaf spot of blueberry Plant Dis. 90 1209 1213
Ojiambo, P.S., Scherm, H. & Brannen, P.M. 2006 Septoria leaf spot reduces flower bud set and yield potential of rabbiteye and southern highbush blueberries Plant Dis. 90 51 57
Patten, K., Neuendorff, E., Nimr, G., Clark, J.R. & Fernandez, G. 1991 Cold injury of southern blueberries as a function of germplasm and season of flower bud development HortScience 26 18 20
Pescie, M., Borda, M., Fedyszak, P. & López, C. 2011 Efecto del momento y tipo de poda sobre el rendimiento y calidade del fruto en arándano altos del sur (Vaccinium corymbosum) var. O’Neal en la provincia de Buenos Aires Rev. de Invest. Agrop. 37 268 274
Rana, V.S., Basar, J. & Rehalia, A.S. 2011 Effect of time and severity of summer pruning on the vine characteristics, fruit yield and quality of kiwifruit Acta Hort. 913 393 400
Roloff, I., Scherm, H. & van Iersel, M.W. 2004 Photosynthesis of blueberry leaves as affected by septoria leaf spot and abiotic leaf damage Plant Dis. 88 397 401
Ryugo, K. 1986 Promotion and inhibition of flower initiation and fruit set by plant manipulation and hormones, a review Acta Hort. 179 301 307
Scherm, H., NeSmith, D.S., Horton, D.L. & Krewer, G. 2001 A survey of horticultural and pest management practices of the Georgia blueberry industry Small Fruits Rev. 1 17 28
Scherm, H., Savelle, A.T., Brannen, P.M. & Krewer, G. 2007 Occurrence and prevalence of foliar diseases on blueberry in Georgia Plant Health Prog 6 June 2014. <http://www.plantmanagementnetwork.org/pub/php/research/2008/blueberry/>
Shutak, V.G. & Marucci, P.E. 1966 Plant and fruit development. In: Eck, P. and N.F. Childers (eds.). Blueberry culture. Rutgers Univ. Press, New Brunswick, NJ
Smith, B.J. 2006a Phytophthora root rot and Botryosphaeria stem blight: Important diseases of southern highbush blueberries in the Southern United States Acta Hort. 715 473 479
Strik, B., Buller, G. & Hellman, E. 2003 Pruning severity affects yield, berry weight, and hand harvest efficiency of highbush blueberry HortScience 38 196 199
Swain, P.A.W. & Darnell, R.L. 2001 Differences in phenology and reserve carbohydrate concentrations between dormant and nondormant production systems in southern highbush blueberry J. Amer. Soc. Hort. Sci. 126 386 393
Swain, P.A.W. & Darnell, R.L. 2002 Production systems influence source limitations to growth in ‘Sharpblue’ southern highbush blueberry J. Amer. Soc. Hort. Sci. 127 409 414
Williamson, J.G. & Darnell, R.L. 1996 Severity and timing of mechanical rejuvenation pruning affects vegetative and reproductive growth of blueberry HortScience 31 663 (abstr.)
Williamson, J.G., Davies, F. & Lyrene, P.M. 2004 Pruning blueberry plants in Florida. University of Florida, Gainesville, FL. 6 June 2014. <http://edis.ifas.ufl.edu/hs223>
Williamson, J.G. & Miller, E.P. 2002 Early and mid-fall defoliation reduces flower bud number and yield of southern highbush blueberry HortTechnology 12 214 216
Williamson, J.G. & Lyrene, P.M. 2004a Blueberry varieties for Florida. University of Florida, Gainesville, FL. 6 June 2014. <http://edis.ifas.ufl.edu/pdffiles/HS/HS21500.pdf>
Williamson, J.G., Lyrene, P.M. & Olmstead, J.W. 2012 Blueberry gardener’s guide. University of Florida, Gainesville, FL. 6 June 2014. <http://edis.ifas.ufl.edu/mg359>
Williamson, J.G., Olmstead, J.W., England, G.K. & Lyrene, P.M. 2014 Southern highbush blueberry cultivars from the University of Florida. University of Florida, Gainesville FL. 7 July 2014. <http://edis.ifas.ufl.edu/hs1245>
Wright, A.F. & Harmon, P.F. 2010 Identification of species in the Botryosphaeriaceae family causing stem blight on southern highbush blueberry in Florida Plant Dis. 94 966 971
Yarborough, D.E. 2006 Blueberry pruning and pollination. In: Childers, N.F. (ed.). Blueberries for growers, gardeners, promoters. Horticultural Publications, Gainesville, FL