). Successful implementation of minimal or machine pruning in vineyards often requires hand follow-up or fruit thinning to achieve desired fruit maturity and composition ( Fendinger et al., 1996 ; Fisher et al., 1996a , 1996b ; Morris, 2005 ; Petrie and
management strategies to maintain fruit size via some form of pre or postbloom flower/fruit thinning has been the subject of recent investigation ( Schoedl et al., 2009 ; Whiting and Ophardt, 2005 ; Whiting et al., 2006 ). To date, inconsistent response of
. Glozer and Hasey (2006) estimated that hand-thinning labor represents 31% of all cultural costs associated with cling peach production, with labor requirements ranging from 25 to over 100 h/acre. Estimates for other fresh fruit peach cultivars are
Production of extra-early cling peach varieties in California typically results in a $988 per hectare loss for Sacramento Valley growers, based on a 2004 University of California cost analysis study. This net loss is due to a number of factors, including lower yields than late-harvested peaches; and pruning, thinning, and harvest labor. The estimated cost per hectare to hand-thin extra-early varieties is $1515, which is 31% of all cultural costs. A conservative estimate for machine thinning with transportation costs would be $136 per hectare, a cost savings of about 90%. Machine thinning operates at about 200 trees per hour with two persons (operator and supervisor), compared to four to six trees per hour with two hand-thinners. In recent years, equipment to mechanically thin and harvest has become more sophisticated. We evaluated different types of equipment and settings in two experimental orchards trained in two pruning systems in 2005. We compared effects of crop load and variability in fruit development at time of shaking, as well as the timing of shaking with respect to fruit growth after bloom and compared mechanical and hand thinning. We found an optimum “window” for mechanical thinning based on fruit size and crop load, with tree architecture less important than these factors. Machine-thinning with follow-up hand-thinning reduced the thinning time by 30% to 41%. When machine thinning without follow-up hand-thinning was compared to hand-thinning alone, total yield was improved by 22% and salable yield was improved by 18% in the machine-thinned trees. The net increase in undersized yield in the machine-thinned only treatment was less than 6%.
Fruit of `Mohawk' in 1986 and 1988 and `Shoshoni' pecan [Carya illinoensis (Wangenh.) C. Koch] in 1986 were thinned during early August using a pecan shaker with modified shaker pads. Fruit removed ranged from 44% to 57% of the crop load. Fruit thinning increased nut size of `Mohawk' in both years, but did not affect nut size of `Shoshoni'. Kernel percentage of thinned `Mohawk' and `Shoshoni' trees increased, and kernel grade of `Mohawk' improved relative to unthinned trees. Return bloom of `Mohawk' was not affected either year by thinning, but return bloom on `Shoshoni' was increased by thinning. Mechanical fruit thinning appears to be a useful commercial tool until better thinning methods are available.
on thinning biennially bearing apple cultivars described in the review by Dennis (2000) . Hypothetically there must be an optimal thinning regime that would provide good fruit size and consistent return bloom and yield every year, leading to
A mechanical bloom-thinning technique, using suspended flexible strands of rubber belting or rope moved through trees on a frame mounted on a forklift, was tested on ‘Early Loring’ peach [Prunus persica (L.) Batsch]. Heaviest thinning occurred in the upper two-thirds of the tree canopy. Shoot orientation and flower position did not affect bloom removal. Maximum bloom removal occurred at full bloom when the thinning machine passed through a tree at least four times. Operating at an increased tractor speed increased thinning. The most effective treatments removed 45% to 59% of the blossoms, reduced number of fruit from 18 to around 10/cm2 limb cross-sectional area (CSA) and reduced hand thinning time by 30%.
of action are normally made during this period to reduce fruit set to commercially acceptable levels that eliminate the need for hand thinning, increase fruit size at harvest, and increase the probability of adequate return bloom in the next year
The use of chemical thinners is an essential component of commercial apple production in Ontario. As chemical thinning options decrease, due to environmental concerns, newer and less toxic alternatives must be found. Benzyladenine (BA), available in the United States as Accel, shows promise as a thinning agent. During the 1994 growing season, Accel was applied under commercial conditions to seven apple cultivars—`McIntosh' (spur), Delicious `Starkrimson', `Empire', `Jonagold', `Golden Delicious', `Jonamac', and Gala `Royal Gala'. Application concentrations ranged from 50 to 75 ppm (a.i. BA), depending on cultivar. Mean king fruitlet diameter at time of application ranged from 9 to 12 mm. The thinning response of Accel was compared with that of traditional chemical (e.g., carbaryl, NAA, or both) or mechanical thinning treatments. At the concentrations used in this experiment, thinning with Accel was comparable or better than traditional methods in the case of `Gala', `Jonagold', `Empire', and `Golden Delicious'. In those cultivar trials displaying an acceptable Accel thinning response, a significant fruit size increase also was observed.
Blossom thinning trials with AKZO Co. surfactant Armothin were carried out on fruitful peach cultivars Early Grande and Babcock during 1993–94. Effective thinning occurred before “full bloom” (40% to 90% FB) at 3% Armothin, increasing between 2% and 4%. However, an improved fruit distribution of `Early Grande' was achieved by repeated application (35% + 75% FB) at 2%. A second spray at 3%, just after FB, thinned some late-blooming flowers on `Babcock' trees, but a temporary leach scorch occurred, as well as with 4% Armothin (single spray) on both cultivars. For a single spray, the optimal stage was found within 60% to 90% FB, at 3% Armothin. Flower biology studies showed susceptibility of the petals to increasing Armothin concentrations at all stages, but pollen tube penetration into the pistils and subsequent fertilization failed only after an earlier application, before anthesis or pollination of the stigma. Within this range of concentration and timing, no damage occurred to the vital fruit set and to commercial yield, provided that weather conditions were favorable during bloom (and spray). Some corrective hand-thinning (20% to 60%) should be applied to the fruitful trees 3 to 4 weeks later to achieve optimal fruit size at harvest. Blossom hand-thinning is still practical in Israel.