Limb Cross-sectional Area Research Articles

BLOOM THINNING OF PEACH AND NECTARINE WITH MONOCARBAMIDE DIHYDROGENSULFATE

Increased fruit weight, advanced fruit maturity, increased shoot growth and greater flower bud formation are positively related to thinning severity and timing. Thinning at bloom shows greatest effects. Although costly, hand removal is the primary thinning method. Chemical means have been used but have had disadvantages and/or lack of industry support. A new compound, monocarbamide dihydrogensulfate, has been used on apple. Trials conducted on `Golden Queen' clingstone peach and `Fantasia' nectarine in New Zealand and on `Winblo' peach in Georgia suggest that this compound has significant potential for use in thinning stone fruit. An effective material rate (79-82% a.i. formulation) of 12 l/ha applied via airblast sprayer (calibrated delivery 1200 l/ha total volume) on peach resulted in a 56% reduction in flowers per limb cross-sectional area compared to unthinned controls when applied at full bloom. No phytotoxicity has been observed.

Influence of orchard management system on canopy composition, light distribution, net photosynthesis and transpiration of apple trees

In a study in Australia, eight orchard management systems with six year old ‘Granny Smith’ and ‘Starking Delicious’ apple trees on ‘Northern Spy’ rootstock were tested: free palmette, central leader, minimal pruning, Lincoln canopy, Tatura trellis, Ebro, Palmette, MIA. These were evaluated for their influence on canopy composition, light distribution (both quantity and quality), net photosynthesis (Pn) and transpiration (E). ‘Starking Delicious’ tended to have a greater density per unit of limb cross-sectional area of flowering, non-flowering spurs, and vegetative shoots than ‘Granny Smith’. For both cultivars the density of flowering spurs per unit limb area was higher in the Tatura trellis and Lincoln canopy than with the free-palmette and central leader trees. The Lincoln canopy and MIA resulted in a greater density of shoots than the palmette, free palmette or central leader. ‘Starking Delicious’ trees had higher levels of photosynthetic photon flux transmission (PPFT) to comparable positions in each canopy type and a greater percentage of their canopy above the 30% PPFT threshold, than ‘Granny Smith’. Trees in the Ebro system had lower values of PPFT at each date than those in the other systems. The palmette and free palmette systems tended to have the highest PPFT values and proportion of the canopy above 30% PPFT late in the season, but the differences were not significantly higher than the central leader, Lincoln canopy, and minimum pruned systems. PPFT values decreased from the top to the bottom of the canopy in all systems. PPFT declined from the periphery toward the centre of the canopy at each level in the following systems: Ebro, minimum pruned, Lincoln, palmette, and free palmette. In the Tatura trellis and MIA, particularly at the 120 and 170 cm canopy heights, PPFT increased from the canopy edges toward the tree centre. Light penetration (400-700 nm) and the red/far-red ratio were higher in the lower canopy for trees in the palmette and central leader trees than the other systems (Ebro, Tatura trellis, minimum pruned, Lincoln, MIA, free palmette). Orchard management system had little influence on Pn and E measured seven times over the season. Shoots had a higher Pn and E than flowering or nonflowering spurs, which did not differ from each other. Generally, the east side of the canopy had higher Pn rates than the west side, while E did not differ. Shoot leaves from the terminal or mid-areas of the shoot had higher Pn and E than basal leaves on the same shoot. The Pn light response curve of shoot leaves on the Palmette had a steeper slope than leaves on the Tatura trellis. Leaves from the lower levels of the canopy of all systems were more responsive to changing light at or above saturation.

Root Restriction Affects Shoot Development of Peach in a High-density Orchard

Planting treatments were evaluated for their influence on shoot development and root distribution of own-rooted `Redhaven' peach [Prunus persica (L.) Batsch] trees planted to high density (5000 trees/ha). Planting in fabric-lined trenches (FLT) or narrow herbicide strips (NHS) reduced the diameter and length of primary shoots, the number and combined length of second-order shoots, and the total length of shoots. Flower density, the number of flowers per node, and the percentage of nodes containing one or more flowers were increased for FLT trees but not for NHS trees when compared with controls. The length of primary shoots increased quadratically for all treatments with increasing limb cross-sectional area (LCA). The total length of shoots increased more with increasing LCA for controls than for FLT trees. The number of flowers per shoot increased linearly for all treatments with increasing LCA values. Root concentration decreased with increasing soil depth and distance from tree rows for all treatments. Reduced widths of weed-free herbicide strips had little effect on root distribution. Roots of FLT trees were reduced in number and restricted vertically and laterally when compared with other planting treatments. The FLT treatment modified shoot development by reducing the length of total shoots and length of primary shoots across LCA values measured when compared with NHS and control-treatments.

Ethephon concentration and timing effects on thinning Winter Cole pears

Ethephon was tested as a thinner for mature Winter Cole pear trees in a trial conducted at Nubeena in south-eastem Tasmania during the 1988-89 season. Trees were treated with ethephon (0, 50, 100, 200 or 400 mg/L) at full bloom or 11 days after full bloom, or at both times. Models were fitted to the response variables of numbers of fruit per cm2 limb cross-sectional area and per 100 blossom clusters. The full bloom sprays removed significantly (P<0.05) more fruit than the later sprays. Spraying at both times gave an unexpected intermediate result between the full bloom and the later sprays. Although most treatments produced more thinning than the control, only the higher concentrations of ethephon applied at full bloom or at both times were close to achieving the required thinning results. It was concluded that although ethephon applied at full bloom is a feasible thinner for pears, further work is needed before accurate recommendations on concentration or time of application can be made.

Mechanical Bloom Thinning of Peach

Abstract 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%.

Apple Fruit Nonstructural Carbohydrates and Abscission as Influenced by Shade and Terbacil

Abstract Terbacil, a photosynthetic inhibitor, and shade applied to apple (Malus domestica Borkh) limbs and whole trees altered the contents of fruit nonstructural carbohydrates and induced fruit abscission. Shade (92%) from 5 to 15, 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) induced fruit abscission. At 15 and 20 DAFB, fruit from limbs shaded for 10 days contained less total nonstructural carbohydrates (TNC) than fruit from limbs shaded for 0 or 5 days. Terbacil at 50 and 100 ppm applied to whole ‘Redchief Delicious’ trees at 15 DAFB markedly inhibited net photosynthesis. Fruit dry weight, TNC, total sugars, and reducing sugars declined with increasing rates of terbacil and 100 ppm resulted in abscission of all fruit. Trees treated with 0 and 50 ppm retained 4.6 and 1.4 fruit per cm2 of limb cross sectional area (LCSA), respectively. Terbacil at 75 ppm and 92% shade were applied to whole ‘Redchief Delicious’ trees at 18, 23, and 28 DAFB. Fruit dry weight and contents of total sugars and reducing sugars were lowered by shading and terbacil. Shade for 5 or 10 days induced total fruit drop. Terbacil at 75 ppm resulted in 0.8 vs. 2.9 fruit per cm2 of LCSA on the controls. Chemical name used: 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedion (terbacil).

Yield Components in ‘Montmorency’ and ‘Meteor’ Sour Cherry

Abstract Two sour cherry (Prunus cerasus L.) cultivars ‘Montmorency’ and ‘Meteor’ were evaluated over two seasons to determine the relative importance of different components of yield. A path coefficient analysis was performed to determine the direct and indirect effects of primary, secondary, and tertiary components on limb yield. Fruit number, fruit weight, the number of lateral buds and spurs, and fruit set were found to be the most important components affecting limb yield in both cultivars. However, the fruiting habits of the two cultivars were significantly different. ‘Montmorency’ produced 68% of its fruit on lateral buds on 1-year-old wood, while ‘Meteor’ had 70% of its fruit on 2-year-old spurs. When the data were standardized by dividing by limb cross-sectional area, ‘Meteor’ had a higher flower bud density (number of flowers/cm2) and yield efficiency (grams of fruits/cm2) than ‘Montmorency’. Although ‘Meteor’ had higher limb yields than ‘Montmorency’, the ‘Montmorency’ trees sampled had about four times more limbs than ‘Meteor’, and, therefore, higher tree yields.

Influence of Time of Summer Pruning and Limb Orientation on Growth and Flowering of Vigorous ‘Delicious’ Apple Trees

Abstract Trees of apple [Malus domestica Borkh. cv. Red Prince Delicious/Malling (M) 9] planted in 1974 on a 1.52 x 3.05 m spacing exceeded the allotted space by 40% at the initiation of the study in 1979. Trees were unpruned (control) and pruned on July 3, August 3, or September 3 in 1979 and 1980. Pruning decreased limb and trunk cross-sectional area. Horizontal limb cross-sectional area increase was less than that of vertical limbs. Pruning increased spur leaf numbers, area, and size on the 1978 limb section but only July and August pruning prevented the decline in spur numbers occurring on control limbs. July pruning increased bloom per cluster but decreased total bloom on the 1978 limb sections. August and September pruning were most efficient in maintaining tree height while all pruning treatments maintained tree spread.