Controlling growth of ‘Delicious’ apple trees with low- dosage applications of Uniconazole or BAS111

Foliar applications of 30, 60 or 120 mg I-1 uniconazole were made to ‘Delicious’ apple trees at full bloom or one, two or three weeks after full bloom. Application at full bloom reduced fruit weight and length/diameter ratio more than when applied two or more weeks after full bloom. In another experiment, a single application of uniconazole was applied to ‘Delicious’ trees three weeks after full bloom at 15, 30, 60, 120, 240 or 480 mg I-1. Posages of 240 or 480 mg I-1 controlled vegetative growth to about 50% of the control values at ten weeks after treatment. Thereafter, the rate of shoot elongation was similar to that of the controls. The lowest dosage to reduce vegetative growth was 15 mgl-1. In a third experiment, uniconazole was compared with BAS111 for controlling vegetative growth of ‘Delicious’ trees. Uniconazole or BAS111 applied six times at 350 mgl'1 reduced growth to 46% and 81% of that of the controls, respectively. Increasing the rate of surfactant from 0.1% to 1.0% reduced growth by an additional 8%. Growth reduction in the year of treatment was similar following uniconazole treatments of 350 mg l_l applied three times or 35 mg I-' applied six times.     

Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Summary

Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21 – 70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex^® Ca [10% (w/w) Ca] and Manni-Plex^® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex^® Ca plus Manni-Plex^® B remains to be elucidated.     

The interaction of Cytolin and NAA on cropping red ‘Delicious’ apple

A trial, at Spreyton in north-western Tasmania, studied the effects of Cytolin and NAA sprays on the thinning and shape of ‘Delicious’ apples. Untreated control and hand thinned trees were compared with trees treated with Cytolin or NAA alone, or in combination. Cytolin was applied at 25 mg 1~‘ at the king petal (KP) stage. NAA was applied at 8 mg I“1 at full bloom (FB) and 7,10, or 15 days after full bloom (AFB). Cytolin alone had no effect on thinning, fruit weight or on pip numbers but it did improve fruit shape. The combination of cytolin and NAA at FB overthinned. Cytolin and NAA combinations applied at all times after FB significantly decreased both mean fruit weight and pip numbers and reduced the percentage of fruit > 70 mm. All Cytolin-NAA combinations and the NAA treatments applied at 10 and 15 days AFB resulted in unacceptably high percentages of apples < 45 mm in diameter (pygmy fruit). It is recommended that Cytolin and NAA should not be used in the same spray programme. NAA alone is a most effective thinner at FB or seven days AFB.     

The thinning effect of benzyladenine on red ‘Fuji’ apple trees

A trial, at the Grove Research Station in southern Tasmania, studied the thinning effect of benzyladenine (BA) on five year old red ‘Fuji’ apple trees. Untreated control trees were compared with trees treated at four timings, from full bloom (FB) to 30 d after full bloom (AFB), with four concentrations of BA (50, 100, 200 or 400 mg I-1). The most effective time of thinning was 20 d AFB, when increasing concentration also increased thinning. Further advantages of this successful thinning were reflected in better fruit size and weight. At 30 d AFB high concentrations of BA depressed fruit weight. Return bloom was improved significantly by both 20 and 30 d. AFB sprays with a concentration effect at 20 d AFB. Timing of sprays had no effect on the incidence of russet which was increased only by applications of 400 mg l-1. Both the higher concentrations and later timings resulted in an increase in shoot numbers and total growth. Reduction in mean shoot length was related more to the concentration of BA used than to differences in the timing of sprays. BA has shown potential as a thinner for red ‘Fuji’ apple at 20 d AFB.     

The influence of fungicides and gibberellin (A4+7) applications on russet control of ‘Golden Delicious’ apple fruit

Summary

Various fungicides, gibberellins (A₄₁₇) and their mixtures were tested for the control of russet of ‘Golden Delicious’ apple fruit in the major apple-growing area in Israel. Four foliar applications of captan, metiram, the strobilurins kresoxim-methyl, trifloxystrobin, azoxystrobin, or the polyoxin B compound Polar from the green tip stage to the end of the petal fall stage gave similar reductions in russeting, compared with the controls, but none eliminated it. Tank mixtures of the gibberellins (A₄₁₇) Regulex and Perlan with captan, each at full rate, did not improve russet control, compared with each component alone at the same rate. Similarly, both captan and trifioxystrobin, and the gibberellin (A₄₁₇) Cytolin or their mixtures at full rates provided similar significant level of control of russet on fruit. Fruit in the upper part of the tree had significantly more russet than fruit in the lower part of the tree, regardless of treatment applied. In addition, russet was more severe on fruits of trees grown in the west side of the row, than those of trees grown on the east side. Data suggest that factors other than fungicides, which may act by reducing russet-inducing microorganisms, may be involved in russet development.     

Effect of part-tree flower thinning on fruiting,vegetative growth and leaf photosynthesis in ‘Cox’s Orange Pippin’ apple

Flower clusters were removed at full bloom from ten year old ‘Cox’s Orange Pippin’ trees on M.9 rootstocks, over the whole tree, on alternate branches or on whole sides. Mean fruit weight per tree at harvest was linearly dependent on leaf area per fruit and on light interception per fruit, both relationships accounting for over 90% of the variance. These relationships did not differ between treatments, implying either a mobile pool of carbohydrate or photosynthetic adjustment within the tree to crop load. Measurements of leaf photosynthesis in July and September showed no statistically significant differences in photosynthetic rate of spur or extension shoot leaves on bearing or non-bearing branches. Although the treatments caused no overall effects on shoot growth or leaf area per tree, sides of trees without fruit had greater leaf area and shoot growth than did sides bearing fruit. Fruit mineral composition and percentage dry weight were not affected by treatment except where the treatments significantly altered fruit size. In the following spring, although the treatments did not affect the total number of flower buds produced, branches that were deflowered in the previous spring carried significantly more flower buds than did branches which had cropped.     

A comparison of high- and low-volume spray techniques in the thinning of ‘Golden Delicious’ apples

A trial at the Grove Research Station, southern Tasmania in 1989-90 examined the thinning of mature ‘Golden Delicious’ apple trees. High-volume sprays were applied at 6,0001 ha^-1 as air blast or vertical boom using NAA at 10mg l^-1 4d after full bloom (AFB) and 18 d AFB. Carbaryl at 1,000 mg l^-1 and thiram at 1200 mg l^-1 were also applied as combined sprays, 30 and 38 d AFB. These high-volume sprays were compared with unsprayed controls and Micron and Micronair low volume sprayers at 200 and 1,1000 l ha^-1. The dosages of the low volume applications were equilibrated to apply the same rates of chemical per hectare as the high-volume sprays, and the timing was the same. All spray treatments reduced crop load to acceptable levels when compared with the overcropped controls. There were no consistent differences between treatments for number of fruit per cm² limb area except that the lowest volume Micron spray thinned significantly less than most other treatments. Considering the number of fruit per 100 blossom clusters the airblast spray was the only treatment to be significantly better than the Micron at 2001 ha^-1. These numbers were reflected in mean fruit weight with the control fruit being significantly lighter than any sprayed fruit. The air blast treatment produced significantly heavier fruit than all other treatments, apart from the other high volume treatment. Fruit size distribution (FSD) showed significant differences between the control and all the spray treatments. The airblast treatment produced significantly more fruit in the 80 mm or larger category than all treatments, apart from the vertical boom application. These preliminary results suggest that although low-volume sprays can thin apple trees, the use of ultra low volumes (ULV) should be explored using machines capable of controlled droplet application (CDA). This may ultimately lead to less chemical being applied per hectare.     

Analysis of S-alleles by PCR for determination of compatibility in the ‘Red Delicious’ apple orchard

Summary

In a previous study, the apple ‘Jonathan’ was shown to be semi-compatible with the ‘Topred’ sport of ‘Red Delicious’, the main cultivar in Israel. This incompatibility led to reduced pollination potency, explaining the low yield obtained from ‘Topred’ rows adjacent to ‘Jonathan’. Hence, the importance of identifying the level of compatibility for all ‘Topred’ pollinators became apparent. By analysing S-allele by PCR with primers for the various S-alleles of the cultivars in the ‘Topred’ orchard, including S10 and S28, which were cloned in this study, it was evident that apart from ‘Jonathan’, the common pollinators for ‘Topred’ are fully compatible with it. The ability to identify all S-alleles in the ‘Topred’ orchard was also utilized to resolve the observation that, although ‘Topred’ is considered self-incompatible, self-pollinated, net-caged, ‘Topred’ flowers set some fruit. Applying PCR-analysis of S-alleles to the progeny of the suspected self-pollinated ‘Topred’ fruit revealed that the fruit-set was the outcome of cross-pollination, perhaps the consequence of fertilization by wind carried pollen. Hence, the notion that ‘Topred’ is totally self-incompatible was confirmed and the efficiency of progeny PCR S-allele analysis for the determination of the pollen donor was exhibited.     

Effects of different rootstocks and training systems on the mineral composition of ‘Delicious’ apple leaves

Leaf mineral composition as affected by different rootstocks, cultivars, training systems and their combinations was measured during 1987 and 1988. Trees on M.7 had significantly higher concentrations of N, P and Fe, whereas those on MM. 106 maintained higher values of K, Ca, Mg and Mn during both years. Between cultivars, Red ‘Delicious’ showed greater accumulation of N, P, Mg and Fe but K and Cu levels were found to be more in Starking ‘Delicious’. All mineral nutrients except Ca and Mg accumulated more in spindle-bush trained trees than those under modified central leader system. The Mineral composition of Starking ‘Delicious’ grafted on M.7 rootstock and trained as a spindle bush produced the best yield efficiency and fruit quality, and fell within the normal range.     

The influence of endothal and 6-benzyladenine on crop load and fruit quality of red ‘Delicious’ apple

Summary

Trial work over a two year period examined the aquatic herbicide endothal as a blossom thinner in conjunction with 6-benzyladenine (CyLex?) as a post-bloom thinner. The aim was to develop an effective thinning programme using endothal and CyLex?, to examine any interactions between the two chemicals, and to assess the impact of endothal on fruit quality. Time of application of endothal was shown to be critical in achieving a satisfactory level of thinning. Multiple applications of lower chemical rates were also successful, and may have potential to provide an effective programme for cultivars with long flowering periods, which are traditionally most difficult to thin. Addition of a surfactant to the spray mix significantly increased the thinning effect of endothal, resulting in severe over-thinning. This work has demonstrated that endothal is an effective thinner of red ‘Delicious’ apples. It is most effective when applied twice during the blossom period, the first application at 20% bloom and the second at 80% bloom. There is no advantage in increasing the concentration above 1.0 cm³ dm^-3 (v/v). Endothal can also be effectively combined in a programme with the post-bloom thinner CyLex? applied at 150 mg l”¹ at a spray volume of 12001 ha^-1. Addition of CyLex? to the spray programme has the added benefits of increasing fruit weight and size. Fruit sugar content and firmness were both increased by application of endothal. The greater the number of applications the higher the firmness and sugar content of the fruit. Both these findings are additional benefits to the thinning effect. Both pip number and fruit length/diameter ratio were slightly reduced by endothal. Cylex and some endothal treatments increased the incidence of fruit russet.     

Studies on the hawthorn (Crataegus azarolus L.): III. A potential rootstock for ‘Golden Delicious9 apple and ‘Williams’ pear

Seedlings of the hawthorn Crataegus azarolus L. were budded with ‘Williams’ pear and ‘Golden Delicious’ apple and followed for compatibility, growth control, precocity and suckering. Four years of observations indicated that the hawthorn is compatible with ‘Williams’ and ‘Golden Delicious’, conferring growth control and precocity; and producing suckers profusely. On the other hand, bud break in ‘Williams’ started 10 d earlier and gave longer shoots than ‘Golden Delicious’. Delayed symptoms of incompatibility and long-term reciprocal influences require further study.     

Determining the probability of bitter pit in ‘Golden Delicious’ apples through the post-harvest mineral content of individual fruit

Summary

Bitter pit fruit in commercial consignments of apples still poses an economic threat to exporters from South Africa. Mineral analysis of fruit has been used with variable success to predict bitter pit prior to harvest. The possibility of increasing the accuracy of existing predictive models by using analysis of individual fruit rather than pooled samples was investigated. By improving the normality of the distributions of the different minerals and decreasing the overlap between pitted and non-pitted fruit classes, we attempted to improve the reliability of predictions based on variable threshold values. Even though our model produced a correct classification of 85% for non-pitted fruit which can be useful, this was still below the required tolerance expected on the market which, at present, is less than 2% bitter pit in an overseas consignment. The classification for pitted fruit, 63%, was not satisfactory.     

Pre-harvest drop control of ‘Red Delicious’ and ‘Jonathan’ apple (Malus domestica) as affected by the synthetic auxin 3,5,6-TPA

Summary

‘Red Delicious’, the main apple cultivar grown in Israel, and ‘Jonathan’, grown on a smaller scale, are prone to substantial pre-harvest drop. Spraying both cultivars with the synthetic auxin 3,5,6-trichloro-2-pyridyl-oxyacetic acid (3,5,6-TPA) reduced pre-harvest fruit drop and increased yield. Application of 40 mg l^–1 3,5,6-TPA 2 weeks before anticipated harvest (WBH), or 30 mg l^–1 3,5,6-TPA at 4 and 2 WBH gave the best results, and were as effective as 2,4,5-trichloro-phenoxypropionic acid (2,4,5-TP) which was the commercial product commonly in use until being withdrawn. There were no negative effects on fruit quality at harvest, or during 8 months of storage. Therefore 3,5,6-TPA can be recommended for routine use on ‘Red Delicious’ and ‘Jonathan’ apples in Israel.     

The effect of boron upon leaf development and growth of the apple cultivar ‘Cox’s Orange Pippin’

One-year-old ‘Cox’s Orange Pippin’ trees planted in pots in sand culture in the spring of 1970 were (during the growing seasons of 1970–72) watered with nutrient solutions containing 0, 0.12, 0.23, 1.2, 3.5 or 7.0 mg boron per litre.

With increasing boron supply, the boron concentration of the leaves increased, the growth of current year’s shoots and to some extent of other plant parts increased, and summer leaf-fall and the occurrence of necrotic leaf spots (‘Cox spots’) decreased. The percentage of healthy leaves was greatest when boron in leaf dry matter was about 30 ppm.

In 1972 the trees with highest boron supply suffered from incipient boron toxicity and increased incidence of ‘Cox disease’ flowering was delayed, and the percentage of dead buds was increased. In the latter part of the summer the leaves curled upwards, turned purple and became brittle.     

Girdling of early season ‘Mayfire’ nectarine trees

The effect of four times of limb girdling on fruit and tree response was examined on ‘Mayfire’ nectarine (Prunus persica (L.) Batsch). Girdling prior to Stage II of fruit growth reduced the lag phase associated with Stage II, and caused peak fruit growth rates to occur earlier in the season than on later girdled or ungirdled trees. Optimum response was obtained by girdling prior to Stage II, when fruit seed length was approximately 10 mm. Girdling at this time increased fruit weight by 22.5% and more than doubled the percentage of fruit in the largest three size categories. Maturity, measured as soluble solids concentration, was increased by 42%. Shoot extension growth was reduced only by early girdling. Leaf weight per unit area was increased, and leaf nutrient concentrations were decreased by all girdling treatments. Leaf conductance to water vapour (g,) was not affected when measured 8 days prior to and 78 days after harvest. Fifteen days after harvest, g, was decreased in all girdling treatments.     

Short-term effects of changes in soil management and nitrogen fertilizer application on ‘Bramley’s Seedling’ apple trees.

Soil managment in a ‘Bramley’s Seedling’ orchard, established in a system of herbicide treated tree rows and mown grass alleys, was changed to provide three treatments: complete grass cover, overall herbicide and a continuation of the existing system. Differential rates of N fertilizer (nil, 62.5 kg ha-1) were applied to each soil management regime. In comparison with herbicide strips, complete grass was intensely competitive, particularly with nil application of N fertilizer, reducing tree growth and yield and greatly decreasing leaf N. Leaves from trees in complete grass (nil N) plots contained higher concentrations of P, K and B but lower ones of Ca, Mn and Cu. Compared with the change from herbicide strip to complete grass management, effects of changing to overall herbicide were smaller. There were slight increases in leaf N concentration but no increases in tree growth or fruit yield. Leaf Mn concentration was increased in overall herbicide. Although application of N fertilizer to grass plots increased leaf N concentration by 0.4% and the three-year girth increment, yield was less than that of trees in herbicide strips. Nitrogen fertilizer applied to herbicide strips or overall herbicide plots slightly increased leaf N content but there was no effect on yield or girth increase. Applying N fertilizer to complete grass plots reduced the concentration of P, K and B in leaves but increased leaf Ca, Mn and Cu.     

The effects of low temperatures on the vegetative growth and flowering of the primocane fruiting raspberry ‘Autumn Bliss’

Summary

The effects of low temperatures on subsequent vegetative growth and flowering in the raspberry ‘AutumnBliss’ were investigated. In the first experiment, a number of lifting dates were used to determine the seasonal pattern of dormancy and the effect of natural chilling on plant development. In the second, different durations of artificial chilling(0, 2, 4, 6, 8 and 10 weeks at 0?C) were combined with two lifting dates to investigate the effect of natural and artificial chilling. In these experiments, plants which received little chilling grew slowly and failed to develop beyond short rosettes of leaves but as chilling increased, the rate of vegetative growth increased. This coincided with a decline in the time toflowering. These two responses, however, were distinct. In a third experiment, the effect of vernalization of actively growing canes was tested in an attempt to separate the effects of cold on time to flowering, and on the removalof dormancy. The plants responded significantly to cold treatment and flowering was advanced, indicating a distinct vernalizing effect     

Inflorescence bud growth,development and abscission in shoots of bearing and disbudded ‘Bianca’ pistachio trees

Summary

Dry-matter accumulation patterns and anatomical aspects of development and abscission of inflorescence buds borne on shoots of fruiting (BF) and non-fruiting (BNF) branches of bearing trees and in non-bearing branches of disbudded (NBD) pistillate trees of pistachio (Pistacia vera L.) were studied from the end of May to mid September. In NBD trees, inflorescence-bud summer drop was negligible and, by the end of the growing season, dry-matter content in NBD buds was three times higher than in BF buds. The anatomical investigation showed that the inflorescence buds, irrespective of their being on shoots of fruiting or not-fruiting branches, undergo the same differentiation process, which is completed by the end of spring. In June and July, signs of degenerations are detectable in the conducting tissue of the buds that will abscise. The degeneration seems to precede and, presumably, trigger the onset of abscission layers, which may develop in different points of the inflorescence. It is suggested that the event triggering the onset of the abscission process precedes the phase of rapid embryo development and that it might be ascribed to the embryo in the phase following the first zygotic division.     

Manipulating Regular Bearing in ‘Golden Delicious’/M9 Apple Trees using GA4+7 and Ethephon

Control of regular cropping in apple is considered critical for fruit growers to ensure their economical sustainability. Irregular flowering can be mitigated by plant growth regulators thanks to their promotion or inhibition effects. In this study, responses of GA₄₊₇ and ethephon on alternate bearing in ‘Golden Delicious’/M9 were examined. GA₄₊₇ and ethephon were applied on the same trees during three consecutive years (2010–12). Flowering, yield, shoot growth, and also some fruit quality parameters were assessed. GA₄₊₇ appeared to be more effectual to regulate alternate bearing. The alternate bearing index calculated with yield in successive years was high in control (0.91), moderate in ethephon (0.71), and low in GA₄₊₇ treated trees (0.41). Modified alternate bearing index, based on cluster number, indicated moderate intensity in GA₄₊₇ (0.53) and high intensity in the others. Although GA₄₊₇ reduced crop density at about 50%, there was little variation in yield per tree and crop efficiency due to increasing of fruit size. GA₄₊₇ did not increase shot length after establishment of equilibrium between vegetative and generative growth in 2012. Ethephon slightly reduced vegetative growth and relatively increased fruit size due to the decrease of fruit set.