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.     

Effect of tree and branch thinning on growth,yield, and fruit quality of persimmon trees in a high-density orchard

A study was conducted to evaluate the effect of branch and tree thinning on growth, yield and fruit quality in 8-year-old non-astringent persimmon (Diospyros kaki L.f.) trees in a high-density orchard over 6 years in Korea. Adjacent trees in the rows were removed in 2008 (first-year thinning) or in 2010 (gradual thinning). Trees in the second treatment also had 25% of the main scaffold branches removed in the first two seasons. Control plots were left unthinned. First-year thinning elevated leaf macro-nutrient concentrations, increased the production of short fruiting shoots (less than 20 cm) per tree, decreased water sprout development and weight of pruned biomass, and increased fruit set compared with values recorded on control trees and with gradual thinning. First-year thinning gave higher photosynthetic photon flux in the centre of the canopy and better fruit quality. There were generally only small differences in total yield across the three treatments in individual years, but much higher total marketable yield from 2010 to 2013 in the first-year thinning plots. First-year thinning improved overall tree productivity, and the gross returns were 80% higher than those of control from 2008 to 2013 when the extra cost of the thinning was taken into account.     

Growth and stability of deep planted red maple and northern red oak trees and the efficacy of root collar excavations

Trees with root systems established well below grade due to deep planting or soil disturbance are common in urban landscapes, yet the long term effects of buried trunks and subsequent remediation strategies, such as root collar excavation are poorly documented. We evaluated the consequences of deep planting over a 10-year period on tree growth and stability, with and without root collar excavation, for red maple [Acer rubrum L. Red Sunset^® (‘Franksred’)] and Northern red oak (Quercus rubra L.) planted at grade or 30-cm below grade. Sleeves to prevent soil-trunk contact were installed around trunks on a subset of deep trees. Root collar excavations were made during the 6th growing season for both species and trees were grown for an additional 4 and 3 growing seasons for red maples and Northern red oaks, respectively. Within two weeks of root collar excavations, pulling tests compared the effect of treatments on stability of red maples. Deep planting generally slowed growth of red maple but had no clear effect on Northern red oak. Root collar excavation had no lasting effect on growth of either species. Approximately 55% of deep red maples and 33% of deep Northern red oaks had roots crossing and in intimate contact with buried trunks, suggesting a potential for future girdling roots. Approximately 25% of deep maples had substantial adventitious rooting. All deep Northern red oaks had new roots emerging just above the first original structural roots but none were clearly adventitious. Trunk sleeves had no effect on growth for either species. Neither deep planting nor root collar excavation resulted in a loss of tree stability compared to trees planted at grade, although failure patterns varied among treatments. Overall, the biggest long term concern for deep-planted trees is the potential for girdling root formation.     

Effect of Hydrogen Cyanamide on Vegetative Growth,Yield, and Fruit Quality of Fig cv. Zidi in a Warm Production Area

The fig tree (Ficus carica L.) is widely cultivated in the Mediterranean region under warm climates. Fig yield is governed by the previous crop load and is strongly dependent on shoot length. Special cultural practices are required to stimulate new vegetative growth that will ensure regular and high productivity. The present study focused on the use of the rest breaking agent hydrogen cyanamide (HC) as Dormex to enhance vegetative growth, which influences the yield. A field trial was held in northern Tunisia (36° 49′ N; 9° 48′ E) on mature fig trees cv. Zidi. In reference to untreated trees as control, two hydrogen cyanamide treatments at 1% and 1.5% HC were considered. Bud break rate, vegetative growth, starch content of shoots, yield, and fruit characteristics were assessed. Results indicated that 1.5% HC significantly increased shoot length, fruit number per shoot, and yield. It advanced bud break by 10 days and fruit ripening by 7 days compared to the control. However, leaf number, leaf area, and starch content seem to be unaffected by hydrogen cyanamide treatments. Regarding fruit quality, a 1.5% HC dose significantly increased dry matter content, while fruit diameter and total soluble solids remain unaffected. In conclusion, hydrogen cyanamide could be used under warm conditions to improve vegetative growth of fig trees cv. Zidi and consequently fig productivity. Application of 1.5% HC 40 days before bud break was the most effective in increasing shoot length and yield.     

Influence of rate and method of application of superphosphate on the growth and nutrient status of newly planted peach trees

A field experiment was carried out with newly planted peach trees to determine the influence of both rate and method of application of superphosphate on tree growth and nutrient status during the first growing season. Superphosphate was applied at planting at rates ranging from ¼ to 9 lb per tree, and applications were made either to the soil surface, in the planting hole, under tree roots, or in a band around the tree at a depth of 6 inches. Trees were grown under straw mulch and were irrigated as required.

Results showed that, in this soil of low initial ? content, trees receiving 9 lb superphosphate on the soil surface or in a ring band grew significantly larger than trees receiving ¼ lb superphosphate per tree (this applied for butt circumference only on surface-treated trees), but high rates of superphosphate in the planting hole or under tree roots resulted in tree death. No significant differences in growth were recorded at harvest between surface and ring-banded treatments at any phosphate rate, but leaf analysis in midsummer and tree analysis at harvest showed that the phosphate status of surface-treated trees was significantly higher than that of ring-banded trees.

At low rates of superphosphate (¼ and 1 lb per tree), surface treatment tended to give larger trees at the end of the growing season than band treatment, but differences were not significant. It is thought that this differential response occurred because the phosphate-fixing potential of the soil increased sharply with depth and hence band applications were inefficient unless very high rates of superphosphate were used.

The tree damage observed when high rates of superphosphate were applied in the planting hole or under tree roots was probably due to a combination of osmotic stress, acidity damage to the roots and possibly toxic nutrient levels in tree tissues. Hence high rates of superphosphate should not be placed close to tree roots at planting.

Leaf analysis in midsummer and tree analysis at harvest showed that the main effect of superphosphate application was on the ? status of the trees, and maximum tree growth in the surface and band treatments corresponded to a value of approximately 0.28% ? (dry weight basis) in the leaves. The efficiency of uptake of applied superphosphate was very low at all rates of application and was especially so at high rates. However, positive growth responses were recorded to 9 lb superphosphate per tree in surface and banding treatments. It is suggested that, although most of the applied superphosphate could not be utilized, tree growth rate was proportional to the concentration of ? in the soil zone which could be exploited by the roots.     

Induction of lateral branches in tree fruit nursery stock with propyl 3-t-butylphenoxy acetate (MB 25, 105) and Promalin (GA4+7 + 6-benzyladenine)

Sprays with 250–2000 mg l^?1 propyl 3-t-butylphenoxy acetate (MB 25,105) and 250 and 500 mg l^?1 GA₄₊₇ + 6-benzyladenine (Promalin) were applied to scion growth of first nursery trees of ‘Bartlett’ pear (Pyrus communis L.), ‘Bing’ cherry (Prunus avium L.) and ‘Oregon Spur II Delicious’ apple (Malus domestica Borkh.) to stimulate lateral branching in the nursery. Most treatments significantly increased branching compared to untreated controls. Combination sprays of the two chemicals were usually better than either used alone. Chemical treatment usually produced greater branching and wider branch angles than mechanical heading. Both chemical and mechanical treatments reduced tree height and caliper, but the decrease was not always statistically significant.     

Climatic response and impacts of drought on oaks at urban and forest sites

This study focuses on the climate and growth response of the sessile oak (Quercus petraea (Matt.) Liebl.) and the northern red oak (Quercus rubra L.) using dendrochronological methods. Tree-ring series of street trees in the city of Dresden, Germany and in a nature reserve close to the urban area were analysed, and the climate and growth response and moving correlation functions (CF) were computed. Moreover, the impact of 13 years of drought was examined by superposed epoch analysis (SEA). Our results show that differences emerge from peculiarities of the different site conditions, indicating that city oaks contain a higher level of noise in their ring width data due to human activities that degrade the strength of growth-climate associations. Importantly, climatic conditions during the previous summer and autumn and during the current spring season display significant correlations with annual growth. The stability of the climate–growth relationship was tested via moving correlation functions. A strong increase in the correlation with the temperature and precipitation in April was found for the trees of northern red oak in forests. Drought years induced significant reductions in radial growth for the northern red oak only. Nevertheless, the long-term impact of drought years must be considered as marginal because of the fast recovery of the radial growth after one to two years. In the future, the growth of the northern red oak may be restricted by an increased frequency of droughts and warmer and drier conditions in April.     

The influence of tree training and plant density on growth,yield components and yield of Arabica coffee cv. Ruiru 11

Assessment of tree growth and yield components of Coffea arabica L. cv. Ruiru 11, as influenced by tree training on single or two-stem systems at densities between 1600-4800 trees per ha during the first production cycle was carried out at Ruiru, Kenya over three years. Trees trained on the two-stem system tended to be taller than those on singlestems. Although the results were not clear, trees at low plant densities had thicker stems irrespective of the training system. The total number of primary branches was significantly higher on trees trained on the two-stem system. However, bearing primaries and productive wood were higher on the single-stem system during the first year of production. The number of bearing primaries and productive wood increased in subsequent production years on the two-stem system. Training trees on the two-stem system significantly depressed yields in the first production year by 245 to 842%, irrespective of plant density. Yields of clean coffee increased significantly with tree density irrespective of the tree training method. Yields over the production period increased by 33, 45,27 and 9% with increases in planting densities from 1600 to 2400, 2400 to 3200, 3200 to 4000 and 4000 to 4800 trees per ha, respectively. However, yields increased at a decreasing rate at densities above 3200 trees per ha. The proportions of the large grade ‘A’ sized coffee beans were not significantly affected by the treatments. It was concluded that it is possible to raise two stems during the first production cycle of ‘Ruiru 11’, although this might not be economical. Single stems would be preferred and a high plant density of between 3200-4000 trees per ha would be optimum during the first coffee production cycle.     

Pecan production increased by larger vegetation-free area surrounding the tree

Vegetation control with herbicides is a common practice in pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards that benefits both non-bearing and bearing trees. However, the appropriate size for the vegetation-free area surrounding bearing trees had not been resolved. Vegetation-free circles centered on the Tree 0, 0.9, 1.8, 3.7, and 7.3 m in diameter were established at planting and tree performance evaluated. This study reports the first six years of production that began in the sixth growing season. Yield was not affected by treatment in the first two years of production while yield was low and some trees had not begun to produce. The next four years were characterized by a strong positive relationship between vegetation-free diameter with annual yield and with cumulative yield. Weight per nut and kernel percentage were rarely affected by treatment. Leaf elemental concentrations of selected essential nutrients were not affected by treatment. Trunk diameter was similar among treatments each year. This indicates that yield was improved by the vegetation-free area impacting pistillate flower induction or flower and fruit retention rather than improved tree growth increasing the bearing surface.     

The effects of mulching on establishment of Syagrus romanzoffiana (Cham.) Becc., Washingtonia robusta H. Wendl. and Archontophoenix cunninghamiana (H. Wendl.) H. Wendl. & Drude in the landscape

Three palm species common to southern California landscapes were grown and established under mulch treatments. Turfgrass clippings and Eucalyptus sideroxylon mulches increased the growth of king and queen palms and increased survival of king palms. Although palms growing under fresh eucalyptus mulches did not display nutrient deficiency symptoms, Mexican fan palm and queen palm were not significantly benefited by mulch treatments. Mexican fan palm was not adversely affected by turfgrass growing around it. However, turfgrass significantly reduced queen and king palm growth and increased mortality of king palms during establishment. Turfgrass increased drought effects and decreased stomatal conductance of palms. Soils under turfgrass were significantly drier than mulched or unmulched soils.     

Investigating the relationship between various measuring methods for determination of establishment success of urban trees

Establishment is a key concept in urban forestry but it is currently inconsistently defined and measured. Thus, several different methods are being used to determine establishment success but their consequences and applications are rarely discussed. With this paper we would like to stimulate an increased discussion regarding these concepts both in relation to a theoretical definition but also to their practical use. The problem was approached through an experiment using sweet cherry (Prunus avium L.) and northern red oak (Quercus rubra L.) trees and the most common methods used for determination of establishment success. The trees were studied during the first three years after transplant and the association between the different measuring methods was examined. A Principal Component Analysis showed that terminal and lateral shoot length were strongly correlated, and that midday- and pre-dawn shoot water potential, and stomatal conductance were strongly correlated. We developed an index for nightly recovery of water status, which showed that terminal shoot growth was not related to nightly recovery until the third year after transplanting. Our results suggest that successful tree establishment is determined differently depending on which method is used for determination but that the differences might decrease with time. The lack of a firm definition of the term establishment may complicate communication, both within the scientific community and in practice.     

Age estimation of different tree species using a special kind of an electrically recording resistance drill

The determination of tree age is an important issue for urban green planning, forestry and dendrology; finding non-destructive and quasi-non-destructive methods for this purpose is of great theoretical and practical importance. The resistance drilling method is quasi-non-destructive because the average diameter of an opening that remains after drilling does not exceed 3 mm. Do electrically recording resistance drills allow precise assessment of tree age? The aim of this study is to assess the accuracy of determining the number of tree rings based on an examination of this special kind of drilling resistance profiles for three tree species, the pine Pinus sylvestris L., the oak Quercus robur L., and the birch Betula pendula ROTH. In 2015 and 2016, 15 pine trees, 15 oak trees, and 15 birch trees were randomly selected. For each studied tree, a measurement was conducted using the electrically recording resistance drill IML-Resi E400 with a flat-tipped 1.5/3 mm steel needle (research sample), and an increment core was taken (reference sample). The drill used was not a real Resistograph^®. The analysis of the E400-profiles underestimated the number of tree rings; the mean bias error (MBE) values were –6.5, –2.5, and –6.0 years for pine, oak, and birch, respectively. The proportion of investigated trees with less than five years difference between the research and reference samples varied from 38.4 (birch) to 66.7 (oak) percent. The accuracy of tree age determination was lowest for birch and highest for oak. The binomial generalised linear model (GLM) revealed that the most accurate tree age assessments were obtained from tree rings wider than 2 mm. The measurements clearly showed that the electrically recording resistance drill IML-Resi E400 enables a quick, although approximate, tree age assessment. Future research should concentrate on electronically regulating and recording drills, providing a higher spatial and signal resolution, and a stronger correlation to wood density.     

Combined effects of leaf/fruit ratios and N and K fertigation levels on growth and distribution of nutrients in pot-grown persimmon trees

Responses of pot-grown persimmon trees (Diospyros kaki cv. ‘Fuyu’) with two different leaf/fruit (L/F) ratios and three different fertigation levels were studied. On July 2, the L/F ratios of 4-year-old trees were adjusted to 20 and 10 by fruit thinning. From July 4 to August 26, each pot was fertigated with a solution containing 0–0 g (none), 10–8 g (medium), or 20–16 g (high) of nitrogen (N) and potassium (K), respectively. The L/F ratio of 10 resulted in higher yields but smaller fruits containing lower soluble solids than the ratio of 20. The non-fertigated trees with the L/F ratio of 10 produced the smallest fruits, but the medium fertigation increased the size of the fruit at this ratio. The high fertigation level decreased fruit skin color at both ratios. Fruit dry weight increased the most among the tree components, accounting for 48–57% of the tree total dry weight at the L/F ratio of 20 and for 64–72% at the ratio of 10. The increase in tree total dry weight at the ratio of 10 was greater than that at the ratio of 20. The trees receiving medium fertigation had higher tree total dry weights than those receiving high fertigation, especially at the ratio of 10. As the L/F ratio changed to 10 from 20, the percentages of N and K partitioned to fruits in the non-fertigated trees increased from 38% to 51% and from 67% to 96%, respectively, of the tree total N and K increases; the percentage decreased with increasing fertigation level. Although fertigation significantly increased total N and K contents of the tree, the increase in K at the ratio of 10 was less in high fertigation rather than in the medium level. The results indicated that adjusting supplemental N and K was necessary to ensure fruit growth and N and K accumulation for trees with high fruit loads, but high levels of fertigation are not necessarily preferable.     

Thinning apples via shading: an appraisal under field conditions

Summary

Fruit development and the fate of fruits was followed on ‘Imperial Gala’ apple (Malus × domestica Borkh.) trees thinned chemically or using shading. The percentage fruit drop, fruit growth rates using callipers and electronic gauges, and whole tree gas exchange rates were measured before, during, and after covering with a shading cloth that blocked 90% of solar radiation, applied for 1 week starting 30 d after full bloom (DAFB). While fruits were thinned to similar crop loads and all reached a similar size at harvest, their growth patterns reflected the treatments applied, with fruit growth slowing down and fruit dropping sooner in chemically-thinned trees which were treated earlier, than in the shading treatment, which took place later. Daily fruit growth patterns changed and were greatly reduced under shading, as were the net carbon exchange rates (NCER), both in total per tree and per unit of light intercepted by the trees. Regression analysis of the NCER per unit of light intercepted revealed no difference between the two treatments before and after shading, but a significantly lower relationship during shading. This work supports the hypothesis that C-starvation may induce fruit abscission at approx. 30 DAFB. Fruit growth patterns, and their changes during shading, were consistent with this hypothesis. This method of thinning, may be of interest to reduce the use of chemicals, and in organic fruit growing. However, before it can be adopted, a method to estimate the length of the period of shading is required.     

The Influence of Simazine or a Straw Mulch on the Establishment of Apple Trees in Grassed Down or Cultivated Soil

The first three years’ growth of Cox’s Orange Pippin on M.26 was compared in a trial in which a four-foot square around the tree received either simazine, or straw mulch, or the same treatment as the surrounding area, which was grass or cultivation. Two rates of Nitrochalk were used.

The treatments influenced leaf area and nutrient composition; shoot number, length and weight; and root size and distribution.

Competition from a partial weed cover in the first year produced a severe growth reduction which persisted in the following years and was not reduced by the higher nitrogen rate.

A four-foot square kept weed-free with simazine enabled trees to be grassed in the year of planting and yet make growth comparable to those kept clean-cultivated. Less than 1% of the applied simazine remained active in the soil at the end of the third year.

Mulching produced the most vigorous trees. It is considered that soil moisture availability was the main factor influencing tree establishment.     

Trees in planters – Growth,structure and ecosystem services of Platanus x hispanica and Tilia cordata and their reaction to soil drought

Urban environments are often characterized by extensive paved surfaces, exacerbating the urban heat island effect. At the same time, limited root space due to underground infrastructure poses a challenge for planting new trees in these areas. Trees in planters have emerged as popular design elements, offering innovative and sustainable greening solutions, particularly in urban environments with limited rooting space. However, growing conditions in planters may strongly impact tree growth and the provision of environmental ecosystem services (ES). In this 3-year study, we analyzed tree growth and ecosystem services (cooling by shading, CO₂-fixation) of London plane (Platanus x hispanica Münchh.) and small-leaved lime (Tilia cordata Mill.) in four planting treatments: in-ground (G), planters in the ground (PG), non-insulated plastic planters (P), and insulated planters (PI). We also recorded soil temperature throughout the experiment and implemented soil drought conditions by reducing soil irrigation for half of the trees after one year. Our findings revealed higher thermal fluctuations in soil temperature within non-insulated plastic planters (P), reaching a maximum of 45 °C, surpassing the critical temperature threshold for plant growth (>38 °C). In contrast, insulated planters (PI) effectively mitigated soil temperatures, staying below 33.8 °C. When planted in the ground (G), P. x hispanica exhibited a significantly higher stem diameter increment (52–66%) compared to other planting treatments, aligning with the provision of ecosystem services. However, T. cordata trees showed a more moderate response to planting treatments in terms of growth and ecosystem service provision. Furthermore, the implementation of soil drought conditions resulted in a reduction of up to 34% in stem diameter increment for P. x hispanica and up to 25% for T. cordata. Our results underscore the necessity of tree species-specific knowledge about growth responses to different planting treatments for effective urban planning perspectives, as the provision of ecosystem services may be influenced differently.     

苹果苗木类型和栽植时间对幼树生长特性的影响

【目的】为了研究不同栽植时间下不同苗木类型的生长特性,【方法】以3 a生‘长富2号’/‘M26’/八棱海棠为试材,测定3个栽植时间(2010年3月10日、4月10日和5月10日)下分枝苗、去分枝苗和单干苗生长特性相关指标。【结果】5月份栽植植株的生长势弱于3、4月栽植的植株;单干苗生长势弱于分枝苗和去分枝苗。栽植后第2年,3、4月栽植植株的株高、主干粗度显著大于5月栽植的植株。去分枝苗和单干苗株高显著大于分枝苗。3种苗木类型主干粗度依次为分枝苗>去分枝苗>单干苗,且相互差异显著。分枝苗和去分枝苗冠径显著大于单干苗。栽植后第3年,分枝苗的花芽数显著高于去分枝苗和单干苗。【结论】苹果苗木在冷藏条件下,4月栽植是可行的,本试验中3月份栽植较为适宜。分枝苗有利于促进幼树提早开花结果。     

Studies in the Development of the Strawberry: III. Flower-Bud Initiation and Development in Large-Fruited Perpetual (“Remontant”) Strawberries

Summary

Four N application rates generated a range of tree N status as indicated by leaf N concentrations in six year old trees of `Mission' almond (Prunus dulcis (Mill.) D. A. Webb). Leaf N concentrations were related positively with concentrations of amino acids - especially asparagine and glutamine - in phloem and xylem saps. A pulse of 1.25 kg N per tree was applied to trees previously receiving 0, 78, 157 or 313 g N per tree, annually. Apparent uptake of soil N into above-ground tree parts was determined over a 39 d period. N uptake was determined as the difference in the products of tree biomass and tissue N concentrations before and after the N pulse. Tissue N concentrations increased signi®cantly in trees previously receiving the two lowest N application rates, whereas trees previously receiving the high N treatments were unresponsive. Tree N contents (0 g N per year, and also 78 g N per year treatments) increased slightly in response to the N pulse, although statistical differences were not observed due possibly to high variability in biomass among trees. At the same time, the amino acid concentrations in phloem exudate and xylem sap were highest in trees grown under the highest N fertilization regime. We suggest that the high amino acid concentrations in the phloem and xylem saps are indicative of a larger pool of amino N cycling throughout the vasculature of high N-status trees. Our data indicate an inverse relationship between tree N status, amino acid concentrations in xylem and phloem saps and capacity for soil N uptake in ®eld-grown trees. These results represent the ®rst ®eld data to correlate the concentration of amino acids circulating in the plant vasculature with soil N uptake. A functional relationship between the amino acid concentrations cycling within the tree and the regulation of soil N uptake has, however, not yet been established.     

Response of young clementine citrus trees to drip irrigation,I, Irrigation amount and number of drippers

Summary

Growth, évapotranspiration, water relations and yield components of clementine trees (Citrus clementine, Hort ex Tan) subjected to differential drip-irrigation treatments were investigated during two seasons (1990–1992), Irrigation treatments were applied in a factorial design of two or four emitters per tree and four amounts of water (50,80,110 and 140% of tree évapotranspiration measured by a large weighing lysimeter located in the same plot), Seasonal water use in the lysimeter was 290 and 397 mm per year for 1990 and 1991, respectively, and the corresponding crop coefficient values were 0, 25 and 0, 31, Soil evaporation during selected periods of 1991 ranged from about 50% of évapotranspira tion in months with frequent rainfall to 8-30% in rainless months, The number of emitters per tree did not significantly affect soil matric tension, tree water status or tree growth, nor flowering, fruit-set or yield, Irrigation amount, however, significantly affected all these variates, Irrigation with 50% ET was insufficient in both seasons, producing high water stress and reducing tree growth, Yield was also reduced by a reduction in fruit number per tree, Optimum growth of the trees was obtained with irrigation at 110% ET which did not differ from that at 140%.     

Use of paclobutrazol sprays at mid-anthesis for increasing fruit size and yield of avocado (Persea americana Mill. cv. Hass)

Mid-anthesis foliar sprays of paclobutrazol (PB) at 2.5, 1.25 and 0.62 g a.i. I-1 reduced spring growth and altered dry-matter distribution in fruiting spring shoots of ‘Hass’ avocado.(Persea americana Mill.) trees. There was a decrease in dry matter allocation to vegetative components and an increase in allocation to fruit. The starch concentration in the wood of spring shoots on trees treated with 2.5 g a.i. I-1 foliar PB was increased by ca. 70% compared with spring shoots from trees of other treatments. The mid-anthesis foliar treatments also reduced summer growth by ca. 20%. Trunk injection of PB at 0.2 g a.i. m~2 of canopy silhouette area when the spring growth matured, in addition to a mid- anthesis foliar spray of 1.25 g a.i. I-1, reduced the length of summer shoots by 36% when compared with untreated trees. The spray treatments of 2.5 and 1.25 g a.i. T1 PB at mid- anthesis increased the mean fruit size at harvest by 16 and 11% respectively. Fruit yield was not significantly affected by PB applications on an annual basis. However, the PB spray treatments of 1.25 and 0.62 g a.i. I-1 significantly increased the two year cumulative yield by ca. 63%. There was no significant effect from the trunk injection treatment on fruit yield in either the season of treatment or the following season.