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  • Author or Editor: Frank Peryea x
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Two multiyear field studies were conducted to compare the phytoavailability and effectiveness of a variety of commercial foliar B fertilizer sprays applied at the pink flowering stage to 'Fuji'/EMLA.26 apple trees grown under irrigated semi-arid conditions. Treatments included products that differed by initial chemical form of B, physical state, and presence of additives of varying composition. Additional treatments were polymeric urea added to one B product and soil application of one B product. Boron application rates varied from 0.56 to 1.68 kg·ha–1·yr–1. All of the B sprays increased flower cluster B concentration in all years. The B sprays at the lower rate sometimes but not always increased leaf B concentration. Increasing the B rate substantially increased plant tissue B concentrations. In general, there was little substantive difference between the tested products/product mixtures on plant tissue B concentrations. Flower cluster B in the ground-applied B treatment was similar to the water control; however, leaf B concentration corresponded to the B spray treatments, indicating effective uptake of B from the soil during the early summer. Sodium polyborate-based products increased flower cluster Na concentration but not leaf Na concentration. The amount of Na contributed by Na polyborate-based products applied at commercial rates apparently was too small to be of horticultural concern. Fruit quality was excellent and was not affected by the experimental treatments in any year. Flower cluster and leaf B concentrations returned to near or at control levels in the season following the last spray application, validating the recommendation for annual B fertilizer applications to maintain adequate tree B status.

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Boron (B) is an essential micronutrient that is often in inadequate supply in many deciduous tree fruit orchards and must therefore be added as fertilizer. It can also occur at phytotoxic levels because of over-fertilization, use of high-B irrigation water, or naturally in arid soils that are natively high in B. Tree B status is usually characterized by leaf analysis although other diagnostic criteria are being evaluated. Several tests are used to characterize soil B status. Symptoms of B deficiency include blossom blast, poor fruit set and development, shortened internodes, terminal bud death, and shoot dieback. To ameliorate deficiency, B fertilizer may be broadcast or sprayed over the soil surface or sprayed on tree canopies. In some regions, maintenance applications of B fertilizer are made to prevent development of B deficiency. Sodium borates or orthoboric acid are usually used. Fertilizer rates and timing vary with location and farming practices. Symptoms of B excess include reduced or no yield, impaired fruit quality, leaf marginal chlorosis and necrosis, defoliation, and shoot dieback. Boron toxicity is alleviated by leaching B-enriched soil to move B below the root zone.

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Differential fertilizer application method (single dry, split dry, fertigated liquid), irrigation method (drip, microjet), and nutrient source (N vs. N+P in year 2+) were established in Spring 1992 in a newly planted Gala and Fuji apple orchard. In Spring 1993, the drip-fertigated Gala trees had 3 times and the drip-fertigated Fuji trees had 8 times more flower clusters per tree than the other treatments Fruiting was not allowed in 1993. Trunk cross-sectional area (TCSA) in Fall 1992 was not influenced by treatments. By Fall 1993, TCSA was still independent of treatment for the Fuji trees; however, the Gala trees fell into two size groups - (larger) microsprinkler-fertigated and split dry broadcast; and (smaller) drip fertigated and single-time spring dry broadcast. TCSA had increased 284% (Fuji) and 265% (Gala) since planting. None of the treatment effects were substantially influenced by fertigating with N+P vs N only. Leaf concentrations of most nutrients were consistently lower in 1993 than in 1992. Leaf Fe was higher in 1993 because the orchard was dustier. Leaf N was lower in the microsprinkler-fertigated trees than in all other treatments. Fertigation with N+P did not consistently produce higher leaf P than the N-only treatments. Leaf Mn varied with treatment: microsprinkler fertigated < drip fertigated, single dry < split dry. Treatment effects on all other elements were inconsistent (K, Ca, Mg, B, Cu) or absent (Zn, Fe).

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Boron (B) deficiency symptoms often appear in the reproductive tissues of apple (Malus domestica Borkh.) and pear (Pyrus communis L.) without attendant vegetative symptoms. The primary symptoms are blossom blast, and internal and external cork in fruit. Leaf analysis is the principal diagnostic procedure for evaluating tree B status in Washington orchards. Because flower cluster and fruitlet B contents are influenced by soil moisture availability during the previous autumn, variability in fall precipitation limits the ability of leaf analysis to accurately predict tree B demands the following spring. In the 1960s, Woodbridge and Crandall of Washington State University reported that the B content of apple and pear buds was constant during the winter. The objective of the current study is to determine if winter bud analysis is an accurate predictor of flower and fruitlet B status. Temporal changes in bud, flower cluster, and fruit B are presented for two apple orchards and one pear orchard during the period 1988 to present, as well as the relationships between bud, flower cluster and fruit B concentrations.

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Concerns about food safety prompted a case study of the arsenic and Pb contents of tree fruits grown on lead arsenate-contaminated soil. The arsenic concentration in apricot (Prunus armeniaca L.) and `Gala' apple (Malus domestica Borkh.) fruit was positively related to concentrated HCl-extractable soil arsenic. Fruit arsenic in both species did not exceed 70 μg·kg-1 fresh weight (fw). Fruit Pb was below the limits of detection of 20 μg·kg-1 fw for apricot and 24 μg·kg-1 fw for apple. All of these concentrations are substantially below levels associated with human health risk. `Riland' apricot trees did not show arsenic phytotoxicity at soil, fruit, and leaf arsenic concentrations associated with phytotoxicity symptoms in `Goldrich' apricots. The apple trees showed no visual symptoms of arsenic phytotoxicity.

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Fruit trees grown in soils contaminated with lead arsenate (PbHAsO4) pesticide residues are subject to arsenic (As) phytotoxicity, a condition that may be exacerbated by use of phosphate fertilizers. A potted soil experiment was conducted to examine the influence of phosphate fertilizer on accumulation of As and lead (Pb) in apricot (Prunus armeniaca) seedlings grown in a lead arsenate-contaminated Burch loam coil. Treatments were fertilizer source (mono-ammonium phosphate [MAP], ammonium hydrogen sulfate [AHS]) and rate (0, 8.7, 17.4, and 26.1 -mmol/liter), and presence/absence of lead, arsenate contamination (231 -mg/kg coil). Plant biomass accumulation was reduced by lead arsenate presence and by high fertilizer rates, the latter due to soil salinization. Phytoaccumulation of As was enhanced by lead arsenate presence and by increasing MAP rate but was not influenced by AHS rate, salinity, or acidity of soil. Phytoaccumulation of Pb was enhanced by lead arsenate presence but was not influenced by fertilizer treatment.

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The recommendations for boron (B) sprays in deciduous tree fruit orchards have changed little over the past 50 years. We conducted two 3-year field studies evaluating the effect of two modifications to the existing recommendation for B maintenance sprays on apple (Malus ×domestica) tree nutritional status. A widely recommended Na polyborate-based commercial B spray product was used as the B source. Postbloom sprays of B applied at the recommended annual B maintenance rate of 0.56 kg·ha-1 to `Scarlet Gala' apple trees consistently increased fruit B concentration but had a weaker effect on leaf B concentration in early August, the recommended timing for sampling leaves for mineral element analysis. Applying half or all of the annual B maintenance rate in a spray at the pink flowering stage increased flower cluster and early-season leaf B concentrations as well as having positive effects on fruit and leaf B concentrations. The pink sprays increased flower cluster Na concentration but had no effect on leaf and fruit Na concentrations. In the second study, one-quarter of the annual B fertilizer requirement was tank-mixed with each of four biweekly CaCl2 sprays applied starting in early June for bitter pit control. This treatment consistently increased `Scarlet Gala' fruit B concentration but had a lesser effect on August leaf B concentration. It did not interfere with fruit Ca status, and increased both fruit and leaf Na concentrations. Leaf Na concentration in all treatments was substantially lower than levels associated with specific Na toxicity of deciduous fruit trees. The results of these experiments indicate that applying B sprays at the pink flowering stage timing and tank-mixing B with CaCl2 sprays applied for bitter pit control are useful practices to enhance B spray efficacy and convenience of application.

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Calcium application trials were undertaken in a 'Braeburn' apple (Malus ×domestica Borkh.) orchard with a history of bitter pit development at harvest. In 2000, an early season calcium chloride application strategy was compared with the unsprayed control and a late season application strategy. From 2001–03, the assessment of timing of calcium chloride sprays was extended by comparing effects of five weekly sprays applied during the growing season either early, middle, or late season. Other Ca application strategies tested included sprays of acidified calcium carbonate suspensions and soil application of calcium thiosulphate. In the first experiment, early application of calcium chloride reduced the occurrence of bitter pit at harvest and after 3 months cold air storage, despite having low harvest fruit Ca concentrations. Late sprayed fruit had a higher incidence of bitter pit. In the second experiment, the later calcium chloride was sprayed in the growing season, the higher the fruit Ca concentration at harvest. Despite this, no bitter pit was measured at harvest for 2 years for early and midseason calcium chloride spray regimes. In 2003, when Ca disorders were severe and fruit large, bitter pit was observed despite early season calcium chloride sprays. Soil calcium thiosulphate application and foliar sprays of acidified calcium carbonate suspensions failed to meaningfully augment harvest fruit Ca concentrations and affect bitter pit incidence.

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Organic orchards represent a significant and growing component of Washington state agriculture. Comparison studies have shown that organic apple systems can be equally profitable yet more environmentally sustainable than their conventional counterparts. Despite this success, sustainable methods of weed control, fertility, and soil quality stabilization and improvement have remained a challenge. Intensive cultivation is commonly used to control weeds in organic orchards. This can lead to reduced or degraded soil organic matter, structure, water infiltration, aerated pore space, and other soil productivity parameters. In addition, tillage accelerates nutrient cycling and can result in the loss of valuable nutrients from the system. To address the need for sustainable organic methods of weed management, an integrated study of alternative understory management options was established in a newly planted orchard in 2005. Weed control measures included efficient tillage using a Wonder weeder, organically approved herbicide, wood chip mulch, and living cover mulches. Three rates of nitrogen (low, medium, and high) were applied across the Wonder weeder, wood chip, and living cover mulch plots in order to determine ideal N fertility rate. Analyses of total C and N and N-15 in organic fertilizers, soil pools, living cover biomass, and tree leaves are being used to track N and C cycling and partitioning, N-use efficiency, soil quality, and to determine optimal fertility guidelines. Preliminary results indicate intense competition between living mulch understory and orchard trees, and a trade-off may exist between maximizing soil quality and orchard productivity.

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