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S.M. Southwick, W. Olson, and J. Yeager

Soil applied potassium (K) may not alleviate K deficiency in fine textured California soils when high numbers of prunes per tree are produced leading to leaf necrosis and limb death. Because K demand is increased by fruit, K nitrate (KN) sprays appear to be a corrective option for growers in this situation. Our objectives were to determine best seasonal KN spray liming strategies to minimize K deficiency, quantify K uptake into leaves after spray and to evaluate spray effects on productivity. Results indicated that regardless of spray timing leaf K was increased by approximately 0.3% and three weeks later decreased 0.2%. Average leaf K in sprayed trees was 0.7% higher than untreated trees at harvest. Fruit fresh to dry weight ratios were lower (better) from summer sprayed trees than spring. Summer KN sprayed trees had yield efficiencies equal to those having soil applied K. Fruit size was similar regardless of K application method. Foliar KN sprays may be a viable K augmentation to soil application in heavy crop years on fine textured soils.

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Geraldine J. Cashion and Thomas H. Yeager

Multiple branched liners of Rhododendron sp. cv. Duc de Rohan were potted in 3-L containers using a 5 pine bark: 5 Florida peat: 1 sand medium (by volume) amended with Prokote Plus (20N–1.3P–8.3K, 9.2 kg·m–3) and placed on one of five treatment platforms (1.2 × 2.4 m) in a commercial nursery in Manatee County, Fla. Treatments were 88 plants per square grid with containers touching (T1), 44 plants per square grid with containers touching (T2), 44 plants per square grid with containers touching in rows and 15 cm between rows (T3), 22 plants per square grid with containers touching (T4), and 22 plants per square grid with 15 cm between containers in rows and 15 cm between rows (T5). Irrigation was applied by overhead impact nozzles (0.13 cm/0.5 h) before collecting runoff. Runoff volume was measured and ppm nitrate N determined on day 6, 23, 38, 63, 92, 161, 189, 217, and 274. Average nitrate N ranged from 97 ppm for T1 to 10 ppm for T5 and corresponded to volumes of 19 and 20 L, respectively. Volumes were not different due to spacing or number of containers; however, nitrate N increased linearly with container number when containers were touching (T1, T2, and T4). Nitrate N in runoff was similar for the same number of containers regardless of spacing.

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Stephen M. Southwick, W. Krueger, J.T. Yeager, and J. Osgood

French prunes (Prunus domestica L.) on myrobalan seedling rootstock were planted in 1981 in an east-west direction with 4.9 m between rows and 2.7 m between trees on a poorly drained Class II soil in Glenn County, CA. A randomized complete block design was used with 8 trees per plot. Trees were pruned by hand to an open-center tree form or pruned by machine to a pyramid form in the dormant or summer season resulting in 6 pruning treatments. This high density system has led to high yields of good quality fruit (9.18 dry tons/acre in 1989, sized at 78 fruit per pound). Hand pruning led to higher yields, larger fruit, lower drying ratios and a greater dollar return per acre than any of the machine pruned trees. Dormant machine pruning led to larger fruit produced than those trees pruned in the summer by machine. Mechanical pruning may be possible for short time periods, but continued practice led to smaller fruit with lower yields than hand pruning. Certain locations within the tree canopy had smaller fruit size and it is within those lower locations where fruit size needs to be improved. These and additional experimental results obtained from 1987 through 1989 growing seasons will be presented.

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S. M. Southwick, K. Shackel, and J. T. Yeager

`Bing' sweet cherry is the most widely planted cultivar grown in the Western US because of widespread market acceptance. High prices are associated with early maturing `Bings' so growers are inclined to plant in early maturing growing regions. High numbers of less marketable, abnormally shaped (deep sutures, spurs, doubles) fruit tend to be produced in these regions. It is thought that abnormal fruit development is associated with high summer temperatures. Dataloggers equipped with thermocouples were located in 7 California cherry growing regions. Thermocouples were positioned throughout tree canopies, monitoring flower bud temperatures for 2 seasons from May to October. A Richard's function was used to describe the relation of average daily temperature (July, August, September to the percentage of fruit with deep suture. Correlation coefficients (R2) of 0.85 and higher were found, with increases in average daily temperatures above 22C associated with the formation of abnormal fruit shapes. Heat lamps were used to increase spur temperatures 5-7C above ambient during the July through September period, High percentages of abnormal flowers were produced in the season after 2 July, but not after 21 August heating, Strategies to lower high summer canopy temperatures helped to reduce abnormal fruit shapes.

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S.M. Southwick, W. Olson, J. Yeager, and K.G. Weis

During the fruit growing season, April through August 1990, 1991, and 1992, four sprays of 20-22 liters/tree of KNO3 were applied to `French' prune trees (Prunus domestica L. syn. `Petite d'Agen). Spray applications of KNO3 were compared to single annual soil applications of KCl (1.4-2.3 kg/tree) and sprays of urea + KNO3 with respect to leaf K and N, fruit size, drying ratio, and dry yield. Potassium nitrate sprays were as effective, or better, than soil-applied K in maintaining adequate levels of leaf K throughout the season. Treatment effects were not carried over into the next year. Lowest leaf K was found in trees where no K had been applied. Those values were below the adequate level of 1.3% K and the untreated group developed K deficiency symptoms. Consistent effects on leaf K were not obtained when urea was applied and no negative effect on leaf K was demonstrated. Equivalent dry yields per tree were obtained by foliar and soil K applications. There was no best time for KNO3 sprays. Yield per tree was not enhanced when foliar K-N sprays were applied to trees that had levels of 1.3% K or more as of 15 Apr. 1992. Trees that were below optimum K in April tended toward improved dry yields after four K-N sprays. Trees that had no applied K were lowest yielding. Drying ratios and fruit size (number of fruit per kilogram) were not different among K treatments. Dry yields per tree were increased without a decrease in fruit size or an increase in drying ratio with either soil or foliar K application. These results suggest that foliar KNO3 sprays applied four times throughout the growing season can be used to correct incipient K deficiency in `French' prune and to obtain dry yields equivalent to those obtained with soil applications of KCl.

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J. Edstrom, W. Krueger, J. Connell, W. Micke, J. Osgood, W. Reil, and J. Yeager

In 1979 a Nonpareil-Price almond orchard, was planted 2.2m × 6.7m (270 trees/acre). Four pruning treatments were imposed on the hedgerow planting at the end of the first year. 1. Interplanted: Trees trained to 3 scaffolds then standard pruned 2nd-6th years. Alternate trees were whisked back during 7th and 8th years and whisked trees removed after 9th year. 2. Permanent Hedge: Trees trained to 3 scaffolds and standard pruned throughout. 3. Two Scaffold Hedge: Heavy 2nd and 3rd year training required to form 2 main scaffolds growing into the row middles then standard pruned. 4. Unpruned Hedge: Trees trained to 3 scaffolds then no further pruning. Treatment with alternate trees whisked back had 15% reduced yield each year following whisking. Removing these heavily pruned alternate trees at the 9th year then reduced yields an additional 30%. Now, three years after removal, yield still lags by 18%. Accumulating six years yield data shows no differences between the three treatment maintained as hedgerows. However, whisking and removing alternate trees resulted in 2000 lbs less yield over the 6 year period.

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J.P. Edstrom, J. Connell, W. Krueger, W. Reil, J. Hasey, and J. Yeager

Four tree training methods have been evaluated since 1979 in California for their affect on yield of “Nonpareil” ctv. almond [Prunus dulcis (Mill.) D.A.Webb] in a tightly spaced “Nonpareil”/”Price” ctvs 1:1 hedgerow planting. Four variations of open center training began at the first dormant pruning in a 2.2 × 6.7-m spacing (667 trees/ha): 1) Temporary Hedge—trees trained to three primary scaffolds, standard pruned with alternate trees gradually whisked back to allow space for permanent trees and then removed at 8th year leaving 4.4 × 6.7-m spacing(333 trees/ha); 2) Permanent Hedge—trees trained to three scaffolds, standard pruned at 2.2-m spacing; 3) Two-Scaffold Hedge—Trees trained into “perpendicular V” two scaffold configuration, standard pruned at 2.2-m spacing; 4) Unpruned Hedge—Trained to three scaffolds then left essentially unpruned at 2.2-m spacing. Replicated yield data accumulated over 15 years shows no difference in production between the three permanent 2.2-m hedgerow methods. Yield for the Temporary Hedge, however, declined 30% the year following alternate tree removal. Adequate canopy expansion resulted in some regained nut production, but yields never recovered and remain 20% below the permanent hedge treatments 13 years post-removal. Observations indicate considerable loss of fruitwood has occurred in the lower canopy of all three 2.2-m hedge treatments, especially in the Unpruned but good commercial production has been maintained at 2400 to 3000 kg/ha The size of almond kernels was not affected by training method. Trunk circumference was affected by treatment. Trees in Temporary Hedge plots grew sustantially larger after alternate tree removal than trees in all 2.2-m hedge treatments that were equal in size.

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Frank T. Yoshikawa, G.C. Martin, D. Ramos, and J.T. Yeager

Various rates of Wilthin were applied at full bloom to limbs carrying 150 to 250 flowers to study their activity on blossom thinning of `Loadel' peaches. Wilthin applied at 0.75% and 1.0% significantly reduced fruit set to 29% and 30%, respectively, while the control produced 94%. The effectiveness of the 0.75% rate was dramatic, but it is interesting to note that the 1.0% rate did not lead to excessive thinning nor phytotoxicity on foliage or fruit. More extensive studies need to be done to fully determine the potential of this material. However, these results suggest that further testing of Wilthin on a larger scale is warranted.

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G. S. Sibbett, D. Goldhamer, S. Southwick, R.C. Phene, J. Yeager, and D. Katayama

Variable lengths of water deprivation immediately prior to harvest were imposed on mature French prune trees for four consecutive years. Irrigation cutoff durations were about 45, 37, 30, 22, 17 and 12 days prior to harvest during 1986-89.

Predawn leaf water potential best reflected water deprivation length and reached minimum values of about -1.5 MPa with the most severe cutoff. Magnitude of peak stomatal conductance was reduced and occurred earlier in the day with longer cutoff regimes.

Rate and time-course development of preharvest fruit drop was variable from year-to-year, but there were no significant differences in total drop between cutoff treatments. Only in the fourth year, following three years of no difference were tree fruit load and yield significantly reduced but then only with the most severe cutoff. Soluble solids were higher and drying ratios lower with the longer cutoffs. Fruit size was significantly reduced in the third year of the experiment. Trunk circumferences were significantly lower only with trees subjected to the longer cutoff regimes.

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K.G. Weis, S.M. Southwick, J.T. Yeager, W.W. Coates, and Michael E. Rupert

The years 1995 and 1996 were low chill years in California with respect to stone fruit dormancy. Advancing reproductive budbreak and flowering was accomplished in `Bing' cherry (Prunus avium) by single-spray treatments of a surfactant {a polymeric alkoxylated fatty amine [N,N-bis 2-(omega-hydroxypolyoxyethylene/polyoxypropylene) ethyl alkylamine]} and potassium nitrate in combination when applied at “tightbud,” ≈ 42 days (1 Feb. 1995) before full bloom and with surfactant and potassium nitrate in combination when 10% green calyx was apparent, 33 days before full bloom. Applying 2% surfactant (v/v) + 6% potassium nitrate (w/v) was most effective in advancing bloom, speeding progression through bloom, and advancing fruit maturity when applied at tightbud stage. Surfactant (2% or 4%) applied with 25% or 35% calcium nitrate (w/v) on 2 Feb. 1996 significantly advanced full bloom compared to nontreated controls. Fruit maturity (1995) was somewhat advanced by surfactant–nitrate treatments, but fruit set and final fruit weight were equivalent among treatments. No phytotoxicity was noted in foliage or fruit. In California, marginal and insufficient winter chilling often causes irregular, extended, or delayed bloom periods, resulting in poor bloom-overlap with pollenizers. As a result, flower and fruit development may be so variable as to have small, green and ripe fruit on the same tree, making harvest more time consuming and costly. Data indicate that this surfactant, in combination with a nitrogenous compound, has potential to advance reproductive budbreak and advance maturity in sweet cherry without reducing fruit set or fruit size. Advancing the ripening time of sweet cherry even 2 to 3 days can increase the price received per 8.2-kg box by $10 to $20.