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Matthew D. Whiting and David Ophardt

The development of novel crop load management techniques will be critical to the adoption and success of high density sweet cherry orchard systems based on new clonal rootstocks. Herein we report on a comparison of potential means of balancing crop load of `Bing' sweet cherry grown on the productive and precocious rootstocks `Gisela 5' and `Gisela 6'. In 2002, thinning treatments were applied to entire trees and consisted of an unthinned control (C), and manual removal of 50% of the blossoms (B) or 50% of 2-year-old and older fruiting spurs (S), throughout the tree. In 2003 all trees were left unthinned to characterize the carry-over effect of thinning treatment in 2002. In 2002, compared to C, thinned trees had 38% to 49% fewer fruit per tree, 22% to 42% lower yield, 8% to 26% higher fruit weight, and 2% to 10% larger fruit diameter. S and B treatments reduced yield by 42% and 22% on `Gisela 5' and by 40% and 31% on `Gisela 6', respectively. `Gisela 5'-rooted trees showed greater improvements in fruit quality than did trees on `Gisela 6'. Compared to C-, S-, and B-treated trees on `Gisela 5' yielded fruit that was 15% and 26% heavier, respectively. Yield of fruit ≥25.5 mm diameter was increased by 240% by S and 880% by B, though yield of this size fruit was still low (1.5 and 5.2 kg/tree, respectively). Neither technique had any beneficial carryover effect in the year following treatment despite S trees bearing about 25% fewer fruit than B and C trees. In both years, `Gisela 5'-rooted trees bore about 15% fewer fruit than trees on `Gisela 6'. Compared to `Gisela 5', `Gisela 6'-rooted trees were about 41%, 46%, and 24% more productive for C, S, and B, respectively. Number of fruit/tree in 2003 was within 4% and 8% of the previous year on `Gisela 6' and `Gisela 5', respectively. Crop value analyses suggest growers would be rewarded for producing high yields of medium size fruit (e.g., 21.5 to 25.4 mm) compared to low yields of high quality fruit.

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Matthew D. Whiting, Gregory Lang, and David Ophardt

Traditional sweet cherry (Prunus avium L.) training systems in the United States are based upon vigorous rootstocks and multiple leader vase canopy architectures. The sweet cherry research lab at Washington State University has been investigating the potential of new rootstocks and training systems to improve production efficiency and produce high quality fruit. This paper describes the effects of three rootstocks—Mazzard (P. avium), `Gisela 6', and `Gisela 5' (P. cerasus × P. canescens)—and four training systems—central leader, multiple-leader bush, palmette, and y-trellis—on `Bing' sweet cherry tree vigor, fruit yield and quality over a seven year period. Compared to trees on Mazzard, trees on `Gisela 5' and `Gisela 6' had 45% and 20% lower trunk cross-sectional areas after 7 seasons, respectively. Trees on `Gisela 6' were the most productive, yielding between 13% and 31% more than those on `Gisela 5' and 657% to 212% more than trees on Mazzard, depending on year. Both Gisela rootstocks significantly improved precocity compared to Mazzard, bearing fruit in year 3 in the orchard. Canopy architecture had only moderate effects on tree vigor and fruit yield. Across rootstocks, bush-trained trees were about 25% less productive compared to the other systems, which exhibited similar cumulative yields (102 kg/tree). Fruit weight was negatively and closely (r 2 = 0.84) related to tree yield efficiency (kg·cm–2). Crop value was related positively to fruit yield.

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Matthew D. Whiting, David Ophardt, and James R. McFerson

The commercial adoption of the relatively new rootstock `Gisela 5' (Prunus cerasus L. × P. canescens L.) has been limited in the United States sweet cherry (P. avium L.) industry despite its ability to induce precocity and productivity and reduce scion vigor compared to the standard Mazzard (P. avium). This is due in large part to inadequate crop load management that has led to high yields of small fruit. This paper reports on sweet cherry chemical blossom thinning trials conducted in 2002 and 2003. Two percent ammonium thiosulphate (ATS), 3% to 4% vegetable oil emulsion (VOE), and tank mixes of 2% fish oil + 2.5% lime sulphur (FOLS) were applied to entire 8- and 9-year-old `Bing'/`Gisela 5' sweet cherry canopies at about 10% full bloom (FB) and again at about 90% FB. In both years, ATS and FOLS reduced fruit set by 66% to 33% compared to the control (C). VOE reduced fruit set by 50% compared to C in 2002 but had no effect in 2003. In 2002, fruit yield was 30% to 60% lower from thinned trees. In 2003, fruit yield was unaffected by thinning treatment. In 2002, ATS and FOLS improved fruit soluble solids but had no effect in 2003. VOE did not affect fruit soluble solids in 2002 and reduced fruit soluble solids by 12%, compared to C, in 2003. In 2002, each thinning treatment nearly eliminated the yield of the small fruit (≤21.5-mm diameter) and increased yield of large fruit (≥26.5 mm) by more than 400%, compared to C. In 2003, ATS and FOLS did not affect yield of small fruit but increased the yield of large fruit by 60%. In 2003, VOE-treated trees yielded 4.3 kg of small fruit per tree compared to about 0.15 kg from C, suggesting a phytotoxic response to VOE beyond that which may effect thinning. Compared to C, ATS and FOLS consistently reduced fruit set and improved fruit quality. We conclude that commercially acceptable yields of excellent quality `Bing' sweet cherries can be grown on size-controlling and precocious rootstocks.

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Edward L. Proebsting, David Ophardt, William E. Howell, Gaylord I. Mink, and Kim D. Patten

Thirty-five `Bing' sweet cherry (Prunus avium L.) clones were collected, primarily from old commercial orchards in central Washington; propagated on P. mahaleb L. rootstock; and their horticultural performance was evaluated. Nine of the 35 clones were not infected with the common pollen-borne ilarviruses prunus necrotic ringspot virus and prune dwarf virus—four of the clones after decades of exposure in commercial orchards. As a group, the nine virus-free clones produced larger trees with earlier fruit maturity and less rain cracking, but softer fruit, than did the 26 infected clones. These data challenge the general assumption that the presence of one or both of these ilarviruses is always detrimental. This assumption has driven development of many valuable virus certification programs and the adoption of virus-free trees as the standard for commercial fruit growing in most states.

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James W. Olmstead, Matthew D. Whiting, David Ophardt, Nnadozie C. Oraguzie, and Gregory A. Lang

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James W. Olmstead, Matthew D. Whiting, David Ophardt, Nnadozie C. Oraguzie, and Gregory A. Lang

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Nnadozie C. Oraguzie, David Ophardt, Matthew D. Whiting, Gregory A. Lang, and Lynn E. Long