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Fenton E Larsen and Stewart S. Higgins

The influence of 9 rootstock on growth and production of `Goldspur' (GS) and `Wellspur Delicious' (WS), and of 3 rootstock on growth and production of `Red King Delicious' (RK) and `Golden Delicious' (GD) apple was evaluated. The spur-type `Delicious' (WS) produced more fruit per tree than the non-spur (RK) strain with Mailing (M) 7 and Malling-Merton (MM) 106 but not with M 26. GD produced more fruit per tree than GS on M 7 and M 26 but not MM 106. Yield efficiencies were usually superior with spurred strains. Efficiency of RK was markedly inferior to GD and WS. Comparing cumulative yields among 9 stocks within spurred strains showed that highest yields were with MM 106 roots. Clonal stocks were more efficient than seedling. The least size-controlling stocks (seedling, MM 104, MM 109, and M 25) tended to be less efficient than M 2, M 7, M 26, MM 106, or MM 111, but the trends throughout the experiment were not consistent. Seedling, MM 104 and MM 109 had the largest trees with spurred tops, and M 26 the smallest.

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Fenton E Larsen and Stewart S. Higgins

The influence of 9 rootstock on growth and production of `Goldspur' (GS) and `Wellspur Delicious' (WS), and of 3 rootstock on growth and production of `Red King Delicious' (RK) and `Golden Delicious' (GD) apple was evaluated. The spur-type `Delicious' (WS) produced more fruit per tree than the non-spur (RK) strain with Mailing (M) 7 and Malling-Merton (MM) 106 but not with M 26. GD produced more fruit per tree than GS on M 7 and M 26 but not MM 106. Yield efficiencies were usually superior with spurred strains. Efficiency of RK was markedly inferior to GD and WS. Comparing cumulative yields among 9 stocks within spurred strains showed that highest yields were with MM 106 roots. Clonal stocks were more efficient than seedling. The least size-controlling stocks (seedling, MM 104, MM 109, and M 25) tended to be less efficient than M 2, M 7, M 26, MM 106, or MM 111, but the trends throughout the experiment were not consistent. Seedling, MM 104 and MM 109 had the largest trees with spurred tops, and M 26 the smallest.

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Fenton E Larsen and Stewart S. Higgins

Artificial defoliation of deciduous fruit tree nursery stock is often necessary so that plants can be dug early enough to escape inclement fall weather. In this research, we assessed the efficacy of abscisic acid (ABA) as a defoliant. ABA was applied as a foliar spray at one of three concentrations—500, 1000, or 2000 ppm a.i. Trees were sprayed either once or twice for a total of six chemical treatments, plus untreated controls. The defoliation and growth responses of eight cultivars were evaluated with the cooperation of commercial nurseries in Washington State. While all treatments caused significantly greater defoliation than was observed in untreated trees, ABA at 500 ppm applied once or twice, or 1000 ppm applied only once, was generally sufficiently effective only on `Bartlett', `Gibson Golden Delicious', and `Law Red Rome', but not on `Imperial Gala', `Scarlet Spur Delicious', `Granny Smith', `Braeburn', or `Red Fuji'. Single or double applications of 2000 ppm or double applications of 1000 ppm often produced faster defoliation than double applications of 500 ppm, but defoliation was not always superior after 4 weeks. No pre-digging field damage was noted, but some treatments appeared to reduce trunk diameter increase after replanting, with no consistent trends among cultivars, except with `Bartlett' pear, which was frequently negatively affected. ABA appears to be very promising as a nursery tree defoliant.

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Fenton E Larsen and Stewart S. Higgins

The influence of five Old Home × Farmingdale (OHF) rootstocks on tree size with 10 Asian pear scion cultivars was examined after 10 years in an experimental orchard in central Washington state. The effect of rootstock on tree size varied among scion cultivars. Within `Chojuro', `Hosui', `Niitaka', and `Seigyoku', trunk cross-sectional areas were similar regardless of rootstock. Within `Li', OHF 333 produced larger trees than OHF 282 and OHF 217. `Okusankichi' trees, which were generally the same size as `Hosui', were significantly larger on OHF 217 and OHF 97 than on OHF 333. `Kikusui' trees, which were generally similar in size to `Niitaka' and `Seigyoku', were larger on OHF 217, OHF 97, and OHF 282 than on OHF 333. `20th Century', which was similar in size to `Chojuro' and `Shinseiki', appeared to be the cultivar most sensitive to rootstock. `20th Century'/OHF 217 were significantly larger than trees on OHF 97 and OHF 282, which were larger than trees on OHF 51. `Shinseiki'/OHF 97 were larger than trees on OHF 333. The smallest trees were `Shinko', with trees on OHF 217, OHF 97, OHF 333, and OHF 51 all being larger than trees on OHF 282. Contrary to research with some European pear scions, consistent trends did not emerge from this research that would allow a general prediction of the relative influence of these five OHF clonal rootstocks on Asian pear tree size.

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Fenton E Larsen and Stewart S. Higgins

Many tree fruit nurseries are limited to fall digging of deciduous nursery stock. Since trees may not defoliate naturally for timely digging, these nurseries may wish to defoliate chemically, which would be less expensive than hand-stripping and may more closely simulate natural leaf abscission. Consequently, test chemicals were applied with hand sprayers at commercial nurseries in central Washington State using single or double applications 1 wk apart. In 1992 on 7 apple cultivars and one pear, 500 ppm NPA + 150 ppm Ethrel significantly enhanced defoliation. Defoliation at 1000 ppm NPA was not superior to that at 500 ppm, and two applications were generally no better than one. However, in 1993, two applications were often more effective than one, and the addition of Ethrel to NPA generally enhanced defoliation if the combination of NPA + Ethrel was applied twice. Alanap and NPA were generally equally effective as defoliants. The addition of Ethrel to Alanap enhanced defoliation in only 3 of 9 cultivars, and then generally only when sprayed twice. Alanap + Ethrel was as effective with Alanap at 300 ppm as with Alanap at 500 ppm Ethrel by itself seldom increased defoliation.

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Fenton E. Larsen and Stewart S. Higgins

Tree size, cumulative yield, yield efficiency and anchorage of 6 micropropagated (MP) apple (Malus domestica Borkh.) cultivars were determined in 1991 after 5 years of production, as compared with trees on seedling (sdlg) or M 7a roots. Trees were planted in 1984, with crops harvested from 1987 through 1991. Trees were generally smallest (trunk cross-sectional area) on M 7a and were largest with 4 cultivars (`Delicious', `Jonathan', `Rome', `Spartan') when micropropagated. `Golden Delicious' (GD) was largest on sdlg. Cumulative yield was affected by a scion × rootstock interaction, with few trends in scion or rootstock effects. Mean cumulative yield was 84 kg tree-1, 71 and 58 for M 7a, MP and sdlg, respectively. Yield efficiency was also affected by a scion × rootstock interaction. In 1991, mean yield efficiency was 0.5 kg cm-2 for sdlg and MP trees, but was 1.05 for M 7a. Efficiency on M 7a was superior to other rootstocks with all scions except `GD', while sdlg and MP trees were statistically similar with all scions. All trees leaned in response to prevailing westerly winds, with trees on sdlg tending to be more upright than MP or M 7a trees.

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Fenton E. Larsen and Stewart S. Higgins

Abscisic acid (ABA) was tested as a defoliant for nursery trees of `Bartlett' pear (Pyrus communis L.) and the apple (Malus×domestica Borkh.) cultivars Imperial Gala, Gibson Golden Delicious, Scarlet Spur Delicious, Law Red Rome, Granny Smith, Braeburn, and Red Fuji. ABA was sprayed once or twice, with 1 intervening week, at 500, 1000, or 2000 ppm. Percentage defoliation was assessed at 1-week intervals for 4 weeks. For all cultivars, two applications of 2000 ppm ABA ranked among the most effective treatments for rapid defoliation; this treatment led to at least 95% defoliation for all cultivars. For many cultivars, however, other treatments caused similar defoliation percentages by digging time. All tested cultivars were effectively defoliated (>80%) by two 1000-ppm applications ABA or one 2000-ppm application. One or two 500-ppm applications effectively defoliated `Bartlett', `Gibson Golden Delicious', and `Law Red Rome'. Nursery managers, therefore, need to consider a range of ABA concentrations and alternative application protocols to obtain optimum benefit from ABA. Although ABA shows promise as a defoliant, it lacks government approval for commercial use.

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Fenton E. Larsen, Virginia S. McCamant, and Stewart S. Higgins

`Schmidt' and `Bing' sweet cherries were planted in 1982 at the W.S.U. Royal Slope orchard near Othello, Wash. `Schmidt' was on Mazzard × Mahaleb (M × M) rootstocks 39, 97, 14, and Mazzard seedling. `Bing' was on East Malling (E.M.) cherry rootstocks 38, 15, 21, 16, 50, and Mazzard and Mahaleb seedling. Yield of `Schmidt'/M × M 39 was greater than all other rootstocks. Trunk diameters of `Schmidt' were greatest on Mazzard and M × M 39. If a standard-size tree is desired, M × M 39 may be useful. `Bing' trees on the E.M. rootstocks tended to be larger than on Mazzard or Mahaleb and are, therefore, not of great interest.

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Stephen R. Drake, Fenton E. Larsen, and S.S. Higgins

Influences of rootstock on the quality of `Granny Smith' and `Greenspur' apples (Malus domestica Borkh.) were evaluated over an extended harvest period and after cold storage. Apples from trees on M.26 rootstock had the higher firmness, soluble solids concentration (SSC), and Ca content, but poorer external color (red blush) and a higher percentage of solar injury than fruit from trees on seedling or MM.111 rootstock. External greenness was best on apples from MM.111 rootstock. `Granny Smith' apples had higher firmness, soluble solids, acids, and carbohydrate contents, and less scald but poorer external greenness than `Green spur' apples. `Granny Smith' or `Greenspur' apples from M.26 rootstock appeared to mature earlier than those on MM.111.