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Ross E. Byers, D.H. Carbaugh and L.D. Combs

Aminoethoxyvinylglycine (AVG) applied as a spray to 'Arlet' apple trees inhibited fruit drop and increased the pull force necessary to detach the fruit. AVG delayed the loss of fruit firmness, starch degradation, fruit shriveling, and red color development. 1-Methylcyclopropene (1-MCP), applied as a gas or spray to trees in the field, did not affect fruit drop or pull force. The combination of AVG + 1-MCP (spray or gas) provided better control of fruit drop, slowed the loss of fruit firmness, starch degradation, and decrease in pull force than AVG alone. Thirty five days after the optimum harvest date, fruit firmness from trees sprayed with AVG + 1-MCP was maintained at 74.3 N. Fruit of the control was significantly lower at 61.4 N firmness. The delay in harvest caused untreated control fruit stems to turn brown and die, but stems on AVG treated trees remained green and fruit continued to grow. In the 35 days after the optimum harvest date, treated fruit increased 2.5 cm in fruit diameter. Chemicals used: Aminoethoxyvinylglycine (AVG), 1-Methylcyclopropene (1-MCP), and trisiloxane ethoxylate methyl ether (an organosilicone surfactant, Silwet L-77).

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John A. Barden, Richard P. Marini and Ross E. Byers

Researchers often apply treatments to limbs rather than to whole trees. This technique allows the application of large numbers of treatments to a limited number of trees, and also allows adequate replication when a chemical is in very limited supply. The obvious assumption is made that results from limb treatments arc representative of those to be expected using whole trees.

Data from several experiments will be discussed that raise serious doubts about the extrapolation of results from limb treatments to whole-trees. The data are from studies with terbacil applied to apple and peach as well as shade treatments to both apple and peach. Girdling studies will also be discussed in which branches isolated by girdling responded very differently than ungirdled branches.

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Daniel L. Ward, Richard P. Marini and Ross E. Byers

Preharvest fruit drop of apple [Malu×domestica (L.) Borkh.] can cause significant crop losses, but factors controlling date of individual fruit drop are unknown. In three types of experiments, we investigated the relationships among seed number/fruit, fruit weight, and day of year of drop. By shading in mid-May and stigma excision before bloom, we induced variability in seed number. Dropped fruit were weighed, and their seeds were counted daily from late August until all fruit had dropped. Nontreated trees were studied similarly. Regression analyses were used to assess relationships among day of drop, fruit weight, and seed number/fruit. Substantial variation in day of drop of individual fruit was not explained by seed number of the fruit in these experiments with `Smoothee Golden Delicious', `Redchief Delicious', and `Commander York'.

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Stephen C. Myers, Amy T. Savelle, D. Stuart Tustin and Ross E. Byers

Partial thinning of peach (Prunus persica L. Batsch) during bloom to 50% of the necessary level by hand, and followed by adjustment hand thinning at 42 days after full bloom (DAFB) was compared to a similar degree of thinning accomplished entirely at 42 DAFB by hand. Partial flower thinning altered the distribution of fruit by diameter, increasing the percentage of large diameter (≥62.0 mm) fruit harvested compared to unthinned trees or trees thinned entirely at 42 DAFB. Although shoot number per limb was not altered by thinning time, the distribution of shoots by length was affected, increasing the percentage of long shoots (≥20.0 cm). Compared to unthinned trees and trees thinned at 42 DAFB, partial flower thinning increased the subsequent development of flower buds per shoot and the number of flower buds per node. Number of flower buds on the proximal five nodes of shoots 15.0-30.0 cm in length was increased, although not on shoots 5.0-7.0 cm in length. Additional trials established that airblast spray application of AMADS was effective in achieving a similar level of thinning as that accomplished by partial flower thinning by hand in previous experiments. The degree of flower removal exhibited a linear response to chemical concentration. Fruit diameter on chemically flower-thinned trees was greater at adjustment thinning time, when compared to trees thinned by hand at 42 DAFB only. Distribution of fruit at harvest indicated a larger percentage of fruit >65.0 mm in trees which received partial flower thinning in comparison to trees thinned at 42 DAFB only. As a result, overall crop value was increased, based on the commercial processing peach price structure at the time of harvest. Chemical name used: 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS)

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Daniel L. Ward, Eric P. Beers, Ross E. Byers and Richard P. Marini

Preharvest abscission of apple [Malus ×domestica (L.) Borkh.] fruits causes significant crop loss in many years. In this study, fruit cutting was used to induce abscission in August and September. Abscission zones of `Redchief Delicious' Mercier strain fruits were sampled 0, 2, 4, and 6 days after cutting. Thin-layer-plate assays were developed and used to identify hydrolytic enzymes active in the abscission zone (AZ) after induction. Increased activity of cellulase, but not polygalacturonase, was detected in the AZ following cutting. Cellulase activity was consistently high in AZs 4 days after cutting. Both AVG (652 mg·L–1) and NAA (10 mg·L–1) applied 2 or 4 days after cutting delayed drop, but NAA delayed drop 1.6 days longer than did AVG. Fruits treated with AVG dropped over a longer period than did control or NAA-treated fruits. Chemical names used: aminoethoxyvinylglycine (AVG); naphthaleneacetic acid (NAA).

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Richard P. Marini, Ross E. Byers, Donald L. Sowers and Rodney W. Young

Five apple (Malus domestica Borkh.) cultivars were treated with dicamba at concentrations of 0 to 200 mg·liter-1 during 3 years. Although the response varied with cultivar, dose, and year, dicamba always delayed fruit abscission. At similar concentrations, dicamba usually reduced fruit drop more than NAA, but less than fenoprop. Dicamba at 10 mg·liter-1 effectively delayed drop of `Delicious', whereas 20 to 30 mg·liter-1 was required for `Red Yorking', `Rome', `Winesap', and `Stayman'. Dicamba did not influence flesh firmness, soluble solids content, water core, or starch content at harvest or after storage. Chemical names used: naphthaleneacetic acid (NAA); 2-(2,4,5-trichlorophenoxy)propionic acid (fenoprop); 3,6dichloro-2-methoxybenzoic acid (dicamba).

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Esmaeil Fallahi, Bahar Fallahi, James R. McFerson, Ross E. Byers, Robert C. Ebel, Robert T. Boozer, Jim Pitts and Bryan S. Wilkins

Effects of Tergitol-TMN-6 surfactant on blossom thinning (fruit set), fruit quality, and yield were studied in different cultivars of peach (Prunus persica [L.] Batsch) during 2003 to 2005, and in one cultivar of nectarine Prunus persica [L.] in one orchard and one cultivar of plum (Prunus domestica [L.]) in two orchards in 2004. In addition to Tergitol-TMN-6, effects of Crocker's fish oil (CFO) alone in three peach cultivars or in combination with lime sulfur in a nectarine cultivar were studied on fruit set, quality, and yield. Tergitol-TMN-6 at 5 mL·L–1 or higher rates, applied at about 75% to 85% bloom, reduced fruit set without russeting peach fruit. Peach fruit size was often increased by Tergitol-TMN-6 treatment. Applications of Tergitol at 20 mL·L–1 or 30 mL·L–1 excessively thinned peaches. Tergitol-TMN-6 at all rates burned foliage, but the symptoms disappeared after a few weeks without any adverse effects on tree productivity. Tergitol-TMN-6 at 7.5 mL·L–1 or 10 mL·L–1, applied either once at about 80% to 85% bloom or twice at 35% bloom and again at 80% to 85% bloom, reduced fruit set without any fruit russeting in nectarine. Tergitol-TMN-6 at 7.5 mL·L–1 to 12.5 mL·L–1 reduced fruit set in `Empress' plum. CFO at 30 mL·L–1 was effective in blossom thinning of some peach cultivars. A combination of lime sulfur and CFO was not effective in blossom thinning of nectarine. Considering results from several orchards in different locations in the Pacific Northwest over 3 years, Tergitol-TMN-6 is an excellent blossom thinner for peach, nectarine, and plum at rates of 7.5 to 12.5 mL·L–1, sprayed at a spray volume of 1870.8 L·ha–1 when about 75% to 85% blooms are open.

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Chad E. Finn and John R. Clark