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- Author or Editor: Max W. Williams x
Aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, applied to ‘Delicious’ apple trees (Malus domestica Borkh.) 2 weeks before harvest reduces loss of flesh firmness of apples in storage and increases vegetative growth in the following growth season. When applied to ‘Delicious’ or ‘Golden Delicious’ trees after full bloom, the “June drop” was completely eliminated; thus, fruit set was significantly increased.
Two chemicals being tested as blossom thinners for apple are effective for bloom thinning of peaches and nectarines. Monocarbamide dihydrogen sulfate (Wilthin) and Endothall applied at 90% of bloom open reduced fruit set by 50%. Fruit size and quality of the crop were improved. Both of the above chemicals gave adequate fruit removal without serious phytotoxic effects on leaves, buds or shoots. With chemical rates which over thinned, no fruit marking occurred on either nectarines or peaches.
Moderate to high vigor and maximum light penetration must be maintained in deciduous fruit trees to assure high yields of good quality fruit. To accomplish the balance between vigor and light penetration, control of excessive shoot growth is required. Dwarfing rootstocks and spur type scion cultivars are reasonably successful in controlling vegetative growth. However, some species have few adequate rootstocks or spur type scions to help control tree growth. Furthermore, even with the best possible combination of rootstock and scion for a particular orchard site, there are periods in the life of the orchard when additional control of vegetative growth is needed. Vigorous growth is necessary in the early years to fill the allotted space with a viable fruiting surface. Fruit set then is increased by controlling excessive vegetative growth. Periodic control of growth can be accomplished by pruning and training of shoot growth, but these methods are often inadequate for maximum fruiting efficiency, since they are labor intensive and cannot always be accomplished in a timely manner.
The growth retardants 2-chloroethylphosphonic acid (ethephon) and succinic acid-2-2-dimethylhydrazide (SADH) increase flower initiation in young apple trees. At comparable rates, ethephon is more effective than SADH. High rates of ethephon cause flower and fruit abscission. When ethephon was combined with SADH and applied 4 to 5 weeks after bloom, satisfactory promotion of flower bud formation was obtained with lower rates of each chemical with a min of undesirable side effects.
In fruit-growing areas where pollination and fruit set conditions are optimum, biennial bearing is a regular occurrence unless steps are taken to reduce fruit set in the heavy bloom year. In the past, a two- or three-spray thinning program was used in the state of Washington on difficult cultivars, consisting of Elgetol at bloom time, followed by a petal fall spray of Amide-thin, followed by a later postbloom spray of NAA or Sevin. In 1989, Elgetol was removed from the market by the manufacturer because of the high cost of re-registration. In 1990, a search for an Elgetol replacement was initiated. Elgetol was a contact spray that damaged flower parts and prevented fertilization of the ovule. Thus, it was logical to look for other products that had a similar mode of action. Sulfcarbamide (monocarbamide dihydrogen sulfate) (D-88) (Wilthin), a foliage desiccant used on potatoes, onions, and alfalfa, and tested as a dilute full-volume spray on apple blossoms, was found to be an effective blossom thinner. Chemical rates of 0.25% to 0.5% (v/v) applied at 80% of bloom open reduced fruit set by 25% to 50% compared to controls.
Biennial bearing of apple trees can be overcome either by the use of a blossom chemical thinner or by early application of a postbloom thinner. Carbaryl (Sevin) is a post-bloom fruit-thinning chemical with an effective thinning period of 4 to 5 weeks after bloom. Sevin was compared in 1992 and 1993 with NAA as an early petal-fall spray. Sevin treatments reduced fruit set to one fruit per cluster with no adverse side effects on the foliage. NAA inconsistently reduced fruit set and the remaining fruit were in clusters, The NAA-treated foliage was adversely affected; having small curled leaves. NAA at 10 ppm under-thinned in 1992 and seriously over-thinned in 1993, whereas Sevin treatments were consistent for fruit thinning in both years. Sevin applied at petal-fall or at petal-fall + 7 days effectively reduced fruit set and reduced fruit competition.
The determination of sugars and sugar alcohols in horticultural crops is time-consuming and often difficult because of interfering substances. The quantitative deteimination of the individual sugars in a sample has until recently been very difficult. The work of Sweeley and co-workers (2), on the formation and subsequent gas chromatography of trimethylsilyl (TMS) ether derivatives of carbohydrates and related polyhydroxy compounds, has made it possible to determine individual sugars quantitatively.
Few agricultural commodities have enjoyed the tremendous success achieved by the Washington State apple industry. The apple acreage in Washington has increased from about 80,000 to over 125,000 acres in recent years. The production reached 72 million boxes in 1981 and will increase to about 85 million by 1985. This expansion is directly related to the improved technology in the production, storage, and marketing of the fruit, which has provided a constant supply of quality fruit to consumers for 11 to 12 months of the year. Much of the success is credited to a strong research effort and the immediate application by the fruit industry of the new technology developed from research.
Cytokinins applied to axillary buds of apple shoots overcame apical dominance. Axillary buds on actively growing apple shoots produced spurs and lateral branches when treated with cytokinins. Buds on shoots that had not received sufficient chilling to break rest were also induced to grow with cytokinins.
The chemical 2,3,5-triiodobenzoic acid (TIBA 1,2) has been reported by workers in the United States (1,2,3,4,8) and other countries (6,7) to influence flower bud initiation and branch angle of apple trees. This report describes injury to fruits and pedicels of Golden Delicious and to foliage of Golden Delicious, Delicious and Winesap apple trees from the application of 25 ppm TIBA about 4 weeks after bloom in North Central Washington.