RESPONSE OF APPLE TREES TO AMINOETHOXYVINYLGLYCINE (AVG) WITH EMPHASIS ON APICAL DOMINANCE, FRUIT SET, AND MECHANISM OF ACTION OF FRUIT THINNING CHEMICALS

AVG applied to apple trees in the fall suppresses ethylene production in the leaf buds during the dormant and early spring periods. The result is a dramatic increase in bud break and lateral growth which increases the total leaf surface on the tree. AVG applied alone at concentrations from 100 to 400 ppm results in significant increases in fruit set and higher average seed counts per fruit. AVG applied to apple trees two weeks after bloom either before or after an application of NAA or carbaryl suppresses the endogenous ethylene production normally stimulated by the chemical thinners, and reduces the amount of fruit abscission. In contrast to NAA, carbaryl does not stimulate as much ethylene production in the leaves, but increases ethylene levels in the fruit to about the same degree as NAA. AVG does not prevent fruit abscission when ethephon or ethylene gas is applied to the trees.