Effects of naphthaleneacetic acid (NAA), aminoethoxyvinylglycine (AVG), and 1-methylcyclopropene (1-MCP) alone or in combination on fruit ethylene production, preharvest fruit drop, fruit quality, and fruit maturation were examined in ‘Golden Supreme’ and ‘Golden Delicious’ apples (Malus ×domestica Borkh.). In ‘Golden Supreme’ apples, the combination of two applications of AVG and one application of NAA 3 and 1 week, respectively, before the anticipated optimum harvest date synergistically inhibited fruit ethylene production and delayed fruit drop and ripening. Compared with one or two applications of AVG, the combination of one application of AVG and two applications of NAA had much lower preharvest fruit drop, although there was no significant difference in fruit ethylene production among these treatments. In ‘Golden Delicious’ apples, 1-MCP at 396 mg·L−1 had a better effect in delaying fruit drop than did AVG at 125 mg·L−1 or NAA at 20 mg·L−1 when they were applied a week before the optimum harvest date. The combination of NAA and 1-MCP or AVG was more effective in delaying fruit drop than were NAA, 1-MCP, or AVG alone. Fruit ethylene production was inhibited by 1-MCP and AVG but not by NAA. 1-MCP and AVG delayed fruit ripening, whereas NAA increased fruit ripening as determined by fruit firmness and starch.

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Shading (92%) of `Redchief Delicious' apple (Malus domestics Borkh.) trees for 10-day periods from 10 to 20, 15 to 25, 20 to 30, and 25 to 35 days after full bloom (DAFB) caused greater fruit abscission than shading from 5 to 15, 30 to 40, 35 to 45, or 47 to 57 DAFB. Fruit 8 to 33 mm in diameter (10 to 30 DAFB) were very sensitive to 10 days of shade, even though fruit sizes of 6 to 12 mm are considered the most sensitive to chemical thinners. In a second test, shading for 3 days caused fruit thinning; 5 days of shade in the periods 18 to 23, 23 to 28, and 28 to 33 DAFB caused greater thinning than 11 to 16 or 33 to 38 DAFB. Shading reduced photosynthesis (Pn) to about one-third that of noncovered trees. Terbacil (50 mg·liter-1) + X-77 surfactant (1250 mg·liter-1) applied with a hand-pump sprayer 5, 10, or 15 DAFB greatly reduced fruit set and caused some leaf yellowing, particularly in the earliest treatments. Terbacil reduced Pn by more than 90% at 72 hours after application. Shoot growth of trees defruited by shade or terbacil was equivalent to defruited or deblossomed trees; ethephon (1500 mg·liter-1) inhibited tree growth and defruited trees. No terbacil residues were dectected in fruit at harvest from applications made 5, 15, 20, 25, or 30 DAFB. Eleven of 12 photosynthesis-inhibiting herbicides were also found to thin `Redchief Delicious' apple trees. Shading caused more thinning than terbacil at the later applications, which may reflect poorer absorption and/or lesser photosynthetic inhibition than when terbacil was applied to older leaves.

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