Apple Thinning by Photosynthetic Inhibition

Abstract

<jats:p>Shading (92%) of `Redchief Delicious' apple <jats:italic>(Malus domestics</jats:italic> 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<jats:sup>-1</jats:sup>) + X-77 surfactant (1250 mg·liter<jats:sup>-1</jats:sup>) 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<jats:sup>-1</jats:sup>) 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.</jats:p>

Environmental Effects on the Performance of Foliar Applied Plant Growth Regulators: A Review Focusing on Tree Fruits

“…Application of thinners to such fruitlets may result in excessive thinning and reduced rates are often recommended (Williams, 1979). Byers et al (1990aByers et al ( , 1990bByers et al ( , 1991 have extensively tested the effect of shading and application of photosynthesis-inhibiting chemicals in early fruit growth, to assess the role of suppressed photosynthesis on degree of fruit thinning both with and without application of chemical thinners. They propose (Byers et al, 1990b) that cloudy periods for as little as 3 d or fewer during the physiological drop period may signifi cantly decrease fruit retention and may infl uence response to chemical thinners.…”

Manipulation of fruit dry matter accumulation and fruit size in ‘Scifresh’ apple through alteration of the carbon supply, and its relationship with apoplastic sugar composition

“…To avoid the confounding effect of shading treatment on fruit drop (Byers et al, 1990), or treatment effects on cell division, all treatments were delayed until 60 d after full bloom (DAFB). The trial also aimed to examine changes in the DM composition of fruit as influenced by these treatments and to examine the use of apoplastic fluid as an indicator of the carbohydrate supply to fruit.…”

Blossom Thinning in Apple and Peach with an Essential Oil

“…Young spur apple leaves play a vital role in supplying the developing fruits with carbohydrates (Corelli Grappadelli, 2003) and in fruit retention (Ferree and Palmer, 1982). A reduction in Pn after application of caustic materials at bloom (McArtney et al, 2006;Noordijk and Schupp, 2003) or from shading or Pn inhibitors (Byers et al, 1990a(Byers et al, , 1990b has been suggested as a causal factor in fruit thinning (Byers, 2003). Injury to spur leaves or shading followed by reductions in Pn could reduce fruit size.…”

“…Injury to spur leaves or shading followed by reductions in Pn could reduce fruit size. However, support for this theory from thinning trials is inconsistent (Byers et al, 1990a(Byers et al, , 1990bFallahi, 1997;Fallahi et al, 1997;Noordijk and Schupp, 2003). In the present study, apple treated with Matran (Table 4) or eugenol (Tables 5 and 6) at sufficient rates to cause phytotoxicity showed no negative effects on fruit size.…”