Volume 58 Number 2 Article 15
Year 2004 Month 4
Title: The Influence of Prohexadione-Calcium Sprays on Apple Tree Growth, Chemical Fruit Thinning and Return Bloom
Authors: R.E. Byers, D.H. Carbaugh and L.D. Combs
Abstract:
P-Ca [formulated as BAS-125 (10% P-Ca) or Apogee™, (27.5% P-Ca + 56.1% (NH4)2S04 + 16.4%
other proprietary additives)] applied to 'Fuji'/M.9 trees in 3 applications at 250 mg.L-1 (a.i.
P-Ca),
increased fruit set compared with the unsprayed control.
Chemical thinning sprays reduced crop load and
promoted tree growth in both P-Ca and non-P-Ca sprayed trees.
P-Ca did not affect chemical fruit
thinning when chemical thinners were applied between the first and second of three P-Ca applications.
Carbaryl + oil, carbaryl + Accel + oil, oxamyl + Accel caused fruit thinning, but ethephon or shading trees
for 3 days did not.
Shading + P-Ca sprays caused additional shoot growth suppression, which suggested
that P-Ca may be light labile.
In a second experiment, three sprays of P-Ca [BAS 125: 10% P-Ca; 90%
(NH4)2SO4] at a low rate of 63 mg.L-1 or ethephon at 135 mg.L-1 applied to 'Fuji'/M.9 did not affect
shoot growth; however, the combination of P-Ca + ethephon at these rates gave good control of tree
growth without influencing flowering, fruit set, or fruit abscission.
In a third experiment, GA3 alone did
not promote shoot growth when compared with the unsprayed control, but GA3 sprays partially
counteracted the shoot growth suppression of P-Ca + (NH4)2SO4 + Regulaid.
Flower bud formation was
inhibited by GA3 in the next season, but P-Ca had no effect on return bloom or return fruit set.
Chemicals used: Prohexadione-calcium (P-Ca) formulated as BAS-125 (10% P-Ca + 90% (NH4)2S04)
or Apogee™, (27.5% P-Ca + 56.1% (NH4)2S04 + 16.4% other proprietary additives), Regulaid® (a
surfactant mixture, polyoxyethylenepolypropoxypropanol, alkyl 2-ethoxethanol, and dihydroxy propane;
Silwet L-77 (polyalkyleneoxide modified heptametyltrisiloxane, silicon surfactant), oxamyl (Vydate;
methyl N',N' dimethyl-N[methylcarbamoyl] (oxy)]-l-thiooxamimidate); superior oil (Drexel Damoil
70 sec delayed dormant spray oil), ethephon (Ethrel, 2-chloroethyl phosphonic acid), (NH4)2SO4;
carbaryl (Sevin XLR, 1-naphthy N-methylcarbamate); Accel (mixture of 6-benzyladenine and gibberellin
A4+7), and gibberellin A3.
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