Applications of endothalic acid, pelargonic acid, and hydrogen cyanamide for blossom thinning in apple and peach

Abstract

Blossom thinning of 'Early Spur Rome' apple (Malus domestica Borkh.) and 'Redhaven' peach (Prunus persica L.) with hydrogen cyanamide (Dormex, 50% a.i.), endothalic acid [(Endothal, 0.4 lb a.i./gal (47.93 g a.i./L)], and pelargonic acid (Thinex, 60% a.i.) was studied in 1995 and 1996. Full-bloom applications of hydrogen cyanamide at 2 pt formulation/100 gal (1288 mg a.i./L) and 2.5 pt formulation/100 gal (1610 mg a.i,/L) or endothalic acid at 1 pt formulation/100 gal (59.9 mg a.i,/L), once at 70% bloom and again at full bloom, reduced apple fruit set. Pelargonic acid was only effective in thinning apple blossoms when applied twice-at 40% bloom and again at full bloom- t 1.5 pt formulation/100 gal (1.12 mL a.i./L) per application. Pelargonic acid marked apples in 1995 but not 1996. Neither hydrogen cyanamide nor endothalic acid marked apples. A single full-bloom application of hydrogen cyanamide, endothalic acid, or pelargonic acid effectively thinned peach blossoms in 1995; however, in 1996, only hydrogen cyanamide at 2.5 pt formulation/100 gal effectively thinned peach blossoms. Peaches did not show fruit marks with any of the peach blossom thinners.