Blossom Thinning of ‘Law Rome Beauty’ Apple with Hydrogen Cyanamide and Monocarbamide Dihydrogensulfate

Blossom thinning of ‘Law Rome Beauty’ apple (Malus domestica Borkh.) with hydrogen cyanamide (Dormex, 50% a.i.) and monocarbamide dihydrogen sulfate (Wilthin, 79% a.i.) were studied over four years. A full-bloom application of Dormex at 2.58 g a i./L (5 ml/L formulation) and 3.09 g a.i./L (6 ml/L formulation) overthinned, while one 1.29 g a.i./L (2.5 ml/L formulation) in both young and mature trees resulted in effective thinning without any adverse effects on the fruit or on return bloom. Wilthin at 4.49 g a.i./L (3.75 ml/L formulation) was effective in thinning and resulted in large fruit; however, fruit from this treatment had unacceptable marking in one out of four years. Application of Wilthin at 2.99 g a.i./L (2.5 ml/L formulation) plus Regulaid (as a surfactant), in one year, showed commercially acceptable thinning without adversely affecting fruit.