Prohexadione-Ca inhibits vegetative growth of 'Smoothee Golden Delicious' apple trees

Experiments to test the effectiveness of prohexadione-Ca as a growth inhibitor in apple trees have been carried out for 3 years in the Middle Ebro Valley (Spain). Also, effects on fruit quality and flower initiation were evaluated. The application of 100-400 mg l(-1) of prohexadione-Ca between 12 and 30 days after full bloom (DAFB) to 'Smoothee Golden Delicious'/M9 apple trees resulted in the inhibition of shoot growth, the effect increasing with concentration, and a greater inhibition was obtained when the trees were first sprayed 12-20 DAFB. A second spray was usually needed to avoid a regrowth of the shoots. The effectiveness of the second application was related to the concentration applied and the date of the first spray. The relative increase in trunk-cross-sectional area was not affected by the growth inhibitor. No negative effects on yield and fruit quality were found except for a reduction of soluble solid content. Flower initiation in the following year was not affected. Concentrations of 100-200 mg l(-1) applied shortly after full bloom should be recommended, bearing in mind that a second application might be necessary 6-8 weeks later. (C) 2004 Elsevier B.V. All rights reserved.