Chemical Stimulation of Branching in Deciduous Tree Fruit Nursery Stock with Ethyl 5-(4-chlorophenyl)-2H-tetrazole-2-acetate1

Abstract

Abstract Ethyl 5-(4-chlorophenyl)-2H-tetrazole-2-acetate (PP528) applied in early summer to apple (Malus domestica Borkh.) and pear (Pyrus communis L.) trees stimulated lateral branching the first year in the nursery. Concentrations of 25 to 50 ppm were effective, while 100 ppm or more sometimes killed shoot terminals and stopped or retarded further vertical growth for the season. Branch angles were not measured, but when terminal meristems were not killed, branch angles were wide. If terminal meristems were killed, the uppermost branch angles were narrow. Double applications 2 weeks apart of 25 or 50 ppm were sometimes more effective than single applications. Timing, uniformity of growth, and application during active growth were important to produce maximum branching effect and branching in suitable locations. PP528 caused more branching in 2 nonspurred ‘Delicious’ apple cultivars (up to 9 times control values) than in ‘Oregon Spur Delicious’ (up to 3 times the control). Treatments with up to 200 ppm were largely ineffective on sweet cherry (Prunus avium L.). Use of 100 or 250 ppm GA was of little benefit in overcoming the stunting effect of high concentrations of PP528.