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Root pruning and prohexadione-calcium affect shoot growth of mature vertical axis apple trees

Fachinello, J. C., Robinson, T. L.
Acta horticulturae 2017 no.1177 pp. 215-218
Malus domestica, additive effect, cultivars, plant growth substances, prohexadione calcium, root pruning, rootstocks, trees, vegetative growth
Root pruning and the plant growth regulator prohexadione-calcium (ProCa) each reduce vegetative growth of apple trees. We evaluated the combined effect of the two treatments on the growth of mature vertical axis apple trees using eleven-year-old 'Gala', 'Marshall Mac', 'Empire' and 'Jonagold' apple trees on M.9 rootstock and 'Red Delicious' apple trees on M.26 rootstock. Treatments included: 1) untreated (control); 2) root pruning at 7 days after petal fall (DAPF); 3) 188 mg L-1 ProCa 7 DAPF, 125 mg 
L-1 ProCa 28 DAPF and 125 mg L-1 ProCa 56 DAPF; and 4) root pruning at 7 DAPF plus 188 mg L-1 ProCa 7, 28 and 56 DAPF. Trees were root pruned along both sides of the row, 60 cm from the trunk, 30 cm deep, with a large coulter wheel type blade. ProCa was more effective in controlling vegetative growth than root pruning. The reduction of vegetative growth by ProCa was different among cultivars with 'Red Delicious' and 'Empire' showing more reduction than the other cultivars. There was no additive effect of combining ProCa and root pruning in reducing shoot growth.