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Arboriculture & Urban Forestry Online
Volume 28, Issue 3 — May 2002

Chilling and Heat Unit Levels Affect Foliar Budbreak of Selected Red and Freeman Maple Cultivars    (View PDF)

Barrett C. Wilson, Jeff L. Sibley, James E. Altland, Eric H. Simonne, and D. Joseph Eakes

Abstract: The effects of six levels of chilling (temp <7°C) on foliar budbreak of red maple (Acer rubrum) cultivars October Glory® and 'Franksred' (Red Sunset®) and Freeman maple (A. ´ freemanii) cultivar 'Autumn Fantasy' were evaluated in a study conducted from December 14, 1999, to April 7, 2000. October Glory had a greater minimum chilling hour requirement to initiate budbreak than 'Autumn Fantasy' and 'Franksred' (Red Sunset). However, once optimal chilling had been satisfied (near 600 hours), October Glory required fewer heat units than the other cultivars to reach 20% and 25% budbreak. For example, estimates for heat units required to reach 25% budbreak for October Glory were less than half that required for 'Autumn Fantasy' and 'Franksred' following 1,200 hours of chilling. Chilling was a determining factor in foliar budbreak for all cultivars, and with all three cultivars, increasing chilling produced greater budbreak percentages and the rate at which budbreak was initiated. All cultivars required fewer heat units for budbreak as chilling increased. All cultivars required over 1,700 heat units to initiate budbreak after 200 hours of chilling, but only 780 to 970 heat units after 600 hours and between 200 and 400 following 1,000 hours of chilling. Information from this and future studies may be used to facilitate the development of models for regional planting recommendations based on the amount chilling received in a given location. Calculated r2 values indicated the models provided a good fit to the data for all cultivars.

Keywords: Dormancy; endodormancy; budbreak; chilling; cold storage; heat requirement; provenance; Acer rubrum; Acer ´ freemanii.

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