Winter Injury to Apple Cultivars as Affected by Growth Regulators, Weed Control Method, and Rootstocks1

in Journal of the American Society for Horticultural Science
M. N. WestwoodDepartment of Horticulture, Oregon State University, Corvallis, OR 97331

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H. O. BjornstadDepartment of Horticulture, Oregon State University, Corvallis, OR 97331

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Effects of cultivars, rootstock, and long-term growth regulator and herbicide treatments on above-ground tree damage from a December 1972 freeze were recorded soon after the freeze and again 7 years later. Ultimate injury was greatest with ‘Jonared’ and least with ‘Golden Delicious’ apple (Malus domestica Borkh.) in the growth regulator plot, while in the herbicide plot it was opposite for the 2 cultivars. There was not a good relationship between injury to specific plant parts (flower buds, spurs, leaders, and lower trunks) observed soon after the freeze, and ultimate tree mortality. Growth regulator treatments significantly increased freeze damage to flowers and spurs, but ultimate tree mortality was reduced by daminozide sprays. Clean cultivation increased flower and spur mortality but did not reduce yield or increase tree mortality compared to the sod treatment. Trees on Mailing (M) 5, M 7 and M 9 rootstocks showed greater initial trunk injury than those on seedling roots, but only those on M 9 showed significantly greater ultimate mortality.

Contributor Notes

Received for publication September 11, 1980, Oregon Agr. Expt. Station Technical Paper No. 5612.

The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

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