EFFECT OF PRIMOCANE SUPPRESSION DATE ON MARION TRAILING BLACKBERRY .2. COLD-HARDINESS

Primocanes of ''Marian'' trailing blackberry plants were suppressed by cutting them off at ground level in either late April, May, June, or July 1991 and 1992, An unsuppressed control was included in which primocanes were not cut. A single cane was removed from each replication of the five primocane suppression dates at monthly intervals from mid-November to mid-February 1991-92, and from mid-November to mid-January 1992-93, One-node samples were exposed to controlled freezing at temperatures of 4, -6, -9, -12, -15, and -18C in November through February, In December and January, the a temperature was replaced with-21C, After 5 days at room temperature following freezing, growing point, budbase, vascular, and pith tissues were evaluated for tissue browning on a 1 to 5 scale. The LT(50) developed for each suppression date was compared to the control, July-suppressed plants were generally hardiest for all tissues, June-suppressed plants were somewhat less hardy than July-suppressed plants, while April-, May- and unsuppressed plants were comparable and least hardy. Cane tissues of July-suppressed and unsuppressed plants had a higher level of soluble carbohydrates than other suppression dates.