Hardiness of Black Walnut and Pecan Cultivars in Response to an Early Hard Freeze

Abstract

A sudden, severe freeze on Oct. 7, 2000 devastated a young black walnut ( Juglans nigraL.) and pecan [ Carya illinoinensis(Wangenh.) K. Koch] orchard in southwest Missouri. Forty-one percent of black walnut and 76% of pecan scions were injured by temperatures that dropped to −6° C at a time when many trees were still fully foliated. Cold injury in pecan was most frequently manifested by total tree dieback to ground level. In contrast, cold injury to black walnut was primarily confined to tissues above the graft union. Six cultivars of each species were evaluated. Pecan trees grafted to ‘Kanza’ exhibited the greatest frequency of total tree dieback whereas trees grafted to ‘Posey’ displayed the least. ‘Posey’ was also the cultivar that suffered the least damage to above-graft portions of the tree. Cold injury in pecan was not related to scion age (1-4 yrs.) or height of graft union. ‘Surprise’ black walnut was significantly less hardy than all other scion cultivars in the test. Walnut scions that had grown for 4 to 5 seasons before the 2000 freeze were hardier than scions that had grown for 1 to 2 seasons. Graft union height did not influence the hardiness of black walnut scions.