Reason for 1991 Delayed Pecan Shuck Opening Remains Elusive

Abstract

Leaf N Yield In 1991, many reports of a delayed shuckopening malady on ‘Stuart’ pecans [Carya illinoinensis (Wangenh.) K. Koch] in the Albany, Ga., area were received regarding apparently well-managed orchards. This is not the late-season shuck necrosis malady attributed to stress (Sparks et al., 1995) and fungi (Reilly, 1994). Drought stress causes shucks to become flaccid and to eventually dry tightly stuck to the shell (Worley, 1982). For the malady described, the shuck remained green and turgid and kernels remained extremely moist with a dark brown seedcoat. Normal shucks would have been dehisced, and nuts would be dry and ready for harvest. A light crop load and low insect and disease pressure in 1990 induced an extremely large crop set in 1991. Abundant rain through the sizing stage made the nuts large, but a drought beginning in mid-August forced many growers to irrigate. Rainfall was 168, 193, 91, 13, 20, and 5 mm for June through November, respectively. The historical norms for these months are 115, 144, 128, 92, 55, and 58 mm, respectively. Mean air temperatures from June through November were 25, 27, 26, 24, 19, and 12C, respectively, with no hard freezes before harvest; historical means for these months are 26, 27, 27, 25, 20, and 15C, respectively. The degree of the malady varied among trees in a research orchard at Tifton. We attempted to determine if the extent of the malady could be associated with pruning, fertilizer treatments, or any of the usual measured characteristics. The orchard was drip-irrigated, insects were controlled, and foliage condition was excellent at harvest (6 Nov. 1991). Nuts were harvested from individual trees. Nuts free of shucks were considered “marketable.” The moist nuts with unopened shucks