Pecan trees, like many fruit trees, have a tendency to bear fruit in cycles, consisting of a large crop in 1 or 2 years, followed by 1 or 2 years with little or no crop. This is termed alternate bearing, and is the most profit-limiting biological problem facing the profitability of pecan production (Amling and Amling, 1983; Wood et al., 2003). The inconsistent production pattern of pecan also generates supply and marketing difficulties that can have severe negative effects on the pecan industry as a whole.
Crane et al. (1934) suggested a positive correlation between kernel development and the number of leaves per fruit, with 8 to 10 leaves being required for optimum kernel quality. Fruit production has been shown to reduce return bloom (Malstrom and McMeans, 1982; Smith et al., 1986; Sparks and Brack, 1972), indicating that excessive crop production enhances alternate bearing. Some pecan cultivars have a stronger tendency to bear irregularly than do others (Conner and Worley, 2000).
Excessive fruiting is also associated with a variety of cultural problems that can reduce pecan profitability. Tree susceptibility to cold damage is reported to be increased following a heavy crop load (Reid et al., 1993; Smith and Cotten, 1985; Smith et al., 1993; Wood, 1986). Incidences of fruit disorders such as shuck decline, water-stage fruit split, and vivipary are also reported to be higher when crop load is heavy (Sparks et al., 1995; Wood and Reilly, 1999). Premature germination or vivipary can occur when green shucks fail to dehisce, and is often associated with high humidity between the shell and shuck and high air temperatures during ripening (Sparks et al., 1995).
Mechanical fruit thinning has been used as a tool to minimize the effects of alternate bearing on several cultivars, including Mohawk, Maramec, Giles, Wichita, Cape Fear, Cheyenne, Kiowa, Barton, Graking, Peruque, and Shoshoni (Goff et al., 1995; McCraw et al., 1996; Smith and Gallot, 1990; Smith et al., 1993; Sparks et al., 1995). While the optimum stage of fruit development at which to crop thin and the optimum crop load for high-quality fruit and adequate return bloom has been established for certain cultivars in Oklahoma and Kansas (Smith and Gallot, 1990; Smith et al., 1993), little work has been conducted regarding the economic value and potential profitability of fruit thinning of pecan cultivars grown in the southeastern United States. We report here the effects of mechanical fruit thinning on yield, quality, and profitability of ‘Sumner’ and ‘Cape Fear’ pecan, two major cultivars produced in the southeastern United States.
Amling, H.J. & Amling, K.A. 1983 Physiological differentiation of pistillate flowers of pecan and cold requirements for their initiation J. Amer. Soc. Hort. Sci. 108 195 198
Crane, H.L., Hardy, M.B., Loomis, N.H. & Dodge, F.N. 1934 Effect of nut thinning on size, degree of filling, and annual yields of pecans Proc. Amer. Soc. Hort. Sci. 45 59 62
Goff, W.D., Nesbitt, M. & McDaniel, R. 1995 Mechanical thinning improves pecan quality and return bloom Proc. Southeastern Pecan Growers Assn. 88 100 105
Malstrom, H.L. & McMeans, J.L. 1982 Shoot length and previous fruiting affect subsequent growth and nut production of ‘Moneymaker’ pecan HortScience 17 970 972
Reid, W., Huslig, S.M., Smith, M.W., Manes, N.O. & Whitworth, J.M. 1993 Fruit-removal time influences return bloom of pecan HortScience 28 800 802
Smith, M.W. & Cotten, B.C. 1985 Relationship of leaf elemental concentrations and yield to cold damage of ‘Western’ pecan HortScience 20 420 422
Smith, M.W., McNew, R.W., Ager, P.L. & Cotten, B.C. 1986 Seasonal changes in the carbohydrate concentration in pecan shoots and their relationship to flowering J. Amer. Soc. Hort. Sci. 111 558 561
Smith, M.W., Reid, W., Carroll, B. & Cheary, B. 1993 Mechanical fruit thinning influences fruit quality, yield, return fruit set, and cold injury of pecan HortScience 28 1081 1084
Sparks, D., Reid, W., Yates, I.E., Smith, M.W. & Stevenson, T.G. 1995 Fruiting stress induces shuck decline and premature germination in pecan J. Amer. Soc. Hort. Sci. 120 43 53
U.S. Department of Agriculture 2009 Georgia pecan report 10 Jan. 2009 <http://search.ams.usda.gov/mnsearch/MNSearchResults.aspx>.
Wood, B.W., Conner, P.J. & Worley, R.E. 2003 Relationship of alternate bearing intensity in pecan to fruit and canopy characteristics HortScience 38 361 366