Performance of the NC-140 cooperative apple rootstock planting II: A 10- year summary of TCA, yield and yield efficiency at 31 sites

In 1984 trees of 'Starkspur Supreme Delicious' apple (Malus x domestica Borkh) on 15 root-stocks were planted at 31 sites in North America according to guidelines established for cooperative testing by the North Central Regional Cooperative Project (NC-140). Six midwestern sites lost 20% or more of the trees over 10 years, while 13 sites had less than 10% loss. The following rootstocks had 60% or higher losses at one or more sites: MAC.39, P.22, M.4, M.26EMLA, P.2, P.16, P.18, C6. B.9 had the best survival of the dwarfing rootstocks in this study with no losses at 14 sites. Sites in KS, CA, IL, CA, VA, MO, NC, and MI had trees with 39 to 16% larger than average trunk cross-sectional area (TCA), while trees in TN, PA, and MEX were 40% smaller than the average of all sites. Averaged across rootstocks, sites with the greatest yield efficiency were MA, CA, OH, and BRC and those with lowest efficiency were KS, TN, MN, NY, AR and NC.