Canopy training affects peach/nectarine vigor and advances planar training system development as well as evaluation of vigor-limiting rootstocks

A 2011 trial of experimental canopy training techniques identified promising horticultural methods for maintaining high density, compact peach/nectarine trees that are more labor-efficient for fruit thinning and harvest. Super Slender Axe ( SSA) short-pruning (dormant) and summer hedging reduced potential crop load before bloom and simplified post-bloom hand-thinning. Three next-generation 2017 trials examined the interactions between rootstock vigor, leader number, SSA-style short-pruning, and summer hedging on tree vigor and productivity. 1) Trees of 'Sunglo', 'SilverGem', and 'Jade' nectarine on 'Lovell' seedling rootstocks were planted at 1 or 2 m tree spacing as single or dual leader trees, respectively, resulting in an equal number of SSA-trained leaders per row. Three summer hedging treatments were imposed. 2) Trees of 'Fantasia' nectarine on 'Lovell' rootstock were developed as 1, 2, 4, 6, or 8 SSA-trained leaders/tree, corresponding to tree spacings at 1, 2, 2, 3, and 4 m, respectively. 3) Trees of 'Cresthaven' peach on eight rootstocks ('Lovell'; 'Guardian (R)'; 'Controller (TM)' 6, 7, and 8; 'RootPac (R)' 20 and 40; and 'MP-29') ranging from dwarfing to extremely vigorous were trained as dual-leader canopies in the coordinated NC140 Regional Rootstock evaluation research project. In all trials, tree vigor was determined by tree trunk cross-sectional area (TCSA), individual leader cross-sectional area (LCSA), and individual leader height. The first potential crops were lost to low temperature damage in 2019 and 2020. In the absence of cropping, leader vigor differed significantly by leader number (and tree spacing) and rootstock. Results are discussed in relation to designing new planar canopy peach/nectarine orchard systems and the potential for canopy training systems to introduce inherent bias into trials that evaluate rootstocks with varying vigor levels. Future trials should be designed with relatively simplified, quantifiable, and proportional canopy modifications to more objectively evaluate comparisons of fruiting and vegetative performance across such rootstocks.