High tunnel sweet cherry studies: innovative integration of precision canopies, precocious rootstocks, and environmental physiology

For intensive sweet cherry (Prunus avium L.) production in non-ideal environments, high tunnel-covered orchard systems have a primary advantage of potentially reducing rain-induced fruit cracking as well as several secondary advantages. In 2005, research to incorporate high tunnels, dwarfing precocious rootstocks, and precision canopy training systems for sweet cherries was initiated at two Michigan State University experiment stations. At the CHES site (Clarksville, Mich.), three 8.6 m wide x 50 m long high tunnels were established over existing ‘Rainier’ trees on Giselaˊ5 (Gi.5) and Gi.6 rootstocks (both P. cerasus L. x P. canescens L. hybrids). At the SWMREC site (Benton Harbor, Mich.), four 7.4×62 m long tunnels were established and planted to a new orchard of ‘Rainier’/Gi.5, ‘Skeena’/Gi.5, and ‘Early Robin’/Gi.12 trees, with 35 other varieties planted in guard rows. Non-covered plots were duplicated as standard comparison orchards. Sub-plots have included orchard floor management (herbicide vs. weed barrier fabric), use of a reflective orchard floor fabric, and use of plastic covers having different light spectral transmittance and dispersion properties. Research objectives have included characterization of environmental modifications (air and soil temperatures, relative humidity, leaf wetness, PAR, and wind speed), evaluation of tree growth (TCSA, lateral shoot number and length, terminal growth), evaluation of reproductive performance (yield, fruit quality, time of ripening), and impact on insect pests and diseases under conditions of minimal or no use of pesticides. After three years, general results can be summarized as: mature tree yields in the tunnel systems have been very good (approximately 18 t/ha), fruit size has been excellent (10 to 12.5 g), young tree growth has been improved (up to 35%), and incidence of some major pests (e.g., japanese beetle [Popillia japonica] and cherry leaf spot [Blumeriella jaapii]) has been reduced dramatically (>90%). Some pest issues remain (e.g., brown rot [Monolinia fructicola] and black cherry aphid [Myzus cerasi]), and some typically minor pest issues became significant (powdery mildew [Podosphaera clandestine]). More than standard orchards, high tunnels provide perhaps the ultimate challenge for integration of environmental physiology, performance-enhancing rootstocks, and precise canopy structures into intensive orchard systems.