Authors: Respectively, Assistant Professor, Sustainable Agriculture Science Center at Alcalde; retired, former Urban Small Farm Specialist, Agricultural Science Center at Los Lunas; and retired, former Agricultural Specialist, Sustainable Agriculture Science Center at Alcalde, all of New Mexico State University.
Department of Plant and Environmental Sciences
Eight apple cultivars ('Imperial Gala', 'Red Fuji', 'Red Chief', 'Red Free', 'Ginger Gold', 'Golden Supreme', 'Lucky Jon', and 'Akane') planted in two training systems (palmette trellis system and free standing modified central leader system) were evaluated at the NMSU Sustainable Agriculture Science Center at Alcalde, NM, for over 10 years. Due to recurring late frosts in the Espaola Valley in northern New Mexico, trees only produced 6 out of 10 years. 'Gala' was the heaviest producer, followed by 'Ginger Gold' and 'Lucky Jon'. 'Red Chief' was the lightest producer. The average weights of cultivars 'Gala' and 'Akane' were smallest. 'Golden Supreme', 'Red Chief', 'Red Free', and 'Lucky Jon' bloomed later than 'Gala', 'Akane', 'Ginger Gold', and 'Red Fuji'. Comparing the two training systems, there was no difference in yield and fruit size; fruit color was better in the trellis system than in the free standing system. The palmette trellis system needed more investment and labor input during the first 3 to 4 training years. Later, it was easy to maintain and saved labor in pruning and harvesting.
In the early 1960s, New Mexico had 950 apple orchards with 50 or more apple trees, totaling 7,000 acres (NMDA, NMSU, and USDA, 1963). At that time, approximately 33% of the trees in New Mexico were 7 years old or younger, and 37% of trees were 14 to 23 years old. Due to severe winter damage in 1971, apple production decreased dramatically in New Mexico and has never recovered to its peak levels of the 1960s. In 1979, there was a total of 285 orchards with 80 trees or more, fewer than half the number of 1969 (617 orchards). About 41% of trees were on dwarf or semi-dwarf rootstocks in 1979 (Matta et al., 1980; NMDA and USDA, 1979). In 2008, apples were still the largest fruit crop in New Mexico, with 807 orchards totaling over 2,050 acres. Rio Arriba County is the leading county in apple production in New Mexico, followed by Otero, San Juan, and Santa Fe Counties (USDA-NASS, 2008).
In the early 1960s, 'Red Delicious' accounted for 58% of New Mexico's apple trees, while 'Rome Beauty' and 'Golden Delicious' accounted for 14% and 8%, respectively (NMDA, NMSU, and USDA, 1963). By the end of the 1970s, 'Red Delicious' was still the most popular cultivar in New Mexico, accounting for 67% of all apple trees, followed by 'Golden Delicious', 'Rome Beauty', 'Jonathan', and 'Stayman' (NMDA and USDA, 1979). 'Fuji' from Japan and 'Gala' from New Zealand became popular and entered the U.S. market in the 1980s (Greene, 1990; Stebbins, 1987). In the 1970s, an apple cultivar and size-controlling rootstock evaluation study was conducted in northern New Mexico (Matta et al., 1980). With the rapid worldwide development of apple cultivars, rootstocks, and training systems in the 1980s and 1990s (Corelli-Grappadelli, 1998; Luby and Bedford, 1992), a renewed interest by local apple growers prompted Extension Horticulture Specialist Dr. Esteban Herrera and the NMSU Sustainable Agriculture Science Center at Alcalde to establish a cultivar trial and training system study in 1996. The objectives of this long-term study were to evaluate a number of cultivars and compare two training systems in northern New Mexico. This orchard also served as a demonstration site for local apple growers.
Materials and Methods
Eight apple cultivars and two training systems were evaluated in a split-plot design with cultivar as main plot and the two training systems as subplots at NMSU's Sustainable Agriculture Science Center at Alcalde, NM, which is in USDA hardiness zone 5 and at an elevation of 1,735 m. In the spring of 1996, eight apple cultivars ('Imperial Gala', 'Red Fuji', 'Red Chief' [a Red Delicious type], 'Red Free', 'Ginger Gold', 'Golden Supreme', 'Lucky Jon' [a bud sport of Jonathan], and 'Akane' [a Jonathan type]) on EMLA7 (a virus-free clone of Malling 7) rootstock were planted with a spacing of 2.3 × 4.3 m (7.5 × 14 ft) (Figure 1). There were 6 trees in each subplot, and the space between blocks or between subplots was 6.4 m. The study site included Alcalde clay and Fruitland sandy loam soils, and the orchard was 300 to 400 m away from the Rio Grande.
Figure 1. Planting map of apple cultivar and training experiment.
Two training systems, free standing modified central leader and palmette trellis, were used for this study. For the free standing modified central leader, trees were initially trained to a slender-spindle system and changed to a modified central leader system three years later. For the palmette trellis system, trees were trained to horizontal trellises with 4 wires running along the row. Wires were spaced at 0.6, 1.5, 2.4, and 3.3 m from the ground. Main branches were tied to the wires horizontally. For the first four years after planting, the emphasis was on intensively training and pruning the trees to conform to the designated systems. Year 2000 was the first formal harvest for this experiment. Due to late frost damage, trees only produced apples in 2000, 2001, 2004, 2006, 2007, and 2009 (no data collection in 2007 and 2009).
The field had been in a mature alfalfa stand before tree planting. During planting, the alfalfa between rows was not disturbed but was mowed. An auger was used for digging planting holes. With several mowings each year plus seeds from flood irrigation water, the alfalfa gradually disappeared and was replaced by a mixture of volunteer grasses and other vegetation. Flood irrigation was used for the first five years after planting. In 2002, micro sprinklers were installed to replace flood irrigation, which saved water, helped to minimize the frost threat by increasing the orchard temperature 1 to 2°C if sprinklers were turned on during frost nights, and reduced leaf chlorosis caused by iron deficiency. At the same time, lower branches from both training systems were removed for better irrigation coverage.
At the beginning of the planting, with alfalfa as cover crop between rows, no nitrogen fertilizer was used. As alfalfa was replaced with volunteer grasses and the trees grew bigger, urea was applied at a rate of 112 kg/ha (100 lb/ac) in the spring and 56 kg/ha (50 lb/ac) in the fall in 2004 and 2006. Biomin Iron (J.H. Biotech, Inc., Ventura, CA) and Metalosate Calcium and Zinc (Albion Plant Nutrition, Clearfield, UT) were used for bitter pit and micronutrient deficiency management. Powdery mildew was common in this orchard, and the fungicide Nova was used whenever necessary. Codling moth was controlled with dormant oil, summer oil, Confirm, and Intrepid. There was light fireblight infection of young shoots in some years, and they were removed from the orchard as soon as the symptoms appeared. No hand thinning or chemical thinning was conducted in this experiment.
Apple yield from the center four trees of each subplot and average fruit weight of 20 apples were collected during each harvest in 2000, 2001, 2004, and 2006. Analysis of variance was conducted with Statistix 7 (Analytical Software, Tallahassee, FL).
Results and Discussions
'Gala' was the most productive of the 8 cultivars tested (Table 1), followed by 'Ginger Gold' and 'Lucky Jon'. 'Red Chief' was a consistently light producer. 'Golden Supreme' was also a light producer, except for 2004. Compared with yield reports from other researchers, the single year yields were reasonable but the cumulative yields were low considering the tree age (Autio et al., 2007; Crassweller et al., 2005). In 2006, 'Red Chief' only produced 12.5 kg/tree, which is very low considering they were 11-year-old trees.
Table 1. Yield Data (kg/tree; LSD, P ≤ 0.05)
|*Any two means within a column not followed by the same letter are significantly different at P < 0.05 with Fisher's protected least significant difference procedure.|
Average Fruit Weight
Average fruit weight varied among cultivars; 'Red Chief', 'Ginger Gold', and 'Golden Supreme' had the largest fruits, followed by 'Red Free', 'Lucky Jon', and 'Red Fuji' (Table 2). 'Akane' and 'Gala' had the smallest apples. Fruit size depends on many factors, such as cultivar, rootstock, crop load, whether or not the tree was thinned, and weather conditions. Growers need to maintain reasonable fruit size, otherwise the market value might drop dramatically.
Table 2. Average Fruit Weight of Different Cultivars and Training Systems (kg/apple; LSD, P ≤ 0.05)
|*Trees were at their early stage of fruiting, and some plots did not have yields in 2000; consequently, no statistics were available on the fruit weight/apple.
**Any two means within a column not followed by the same letter are significantly different at P < 0.05 with Fisher's protected least significant difference procedure.
Bloom Time and Training Effect
Flower buds in the trellis system developed slightly earlier (1 to 2 days) than those in the free standing modified central leader system (Table 3). 'Golden Supreme', 'Red Chief', 'Red Free', and 'Lucky Jon' bloomed later than 'Gala', 'Akane', 'Ginger Gold', and 'Red Fuji' (data not shown).
Table 3. Apple Tree Bud Development of Different Cultivars and Training Systems in 2004 (LSD, P ≤ 0.05)
|*Apple bud development stages: 0 = dormant bud, 1 = silver tip, 2 = green tip, 3 = half-inch green, 4 = tight cluster, 5 = first pink, 6 = full pink, 7 = first bloom, 8 = full bloom, 9 = post bloom.
**Any two means within a column not followed by the same letter are significantly different at P < 0.05 with Fisher's protected least significant difference procedure.
The trellis system improved the light penetration in the canopy, and fruits therefore had better color and more uniform size than fruits on the free standing trees (data not shown).
Late Frosts and Fruit Sets
At Alcalde, apple full bloom normally occurs from mid- to late April. As indicated in Figure 2, there were freezing temperatures during the first half of May in almost half of the years. Years 2003, 2008, and 2010 had very cool springs with 17, 16, and 13 days with minimum temperatures below −1.1°C, respectively (Figure 2). Year 2005 had temperatures of −7.8°C on April 2 and −4.4°C on April 14, which killed most of the flowers. Year 2009 had cold weather in early April, but no temperatures below −2.2°C around or after bloom time. Longstroth (2009) summarized that −2.2°C would be the 10% killing temperature from first pink stage to post bloom. The crop load of a specific year is generally determined by the biennial bearing of the trees, mid-winter damage (NMDA and USDA, 1979), cultivar frost tolerance, and the occurrence of late frosts around blooming time.
Figure 2. Days with minimum temperatures below -1.1 °C from April 1 to May 20, 2000-2010.
Comparing the two training systems, even though there were no significant differences for total yield and fruit size, the palmette trellis training system was more expensive to establish than the free standing modified central leader system and required more labor to train the branches into position. Once established, though, it allowed for easier maintenance, pruning, and harvesting, which may result in labor savings to offset the installation costs. Fruit color was also improved with the trellis system (data not shown). Over the 15 years of this study, the free standing system was modified from the originally designed slender spindle system to a modified central leader system. Also, trees produced no crop in some years due to killing frosts, and the pruning in these years was therefore harder than with trees that produce annually due to the very vigorous vegetative growth.
Trellis systems are an alternative to the traditional central leader system, especially in medium- to high-density orchards, and allow trees to be fully exposed to sunlight, and growers can use platforms for picking, thinning, and pruning (Weber, 2000). The early investment and maintenance are high, but later they are easy to maintain and make pruning and harvesting easier. Beginning in the 1990s, other training systems (super spindle, tall spindle, and vertical axe) for high-density plantings were used in many commercial orchards. These also require trellises and support, but they are easier to maintain and train the trees (Robinson et al., 2006; Perry, 2000; Weber, 2000). Trees in those systems are also more precocious than in the palmette trellis system.
For cultivar selection, 'Gala', 'Ginger Gold', and 'Golden Supreme' are good-performing cultivars in northern New Mexico. Also, for newer cultivars, 'Honeycrisp' should be a good choice; it is also a late-blooming cultivar, which may give it a better chance of avoiding late frosts. 'Honeycrisp' is a heavy bearer, but not a vigorous-growing cultivar like 'Gala'. It would need more vigorous rootstocks than 'Gala' to stimulate its tree growth.
In this experiment, EMLA7 rootstock was too vigorous for this soil type and planting density, and the late frost interference made the pruning and size control more difficult. Dwarf rootstocks such as M.9 or B.9 are possible options, allowing row spacing of 4.3 m or less. For soil and weather conditions similar to the site used in this study, it is recommended that if EMLA7 is chosen, the space between rows should be more than 4.3 m. The non-crop years made the trees more vigorous than they normally would be. Growers should consider the soil conditions, economic situation, weather conditions, and equipment sizes they have in order to choose a suitable combination of rootstock, cultivar, and training system for their orchards.
The authors would like to thank the New Mexico Apple Commission, Cooperative Extension Service's Rural Agricultural Improvement and Public Affairs Project, and the New Mexico Department of Agriculture for their support of this project and the technical support from David Archuleta, Val Archuleta, David Salazar, and Greg Sopyn. Special thanks to Dr. Esteban Herrera, who designed this experiment.
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