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2001 Fruit and Vegetable Crops Research Report
Introduction ! Tree Fruits ! Small Fruits ! Vegetables ! Greenhouse Production ! Diagnostic Laboratory ! Appendix

Tree Fruits

Rootstock and Interstem Effects on Pome and Stone Fruit Trees

Gerald R. Brown and Dwight Wolfe, Department of Horticulture

Introduction

Although apples are the principal tree fruit grown in Kentucky, the hot, humid summers and heavy clay soils in Kentucky make apple production here a more difficult task for growers in this state than for growers in the major apple-producing regions where soil and climate are more favorable. Also, peach production can be expected to be erratic because of extreme temperature fluctuations that occur in the winter and spring in Kentucky.

In spite of these challenges, productive orchards are one of the highest per acre income enterprises suitable for rolling, upland soil. Furthermore, in these upland sites, orchards have a low potential for soil erosion. Kentucky still imports more apples than it produces, and the strong market for peaches continues to encourage growers to plant peach trees.

Continued identification of improved rootstocks and cultivars is required for growth of the Kentucky fruit industry. For this reason, Kentucky continues to be a cooperator along with 39 other states and three Canadian provinces in the Cooperative Regional NC-140 Project: Rootstocks and Interstem Effects on Pome and Stone Fruit.

The NC-140 plantings are of utmost importance to Kentucky for gaining access to and testing new rootstocks from around the world. The detailed and objective evaluation of these rootstocks will provide growers with the information needed to select the most appropriate rootstocks for their needs when they become commercially available in the future.

The 1994 and 1999 apple rootstock plantings will provide us with needed information on adaptability of the slender spindle and the vertical axe systems to trees grown on our fertile soils. Also, the non-trellised, semi-dwarf group of rootstocks in the 1999 Apple Rootstock planting will provide us with information on the ability of these rootstocks to support themselves on their own root systems. The 1994 Peach Planting should provide us with needed information to determine if tree survival, winterhardiness, and cropping frequency can be improved by using any of the recently developed rootstocks.

The NC-140 orchard plantings are regularly used as demonstration plots for visiting fruit growers, Extension personnel, and research scientists. The research data collected in these trials will help to establish base-line production and economic records for the various orchard system/rootstock combinations that can be later utilized by orchardists in Kentucky.

Materials and Methods

Scions of known cultivars on various rootstocks were produced by commercial nurseries and distributed to cooperators for each planting. The University of Kentucky has three NC-140 rootstock plantings at the UK Research and Education Center at Princeton:

I. 1994 apple rootstock planting consisting of `Red Gala' on six rootstocks and 10 replications per rootstock. Trees are spaced 13 feet apart within rows 18 feet apart.

II. 1999 dwarf and semi-dwarf apple rootstock planting consisting of two groups of apple rootstocks:

i) dwarfing group with 11 rootstocks and planted on a 10-foot x 16-foot spacing.

ii) a semi-dwarfing group with six rootstocks and planted on a 13-foot x 20-foot spacing.

III. 1994 peach rootstock planting consisting of `Redhaven' peach on 12 different rootstocks and eight replications per rootstock. Trees are spaced 16 feet apart within rows 20 feet apart.

Trees of each rootstock were allocated to blocks (rows) in a randomized block design [i.e., each rootstock appears once and at random within each block (row)]. Soil management was a 6.5-foot herbicide strip with mowed sod alleyways. Trees were fertilized and sprayed according to local recommendations (1,2). Yield, trunk circumference, and maturity indices such as soluble solids were measured for each planting.

Results and Discussion

The winter of 2001 was mild, followed by several spring freezes and below normal rainfall from March through April in Central and Eastern Kentucky and below normal rainfall from March through June for Western Kentucky. Rainfall was moderate to above normal throughout the remainder of the growing season. Most fruit crops were harvested roughly 10 days earlier than normal. A late September hailstorm severely damaged the fruit in the 1999 NC-140 dwarf and semi-dwarf apple planting at Princeton, Kentucky.

I. 1994 Apple Semi-Dwarf Rootstock Planting

The 1994 semi-dwarf apple rootstock planting is the first trial at this station to be trained to the French vertical axe system. It also includes a number of new rootstocks, along with some that have performed well in previous plantings at UK Research and Education Center at Princeton.

This planting was established as planned, except for the substitution of B.9 for P.1. Trickle irrigation was installed, and a trellis system was constructed in 1995. The mortality of trees on M.26 (10 percent survival) differed significantly from trees on the other three rootstocks. Cumulative yield, yield in the year 2001, fruit size, trunk circumference, and number of root suckers varied significantly by rootstocks (Table 1). No significant differences were observed for either flesh firmness or percent soluble solids. Trees on CG.30 and V.2 have been the most productive ones in this planting.

II. 1999 Dwarf and Semi-Dwarf Apple Rootstock Plantings

This planting consists of two groups of apple rootstocks, a dwarfing group with 11 rootstocks, and a semi-dwarfing one with six rootstocks. Eight of the dwarfing rootstocks and three of the semi-dwarfing ones had not been previously tested at the Princeton station.

Ninety trees of a possible 108 are in our planting because 12 were not available for our site (one CG.16N, two CG.4013, three CG.3041, one CG.4814, and four CG.30N). Further, three trees never leafed out after planting (one CG.16T, one CG.16N, and one CG.3041). However, all the other trees are alive.

For both groups, significant differences among rootstocks were observed for trunk circumference, yield, number of fruit harvested, average fruit weight, and the number of flower clusters per tree (Table 2). The number of root suckers and the percent soluble solids varied significantly only among the dwarf rootstocks. Flesh firmness did not vary significantly by rootstocks for either the dwarf or semi-dwarf group. Twenty-two of the 31 trees planted have been supported by tree stakes due to their lean exceeding 30 degrees from vertical.

III. 1994 Peach Rootstock Planting

Peaches are one of the most popular fruits in Kentucky. The strong market for this crop continues to entice growers to plant trees in spite of the fact that one can expect erratic production due to the extreme temperature fluctuations that occur in the winter and spring in this state.

A rootstock that is more suitable to Kentucky's climate than ones traditionally used would be of great value to the fruit industry in the state. A rootstock that could significantly delay bloom would change the future of the Kentucky peach industry. To date, 75 of the 94 trees planted are alive (80 percent survival).

Statistical differences were observed for trunk circumference, yield in 2001, fruit size, flesh firmness, and percent soluble solids (Table 3) but not for cumulative yield, date of bloom, and number of root suckers. The Julian date for 90 percent bloom was 98 (April 8, 2001). The Julian date for 10 percent fruit maturity was 184 (July 3, 2001).

Literature Cited

  1. G.R. Brown, R.T. Jones, J.G. Strang, L.A. Lester, J.R. Hartman, D.E. Hershman, R.T. Bessin. 1998 Commercial Tree Fruit Spray Guide. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-98.
  2. Midwest Tree Fruit Handbook. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-93.

Table 1. 2001 results of the NC-140 1994 apple semi-dwarf rootstock planting.1
Rootstock2 Cumulative yield per live tree (lb) 2001 yield (lb/tree) Fruit size (oz/fruit) Mean pressure (lb) Percent soluble solids Trunk circumference (in.) Number of root suckers
CG.30 600 214 6.1 18.7 13.8 11.2 10
V.2 507 165 6.1 19.1 13.7 10.8 1
M.26 EMLA 386 99 5.4 19.7 15.0 9.1 0
B.9 240 71 5.4 18.9 14.1 6.6 2
Mean 439 146 5.9 19.0 14.0 9.5 4
LSD (0.05) 143 57 0.7 3.3 1.5 1.6 8
1 University of Kentucky Research and Education Center, Princeton, Ky.
2 Arranged by cumulative yield in descending order.

Table 2. 2001 results of the NC-140 1999 apple dwarf and semi-dwarf rootstock planting.1
Rootstock Yield (lb/tree) Number of fruits Average fruit weight (oz/fruit) Number of flower clusters Number of root suckers Trunk circumference (in.) Percent soluble solids
Dwarfing2
Supporter 3 27.2 88 4.9 176 1.2 4.6 12.2
G.16N 26.6 79 5.5 156 1.5 5.9 12.1
CG.4013 25.7 71 5.6 77 8.3 6.8 13.1
G.16T 24.0 70 5.9 124 2.6 5.9 13.4
Supporter 1 24.0 82 4.8 157 2.8 4.7 12.2
Supporter 2 20.5 58 5.9 119 0.3 5.1 12.7
CG.3041 18.3 52 5.7 60 0.5 4.9 12.8
M.9 NAKBT 337 8.9 21 7.1 28 2.2 4.7 13.7
CG.5179 6.7 18 6.3 29 4.5 5.2 13.1
M.26 EMLA 4.5 11 7.2 24 1.0 5.1 14.1
CG.5202 4.2 12 6.6 17 5.0 6.1 12.9
Mean 16.7 50 6.0 89 2.7 5.3 12.9
LSD (0.05) 10.9 32 1.3 50 4.1 0.7 1.3
Semi-Dwarfing2
CG.30N 17.2 44 6.4 83 5.0 6.6 13.1
M.26 EMLA 10.6 29 5.8 43 0.5 5.0 13.6
Supporter 4 9.2 26 6.3 54 3.5 4.9 12.3
M.7 EMLA 7.9 25 5.2 49 18.3 6.1 13.2
CG.7707 2.3 6 7.7 21 3.7 6.6 13.2
CG.4814 1.2 4 5.3 11 7.2 5.8 13.6
Mean 7.1 20 6.1 39 6.5 5.7 13.1
LSD (0.05) 6.5 20 1.8 29 16.3 1.3 2.0
1 University of Kentucky Research and Education Center, Princeton, Ky.
2 Within group, arranged by yield in descending order.

Table 3. 2001 results of the 1994 NC-140 peach rootstock planting.1
Rootstock2 Cumulative yield per
live tree (lb)
2001 yield (lb/fruit) Truck circumference (in.) Average fruit wt. (oz/fruit) Flesh firmness (lb) Soluble solids (%)
GF 305 507 148 18.4 8.8 3.1 9.7
Lovell 507 115 18.7 7.6 2.6 10.2
BY 520-9 503 146 18.3 9.2 1.3 10.0
Rubira 460 108 17.9 8.8 2.0 10.5
Montclar 459 99 18.5 9.4 2.9 10.6
Stark's Redleaf 443 95 18.7 9.0 2.2 10.0
Ta Tao 5 437 119 15.9 7.4 6.8 10.8
BY 520-8 437 75 18.0 6.4 1.3 10.5
Tenn Natural 428 112 16.0 7.9 3.3 10.9
Bailey 408 95 15.4 8.4 3.3 11.2
Ishtara 397 104 14.3 7.7 4.2 9.6
Higama 375 82 16.4 8.4 2.6 9.8
Mean 448 108 17.3 8.4 3.1 10.3
LSD (0.05) 90 42 1.6 7.7 2.0 1.1
1 University of Kentucky Research and Education Center, Princeton, Ky.
2 Arranged by cumulative yield (kg/tree) in descending order.

Optimal Training of Apple Trees for High Density Plantings

Gerald R. Brown and Dwight Wolfe, Department of Horticulture

Introduction

Kentucky apple growers often have a problem with excessive vegetative growth or vigor, which greatly reduces the production that can be achieved from high density apple plantings. Early production and optimal fruit size on vigorous sites are obtained when photosynthates are balanced properly between flower bud initiation and vegetative growth. Pruning and training are possibly the most important operations performed by growers to maintain the proper balance between flower bud initiation and vegetative growth. Identification of effective pruning and training techniques for vigorous sites is required for continued expansion of apple production in Kentucky. The University of Kentucky College of Agriculture and the Kentucky State Horticultural Society have made long-term commitments to help meet this need. For this reason, ongoing research has been conducted to determine the training and pruning practices needed to obtain early production and optimal fruit size from trees trained to either the slender spindle or the French axe system.

Materials and Methods

One hundred-eighty trees of Golden Delicious on M.9 rootstocks were set out in May 1997 in a randomized complete block design with eight treatment combinations (five rows, 32 trees/row). Trunk circumference averaged 2.4 inches at planting and did not vary significantly among rootstocks. A trellis was constructed, and trickle irrigation was installed. Trees were spaced 8 feet apart within rows 16.4 feet apart. Soil management was a 6.5-foot herbicide strip with mowed sod alleyways. Trees were fertilized and sprayed according to local recommendations (1,2). Yield (beginning with 1998 yield), trunk circumference, and maturity indices such as soluble solids and flesh pressure were measured.

The trees were trained according to prescribed treatment protocols (Table 1). Trees began to fill their allotted space in 1999, and leader management was modified to maintain leaders at specified heights (Table 1). Limbs of one tree that overlapped or touched those of adjacent trees were headed back into two-year-old wood.

Results and Discussion

No differences among the four pruning levels were observed for cumulative yield (1998-2001), yield in 2001, fruit size (average fruit weight), trunk circumference, number of root suckers, flesh firmness, and soluble solids (Table 2). No significant differences were observed between the French axe and slender spindle training systems for any of these variables.

The light crop in 2000, which yielded less than 10 percent of that in 2001, resulted in an increase in vegetative growth that consequently increased the amount of detailed pruning required in 2001—9.6 minutes—compared to the time of 3 minutes required in 2000 (Table 2).

This planting has been regularly used as a demonstration for visiting apple growers, Extension personnel, and research scientists. The research data collected in these trials has helped to establish baseline economics and production methods for the various orchard system/rootstock combinations that can be utilized by orchardists in Kentucky.

Literature Cited

  1. G.R. Brown, R.T. Jones, J.G. Strang, L.A. Lester, J.R. Hartman, D.E. Hershman, R.T. Bessin. 1998 Commercial Tree Fruit Spray Guide. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-98.
  2. Midwest Tree Fruit Handbook. University of Kentucky College of Agriculture Cooperative Extension Service, Publication ID-93.

Table 1. Pruning/training treatments of the UK-KSHS apple training study at Princeton, Ky.
System Amount of one-year-old
wood left
after heading
at planting
Angle1 Limbs2
Pruning Leader management
Level Interval in wks
19993 20004
French Axe Light 1 Not headed 45 No D 12
French Axe Moderate 2 12-16 in. 45-60 Yes C&D 11
French Axe Moderate 1 12-16 in. 45-60 Yes D 11
French Axe Heavy 1 8-12 in. 60-90 Yes D 10
Slender Spindle Light 1 Not headed 45 No A 9
Slender Spindle Moderate 2 14-20 in. 45-60 Yes B 9 Y
Slender Spindle Moderate 1 14-20 in. 45-60 Yes B 9 Y
Slender Spindle Heavy 1 10-14 in. 60-80 Yes C 9 Z
1 Angle limbs are to be positioned.
2 French Axe--completely remove overly vigorous branches with narrow angles when 3 to 6 inches long. Slender Spindle--completely remove branches that compete with leader. In 2000, for both training systems, limbs overlapping or touching those of adjacent trees were headed back into two-year-old wood.
3 A = weak leader renewal and new leader headed at 12 inches. B = bend leader at 60 angle, alternating direction with every 18 in. of new growth. C = leader bagged 1 month prior to bud break and bag removed at appropriate time. D = leader bent to horizontal, alternating direction after buds break on top side.
4 Leaders were maintained at specified heights (in feet) by cutting to an alternate leader when necessary. Y = Alternate leader was bent to horizontal for 6 weeks. Z = Alternate leader was "snaked" throughout growing season. Leader management was the same in 2001 as in 2000.

Table 2. Time requirements and effects of summer apple pruning/training treatments on apple yields in the UK-KSHS apple training study at Princeton, Ky., 2001.
Pruning level1 -interval in wks Trunk circumference (inches) Yield2 per tree (lb) Average fruit wt. (oz) Minutes per tree3 Total minutes per tree Minutes per lb of fruit
Cumulative 2001 1997 1998 1999 2000 2001
Light - 1 7.7 125 93 7.1 12.2 10.2 18.2 4.4 9.6 54.6 0.44
Moderate - 2 7.7 131 83 6.9 9.6 8.6 16.5 3.4 9.6 47.7 0.36
Moderate - 1 7.7 128 86 7.0 11.4 11.1 19.1 2.1 9.6 53.3 0.42
Heavy - 1 7.7 124 80 6.7 11.9 12.0 21.6 2.5 9.5 57.5 0.46
Mean 7.7 127 86 6.9 11.3 10.3 18.9 3.0 9.6 53.1 0.42
LSD (0.05) 0.6 24 21 0.4
1 The protocol was changed in year 2000 from 1) pruning every week and 2) pruning every other week to pruning once early in the season on all treatments.
2 Yield is the sum of picked and dropped fruit. Dropped fruit averaged 9.1 lb/tree.
3 Total pruning and training periods were 14 weeks (1997); 12 weeks (1998); 18 weeks (1999), 4 weeks (2000), and 4 weeks (2001).

Introduction ! Tree Fruits ! Small Fruits ! Vegetables ! Greenhouse Production ! Diagnostic Laboratory ! Appendix


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