 |
| Figure 1. Interactions between time of application and bending and heading vigorous lateral on the central leader of 'Red Cort' on M.7 rootstock apple trees on terminal shoot length on the lateral (A), total shoot length (B), and total flowers (C). |
David C. Ferree and John C. Schmid
Vigorous one-year-old upper limbs on the central leader of young 'Gala' and 'Red Cort' apple trees on M.7 rootstocks were subjected to bending at different times to determine the effect on growth and flowering. Bending vigorous laterals resulted in more flowering spurs than heading for both cultivars, but neither treatment differed from the control. Generally, bending and heading reduced terminal shoot growth on the laterals of both cultivars, and the combination of the two treatments had a greater effect than either alone. All treatments on the laterals of 'Gala' decreased flowering, but only treatments including heading reduced the total flowering of 'Red Cort.' Significant reductions in growth of the terminal shoots occurred from May 23 through June 20 for laterals headed or headed and bent. Bending on or before May 9 caused a reduction in terminal growth of 'Gala,' but none of the treatments affected terminal growth of 'Red Cort' during this time. Bending in the spring had no effect on total shoot growth of 'Red Cort,' but with 'Gala,' bending early in the spring caused a greater reduction in total shoot growth than bending later in the spring (June).
In a second study, central leaders on vigorous trees were bent first to the north for 15, 30, or 45 days and then to the south for the same time period at three different times during spring. No interaction occurred between time of season and length of bending time for the central leader or between treatments and cultivars. Scoring or heading the leader had no significant effect on number or length of laterals formed on the leader or flowering the following year. Contrast analysis indicated average lateral shoot length was greater on leaders bent April 11 than when bent May 9. Numbers of lateral flowers were generally greater on leaders bent 15 days than when bent 30 days.
In modern high-density systems, achieving early production is critical to assist in maintaining an optimum balance of growth and fruiting. Often techniques such as bending and scoring are used to reduce growth and induce flowering. Bending branches has been a common practice to reduce shoot extension (6, 7, 8, 12, 14, 17, 18) and promote flowering (7, 8, 12, 14, 17). However, increased flowering and fruiting have not been consistently found in studies utilizing bending (6, 10). Bending the leader is often recommended for slender spindle or HYTEC training systems to encourage growth in the lower scaffolds and to weaken the leader on vigorous cultivars or sites (1, 6, 13, 14). Although bending the leader in one direction and reversing it is often recommended on vigorous sites to control growth, Parker and Young (13) found they got asymmetrical growth and considered the treatment a failure.
Bending scaffolds increased flowering of 'Smoothee Golden Delicious,' and trees of 'Lawspur Rome Beauty' had increased flower density (6). Cumulative yields were increased on trees on Mark rootstock (11%), while having no yield influence on more vigorous trees on M.7 rootstock (6). A heading pruning cut is often used as a quick replacement for bending to induce branching on vigorous trees. Elfving (3, 4) has shown that annual dormant heading of 'Delicious' and 'Empire' reduced yield. Ferree and Schmid (7) reported that heading young 'Fuji' trees increased growth, but the increase did not result in increased flowering.
The present study was initiated to examine differences in the time of bending on growth and flowering of two apple cultivars vigorously growing on M.7 rootstock. Trees of 'Regal Gala,' a cultivar prone to producing flowers laterally on one-year wood, were compared to 'Red Cort' which is generally a terminal bearing cultivar.
Leader Bending
At the beginning of the third growing season, leaders of free-standing central-leader trees of 'Red Cort'/M.7 (second-year leader length 87 cm) and 'Regal Gala'/M.7 (second-year leader length 89 cm) were given one of the following 12 treatments: 1. Control; 2. Headed – removal of 30% of terminal; 3. Score – cut through bark with a knife encircling the leader just above the bud-scale scars at the base on April 11; 4-12.Bending at various developmental stages and for various time periods – leader bend approximately 70° off vertical by tying it to a lower branch.
Bending was performed April 11 when terminals were just showing green, April 25, or May 9, which was one week past bloom on older trees in this orchard. Bending was first to the north for 15, 30, or 45 days and then reversed to the south for the same amount of time. When the treatment time was complete, the string used for bending was removed. The treatments were arranged as a randomized block with six single tree replications of each treatment. Cultivars were in adjacent rows in a commercial orchard at Pataskala, Ohio. In addition to analysis of variance, single degree of freedom contrasts were made to evaluate dates during the season, length of bending time, and interaction between these factors.
Bending Upper Limbs
Trees in a second group in this same orchard were selected so that each tree had four vigorous laterals of approximately equal length on the upper portion of last year's central leader. The following treatments were applied to the laterals at random: 1. Control; 2. Bend – lateral bent to approximately 50° to 60° from vertical; 3. Head – 25% of the lateral removed by a heading cut; 4. Bend and head – a combination of the latter two treatments.
These treatments were applied at the following times – April 16 (half-inch green stage), April 25, May 9 (one week past bloom), May 23, June 6, and June 20. The treatments were arranged as a randomized complete block with 10 single-tree replicates for 'Red Cort' and nine for 'Regal Gala.'
For both studies, at the end of the growing season, lateral growth and terminal growth were measured and the following spring, terminal, lateral, and spur flowers were counted.
Leader Bending
One of the purposes of this study was to determine if an interaction existed between the time of season the leader was treated by bending and the length of time it was held in the bent position. No interaction occurred between time of season and length of bending time or between the treatments and cultivar. Thus, only main effects are presented.
Scoring or heading the leader had no significant effect on current season shoot growth or flowering the following spring (Table 1). Bending the leader first to the north and then to the south for periods of 15 to 45 days had no effect on shoot growth or flowers produced by the leader compared to the control. Contrast analysis indicated that average lateral shoot length was greater on leaders bent April 11 than when bent May 9. Lateral and total flower numbers were greater on leaders bent 15 days than when the leaders were bent 30 days.
Table 1. Influence of Time of Season and Duration of Bending and Reverse Bending of Leaders on Growth and Flowering of Three-Year-Old 'Regal Gala' and 'Red Cort' Apple Trees on M.7 Root-stock. |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Bending Time | Lateral Shoots | Flowers | |||||||
| Factor | Beginning Date | Length of Time (days) | Terminal Shoot Length (cm) | No. of Laterals | Mean Length (cm) | Terminal | Lateral | Spur | Total |
| Treatment | |||||||||
| Control |
--
|
--
|
40.6 abcdz
|
12.2 a
|
28.5 abc
|
6.6
|
38.4 ab
|
4.7
|
49.9 ab
|
| Score |
--
|
--
|
47.8 ab
|
10.6 ab
|
30.1 abc
|
6.8
|
25.5 ab
|
4.7
|
37.1 ab
|
| Heading |
--
|
--
|
49.1 a
|
11.1 ab
|
35.2 a
|
7.7
|
41.9 a
|
3.0
|
52.7
|
| Bending |
4/11
|
15
|
43.0 abc
|
12.8 a
|
33.2 ab
|
9.4
|
37.4 ab
|
3.1
|
50.0 ab
|
|
4/11
|
30
|
26.5 d
|
10.1 ab
|
27.8 abc
|
5.8
|
20.6 b
|
5.3
|
31.7 ab
|
|
|
4/11
|
45
|
26.8 d
|
9.6 ab
|
34.8 a
|
6.2
|
24.9 ab
|
4.7
|
35.8 ab
|
|
|
4/25
|
15
|
33.3 cd
|
10.5 ab
|
31.7 ab
|
6.5
|
36.1 ab
|
4.3
|
47.0 ab
|
|
|
4/25
|
30
|
29.0 cd
|
7.9 b
|
32.7 ab
|
5.5
|
18.4 b
|
4.9
|
28.8 b
|
|
|
4/25
|
45
|
34.8 bcd
|
10.8 ab
|
27.8 abc
|
7.2
|
26.3 ab
|
5.4
|
38.9 ab
|
|
|
5/9
|
15
|
31.4 cd
|
9.9 ab
|
21.3 c
|
7.4
|
23.4 ab
|
3.2
|
34.0 ab
|
|
|
5/9
|
30
|
27.7 d
|
12.0 a
|
23.8 bc
|
7.2
|
18.1 b
|
4.0
|
29.3 b
|
|
|
5/9
|
45
|
41.1 abcd
|
10.0 ab
|
34.1 ab
|
7.6
|
33.7 ab
|
31
|
44.5 ab
|
|
| Cultivar | |||||||||
| Red Cort |
--
|
--
|
26.0 b
|
22.6 b
|
22.6 b
|
8.7 a
|
4.9 b
|
6.1 a
|
19.9 b
|
| Regal Gala |
--
|
--
|
47.1 a
|
38.1 a
|
38.1 a
|
5.1
|
54.7 a
|
2.2 b
|
62.1 a
|
| z Means within a column are separated by Duncan's multiple range test (P = 0.05). Columns without letters were nonsignificant. | |||||||||
'Gala' was more vigorous than 'Red Cort,' having more and longer shoots. 'Red Cort' had more terminal flowers and more flowers on spurs than 'Gala.' 'Gala' had a very large number of lateral flowers on one-year wood compared to 'Red Cort.'
Upper Limb Bending or Heading
'Red Cort'
The time of treatment had no effect on the number of flowering spurs produced
on last year's laterals, but treatment on June 6 resulted in more vegetative
spurs than treating on May 9 or April 25 (Table 2). Bending resulted in
more flowering spurs than heading, but neither treatment differed from the control.
Generally, the earlier the lateral shoots were manipulated, the greater the
growth of the terminal shoot on the lateral. Timing had little effect on the
total length of secondary lateral shoots or on flowering. Heading the laterals
decreased the length of the terminal shoot on the lateral and decreased the
number and total length of secondary laterals. Bending alone had no effect on
flowering, while heading decreased terminal and total number of flowers.
Table 2. Influence of Bending and Heading Times on the Growth and Flowering One-Year-Old Lateral Limbs on the Central Leader of Three-Year-Old 'Red Cort' Apple Trees on M.7 Root-stock. |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Spurs/Limb | Flowers/Limb | ||||||||
| Factor | Flowering | Vegetative | Terminal Shoot Length (cm) | No. of Secondary Lateral Shoots | Total Secondary Lateral Length (cm) | Total Shoot Length (cm) | Terminal | Lateral | Total |
| Times | |||||||||
| 4/16 |
2.5
|
0.42 abz
|
35.8 a
|
4.0 ab
|
100
|
136
|
4.5
|
3.6
|
10.7
|
| 4/25 |
2.0
|
0.22 b
|
31.7 ab
|
3.6 ab
|
84
|
115
|
4.4
|
3.2
|
9.7
|
| 5/9 |
2.6
|
0.28 b
|
32.0 ab
|
3.6 ab
|
85
|
116
|
4.1
|
2.7
|
9.5
|
| 5/23 |
2.8
|
0.38 ab
|
25.8 bc
|
3.6 ab
|
85
|
112
|
4.3
|
3.4
|
10.6
|
| 6/6 |
2.9
|
0.83 a
|
23.9 c
|
3.0 b
|
88
|
118
|
3.5
|
2.5
|
9.1
|
| 6/20 |
2.2
|
0.64 ab
|
28.2 bc
|
4.4 a
|
108
|
138
|
4.6
|
2.9
|
9.8
|
| Limb Treatment | |||||||||
| Control |
2.5 ab
|
0.56
|
35.0 a
|
5.4 a
|
123 a
|
158 a
|
5.9 a
|
3.2 a
|
11.7 a
|
| Bend |
2.9 a
|
0.40
|
31.8 ab
|
5.1 a
|
111 a
|
143 a
|
5.5 a
|
2.6 b
|
11.0 a
|
| Head |
2.0 b
|
0.33
|
29.8 b
|
2.0 b
|
64 b
|
96 b
|
2.6 b
|
4.4 a
|
9.2 b
|
| Bend+Head |
2.6 ab
|
0.52
|
22.0 c
|
2.2 b
|
60 b
|
85 b
|
2.9 b
|
2.0 b
|
7.6 c
|
| F Significance | |||||||||
| Time |
NSy
|
**
|
**
|
NS
|
NS
|
NS
|
NS
|
NS
|
NS
|
| Treat |
*
|
NS
|
**
|
**
|
**
|
**
|
**
|
**
|
**
|
| Time x Treatment |
NS
|
NS
|
**
|
NS
|
NS
|
*
|
NS
|
NS
|
*
|
| z Means within
a column are separated by Duncan's multiple range test (P = 0.05). Columns
without letters were nonsignificant. y NS, *, ** nonsignificant or significant at P"e 0.05 or 0.01, respectively. |
|||||||||
Significant interactions occurred between time and treatment for terminal shoot length, total shoot length, and total number of flowers. The length of the terminal shoot on each lateral for the control and bending treatments was similar over all times, while terminal length for treatments involving heading was reduced from May 23 onward (Figure 1A). This same pattern was observed for total shoot length (Figure 1B). Laterals that were bent on May 23 through June 20 had more total flowers than laterals that had both heading and bending, while total flower number on laterals that were untreated or received heading only were not influenced by time of treatment (Figure 1C).
|
| Figure 1. Interactions between time of application and bending and heading vigorous lateral on the central leader of 'Red Cort' on M.7 rootstock apple trees on terminal shoot length on the lateral (A), total shoot length (B), and total flowers (C). |
'Regal Gala'
The time of treatment had no effect on spur development, but treating on
June 6 resulted in less shoot growth than some of the earlier treatments (Table
3). The number of terminal flowers formed was higher when lateral limbs were
treated April 16 or in June, compared to treating on April 25. 'Gala'
produced many more lateral flowers than were formed on either spurs or terminals,
but timing did not influence lateral flowers.
Table 3. Influence of Bending and Heading Times on the Growth and Flowering One-Year-Old Lateral Limbs on the Central Leader of Three-Year-Old 'Regal Gala' Apple Trees on M.7 Root-stock. |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Spurs/Limb | Flowers/Limb | ||||||||
| Factor | Flowering | Vegetative | Terminal Shoot Length (cm) | No. of Secondary Lateral Shoots | Total Secondary Lateral Length (cm) | Total Shoot Length (cm) | Terminal | Lateral | Total |
| Times | |||||||||
| 4/16 |
0.7
|
8.3
|
42.8 abz
|
5.3 a
|
130 ab
|
173 a
|
2.7 a
|
14.1
|
17.5
|
| 4/25 |
0.7
|
8.3
|
42.6 ab
|
4.9 a
|
123 ab
|
166 a
|
1.5 c
|
10.2
|
12.4
|
| 5/9 |
0.6
|
11.0
|
48.6 ab
|
4.4 ab
|
134 a
|
181 a
|
1.6 bc
|
14.9
|
17.2
|
| 5/23 |
0.8
|
9.2
|
37.3 bc
|
4.1 ab
|
108 ab
|
145 ab
|
2.0 bc
|
12.5
|
15.3
|
| 6/6 |
1.5
|
8.3
|
33.0 c
|
3.5 b
|
89 b
|
122 b
|
2.6 ab
|
11.9
|
16.0
|
| 6/20 |
1.0
|
8.0
|
40.0 bc
|
4.5 ab
|
122 ab
|
163 ab
|
2.5 ab
|
13.9
|
17.5
|
| Limb Treatment | |||||||||
| Control |
1.0 a
|
10.6 a
|
55.4 a
|
6.1 a
|
155 a
|
210 a
|
2.5 a
|
22.7 a
|
26.3 a
|
| Bend |
1.3 a
|
10.6 a
|
35.3 ab
|
4.7 b
|
111 bc
|
146 b
|
2.5 a
|
9.8 bc
|
13.6 bc
|
| Head |
0.5 b
|
6.4 c
|
42.7 b
|
4.1 b
|
119 b
|
162 b
|
1.9 ab
|
11.8 b
|
14.3 b
|
| Bend+Head |
0.7 ab
|
8.4 b
|
28.5 c
|
3.0 c
|
87 c
|
115 c
|
1.7 b
|
7.2 c
|
9.7 c
|
| F Significance | |||||||||
| Time |
NSy
|
NS
|
**
|
**
|
*
|
**
|
**
|
NS
|
NS
|
| Treat |
*
|
**
|
**
|
**
|
**
|
**
|
**
|
**
|
**
|
| Time x Treatment |
NS
|
NS
|
**
|
NS
|
*
|
**
|
NS
|
NS
|
NS
|
| z Means within
a column are separated by Duncan's multiple range test (P = 0.05). y NS, *, ** nonsignificant or significant at P"e 0.05 or 0.01, respectively. |
|||||||||
Heading reduced both flowering and vegetative spurs. All treatments reduced terminal shoot length, lateral shoot number, and total length, and generally the combination of bending and heading caused the greatest reduction in growth. In general, lateral flowering followed the same pattern as growth being reduced by all treatments. Formation of terminal flowers was only reduced by the combination treatment.
The interaction between time of season and the limb treatments was significant for the following factors – terminal shoot length, total secondary lateral shoot length, and total secondary shoot length.
Terminal shoot length was reduced by bending consistently over the season, while heading had little effect on terminal length through May 9, but caused a reduction after that date (Figure 2A). For both total shoot length (Figure 2B) and total lateral length (Figure 2C), bending caused a significant reduction in growth early in the season, but the effect was less in June. Heading had no effect on these indices through May 9, but after that time caused a significant decrease in both total shoot length and total length of secondary laterals.
 |
| Figure 2. Interactions between time of application and bending and heading vigorous lateral on the central leader of 'Regal Gala' on M.7 rootstock apple trees on terminal shoot length on the lateral (A), total shoot length (B), and total flowers (C). |
The length of time of bending the leader had no effect on shoot growth, but 15 days appears to increase flowering and additional time had no benefit. Leopold (9) reported that physical bending of stems of several tree species resulted in a large increase in endogenous ethylene content. In further work, Robitaille and Leopold (15) reported the rise in ethylene content in apple stems reached a maximum two days following bending and returned to levels in control plants after three weeks. Thus, it is not surprising to see the effect on flowering being exhibited following the shortest period (15 days) in this study. It is surprising that bending the leaders on these trees had no effect on growth compared to the control trees. This may have been due to the minimal pruning of these trees as the central leader averaged approximately half the growth that occurred the previous year.
The hypothesis that the response to bending may differ at various times during the period of rapid shoot growth in the spring was refuted in this work. The bending response was similar from mid-April through mid-June for both cultivars (Figure 1A and Figure 2A). Bending had no effect on growth of 'Red Cort,' but caused a reduction at all dates with 'Gala.' The authors are unaware of other work comparing various times of bending during the period of active growth.
Heading lateral shoots on the central leader prior to May 9 had little effect on subsequent length of the terminal shoot growth on the lateral or total growth. This was probably because the early stage of development and regrowth could compensate for the growth removed; however, after May 9 regrowth from heading was unable to compensate for the growth removed. Results of summer pruning trials indicate that the earlier in the season pruning is accomplished, the greater the regrowth that occurs (11, 16).
Time during the spring when laterals were manipulated had no effect on flowering the following season. Heading consistently decreased flowering of both apple cultivars. This is consistent with previous findings showing the negative effect of heading on flowering and fruiting (2, 3). Bending did not increase flowers in this study no matter when it was performed during the early spring period of active growth, as has been found in other studies (6, 10), although many studies report increased flowering (7, 8, 12, 14, 17). In fact, lateral flowering of 'Gala' was decreased with bending and when combined with heading, both terminal flowering and total flowering of 'Red Cort' were decreased. Some studies (5, 7, 8) show that flowering on young trees is related to total growth which could possibly explain the results in this study since growth was reduced by these treatments.
In summary, the length of time the bend was in place or the time during early spring (mid-April through mid-June) had little effect on the response to bending leaders or branches of young vigorous apple trees. Heading laterals reduced flowering the following year. The effect of heading on regrowth of the leader and total lateral growth was greatest from mid-May through mid-June with much less effect earlier in the season.
Appreciation is extended to Lynd Fruit Farm, Pataskala, Ohio, for permitting manipulation and measurement of these trees and for general maintenance of the trees during the study.