Light Management in Pecan
Orchard in Semi-Arid Regions
Jim Walworth, University of Arizona
&
Richard Heerema, New Mexico State University
Optimize ‘Orchard Light Environment’
Crowded Orchards Cause Major Problems
•
•
•
•
Poor spray coverage
Greater alternate bearing
Diminished nut yield and quality
Greater disease & insect pressure and susceptibility
Options for increasing sunlight interception
•
•
•
•
Planting Density/Tree thinning
Hedge-pruning
Selective pruning
Chemicals
Orchard Planting Density
Theoretical cash flow curves
• The ideal orchard
planting density
minimizes the time to
break even while
maximizing nut
production and
quality at maturity
Lower Density
Higher Density
Accumulated Cash Flow ($/ha)
• Orchard light
management should
begin at planting!
adapted from Hoying, Robinson, & DeMarree (for apple)
0
0
Year
Rectangle
Design
Common planting design in new
orchards in the semi-arid region
of the US
Depending on cultivar, it may be possible to
reduce the row spacing as low as 9 meters
6 meters
12 meters
Much less than 6 meters between
trees in the row is not advised
N
Temporary
Trees
6 meters
12 meters
6 meters
With the 6 x 12 meter plantings, temporary trees
may be placed between the permanent rows
• Temporary trees should be removed 12-15
years after planting
• Use very precocious cultivars in temporary
rows
N
Crowded Orchards
Tree Thinning
Hedge-pruning goals
Hedge-pruning negatives
• Improve sunlight
penetration
• Manage crop load
• Reduce or eliminate
alternate bearing
• Improve nut quality
• Improve spray coverage
• Rejuvenate older trees
• Avoid tree thinning
• Cost of pruning
• Cost of cleaning up limbs
• Short-term loss of yield
What are the effects of hedge-pruning?
Alternate Bearing
In-Shell Yield
(Millions of Pounds) l
700
Pecan
I = 0.27
600
500
Alternate Bearing Intensity (I)
400
300
200
100
| an  an  1 | 
 1   | a 2  a1 | | a 3  a 2 |
I 

... 


n

1
a
2

a
1
a
3

a
2
a
n

a
n

1

 

0
In-Shell Yield
(Millions of Pounds) l
700
Walnut
600
I = 0.07
500
Where n is the number of years and a1, a2, an-1 and an are yield of
corresponding years
400
300
200
100
0 = no alternate bearing
1 = complete alternate bearing
0
Pistachio
600
I = 0.21
500
400
300
200
100
20
06
20
05
20
04
20
03
20
02
20
01
20
00
19
99
19
98
19
97
19
96
19
95
19
94
19
93
19
92
0
19
91
In-Shell Yield
(Millions of Pounds) l
700
Effect of hedge pruning on alternate bearing (Australia)
Hedging/topping
one face (N-E-S-W) every
other year (8 year cycle)
Hedging/topping
2 year cycle
• 25 year old ‘Wichita’
and ‘Western Schley’
– 8 year cycle: discrete
hedge-pruning
– 2 year cycle: continuous
hedge-pruning
Hedge Pruning Pecan. 2004. B. Wood and D. Stahmann
Effect of four-year continuous hedging cycle on
alternate bearing in Arizona
Western Schley
4,000
3,500
In-shell Yield (lb/ac)
3,000
2,500
2,000
1,500
1,000
500
-
Before
I = 0.412
Yield = 2,126 lb/ac
Hedging
started
After
I = 0.162
Yield = 2,074 lb/ac
Wichita
3,500
3,000
In-Shell Yield (lb/ac)
2,500
2,000
1,500
1,000
500
-
Before
I = 0.164
Yield = 1,549 lb/ac
Hedging
started
After
I = 0.069
Yield = 2,329 lb/ac
Hedging Options
•
•
•
•
•
Hedging pattern?
Hedging direction?
Hedging frequency?
When in alternate bearing cycle?
Canopy height and width?
Hedging Patterns: Discrete vs Continuous Hedge-Pruning
vs
Pattern
Year 1
Year 2
In-shell yield
(lb/ac)
Discrete
Between rows & tops
Between trees & tops
3380 a
0.34
61.7
Continuous
Between rows & tops
Between rows & tops
3607 a
0.12
62.2
Discrete
Between rows & tops
Between trees & tops
3022 a
0.12
56.4
Continuous
Between rows & tops
Between rows & tops
3234 a
0.12
57.5
Cultivar
Alternate
bearing index
% kernel
Wichita
Western
Schley
Six-year average
Hedge Pruning Pecan. 2004. B. Wood and D. Stahmann
N-S versus E-W hedge-pruning
Influence of Row Orientation
Wichita
Western
Schley
Row
Orientation
Yield (lb/ac)
Kernel %
Nuts/lb
(Nuts/kg)
N-S
3121 b
61.7
51 (113)
E-W
1973 a
61.2
49 (108)
N-S
2536 b
55.9
65 (143)
E-W
1459 a
57.9
64 (141)
Hedge Pruning Pecan. 2004. B. Wood and D. Stahmann
How often should trees
be hedge-pruned?
Year 1
Year 4
Year 2
Year 3
Year 1
Year 4
Year 2
Year 3
Tree response to a 4 year hedging pattern
(Arizona): Every 4th row pruned every
4th year in a continuous pattern
Year 1
Year 2
Year 3
Year 4
– Western Schley trees 18 x 18 m spacing
– Wichita trees 9 x 18 m spacing
4000
3000
Optimum economic hedge-pruning cycle
2000
•
Wichita: 3 to 4 years (dependent on
market price)
•
Western: 4 years
1000
0
0
1
2
3
4
5
Average all years
Western
In-Shell Yield (lbs/acre)
In-Shell Yield (lbs/acre)
Wichita
4000
3000
2000
1000
0
0
1
2
3
Average all years
4
5
% Kernel
Western Schley
68
62
66
60
64
% Kernel
% Kernel
Wichita
A
A
AB
62
58
A
A
A
56
B
60
54
58
B
52
1
2
3
Seasons after hedging and topping
4
1
2
3
Seasons after hedging and topping
4
Average nut weight
(g/nut)
Wichita
Western Schley
7.5
7.0
A
A
AB
7.0
B
6.5
6.0
Average Nut Weight (g/nut)
Average Nut Weight (g/nut)
8.0
6.5
A
AB
AB
6.0
B
5.5
5.0
1
2
3
Seasons after hedging and topping
4
1
2
3
Seasons after hedging and topping
4
Control = Un-pruned since 2005/06
1 = pruned every season
2 = pruned every other season
3 = pruned every third season
Annual Nut Yield
ALL
Pruned
1,3
1,2
1
1,2
1
1,2,3
1
1,2
3500
Inshell Yield
(Pounds per Acre)
3000
2500
CONTROL
TRT 1
2000
TRT 2
TRT 3
1500
1000
500
0
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
Cumulative Yield
16
Cumulative In-shell Yield
(1000 Pounds per Acre)
14
12
10
8
6
TRT 1
4
TRT 2
TRT 3
2
0
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
On years
On years
Off years
60
110
104.7
100
91.2
89.2
89.1
85.4
85
84.0
79.2
80
58.9
58.6
58.0
58
57
57.3
56.9
57.5
56
54.9
55
54
53
75
52
70
TRT 1
TRT 2
TRT 3
TRT 1
CONTROL
TRT 2
TRT 3
CONTROL
0.70
Nut Quality
0.60
Alternate Bearing Intensity
Nuts/lb
90
93.6
59.5
59
Kernel Percentage (%)
105
95
Off years
0.50
0.40
0.30
0.20
0.10
0.00
TRT 1
TRT 2
TRT 3
CONTROL
• What kind of hedging pattern?
– Continuous hedge-pruning is most common
– Discrete hedge-pruning may be appropriate in some orchards
• What direction should rows be hedged?
– North-South
• How often should trees be hedge-pruned?
– 1, 2, 3, or 4 year cycle
– Depends on tree cultivar, vigor, spacing, light environment, market
• When should trees be hedge-pruned?
– Dormant season (before ON year if orchard is alternate bearing)
• How much should trees be cut?
– Height = 1 to 1.25 x row width
– Hedge sides at 5-10 degree angle)
– Leave ~ ⅓ of middles open to sunlight
⅓ to ½ X
X
⅓ to ½ X
X
Light Management with
Chemicals:
The Gibberellins-Class of Plant
Hormones
Photo from articles.extension.org
Taiz and Zeiger, 2002
Light Management with Chemicals
• Several inhibitors of GA biosynthesis have been
developed
– Best known examples are triazoles like
Paclobutrazol (‘PBZ’ - trade names such as Cultar®)
– PBZ has effectively been applied to soil, by trunk
injection, by bark painting, or as foliar spray (follow
label)
A few words of caution before we go on:
- The full effect is not always seen immediately
- May continue to suppress growth for years
- It is irreversible!
- Be very conservative if you decide to experiment
Light Management with Chemicals
• Other reported effects of PBZ in some plants:
– Increased flowering and fruiting
– Increased or decreased fruit size (depending on spp)
– Increased, unchanged, or decreased yield
(depending on spp.)
– Few or no effects on fruit quality (depending on spp)
Light Management with Chemicals
PBZ Treatment at Bud-break (1984)
• High rates caused
reduction in nut
yield due to
reduced leaf area
and internal shading
10-Year-Old 'Cheyenne’ Trees
Annual Shoot Growth (cm)
70
60
50
40
30
20
10
0
1984
1985
0
Adapted from Wood, 1988
132
264
1986
-2
528 µmol·cm TCSA (drench)
• Another study
showed that PBZ
can increase nut
size for immature
trees
Light Management with Chemicals
• PBZ was effective
both via trunk
injection and as soil
spray
PBZ Treatment (Soil Spray), Spring 1983
75-year-old 'Stuart' Trees
Terminal Shoot Growth (cm)
14
12
• Yields increased in 2nd
year for soil
application
10
8
6
4
2
0
1983
1984
0
19
1985
38
76 g/tree
1986
• % kernel and nut
volume were
unaffected
Light Management with Chemicals
• PBZ was applied as a
basal trunk drench at
beginning of study
• Yields per tree increased
on thinned ‘Desirable’
treatment
• No significant effect of
PBZ on yield per tree
Per Tree Yield (Mean for 7 Yrs)
Annual In-Shell Yield (kg/tree)
50
45
40
35
30
25
20
15
10
5
0
Control
SLP
Thinning
Desirable
Adapted from Worley et al, 1996.
SLP+GRL
SLP+GRH
Wichita
SLP = Selective Limb Pruning
GRL = Growth Retardant (PBZ) Low Rate (2.24 kg/ha)
GRH = Growth Retardant (PBZ) High Rate (3.36 kg/ha)
Light Management with Chemicals
Per Hectare Yield (Mean for 7 Years)
Annual In-Shell Yield (kg/Ha)
• Yield per acre
decreased
thinned ‘Wichita’
• No significant
effect of PBZ on
yield per acre
Control
SLP
Thinning
Desirable
Adapted from Worley et al, 1996
SLP+GRL SLP+GRH
Wichita
SLP = Selective Limb Pruning
GRL = Growth Retardant (PBZ) Low Rate
GRH = Growth Retardant (PBZ) High Rate
Questions?