Light Management in Pecan Orchard in Semi-Arid Regions. Jim Walworth, University of Arizona & Richard Heerema, New Mexico State University

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1 Light Management in Pecan Orchard in Semi-Arid Regions Jim Walworth, University of Arizona & Richard Heerema, New Mexico State University

2 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

3 Options for increasing sunlight interception Planting Density/Tree thinning Hedge-pruning Selective pruning Chemicals

4 Accumulated Cash Flow ($/ha) Orchard Planting Density Orchard light management should begin at planting! The ideal orchard planting density minimizes the time to break even while maximizing nut production and quality at maturity 0 0 Theoretical cash flow curves adapted from Hoying, Robinson, & DeMarree (for apple) Lower Density Higher Density Year

5 6 meters Rectangle Design 12 meters 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 N Much less than 6 meters between trees in the row is not advised

6 6 meters Temporary Trees 12 meters With the 6 x 12 meter plantings, temporary trees may be placed between the permanent rows Temporary trees should be removed years after planting Use very precocious cultivars in temporary rows N 6 meters

7 Crowded Orchards

8 Tree Thinning

9 Hedge-pruning goals Improve sunlight penetration Manage crop load Reduce or eliminate alternate bearing Improve nut quality Improve spray coverage Rejuvenate older trees Avoid tree thinning Hedge-pruning negatives Cost of pruning Cost of cleaning up limbs Short-term loss of yield

10 What are the effects of hedge-pruning?

11 In-Shell Yield (Millions of Pounds) l Alternate Bearing In-Shell Yield (Millions of Pounds Pecan I = 0.27 Alternate Bearing Intensity (I) In-Shell Yield (Millions of Pounds Walnut I = 0.07 I 1 a2 a1 a3 a2 an an 1... n 1 a2 a1 a3 a2 an an 1 Where n is the number of years and a 1, a 2, a n-1 and a n are yield of corresponding years Pistachio I = = no alternate bearing 1 = complete alternate bearing

12 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 B. Wood and D. Stahmann

13 In-shell Yield (lb/ac) Effect of four-year continuous hedging cycle on alternate bearing in Arizona Western Schley 4,000 3,500 Before I = Yield = 2,126 lb/ac Hedging started After I = Yield = 2,074 lb/ac 3,000 2,500 2,000 1,500 1,

14 In-Shell Yield (lb/ac) Wichita 3,500 3,000 Before I = Yield = 1,549 lb/ac Hedging started After I = Yield = 2,329 lb/ac 2,500 2,000 1,500 1,

15 Hedging Options Hedging pattern? Hedging direction? Hedging frequency? When in alternate bearing cycle? Canopy height and width?

16 Hedging Patterns: Discrete vs Continuous Hedge-Pruning vs Cultivar Pattern Year 1 Year 2 In-shell yield (lb/ac) Alternate bearing index % kernel Wichita Western Schley Discrete Between rows & tops Between trees & tops 3380 a Continuous Between rows & tops Between rows & tops 3607 a Discrete Between rows & tops Between trees & tops 3022 a Continuous Between rows & tops Between rows & tops 3234 a Six-year average Hedge Pruning Pecan B. Wood and D. Stahmann

17 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 (113) E-W 1973 a (108) N-S 2536 b (143) E-W 1459 a (141) Hedge Pruning Pecan B. Wood and D. Stahmann

18 How often should trees be hedge-pruned? Tree response to a 4 year hedging pattern (Arizona): Every 4th row pruned every 4th year in a continuous pattern Year 1 Year 4 Year 2 Year 3 Year 1 Year 4 Year 2 Year 3 Year 1 Year 2 Year 3 Year 4

19 In-Shell Yield (lbs/acre) In-Shell Yield (lbs/acre) Western Schley trees 18 x 18 m spacing Wichita trees 9 x 18 m spacing 4000 Wichita Average all years 4000 Optimum economic hedge-pruning cycle Wichita: 3 to 4 years (dependent on market price) Western: 4 years Western Average all years

20 % Kernel % Kernel % Kernel Wichita Western Schley A AB A A A A B B Seasons after hedging and topping Seasons after hedging and topping

21 Average Nut Weight (g/nut) Average Nut Weight (g/nut) Average nut weight (g/nut) Wichita Western Schley A AB A 6.5 A AB AB 7.0 B 6.0 B Seasons after hedging and topping Seasons after hedging and topping

22 Control = Un-pruned since 2005/06 1 = pruned every season 2 = pruned every other season 3 = pruned every third season

23 Inshell Yield (Pounds per Acre) Annual Nut Yield Pruned ALL 1 1,2 1,3 1,2 1 1,2,3 1 1, CONTROL TRT 1 TRT 2 TRT

24 Cumulative In-shell Yield (1000 Pounds per Acre) Cumulative Yield TRT 1 TRT 2 TRT

25 Alternate Bearing Intensity Nuts/lb Kernel Percentage (%) On years 93.6 Off years On years Off years TRT 1 TRT 2 TRT 3 CONTROL 52 TRT 1 TRT 2 TRT 3 CONTROL Nut Quality TRT 1 TRT 2 TRT 3 CONTROL

26 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 X ⅓ to ½ X

27 Light Management with Chemicals: The Gibberellins-Class of Plant Hormones Photo from articles.extension.org Taiz and Zeiger, 2002

28 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

29 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)

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31 Annual Shoot Growth (cm) Light Management with Chemicals PBZ Treatment at Bud-break (1984) 10-Year-Old 'Cheyenne Trees µmol cm -2 TCSA (drench) High rates caused reduction in nut yield due to reduced leaf area and internal shading Another study showed that PBZ can increase nut size for immature trees Adapted from Wood, 1988

32 Terminal Shoot Growth (cm) Light Management with Chemicals PBZ Treatment (Soil Spray), Spring year-old 'Stuart' Trees g/tree PBZ was effective both via trunk injection and as soil spray Yields increased in 2 nd year for soil application % kernel and nut volume were unaffected

33 Annual In-Shell Yield (kg/tree) Light Management with Chemicals Per Tree Yield (Mean for 7 Yrs) Control SLP Thinning SLP+GRL SLP+GRH 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 Adapted from Worley et al, Desirable 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)

34 Annual In-Shell Yield (kg/ha) Light Management with Chemicals Per Hectare Yield (Mean for 7 Years) Yield per acre decreased thinned Wichita No significant effect of PBZ on yield per acre Control SLP Thinning SLP+GRL SLP+GRH Desirable Wichita Adapted from Worley et al, 1996 SLP = Selective Limb Pruning GRL = Growth Retardant (PBZ) Low Rate GRH = Growth Retardant (PBZ) High Rate

35 Questions?