Clive H. Bock 1 Mike W. Hotchkiss 1 , Katherine Stevenson 2 , Tim B. Brenneman 2 , Mike W. Smith 3 , Bill Goff 4 , Lenny Wells 5 and Bruce W. Wood 1 1 USDA-ARS-SEFTNRL, 21 Dunbar Rd., Byron, GA 31008; 2 Natural Products Laboratory, Department of Plant Pathology, 2360 Rainwater Road, Tifton, GA 31793; 3 Horticulture and Landscape Architecture, 358 Agricultural Hall, Oklahoma State University, Stillwater, OK 74078; 4 Department of Horticulture, 118 Extension Hall, Auburn University, Auburn, AL; 5 Department of Horticulture, University of Georgia, 4604 Research Way, Tifton, GA 31793
Pecan scab ( Fusicladium effusum ) o Lifecycle of Fusicladium effusum , cause of pecan scab Epidemics build up on fruit (conidia) Summer Polycyclic Fungus becomes pathogen (rain dormant as and wind) stroma and Autumn Spring overwintering Epidemics conidia (twigs and shucks) build up on young leaves (conidia) Winter Overwinters as 3-week old culture stroma and conidia of F. effusum on oatmeal agar
Spray coverage in mature trees Water sensitive cards Card height in the trees Water sensitive cards placed in trees 25 m [82 ft] Three experiments (2012) o Cv. Moneymaker ~25 m (~80 ft) tall 15 m [50 ft] o Water sensitive cards (Syngenta) placed at different 12.5 m heights (up to 15 m) in the canopy of mature pecan trees [41 ft] o Inner and outer canopy locations 10 m [33 ft] o Sprayer: Durand-Wayland 3210A, 3.2 kph (2 mph), 935 7.5 m [25 ft] L/ha [100 gpa] 5 m o Replicated three times (3 trees). Repeated experiment [16 ft] twice. 0 m [0 ft] o Analyzed using generalized linear mixed modeling
Fungicide coverage in pecan trees Expt 1 Expt 3 Expt 2 28 September 2012 (PM) 17 October 2012 (AM) 17 October 2012 (PM) Height F-value = 12.7, P-value = <0.0001 Height F-value = 13.4, P-value = <0.0001 Height F-value =17.5, P-value = <0.0001 Position F-value = 4.0, P-value = 0.06 Position F-value = 2.2, P-value = 0.2 Position F-value = 1.8, P-value = 0.2 Height × Position F-value = 3.5, P-value = 0.03 Height × Position F-value = 0.4, P-value = 0.8 Height × Position F-value = 1.5, P-value = 0.2 60 60 60 A A Range: 0.01-34.8% Range: 0.01-73.5% Range: 0.02-56.3% Card area sprayed (%) Inner Card area sprayed (%) A Card area sprayed (%) 50 50 50 A Outer 40 40 AB 40 AB ABC AB ABC 30 30 30 A A ABC ABC AB ABC 20 20 20 ABCD ABCD BCD 5 m [16 ft] ABCD BC BCD BCD 10 ABCD 10 10 BCD C 7.5 m [25 ft] C D CD CD D 10 m [33 ft] 0 0 0 5.0 7.5 10.0 12.5 15.0 5.0 7.5 10.0 12.5 15.0 5.0 7.5 10.0 12.5 15.0 12.5 m [41 ft] 15 m [50 ft] Sample height (m) Sample height (m) Sample height (m) o Coverage declined with sample (tree) height in all three experiments o Was statistically similar to 10.0-12.5 m (33 – 41 ft) o At sample ≥12.5– 15.0 m (41-50 ft) was most often significantly less compared to lower in canopy (indicated by red arrow) o Coverage was numerically slightly higher in the inner canopy Representative water sensitive cards Tree height 0 m 5 m 7.5 m 10 m 12.5 m 15 m [0 ft] [16 ft] [25 ft] [33 ft] [41 ft] [50 ft]
Hedging effects on scab o Fresh growth produced throughout the season on hedged trees is susceptible to scab (susceptible cultivars) o This could be more difficult to control in the southeast o Consequently, fruit on hedged trees may have more severe scab o However, an advantage may be hedged orchards are more open (more air movement, therefore conditions less conducive to scab) o Managing scab may be easier in shorter trees (better fungicide coverage) Not hedged Hedged
Hedging experiment – site 1, Weston, GA o Pawnee trees 14 m (46 ft) tall (planted 2000, 14 y old) o Received the same fungicide treatments (12 airblast sprayer applications) o But different tree hedging/tree removal management practice o Hedged to 12-14 m [40-45 ft] (and ~4 m [~12 ft] from trunk) o Sampled at 5, 8 and 11 m (15, 26 and 37 ft) Fungicide treatments applied to Pawnee hedging experiment No. Date Fungicide Rate/A Method 1 9-Apr Sovran (kresoxim-methyl), Fungiphyte (phosphorous acid), Nickel CBM (Ni) 22 oz, 2.5 gal, 1 gal Ground 2 21-Apr Sovran (kresoxim-methyl), Fungiphyte (phosphorous acid), Nickel CBM (Ni) 22 oz, 2.5 gal, 1 gal Ground 3 8-May Topsin-M (thiophanate-methyl), Toledo (tebuconazole), Nickel CBM (Ni) 5 qts, 54 oz, 5 qts Ground 4 22-May AgriTin (TPTH), Fungiphite (phosphorous acid) 120 oz, 2.5 gal Ground 5 1-Jun AgriTin (TPTH), Elast (dodine) 120 oz, 3 gal Ground 6 12-Jun QuadrisTop (difenoconazole + azoxystrobin), Fungiphite (phosphorous acid) 1 gal, 2.5 gal Ground 7 23-Jun AgriTin (TPTH) 120 oz Ground 8 2-Jul QuadrisTop (difenoconazole + azoxystrobin), Fungiphite (phosphorous acid) 1 gal, 2.5 gal Ground 9 15-Jul Elast (dodine) 4 gal Ground 10 24-Jul QuadrisTop (difenoconazole + azoxystrobin), Fungiphite (phosphorous acid) 1 gal, 2.5 gal Ground 11 6-Aug AgriTin (TPTH), Elast (dodine) 120 oz, 3 gal Ground 12 21-Aug AgriTin (TPTH), Fungiphite (phosphorous acid) 120 oz, 2.5 gal Ground
Hedging experiment – site 1, Weston, GA Hedging and thinning treatments Treatment East hedged West hedged North hedged South hedged East hedged West hedged Tops hedged 2012 Tops hedged 2013 Tops hedged 2014 Jan-Feb 2012 Jan-Feb 2012 Mar 2013 Mar 2013 Mar 2014 Mar 2014 May July May July May July 1. No thinning or hedging (check) No No No No No No No No No No No No 2. Pattern thinned on diagonal No No No No No No No No No No No No 3. Selectively tree thinned (Dr. Bill No No No No No No No No No No No No Goff’s method). Replanted with spaded trees of high scores 4. Dormant hedged on 2 sides, Yes Yes Yes Yes Yes Yes No No No No No No following year hedged on opposite 2 sides. Cuts 12 feet from trunk on each side. Cut tops on hedged sides when height exceeds row width (started cutting tops in 2013). Repeat the pattern over 2-year periods 5. Hedge one side of the tree each Yes No Yes No No Yes No No No No No No year. Also cut tops on hedged sides when height exceeds row width (started cutting tops in 2013) 6. Repeat 4, except only on expected No No Yes Yes Yes Yes No No No No No No “on year” 7. Hedge tops mid May. Repeat July No No No No No No Yes Yes Yes Yes Yes Yes every year. Hedge 2 sides July during “on year”. Opposite 2 sides next “on year ”
Hedging experiment – site 1, Weston, GA Scab severity (% area) on foliage July 2014 Height effects Treatment effects Height F=54.7, P<0.0001 Treatment F=4.9, P<0.0001 Severity per infected leaf Severity (% area diseased) 2.5 2.0 A A A AB BC C (% area diseased) C 2.0 C 1.5 B A 1.5 1.0 1.0 0.5 0.5 0.0 0.0 Control Thin diag Thin Goff Hedge Hedge 1 Hedge on Hedge 5 8 11 dorm 2 side tops Sample ht (m) Treatment 15, 26 and 37 ft o A low severity on foliage on all treatments (mean severity <1.71% leaflet area diseased on infected leaflets; range 1.54-1.71%) o More severe scab high in the canopy o A significant height effect Data analyzed using generalized linear mixed modeling. Letters indicate significant differences based Bock et al., (unpublished data) on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.
Hedging experiment – site 1, Weston, GA Scab severity (% area) on fruit Sept 2014 Treatment effects Height effects Treatment F=25.43, P<0.0001 Height F=11.3, P<0.0001 Severity (% area diseased) 60 80 A C B Severity per fruit (% area diseased) 70 50 C C CD DE 60 E 40 50 B 30 40 20 30 A 10 20 0 10 Control Thin diag Thin Goff Hedge Hedge 1 Hedge on Hedge 0 dorm 2 side tops 5 8 11 Sample ht (m) Treatment 15, 26 and 37 ft o Some difference among treatments (34.7% for the diagonally thinned, and 51.9% for the dormant hedged on two sides sequentially, control = 37.0%) 20 13 Treatment effects o Differences in treatment effects compared to 2013 data 80 A % fruit area scabbed B B o Scab was severe - more severe higher in the canopy BC 60 BC C D o A pronounced height effect (6x more severe at 11 m [37 ft]) 40 20 0 1 2 3 4 5 6 7 Treatment Data analyzed using generalized linear mixed modeling. Letters indicate significant differences based Bock et al., (unpublished data) on t-grouping ( α =0.05). 95% Confidence Intervals are indicated.
Hedging experiment – site 1, Weston, GA Height and the relationship between scab severity and fruit weight Sept 2014 5 m [15 ft] 60 y = -0.09x + 25.7 50 R² = 0.02 40 30 20 10 0 0 20 40 60 80 100 o There was no relationship between scab 8m [26 ft] severity on fruit and fruit weight at 5m (15 ft) 60 Fruit weight (g) y = -0.06x + 25.9 50 or 8 m (26 ft) above ground (despite more R² = 0.05 40 severe disease at 8 m [26 ft]) 30 o At heights ≥11 m (≥37 ft) there is more severe 20 10 disease on the fruit 0 0 20 40 60 80 100 o Despite this, there was only a very weak 11 m [37 ft] relationship between scab and fruit weight at 60 y = -0.10x + 28.6 50 heights ≥11 m (≥ 37 ft) R² = 0.15 40 o Pawnee may be better able to tolerate scab 30 20 damage with less impact on yield; timing of 10 infection in relation to fruit maturity may 0 0 20 40 60 80 100 affect this Severity per fruit (% area diseased) Bock et al., (unpublished data)
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