Disease and spray coverage in pecan trees Clive H. Bock USDA-ARS-SEFTNRL, 21 Dunbar Rd., Byron, GA 31008
Overview of presentation Background, challenges to good fungicide • coverage (particularly in relation to pecan scab) Describe results of some recent • experiments Scab distribution in the tree • Spray coverage results • Summarize these in the context of options • for control of scab Issues that remain to be resolved (aerial • vs. ground based spraying)
Background Mature pecan trees are tall (>15 m [>50 ft]) • Major disease is scab ( Fusicladium effusum ) • Various fungicides are used to control scab • Much of the application is by ground-based air-blast sprayers • Good scab control in the top of the tree is perceived to be challenging • (especially if wet) Fungal plant pathogens differ to insect pests – they are not mobile • Many factors affect spray coverage – tractor speed, application volume, • weather conditions, tree architecture and tree height Objective: to characterize scab distribution and the impact of scab • management in the canopy of mature pecan trees
Pecan scab life cycle ( Fusicladium effusum ) Epidemics build up on fruit (conidia) Summer Epidemics Fungus build up becomes on young Spring dormant as Autumn leaves ‘stroma’ and (conidia) overwintering conidia Winter Overwinters as conidia and stroma
Experiment design and procedures Vertical distribution of pecan scab in mature trees Cv. Desirable 2010, 2011, cv. Wichita 2011, mature trees (>15 m • [~50 ft]). Trees received fungicide (propiconazole, TPTH) by air-blast • sprayer (Aerofan D2/40 1000), Ground speed 2 mph, 100 gallons per acre) or were non-treated 4 replicates of each treatment. Fully randomized design • Leaves and fruit assessed for scab incidence and severity in Jun, • early-Aug and early Oct, respectively Samples (10 leaves or fruit) taken at <5.0, 5.0-7.5, 7.5-10.0, 10.0- • 12.5 and >12.5 m [<16, 16-25, 25-32, 32-40, >40 ft] Data analyzed using a generalized linear mixed model with an • analysis of simple effects Y ijk = θ + α i + β j + (αβ) ij + e ijk , (where θ is a constant (intercept term), α i is the main effect of fungicide • treatment, β j is the main effect of height, and (αβ) ij the interaction term, and e ijk the residual error)
Weather and timing of fungicide sprays 2010 120 Rainfall (mm) 100 Rainfall (mm) 80 Fungicide application 60 40 20 0 15-Mar-10 15-Apr-10 15-May-10 15-Jun-10 15-Jul-10 15-Aug-10 15-Sep-10 15-Oct-10 2011 120 Rainfall (mm) 100 80 60 40 20 0 15-Mar-11 15-Apr-11 15-May-11 15-Jun-11 15-Jul-11 15-Aug-11 15-Sep-11 15-Oct-11 54-y average 15 Mar-15 Oct is 739 mm (29 ins) • 2010 was an average year with evenly distributed rainfall (766 mm [30 ins]) • 2011 was a relatively dry year (591 mm [23 ins]) •
Vertical distribution of pecan scab on leaflets June/July Desirable, 2010 Desirable, 2011 Wichita, 2011 3.0 0.35 0.5 Control (% leaflet area) Scab severity 0.30 2.5 Fungicide 0.4 0.25 2.0 0.3 0.20 1.5 0.15 0.2 1.0 0.10 0.1 0.5 0.05 0.0 0.00 0.0 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 ab a b b b a a a a a a ab bc abc c l lm lm lm m l l l l l l lm m lm lm Sample height (m) [<16, 16-25, 25-32, 32-40, >40 ft] Trends differed on fungicide treated and non-treated trees • On non-treated trees more severe disease in the lower canopy 2010 (cv. Desirable) • and 2011 (cv. Wichita). No difference on cv. Desirable (2011) Inconsistent on fungicide-treated trees. Less disease in the lower canopy on cv. • Desirable (2010), similar disease on cvs. Desirable and Wichita (2011) Spring 2011 was very dry. Fungicide timing? • Within treatment, bars with different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals
Vertical distribution of pecan scab on fruit August Desirable, 2010 Desirable, 2011 Wichita, 2011 70 5 30 Control 60 Scab severity (% fruit area) 25 Fungicide 4 50 20 3 40 15 30 2 10 20 1 5 10 0 0 0 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 a a b b c a bc b c c a bc b c c l lm lm l m l l l l l l l l l l Sample height (m) [<16, 16-25, 25-32, 32-40, >40 ft] Trends differed on fungicide treated and non-treated trees • On non-treated trees most severe disease was in the lower canopy • Fungicide-treated trees had either less severe disease in the lower • canopy (cv. Desirable, 2010) or similar severity at all heights (cvs. Desirable and Wichita, 2011 ) Within treatment, bars with different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals
Vertical distribution of pecan scab on fruit October Desirable, 2010 Desirable, 2011 Wichita, 2011 100 35 40 Control 35 Scab severity (% fruit area) 30 Fungicide 80 30 25 25 60 20 20 15 40 15 10 10 20 5 5 0 0 0 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 a b b b b bc ab a c c a b b b b l l l l l l l l l l l l l l l Sample height (m) [<16, 16-25, 25-32, 32-40, >40 ft] Trends differed on fungicide treated and non-treated trees • On non-treated trees most severe disease was in the lower to mid- • canopy Fungicide-treated trees had similar scab severity at all heights • Within treatment, bars with different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals
Desirable, Desirable, Wichita, Vertical distribution of scab in August 2010 August 2011 August 2011 the pecan canopy 70 5.0 30 60 25 4.0 50 a 20 3.0 40 15 a 30 August 2.0 a a >12.5 m 10 20 a a 1.0 5 [>40 ft] 10 0 0.0 0 Control Fungicide Control Fungicide Control Fungicide Severity declined with tree • Scab severity (% shuck area diseased) 70 5.0 30 height in all seasons 60 25 a 4.0 50 20 3.0 40 15 b 10.0-12.5 m 30 2.0 Fungicide treatment has a a • a 10 a 20 a [32-40 ft] 1.0 5 10 significant effect reducing 0 0.0 0 Control Fungicide Control Fungicide Control Fungicide scab in the low-mid canopy Tree height 70 5.0 30 60 a 25 (<10 m [32 ft]) 4.0 50 a 20 3.0 40 b 7.5-10.0 m 15 b a 30 2.0 10 Above 12.5 m [40 ft], there [25-32 ft] 20 • b 1.0 5 10 was no significant effect of 0 0.0 0 Control Fungicide Control Fungicide Control Fungicide fungicide on scab severity 70 5.0 30 a 60 25 4.0 50 20 3.0 5.0-7.5 m 40 b a 15 30 2.0 [16-25 ft] b 10 a 20 a 1.0 5 10 0.0 0 0 Control Fungicide Control Fungicide Control Fungicide 70 5.0 30 a a a Control 60 25 4.0 Fungicide 50 20 <5.0 m 3.0 40 15 [<16 ft] b 30 2.0 10 b 20 b 1.0 5 10 0 0.0 0 Control Fungicide Control Fungicide Control Fungicide Within each column of charts, bars with the different letters are significantly different Treatment (P=0.05). Whiskers are 95% confidence intervals
Desirable, Desirable, Wichita, Vertical distribution of scab in August 2010 August 2011 August 2011 the pecan canopy 90 35 45 30 75 a 25 60 30 b 20 a 45 October 15 a a >12.5 m 30 15 10 a 15 5 [>40 ft] 0 0 0 Severity declined with tree • Control Fungicide Control Fungicide Control Fungicide Scab severity (% shuck area diseased) 90 35 45 height in all seasons 30 75 a 25 60 30 a 20 a 45 a Fungicide treatment most • 15 10.0-12.5 m a 30 15 b 10 [32-40 ft] often had a significant effect 15 5 0 0 0 Control Fungicide Control Fungicide Control Fungicide reducing scab in the low-mid 90 35 45 Tree height a canopy (<10 m [32 ft]) 30 75 25 60 30 a b 20 a 45 7.5-10.0 m a At 7.5 m [25 ft] and below, 15 • b 30 15 [25-32 ft] 10 15 5 there was a consistent effect 0 0 0 Control Fungicide Control Fungicide Control Fungicide of fungicide on scab severity 90 35 45 a 30 75 25 a 60 30 b 5.0-7.5 m 20 45 a 15 [16-25 ft] b 30 15 10 b 15 5 0 0 0 Control Fungicide Control Fungicide Control Fungicide 90 35 45 Control a a 30 75 a Fungicide 25 60 30 <5.0 m b 20 45 [<16 ft] 15 30 15 b 10 b 15 5 0 0 0 Control Fungicide Control Fungicide Control Fungicide Within each column of charts, bars with the different letters are significantly different Treatment (P=0.05). Whiskers are 95% confidence intervals
The difference in pecan scab severity between treated and non treated trees Fungicide treatment and height [<16, 16-25, 25-32, 32-40, >40 ft] June: severity per August: severity per October: severity per infected leaflet (% area) fruit (% area) fruit (% area) 150 150 150 Desirable 2010 Reduction in scab 100 Desirable 2011 100 100 severity (%) Wichita 2011 50 50 50 0 0 0 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 <5 7.5 10 12.5 >12.5 -50 -50 -50 -100 -100 -100 -150 -150 -150 -200 -200 -200 Sample height (m) On leaves and fruit in August there was a consistent fungicide effect on • scab at heights ≤10 m [32 ft] [(Control -Treated)/Control]*100 On leaves and fruit in August at >10 m [32 ft] there was an inconsistent • effect of fungicide In October on fruit fungicide reduced scab at all heights • Is this due to a direct fungicide effect, or a cumulative effect on the • epidemic in the tree?
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