Disease and spray coverage in pecan trees

1. Disease and spray coverage in pecan trees Clive H. Bock, Mike. W. Hotchkiss, and Bruce W. Wood USDA-ARS-SEFTNRL, 21 Dunbar Rd., Byron, GA 31008

2. Overview of presentation • Background, challenges to good fungicide coverage (particularly in relation to pecan scab) • Describe results of some recent experiments • Spray coverage results • Scab distribution in the tree • Summarize these in the context of options for control of scab

3. 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 begin characterizing spray coverage from an air-blast sprayer and assess scab distribution on fruit in the canopy of mature pecan trees

4. Wind speed achieved by an air-blast sprayed Experiments to characterize the wind speed profile of an air-blast sprayer • How does wind speed declines with distance from the fan? • How does that relate to spray deposition? • Use sonic anemometer to record wind speeds from air blast sprayer. Recorded data to 1/100th of a second • Set anemometer at 5 heights (1.5, 5, 10, 13 and 15 m [5, 15, 30, 42, 49 ft]) and three distances (2, 6 and 12 m [6, 20, 39 ft]). Operate for 2-min intervals and record mean wind speed (m sec-1) • Background wind 1.03 m sec-1 (st dev 0.49) [2.03 mph (st dev 1.09)] Sonic anemometer (Windsonic, Gill Instruments) Layout of sprayer and sample distances of wind speeds from sprayer 12 m 6 m 2 m

5. Characteristics of wind from an air-blast sprayer Wind profile from an air-blast sprayer • Wind speed velocity 2 m (6.5 ft) from the fan is substantial (>20 m/sec [45 mph]) • The wind impacts stationary air and consequently there is a rapid decline in wind speed 5 heights (1.5, 5, 10, 13 and 15 m [5, 15, 30, 42, 49 ft]) 3 distances (2, 6 and 12 m [6, 20, 39 ft])

6. Wind speed achieved by an air-blast sprayed Wind speed profile of an air-blast sprayer Background wind 1.03 m sec-1 (st dev 0.49) Drive-by (2 mph) at 2 m distance and 5 m height Wind speed (m sec-1) Wind speed (m sec-1) Wind speed (m sec-1) Height (m) Horizontal dist (m) Time (100ths sec) • There is a rapid decline in wind speed with height • There is a rapid decline in wind speed with horizontal distance from the sprayer • By approx. 10 m [30 ft] distance wind speed is ≤3.2 m/sec (6.5 mph), and by 12-15 m (39-45 ft), wind speeds approximate to ambient • During spraying, there is a very brief period (15-20 100ths sec.) when the wind is above ambient, • There is a spike in wind speed of 6 100ths sec.

7. Air-blast sprayers - spray distribution with height Vertical distribution of spray 2. Water sensitive cards attached to string Detect spray deposition when there is no canopy to impact/deflect spray • Water sensitive cards placed in trees • Detect spray deposition in the canopy Water sensitive cards • Used water sensitive cards (Syngenta) at different height in the canopy to measure spray distribution • Moneymaker trees up to ~25 m (80 ft)

8. Spray coverage in mature trees Water sensitive cards placed in trees 2012 20 m [60 ft] Card height on strings Card height in the trees • Tree - placed two cards (one in the canopy, one outside) at each of 6 heights (0, 5, 7.5, 10, 12.5 and 15 m [0, 15, 24, 30, 39, 45 ft]) • Strings - placed two cards (one facing up, one down) at 5 heights (0, 5, 10, 15 and 20 m [0, 15, 30, 45, 60 ft]) • Replicated three times (3 trees and three strings) • Repeated on three occasions • Analyzed using a generalized linear mixed model 25 m [80 ft] 15 m [45 ft] 10 m [30 ft] 15 m [45 ft] 12.5 m [39 ft] 5 m [15 ft] 10 m [30 ft] 7.5 m [24 ft] 5 m [15 ft] 0 m [0 ft] 0 m [0 ft]

9. Fungicide spray coverage in mature trees Water sensitive cards from a tree canopy • A decrease with spray coverage with height • Up to ~10+ m [~30+ ft], spray coverage appears good • Performed image analysis cards to measure area covered (and number of droplets) • Compared coverage to height in the tree 15 m [45 ft] 12.5 m [39 ft] 1. Card is photographed and digitized 2. Image analysis is used to separate spray area from background 10 m [30 ft] Height in tree/string 7.5 m [24 ft] 3. The area covered by spray is measured 4. The number of spray droplets are counted 5 m [15 ft] 0 m [0 ft]

10. Fungicide spray coverage in mature trees Percent card area covered • In trees there was a Height (F value = 9.6 [P<0.0001]) and Canopy Location effect (F value = 4.2 [P<0.05]) • Slightly more spray collected on the inner canopy, and the percent area coverage was significantly less at heights ≥10 m [30 ft] • On the string, there was a Height x Card Orientation effect (F value = 17.8 [P<0.01]) • Cards face down received more spray at heights <15 m Trees - percent card area covered by spray Strings - percent card area covered by spray Area covered by spray (%) Area covered by spray (%) • Cards with heavy spray: • Easy to estimate area covered • Difficult to estimate number of droplets Height (m) Height (m) [0, 15, 24, 30, 39, 45 ft] [0, 15, 30, 45, 60 ft] Data analyzed using generalized linear mixed modeling. Letters indicate significant differences using T-grouping. 95% Confidence Intervals are indicated.

11. 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 • Fruit assessed for scab incidence and severity in early-Aug and early Oct, respectively • Samples (10 fruit) taken at <5.0, 5.0-7.5, 7.5-10.0, 10.0-12.5 and >12.5 m [<15, 15-24, 24-30, 30-39, >39 ft] • Data analyzed using a generalized linear mixed model with an analysis of simple effects • Yijk = θ + αi+ βj+ (αβ)ij + eijk, (where θ is a constant (intercept term), αi is the main effect of fungicide treatment, βj is the main effect of height, and (αβ)ij the interaction term, and eijk the residual error)

12. Desirable, August 2010 Desirable, August 2011 Wichita, August 2011 Vertical distribution of scab in the pecan canopy August >12.5 m [>39 ft] • Severity declined with tree height in all seasons • Fungicide treatment has a significant effect reducing scab in the low-mid canopy (<10 m [30 ft]) • Above 12.5 m [39 ft], there was no significant effect of fungicide on scab severity 10.0-12.5 m [30-39 ft] Scab severity (% shuck area diseased) Tree height 7.5-10.0 m [24-30 ft] 5.0-7.5 m [15-24 ft] <5.0 m [<15 ft] Within each column of charts, bars with the different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals Treatment

13. Desirable, Oct 2010 Desirable, Oct 2011 Wichita, Oct 2011 Vertical distribution of scab in the pecan canopy October >12.5 m [>39 ft] • Severity declined with tree height in all seasons • Fungicide treatment most often had a significant effect reducing scab in the low-mid canopy (<10 m [30 ft]) • At 7.5 m [24 ft] and below, there was a consistent effect of fungicide on scab severity 10.0-12.5 m [30-39 ft] Scab severity (% shuck area diseased) Tree height 7.5-10.0 m [24-30 ft] 5.0-7.5 m [15-24 ft] <5.0 m [<15 ft] Within each column of charts, bars with the different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals Treatment

14. Summary • Wind speed from air-blast sprayers declines rapidly with distance and height (≤3 m/sec – ambient 10+ m [30+ ft]) • The spray coverage is very effective to at least 10+ m [30+ ft] • Which was the height to which disease was consistently reduced • Non-treated and fungicide treated trees differed in scab distribution • In treated trees there was less disease in the lower canopy • So… • Ground based spraying is likely inadequate for mature trees when/where scab is an issue (if much taller than 10 m [30 ft]) • Questions remain…. • How effectively does aerial application fill this gap? • Can we adjust ground-based spray volume/speed for better coverage in tall trees? • What about hedging to keep tree height below that for which air blast sprayers are efficacious? • Fungicide resistance….

15. Acknowledgements We thank the GA Pecan Commodity Commission for financial support to aid the research Scientific/technical support: also Shad Stormant, Emma Cutchens, Keith Hough, Bridget Rawls, Stephanie de Vos, Wanda Evans, Shirley Anderson, Ginger Moreland and Sam Njoroge

16. Thank you, and any questions?