pecan scab control and fungicide coverage from ground ... · ted e. cottrell, and bruce w. wood...
TRANSCRIPT
Pecan scab control and fungicide coverage from ground-based
sprayers Clive H. Bock, Mike W. Hotchkiss,
Ted E. Cottrell, and Bruce W. Wood
USDA-ARS-SEFTNRL, 21 Dunbar Rd., Byron, GA 31008
Overview of presentation
• Background, challenges to good fungicide coverage
• 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
Background • Mature pecan trees are tall (>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 – 2013 is a case in point)
• 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 management on scab severity in the canopy of mature pecan trees
Pecan scab life cycle (Fusicladium effusum)
Overwinters as conidia and stroma
Epidemics build up on
fruit (conidia)
Autumn
Winter
Summer
Spring Fungus
becomes dormant as ‘stroma’ and
overwintering conidia
Epidemics build up on young leaves
(conidia)
Conidia from stroma infects young foliage early in spring
Experiment design and procedures
• Cv. Desirable 2010, 2011, cv. Wichita 2011, mature trees (>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 were assessed for scab incidence and severity in early-Aug and early Oct
• Samples (10 fruit) taken at <15, 15-25, 25-35, 35-40 and >40 ft
• Data analyzed using a generalized linear mixed model with an analysis of simple effects and means separation
Vertical distribution of pecan scab in mature trees
012345
15-Mar-11 15-Apr-11 15-May-11 15-Jun-11 15-Jul-11 15-Aug-11 15-Sep-11 15-Oct-11
012345
15-Mar-10 15-Apr-10 15-May-10 15-Jun-10 15-Jul-10 15-Aug-10 15-Sep-10 15-Oct-10
Rainfall (ins)Fungicide application
Weather and timing of fungicide sprays
• 54-y average 15 Mar-15 Oct is 29.09 ins (739 mm) • 2010 was an average year with evenly distributed rainfall 30.16 ins (766 mm) • 2011 was a relatively dry year 23.37 (591 mm)
2010
2011
Rain
fall
(ins)
Ra
infa
ll (in
s)
Scab
sev
erit
y (%
shu
ck a
rea
dise
ased
)
• On non-treated trees severity declined with tree height in all seasons
• Fungicide treatment has a significant effect reducing scab in the low-mid canopy (≤35 ft)
• Above 40 ft, there was no significant effect of fungicide on scab severity
Treatment
<15.0 ft
Tree
hei
ght
Vertical distribution of scab in the pecan canopy
15-25 ft
25-35 ft
35-40 ft
>40 ft August
Within each column of charts, bars with the different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals
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Control Fungicide
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010203040506070
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Desirable, August 2010
Desirable, August 2011
Wichita, August 2011
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Scab
sev
erit
y (%
shu
ck a
rea
dise
ased
)
• On non-treated trees severity declined with tree height in all seasons
• Fungicide treatment most often had a significant effect reducing scab in the low-mid canopy (≤35 ft)
• At 25 ft and below, there was a consistent effect of fungicide on scab severity
Treatment
<15 ft
Tree
hei
ght
15-25 ft
25-35 ft
35-40 ft
>40 ft October
Within each column of charts, bars with the different letters are significantly different (P=0.05). Whiskers are 95% confidence intervals
Vertical distribution of scab in the pecan canopy
Desirable, October 2010
Desirable, October 2011
Wichita, October 2011
Water sensitive cards placed in trees
• Used water sensitive cards (Syngenta) at different heights in the canopy to measure spray distribution • Placed two cards at each of 5 heights in both the inner and outer canopy of three trees (at 15, 25, 35, 40 and 50 ft) • Moneymaker trees up to ~80 ft • Durand-Wayland m3210 • Replicated three times (3 trees) • Analyzed using generalized linear mixed model
Spray coverage in mature trees
Water sensitive cards
2012
Water sensitive cards • A decrease with spray coverage with height • Up to 35 ft, spray coverage appears good • Performed image analysis cards to measure area
covered and the number of droplets • Compared coverage to height in the tree
Fungicide spray coverage in mature trees
0 ft
Tree
hei
ght
15 ft
25 ft
35 ft
40 ft
50 ft
1. Card is photographed and digitized
2. Image analysis is used to separate spray area from background
3. The area covered by spray is measured
4. The number of spray droplets are counted
Are
a co
vere
d by
sp
ray
(%)
Height (ft)
• Percent area coverage is significantly less at heights >35 ft • But up to 35 ft, spray coverage appears comparable at all heights
tested • The height to which scab control was observed in trees described in
earlier experiments
Fungicide spray coverage in mature trees
Percent card area covered by spray
Data analyzed using a generalized linear model. Letters indicate significant differences using the slice option (P=0.05). 95% Confidence Intervals are indicated.
ab
abc
a
cdede
bd
ab
ab
e e
0
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50
15 25 35 40 50
Inner canopy
Outer canopy
50 ft40 ft
35 ft25 ft
15 ft
0
500
1000
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2000
2500
50 ft 40 ft 35 ft 25 ft 15 ft
Frequency of droplet size range counted on spray cards at different heights
Droplet size (mm)
Num
ber
of d
ropl
ets
Fungicide spray coverage in mature trees
• Droplet number was significantly less at heights >35 ft
• But up to 35 ft, droplet numbers were comparable at all heights tested
• The frequency of droplet size varied with height
• Fewest droplets of all sizes (particularly droplets >0.1 mm2) were collected at heights 35 ft
Data analyzed using a generalized linear mixed model. Letters indicate significant differences using the slice option (P=0.05). 95% Confidence Intervals are indicated.
aa a
b
b
0
1000
2000
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7000
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15 25 35 40 50
Num
ber
of
drop
lets
/car
d
Height (ft)
Least square means of droplets counted on spray cards at different heights
Wind speed achieved by an air-blast sprayer Experiments to characterize the wind speed profile
of an air-blast sprayer used in pecan orchards
• 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 (6, 15, 35, 40 and 50 ft) and three distances (6, 20 and 40 ft). Operated for 2-min intervals and record mean wind speed (mph)
• Background wind 2.3 mph (st dev 1.1) Sonic anemometer (Windsonic, Gill Instruments)
6 ft 20 ft 40 ft
Layout of sprayer and sample distances of wind speeds from sprayer
Wind speed achieved by an air-blast sprayed Experiments to characterize the wind speed
profile of an air-blast sprayer
Sprayer set-up
Position Disc no.
Front Rear
13 6 6
12 6 6
11 6 6
10 6 6
9 4 4
8 3 3
7 2 2
6 2 2
5 2 2
4 2 2
3 2 2
2 2 X
1 2 X
• Durand-Wayland Millenium 3210
• Powered by a 350 hp turbo-diesel
• 26 nozzles operated per side (ceramic disc and swirl plates)
• Pump was operated at 150 psi and 100 gpm
• Drove at 2 mph
• Calibrated for 100 gal/acre
All nozzles were fit with a no. 25 swirl plate
Characteristics of wind from an air-blast sprayer
• Wind speed velocity 6 ft from the fan is substantial (>45 mph)
• The wind impacts stationary air and consequently there is a rapid decline in wind speed
• By approx. 35 ft height wind speed is ≤6.5 mph, and by 40-50 ft, wind speeds approximates to ambient
Wind profile from an air-blast sprayer
Horizontal dist (ft) Height (ft)
Win
d sp
eed
(mph
)
Win
d sp
eed
(mph
)
Distance from fan Height from fan
0
10
20
30
40
50
60
6 15 35 40 50
6
20
40
0
10
20
30
40
50
60
6 20 40
6
15
35
40
50
Limitations of ground-based spray application
• Thus limitations of the spray equipment preclude efficacious scab control, particularly in seasons like 2013
• The data show that the quantity of spray getting to heights ≥40ft is significantly less compared to lower in the canopy
• Aerial application might help address this shortcoming
• But hedging may also help reduce scab…
Photo courtesy of Royalty Pecans, www.royaltypecans.com Photo courtesy of Royalty Pecans, www.royaltypecans.com
Hedging – spin-off benefits in managing pecan scab? How might hedging help?
Hedging alternate sides every 2 y reduces tree height
More of the tree on the hedged side is exposed to spray
On the non-hedged side there is more spray obstruction reducing spray access to greater heights
• A greater proportion of total fruit may be within the area of efficacious scab control, which could result in lower yield losses overall
Potential disadvantages of hedging for scab
Spray coverage is better, but…
….there is substantially more susceptible foliar material in the top of the tree throughout the season
The new growth is very susceptible at a time when there is plenty of inoculum available for infection – the result is scab despite intensive spraying
How might hedging hinder?
Hedging – what we are doing
• We are collaborating with three growers in the region monitoring scab at different heights in hedged and non-hedged trees
• The initial observations indicate hedged trees still have scab in the upper canopy
• Results should be available in 2014
Photo courtesy of Royalty Pecans, www.royaltypecans.com
Preliminary results
0.0
5.0
10.0
15.0
20.0
25.0
30.0
<15 15 to 25 >25
Scab
inci
denc
e (%
infe
cted
leaf
let)
Canopy height
Scab incidence on non-hedged trees
East sideWest side
0.0
5.0
10.0
15.0
20.0
25.0
30.0
<15 15 to 25 >25
Scab
inci
denc
e (%
infe
cted
leaf
let)
Canopy height
Scab incidence on hedged trees
East sideWest side
• Incidence of scab on leaflets - July (percent leaflets scabbed)
• There is a numeric reduction at >25 ft compared to non-hedged trees
• But this was early in the season and we are still collecting and analyzing data
Summary • Scab distribution differed in non-treated and fungicide treated
trees • In treated trees there was less disease in the lower canopy • Ground-based spray coverage is effective to at least 35 ft, which
was the height to which disease was consistently reduced (≤35 ft) • Wind speed declined rapidly with height and distance from the fan • Thus ground based spraying is likely inadequate for mature trees
when/where scab is an issue (particularly if much taller than 35 ft) Questions: • How effectively does aerial application fill this gap? • Can we adjust ground-based spray volume/speed for better coverage
in tall trees? • Where scab is an issue, can pruning or hedging keep tree height
below that for which air blast sprayers are efficacious? • Fungicide resistance….
We thank the GA Pecan Commodity Commission for financial support to aid the research Help with collection and assessment of samples: Shad Stormant, Emma Cutchens, Keith Hough, Bridget Rawls, Stephanie de Vos, Wanda Evans, Shirley Anderson, Ginger Moreland and Sam Njoroge
Acknowledgements
Thank you, and any questions?