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

a

b

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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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05

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Control Fungicide

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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15 25 35 40 50

Inner canopy

Outer canopy

50 ft40 ft

35 ft25 ft

15 ft

0

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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

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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?