Disease and spray coverage in pecan trees

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
build up
on young
leaves
(conidia)
Fungus
becomes
dormant as
Autumn
‘stroma’ and
overwintering
conidia
Spring
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, 10.012.5 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
•
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)
Weather and timing of
fungicide sprays
Rainfall (mm)
2010
120
100
80
60
40
20
0
15-Mar-10
Rainfall (mm)
Fungicide application
15-Apr-10
15-May-10
15-Jun-10
15-Jul-10
15-Aug-10
15-Sep-10
15-Jul-11
15-Aug-11
15-Sep-11
15-Oct-10
Rainfall (mm)
2011
120
100
80
60
40
20
0
15-Mar-11
15-Apr-11
15-May-11
15-Jun-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
Scab severity
(% leaflet area)
3.0
Desirable, 2011
Control
Fungicide
2.5
Wichita, 2011
0.35
0.5
0.30
0.4
0.25
2.0
1.5
1.0
0.20
0.3
0.15
0.2
0.10
0.5
0.1
0.05
0.0
0.00
<5
7.5
10
12.5
>12.5
ab
a
b
b
l
lm
lm
lm
0.0
<5
7.5
10
12.5 >12.5
b
a
a
a
a
m
l
l
l
l
<5
7.5
10
12.5
>12.5
a
a
ab
bc
abc
c
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
Scab severity
(% fruit area)
70
Desirable, 2011
Control
60
Fungicide
50
Wichita, 2011
5
30
4
25
40
3
30
2
20
15
20
10
0
10
1
5
0
0
<5
7.5
10
12.5
>12.5
<5
a
a
b
b
c
a
l
lm
lm
l
m
l
7.5
10
12.5
bc
b
c
l
l
l
>12.5
<5
7.5
10
12.5
>12.5
c
a
bc
b
c
c
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
Scab severity
(% fruit area)
100
Desirable, 2011
Control
Fungicide
80
Wichita, 2011
35
40
35
30
25
20
15
10
5
0
30
25
60
20
40
15
10
20
5
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
bc
ab
a
c
c
a
b
b
b
b
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 midcanopy
• 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,
August 2010 August 2011 August 2011
Vertical distribution of scab in
the pecan canopy
August
>12.5 m
[>40 ft]
7.5-10.0 m
[25-32 ft]
5.0-7.5 m
[16-25 ft]
Scab severity (% shuck area diseased)
10.0-12.5 m
[32-40 ft]
Tree height
• Above 12.5 m [40 ft], there
was no significant effect of
fungicide on scab severity
a
5.0
30
4.0
25
70
60
50
40
30
20
10
0
a
1.0
<5.0 m
[<16 ft]
a
b
30
25
20
15
2.0
a
a
30
4.0
25
20
3.0
b
Fungicide
Control Fungicide
30
4.0
25
20
3.0
15
a
a
5.0
a
b
10
5
0
Control Fungicide
Control Fungicide
30
a
a
25
4.0
20
3.0
b
5
5.0
0.0
Control
b
10
0
2.0
a
a
15
a
Control Fungicide
1.0
a
Control Fungicide
5.0
0.0
b
a
5
0
1.0
a
10
Control Fungicide
2.0
a
Control Fungicide
4.0
0.0
b
a
5
5.0
1.0
a
10
0
3.0
15
2.0
1.0
b
0.0
Control Fungicide
Within each column of charts, bars with the different letters are significantly different
(P=0.05). Whiskers are 95% confidence intervals
a
Control Fungicide
Control Fungicide
70
60
50
40
30
20
10
0
a
0.0
Control Fungicide
70
60
50
40
30
20
10
0
15
2.0
Control Fungicide
70
60
50
40
30
20
10
0
20
3.0
Control Fungicide
• Severity declined with tree
height in all seasons
• Fungicide treatment has a
significant effect reducing
scab in the low-mid canopy
(<10 m [32 ft])
70
60
50
40
30
20
10
0
10
b
5
0
Control Fungicide
Treatment
Control Fungicide
Desirable,
Desirable,
Wichita,
August 2010 August 2011 August 2011
Vertical distribution of scab in
the pecan canopy
60
a
b
30
>12.5 m
[>40 ft]
Tree height
10.0-12.5 m
[32-40 ft]
7.5-10.0 m
[25-32 ft]
5.0-7.5 m
[16-25 ft]
15
0
35
30
25
20
15
10
5
0
Control Fungicide
Scab severity (% shuck area diseased)
• Severity declined with tree
height in all seasons
• At 7.5 m [25 ft] and below,
there was a consistent effect
of fungicide on scab severity
75
45
October
• Fungicide treatment most
often had a significant effect
reducing scab in the low-mid
canopy (<10 m [32 ft])
90
90
75
60
a
a
45
30
15
0
a
75
60
b
45
30
15
0
35
30
25
20
15
10
5
0
75
60
45
a
b
30
15
0
35
30
25
20
15
10
5
0
75
<5.0 m
[<16 ft]
60
45
Control
a Fungicide
b
30
15
0
Control Fungicide
Within each column of charts, bars with the different letters are significantly different
(P=0.05). Whiskers are 95% confidence intervals
15
35
30
25
20
15
10
5
0
a
Control Fungicide
45
30
a
a
a
15
b
0
Control Fungicide
45
30
a
a
a
b
15
0
Control Fungicide
45
a
30
a
b
15
b
0
Control Fungicide
35
30
25
20
15
10
5
0
a
0
Control Fungicide
Control Fungicide
90
a
Control Fungicide
Control Fungicide
90
30
a
Control Fungicide
Control Fungicide
90
45
Control Fungicide
45
a
a
30
b
15
b
0
Control Fungicide
Treatment
Control Fungicide
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
infected leaflet (% area)
Reduction in scab
severity (%)
150
100
50
Desirable 2010
Desirable 2011
Wichita 2011
<5
7.5
10
12.5 >12.5
October: severity per
fruit (% area)
150
150
100
100
50
50
0
0
-50
August: severity per
fruit (% area)
-50
0
<5
7.5
10
12.5 >12.5
-50
-100
-100
-100
-150
-150
-150
-200
-200
-200
<5
7.5
10
12.5 >12.5
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?
Spray coverage in mature trees
Water sensitive cards
2012
• Used water sensitive cards (Syngenta) at
different height in the canopy to measure
spray distribution
Water sensitive cards placed in trees
• Placed two cards at each of 6 heights in the
canopy of three trees (0, 1.5, 5, 10, 14 and 16
m [0, 5, 16, 32, 45, 52 ft])
• Moneymaker trees up to ~25 m (80 ft)
• Durand-Wayland m3210
• Replicated three times (3 trees)
• Analyzed using a general linear model
Fungicide spray coverage in mature trees
Water sensitive cards
16 m
[52 ft]
Tree height
14 m
[45 ft]
• A decrease with spray coverage with height
• Up to 10 m [32 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
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
10 m
[32 ft]
5m
[16 ft]
1.5 m
[5 ft]
0m
[0 ft]
Fungicide spray coverage in mature trees
• Percent area coverage is significantly less at heights >10 m [32 ft]
• But up to 10 m [32 ft], spray coverage appears comparable at all
heights tested
• Number of droplets followed a similar trend
• The height to which scab control was observed in trees described in
earlier experiments
Number of droplets
per card
Percent card area
covered by spray
50
40
35
a
a
a
30
25
20
b
15
b
10
5
0
Number of droplets
per card
Area covered by
spray (%)
45
10000
a
a
9000
7000
a
a
8000
ab
6000
bc
5000
c
4000
3000
2000
1000
0
0
1.5
5
10
Height (m)
14
16
[0, 5, 16, 32, 45, 52 ft]
0
1.5
5
10
14
16
Height (m)
Data analyzed using general linear modeling. Letters indicate significant differences using the
Student-Newman-Keuls test (P=0.05). 95% Confidence Intervals are indicated.
Summary
• Non-treated and fungicide treated trees differed in scab distribution
• In treated trees there was less disease in the lower canopy
• Fungicide reduced the overall epidemic within treated trees in Oct
• Ground-based spray coverage is effective to at least 10 m [32 ft]
• Which was the height to which disease was consistently reduced (≤10m)
So…
• Ground based spraying is likely inadequate for mature trees when/where
scab is an issue (particularly if much taller than 10 m [32 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 pruning appropriately or hedging to keep tree height below
that for which air blast sprayers are efficacious?
• Fungicide resistance….
Acknowledgements
We thank the GA Pecan Commodity Commission for financial
support to aid the research
Dr Bruce Wood
Dr Mike Hotchkiss
Also Shad Stormant, Emma Cutchens, Keith Hough, Bridget
Rawls, Stephanie de Vos, Wanda Evans, Shirley Anderson,
Ginger Moreland and Sam Njoroge
Thank you, and any questions?