What are the challenges to scab management? Fusicladium effusum is - - PowerPoint PPT Presentation

What are the challenges to scab management?

• Fusicladium effusum is a variable pathogen (a record
• f host resistance breaking down)
• Current fungicides – and fungicide resistance
• Weather – can preclude timely spray application (for

example, 2013)

• Pecan trees eventually grow tall (>15 m, >50 ft)

Hedging and scab

• Hedging is done for several reasons. But how

might it influence scab and scab management in the southeast?

• We explored this for the first time in 2013

– Results of experiments at three locations in GA (Weston, Marshallville and Valdosta) – Experiments in Weston and Marshallville trees 14 m (~45 ft) – At Valdosta site, trees 18 m (60+ ft) – Allows a contrast of hedging effects on scab in trees

• f different heights
• 2013 was a year conducive to the disease (it

was wet, with regular rainfall)

• Susceptible cultivars developed severe scab

despite frequent fungicide application

Hedging – the process

Hedging and scab - concerns

• Fresh growth produced throughout the season on hedged trees is

susceptible to scab (susceptible cultivars)

• This could be more difficult to control in the southeast
• Consequently, fruit on hedged trees may have more severe scab
• However, an advantage may be hedged orchards are more open (more

air movement, therefore conditions less conducive to scab)

Not hedged Hedged New growth produced throughout season What if this is the outcome……?

• Three experiments on commercial orchards in 2013
• Weston, Marshallville and Valdosta,

So what effect does hedging have on pecan scab?

• All experiment treatments replicated

(3 to 5 times). Standard experiment designs

• Assessed for scab at 3 to 4 heights
• n 1 to 4 occasions
• Only sampled row-sides
• Analyzed using general linear

modeling with means comparison by t- grouping

Fungicide treatments (12 applied) – all ground applications Date Fungicide and rate (100 gal/acre) 04-03-13 Sovran- 3 oz (every other middle) 04-08-13 Sovran- 3 oz (every other middle) 04-17-13 Sovran- 3 oz + Fungiphite- 32 oz + Nickel CBM- 16 oz 04-30-13 Topsin- 19.2 oz 05-15-13 AgriTin- 9.6 oz 06-02-13 Agri Tin- 12 oz + Fungiphite- 32 oz 06-13-13 Quadristop- 12.8 oz 06-27-13 AgriTin- 12 oz + Fungiphite- 32 oz 07-12-13 AgriTin- 12 oz + Elast- 25.6 oz 07-22-13 AgriTin- 12 oz + Fungiphite-32 oz 08-03-13 AgriTin- 12 oz + Elast- 25.6 oz 08-16-13 AgriTin- 12 oz Treatment East hedged Jan-Feb 2012 West hedged Jan- Feb 2012 North hedged 8 Mar 2013 South hedged 8 Mar 2013 Tops hedged 16 May 2013 Tops rehedged 16 Jul 13

• 1. No thinning or hedging (check)

No No No No No No

• 2. Pattern thinned on diagonal

No No No No No No

• 3. Selectively tree thinned (Dr. Bill Goff‟s method). Replanted with

spaded trees of high scores No No No No No No

• 4. Dormant hedged on 2 sides, following year hedged on opposite 2
• sides. Cuts 12 feet from trunk on each side. Cut tops on hedged sides

when height exceeds row width (started cutting tops in 2013). Repeat the pattern over 2-year periods Yes Yes Yes Yes No No

• 5. Hedge one side of the tree each year. Also cut tops on hedged sides

when height exceeds row width (started cutting tops in 2013) Yes No Yes No No No

• 6. Repeat 4, except only on expected “on year”

No No Yes Yes No No

• 7. Hedge tops mid May. Repeat July every year. Hedge 2 sides July

during “on year”. Opposite 2 sides next “on year” No No No No Yes Yes

• Pawnee trees ~45 ft tall and hedged to 40-45 ft (planted 2000, 14 y old)
• All received the same fungicide treatments
• But different tree hedging/removal management practice
• Sampled at 5, 8 and 11 m (15, 26 and 37 ft)

Tree management and fungicide treatments – Weston, GA

B BC D BC B C A 20 40 60 80

1 2 3 4 5 6 7 % fruit area scabbed

Treatment = F=21.3, P<0.0001

Treatment effects on scab on leaflets and fruit 9 September 2013

Hedging experiment - Weston, GA

Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α=0.05). 95% Confidence Intervals are indicated.

Treatments Pawnee (40-45 ft tall) Seven treatments

• 1. Not hedged (control)
• 2. Pattern thinned on diagonal
• 3. Selectively tree thinned

(using Dr. Bill Goff‟s method). Replanted with spaded trees

• f high scores
• 4. Dormant hedged on 2 sides.

Following year hedged on

• pposite 2 sides. Cuts 12 feet

from trunk on each side. Repeat the pattern over 2- year periods

• 5. Hedge one side of the tree

each year

• 6. Repeat 4, except only on

expected “on year”

• 7. Hedge tops mid May.

Repeat July every year. Hedge 2 sides July during “on year”. Opposite 2 sides next “on year”.

• On foliage incidence ranged

from 1 to 6% leaflets infected

• On foliage scab was least on the

check, and treatments 2, 5 and 6

• It was most on leaves of

treatments 4 and 7

• On fruit all treatments had

severity ≥40%

• Treatment 3 had least severe

scab (40%)

• Treatments 2,4 and 5 had

severity similar to the control (1)

• Treatment 7 had most severely

scabbed fruit (>63%)

Severity on fruit

Treatment F=7.9, P<0.0001

C C B AB C C A 3 6 9 12

1 2 3 4 5 6 7 % leaflets with scab

Incidence on leaves

C B A 2 4 6 8 10

5 8 11 % leaflets scabbed

C B A 20 40 60 80 100

5 8 11 % fruit area scabbed Sample height (m)

F=31.4, P<0.0001

Tree height effects on scab, 9 September 2013

Hedging experiment - Weston, GA

Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α =0.05). 95% Confidence Intervals are indicated.

• Disease control measures are less efficacious at greater heights

(even in hedged systems in years of severe epidemics)

• Despite a rigorous fungicide program (12 fungicide applications)

15 ft 26 ft 37 ft

F=637.4, P<0.0001

Severity on fruit Incidence on leaves

15 ft 26 ft 37 ft

Sample height (m)

Fungicide treatments (14 applied) Dates Type Fungicide and Rate (100 gal/acre) 4-9-2013 Ground AgTin 12 oz 4-22-2013 Ground AgTin 6 oz + Bumper (propiconazole) 6 oz 5-6-2013 Ground Absolute 500SC 6 oz 5-20-2013 Ground Absolute 500SC 6 oz 6-4-2013 Ground AgTin 12 oz 6-12-2013 Ground AgTin 12 oz 6-26-2013 Ground AgTin 12 oz 7-8-2013 Aerial AgTin 12 oz 7-15-2013 Ground AgTin 12 oz 7-29-2013 Ground AgTin 12 oz 8-6-2013 Aerial AgTin 12 oz 8-12-2013 Ground Absolute 500SC 6 oz 8-21-2013 Aerial Absolute 500SC 6 oz 8-26-2013 Ground SuperTin 12 oz

Hedging experiment – Marshallville, GA

• Desirable trees 14 m (~45 ft) and hedged to 12-14 m (40-45 ft)
• Planted 1996, 18 y old
• Hedged one side 2 March 2013
• All received the same fungicide treatments
• Sampled at 6, 6-9 and >9 m (<20, 20-30 and >30 ft)

Marshallville, GA Desirable (14 m, 45 ft tall) Two treatments

• 1. Not hedged (control)
• 2. One side hedged

A A 10 20 30

One side hedged Not hedged % leaflets with scab

A A 10 20 30 40

Hedged Not hedged % leaflets with scab

10 Oct 2013

Treatment × Height F=3.9, P=0.02

CB B B CB C A 10 20 30 40 50 60

<6 m 6 to 9 m >9 m <6 m 6 to 9 m >9 m % leaflets with scab

Treatment F=0.01, P=0.9

B A A 10 20 30 40

<6 m 6 to 9 m >9 m % leaflets with scab Height F=7.6, P=0.0005

8 Aug 2013

Treatment F=0.4, P=0.6

Hedging experiment – Marshallville, GA

Treatment and height effects on scab on leaflets

• No effect of hedging on the incidence of infected leaflets
• A pronounced effect of height on incidence of infected leaflets

(Treatment × Height interaction in October)

Marshallville, GA Desirable (14m, 45 ft tall) Two treatments

• 1. Not hedged (control)
• 2. One side hedged

<20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft

Marshallville, GA Desirable (14 m, 45 ft tall) Two treatments

• 1. Not hedged (control)
• 2. One side hedged
• Hedged treatment no different to non-hedged in

August

• By October, the fruit on the hedged trees has

slightly more disease compared to the non-hedged

Hedging experiment – Marshallville, GA

Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α =0.05). 95% Confidence Intervals are indicated.

8 August 2013 Treatment F=5.01, P=0.03 Treatment F=1.7, P=0.2 10 October 2013

Treatment effects on scab on fruit

A B 15 30 45 60

Hedged Not hedged Severity (% area)

A A 3 6 9 12

Hedged Not hedged Severity (% area)

C B A 15 30 45 60 75 90

<6 m 6 to 9 m >9 m Severity (% area)

C BC A BC BC B 5 10 15 20

<6 m 6 to 9 m >9 m <6 m 6 to 9 m >9 m Severityy (% area)

8 August 2013 10 October 2013

Treatment x Height effect, F=3.8, P=0.02 Height effect F=104.8, P=<0.0001

Marshallville Desirable (14 m, 45 ft tall) Two treatments

• 1. Not hedged (control)
• 2. One side hedged

Hedging experiment – Marshallville, GA

Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α =0.05). 95% Confidence Intervals are indicated.

• August – hedged trees have more disease only at

heights >9 m (30 ft)

• By October there was no Treatment × Height

interaction (only height effect)

Not hedged Hedged

Tree height effects on scab severity on fruit

<20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft <20 ft 20-30 ft >30 ft

Thus far all trees in hedged and non-hedged treatments have been approximately the same height (12-14 m, ~40-45 ft)… ...but what about effects on trees in excess of 18 m (60 ft) that are hedged?

• Two previous experiments suggest little difference in scab

severity on foliage or fruit in trees hedged to 14 m (45 ft)

• Our data has consistently demonstrated that tree height is

an important factor in scab management

• What about taller trees? How are fruit distributed in the

canopy?

• How does the distribution of disease in the canopy relate to

the distribution of fruit?

• Some limited previous work has indicated the distribution of

fruit

• Majority of fruit are borne in the midsection of the tree (only a

small proportion at heights <25% or >25% tree height)

• Thus the taller a tree, the greater the impact of scab in portions
• f the tree not as well protected by fungicide

Fruit distribution

25%

• f

height 50%

• f

height 75%

• f

height 100%

• f

height

26-year old „Success‟ tree Riverside seedling stock Texas A&M University Plantation Tree spacing 15.2 m × 15.2 m (50 ft × 50 ft) Semi-crowded situation Tree height 15 m (50 ft) Minimum ht of canopy 1.07 (3.5 ft) m above ground

Lozano-Gonzalez et al. 1992. Three-dimensional characterization of bearing pecan tree. HortScience 27: 1181-3.

9.1%

• f

yield 46.6%

• f

yield 37.1%

• f

yield 7.3%

• f

yield

Valdosta, GA: Desirable (18 m, 60 ft tall), Three treatments

• 1. Not hedged (control), 2. One side hedged, 3. Both sides hedged

Heights sampled = <7, 7-10, 10-14 and >14 m (<23, 23-33, 33-46, >46 ft)

Hedging experiment - trees 18 m (60 ft), Valdosta, GA

Fungicide treatments, 100 gallons/acre (24 applied, FS = full spray, AM = alternate middle) Dates Type Fungicide and Rate (100 gal/acre) 4-9-2013 Ground (FS) ProPhyt 2 qt 4-18-2013 Ground (FS) SuperTin 6.4 oz + Elast 25 oz 5-1-2013 Ground (FS) Absolute 5 oz + Tebuzol 3 oz 5-7-2013 Ground (AM) Absolute 5 oz + Tebuzol 3 oz 5-13-2013 Ground (AM) Absolute 5 oz + Tebuzol 3 oz 5-19-2013 Ground (AM) ProPhyt 2 qt 5-28-2013 Ground (AM) ProPhyt 2 qt 6-4-2013 Ground (AM) ProPhyt e 2 qt + SuperTin 12.8 oz 6-9-2013 Ground (AM) ProPhyt 2 qt + SuperTin 12.8 oz 6-14-2013 Ground (AM) SuperTin 9.6 oz + Elast 38 oz 6-19-2013 Ground (AM) SuperTin 9.6 oz + Elast 38 oz 6-25-2013 Ground (AM) SuperTin 9.6 oz + Elast 38 oz 6-26-2013 Ground (AM) Quadris Top 11 oz + ProPhyt 1.5 qt 7-3-2013 Ground (FS) Quadris Top 11 oz + ProPhyt 1.5 qt 7-11-2013 Ground (FS) Elast 50 oz + Supertin 6.5 oz 7-13-2013 Aerial (FS) Absolute 5 oz + Tebuzol 5 oz 7-17-2013 Ground (FS) Quadris Top 14 oz + ProPhyt 1.5 qt 7-23-2013 Ground (FS) Elast 50 oz + Supertin 6.5 oz 7-27-2013 Aerial (FS) Supertin 12 oz 7-30-2013 Ground (FS) Supertin 12 oz 8-5-2013 Ground (FS) Elast 50 oz 8-12-2013 Ground (FS) Supertin 12 oz 8-21-2013 Ground (FS) Elast 50 oz 8-29-2013 Ground (FS) Supertin 12 oz

Not hedged (control) One side hedged Both sides hedged 45 ft 60 ft 45 ft 60 ft 45 ft

DE C B E D B * D C C A 10 20 30 40 50 60

% leaflets with scab

Hedging experiment - trees 18 m (60 ft), Valdosta, GA

26 Sep 2013

Percent leaflets scabbed

Treatment × Height, m F=3.8, P=0.002

• Up to 14 m more leaflets scabbed on the double hedged compared to the non-hedged

treatment, but one-side hedged not different to either other treatments

• In Sept, including all heights >14 m there was no difference among treatments on foliage
• Height had a highly significant effect on disease

Not hedged Hedged (both sides) Hedged (one side)

<23, 23-33, 33-46, >46 ft <23, 23-33, 33-46, >46 ft <23, 23-33, >33 ft

Solid bars = only heights <14 m (3 hts), Downward diagonal bars = all heights (4 hts) For three heights (<14 m), F=2.1, P=0.1, For all heights, F=1.46, P=0.2

A AB B L L L 5 10 15 20 25 30 35

Hedged (both sides) One side hedged (cut) Not hedged % leaflets with scab

A AB B 5 10 15 20 25

Hedged (both sides) One side hedged (cut) Not hedged % leaflets with scab

26 Jul 2013 Only 3 heights assessed 4 heights assessed

Treatment F=3.8, P=0.02 C B A 5 10 15 20 25 30

<7 7 to 10 10 to 14 % leaflets with scab

Height, m F=32.6, P<0.0001

<23, 23-33, >33 ft Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α=0.05). 95% Confidence Intervals are indicated. * = non-estimable

A AB B 2 4 6 8

Hedged (both sides) One side hedged Not hedged % fruit area scabbed

Valdosta Desirable Three treatments

• 1. Not hedged (control)
• 2. One side hedged
• 3. Both sides hedged

Hedging experiment - trees 18 m (60 ft), Valdosta, GA

CD CD B CD C B D CD A 5 10 15

% fruit area scabbed

Treatment

Scab severity on fruit, 26 July 2013 (3 heights only)

Treatment × Height F=2.4, P=0.09 F=2.4, P=0.05

• Only heights up to 14 m (45 ft) sampled in July 2013
• No significant difference between hedged and not-

hedged (1-side hedged significantly lower)

• There was a Treatment × Height interaction with

more disease at greater heights

Not hedged Hedged (both sides) Hedged (one side)

<23, 23-33, >33ft <23, 23-33, >33ft <23, 23-33, >33ft Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α=0.05). 95% Confidence Intervals are indicated.

G D B G F C * G E B A 20 40 60 80 100

% fruit area scabbed

Scab severity on fruit, 26 September 2013 (up to 4 heights)

• All heights up to 18 m (60 ft) sampled in September 2013
• No significant difference between hedged and not-

hedged (1-side hedged significantly lower)

• There was a Treatment × Height interaction with more

disease at greater heights

Hedging experiment - trees 18 m (60 ft), Valdosta, GA

Not hedged Hedged (both sides) Hedged (one side)

Valdosta Desirable Three treatments

• 1. Not hedged (control)
• 2. One side hedged
• 3. Both sides hedged

Treatment × Height

F=3.1, P=0.009

Treatment

<23, 23-33, >33 ft <23, 23-33, 33-46, >46 ft <23, 23-33, 33-46, >46 ft * = non-estimable For three heights (<14 m), F=5.7, P=0.003 For all heights, F=6.2, P=0.002 Solid bars = only heights <14 m (46 ft) Downward diagonal bars = all heights

A B A L L M 10 20 30 40 50 60

Hedged (both sides) One side hedged Not hedged % fruit area scabbed

Data analyzed using general linear modeling. Letters indicate significant differences based on t-grouping (α=0.05). 95% Confidence Intervals are indicated.

Thus the amount of crop born above 14 m (46 ft) is going to have a dramatic effect on yield when (or where) disease pressure is high….

• Distribution of fruit on a mature tree

has been characterized (Lozano-Gonzalez et

• al. 1992. Three-dimensional characterization of bearing

pecan tree. HortScience 27: 1181-3)

• How might fruit be distributed in a

hedged tree?

• In tall, non-hedged trees more

than 50% of the crop can be above the level of effective scab control

• In hedged trees, a greater

proportion of the crop can be reached by a ground-based application

5 10 15 20 25 30 5 10 15 20 25 Proportion of yield (%) Height (m) Tree hedged to ~12 m (~40 ft) Tree not hedged ~22 m (~70 ft)

(16 ft) (33 ft) (49 ft) (65 ft) (82 ft)

Summary

• There were some slight, inconsistent effects of hedging
• n scab, but hedging does not results in more scab when

trees receive equal disease control measures

• This is true despite exposure of susceptible foliage for a

prolonged period

• Thus in trees of about the same height there was no

effect of hedging on scab severity on fruit in year one of hedging

• In trees >45 ft there was an increasing advantage to

hedging as more of the fruit are beyond the reach of effective fungicide application

• Declining spray coverage with height leads to poor scab

control (selection for fungicide resistance)

• These data were collected during an extreme scab year;

in average or mild epidemic years the comparison between treatments may be even closer. We need to study this

40-45 ft 60+ ft

We thank the GA Pecan Commodity Commission for financial support to aid the research Also our thanks to Buck Paulk, Mike Jaros and Richard Merritt for allowing us access to their orchards, and for use of lift equipment to sample the trees Tom Stevenson, Orchard Management Services, LLC, for some of the images We also thank Wanda Evans, Shirley Anderson and Jacob Werner at the USDA-ARS, and John Bentley at Merritt Pecan Co.

Acknowledgements

The numbers sampled and assessed Leaflets Fruit valves (fruit) 64,350 19,800 (4,950)

Thank you, and any questions?