Pecan scab managementClive Bock, USDA-ARS-SEFTNRL, Byron, GA

Structure of presentation Describe the disease and pathogen Major considerations to manage pecan scab

Cultivars Air-blast sprayers and sprayer set-up Spraying options (volutes, aerial) Tree size (tree management/mechanical hedge-pruning/spacing) Timing of sprays (pre or post pollination) Chemistry (conventional and organic)

2/3

1/3

Upper half of canopy

Lower half of canopy

Pecan scab (Venturia effusa)Lifecycle of Venturia effusa, cause of pecan scab

Autumn

Winter

Summer

Spring

Fungus becomes dormant as stroma and

overwintering conidia (twigs and shucks)

Epidemics build up on

young leaves (conidia)

Overwinters as stroma and conidia

Epidemics build up on

fruit (conidia)

Polycyclic disease (rain and wind)

The sexual stage of this fungus has been identified (Drs. Young and Charlton, Noble Research Institute).

The role of the spores produced by the sexual stage are unknown but may play an important role in disease development.

Fungicide applications to

control scab

Late August to early September

Mid-late April

Cultivars, tree size, and appropriate equipment

If planting new in the southeastern region endeavor to obtain scab resistant cultivars (Excel, Elliott, Avalon,….). Availability?

Susceptible cultivars will require fungicide sprays in most or all seasons/locations (and they are very widely grown)

It is possible to spray small trees with less powerful sprayers (<25-30 ft)

Once tree height exceeds ~25 ft, a full sized orchard sprayer is a necessity

Sprayer set-up and coverage

Sumner, P.E. 2004. Experiences with Pecan Air Blast Sprayers. Presented at The 2004 American Society of Agricultural Engineers/Canadian Society of Agricultural Engineers Annual International Meeting, Fairmont Chateau Laurier, The Westin, Government Centre, Ottawa, Ontario, Canada, 1 - 4 August 2004.

⅔ to ¾ of spray directed to upper ½ of the canopy Adjust the vanes/sprayer nozzles accordingly Even with perfectly adjusted vanes, the velocity of

the air declines with distance from the sprayer Volume can be determined based on tree size Sprayer calibration

Adapted from Sumner (2004)

2/3

1/3

Small to medium height trees (<40 ft)

= nozzle

Upper 10 nozzles: 2 x D7-45, 4 x D6-45 , 4 x D5-45Lower 7 nozzles: 4 x D5-45, 2 x D4-45, 1 x D3-45

88 GPA @ 1.5 mph for a 60 ft spacing

Upper half of canopy

Lower half of canopy

3/4

1/4

Mature, tall trees (>40 ft)

Upper half of canopy

Lower half of canopy

Upper 12 nozzles: 2 x D7-45, 6 x D6-45, 4 x D5-45Lower 6 nozzles: 2 x D5-45, 2 x D4-45, 2 x D3-45

93 GPA @ 1.5 mph for a 60 ft spacing

A

A

ABC

ABC

C

A

AB

ABC

C

BC

0 20 40 60

16

25

33

41

50Outer

Inner

Spray distribution and disease

Bock, C.H., Hotchkiss, M.W., Cottrell, T.E. and Wood, B.W. 2015. The effect of sample height on spray coverage in mature pecan trees. Plant Dis. 99: 916-925.

Height F-value =17.5, P-value = <0.0001Position F-value = 2.2, P-value = 0.2Height × Position F-value = 1.5, P-value = 0.2

Spray coverage declines with tree height

Planting distance/tree structure Air-blast sprayers provide good

protection up to ~40 ft. Protection dependent on season

Range: 0.01-73.5%

Card area sprayed (%)

Hei

ght

in c

ano

py

(ft)

B

B

B

A

0 5 10 15 20 25 30

15

25

40

55

D

C

B

A

0 20 40 60 80 100

15

25

40

55

F-value =63P-value = <0.0001

Hei

ght

in c

ano

py

(ft)

Scab severity (% fruit surface scabbed)

2013

F-value =285 P-value = <0.0001

2014

Bock, C. H., Hotchkiss, M. W., Brenneman, T. B., Stevenson, K. L., Goff, W. D., Smith, M.W., Wells, L., and Wood, B. W. Severity of scab and its effect on fruit weight inmechanically hedge-pruned and topped pecan trees. Plant Disease 101: 785-793. 2017.

15.0 m

12.5 m

10.0 m

7.5 m

5.0 m

Fruit weight with tree height

The nuts will be larger and of higher quality where spray coverage (scab control) is better

Hedge-pruning reduces tree height and ensures more spray reaches the foliage and fruit

The relationship between scab and fruit weight at different heights

y = -0.24x + 41.7R² = 0.09

0

10

20

30

40

50

60

0 20 40 60 80 100

y = -0.20x + 42.3R² = 0.410

10

20

30

40

50

60

0 20 40 60 80 100

y = -0.20x + 42.2R² = 0.40

0

10

20

30

40

50

60

0 20 40 60 80 100

y = -0.34x + 51.2R² = 0.54

0

10

20

30

40

50

60

0 20 40 60 80 100

Results from an experiment in 2013 (a wet, scab

conducive year) in non-hedged trees of cv Desirable

Fru

it w

eigh

t (g

)

Severity per fruit (% area diseased)

<21 ft

21-33 ft

33-46 ft

>46 ft

Bock, C. H., Hotchkiss, M. W., Brenneman, T. B., Stevenson, K. L., Goff, W. D., Smith, M. W., Wells, L., andWood, B. W. Severity of scab and its effect on fruit weight in mechanically hedge-pruned and topped pecantrees. Plant Disease 101: 785-793. 2017.

Tree size - hedging

A

B B

0

10

20

30

40

50

No hedging One sidehedged

Both sideshedged

A

B B

0

2

4

6

8

No hedging One sidehedged

Both sideshedged

F-value =26.6P-value = <0.0001

Scab

sev

erit

y (%

fru

it s

urf

ace

scab

bed

) 2013F-value =6.2P-value = 0.002

2014

Scab

sev

erit

y (%

fru

it s

urf

ace

scab

bed

)

Hedge pruning reduces tree height

More spray reaches the foliage and fruit

Tall, non-hedged trees have significantly more severe scab (and hence yield loss)

A 2 to 4 y cycle of hedging? In regard to scab control, shorter trees will always be better

Hedge-pruning ~60 ft

trees to ~40 ft

Bock, C. H., Hotchkiss, M. W., Brenneman, T. B., Stevenson, K. L., Goff, W. D., Smith, M.W., Wells, L., and Wood, B. W. Severity of scab and its effect on fruit weight inmechanically hedge-pruned and topped pecan trees. Plant Disease 101: 785-793. 2017.

Sprayer set-up - volutes

Increases spray volume going to the upper canopy of tall trees

Do not have much data on the spray coverage or efficacy of volutes applied spray

Sprayed (no volute) Sprayed (with volute)

Demonstration spray results at USDA-ARS-SEFTNRL pecan field day, September 2015. Spray applied using a regular orchard sprayer (no volute) or spray applied using a volute

Aerial application

0

20

40

60

80

5.0 7.5 10.0 12.5 15.0

Control Air-blast Aerial Air-blast+Aerial

0

10

20

30

5.0 7.5 10.0 12.5 15.0

5.0 7.5 10.0 12.5 15.0

Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air

ab e bcde e a e abc e a e de e ab cde de e bcd bcde de e

5.0 7.5 10.0 12.5 15.0

Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air Control Ground Aerial Gnd_Air

a c c c b c c c b c c c b c c c b b c c

The same number/timing of aerial sprays as ground may provides a similar level of control

Both combined minimize disease throughout canopy If limited then apply as many aerial sprays as possible to

complement ground sprays during nut development Economics?

2013

2014

3 September

10 October

6 sprays applied

5 sprays applied

Height (m)

Treatment × heightF = 16.0 (P<0.0001)

Treatment × heightF = 8.7 (P<0.0001)

Ground = 100 GPAAerial = ~10 GPA

Scab

sev

erit

y

(% f

ruit

su

rfac

e sc

abb

ed)

Scab

sev

erit

y

(% f

ruit

su

rfac

e sc

abb

ed)

Bock et al. (unpublished)

Chemistry and timing of sprays (pre/post pollination)

UGA spray guide outlines well the chemistries and timing of sprays available for managing pecan scab

Two periods: Pre pollination (10-14 day intervals) and post pollination (10 to 21 day intervals)

Some fungicides are known to be inherently efficacious on leaf or nut scab

Tin and Elast on fruit (also combinations and Quadris top) Phosphites and other products on foliage Fungicide resistance is an issue and should be considered in

the program

Conventional fungicdes

No. Fungicide group FRAC code

Common name Trade names Risk of resistance

1 MBCs (benzimidazoles) 1 thiophanate-methyl Topsin-M High

2 DMIs (sterol inhibitors) 3 Propiconazole Orbit, Propimax,Bumper, Quilt, Quilt Excel

Medium

Febuconazole Enable

Tebuconazole Folicur, Tebuzole, Monsoon, Orius, Toledo, Absolute

Metaconazole Quash

Difenconazole Quadris Top

3 QoIs (strobilurins) 11 Kresoxim-methyl Sovran Medium-low

Azoxystrobin Abound, Quilt, Quilt Excel, Quadris Top

Pyraclostrobin Headline

Trifloxystrobin Absolute

4 Guanadines U12 Dodine Elast Medium-low

5 Organotins 30 Fentin hydroxide SuperTin Medium-low

AgriTin

6 Phosphites 33 Phosphorous acid Phostrol, ProphytFungiphite, Reliant

Medium-low

7 Ziram M3 Zinc dimethyldithiocarbamate

Ziram Low

Fungicides available to manage pecan scab (GA Pest Management Handbook, http://www.ent.uga.edu/pmh/)

a

ab

cd

d

bc

d

bc

d

d

d

0

2

4

6

8

10

12

0

4

8

12

Control(untreated)

Phosphite TPTH

7-Jul-10

Scab

sev

erit

y (p

erce

nt

area

infe

cted

)

Scab

sev

erit

y (p

erce

nt

area

infe

cted

)Phosphites – updates

0

10

20

30

40

50

60

70

80

90

100Rep 1 Rep 2

y = 17.1x - 4.6R² = 0.95

0

50

100

0 1 2 3 4 5

Fungicide resistance is an issue in scab

Phosphites are efficacious – particularly on foliage

We have demonstrated that higher rates effective on fruit

Worked with the pecan industry to generate data on phosphite usage in light of recent phosphiteMRLs in the EU

MRL ruling in Dec 2017 = 500 ppm

Ph

osp

hit

e(p

pm

)

Spray dates (no. of sprays)

Phosphites are efficacious – fruit and foliage

Higher rates are more efficacious – especially on fruitResidues were an issue 2013-2018 – now resolved

Phosphiteapplied at 3 pt/100 g/acre

Rate of phosphite (in 100 g/acre)

Phosphiteapplied at 3 pt/100 g/acre

Bock CH, Brenneman TB, Hotchkiss MW, Wood BW. 2012. Evaluation of a phosphite fungicide to control pecan scab in the southeastern USA. Crop Protection 36: 58-64.

Organic chemistry to manage scab

aa

a

aa

a

b

b a

a

a

a

b a

0

10

20

30

40

50

60

70

80

2011 2012 2014 2015 2016 2014 2015

Control Bordeaux mixture

Byron, GA Colquitt, GA

Historically Bordeaux mixture (hydrated lime + copper sulfate) was used to manage scab (~1960)

We have tested Bordeaux mixture in multiple trials over several years and at two sites. Number of applications:

Byron, GA 2011 (6), 2012 (5), 2014 (5), 2015 (6) and 2016 (6)

Colquitt, GA 2014 (5) and 2015 (5)

Efficacy is not reliable, and level of control is not particularly impressive

Although some historical reports indicated it could be effective

Scab

sev

erit

y

(% f

ruit

su

rfac

e sc

abb

ed)

Location and year

cv. Stuart (80 y old trees)

Fruit disease assessments: Byron, GA2011 (12 Oct), 2012 (8 Oct), 2014 (18 Aug), 2015 (12 Aug) and 2016 (22 Aug)Colquitt, GA 2014 (20 Aug) and 2015 (1 Sep)

Means within the same year with different letters are significantly different (α = 0.05)

Bock, C.H., Hotchkiss, M.W., Shapiro-Ilan, D.I., Wells, L., Brock, J., Brenneman., and Mizell., R. 2018. Efficacy of Bordeaux mixture in reducing pecan scab in the southeastern USA. Organic Agriculture. https://doi.org/10.1007/s13165-018-0218-x

New organic chemistry?

a

cd cd

bcab

ab

bc

d

0

2

4

6

8

10

12

a aa a

b

a a

b

0

10

20

30

40

50

60

70

80

90

Explored a range of OMRI approved alternatives to Bordeaux mixture

A total of 5 sprays applied in both 2012 and 2014

Assessments made on 19 October 2012 and 18 August 2014

Regalia consistently, and to a lesser extent Serenade reduced severity of pecan scab

Efficacy variable between years with different products (inoculum pressure?)

Scab

sev

erit

y (%

fru

it s

urf

ace

scab

bed

)

Product

Scab

sev

erit

y (%

fru

it s

urf

ace

scab

bed

)

2012 2014

Bock, C.H., Hotchkiss, M.W., Shapiro-Ilan, D.I., Wilkins, B., Wells., D.E., Brock, J., Brenneman., Wells, L., and Mizell., R. 2018. A comparison of organic fungicides: alternatives for reducing scab on pecan. Organic Agriculture. (Accepted)

Summary Scab is a difficult disease to manage

Fortunately there are several angles form which we can approach management of scab

Cultivars (if planting a new orchard select a scab resistant cultivar if possible)

Tree spacing (wider the better to reduce scab)

Tree size (hedge-pruning?)

Chemistry (alternate modes of action). Organic options available

Ground and aerial application (ensure calibrated appropriately)

Acknowledgemnts

Funding:Georgia Commodity Commission for Pecans

USDA-ARS project 6606-21220-011–00D

USDA-National Institute of Food and Agriculture award #2013-51106-21234 (Organic Transitions Program)

Collaborators and technical assistance at the USDA-ARS, Byron :Dr. Mike Hotchkiss, Dr. Bruce Wood (retired), Wanda Evans, Minling Zhang, Unicka Stokes, Sue Burrell, Jason Shipp, Caylee Carson, Sarah Morrel

Collaborators at the University of Georgia, Tifton: Dr. Tim Brenneman, Dr. Lenny Wells, Dr. Katy Stevenson

Thank you

Questions?