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Late Blight FungicidesGetting the Most Bang for Your Buck

Jeff Miller

The Disease Triangle

HostPotato &Tomato

PathogenP. infestans

Environment

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Late Blight Disease Cycle

Spores producedunder cool, humidconditions

Cull pile, volunteer, seed

Effect of Irrigation on Tuber Late Blight

Ranger Russet near Bruce, WA, 1999. Russet Burbank near Moses Lake, WA, 1998.

From Johnson, D.A. et al. 2003, Plant Disease 87:977-982.

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Late Blight Management

1. Destroy cull piles and volunteers (tomatoes?)

2. Know your seed – treat with an effective fungicide

3. Scout fields and watch the weather (disease forecasting)

4. Maintain an effective fungicide program until harvest

5. Ensure vines are dead prior to harvest

6. Apply an effective fungicide as a soil barrier

7. Apply a post-harvest phosphite-based fungicide

Disease Forecasting

• Linear discriminant analysis – prediction by June 1• Johnson et al., Phytopathology 86:480-484.

• Logistic regression analysis – prediction by June 1• Henderson et al., Plant Disease 91:951-956.

• Blitecast• Not effective in Pacific Northwest

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Fungicides Effective against Foliar Late Blight

Moderate activity

• Chlorothalonil

• Headline

• Mancozeb/metiram

• Quadris

• Reason

High activity• Curzate/Tanos• Forum• Gavel/Zing!• Omega• Orondis• Previcur• Ranman• Revus Top (Revus)• Ridomil (Bravo, MZ, Cu)• Super Tin• ZamproUse the rate labeled for late blight.

Fungicides NOT Recommended for Foliar Late Blight

Weaker activity

• Copper-based sprays

No activity

• Luna Tranquility

• Endura

Copper does have activity, but it is much weaker than the previously listed fungicides.

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July 30 Aug 6 Aug 13 Aug 20 Aug 27 Sep 3 Sep 10 Sep 17 Foliar Late Blight Severity

-- -- -- -- -- -- -- -- 60 a

Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS 2 bc

Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS 5 b

Bravo Ultrex Reason Reason Reason Reason Bravo UltrexPrevicur

-- -- 2 bc

Bravo Ultrex ReasonPrevicur

ReasonPrevicur

ReasonPrevicur

ReasonPrevicur

Bravo Ultrex -- -- 3 bc

Ranman Headline Ranman Headline Ranman Headline -- -- 3 bc

Ranman Ranman Ranman Ranman Ranman Ranman Ranman Ranman 3 bc

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

3 bc

Equus ManzateSuper Tin

Equus ManzateSuper Tin

Equus ManzateSuper Tin

Equus ManzateSuper Tin

4 bc

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

2 bc

Omega Omega Omega Omega Omega Omega Omega Omega 2 bc

Headline Bravo Ultrex Headline PolyramSuper Tin

PolyramSuper Tin

PolyramSuper Tin

PolyramSuper Tin

2 bc

Headline Bravo Ultrex Headline PolyramAcrobat

PolyramAcrobat

PolyramAcrobat

PolyramAcrobat

1 c

Dithane Dithane Quadris Gavel Quadris Gavel Gavel Gavel 2 bc

Bravo Bravo Quadris Gavel Quadris Gavel Gavel Gavel 1 c

0 10 20 30 40 50 60 70

Untreated 1

Bravo WS

Dithane RS

Bravo/Reason/Previcur

Bravo/Previcur/Reason

Bravo/Reason

Ranman(1)/Headline

Ranman(2)/Headline

Ranman

Ranman(2)/Headline(2)

Champ/Bravo(1)

Champ/Bravo(2)

Equus/Manzate/ST

Equus/Manzate/ST

Equus/Kocide/Manzate/ST

Omega

Headline/Bravo/Polyram/ST

Headline/Bravo/Polyram/Acrobat

Dithane/Quadris/Gavel

Bravo/Quadris/Gavel

Untreated 2

Inoculated late blight trial, Bonners Ferry, ID 2002

Relative AUDPC (0-100)

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July 30 Aug 6 Aug 13 Aug 20 Aug 27 Sep 3 Sep 10 Sep 17 Tuber Blight Incidence

-- -- -- -- -- -- -- -- 2.0

Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS Bravo WS 1.3

Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS Dithane RS 0.6

Bravo Ultrex Reason Reason Reason Reason Bravo UltrexPrevicur

-- -- 0

Bravo Ultrex ReasonPrevicur

ReasonPrevicur

ReasonPrevicur

ReasonPrevicur

Bravo Ultrex -- -- 0

Ranman Headline Ranman Headline Ranman Headline -- -- 0

Ranman Ranman Ranman Ranman Ranman Ranman Ranman Ranman 0.3

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

ChampBravo Ultrex

0.8

Equus ManzateSuper Tin

Equus ManzateSuper Tin

Equus ManzateSuper Tin

Equus ManzateSuper Tin

0

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

EquusKocide

ManzateSuper Tin

0.1

Omega Omega Omega Omega Omega Omega Omega Omega 1.4

Headline Bravo Ultrex Headline PolyramSuper Tin

PolyramSuper Tin

PolyramSuper Tin

PolyramSuper Tin

0.5

Headline Bravo Ultrex Headline PolyramAcrobat

PolyramAcrobat

PolyramAcrobat

PolyramAcrobat

0

Dithane Dithane Quadris Gavel Quadris Gavel Gavel Gavel 0

Bravo Bravo Quadris Gavel Quadris Gavel Gavel Gavel 0.4

0 5 10 15 20

Untreated Control

Ranman+Silwet

Ranman+Silwet+SuperTin

Bravo/Ranman+Silwet

Bravo/Omega/Ranman+Silwet

Reason+Bond/Bravo

Fosphite

Fosphite/Quadris/Dithane

Dithane/Quadris

Dithane

Inoculated late blight trial (US-8), Bonners Ferry, ID 2003

% Foliar Blight Severity

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0 5 10 15 20 25

Untreated Control

Ranman+Silwet

Ranman+Silwet+SuperTin

Bravo/Ranman+Silwet

Bravo/Omega/Ranman+Silwet

Reason+Bond/Bravo

Fosphite

Fosphite/Quadris/Dithane

Dithane/Quadris

Dithane

Inoculated late blight trial (US-8), Bonners Ferry, ID 2003

% Blighted Tubers

What does 2% LB Severity look like?

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Effect of Fungicide Program/Variety on Foliar Blight

0

5

10

15

20

25

30

35

40

45

Ranger Burbank

%La

teB

ligh

tSe

veri

ty

Protectant-7 Premium-7 Protectant-14 Premium-14 UTC

$42 $99 $23 $62Natural infection,US-23

Effect of Fungicide Program/Variety on Tuber Blight

0

0.5

1

1.5

2

2.5

Ranger Burbank

%Tu

ber

sIn

fect

ed

Protectant-7 Premium-7 Protectant-14 Premium-14 UTC

$42 $99 $23 $62Natural infection,US-23

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Influence of Weather on % Disease Control

From 1997 North American Late Blight Fungicide Trial, D. A. Inglis, M. L. Powelson, B. Gunderson, and M. Cappeart

0

10

20

30

40

50

60

70

80

90

100

Mild Moderate Severe

%D

isea

seC

on

tro

l

Soil-Applied Fungicides for Late BlightL.D. Porter, et al., Plant Disease 90:964-968

0

10

20

30

40

50

60

70

80

90

100

Water Kocide Bravo WS Super Tin Curzate Polyram +ST

Polyram Penncozeb

%Tu

ber

sIn

fect

ed

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Soil-Applied Fungicides for Late BlightL.D. Porter, et al., Plant Disease 90:964-968

0

10

20

30

40

50

60

70

80

90

100

Water Kocide Bravo WS Super Tin Curzate Polyram +ST

Polyram Penncozeb

%Tu

ber

sIn

fect

ed

How Important is Fungicide Timing?

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Late July, before rain stormLate July, after rain storm

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Ranger Russet, 14-day schedule Russet Burbank, no fungicide

Photo courtesy of Dr. Dennis Johnson

Fungicide applications mayneed to continue until allgreen material is gone.

Sporulating lesions found after sulfuric acid application

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Effect of Application Method on Residues

0

5

10

15

20

25

30

35

40

45

50

12-Jul 19-Jul 26-Jul 2-Aug 9-Aug

0

5

10

15

20

25

30

35

40

45

50

12-Jul 19-Jul 26-Jul 2-Aug 9-Aug0

5

10

15

20

25

30

35

40

45

50

12-Jul 19-Jul 26-Jul 2-Aug 9-Aug

ChemigationAerial

Top Leaves Lower Leaves Stems

Application Method – Stem Residues

0

0.2

0.4

0.6

0.8

1

1.2

1.4

12-Jul 19-Jul 26-Jul 2-Aug 9-Aug

ug

Mn/g

leaf

tiss

ue

Chemigation

Aerial

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Post-Harvest Fungicides for Tuber Late Blight Control

0

20

40

60

80

100

0 1 2 4 6

%Tu

ber

sIn

fect

ed

Hours from Inoculation to Treatment

UntreatedHPPAPA

HPPA = Hydrogen peroxide/peroxyacetic acid (Oxidate)PA = phosphorous acid (Phostrol)