Management of fire blight

Virginia Stockwell

Department Botany and Plant Pathology

Oregon State University

Corvallis, Oregon USA

OUTLINE

Cultural practices and host resistance

Reducing bacterial inoculum

Preventatives

Chemicals

Biological

Cultural practices affecting development of fire blight

Fertility

High levels of nitrogen stimulate growth of young succulent shoots susceptible to shoot blight.

Tree density

Plant resistance

Apple cultivars Most Resistant

Delicious

Liberty

Quinte

Winesap

Susceptible

Golden Delicious

Fuji

Gala

Jonagold

Rome Beauty

Rootstock:

M9

M26

Mark

Rootstock:

Geneva series

M7

Resistant cultivars will provide long term protection from fire

blight

Reduce bacterial inoculum

Exclusion

Clean nursery stock

Eradication

Dormant copper sprays

SANITATION!!!! REMOVE DISEASED BRANCHES!

Preventatives

Disease cycle: Fire blight

Focus on managing blossom blight phase

Blossom blight causes most severe damage

Infected blossom clusters provides inoculum for summer disease cycles (secondary bloom blight, shoot blight, fruit blight)

AND—pathogen is growing on surface of plant before infection and exposed to preventatives

Preventatives

Copper

Dormant treatment to kill over wintering cells in

and near cankers

Bloom sprays

May russet fruit surface and mark leaves

Efficacy is low

Preventatives

Streptomycin, gentamicin, oxytetracycline, and oxolinic acid (Antibiotics)

Effective! Suppress growth of pathogen on the surfaces of plants

Generally are not phytotoxic

Activity of antibiotics for control of fire blight over time

Data from: Vanneste 1996. Biocontrol News Inform. 17:67N-78N &

Shtienberg et al. 2001 Phytoparasitica 29:143-154

0

20

40

60

80

100

0 1 2 3 4 5

Days from treatment to inoculation

Pe

rce

nt

dis

ea

se

co

ntr

ol

Oxolinic acid 300g/ml

Streptomycin 100g/ml

Preventatives

Streptomycin, gentamicin, oxytetracycline, and oxolinic acid (Antibiotics)

Effective! Suppress growth of pathogen on the surfaces of plants

Generally are not phytotoxic

Limitations

Resistance may develop

Registration issues over use of human medicines on plants

Antibiotic resistance management

Minimize number of antibiotic applications

Antibiotics are effective only before symptoms are visible: When the pathogen is on the surface of flowers or on fresh wounds on shoots or leaves.

Antibiotic resistance management

Combine or alternate antibiotic sprays

Growth of streptomycin-resistant Erwinia amylovora is inhibited by oxytetracycline.

Effect of antibiotics on growth Erwinia amylovora on blossoms

McManus & Jones, 1994. Phytopathology 84:627-633

Antibiotic resistance management

Combine or alternate antibiotic sprays with biological control agents

Biological control agents are equally effective against antibiotic resistant and antibiotic sensitive strains of Erwinia amylovora.

Biological control of fire blight

The fire blight pathogen grows on floral stigmas to populations of 106 to 107

cells per flower

stigma

The stigma is not selective, meaning that other,

nonpathogenic bacteria also can grow on its surface

Biological control

Current products in US

Serenade—AgraQuest

Bacillus spp. sprayed during and after bloom.

Provided significant control of fire blight in some field trials

Biological control

Current products in US

BlightBan A506—NuFarm Americas

Beneficial bacterium called Pseudomonas fluorescens A506

In registration pipeline:

BlightBan C9-1—NuFarm Americas

Bloomtime—Northwest Agricultural Products

Beneficial bacteria called Pantoea agglomerans

BlightBan A506

Bacterium found on a pear tree in California

Dr. Steven Lindow (UC Berkeley) found that the bacterium grows very well on apple and pear flowers

Populations of A506 on pear blossom

tissues

3

4

5

6

7

0 50 100 150

Time after inoculation (h)

3

4

5

6

7

0 50 100 150

Time after inoculation (h)

Data from: Wilson and Lindow, 1993, Phytopathology

Log (

CF

U/t

issu

e)

Pistil Nectary

BlightBan A506

BlightBan A506 blocks the fire blight pathogen from growing to high populations on stigmas, which reduces disease

BlightBan A506 can be combined with streptomycin

BlightBan A506 may also reduce some types of fruit russett and light frost damage

Timing of biological sprays

Spray biological control agents BEFORE the pathogen is growing on flowers (mid-bloom, full-bloom, and at petal fall)

And when orchard temperatures are warm to support growth of biologicals

Warm weather (>12°C) is important for growth of

biological control bacteria on open flowers

Mean populations of A506 on pear and apple blossoms

7

10

13

16

19

Me

an

da

ily t

em

p. (C

)

0

5

10

15

Rain

fall (

mm

)

3

4

5

6

7

Lo

g C

FU

pe

r b

los

so

m

1999 1998

Incidence of fire blight on Golden Delicious Apple in Corvallis, Oregon in 1995

0

10

20

30

40

50

Dis

ease I

ncid

en

ce

Water

A

Streptomycin

C

A506

B

Oxytetra-

cycline

B

Improving biological control

Three methods

Combining biological control with antibiotics

Adding an iron-chelate to BlightBan A506

Combining BlightBan A506 with another bacterium BlightBan C9-1

Disease control with BlightBan A506 combined with streptomycin in 1998

0

50

100

150

200

250

300

350

Avera

ge s

trik

es p

er

tree

A

B

D C

C

Combining BlightBan A506 with an iron chelate

A506 makes an antibiotic when iron is abundant

E. amylovora

A506 on iron-rich medium

Testing FeEDDHA (Sequestrene 138) on plants

FeEDDHA (Sequestrene 138) is non-toxic to plants

WATER FeEDDHA Metalosate-Fe

Fire blight control with BlightBanA506 & FeEDDHA on pear and apple

0

0.2

0.4

0.6

0.8

1

Rela

tive d

isease

inc

ide

nc

e

Water FeEDDHA oxyTet A506 A506 & FeEDDHA

Strep

A

C

B

D D

AB

Combination of biological control agents

Pseudomonas fluorescens A506 (Blightban A506) and the biocontrol agent Pantoea agglomerans C9-1 grow well together on flowers

A combination of biological control agents has provided

excellent control of fire blight in repeated field trials

Inoculated OSU Fire Blight Trials: Relative Incidence of Blossom Blight

0 20 40 60 80 100 120

A506

C9-1

A506 & C9-1 &

FeEDDHA-

A506 +

FeEDDHA

0 20 40 60 80 100

n = 8

n = 19

n = 16

n = 23

Oxytet

n = 12

Water

n = 29 Strep

n = 29

n = 7

A506 & C9-1

Summary

Resistant cultivars will be best long-term solution to fire blight

Sanitation is an essential tool for disease control

Antibiotics are good preventatives, but resistance must be managed

Biological controls have promising activity