Fire Blight in Utah - Utah State Horticultural Association Homepage

Fire Blight in Utah 

What we found in 2006, field trial results, and news on 

Kasumin (kasugamycin) 

Kent Evans - Extension Plant Pathology 

Specialist, Utah State University, Logan 

ckevans@cc.usu.edu - 435-797-2504

An outline of this presentation: 

A brief review of the biology of Erwinia amylovora (Ea), the 

pathogen causing fire blight in apple and pear worldwide. 

A brief review of what we know about antibiotic resistance in 

Ea populations, elsewhere and here in Utah. 

A presentation of the 2006 Kaysville shoot blight experiment. 

Survey results of Ea populations in Utah County and a few 

other places in Utah as reference. 

News about Kasugamycin - Where do we go from here

Significance 

Erwinia amylovora is a native pathogen of wild, rosaceous 

hosts in eastern North America. 

These hosts include hawthorn, serviceberry, and mountain 

ash. Other introduced hosts include cottoneaster, 

pyracantha etc. 

Early European settlers introduced apple and pear to North 

America. 

The first report of fire blight as a disease of apple and pear 

occurred in 1780, in the Hudson Valley of New York. In 

California, the disease was first reported in 1887.

Washington Agricultural Exp. Stn. 

1915, Popular Bulletin No. 80.

Pathogen biology 

Ea is a member of the family 

Enterobacteriacae. 

Cells of Ea are gram-negative, rodshaped, 

measure 0.5-1.0 x 3.0 μm, 

and flagellated on all sides 

(peritrichous). 

Optimum temperature for growth is 27°C (81°F), with cell division 

occurring at temperatures ranging from 5- 31°C (41-88°F). 

Identification of Ea isolates is based on biochemical and serological 

tests, diagnostic culture media, inoculation of immature pear fruits 

and apple seedlings, and DNA hybridization assays.

Disease Cycle

Symptomology

Control of Fire Blight 

Streptomycin 

Oxytetracycline 

Copper 

Growth inhibitors (of apple) 

Biologicals 

Pruning 

Burning

Agricultural Antibiotics 

Mode of Action: Inhibits prokaryote protein 

synthesis. Binds to S12 protein of 30S 

ribosomal subunit, preventing the transition 

from initiation complex to chain-elongating 

ribosome, causing miscoding from DNA or 

inhibiting initiation of protein synthesis. 

C 21 H 39 N 7 O 12 ·1.5H 2 O 4 S 

Streptomycin-sulfate salt 

Streptomyces griseus 

Mode of Resistance: Mutation in rpsL (gene 

for S12 ribosomal protein) prevents binding 

of streptomycin to ribosome. Aminoglycoside 

phosphotransferase also inactivates. 

Streptomycin resistant strains of Ea were first reported in California orchards in 1972. 

Since then, strep-resistance has been widely reported and was first detected in Utah 

by Dr. S. V. Thomson circa 2000-2002().


Mode of Action: Inhibits prokaryote protein 

synthesis. “Messes with tRNA” binding to 

the ribosome thus affecting coding of 

protein syntheses. 

No observed resistance in populations 

of Ea in fruit orchards to date. 

C 22 H 24 N 2 O 9 ·2H 2 O 

Oxytetracycline dihydrate 

Streptomyces rimosus


C 14 H 25 N 3 O 9 · HCl 

Kasugamycin hydrochloride 

Streptomyces kasugaensis 

Mode of Action: prevents the inocrporation 

of amino acids by inhibiting the binding of 

the aminoacyl-tRNA-message complex and 

the ribosome.. protein synthesis inhibitor. 

May cause phytotoxicity of apple and pear 

but some disagreement about this. 

Readily metabolized in bodies of mamallian species.

2006 Kaysville Shoot Blight Experiment 

Null hypotheses (assumptions that might be or 

might not be correct): 

• Antibiotics are no better than water inoculated treatment to 

prevent Ea shoot strikes. 

• Kasugamycin is no better than any of the other agricultural 

antibiotics. 

• If data are not promising.....not a need for further testing. 

• Kasugamycin will cause phytoxicity.


4 apple cultivars 

4 replications 

Inoculated 10 shoots/tree 

using a non-antibiotic resistant Ea 

Assessments ranged from 1-4 

1=no strike 

2> = strike 

Four spray treatments, and control, applied prior to inoculation: 

1. Water inoculated control (no antibiotic) 

2. Kasugamycin-low (Arysta - 80 ppm) 

3. Kasugamycin-high (Arysta - 100 ppm) 

4. Streptomycin (Agri-Mycin - 100 ppm) 

5. Oxytetracycline (Mycoshield -100 ppm)

2006 Kaysville Shoot Blight Experiment





Results: 

Dixie Red was most resistant cultivar. 

Ea infection greatest on water-sprayed 

control. 

Oxytet was significantly better 

controlling shoot strikes in Gala and Ida 

Red, was significantly better than water 

control in all cultivars, and overall trend 

shows it was better than other 

treatments on all cultivars tested. 

Kasugamycin was significantly better than streptomycin controlling shoot strike on Ida Red; 

was significantly (@100 ppm) better than water inoculated control in all Ea-suscept cultivars; 

was equal to or better than strep (100 ppm for both) in all cultivars. 

Control of Ea-shoot strike in Gala and Ida Red, with streptomycin, was no better than water 

(no control).


Conclusions: 

1. No phytotoxicity was observed in any Kasugamycin-treated apples. 

2. 2006 Kasugamycin results demonstrate antibiotic efficacy against Ea 

shoot blight. 

3. Kasugamycin was, at times, better than streptomycin controlling shoot 

strikes. 

4. Bad news: shoot blight is extremely difficult to control effectively. 

5. Data indicates need for further testing in 2007. 

6. 2007 testing to include blossom blight component and repeat shoot strike 

experiment. 

7. 2007 on-farm trial Arysta will provide some compound. Who wants to 

try it What will be measured as variables to indicate efficacy

2006 - Surveyed population of Ea in Utah County and a few 

other places in Utah as reference 

• OBJECTIVES: 

• Evaluate a large number of Ea isolates for reaction to 

streptomycin, oxytetracycline, and Kasugamycin 

• Determine the extent of resistance in any isolate of Ea found to 

be resistant to strep or other antibiotics (if any) 

• Evaluate Ea isolates reaction to Kasugamycin in laboratory 

testing

2006 - Surveyed population of Ea in Utah County and a 

few other places in Utah as reference. 

Over 300 Ea-suspect samples collected. 

Some samples were donated. 

Utah County, Box Elder County, Cache 

County were primarily sampled for Ea. 

Samples were processed in laboratory by 

culturing in nutrient broth. 

About 3000 serial dilutions were made. 

About 1500 cultures were plated on 

nutrient agar medium. 

Individual colonies of bacteria were 

selected and plated on to CCT. 

Ea colonies were selected, serial diluted, 

and subsequently re-inoculated on to 

CCT in order to insure culture identity. 

Erwinia amylovora positive 

NOT - Ea



Each Ea isolate was screened on 3 plates each of (this was 

done twice): 

1. Streptomycin amended nutrient agar (30 and 100 ppm) 

2. Oxytetracyline amended nutrient agar (30 and 100 ppm) 

3. Kasugamycin amended nutrient agar (30 and 100 ppm 

Isolates of Ea found to resistant to streptomycin were 

retested on: 

200 

What do you think 

400 ppm streptomycin amended nutrient agar 

1000} 

we found



• 122 Erwinia amylovora isolates were made from infected apple tissues in 2006 (40.6% 

of samples). 

• 32 Ea isolates were found to resistant to commercial rates of strep (100 ppm). 

• Resistant isolates were found at all commercial sites sampled (uniform distribution). 

32 

26% 

90 

74%



Of the 32 isolates resistant to streptomycin at 100 ppm, 18 of those were resistant at 200 ppm 

and 14 were found to be resistant at 400 ppm (not immune as none were resistant at 1000 ppm). 

None of these isolates were observed to be resistant to Kasugamycin at 100 ppm in 

laboratory screens. 

14 

44% 

18 

56%



Conclusions: 

• High level of streptomycin resistance exists in Erwinia amylovora 

populations in commercial apples in Utah. 

• None of the isolates observed to be resistant to streptomycin were 

found to be resistant to Kasugamycin at 100 ppm in laboratory 

screening. 

• One isolate of Ea was found to be resistant to Kasugamycin at 30 

ppm but the good news is that it was susceptible to streptomycin at 

100 ppm. Resistance to one antibiotic does not automatically 

mean resistance to another antibiotic. Rotation of antibiotics is 

critical to maintain efficacious control of Ea. 

• Evidence suggests a strong need to obtain Section-18 labeling for 

use of Kasugamycin in commercial apples in Utah.

Thanks: 

Kirstin Lindstrom 

Tyler Olsen 

Joshua Pope 

Eric Ripplinger 

Kaysville: 

Thor Lindstrom 

Erin Petrizzo 

Additional thanks: 

•Wayne McBride (IFA-commercial ag-antibiotic donation) 

•Layne Wade (Arysta Life Science - Kasumin donation) 

•Utah State Horticultural Association (funding assistance) 

•Utah Co. apple growers for sample donations 

•Dr. George Sundin, Michigan State University (strep-resistant Ea)

Special Thanks:

Fire Blight in Utah - Utah State Horticultural Association Homepage

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