Animal and Plant Health Inspection Service

Plant Protection and Quarantine 

United States Department of Agriculture

Pest Alert

United States Department of Agriculture

Ralstonia solanacearum race 3 biovar

2 is a bacterial pathogen that infects

certain vegetables and ornamental

crops, causing brown rot of potato,

bacterial wilt of tomato and eggplant,

and southern wilt of geranium. The

pathogen is not harmful to humans or

animals. It is not known to occur in the

United States.

In April 2020, the U.S. Department

of Agriculture’s (USDA) Animal and

Plant Health Inspection Service

(APHIS) confirmed the detection of

R. solanacearum race 3 biovar 2 in a

U.S. greenhouse that had purchased

geranium cuttings from an offshore

production facility. This is the first

confirmed detection of this pathogen

in a U.S. greenhouse since 2004.

APHIS has successfully eradicated

all previous detections of this

pathogen in U.S. greenhouses.

Symptoms

In geraniums, R. solanacearum race

3 biovar 2 causes a disease called

southern wilt. Look for upwardly

curling leaves, often beginning near

the bottom of the plant. Affected

leaves will become limp, wilted, and

yellowed. In advanced stages of the

disease, the lower stem may become

discolored and browning of roots

can occur. Symptoms of southern

wilt may appear similar to those of

bacterial blight, which is caused

by Xanthomonas campestris pv.

pelargonii; however, bacterial blight

causes leaf spots that are not typical

of R. solanacearum.

In potatoes, R. solanacearum

race 3 biovar 2 causes potato 

brown rot (also known as bacterial 

wilt). Symptoms include wilting, 

stunting, yellowing, upward curling 

of the leaves, and eventually death. 

Symptoms may occur at any stage of 

potato growth. Wilting may be severe 

in young plants of highly susceptible 

varieties. In the early stages of the 

disease, only one leaf or branch of 

a plant may show wilting. But as 

the disease develops rapidly, all 

branches may wilt quickly. Young 

potato plants may develop dark 

narrow streaks on the stem.

Brown rot symptoms may be visible 

in potato tubers in the later stages 

of the disease. A cross section of an 

infected potato may show a graybrown ring that extends into the 

center of the tuber. Infected potatoes 

may ooze a milky-white substance. 

Symptoms in potatoes can be 

confused with bacterial ring rot.

In eggplant and tomato, 

R. solanacearum race 3 biovar 2

causes bacterial wilt. Look for severe

rapid wilting of leaves, particularly

in lower areas of the plant where 

moisture accumulates. Infected 

tomato plants may also have pale 

or yellow leaves. Glistening beads 

of dark gray, slimy ooze may appear 

at cross sections of the stem. When 

stems are cut and placed in water, 

fine, milky white strands will be 

visible to the naked eye. Infected 

plants may not show any symptoms 

for long periods of time.

Transmission

R. solanacearum race 3 biovar

2 is transmitted mainly through

contaminated water, including

shared water systems. It can also

be spread through contaminated

soil and equipment or inadvertently

by people. For example, people can

spread it by propagating infected

plants, taking cuttings without

disinfecting tools between plants,

and pinching buds of infected

plants without sanitizing hands. The

pathogen is not readily spread from

plant-to-plant contact or aerially.

Ralstonia solanacearum race 3 biovar 2

Symptoms of bacterial wilt of tomato caused by Ralstonia solanacearum race 3 biovar 2. 

Photo courtesy of C. Allen, University of Wisconsin.
Management

There is no effective chemical 

control for R. solanacearum race 

3 biovar 2. Prevention is critical.

Geranium growers should start by 

purchasing clean cuttings. They 

should label and separate geranium 

varieties and avoid using subirrigation systems in greenhouses. 

Greenhouse workers should wear 

gloves or wash hands between 

handlings of different varieties and 

use footbaths between houses.

Potato growers should start with 

certified seed potatoes to avoid 

R. solanacearum race 3 biovar 2.

If you suspect R. solanacearum in geranium, potato, tomato, 

pepper, or eggplant, contact your nearest APHIS office or State 

department of agriculture immediately for further instructions. For 

a list of APHIS offices, go to www.aphis.usda.gov/planthealth/sphd.

A directory of State Plant Regulatory Officials is available on the 

National Plant Board website at www.nationalplantboard.org/

membership.

Homeowners and gardeners who recently purchased geraniums

from a retail store, nursery, or greenhouse should monitor the plants

for signs of disease and place any dead or wilting plants, along with

their pots and soil, in a sturdy garbage bag. Do not discard diseased

or dying geraniums or contaminated potting soil in a compost pile.

Instead, place the bagged plants, pots, and soil in a trash can with 

refuse that will ultimately end up in a landfill. 

FOR MORE INFORMATION

Guidance for Homeowners and Gardeners

Symptoms of brown rot of potato caused by 

Ralstonia solanacearum race 3 biovar 2. 

Photo courtesy of P. Champoiseau, University 

of Florida.

APHIS 81-35-036

Issued May 2020 

USDA is an equal opportunity provider, employer, and lender.

Symptoms of southern wilt of geranium caused by Ralstonia solanacearum race 3 biovar 2. 

Photo courtesy of the Wisconsin Department of Agriculture, Trade and Consumer Protection.