• TABLE OF CONTENTS
HIDE
 History and host range
 The pathogen
 Sources of inoculum and soil...
 Symptoms and growth of the bacterium...
 Control
 Figures 1-14






Group Title: Circular - Florida Cooperative Extension Service - 1207
Title: Bacterial wilt of row crops in Florida
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00014480/00001
 Material Information
Title: Bacterial wilt of row crops in Florida
Series Title: Circular
Physical Description: 9 p. : col. ill. ; 28 cm.
Language: English
Creator: Kucharek, Tom, 1939-
Florida Cooperative Extension Service
Publisher: University of Florida, Institute of Food and Agricultural Sciences, Florida Cooperative Extension Service
Place of Publication: Gainesville
Publication Date: 1998
 Subjects
Subject: Bacterial wilt diseases -- Prevention -- Florida   ( lcsh )
Agricultural pests -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Tom Kucharek.
General Note: Caption title.
General Note: "Printed August 1998"--Colophon.
Funding: Circular (Florida Cooperative Extension Service) ;
 Record Information
Bibliographic ID: UF00014480
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 002438388
oclc - 40802111
notis - AME3571

Table of Contents
    History and host range
        Page 1
    The pathogen
        Page 2
    Sources of inoculum and soil survival
        Page 3
    Symptoms and growth of the bacterium in the plant
        Page 4
    Control
        Page 5
        Page 6
    Figures 1-14
        Page 7
        Page 8
        Page 9
Full Text
/o/

f1 UNIVERSITY OF
420 FLORIDA

Cooperative Extension Service
Institute of Food and Agricultural Sciences



Bacterial Wilt of Row Crops in Florida'


Tom Kucharek2


History and Host Range

Bacterial wilt was first identified in Mississippi in
tomato and potato in the early 1890's and in tomato in
Florida in 1897. However, this disorder was well known
by growers around the world several hundred years prior
to its formal identification. In Florida, bacterial wilt
(BW) of solanaceous crops occurs commonly in tomato
and potato and it has occurred occasionally in tobacco and
eggplant. For example, only one major case of BW in
tobacco has occurred in Florida in the past 28 years
(Union County). Nearly 50 years ago a severe case of BW
occurred in shade tobacco in Gadsden County. In other
locations around the world, BW occurs commonly in
tobacco. For example, BW is a major disease of flue-cured
tobacco in North Carolina and South Carolina. Bacterial
wilt became so severe in tobacco in Granville County,
North Carolina from 1920 to1940 that hundreds of farm
families sold their farms and moved elsewhere. Bacterial
wilt is commonly called brown rot in potato and Granville
wilt in tobacco. In recent years in Florida, BW of
eggplant has been identified occasionally in Alachua
county in gardens and once in a commercial field in
Gadsden County. However, BW was reported in 1940 to
be a severe problem in eggplant in northeast Florida.

For the past 30 to 40 years, BW has not been a
problem at all in pepper in Florida. Pepper is generally
considered to be less susceptible than the aforementioned
crops in the plant family, solanaceae. However, BW can
occur in pepper when artificially inoculated. Also, prior to


1940 BW was a severe problem in pepper that was
planted following potato in northeast Florida. The only
other row crop known in Florida to have sustained damage
from BW is sunflower. Bacterial wilt was one of several
problems with pests and production that prevented a
fledgling sunflower industry from growing in north Florida
in the mid 1970's.

It is not possible to provide an exact host range for the
bacterium causing BW because of the extreme variation in
pathogenicity within this bacterial species and the
variation in susceptibility of numerous plant species and
their respective commercial varieties to this bacterium.
More than 200 plant species in at least 34 plant families in
different locations around the world have been associated
with BW from natural infection or from experimental
inoculations. Some of the notable crop species, in
addition to those mentioned previously, that sustain
natural damage from BW in the world include: peanut,
banana (moko disease), plantain, marigold,
chrysanthemum, nasturtiums, dahlia, Gerbera daisy,
impatiens, lantana, Pothos, brown Indian hemp, ginger,
and sesame.

Interestingly, BW is a severe problem in peanut in
Africa, China, Indonesia, and Vietnam but it is not a
problem in peanut in the United States. Several reports in
the first half of the 20th century indicate that BW was a
fairly common disease in peanut in some southeastern
states in the U.S. If BW was a problem back then, one
might hypothesize that it's contemporary absence is
related to the different varieties planted in the two different


1. This document is Cir 1207, one of a series of the Department of Plant Pathology, Florida Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida. Published: August 1998. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu.
2. Tom Kucharek, Professor, Department of Plant Pathology, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida,
Gainesville, 32611.
le Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational
formation and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.
>r information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative
pensionn Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Waddill, Dean


UNIVeSUW1 1 r rL'AuALUA LI.aOVKKiLS


Cir 1207


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UNIVERSITY OF FLORIDA

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3 1262 07009 5939 'rops in Florida


eras. However, it is questionable that BW was even an
/7 6 uncommon problem in peanut back then because not one
case of BW has been seen in peanut in Florida and some
I 0 '7 other peanut producing states for at least the past 40 years.

SCIENCE Some of the notable weeds that have been infected
LULRARlith this bacterium are: black nightshade, cutleaf ground
cherry, common ragweed, Spanish needles, horseweed,
cocklebur, and Jimson weed. In Florida, it has not been
determined how important the aforementioned weeds or
other possible weed hosts are in relation to sustaining
populations of this bacterium. Another factor that adds to
the possible sources of inocula for this bacterium is that
many plant species, including some grass species, can
maintain populations of P. solanacearum in their root
systems without causing symptoms.

The Pathogen

The bacterium causing BW is called Ralstonia
solanacearum. Prior synonyms include Burkholderia
solanacearum, Pseudomonas solanacearum,
Xanthomonas solanacearum, Phytomonas
solanacearum, Bacterium solanacearum, and Bacillus
solanacearum. This bacterium is capable of producing
billions of microscopic cells in one plant. Each bacterial
cell is about 1/37,500" long and 1/12,250" wide.
Multiplication occurs by each cell dividing to make two
new cells. The interval between each cell division is about
one hour. Thus, from one cell, about eight million cells
may be formed in 24 hours. Each cell has one or more tails
flagellaa) that assist with movement within water. In mass,
these cells form a whitish slime or colony.

Because of variation among the numerous strains of
this bacterium, the optimum temperature for multiplication
(growth) ranges between 81 and 980 F (27-370 C).
Maximum temperature for growth ranges from 95 to 1060
F (35-41 C) and minimum temperature for growth
ranges from 47 to 650 F (8-18 C). BW is generally
considered to be a warm to hot weather disease. In the
United States, bacterial wilt rarely occurs in the field
above a latitude equivalent to Virginia because R.
solanacearum has a high temperature requirement for
growth. Bacterial wilt typically occurs in the tropical and
the warm temperate regions in the world. In the United
States, BW is found commonly in the southeastern states
where the climate and soil has extended moist and warm
periods. The importance of warm soils for the
development of BW is indicated by the reduction of BW
from 93%, when tomatoes were planted in the Ft Pierce
area in 1978 during the last week in September, to 17%,
when the tomatoes were planted during the second week in
November.


Even though R. solanacearum survives and multiples
at warm temperatures, it can be reduced if the soil
temperature gets too hot. In locations where many clear
days occur, such as in Israel, BW and other diseases have
been reduced by allowing clear plastic to remain on the
soil and heating the soil to thermal death points for the
pathogens involved. This practice is called soil
solarization. It has been used in Florida experimentally
and on a limited basis in commercial settings for
suppression of BW in tomatoes in north Florida.
Combining soil solarization with soil fumigation is more
effective for suppressing BW. Remembering that R.
solanacearum can exist deep in the soil, it is not
surprising that soil solarization is only partially effective.
Soil solarization is highly effective for suppressing pest
population in the upper few inches of soil, but it becomes
progressively less effective at greater depths in the soil.
For example, in one situation in Florida, soil solarization
with clear plastic heated the soil at the two- inch depth to
1100 F for 69 hours but at a 10-inch depth the soil never
exceeded 1050 F. Similarly, at a common point in time,
the temperature in solarized soil at a two- inch depth
exceeded 1200 F where immediately below at a 10-inch
depth, the soil temperature was 1040 F.

Bacterial wilt has been introduced via transplants to
northern states, but typically it does not survive at high
enough levels outdoors in the cold soils to cause disease.
One known exception to that is when it overwintered and
caused disease in tomatoes in New Jersey in 1940 after
being introduced in tomato transplants imported from
Georgia. Bacterial wilt has not been found west of New
Mexico. It has been found on all the continents except
Antarctica and many tropical islands including those in the
Caribbean Basin. Occasionally, BW has been found in
potato in colder climates such as in Sweden and the
Netherlands and at higher altitudes in Costa Rica,
Columbia, Peru, and Sri Lanka because a certain "potato
strain" is adaptive to cooler climates. Conceivably, this
bacterium could survive in northern climates within
greenhouses, hotbeds or cold frames.

One of the most confusing aspects of this disease is its
variability with respect to infection of different plant
species in different locations. As mentioned above,
bacterial wilt is a major problem in tobacco in the North
and South Carolina but not in Florida in fields known to
be infested with the bacterium. Similarly, peanuts do not
sustain any damage from BW in Florida, but tomatoes
grown in the same fields may be totally destroyed by BW.
One possible explanation for such phenomena is the
existence of groups, strains, races, biovars, pathovars, and
divisions of R. solanacearum. While these classification
schemes may be helpful in some instances, common


September 1998


Page 2







Batra-ito o rp inFoiaPn


agreement among scientists does not exist for their use in a
dependable manner. The reader should remember that all
aspects (e.g. soil survival, pathogenicity, host range,
symptom expression, etc.) of BW are influenced
differentially by the various strains of this bacterium

Sources of Inoculum and Soil Survival

The most common source of inoculum for BW in
Florida is within the soil. Bacterial wilt has occurred in
fields in Florida that had never been planted to a crop and
contained only native vegetation. This bacterium can
survive in association with old crop debris or live in plant
tissues deep in the soil. In general, R. solanacearum
survives best in the upper 12 inches of soil, but it has been
found 30 inches deep. Because of the depth of survival of
this bacterium and other factors, attempts to suppress BW
with preplant soil fumigation or soil solarization have
typically resulted in moderate and short term suppression
of this disease.

While it is commonly indicated that the bacterium is
capable of surviving in "the soil," for long periods of time
(years, decades), it has been shown that over a 20 week
period, the bacterium progressively declines in population
in some soil unless the roots of host weeds or crops are
present. When roots of susceptible or even some non-host
plant species (e.g. corn, soybean, bean, green pea, &
sorghum) are present, this bacterium can survive, multiply
to low levels, and maintain enough of a population to
cause disease in a known susceptible crop such as tomato.
Similarly, because of the apparently high number of weeds
that can maintain populations of R. solanacearum, less
BW occurs sometimes following corn rather than weed
fallow. Some have professed that maintaining a field free
of plants of any kind for one season helps in minimizing
BW. Although rotation with non-host crops maintains
populations of this bacterium at low levels, such a rotation
has an overall affect of reducing populations of this
bacterium over time when compared to the continual
cropping of susceptible crops such as tomato. Similarly,
rotation with eggplant will maintain populations of the
bacterium even though eggplant is typically not as
susceptible as tomato. Resistant varieties of tomato may
not express symptoms of BW but they too can act as
carriers of the pathogen. Rice does not maintain
populations of this bacterium and has been found to be a
crop which helps to significantly reduce, not eliminate,
BW when used in crop rotation schemes. Granville wilt in
tobacco has been reduced significantly with rotations
including fescue when compared to continual growing of
tobacco.


Soil factors influence survival of this bacterium. In
Florida, BW occurs throughout the state with the
exception of the soil with high pH (7.2 to 8.4) around
Homestead in Dade County. Attempts to lime soils to
higher pH's has led to slight suppression of BW possibly
because the lime was not mixed in the deeper portions of
the soil. In general, soils that are commonly warm,
frequently wetted, and with moderate pH will support
populations ofR. solanacearum. To exemplify the degree
of difficulty in attempts to suppress BW by adjusting soil
pH, large volumes of sulfur (800-1200 Ibs/acre) were
added to the soil in June to drop the pH to near 4.0 at
which point, this bacterium does not survive well.
Because this pH is too low to grow eggplant, tomato, and
potato, the pH was raised to the original level prior to
planting by adding 2000 lb of lime per acre in January.
This is not done in contemporary times because of the
intense logistical problems and cost.

Some soils suppress this bacterium and are referred to
as "suppressive soils." The nature of these suppressive
soils is not clearly understood, but they are thought to
possess bacterial and actinomycotic antagonists to this
bacterium. It is not uncommon to see BW commonly at a
site year after year but not at a nearby site even when the
bacterium is introduced into the latter site. Soils that are
commonly dry, such as in the southwestern United States
are not conducive for the survival ofR. solanacearum.

Another source of inoculum is transplants infected
with the bacterium. The transplants may not be
expressing symptoms at the time of being produced or
during transport. Because of the common occurrence of
BW in the southeastern U.S., seed is not generally
considered to be a major source, if at all, of R.
solanacearum. However, seed transmission of R.
solanacearum has been reported for peanut and tomato in
Asia and India. It is likely that infested soil adhering to
seed could provide a mechanism for transmission. Seed
pieces of potato or other clonally propagated material,
such as ginger rhizomes, provide sites for the bacterium to
exist while being transported. Field equipment (e.g.
tractors, implements, hand tools, irrigation equipment,
etc.) and pond water that are contaminated with soil from
infested sites can be sources of inoculum.

This bacterium can be transported within a field or
greenhouse or between sites with contaminated hands,
tools and any other object that comes into contact with the
bacterium. Such can happen during pruning and tying of
tomatoes, suckering and topping of tobacco or root
pruning from cultivation. Clipping and mowing plants
such as tomato or tobacco is an effective method of
transmitting pathogens including R. solanacearum.


September 1998


Bacterial Wilt of Row Crops in Florida


Page 3







Bacteria Wilt of Row CroDs in Florida.


Damage to roots from nematodes has increased the
incidence of BW. Although wounding from nematodes
and root damage can increase BW, the bacterium can
infect roots without such damage. Roots are naturally
damaged as they grow through the soil and as new
emerging roots from older roots cause tears in the root
tissue which provide avenues for bacterial ingress into the
plant. Thus, the bacteria associated with one infected plant
can spread to nearby plants and enter into a healthy root
system that contains natural wounds. If running water is
present such as after a flooding event or in a hydroponic
system, the bacterium can move longer distances quickly
and ingress into more distant plants.

Besides causing disease inside the plant, this
bacterium has an "exterior" phase (epiphyte) where it can
reside on the outside of the plant. Wounding infected
plants is one way of allowing the bacterium to exude from
the inside to the outside of the plant. The bacterium can
occur at high populations on the soil near infected plants.
From these sources, the bacterium may be splashed with
rain or irrigation. This bacterium has survived for 15 days
outside of the plant when the relative humidity was in
excess of 95%. It does not survive for long periods of
time outside of the plant when exposed to hot and dry
conditions, especially when sunlight is intense.
Conceivably, insects could be attracted to bacterial slime
produced on plants or soil and then carry the bacterium to
other locations. This has been shown to be an important
means of dissemination in banana. Occasionally, R.
solanacearum infects leaves; such infections occur when
the bacteria enter into wounds or stomates (breathing
pores in leaves and stems).

Symptoms and Growth of the
Bacterium in the Plant

After entering into a susceptible plant, R.
solanacearum, multiplies in soft, non-vascular tissues
first. Usually infection occurs in the roots, but infections
in stems or leaves are possible. Through enzymatic
activity, the bacterium causes cells within the soft tissues
of the plant to bulge and grow into nearby hard vascular
cells (tube-like cells that transport water) causing plugs
(tyloses) that serve to interfere with water transport from
the roots to the upper potions of the plant. As the
infection progresses, more vascular tissue is plugged by
the tyloses, polysaccharides (complex sugars), and other
products produced by limited enzymatic activity from the
bacterium. The bacteria, themselves, become so numerous
that they add to the plugging significantly and
progressively more plant wilting occurs. Such vascular
plugging becomes strongly evident in susceptible plants


such as tomato and tobacco as the vascular tissue turns
yellow to yellow brown and later reddish-brown. The
discoloration appears as dark linear streaks when the
stems are cut lengthwise. (Figures 1, 2, 3, and 4). The
entire infection process from the time of bacterial ingress
into the root until the bacteria multiply in the vascular
tissue is progressively faster with increasing rates of soil
moisture. For example, in one test it required 72 hours for
the bacteria to abound in the vascular tissue of plants
grown in dry soil compared to 20 hours when grown in
wet soil.

In addition to vascular discoloration, soft tissues such
as the pith in the center of stems will be discolored as the
disease progresses (Figures 2, 3, and 4). Roots of
infected plants appear dark and decayed. In potato,
vascular tissue extends into the tuber and this tissue,
which occurs as a ring near the outside of the tuber, can
also be discolored from infection with R. solanacearum
(Figure 5). Symptoms of BW can occur in tubers after
harvest and has been more severe when tubers are
harvested from infested fields when soils are warmer due
to later harvests or during hotter seasons.

The mass of bacteria become so numerous in the
vascular tissue that when a stem of an infected plant is cut
and placed into water, the bacteria exude linear streams of
slime (Figures 6 and 7). For potato, do not squeeze the
stems when placing the stem into water because another
bacterial disease called ring rot is more likely to exude the
bacterial slime if the stem is squeezed. Ring rot has not
been found in Florida for the past several decades, but it
was present in Florida in the 1930's and 1940's. In some
plant species, such as strawberry, normally considered as
resistant to this bacterium, a small amount of infection and
vascular plugging occur, but it is not enough to cause
wilting. In pepper, true wilt does not occur in Florida
(Figure 8), but streaks of vascular browning may be seen
when the lower stem is cut lengthwise and leaves may
drop.

In susceptible plants, initial wilt may be seen in the
plant (Figure 9) between two to 14 days after infection.
Longer intervals for symptom expression to occur may
result if cooler weather prevails. Typically, soil
temperatures need to be 70 F or above at a five- to six-
inch depth for active growth ofR. solanacearum. At early
stages, vascular discoloration may be slight Commonly,
the earliest wilt symptoms occur during the day but are
absent during the nighttime or overcast days when it is
cooler and moisture demand of the plant is reduced. Entire
plants may remain green but exhibit strong wilt ( Figure
10). As the vascular tissue becomes progressively more
occluded (plugged), wilting becomes more severe, is less


September 1998


Page 4


Bacterial Wilt of Row Croos in Florida







Bactria Wit ofRowCros inFloidaPaae 5


likely to disappear during cooler periods of time, and is
more apt to be accompanied by yellow and brown leaves
(Figures 11, 12, and 13). Stunting is likely to occur when
young plants are infected. Diseased plants may be
restricted to localized areas of fields (Figures 12 and 13)
or throughout a field (Figure 11). In ebb and flow
(hydroponic) production systems in greenhouses, the
occurrence of one infected plant on one day can result in
all plants being infected in a few days because of the
movement of these bacteria through a common water and
nutrient system.

Sometimes other pathogens, such as Pseudomonas
corrugata, may be present by themselves or as a mixed
infection with R. solanacearum and cause similar
symptoms to BW (Figure 14). Pseudomonas corrugata
causes a disease called pith necrosis (stem necrosis) in
tomato where the central pith of the stem becomes
hollowed out in pockets. This latter disease will
sometimes result in a plant reverting back to a normal
appearance, but with BW that will not occur except as
described earlier.

Plants infected with either R. solanacearum or P.
corrugata may form bumps at the base of the stem in
tomato. These are root initials for secondary
adventitiouss) roots formed on the stem. Although this
symptom is considered one of the diagnostic features for
BW and pith necrosis, it should not be relied upon for that
purpose. Other dysfunctions in tomato and other plants
cause formation of adventitious roots.

Control

Bacterial wilt is among the most difficult diseases to
control. The only way to totally control BW is to not plant
in fields or greenhouses infested with the pathogen. Crop
rotation may help somewhat but is typically not a reliable
control for BW. Rotation with fescue has been beneficial
for suppression of BW in tobacco in North Carolina, but
fescue is not currently grown in Florida. One of the most
promising tactics developed so far for suppression of BW
in potatoes in the Hastings area is the use of sorghum or
sorghum-Sudan hybrids as a summer crop followed by the
incorporation of the dried stalk and leaf debris into the soil
when the cover crop is mature. Care must be taken not to
incorporate these cover crops as a green manure because,
BW is likely to be enhanced. Disease incidence was
reduced from over 80% to less than 5%. Because some
fields are suppressive to R. solanacearum, try to use fields
that do not buildup this bacterium.

Resistant varieties are available in tobacco to a
limited extent but the resistance is incomplete; some plants


will become wilted or mildly infected. Fortunately, BW is
not a major problem in tobacco in Florida. Resistant
varieties are also available in potato but like the resistance
in tobacco, the resistance in potato is incomplete. Some of
the old line potato varieties such as Sebago, Katahdin, Bel
Rus, Ontario (not currently available), La Chipper, Russet
Burbank, and Green Mountain are moderately resistant.
Interestingly, Bel Rus was found to be a carrier of the
bacterium even though it appeared resistant. In the late
1970's and early 1980's, BW recurred as a severe problem
in northeast Florida when growers began growing
susceptible varieties or those with just intermediate
resistance such as Atlantic. From 1941 to 1978, Sebago
and Katahdin were the dominant varieties in northeast
Florida and during that time BW occurred but ceased to be
a major problem when compared to earlier years.

Resistant varieties in tomato are available, but in
some of the varieties the fruit size is small (e.g. Venus,
Saturn). Some of the more recent varieties with resistance
have larger fruit size (e.g. Capitan). These varieties might
be acceptable for utilization in gardens, but, so far, they
have not been acceptable to the commercial tomato
industry. Available resistant varieties may not be resistant
at multiple locations. Because of the multiple strains of
the bacterium that exist, it would not be unexpected that a
variety would be resistant at one location but not at
another location. Warmer soil temperatures may offset the
level of resistance in some tomato varieties because
warmer soils support higher populations of this bacterium.
Recently, considerable gains have been made to develop
tomato genotypes that have resistance to BW and yet have
marketable fruit.

Planting when the soil is cool can reduce the level of
BW. In north Florida, planting early in the spring can
reduce the exposure time of the plants to R.
solanacearum. This tactic will not eliminate the problem
but would be expected to help in some seasons. This
technique is risky unless you have the ability to cover the
plants during periods of time when frosts or freezes occur.
For home gardeners, this technique is easy to do. Methods
for protecting commercial plantings from cold damage are
available, but they are expensive and labor intensive.
Planting later in the fall in south Florida has been
beneficial for suppression of BW. Again, home gardeners
have an advantage. For commercial situations, later
planting might eliminate favorable marketing periods.

Various sanitary techniques can be employed.
Sanitation is used primarily to avoid contamination of an
area not already infested with these bacteria. For example,
washing soil off of field equipment after it is used in
contaminated fields is helpful. This can be done with


September 1998


Bacterial Wilt of Row Crops in Florida


Paae 5







.Bacterial Wilt of Row Crons in Florida


pressure water washing or use of steam cleaners.
Similarly, movement of people or livestock from
contaminated fields to non infested fields will allow for
movement of these bacteria. Avoid planting in fields that
receive water runoff from infested fields. Avoid irrigating
with pond or ditch water. Another sanitary technique is the
use of well water for irrigation or other purposes.
Although well water can be contaminated with pathogens,
it is less likely to be so compared to pond or ditch water.

In greenhouse production for fruit or transplants,
sanitation is imperative. Plant and transplant production
systems should be isolated from crop production fields.
Wind-blown soil and insects may carry pathogens from the
outside into the interior production areas. Soil from the
outside should not be brought in plant production areas or
transplant areas. Implements, shoes, gloves and other
materials used for indoor production should not be taken
outside for use. Soil mixes should be sterilized or
pasturized and containers or materials used for production
of transplants or fruit-bearing plants should be sanitized
before use. Never allow these materials to come into
contact with floors or soil when storing them or during
planting operations. Keep them elevated from the floor
and soil in a location where they will not be contaminated
from floor washing or splashing rain. Transplants should
be produced on raised benches.

Sumps for ebb and flow irrigation systems should be
protected from contamination. Chlorine-containing
materials (e.g. bleach) should be used for sanitizing plant
production equipment between crops. Clean out all old
crop debris from production systems such as PVC lines,
sumps and trays before sanitizing them. Do not allow
diseased plants or old debris to stay within crop
production systems or nearby cull piles. Restrict the
people who enter production areas to those who need to
enter. Having a foot wash with a bleach solution at the
point of entry is suggested. Inspect all plants for
dysfunctions and determine as soon as possible what is
causing the problem. If it is parasitic disease, such as BW,
those plants or trays of transplants should be removed
from the premises immediately. For BW in ebb and flow
systems, it may be already too late. One system that
should be fairly easy to keep from being contaminated is
the bag system (one plant/bag) that is irrigated with a drip
system from well water.

Use disease-free transplants. Similarly, use only
disease-free seed piece stock for potatoes. You should
purchase transplants and seed pieces that have been
inspected and certified as disease-free within the limits of
the inspection process.


Treating soil with chemicals has been attempted many
times for suppression of BW. Amending soil with lime to
raise the pH has been somewhat helpful. However, if only
the upper few inches of soil are treated, it is not likely to
provide satisfactory suppression because the roots will
eventually grow into the untreated soil. Treatment with
lime must include the liming of the deeper strata of soil
also for best results. This is difficult to do with available
tractor-drawn equipment.

Treating the soil with pesticides has been used also.
Because the roots commonly grow out of treated zones of
soil or the treated zone becomes recontaminated, such
treatments provide partial suppression or delayed
occurrence of BW. Soil fumigants with multi-spectrum
products such as methyl bromide, chloropicrin or SMDC
provide temporary suppression. Fumigant nematicides
such as 1,3D provide suppression of nematodes which can
enhance BW, but again, the level of suppression will be
partial. Granular nematicides are not consistently
effective. Combining the use of soil fumigants with
resistant varieties has been effective for production of
potatoes.

Amending the soil with various types of compost has
not been consistently effective. Research on this subject is
being conducted, but no soil amendment has excelled up to
this point in time. One of the most promising tactics
developed so far for suppression of BW in potatoes in the
Hastings area is the use of sorghum or sorghum-Sudan
hybrids as a summer crop followed by its incorporation
into the soil as a green manure when the cover crop is
mature. Disease incidence was reduced from over 80% to
less than 5%.

Soil solarization has been somewhat effective in
Florida in reducing BW as mentioned earlier. It is more
effective when combined with the use of broad spectrum
fumigants. Soil is solarized by maintaining a clear plastic
cover over the soil for at least one month; longer periods
of time are likely to be more effective. The key to success
with solarization is to have sunny days. If cloudy days
prevail, solarization will be considerably less effective.


September 1998


Page 6


R~CtATiAI Wilt of ROW Croos in Florida








Bacterial Wilt of Row Crops in Florida Page 7


Figure 3. Dark vascular bands in tobacco stem with bacterial
wilt.


Figure 1. Dark vascuclar bands in tomato stem with bacterial
wilt.


Figure 4. Dark vascular bands and pith in tobacco stem with
bacterial wilt.


Figure 5. Dark vascular bands in stem and tuber in potato with
bacterial wilt.


Figure 2. Dark vascular bands and pith in tomato stem with
bacterial wilt.


September 1998


Bacterial Wilt of Row Crops in Florida


Page 7







Page 8


Figure 6. Bacterial flow from bacterial wilt-infected tomato stem
immersed in water.


4, -


'"S

A










Figure 9. Initial wilting of some leaves in potato with bactena
wilt.


Figure 7. Bacterial flow from bacterial wilt-infected tobacco
stem immersed in water.


Figure 10. Bacterial wilt in tomato with green leaves.


Figure 8. Symptoms of bacterial wilt in tomato out absent in
pepper.


September 1998


Bacterial Wilt of Row Crops in Florida








BC inPane 9


Figure 11. Bacterial wilt in tomato with green and brown
leaves.


Figure 14. Bacterial wilt and pith necrosis in tomato.


Figure 12. Bacterial wilt (Granville wilt) in tobacco.


gure I BacTenai win (tranvine win) in toDacco.


September 1998


Bacterial Wilt of Row Crops in Florida


Pane 9




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