Group Title: Research report - Ft. Pierce Agricultural Research and Education Center ; FTP 84-5
Title: The impact of cultural practices on soil-borne fungal and bacterial diseases of vegetables grown on small farms on southeast Florida sandy soils
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Permanent Link: http://ufdc.ufl.edu/UF00055971/00001
 Material Information
Title: The impact of cultural practices on soil-borne fungal and bacterial diseases of vegetables grown on small farms on southeast Florida sandy soils
Series Title: Ft. Pierce AREC research report
Physical Description: 10 leaves : ; 28 cm.
Language: English
Creator: Sonoda, Ronald M
Agricultural Research and Education Center (Fort Pierce, Fla.)
Publisher: University of Florida, Insititute of Food and Agricultural Sciences, Agricultural Research and Education Center
Place of Publication: Fort Pierce Fla
Publication Date: [1984]
 Subjects
Subject: Soilborne plant diseases -- Florida   ( lcsh )
Vegetables -- Field experiments -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaf 10).
Statement of Responsibility: R.M. Sonoda.
General Note: Caption title.
General Note: "November, 1984."
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Bibliographic ID: UF00055971
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 67107003

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SFt. Pierce AREC Research Report FTP 84-5 November, 1984


The impact of cultural practices on soil-borne'fungal and bacterial
diseases of vegetables grown on small farms on southeast Florida
sandy soils.

R. M. S6toda B

Soil-borne diseases of vege ablejcrops in south ast Florida
sandy soils caused by fungi and bacteria can cause h avy yield
losses of these crops. The cult ral practices used to grow these
crops can greatly influence the ri idence ahd.'s riiy. of soil-borne
diseases. Cultural practices do not have as great-ani effect on
incidence and severity of foliar diseases. The following is a
discussion of the incidence of soil-borne fungal and bacterial
diseases as related to the cultural practice systems used in
growing.a particular vegetable crop.

The cultural practice systems used to grow the various common
vegetable crops on southeast Florida sandy soils vary from 1) virgin
land farming (V), land used for the first time for crop production;
2) previously cropped soil with broad spectrum fumigant and full-bed
plastic mulch (PFM); 3) previously cropped soil with fumigation
but no mulch (PF); 4) previously cropped soil with mulch but no
fumigation (PM); and 5) previously cropped soil with no mulch or
fumigation (P). Virgin land farming was common in the area when
uncultivated land was abundant. Soil-borne diseases were
Virtually non-existent when crops were grown on virgin soil.
Virgin land suitable for vegetable farming has become a rare
commodity. Pasture land previously uncropped to vegetables is
used by some growers. These soils are generally free of vegetable
crop pathogens and can usually be considered as being similar to
virgin soil. When the same soil is sequentially planted to the same
crop, heavy yield losses to soil-borne diseases specific to the crop
can be expected after the second cropping. Population increases
of non-specific pathogens, such as Pythiums and Rhizoctonias, that
cause damp-off also occur.' after a few crops.

Broad-spectrum fumigants \on previously cropped soil can
substantially reduce populations of many soil-borne fungal and
bacterial pathogens. These fumigants can also reduce populations
of other pests, e.g., nematodes, soil insects and weeds. Fumigation
can also result in 'increased growth response' of crops. Several
theories have-been proposed to explain this response.

Fumigants can be broadcast over the whole field or more
typically for most vegetable crops in the area, the planting
beds are fumigated and the furrows in between are not. These
unfumigated furrows can serve as important sources of inoculum
of some soil-borne pathogens.


S Professor of Plant Pathology, University of Florida, Institute of
Food and Agricultural Sciences, Agricultural Research and
Education Center, Fort Pierce, FL 33454.





(2)

The plastic mulch used with broad-spectrum fumigants has made
fumigation more effective and served several other functions..
Plastic mulch can serve as an effective barrier against soil-borne
fungi that attack fruit laying on the ground. It helps to reduce
rain splash-up of pathogen inoculum from soil. It aids in weed
control, stabilizing plant beds and reducing fertilizer leaching.

The combination of broad-spectrum fumigation and plastic mulch
may be effective and economical in many cases. In other cases 1) the
system may be effective but uneconomical; 2) the system may not
significantly reduce important soil-borne diseases of a particular
crop; 3) other less costly, but as effective, systems may be
available for soil-borne diseases important on the crop; 4) there
may not be an important soil-borne disease of a particular crop in
southeast Florida; or 5) the use of fumigation may increase the
incidence of a disease. Careful consideration of the benefits of
a fumigation and mulch system should be made. An important
consideration will be presence or absence of important nematode
species. Broad spectrum fumigants are effective in reducing
populations of important nematode pests.

The cultural systems, with various modifications, are used to
a different extent on the small farms scattered over southeast
Florida sandy soils. There are a few greenhouse grown vegetables
in the area. In general soil-borne diseases are similar in the
greenhouse when plants are planted directly in soil. Soil-borne
diseases are in general reduced when plantings are established
in bag culture, i.e., use of plastic bags containing peat and
vermiculite mix as the planting medium.

Temperature and rainfall have a significant effect on disease
development, thus the time of year that crops are grown can greatly
influence disease incidence. Some vegetable pathogens can incite
diseases in cool weather, others are warm weather pathogens. A
few pathogens can cause disease throughout the year, although to
different extents. The stage of growth of crops can also be an
important factor in disease development. Some pathogens attack
only young succulent seedlings while others attack mature tissue
as well as young tissue.

Below we list the important soil-borne fungal and bacterial
diseases of common vegetable crops grown on small farms on
southeast Florida sandy soils. An estimate is made of the
prevalence of each disease under different cultural systems. The
estimates are based on the experience of the author as well as.
information obtained from publications and personal
communications with other researchers working on diseases of
vegetables.







(3)


W Tomatoes

Tomatoes are grown using most of the cultural systems described.
In addition, most of the crop is grown on supports consisting of
wood stakes and twine. The addition of staking has virtually
eliminated important soil-borne fruit-rotting diseases such as
Rhizoctonia soil rot (Rhizoctonia solani); southern blight
(Sclerotium rolfsii) and cottony leak (Pythium aphanidermatum)
as well as other soil-borne fruit pathogens. Of the diseases
listed in Table 1, Fusarium crown rot is a cool weather disease;
Rhizoctonia soil rot and buckeye rot are important during moderate
to warm weather; southern blight, southern bacterial wilt and
damp-off caused by Pythium aphanidermatum are important in warm
weather and are infrequent during the cooler months of the year.
Fumigation with a broad-spectrum fumigant was ineffective in attempts
to control Fusarium crown rot. All of the diseases listed on
Table 1 except Fusarium crown rot have been found throughout
previously cropped southeast Florida sandy soils. Fusarium crown
rot has been identified only from Jupiter south to Delray Beach on
the east coast.

An assumption made in developing Table 1 is that growers in the
area will use cultivars developed for Florida that have genetic
resistance to Fusarium wilts caused by Fusarium oxysporum f. sp.
* lycopersici race 1 and race 2. These two diseases can be
devastating if a susceptible cultivar is grown in unfumigated
soil during the warmer months.

A third race of the pathogen has been found on the west coast
of Florida. Fumigation will reduce the incidence of this disease,
but as with race 1 and 2, the more effective means of control will
be the development of resistant cultivars.





(4)





Table 1. Estimated incidence of soil-borne disease of tomato grown
under different cultural systems.

Cultural systems*
V P PS PM PMS PF PFS PFM PFMS
Disease
1. Fusarium crown rot** _a 4- + ++ 4-+ ++'++ ++
2. southern bacterial wilt ++ ++ ++ ++ ++ ++- ++ +- ++
3. damping-off + +++ ++++ ++++ ++-H- + + + +
4. southern blight ++++ ++I ++++ ++++ ++ ++ --+ -+
5. Rhizoctonia soil rot ++++ + + + -
6. buckeye rot +++ ++ ++ + ++ + ++ +



*V = virgin land; P = previously cropped land, no fumigation, no mulch;
PS = P with tomatoes grown on supports; PM = P mulched but not
fumigated; PMS = PM with plants on supports; PF = P with fumigation,
no mulch; PFS = PF with plants on supports; PFM = P with fumigation
and mulch; and PFMS = PFM with plants on supports.
**l. Fusarium oxysporum f. sp. radicis-lycopersici; 2. Pseudomonas
* solanacearum; 3. Pythium aphanidermatum and Rhizoctonia solani;
4. Rhizoctonia solani 5. Sclerotium rolfsii; 6. Phytophthora
capsici and Phytopthora parasitica.
a = disease not observed; + = disease rarely found or expected;
++ = scattered instances of disease found or expected; +++ = moderate
incidence of disease found or expected; +H4+ = disease generally
found or expected.





(5)



Peppers

Peppers are generally grown in previously cropped soil with
fumigation and plastic mulch or occasionally on unfumigated
unmulched beds. The advantage of mulched, fumigated .beds as
far as disease control is concerned will be good control of
damping-off caused by Pythium aphanidermatum, Phytophthora
capsici and Rhizoctonia solani. Other pathogens as well as
nematodes may be reduced with fumigation. Inoculum of
P. aphanidermatum and P. capsici can be splashed up onto plants
during heavy beating rains from furrows in fields with fumigated,
plastic mulched covered beds. Unless pepper plants are very young,
P. aphanidermatum has little or no effect on them. P. capsici,
on the other hand can infect mature plants as well as young plants
causing crown rot, cankers in plant crotches, and leaf lesions.

Table 2. Estimated incidence of soil-borne diseases of pepper
grown under different cultural systems.

Cultural systems*
V P PM PF PMF
Diseases
1. damping-off** -a H-++++ + +
2. Phytophthora ++++ -H- ++++
3. Sclerotinia -++ ++ -H+- +++
4. southern blight +- +++ +++' +++


*V = virgin land; P = previously cropped land, no fumigation, no
mulch; PM = P mulched but not fumigated; PF = P fumigated but not
mulched; and PMF = P fumigated and mulched.
**1. Pythium aphanidermatum, Phytophthora capsici, Rhizoctonia solani;
2. Phytophthora capsici; 3. Sclerotinia sclerotiorum; 4. Sclerotium
rolfsii.
a = disease not observed; + = disease rarely found or expected;
++ = scattered instances of disease found or expected;
+++-- = moderate incidence of disease found or expected;
-++-I = disease generally found or expected.





(6)


Cucumbers

Cucumbers are grown. on unmulched, unfumigated beds; on
fumigated, plastic-mulch covered beds, frequently following a
tomato crop; or trained upright, on twine in the greenhouse in 'bag'
culture, using peat and vermiculite in plastic bags as growing medium.
If cucumbers are planted for 2-3 times on the same site in field,
diseases such as Fusarium wilt, belly rot caused by Rhizoctonia
solani, cottony leak caused by Pythium aphanidermatum, and damping-off
caused by Pythium spp. and Rhizoctonia solani may become severe
problems by the third planting. These problems have not been
observed on large commercial plantings -often as most of these
operations are moved from location to location after 1 or 2 plantings
or cucumbers are planted in plastic-mulch covered beds following
tomato production. No Fusarium wilt resistant cucumber varieties
are available. If cucumbers are trellised, the fruit rots, belly
rot and cottony leak, would be eliminated.

In greenhouse plantings made directly into fumigated or
unfumigated soil, Pythium aphanidermatum, frequently causes a
mature plant to wilt. The incidence of this disease is greatly
reduced with the'use of 'bag' culture. Use of these bags for more
than a few crops, may result in problems with soil-borne diseases.

Watermelons have diseases similar to those affecting cucumbers.
Fusarium wilt resistant varieties of watermelon, however, are
available. Even with resistant varieties some wilting of these
'resistant' varieties can occur in infested soil. No important
soil-borne diseases of cantaloupe are listed in the
University of Florida Plant Disease Control Guide.

Table 3. Estimated incidence of soil-borne diseases of cucumber
grown under different cultural systems.

Cultural system*
V P PS PM PMS PF PFS PFM PFMS
Disease

1. Fusarium wilt ** a ++ ++ ++ -+ + + + +
2. Rhizoctonia belly rot + + + +
3. damping-off +H+++ ++++ -++ ++++ + + + +
4. cottony leak +++ + + +

V = virgin land; P = previously cropped land, no fumigation, no
mulch; PS = P with cucumbers trained on supports; PM = P with
mulch, no fumigation; PMS = PM with plants on supports; PFM = P
with fumigation and plastic mulch; and PFMS = PFM with plants on
supports.
** 1. Fusarium oxysporum f. sp. cucumerinum; 2. Rhizoctonia solani;
3. Pythium spp., Rhizoctonia solani; 4. Pythium aphanidermatum.
a = disease not observed; + = disease rarely found or expected;
++ = scattered instances of disease found or expected;
+++ = moderate incidence of disease found or expected;
-+I+ = disease generally found or expected.






(7)

Beans

Snap beans are generally grown in previously cropped soil with no
fumigation or mulch. Pythium aphanidermatum, other Pythium spp.,
Rhizoctonia solani, and Fusarium solani are important.soil-borne
diseases of beans. These pathogens generally cause hypocotyl rot,
root rot and wilt of beans. These diseases can occur throughout the
bean growing season. Some reduction in incidence of these diseases
can be attained with seed treatment or in-the-furrow fungicide
treatments. Sclerotinia sclerotiorum, white mold can be an important
problem during the cooler months. Sclerotium rolfsii can be an
important problem during warmer months. The listing on the table for
Rhizoctonia solani is for root-rotting strains of the pathogen.
There are soil-borne R. solani that cause a foliar blight.

Table 4. Estimated incidence-of soil-borne diseases of snap
beans grown under different cultural systems.


Cultural Systems*
Diseases V P PM PF PMF

1. Pythium wilt ** -a -H- ++H+ ++ +
2. Rhizoctonia root rot H-H+ ++-+ ++ +
3. Fusarium root rot ++++ +++ ++ +
4. southern blight +++ ++- ++ ++
5. white mold +++ +++ +++ +++


*V = virgin land; P = previously cropped land, no fumigation, no
mulch; PM = P with mulch, no fumigation; PF = P.with fumigation,
no mulch; PMF = P with fumigation and plastic mulch.
** 1. Pythium aphanidermatum, Pythium spp.; 2. Rhizoctonia solani;
3. Fusarium solani; 4. Sclerotium rolfsii; 5. Sclerotinia
sclerotiorum
a = disease not observed; += disease rarely found or expected;
++ = scattered instances of disease found or expected;
+++= moderate incidence of disease found or expected;
-H-+ = disease generally found or expected.





(8)

Squash

* Squash, yellow straight or crookneck, and zucchini is grown on
previously cropped soil using unmulched and unfumigated beds. A
few farms may have squash in fumigated plastic-mulch-covered beds.
Damping-off caused by Pythium aphanidermatum is an important problem
during warm wet weather in unfumigated, previously cropped soil.
Phytophthora capsici can be a problem during warm winter storms
when heavy, beating rains occur. Plant losses may occur in fumigated,
plastic-mulch-covered beds as inoculum is splashed up from untreated
alleyways. Plant losses can be heavier on unfumigated, unmulched
beds on previously cropped soil.

Table 5. Estimated incidence of soil-borne diseases of squash
grown under different cultural systems.

Cultural Systems*
V P PM PF PMF
Diseases
1 damping-off** -a ++- +H + +
2. Phytophthora blight ++++ ++++ +++ +++
3.. Southern blight -H+ ++++ 4-H- ++

V = virgin land; P = previously cropped land, no fumigation,
no plastic mulch; PM = P with mulch, no fumigation; PF = P
with fumigation, no mulch; PMF = P withmulch and fumigation.
**l. Pythium aphanidermatum, Pythium spp., Rhizoctonia solani;
2. Phytophthora capsici; 3. Sclerotium rolfsii.

a = disease not observed; + = disease rarely found or expected;
++ = scattered instances of disease found or expected;
+++ = moderate incidence of disease found or expected;
-HH- = disease generally found or expected.








(9)

Eggplant

Eggplants are grown on mulched, fumigated beds or unmulched,
unfumigated beds on previously cropped soil. Although Verticillium
wilt and southern bacterial wilt are reported on the crop in
southeast Florida, the most common disease problem in recent years
has been various symptoms caused by Phytophthora capsici. The
pathogen causes crown rot, wilt, stem blight, fruit rot, and leaf
lesions. Although fumigation reduces inoculum of the pathogen,
inoculum from unfumigated alleyways have been sufficient to cause
significant losses of plants and fruits in the past few years.
The disease is associated with warm tropical storms that occur
periodically during the growing season.

Table 6. Estimated incidence of soil-borne diseases of eggplant
grown under different cultural systems.

Cultural Systems*
Diseases** V P. PM PF PMF

1. Verticillium wilt -a + + -
2. southern bacterial wilt ++ --+ ++ ++ ++
3. Phytophthora diseases ++H + -H-- S+ H
4. damping-off +t +f- + +
5. southern blight +++ -+ ++ ++


* Virgin soil; P = previously cropped soil, no fumigation, no
plastic mulch; PM = P with mulch, no fumigation; PF = P with
fumigation, no plastic mulch; PMF = P with fumigation and plastic
mulch.

** 1. Verticillium albo-atrum; 2. Pseudomonas solanacearum;
3. Phytophthora capsici; 4. Rhizoctonia solani;
5. Sclerotium rolfsii

a = disease not observed; + = disease rarely found or expected;
++ = scattered instances of disease found or expected;
+++ = moderate incidence of disease found or expected;
+HH = disease generally found or expected.






(10)


SCrucifers

Most crucifers, e.g. cabbage, cauliflower, etc. are grown on
unmulched, unfumigated beds. Damping-off caused by several patho-
gens can be avoided for transplanted crucifers if seedbed soil is
virgin or fumigated. The most important soil-borne problem noticed
in the field in recent years has been Rhizoctonia root rot. This
disease can.be reduced if soil is fumigated.

Sweet Corn

Sweet corn is usually grown on unmulched, unfumigated beds.
Soil-borne diseases have not been an important problem with most
cultivars of this crop.

-Onion

Onions are generally grown on unmulched, unfumigated beds.
Damping-off caused Pythium spp. and Rhizoctonia solani may
reduce stands. Other soil-borne diseases observed on onion have
been Sclerotium rolfsii and Fusarium bulb rot. Yield losses to
soil-borne diseases have been limited in the small acreage of onions
grown in the area.

Strawberries

Strawberries are affected by a multitude of soil-borne pathogens.
Nematodes, however, are the most important soil-borne problem. Straw-
berries should be grown on fumigated soil, unless virgin soil is used.

Okra

Okra is generally grown on unmulched, unfumigated beds. The
most important soil-borne diseases of-the crop are damp-off caused
by Pythium spp. and southern blight caused by Sclerotium rolfsii.

Afterword

This information should be used as one factor in deciding what
cultural practice system to use in growing a particular vegetable
crop on southeast Florida sandy soils. Whenever possible cultivars
tolerant to important soil-borne and foliar pathogens should be
used. The history of previously grown crops will be of value in
deciding if pathogens potentially hazardous to intended crops may
be present in the soil. Knowledge of nematode population is
important in determining what system to use in growing a particular
crop.

The University of Florida, Institute of Food and Agricultural
Sciences, Florida Disease Control Guide and the Florida Nematode
* Control Guide, both available through the University of Florida
Agricultural Extension Service should be consulted for methods of
managing diseases and nematodes.




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