Group Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Title: Evaluation of soil solarization for management of soilborne pests
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 Material Information
Title: Evaluation of soil solarization for management of soilborne pests
Series Title: Research report (North Florida Research and Education Center (Quincy, Fla.))
Physical Description: 21 pages : ill. ; 28 cm.
Language: English
Creator: Chellemi, Daniel Owen
North Florida Research and Education Center (Quincy, Fla.)
Publisher: North Florida Research and Education Center
Place of Publication: Quincy Fla
Publication Date: 1993}
 Subjects
Subject: Soil solarization   ( lcsh )
Tomatoes -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
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Bibliography: Includes bibliographical references.
Statement of Responsibility: D.O. Chellemi ... et al..
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Bibliographic ID: UF00066110
Volume ID: VID00001
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Resource Identifier: oclc - 71173626

Full Text
/ NFREC QUINCY RESEARCH REPORT 93-8




EVALUATION OF SOIL SOLARIZATION FOR
MANAGEMENT OF SOILBOINESTS
3 0 1993
AR 3 0 1993


University aFlorida

_._ -- _


I UIWNIYVA FLOFA-
Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville


~a













NFREC Research Report 93-8


Evaluation of soil solarization for management of
soilborne pests.



D.O. Chellemi', S.M. Olson', J.W. Scott2, D.J. Mitchell3,
and R. McSorley4.




'University of Florida, North Florida Research and
Education Center, Route 3 Box 4370, Quincy, FL 32351. -
2University of Florida, Gulf Coast Research and -
Education Center, Bradenton, FL 34203.
3University of Florida, Department of Plant Pathology,
Gainesville, FL 32611.
4University of Florida, Department of Entomology and
Nematology, Gainesville, FL 32611.



The authors would like to thank AEP Industries for
donation of the solarization film and the Gadsden
County Tomato Growers Association for financial
support.











Abstract

The effects of soil solarization and tomato
(Lycopersicon esculentum) genotype on soilborne pests
were examined in North Florida during 1992. Treatments
consisted of soil solarization over a 32-day period
between 19 June and 21 July, fumigation at 448 kg/ha
with a 67:33 mixture of methyl bromide-chloropicrin,
solarization + fumigation, and a fallow control.
Maximum soil temperatures achieved under solarization
treatments were 49.5, 46, and 40.5 C at depths of 5,
15, and 25 cm, respectively. Soil solarization
resulted in a 10-fold reduction of the density of
Phytophthora parasitica var parasitica, causal agent of
root rot and foot rot of citrus, and Fusarium oxysporum
f.sp. radicis-lycopersici, causal agent of Fusarium
crown rot of tomato, in infested soil. However,
solarization was not as effective as fumigation, which
reduced the density of both fungi in infested soil to
undetectable levels. Fumigation had no effect on the
density of Pseudomonas solanacearum, causal agent of
bacterial wilt of tomato, in infested soil. Soil
solarization resulted in a 10-fold reduction of P.
solanacearum in infested soil. A.100-fold reduction-
was achieved when solarization was combined with
fumigation. At 75-days after transplanting, the:
incidence of bacterial wilt on the cultivar Solar Set
was 36% in solarization and control plots and 21% in
plots treated with fumigation. When solarization was
combined with fumigation, incidence of bacterial wilt
was reduced to 6%. The incidence of bacterial wilt on
the breeding line Fla 7421 was 5% in control plots and
less than 2% in all other treatments. At 83-days after
transplanting, soil solarization reduced (P < 0.05)
populations of stubby root nematode (Paratrichodorus
minor) and reniform nematode (Rotylenchulus reniformis)
on 'Solar Set'. Soil solarization reduced (P < 0.10)
populations of P. minor and Criconemella spp. on Fla.
7421. Nematode reductions by soil solarization were
similar to those achieved by fumigation. Fla. 7421
significantly reduced populations of R. reniformis when
compared to 'Solar Set'. This study demonstrates the
potential of soil solarization as a tactic for managing
soilborne pests under a climatic regime characterized
by periods of abundant rainfall and extended cloud
cover.











Introduction

Chemical fumigants including methyl bromide,
chloropicrin, 1,3-dichloropropene/l,2-dichloropropane
(DD), ethylene dibromide (EDB), and 1,2-dibromo-3-
chloropropane (DBCP) have been widely marketed in the
United States since World War II for the control of
soilborne pests (8). Due in part to their
effectiveness against a wide range of organisms,
relatively low cost, and ease of use (22), vegetable
production industries in the southeastern United States
have become increasingly dependent upon these materials
to manage soilborne pests. Environmental concerns
regarding the use of agricultural pesticides have led
to increasing social and legislative pressure to remove
many of these materials from the market place. For
example, legislation enacted in the late 1970s and
early 1980s resulted'in the removal of DBCP, EDB, and
DD from United States markets. Recently, a phase-out
of methyl bromide from agricultural use has been
proposed (16). Reliance of agricultural industries on
chemical fumigants coupled with potential removal of
these materials from the marketplace necessitate
evaluation of alternative, nonchemical approaches for
the management of soilborne pests.
The benefits of solar heating beneath a mulch for
nematode control were first recognized in Hawaii in the
early 1930's (4). In the early 1970s, while covering
methyl bromide treated soils with polyethylene film,
growers and extension workers in the desert regions of
Israel noticed that the soil under the film was
significantly heated by solar radiation. Further
investigations led to a publication in Phytopathology
in 1976 (9) describing the suppression of several
soilborne diseases by solar heating of the soil. This
technique was given the name soil solarization and has
subsequently been shown to suppress 18 different
soilborne fungal pathogens, two bacterial pathogens, 15
species of plant parasitic nematodes and 32 weed
species (21). By 1990, soil solarization had been used
in 38 countries around the world and over 300
publications were available on the subject (10).
A working definition of soil solarization is the use
of solar radiation to heat moistened soil under a
polyethylene mulch. The desired effect from soil
solarization is to produce temperatures which are
detrimental to soilborne pests of crop plants. This
direct action of heat on the pest organism is called
thermal inactivation.
Soil solarization also indirectly affects pest
populations in the soil and the resistance and
biological yield of crop hosts. The biotic composition










of solarized soils is altered either directly through
the action of heat or indirectly via changes in soil
tilth or soluble minerals available for plant and
microbial growth. Changes in the biotic composition of
the soil can result in biological control of soilborne
pests via increased competition, antagonism, or
antibiosis. These same changes also increase
populations of rhizosphere competent bacteria which
cause an increased growth response of the host plant.
Another benefit of soil solarization is that
surviving soilborne pests are weakened by heat stress
and become more sensitive to soil fumigants,
antagonistic organisms, and to a changing gas
environment that develops during solarization (2).
Finally, because soil solarization usually occurs at
temperatures around 50 C, it is narrower in its
spectrum of kill than soil steaming and fungicides.
The result is a delay in reinfestation of solarized
soils by pest organisms when compared to the
reinfestation rate of sterilized or fumigated soils.
The successful heating of soils through solar
radiation is dependent upon soil color and structure,
air temperature, length of day, and most importantly,
the intensity of solar radiation. Although soil
moisture does not contribute significantly to increases
in soil temperature, it is critical for the maximum
transfer of heat energy from soil to soilborne
organisms.
The majority of successful applications of soil
solarization have been from areas characterized by hot,
arid climates. Conditions may be less favorable for
solarization in the southeastern United States, where
the warmest temperatures occur from June to September,
coinciding with periods of maximum rainfall and
frequent cloud cover. Nevertheless, management of
soilborne pests by solarization has demonstrated
potential in South Florida. Season-long reductions in
populations of P. minor and galling of roots by
rootknot nematode species were reported on tomato
(Lycopersicon esculentum) (12,17) and the incidence of
verticillium wilt of tomato was also significantly
reduced (17). While soil solarization was not as
effective as broad-spectrum fumigation in previous
studies conducted in Florida, subsequent developments
in the technology of plasticulture warrant further
investigation of the potential of soil solarization in
the southeastern United States.
The objective of this study was to evaluate the
potential of soil solarization for reducing inoculum
densities of several plant pathogens and for providing
season-long suppression of phytoparasitic nematodes and
bacterial wilt of tomato in North Florida. Unlike











previous reports from South Florida, which were
characterized by subtropical conditions, this study was
conducted in a physiogeographic region more typical of
those found in the southeastern United States. In
addition, a photo-selective polyethylene mulch was
incorporated to reduce the possibility of weed
germination and growth under the mulch during periods
of extended cloud cover.

Materials and Methods

The experiment was conducted in 1992 on a commercial
tomato farm in Gadsden County, Florida. The study site
was located at 30.30 N and 84.40 W, or approximately 285
km northwest of previous solarization studies in
Florida (17). The site had been removed from tomato
production due to a severe epidemic of bacterial wilt,
caused by Pseudomonas solanacearum, the preceding year.
The soil type was an Orangeburg loamy fine sand (Typic
Paleudult: fine-loamy, siliceous, thermic) with a pH of
6.8 and an organic carbon content of 4.9%. Soil
texture ranged from 73-86% sand, 4-12% silt, and 9-20%
clay. Four main treatments were arranged in a
randomized complete block design with three
replications per treatment. Plots were 9 m wide and
30.5 m long. Treatments consisted of solarization,
fumigation (448 kg/ha of a 67:33 mixture of methyl
bromide-chloropicrin), solarization plus fumigation,
and an untreated, fallow control. The plastic mulch
used in solarization and fumigation treatments was a
0.025 mm thick, green polyethylene mulch that
selectively blocked 65% of the incoming
photosynthetically active radiation (AEP Industries,
Hackensack, NJ). Sheets of mulch were 3 m wide and
sealed together with glue to cover the entire 9 m width
of a plot.
Prior to the treatments, the field was deep-plowed
and rotovated. Soil moisture at the time treatments
were applied was 12% on a dry weight basis. Treatments
were applied on 19 June. Plastic mulch was removed
from the fumigation treatment after 48 hr and from the
solarization treatments after 32 days. Hourly changes
in soil temperature in bare soil and the solarization
treatments were monitored at depths of 5, 15, and 25 cm
using thermocouple sensors. An electronic data logger
automatically processed and recorded analog signals
from the sensors (Omnidata Int, Logan, UT). Ambient
air temperature and daily precipitation totals were
obtained from the National Weather Service (Reporting
Station 3SSW), located approximately 2 km from the
experimental site.










Effect of soil solarization on inoculum density of
plant pathogens. A strain of P. solanacearum, isolated
from an infected tomato plant at the same site during
the previous years epidemic, was streaked onto nutrient
broth yeast extract agar and incubated for 48 hr at 27
C. Following incubation, bacterial suspensions were
diluted with sterile tap water to 5.0 x 108 cfu/ml
(OD6,=0.77) and 0.3 ml aliquants were added to 5 cm2
bags containing 3 g pasteurized soil adjusted to a
moisture content of -100 mbar tm to make a final
inoculum preparation of 5.0 x 107 cfu/g soil. Bags
were constructed from 0.2 lm diameter Versapor
membranes (Gelman Sciences, Ann Arbor, MI) and Arclad
S-5913 adhesive (Adhesives Research Inc, Glen Rock,
PA).
Fusarium oxysporum f.sp. radicis-lycopersici,
isolated from a tomato crown, and Phytophthora
parasitica var parasitica, isolated from a citrus root,
were grown on potato-dextrose-agar at 25 C in petri
plates. Inoculum of each fungus was produced on an
autoclaved mixture of 100 g wheat seed and 100 ml
deionized water in a 1-liter flask. Three 3-mm disks
of a 7-day-old culture of each fungus were added to
each of three flasks of wheat seed. The flasks were
maintained at 25 C for 14 days, and the infested seed
shaken vigorously every 3 days to insure uniform growth
of the fungi. After 14 days, 0.2 g of each fungus was
added to separate bags containing 3 g pasteurized soil.
Bags were constructed from 3 Am Versapor membranes and
Arclad tape.
Separate bags containing each pathogen were buried
at depths of 5, 15, 25, 35, and 45 cm in each replicate
plot prior to the treatments. The bags were recovered
after 32 days in the field. Upon recovery, soil was
plated on a medium selective for P. solanacearum (1),
Phytophthora spp. (13) and Fusarium oxysporum (11) and
the inoculum density determined.

Effect of soil solarization on bacterial wilt of
tomato. Following removal of the solarization film,
two raised beds covered by opaque polyethylene mulch
were immediately prepared in the center of each plot.
Beds were 0.9 m wide, 16 m long and arranged on 1.8 m-
centers. Irrigation was provided through drip tubing
with a separate hookup for each plot to minimize
contamination between plots. Thirty plants of 'Solar
Set' and Fla. 7421 were transplanted into the beds on 7
August using a plant spacing of 0.5 m. Solar Set is a
hybrid cultivar widely used by the commercial tomato
industry while Fla. 7421 is a open pollinated, heat
tolerant breeding line developed for tolerance to











bacterial wilt.
The incidence of bacterial wilt was monitored every
2-3 days following planting of tomato up to 75 days
after transplanting. Yield data was obtained from the
plots beginning 75 days after transplanting.

Effect of soil solarization on phytoparasitic
nematodes. Soil samples for nematode analysis were
collected 83 days after transplanting by removing and
compositing a single soil core 2.5 cm in diameter and
20 cm deep from the root zone of each of six plants per
plot. Nematodes were extracted from 100-cm3 soil
subsamples with a modified sieving and centrifugation
procedure (7). In addition, three root systems were
removed from each plot and rated for root-knot galling
on a 0-5 scale (23), where 0=0 galls per root system,
1=1-2 galls, 2=3-10 galls, 4=31-100 galls, and 5=more
than 100 galls per root system.
Nematode data were log-transformed (logo0[x+l]),
subjected to analysis of variance, and where
significant (P < 0.10 or P < 0.05), differences among
means examined by Duncan's multiple-range test.
Temperature data were expressed as the maximum daily
temperature achieved at the various depths and .
treatments for each day the solarization film was in
the field.

Results

A total of 15.4 cm of precipitation were received
during the 32 day solarization period, with rain events
occurring on 14 days. The maximum ambient temperature
was 35.6 C, recorded on 12 July. The maximum
temperatures in bare soil were 40.7, 38.2 and 35.6 at
depths of 5, 15 and 25 cm, respectively (Fig. 1). In
the solarized plots, the maximum soil temperatures were
49.5, 46, and 40.5 at depths of 5, 15, and 25 cm,
respectively. Two periods of intermittent temperature
reduction, from 30 June to 1 July and from 14 July to
16 July were observed. A total of 9.6 cm, 62% of the
precipitation received during the entire solarization
period, fell during these two periods. Although weed
pressure in areas surrounding the plots was intense,
not a single weed germinated under the solarization
film during the 32 day period.

Effect of soil solarization on inoculum density of
plant pathogens. Fumigation did not significantly
affect the density of P. solanacearum in infested soil
(Table 1). Solarization resulted in a 10-fold
reduction in inoculum density, but this reduction was











not significant at P < 0.05. Solarization did reduce
the density of P. solanacearum in the upper 5 cm of the
soil (Fig. 2), where temperatures approached 50 C.
When solarization was combined with fumigation, a 100-
fold reduction (P < 0.05) was obtained.
Solarization significantly (P < 0.05) reduced the
density of F.o. radici-lycopersici by 10-fold (Table
2). Fumigation was even more effective than
solarization as it reduced the density of F.o. radici-
lycopersici to undetectable amounts. The same results
were obtained for P. parasitica (Table 3).

Table 1. Effect of solarization and fumigation on
inoculum density of Pseudomonas solanacearuma.


ANOVA
Mean Smaire F Va


1ue Pr >F


Model 5.'71 1.90 0.036
Error 3.00
Treatments 21.22 7.50 < 0.001
Depth 5.39 1.79 0.146
Interaction 1.94 0.65 0.793
Mean Separation


Treatment Mean SE
Control 3.0x10S Ab 3
Fumigation 2.7x105 A 11
Solarization 2.9x104 A 63
Solarization+ 1.4x103 B 293
Fumigation
Depth Mean SE
5 cm 2.9x103 125
15 cm 4.1x104 51
25 cm 5.1x104 80
35 cm 1.4x105 61
45 cm 4.5x104 109
Data transformed by logjo(x+l) prior to ANOVA.
"bags containing 5.0 x 107 cfu/g soil were placed in
soil for 33 days. Populations in bags held over the
same 33 day period in airtight bags in the laboratory
decreased to 3.6 x 107.
'means and standard error back transformed after ANOVA.
Means followed by the same letter are not significantly
different at P=0.05 according to the Waller/Duncan K-
ration test.











Table 2. Effect of solarization and fumigation on
inoculum density of Fusarium oxysporum f.sp. radici-
lycopersici .

ANOVA
Source Mean Square F Value Pr > F
Model 20.78 32.77 < 0.001
Error 0.63
Treatments 128.91 203.29 < 0.001
Depth 0.56 0.88 0.487
Interaction 0.48 0.76 0.682
Mean Separation
Treatment Mean SE
Control 7.9x105 ab 2.9
Solarization 7.4x104 b 26.4
Fumigation 0.0 c 0.0
Solarization+ 0.0 c 0.0
Fumigation
Depth Mean SE
5 cm 110 704.7
15 cm 335 835.6
25 cm 210 496.6
35 cm 310 765.6
45 cm 412 1,094.0
Data transformed by logo0(x+l) prior to ANOVA.
"bags containing infested wheat seed and pasteurized
soil were placed in plots for 33 days.
means and standard error back transformed after ANOVA.
Means followed by the same letter are not significantly
different at P=0.05 according to the Waller/Duncan K-
ration test.










Table 3. Effect of solarization and fumigation on
inoculum density of Phytophthora parasitica var
parasitica".

ANOVA
Source Mean Square F Value Pr > F
Model 2.83 9.53 < 0.001
Error 0.30
Treatments 11.63 39.10 < 0.001
Depth 1.95 6.57 < 0.001
Interaction 0.93 3.12 < 0.001
Mean Separation
Treatment Mean SE
Control 110.7 ab 9.3
Solarization 12.1 b 16.7
Fumigation 0.0 c 0.0
Solarization+ 0.0 c 0.0
Fumigation
Depth Mean SE
35 cm 13.2 a 21.3
45 cm 12.9 a 19.0
25 cm 3.4 b 10.3
15 cm 2.1 b 6.6
5 cm 1.8 b 5.5
Data transformed by log,0(x+l) prior to ANOVA.
"bags containing infested wheat seed and pasteurized
soil were placed in plots for 33 days.
means and standard error back transformed after ANOVA.
Means followed by the same letter are not significantly
different at P=0.05 according to the Waller/Duncan K-
ration test.

Effect of soil solarization on bacterial wilt of
tomato. Solarization did not have an affect upon the
incidence of bacterial wilt in the susceptible cultivar
Solar Set (Fig. 3). Disease incidence in both the
control plots and the solarization plots was 36%.
Fumigation reduced the incidence of disease to 22%.
When fumigation was combined with solarization, the
incidence of bacterial wilt was reduced from 36% to 6%.
The incidence of bacterial wilt in the breeding line
Fla 7421 was 5% in the untreated control plots (Fig.
4). The incidence of bacterial wilt in all treated
plots was reduced to less than 2%.
For the first harvest date, the marketable yield of
'Solar Set' was greatest in the combined solarization
and fumigation treatment (Table 4). Yields in the
solarization and untreated control plots were
significantly less. Treatments did not have a
significant effect (P < 0.05) on yield of Fla 7421. As
with 'Solar Set', yield of Fla 7421 was greatest in the











combined solarization and fumigation treatment. Yield
of 'Solar Set' averaged 140 boxes/A more than the yield
of Fla 7421. Although abundant quantities of
marketable fruit were still present on the vines, no
additional yield data was obtained because the
commercial grower inadvertently harvested the plots.
Solarization and fumigation had a pronounced affect
upon plant vigor. Plants in all of the treated areas
(solarization or fumigation) were 1-2 ft taller than-
plants in the control treatments, regardless of the
genotype. The phenomena is attributed to the increased
growth response of plants in treated soil.

Table 4. Effect of solarization and fumigation on
yield in bacterial wilt infested plots harvested
21 October, 1992.

Treatment Marketable' Packout
Solar Set
Solarization
+ Fumigation 780.0 ab 88% a
Solarization 414.7 bc 91% a
Fumigation 648.1 ab 90% a
Control 304.5 c 93% a
Fla 7421
Solarization
+ Fumigation 641.5 ab 94% a
Solarization 584.8 a 96% a
Fumigation 518.5 a 93% a
Control 617.2 a 92% a
aMarketable yield includes weights of medium,
large and extra large grades. Packout equals the
ratio of marketable yield to total yield. Yield
measured in number of 25 lb boxes per acre.
Means followed by the same letter within a column
are not statistically different at P=0.05.

Effect of soil solarization on phytoparasitic
nematodes. Soil treatment had a significant effect (P
< 0.05) on populations of P. minor, Criconemella spp.,
and R. reniformis Linford and Oliveira but not
Helicotylenchus spp. and Meloidogyne incognita (Table
5). Tomato genotype had a significant effect (P <
0.10) on populations of R. reniformis with
significantly fewer numbers present on Fla. 7421 (Table
6). No significant interactions (P < 0.10) between
genotype and treatment were observed for any nematode
species.
For 'Solar Set', solarization and fumigation
significantly reduced populations of P. minor and R.
reniformis but had no effect on species of










Helicotylenchus and Criconemella (Table 6). Although a
dramatic reduction in M. incognita also occurred, the
reduction was not significant due to the high variation
among samples.
For Fla. 7421, solarization and fumigation
significantly reduced populations of P. minor and
Criconemella spp. Only fumigation significantly
reduced populations of R. reniformis, while no
treatments had an effect on Helicotylenchus spp. As
observed with 'Solar Set', a dramatic reduction in M.
incognita occurred but the reduction was not
significant due to the high variation among samples.
Galling from M. incognita was observed on only two
plants, one Fla. 7421 and one 'Solar Set'. Both plants
were obtained from control plots.

Table 5. Two-way analysis of variance for effect of
treatment and tomato genotype on populations of
phytoparasitic nematodes 83 days after transplanting.

Effect Df MSt F-value P > F
Paratrichodorus minor
Block 2 0.32 1.77 0.205
Treatment 3 1.94 10.71 < 0.001
Genotype 1 0.21 1.15 0.301
Treatment x genotype 3 0.05 0.25 NSt
Helicotylenchus spp.
Block 2 0.20 1.19 0.332
Treatment 3 0.23 1.37 0.293
Genotype 1 0.11 0.67 NS
Treatment x genotype 3 0.04 0.22 NS
Meloidogyne incognita
Block 2 1.24 1.92 0.183
Treatment 3 1.33 2.05 0.152
Genotype 1 0.29 0.44 NS
Treatment x genotype 3 0.06 0.09 NS
Rotylenchulus reniformis
Block 2 1.59 5.12 0.021
Treatment 3 5.24 16.89 < 0.001
Genotype 1 1.08 3.47 0.083
Treatment x genotype 3 0.47 1.53 0.251
Criconemella spp.
Block 2 0.01 0.06 NS
Treatment 3 0.36 5.30 0.011
Genotype 1 0.01 0.01 NS
Treatment x genotype 3 0.01 0.09 NS
tMean square.
probability > 0.40.











Table 6. Effect of solarization, fumigation, and
tomato genotype on densities of phytoparasitic
nematodes 83 days after transplanting.

Fla 7421 Solar Set
Treatment Meant SE Mean + SE
Paratrichodorus minor
Control 153.0 25.5 a 149.3 11.3 a
Solarization+Fumigation 17.3 7.8 b 16.3 9.0 b
Solarization 15.0 0 b 6.0 1.5 b
Fumigation 27.7 13.6 b 12.0 9.0 b
Helicotylenchus spp.
Control 14.7 14.7 a 2.0 2.0 a
Solarization+Fumigation 2.0 2.0 a 0 0 a
Solarization 0 0 a 0 0 a
Fumigation 0 0 a 0 0 a
Meloidogyne incognita
Control 299.0 298.0 a 181.3 181.3 a
Solarization+Fumigation 0.7 0.7 a 0 0 a
Solarization 9.0 9.0 a 0 0 a
Fumigation 0 0 a 0 0 a
Rotylenchulus reniformis
Control 186.0 82.9 a 860.7 385.5 a
Solarization+Fumigation 0.3 0.3 b 86.7 82.2 b
Solarization 50.7 51.5 ab 16.3 8.6 b
Fumigation 0.7 0.3 b 2.3 1.4 b
Criconemella spp.
Control 3.7 2.0 a 3.3 2.4 a
Solarization+Fumigation 0 0 b 0 0 a
Solarization 0 0 b 0.3 0.3 a
Fumigation 0 0 b 0 0 a
For each nematode genus, means in columns followed by the same
letter do not differ (P 5 0.05) according to Duncan's multiple-
range test except for P. minor and Criconemella spp. on Fla. 7421
where mean separation was performed at P 5 0.10.
t448 kg/ha of a 67:33 mixture of methyl bromide:chloropicrin.
SNematodes per 100 cm3 soil.

Discussion

When compared to the ambient air temperature,
solarization increased soil temperatures by as much as
14, 10.5, and 5 C at depths of 5, 15, and 25 cm,
respectively. Solarization also increased temperatures
by as much as 9, 8, and 5 C over temperatures in bare
soil at depths of 5, 15, and 25 cm, respectively. The
daily maximum temperature range in solarization
treatments at 15 cm was 30-46 C. While this was not as
large as the range of 28-52 C reported by McSorley and
Parrado (12) in south Florida, solarization was
conducted for a 32-day period in this experiment as










compared to 63 days in their study (12). Extension of
the solarization period may have provided greater
opportunity to encounter additional hot, cloudless
days, further elevating soil temperatures. However,
soil temperatures in the solarization treatment at 15
cm depths were approximately 4 C higher than those
reported by Overman in South Florida (17) and several
degrees higher than those reported by Heald and
Robinson in the Lower Rio Grande Valley of Texas (6).
The direct affect of solarization on yield of tomato
could not be examined due to the lack of additional
harvests. Normally, the fall tomato crop in North
Florida is harvested 3-4 times and total marketable
yields of 2694 25 lb. boxes per acre can be expected
for 'Solar Set' during the fall production season in
North Florida (S.M. Olson, unpublished data). Thus,
although the trends for increased yields in the treated
plots were already present at the first harvest, the
magnitude of difference in yield between treatments
would have been larger had additional harvests been
possible. Also, the failure to obtain an estimate of
total yield prevented a comparison of performance
between 'Solar Set' and Fla 7421.
The lack of a commercially compatible disease
control strategy for bacterial wilt of tomato has
resulted in devastating economic losses to tomato
producers in North Florida and South Georgia in
previous years. Broadcast fumigation with high rates
of chloropicrin can provide season long control of
bacterial wilt of tomato in the southeastern United
States (3), but the high cost of chloropicrin and the
unpredictability of results make this tactic unsuitable
for commercial production. While resistance to
bacterial wilt does exist in Lycopersicon species,
development of a commercially acceptable cultivar with
high levels of resistance has been difficult (19, 20).
In this study, the combination of soil solarization
with a standard application of fumigation or soil
solarization with a disease tolerance genotype provided
season-long control of bacterial wilt of tomato. The
ability to reproduce these results will significantly
impact future tomato production in North Florida.
Season-long reductions of R. reniformis by
solarization were reported on lettuce and chickpea in
the Lower Rio Grande Valley (6), where climatic
conditions are more typical of those found in arid
regions of the world. This is the first report of
season-long control of R. reniformis on tomato in the
southeastern United States. The soil temperatures at
15 cm depths in this study were above the threshold of
42.5 C selected by Heald and Robinson (6) as the
maximum daily temperature required to achieve lethal











conditions for R. reniformis.
Solarization also significantly reduced populations
of P. minor in accordance with results obtained by
Overman (17). Solarization also reduced populations of
Criconemella spp., which is a first report for the
southeastern United States.
The damaging effects of root-knot nematodes on
tomato are well documented and recognized (15).
Although less well documented, R. reniformis can also
cause significant reductions in yield of tomato (5),
while trichodorid nematodes have been reported to be
pathogenic on tomato (14, 18).
The reduction of R. reniformis by Fla. 7421 was
unexpected. Resistance to R. reniformis in tomato has
not been previously reported. Fla. 7421 was developed
from Hawaii 7997, a tomato genotype that has been
reported to be highly resistant to bacterial wilt (20).
It is not known whether any genetic linkage exists
between resistance to bacterial wilt and R. reniformis.
The results obtained in this study indicate that
soil solarization, even when interrupted by cloud cover
and rainfall, can reduce populations of soilborne plant
pathogens, provide season-long suppression of plant
pathogenic nematodes, and when used in combination with
other disease control tactics, provide season-long
control of bacterial wilt of tomato in the southeastern
United States.
Additional studies are under was to further evaluate
and improve the potential of soil solarization as a
nonchemical approach for managing soilborne pests
including nematodes. Studies include in vitro
experiments to determine the thermal inactivation point
of P. solanacearum, F.o. radicis-lycopersici, and P.
parasitica. Two additional field studies will be
conducted in Gadsden county in 1993.

Literature Cited

1. Chellemi, D.O., D.J. Mitchell, and A.W. Barkdol.
1992. Effect of composted organic amendments on
the incidence of bacterial wilt of tomato. Proc.
Fla. Hort. Soc. 105:IN PRESS.
2. DeVay, J.E. and J. Katan. 1991. Mechanisms of
pathogen control in solarized soils. Pp 87-102 in
J. Katan and J.E. Devay, eds. Soil solarization.
Boca Raton, FL: CRC Press.
3. Enfinger, J.M., S.M. McCarter, and C.A. Jaworski.
1979. Evaluation of chemicals and application
methods for control of bacterial wilt of tomato
transplants. Phytopathology 69:637-640.
4. Hagan, H.R. 1933. Hawaiian pineapple field soil
temperatures in relation to the nematode










Heterodera radicola (Greef) Muller. Soil Science
36:83-95.
5. Heald, C.M. 1978. Effect of the reniform nematode on
vegetable yields. Plant Disease Reporter 62:902-
904.
6. Heald, C.M., and A.F. Robinson. 1987. Effects of
soil solarization on Rotylenchulus reniformis in
the Lower Rio Grande Valley of Texas. Journal of
Nematology 19:93-103.
7. Jenkins, W.R. 1964. A rapid centrifugal-flotation
technique for separating nematodes from soil.
Plant Disease Reporter 48:692.
8. Johnson, A.W., and J. Feldmesser. 1987.
Nematicides a historical review. Pp. 448-454 in
J.A. Veech,.and D.W. Dickson, eds. Vistas on
Nematology. Hyattsville, MD: Society of
Nematologists.
9. Katan, J., A. Greenberger, H. Alon, and A.
Grinstein. 1976. Solar heating by polyethylene
mulching for the control of diseases caused by
soilborne pathogens. Phytopathology 66:683-688.
10. Katan, J., and J.E. DeVay. 1991. Soil solarization:
historical perspective, principles and uses. Pp
23-37 in J. Katan and J.E. Devay, eds. Soil
solarization. Boca Raton, FL: CRC Press.
11. Komada, H. 1975. Development of a selective medium
for quantitative isolation of Fusarium oxysporum
from natural soil. Rev. Plant Prot. Res. 8:114-
125.
12. McSorley, R., and J.L. Parrado. 1986. Application
of soil solarization to Rockdale soils in a
subtropical environment. Nematropica 16:125-140.
13. Mitchell, D.J., and M.E. Kannwischer-Mitchell.
1992. Phytophthora. Pp. 31-38 in L.L. Singleton,
J.D. Mihail, and C.M. Rush, eds. Methods for
Research on Soilborne Phytopathogenic Fungi. APS
Press, St. Paul, MN.
14. Netscher, C. 1970. Les nematodes parasites des
cultures maraicheres au Senegal. Cahiers
O.R.S.T.O.M. Serie Biologie 11:209-229.
15. Netscher, C., and R.A. Sikora. 1990. Nematode paras
ites of vegetables. Pp. 237-283 in M. Luc, R.A.
Sikora, and J.Bridge, eds. Plant parasitic
nematodes in subtropical and tropical agriculture.
Wallingford, UK: CAB International.
16. Noling, J.W., and D.W. Dickson. 1992. The fate of
methyl bromide within Florida agriculture. Citrus
& Vegetable Magazine. August:19-24.
17. Overman, A.J. 1985. Off-season land management,
soil solarization and fumigation for tomato. Soil
and Crop Society of Florida Proceedings 44:35-39.
18. Rohde, R.A., and W.R. Jenkins. 1957. Host range of











a species of Trichodorus and its host-parasite
relationships on tomatoes. Phytopathology 47:295-
298.
19. Scott, J.W., G.C. Somodi, and J.B. Jones. 1993.
Testing tomato genotypes and breeding for
resistance to bacterial wilt in Florida. Proc.
Intl. Bacterial Wilt Symp. Kaoshiumg, Taiwan, ROC.
(in press).
20. Sonoda, R.M., J.J., Augustine, and R.B. Volin.
1979. Bacterial wilt of tomato in Florida:
history, status, and sources of resistance.
Proceedings of the Florida State Horticultural
Society 92:100-102.
21. Stapleton, J.J. and J.E. DeVay. 1986. Soil
solarization: a nonchemical method for management
of plant pathogens and pests. Crop Prot. 5:190-
198.
22. Stapleton, J.J.,'and C.M. Heald. 1991. Management
of phytoparasitic nematodes by soil solarization.
Pp 51-59 in J. Katan and J.E. Devay, eds. Soil
solarization. Boca Raton, FL: CRC Press.
23. Taylor, A.L., and J.N. Sasser. 1978. Biology,
identification and control of root-knot nematodes
(Meloidogyne species). Raleigh: North Carolina
State Univ. Graphics.
















50 I I '



45 O 00\ 0



40 -


F-- 35A






H-
25-- A 0 Solarized Soil 0 5 cm
O 15 cm
A 3 Bare Soil
A 25 cm
20 | I I I I I
19 23 27 1 5 9 13 17 21
JUNE JULY




Fig. 1. Daily maximum temperatures recorded in bare soil
and under solarization treatments at three depths during
a 32-day solarization period in June-July, 1992.
















1010

10
109

108

107

106

105

104

103

102

101

100

10
lO~


Fig. 2. Effect of
a 67:33 mixture
inoculum density
in infested soil.


I I I I I


-U -*


0 0







0 SOLARIZATION
* SOLAR+FUM
I I


E FUM
o CONTROL


15 25 35 45
DEPTH (cm)

soil solarization and fumigation with
of methyl bromide-chloropicrin on the
of Pseudomonas solanacearum
Means and 95% confidence intervals.














50%


S I I SOLRI I N I IG I A I
SOLARIZATION+FUMIGATION
Ol,T A'rTI A mTg^ST


I iAL.IALIU
_I -----FUMIGATION
........... CONTROL

- 0

0 30% -


S.
S20% -

* : /
-I
O 10%- -
S/ I

0% I I
0 10 20 30 40 50 60 70 80


DAYS AFTER TRANSPLANTING



Fig. 3. Progression of bacterial wilt of tomato
from transplanting until the first harvest date
on the cultivar Solar Set.















SOLARIZATION+FUMIGATION
SOLARIZATION
------ FUMIGATION
........... CONTROL







-*""


F-




0
LL




0
LLJ
C)


L5


* I I I


,/, .


0 10 20 30 40 50 60 70 80


AFTER TRANSPLANTING


Fig. 4. Progression of bacterial wilt of tomato
from transplanting until the first harvest date
on the breeding line Fla 7421.


10%


8%


........................


6%



4%



2%



0%


DAYS







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