Impact of Solarization and Soil Fumigants on Hot Pepper Production in High-Tunnels
Bielinski M. Santos,
Jorge E. Mora-Bolanos
J. Arturo Solorzano-Arroyo
High-tunnel studies were conducted in
La Ceiba, Alajuela, Costa Rica, to examine the effect of fumigants and
solarization on soilborne pest control and Campana hot pepper (Capsicum
frutescens L.) marketable yield. Fumigant treatments were: (a) methyl
bromide plus chloropicrin (MBr + Pic 98:2 w/w) at a rate of 500 kg ha-1,
(b) emulsifiable concentrate of 1,3-dichloropropene (1,3-D) plus Pic at
275 L ha-1, (c) emulsifiable concentrate of metam sodium (metam-Na)
at 275 L ha-1 and (d) non-treated control. Soil was either
solarized for 8 weeks (average maximum temperature ≈ 60 °C)
or not solarized. Solarization reduced the weed densities, but not rootknot
nematode populations (Meloidogyne sp.). Similarly, there was no
solarization effect on hot pepper yield. Among the fumigants, MBr + Pic
and 1,3-D + Pic had the best performance controlling the nematode. Pepper
yield in 1,3-D + Pic-treated plots was equal as with MBr + Pic.
In Costa Rica, vegetable production under tunnels has
steadily increased during the last several years. Small and medium-size
coffee growers have mostly developed this activity, hoping to compensate
with agricultural diversification for the current low international coffee
prices. Intensive vegetable production, mainly with crops in the Solanaceae
family, has become a permanent activity in Costa Rica`s Central Valley
and in many cases has replaced coffee. Although official statistics are
lacking, current estimations indicate that there are 1080 tunnels (covering
approximately 180 ha) within the Central Valley, which benefit about 340
growers, 38% of which have more than 0.1 ha (J.E. Mora, personal communication).
The most important problem in the Costa Rican vegetable
tunnel production is managing soilborne pests. The main soilborne diseases
are Phytophthora sp., Phytium sp. and Rhizoctonia solani
Kuhn, as well as bacterial species from the Ralstonia (Pseudomonas)
genus and nematodes such as Meloidogyne sp. and Pratylenchus
sp. Preliminary soil samples collected in the production area showed Meloidogyne
populations of 25,000 juveniles/100 mL soil. These nematode genera
occur naturally in coffee fields without causing apparent economic damages.
However, as the vegetable production intensifies, nematode populations
have abruptly increased, causing significant yield losses.
Chemical control, mainly with Methyl Bromide (MBr), has
been the main tool to reduce the incidence of soilborne pests in tunnel
production. This fumigant is widely utilized in for both muskmelon (Cucumis
melo L.) and cutflower production. However, in compliance with the
Montreal Protocol, methyl bromide has been removed from most agricultural
markets due to its ozone-depleting properties (Watson et al., 1992).
Because of this situation, additional research must be conducted to identify
alternatives for soilborne pest control in vegetable crops grown under
Soil solarization is a non-chemical soilborne pest management
method which provided adequate yellow and purple nutsedge control when
used in the summer months (Chase et al., 1997a, b; Chellemi et
al., 1997). This methodology has been proposed as a non-chemical alternative
to MBr fumigation. Soilborne pest control with solarization is accomplished
by heating the soil prior to crop establishment. High soil temperatures
lethal to soilborne pest propagules are obtained by covering the soil
with transparent polyethylene film for 6 to 8 weeks. Other experiments
obtained 100% mortality of nutsedge tubers with soil temperatures between
50 and 55 °C (Chase et al., 1999). However, other results have
been variable and inconsistent (Gilreath et al., 2005). Therefore,
more research is needed to validate this methodology for commercial settings.
The objective of this study was to compare the combination of soil solarization
and chemical methyl bromide alternatives for soilborne pest control in
MATERIALS AND METHODS
Two tunnel studies were conducted in 2004 and 2005 at
Alajuela, Costa Rica, located at 1100 m above sea level. The experiment
was established in a 10 m high 4500 m2 clear-plastic tunnel.
The soil in the experimental site is a deep Andosol with adequate drainage,
medium fertility and high phosphorus retention. This soil was used for
coffee production during more than 50 years. Raised beds inside the tunnel
were 1.0 m wide by 0.25 m tall. Campana hot pepper seedlings were transplanted
0.5 between plants and double rows. Planting beds were 1.2 m apart from
Treatments were distributed in a split-plot design with
4 replications. Each experimental unit was 12 m2. Main plots
had either solarized or non-solarized soil. In the subplots, the fumigant
treatments were: (a) non-fumigated control, (b) MBr + chloropicrin (Pic)
67:33 (v/v) at a rate of 450 kg ha-1, (c) emulsifiable formulation
of 1,3-dichloropropene (1,3-D) + Pic 65:35 (v/v) at 500 L ha-1
and (d) emulsifiable formulation of metam-Na at 600 L ha-1.
The fumigants were applied 3 weeks before transplanting. Soil solarization
was achieved by covering the corresponding plots with clear plastic mulch
for 8 weeks.
Weed control by species, nematode population in the soil
and hot pepper plant height were recorded at 7 WAT. Weed control (0-100%
scale, where 0 = no control and 100% = total control) data was related
to the MBr + Pic plots, which were weed-free throughout the season. Soil
samples for nematode identification and enumeration were collected with
a 2.5 cm-wide probe inserted 20 cm into the soil within the root zone
of 8 to 10 plants per plot. Nematodes were separated from 100 mL of soil
using a standard sieving and centrifugation procedure (Jenkins, 1964).
At the end of the cropping season, the commercial fruit yields of eight
harvests were added and analyzed with analysis of variance (ANOVA). Weed
and nematode data were transformed before ANOVA by using a log10
+ 1 transformation to stabilize variances. Treatment means were separated
using the least significant difference comparison procedure at the 5%
significance level (SAS Institute, 2000).
RESULTS AND DISCUSSION
Solarized soil reached a maximum daily temperature of
60 °C, which was significantly higher than the average maximum temperature
for non-solarized soil (30 °C). Weed control in the solarized plots
without fumigation was about 100%, whereas in the non-solarized and non-fumigated
treatments the weeds Digitaria sp., Panicum trichoides Sw.,
Eleusine indica (L.) Gaertn, Commelina diffusa Burm., Portulaca
oleracea L., Ricardia scabra L., Galinsoga parviflora
Cav. and Sonchus oleraceus L. were the most dominant species in
the transplanting holes (data not shown).
There was no significant solarization effect on plant
height, rootknot nematode populations and hot pepper yield. However, fumigant
treatments affected all these variables. For hot pepper plant height,
plots treated with either MBr + Pic or 1,3-D + Pic had the tallest plants
with 103 and 101 cm, respectively (Table 1). There was
no metam-Na effect on plant height as compared to the non-treated control,
which was approximately 10% shorter than the plants fumigated with MBr
Fumigation with MBr + Pic resulted in the lowest rootknot
nematode populations (60 juveniles/100 mL soil), followed by 1,3-D + Pic
(1,200 juveniles/100 mL soil). The non-treated control and metam-Na had
the highest nematode populations (Table 1). The nematode
population in the 1,3-D + Pic treatment (1,200 juveniles/100 mL soil)
appeared to be below the damage threshold, whereas the nematode population
in the control plots (2,580 juveniles/100 mL) reduced yield by approximately
23%. This suggested that the critical nematode population threshold occurred
between 1,200 and 2,580 juveniles/100 mL. For marketable hot pepper weight,
the application 1,3-D + Pic (118 t ha-1) resulted in higher
yield than the non-treated control (91 t ha-1) and
||Effect of soil fumigants on rootknot nematode (Meloidogyne
sp.) populations and hot pepper (Capsicum frutescens) plant
height and marketable yield, Alajuela, Costa Rica
|a: Plant height and rootknot nematode data
collected at 50 days after transplanting. Values separated within
columns by LSD multiple comparison procedure. Values with the same
letter(s) within columns do not differ at the 5% significance level
within each year
metam-Na (93 t ha-1), but equal to MBr + Pic
(109 t ha-1). There was no yield difference between metam-Na
and the non-treated control.
These results indicated that under the conditions of
this trial, solarization had a significant impact on weed densities, which
agrees with previous reports on the effect of this practice on weed control
(Chase et al., 1997a, b; Chellemi et al., 1997). However,
it was not sufficient to reduce nematode populations and to increase hot
pepper fruit yield, which could indicate that soil temperatures in the
solarized plots might not have been high enough to affect nematode populations.
In contrast, 1,3-D + Pic proved to be a valuable means to control soilborne
pests in tunnel hot pepper production.
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