*Corresponding author. Tel.: 39-011-6708539; fax: 39-011-6708541. E-mail address:[email protected] (M.L. Gullino)
Reduced dosages of methyl bromide applied under gas-impermeable
plastic
"
lms for controlling soilborne pathogens of vegetable crops
Andrea Minuto, Giovanna Gilardi, M.L. Gullino
*
, Angelo Garibaldi
Dipartimento di Valorizzazione e Protezione delle Risorse agro-forestali, Patologia Vegetale, Via Leonardo Da Vinci, 44, 10095 Grugliasco TO, Italy
Received 30 October 1998; received in revised form 26 February 1999; accepted 26 March 1999
Abstract
Four experimental trials were carried out at Albenga (Northern Italy) to evaluate the e!ectiveness of reduced dosages of methyl bromide (MB) applied under gas-impermeable"lms in controlling soilborne pathogens of vegetable crops. Forty and thirty g/m2of MB applied under di!erent types of gas-impermeable "lms controlled Rhizoctonia solani on bean, lettuce and basil, Fusarium
oxysporumf. sp. basilicion basil andSclerotinia sclerotiorum on lettuce. Such treatments greatly decreased survival of arti"cially
introduced pathogen inoculum in the soil, withFusarium oxysporumf. sp.basilicibeing the most di$cult pathogen to control. Gas impermeable"lms permitted increased retention of MB, thus resulting in higherC]¹(concentration]time) product values and
reduced emissions into the atmosphere, as indirectly shown by measurements carried out by using a portable Fumiscope gas detector. ( 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Soil fumigation with methyl bromide (MB), applied at 60 g/m2, under low density polyethylene (LPDE) plastic "lm, is a common practice for the control of a wide spectrum of soilborne pathogens in many crops (Garibaldi and Gullino, 1995) and, particularly, vegetable crops (Katan, 1984). However, during recent years, con-cern regarding the potential of MB to interfere with the ozone layer led to its inclusion on the list of ozone-depleting substances regulated by the Montreal Protocol (Bell et al., 1996; Ristaino and Thomas, 1998). The strict rules that limit its usage, prior to its phasing-out, stimu-lated the development of methods to reduce dosages and, consequently, emissions of MB into the atmosphere (Gamliel et al., 1997a).
The study in Northern Italy evaluates the possibility of adopting gas-impermeable"lms with reduced dosages of MB for the control of important pathogens of vegetable crops.
2. Materials and methods
2.1. Layout of trials
Three of the trials at Albenga (Northern Italy) at the Centro di Sperimentazione e Assistenza Agricola (CeRSAA) of the Chamber of Commerce of Savona in 1996 (Table 1) assessed the e$cacy against soilborne diseases as well as MB concentration under the tarp. In the fourth trial only MB concentration under the plastic "lm was measured. All trials were carried out in a sand : silt : loam (75 : 20 : 5) soil, pH 8, 2.5% organic material. Soil moisture ranged from 6 to 14% during the di!erent stages of the trials. In trials 1 and 2, the e!ect of the fumigation treatment on pathogen survival was also evaluated. Climatic conditions during the fumigation and the period immediately after fumigation were recorded.
2.2. Soil infestation with pathogens
To achieve a uniform soil infestation, and higher dis-ease incidence, the inoculum of the following pathogens was incorporated into the soil by rototilling at a depth of 5}10 cm prior to fumigation at the dosages reported in Table 1:Rhizoctonia solani, as infected wheat kernels in trial 1;R. solani, as infected kernels,Fusarium oxysporum
Table 1
Outline of the four experimental trials
Trial number and code Location, plots surface and number of replicates
Arti"cial infestation on Soil infestation with Crop grown
1. MU 1 Ce.R.S.A.A.,
Albenga, plastic tunnel, 60 m2, 3 replicates
15/03/96 Rhizoctonia solani, 30 g/m2
of infected kernelsFusarium oxysporumf. sp.basilici 1]105CFU/ml of soil of chlamydospores on talc Basil plants infected with Colletotrichum gloeosporioides
Basil (cv Genovese gigante)
2. SC 1 Ce.R.S.A.A.,
Albenga, open"eld, 50 m2, 3 replicates
05/04/96 R. solani, 30 g/m2of infected kernels
Bean (cv Bobis, Canellino, Anellino) Lettuce (cv Lido)
3. SC 3 Ce.R.S.A.A.,
Albenga, open"eld, 50 m2
3 replicates
30/07/96 R. solani, 30 g/m2infected kernelsSclerotinia scler-otiorum, 30 g/m2infected kernels
Bean (cv Bobis, Canellino) Lettuce (Gheisa, Foglia di quercia)
4. CO 3 Ce.R.S.A.A.,
Albenga, open"eld, 50 m2
3 replicates
*! * *
!No arti"cial infestation.
f. sp.basilici(FOB) as chlamydospores suspended in talc (Locke and Coulhoun, 1974) and Colletotrichum
gloeo-sporioidesas heavily infected basil plant pieces in trial 2;
R. solaniandSclerotinia sclerotiorumas infected kernels
in trial 3. In addition, in order to evaluate the direct e!ect of fumigation on the survival of the pathogens in trials 1 and 2, the inoculum of the pathogens was buried in the soil at 10 and 20 cm depths, in the central part of the plots. In trial 1R. solaniandF. o. basiliciwere used, while
R. solani, F. o. basilici and Pythium ultimum were used
in trial 2. R. solani and P. ultimum were introduced as infected kernels; F. basilici as talc infested with chlamydospores. In the case ofF. o. basiliciinfested talc, a mixture (1 : 1.5 talc : perlite v/v) was used; perlite was mixed to talc in order to improve gas permeability of the last material. Seven grams inoculum of each pathogen was put separately into small gas permeable tissue bags (5 cm diam) and buried into the soil 12}18 h before the fumigation treatment. Two bags per pathogen were in-troduced into each plot, one at 10 and one at 20 cm depth. The bags were taken out 7 days after fumigation when the soil was uncovered.
2.3. Plastic mulch
Soil mulching was carried out by using standard, transparent, LPDE (Ei!el, Fontanellato, Italy, 40lm thick) and two virtually impermeable, transparent"lms
(VIFs): Bromotech (LMG Smith Brothers. Bristol UK, 30lm) coded as LMG, Barromid (Plastopil, Kibbutz Hazorea, Israel, 30lm) coded as PP. Moreover, two coloured impermeable "lms, provided by Societa' Italiana Sterilizzazioni (Vittoria, Italy), and coded as SIS white and SIS grey were tested in trial 4.
Tarps were manually removed from soil seven days after the fumigation treatment, in accordance with Italian law.
2.4. Fumigation treatments
Methyl bromide (Metabrom, 98% a.i., Bromine Com-pounds, Israel) was applied by licensed fumigators through drip lines placed under the"lm, using the hot gas method, at the dosages reported in Tables 2}9. In trial 1, one treatment consisted in the addition of 5 T/ha of cow manure to the soil before fumigation (on March 11, 1996) in order to evaluate a possible negative interaction between fertilization with manure and MB fumigation.
2.5. Pathogen inoculum survival
Table 3
E!ect of fumigation with methyl bromide under di!erent plastic mulch on the survival of soil buried pathogens in trial 2 Treatment, with
MB, g/m2and plastic cover!
CFU/g ofF. basiliciat a depth of Percentage of kernels infected with R. solaniat a depth of
Percentage of kernels infected withR. solaniat a depth of
10 cm 20 cm 10 cm 20 cm 10 cm 20 cm
* 9.0]107b" 6.0]107b 95.0 b 94.8 b 97.0 b 94.3 b
60/LPDE 3.6]102a 6.5]102a 0.0 a 0.0 a 0.5 a 0.0 a
40/LPDE 2.4]103a 1.7]103a 0.0 a 0.0 a 0.0 a 0.0 a
20/LPDE 5.1]104a 1.7]104a 0.3 a 0.0 a 1.8 a 0.5 a
40/LMG 7.9]102a 4.3]102a 0.0 a 0.0 a 0.0 a 0.0 a
20/LMG 1.0]104a 7.2]103a 0.5 a 0.0 a 1.0 a 0.5 a
40/PP 4.3]102a 3.3]102a 0.0 a 0.0 a 0.0 a 0.0 a
20/PP 1.8]103a 2.4]102a 0.0 a 0.3 a 0.3 a 1.0 a
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05). Table 2
E!ect of fumigation with methyl bromide under di!erent plastic mulch on the survival of soil buried pathogens in trial 1
Treatment, with MB, g/m2and plastic cover!
CFU/g ofF. basiliciat a depth of
Percentage of kernels infected withR. solaniat a depth of
10 cm 20 cm 10 cm 20 cm
* 3.1]107b" 8.7]107b 98.0 b 100.0 b 60/LPDE 2.1]101a 1.5]102a 2.0 a 1.0 a 30/LPDE 1.7]102a 7.2]101a 1.0 a 0.0 a 30/LMG 8.2]101a 5.2]101a 1.0 a 0.0 a 30/PP 1.7]102a 6.7]101a 0.3 a 0.3 a 60/LPDE
Man#
4.6]101a 1.4]102a 0.0 a 0.0 a
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
#Plots were treated with manure (5 T/ha).
dilutions in sterile water and plated on Komada medium (Komada, 1975). After 7 days of incubation at 243C, the number of colony forming units (CFU) was counted. In the case ofR. solaniandP. ultimum, 100 infected kernels/ bag were directly plated on Petri plates (10 kernels/plate)
on aRhizoctoniasemi-selective (Migheli et al., 1990) and
on a oomycete selective medium (Masago et al., 1977), respectively. Inoculated plates were incubated for 5}7 days at 243C. The number of kernels from which my-celium grew was counted, and the data expressed as percent of plated kernels.
2.6. Crops grown
In experiment 1, carried out under plastic tunnel, soil fumigation was carried out on March 20, 1996,
soil was unmulched on March 27, 1996, then rototilled and irrigated on April 2, 1996. Two subsequent crops of basil (cv Genovese gigante) were grown. The "rst sowing took place on April 4, 1996; the second one on May 20, 1996. In both the cases, 3 g of seed/m2were used.
In experiment 2, carried out in the open"eld, fumiga-tion was done on April 17, 1996, soil was unmulched on April 26, 1996, then rototilled and irrigated on May 15, 1996. Bean (cv Bobis, Canellino and Anellino) and lettuce (cv Lido) were grown. Bean was seeded at 200 seeds/plot on May 24, 1996; lettuce was transplanted (160 plants/ plot) on May 28, 1996.
In experiment 3, carried out in the open "eld, soil fumigation was carried out on August 6, 1996, soil was unmulched on August 13, 1996, then rototilled and ir-rigated on August 20, 1996. One crop of bean (cv Bobis and Canellino) and two crops of di!erent cultivars of lettuce (cv Gheisa and Foglia di quercia) were grown. Bean was seeded at 200 seeds/plot on September 2, 1996; lettuce cv Gheisa was transplanted (100 plants/plot), while cv Foglia di quercia was sown at 300 seeds/m2on September 2, 1996.
In trial 4 no crop was grown.
All crops were sprinkle irrigated and grown according to the cultural practices adopted by commercial growers in the region.
2.7. Disease evaluation
Disease development was evaluated at regular inter-vals by counting the number of plants with symptoms (incidence) or by using a subjective disease index scale for the di!erent pathogens ranging from 0 (healthy plant) to 5 (dead plant) (disease severity).
Table 4
E!ect of fumigation with methyl bromide (MB) under di!erent mulch"lms on the incidence ofRhizoctonia solani,Fusarium oxysporum f. sp. basiliciand Colletotrichum gloeosporioidesinfections and on yield of basil (cv Genovese gigante) (trial 1,"rst crop)
Treatment with MB, g/m2and plastic cover!
Percentage of infected plants 34 days after sowing Yield (g/m2)
R. solani C. gloeosporioides F. basilici Total
* 28.9 b" 5.8 b 16.0 b 50.7 b 2172 b
60/LPDE 4.3 a 0.1 a 0.3 a 4.7 a 3404 a
30/LPDE 1.9 a 1.6 a 1.1 a 4.6 a 3030 a
30/LMG 3.2 a 0.2 a 0.5 a 4.0 a 3193 a
30/PP 2.1 a 0.2 a 1.9 a 4.3 a 2785 ab
60/LPDE Man# 0.3 a 0.4 a 0.6 a 1.4 a 2906 ab
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05). #Plots were treated with manure (5 T/ha).
Table 5
E!ect of fumigation with methyl bromide (MB) under di!erent mulch
"lms againstRhizoctonia solaniinfections on three cultivars of bean. Data expressed as percent of infected plants (IP) and disease index (DI, 0}5) (trial 2,"rst crop)
Treatment with MB, g/m2and plastic cover!
Percentage of infected plants (IP) and disease index (0}5) 58 days after sowing
cv Bobis cv Anellino cv Canellino
% IP DI % IP DI % IP DI
* 80 d" 2.0 d 78 d 1.9 c 86 d 2.2 b
60/LPDE 12 a 0.1 a 9 a 0.1 a 11 a 0.1 a
40/LPDE 54 c 0.9 c 43 c 0.8 b 41 a 0.7 a
20/LPDE 38 b 0.6 bc 45 c 0.9 b 46 c 0.9 a
40/LMG 8 a 0.1 a 8 a 0.1 a 16 ab 0.2 a
20/LMG 36 b 0.6 bc 30 c 0.5 ab 23 abc 0.3 a
40/PP 9 a 0.1 a 11 ab 0.1 a 14 ab 0.4 a
20/PP 34 b 0.5 ab 28 bc 0.3 a 36 abc 0.6 a !LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
Table 6
E!ect of fumigation with methyl bromide (MB) under di!erent plastic mulch"lms on the incidence ofSclerotinia sclerotioruminfections on lettuce (cv Gheisa) (trial 3,"rst crop)
Treatment with MB, g/m2and plastic cover!
Percentage of infected plants 78 days after transplanting
* 14.1 b"
60/LPDE 3.9 a
40/LPDE 1.6 a
30/LPDE 2.3 a
40/LMG 3.9 a
30/LMG 3.1 a
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
Table 7
E!ect of fumigation with methyl bromide (MB) under di!erent plastic mulch"lms againstRhizoctonia solanion bean (cv Bobis and Canel-lino), expressed as percent of emerged plants (% E) and Disease Index (DI, 0}5), 53 days after sowing (trial 3,"rst crop)
Treatment with MB, g/m2and plastic cover!
cv Bobis cv Canellino
% E DI % E DI
* 19.8 b" 1.3 b 50.0 a 1.6 b
60/LPDE 48.0 ab 0.8 a 71.3 a 0.9 a
40/LPDE 39.4 ab 0.7 a 58.0 a 0.6 a
30/LPDE 45.5 ab 0.6 a 60.0 a 0.8 a
40/LMG 50.0 a 0.7 a 67.8 a 0.6 a
30/LMG 41.9 ab 0.8 a 60.3 a 1.0 a
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
2.8. MB measurements
MB concentrations in the air trapped under the tarp were measured at constant intervals after fumigation using a FUMISCOPE D (Key Chemical & Equipment Co., Clearwater, FL, USA), a portable instrument com-monly used for measuring the concentration of MB in fumigation chambers. The instrument is based on the principle of thermal conductivity (Chakrabarti, 1996) and can detect concentration of the gas in the atmo-sphere up to 1999 g/m3.
Table 8
Methyl bromide (MB) measured under the tarp at di!erent intervals after fumigation (trial 3)
Treatment with MB, g/m2and plastic cover!
(g/m3) of MB at minutes from the start of fumigation
6 60 120 180 600 1200
60/LPDE 919 bc" 363 bc 332 a 259 a 185 ab 156 a 40/LPDE 1035 b 395 b 266 b 252 a 197 ab 174 a 40/LMG 1568 a 645 a 348 a 251 a 181 b 157 a
30/LMG 720 c 303 c 284 b 279 a 214 a 171 a
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
Table 9
Methyl bromide (MB) measured under the tarp at di!erent intervals after fumigation (trial 3)
Treatment with MB, g/m2and plastic cover!
(g/h/m3) at minutes from the start of fumigation
6 60 120 180 600 1200
60/LPDE 122 b" 654 b 997 b 1288 b 2706 b 4381 b 40/LPDE 115 b 608 b 926 b 1180 b 2707 b 4540 ab 40/LMG 151 a 1004 a 1480 a 1781 a 3322 a 4987 a 30/LMG 73 c 474 b 763 b 1035 b 2658 b 4537 ab
!LPDE: low density polyethylene; LMG: LMG Smith Brothers gas-impermeable"lm; PP: Plastopil gas-impermeable"lm.
"Means of the same column, followed by the same letter, do not signi"cantly di!er following Duncan's Multiple Range Test (P"0.05).
Techniques de Fumigation et de Protection des DeHnreHes StockeHes (L.N.D.S) du Ministe`re de l'Agriculture at Bordeaux (France) (P. Ducom and M. Guinet. pers. comm.). The concentration of MB present in the air trapped under the plastic"lm was measured at a distance of at least 1.5 m inward from the plot border, and of 4}5 m from the fumigant injection points. Measures started 6 min after beginning of fumigation. Data are expressed as g/m3 and as C]¹ (concentration]time) products. This last value is the product of multiplying MB concentration (C) by the duration of the exposure time (¹).
3. Results
3.1. Ewect ofxlm type and MB dosages on pathogen
survival
All treatments signi"cantly reduced (98}100% reduc-tion) survival of the pathogens arti"cially introduced into the soil in both trials 1 and 2 (Tables 2 and 3). Also, the lowest tested dosage of MB (20 g/m2) under gas-impermeable plastic "lm strongly reduced the sur-vival of the pathogens, both at 10 and 20 cm depths. However, onlyR. solaniandP. ultimumwere completely inactivated by some treatments. In the case of FOB, the tested treatments strongly reduced but did not completely kill the inoculum (Tables 2 and 3). Con-sidering the e!ect on FOB, the e$cacy of the treatments was higher in trial 1 than in trial 2. No signi"cant di! er-ences on the e!ect on the pathogen's inocula were ob-served among treatments, indicating that all tested dosages of MB, applied under di!erent"lms, gave similar results.
3.2. Ewect ofxlm type and MB dosages on disease control
In the trial carried out against R. solani, FOB and
C. gloeosporioides, all the tested treatments signi"cantly
reduced the incidence of all three pathogens (1}28% re-duction) on the"rst crop of basil (Table 4). No signi"cant di!erences among treatments were observed concerning the level of disease control and basil yield (Table 4). The addition of manure before treatment with MB, applied at 60 g/m2 under standard LPDE"lm, did not a!ect the e$cacy of the treatments (Table 4).
In a second trial, carried out againstR. solanion bean, 60 g/m2of MB applied under standard LPDE or 40 g/m2 under LMG"lm provided the best disease control on the three tested cultivars of bean (Table 5). The results ob-tained by applying 40 g/m2under PP were only slightly inferior. Forty grams of MB under standard LPDE or 20 g/m2 under gas impermeable "lm did not provide a satisfactory disease control (Table 5). As in trial 2,R.
solanisymptom incidence was signi"cantly reduced by all
treatments in the case of lettuce (cv Lido), in comparison with the control, but yield was not a!ected by any of the treatments (data not shown).
In trial 3,S. sclerotiorumsymptom incidence was sig-ni"cantly reduced by all tested treatments on lettuce (cv Gheisa) (Table 6) as well as on the second crop (cv Foglie di quercia) (data not shown). On cv Bobis, only 40 g/m2 of MB, applied under LMG, signi"cantly reduced the incidence ofR.solani, while on cv Canellino, no signi" cat-ive di!erences were observed among treatments (Table 7).
3.3. Permeability ofxlms
compared with those covered by LMG and treated with 30 g/m2of MB and those covered with standard LPDE, fumigated with 60 and 40 g/m2(Table 8). The same trend is shown whenC]¹products are considered: the high-est concentrations of MB were observed when the fumigant was applied at 40 g/m2, under gas-impermeable "lm, in comparison with those achieved under LPDE with an initial dosage of 60 g/m2of MB (Table 9). This indirectly shows that emissions of MB into the atmo-sphere are signi"cantly reduced by the use of gas-imper-meable"lms, in comparison with the standard dosage of MB under LPDE.
In trial 4, LMG"lm applied on plots fumigated with 40 g/m2of MB con"rmed its capability of retaining MB under the tarp (data not shown).
In both trials the di!erences of the MB concentrations measured under the di!erent plastic "lms signi"cantly decreased over time. The di!erences between someC]¹ products remained statistically signi"cant. Particularly, such value remained signi"cantly higher in the case of the treatments carried out under LMG at 40 g/m2. Less promising results were obtained with the two experi-mental"lms coded as SIS (data not shown).
4. Discussion
The results presented, obtained in a variety of experi-ments, with di!erent crops and pathogens, show the possibility of reducing the dosages of MB for soil disin-festation from 60 g/m2to 40 and 30 g/m2, with still very e!ective control of important soilborne pathogens, when gas-impermeable"lms are used for mulching. The results obtained in terms of disease control were generally sim-ilar to those achieved with 60 g/m2of MB under LPDE. The dosage of 20 g/m2, although still e!ective in some cases, did not always ensure satisfactory disease control. For this reason, this dosage cannot be advised under practical conditions, at least under those circumstances where fungal pathogens are the major problem.
The results obtained by evaluating the direct e!ect of MB applied at di!erent dosages under di!erent "lms, con"rm the relatively high sensitivity ofP. ultimum and
R.solanito the fumigant in comparison toF. oxysporum,
as already shown (Munnecke et al., 1978; Ebben et al., 1983). The Fusariumpopulation was, however, strongly reduced. It is possible that the level of inoculum of F.
basilicisurviving the treatment is not su$cient to cause
disease: actually, it has been shown that 3]102CFU/ml of soil are necessary in order to cause the appearance of symptoms on the cv `Genovese gigantea of basil (A. Garibaldi and G. Minuto, unpublished). In similar experiments carried out in Israel by infesting soil with basil stems infected with F. basilici, the pathogen was completely killed by MB treatment at full dosage under LPDE or at reduced dosage under gas-impermeable"lm
(Gamliel et al., 1998b). The lower mortality observed in our experiments can be explained by the higher resist-ance to the fumigation treatment of chlamydospores of the pathogen in comparison to spores and mycelium present on infected stems.
The results obtained in the tests on pathogen survival con"rm the results obtained in terms of disease control: 20 g/m2of the fumigant, applied under any of the tested gas-impermeable"lms did not give complete control of
R. solaniandP. ultimum.
The di!erent levels of control ofR. solaniachieved with reduced dosages of MB under gas-impermeable"lm on bean, lettuce and basil could be, at least partially, ex-plained with a di!erent virulence of the pathogen on the tested crops, bean being a very susceptible crop to
R. solaniinfections.
A long-term e!ect of MB at a reduced dosage under gas-impermeable"lm was observed in trial 3 on lettuce. This long-term management of soilborne pathogens on more than one crop allows a greater interval between fumigation treatments, with positive implications from an economic point of view. Moreover, a long-term e!ect, coupled with the reduction in dosage by using gas-imper-meable"lm should reduce the emissions of MB into the atmosphere, thus further adding to the environmental and economic bene"ts.
Among the tested gas-impermeable"lms, both LMG and PP provided consistent results both in terms of disease control and retention of the fumigant under the tarp, as indirectly measured with our system. In other studies, both"lms were very e!ective in retaining higher concentration of MB in the soil and reducing MB emis-sions into the atmosphere under laboratory and "eld conditions (Gamliel et al., 1998a,b).
Reduced dosages of MB applied under gas-imperme-able"lm also were demonstrated in other pathogen-crop systems (Cebolla et al., 1996; Gamliel et al., 1997b; Gul-lino et al., 1996; Minuto et al., 1998a,b). The availability of better quality gas-impermeable"lms will allow expan-sion of the application technique in an increasing number of situations. At this stage, VIFs are more expensive than LPDE, but allowing MB dosage reduction may compen-sate for the additional cost. Hopefully, expanding their usage will help reducing their production costs.
The usage of VIFs with reduced dosages of MB will help agriculture, in the short term, to conform to Mon-treal Protocol requirements, while reliable, long term solutions are developed.The application of reduced dos-ages of MB under gas-impermeable plastics, if combined with other methods of soilborne disease management, may enable even further reductions of MB emissions into the atmosphere.
Acknowledgements
Work carried out with grants from Ministry of Envi-ronment } S.I.A.R., Italy and Regione Liguria. The authors thank Prof. Jaacov Katan and Prof. Alberto Matta for critically reviewing the manuscript and the anonymous reviewers for their valuable comments.
The "rst author carried the experimental"eld work, collected and elaborated the data and participated into the planning of the experiments during the preparation of his Ph.D thesis, the second author cooperated into part of the"eld work and carried the laboratory experiments during the preparation of her Master thesis, the third author planned the work and wrote the manuscript. The fourth author participated into the planning of the ex-periments and reviewed the manuscript.
References
Bell, C.H., Price, N., Chakrabarti, B. (Eds.), 1996. The Methyl bromide issue. Wiley, New York, 400 pp.
Cebolla, V., Tuset, J.J., Guinet, N., Molina, A., Mira, J.L., Hinarejos, C., 1996. New technologies for methyl bromide emission reduction from soil fumigation in Spain. Proceedings of the Annual Inter-national Research Conference on MB Alternatives and Emission Reduction, Orlando, FL, pp. 35}36.
Chakrabarti, B., 1996. Methyl bromide in storage practice and quaran-tine. In: Bell, C., Price, N., Chakrabarti, B. (Eds.), The methyl bromide issue. Wiley, New York, pp. 237}274.
Ebben, M.N., Gandy, D.G., Spencer, D.M., 1983. Toxicity of methyl bromide in soilborne fungi. Plant Pathology 32, 429}433. Gamliel, A., Grinstein, A., Beniches, M., Katan, J., Fritsch, J., Ducom,
P., 1998a. Permeability of plastic"lms to methyl bromide: a com-parative laboratory study. Pestic. Sci. 53, 141}148.
Gamliel, A., Grinstein, A., Beniches, M., Klein, L., Cohen, Y., Katan, J., 1998b. Permeability of plastic"lms to methyl bromide:"eld study. Crop Protection 17, 241}248.
Gamliel, A., Grinstein, A., Katan, J., 1997a. Improved technologies to reduce emissions of methyl bromide from fumigated soil. Phytoparasitica 25 (Suppl.), 21S}30S.
Gamliel, A., Grinstein, A., Peretz, Y., Klein, L., Nachmias, A., Tsor, L., Livescu, L., Katan, J., 1997b. Reduced dosages of methyl bromide for controlling Verticillium wilt of potato in experimental and commercial plots. Plant Disease 81, 469}474.
Garibaldi, A., Gullino, M.L., 1995. Focus on critical issues in soil and substrate disinfestation towards the year 2000. Acta Horticulturae 382, 21}36.
Gullino, M.L., Minuto, G., Mocioni, M., Garibaldi, A., 1996. Reduction of dosages of methyl bromide for soil disinfestation in Italy. Med. Fac. Landbouww. Univ. Gent. 61, 547}553.
Katan, J., 1984. The role of soil disinfestation in achieving high produc-tion in horticulture crops. Proceedings of the Brighton Crop Protec-tion Conference, vol. 3, pp. 1189}1193.
Komada, H., 1975. Development of selective medium for quantitative isolation ofFusarium oxysporumfrom natural soil. Rev. Plant Prot. Res. 8, 114}124.
Locke, T., Coulhoun, J., 1974. Contribution to a method of testing oil palm seedlings for resistance toFusarium oxysporum f.sp. elaeidis Toovey. Phytopath. Z. 79, 77}92.
Masago, H., Yoshikawa, M., Fuhada, M., Nakanishi, N., 1977. Selective inhibition of Pythium spp. on a medium for direct isolation of Phytophthora spp. from soil and plants. Phytopathology 67, 425}428.
Migheli, Q., Minucci, C., Garibaldi, A., 1990. Messa a punto di un substrato selettivo per l'isolamento diRhizoctonia spp. da tessuti infetti e dal terreno. Rivista di Patologia vegetale, S. IV 26, 23}37.
Minuto, A., Gullino, M.L., Baruzzi, G., Faedi, W., Lucchi, P., 1998a. Possibilita'di ridurre il bromuro di metile nella fumigazione del terreno: risultati su fragola.Atti Convegno SOI`La fragola verso il 2000a. Verona 1998, 215}224.
Minuto, A., Minuto, G., Gullino, M.L., Garibaldi, A., 1998b. Prove sulla riduzione delle dosi di impiego di bromuro di metile per la disinfezione del terreno. Atti Giornate Fitopatologiche, 671}676.
Munnecke, D.E., Bricker, J.L., Kolbezen, M.J., 1978. Comparative toxicity of gaseous methyl bromide to ten soilborne phytopatho-genic fungi. Phytopathology 68, 1210}1216.
